.rs .\" Troff code generated by TPS Convert from ITU Original Files .\" Not Copyright ( c) 1991 .\" .\" Assumes tbl, eqn, MS macros, and lots of luck. .TA 1c 2c 3c 4c 5c 6c 7c 8c .ds CH .ds CF .EQ delim @@ .EN .nr LL 40.5P .nr ll 40.5P .nr HM 3P .nr FM 6P .nr PO 4P .nr PD 9p .po 4P .rs \v | 5i' .sp 2P .LP \fB6\fR \fBPacket communications procedures\fR .sp 1P .RT .PP This section is intended to explain the role of the D\(hychannel signalling procedures in the support of packet communications in an ISDN. A complete description of terminal adaptor functions can be found in Recommendation\ X.31. .EF '% Fascicle\ VI.11\ \(em\ Rec.\ Q.931'' .OF '''Fascicle\ VI.11\ \(em\ Rec.\ Q.931 %' .PP According to Recommendation X.31, the user may access packet facilities by means of one of the following alternatives: .RT .LP a) circuit\(hyswitched access to PSPDN services (Case A) .LP by establishing a transparent circuit\(hyswitched access connection through the ISDN to the access port of a public network (e.g.,\ PSPDN) referred to as \*Qaccess unit (AU)\*U in the following sections. This connection may be initiated by the user or the AU. From the ISDN point of view, the circuit\(hyswitched call control procedures of \(sc\ 5 apply. Only the B\(hychannel is used in this case. .LP b) packet\(hyswitched access to an ISDN virtual circuit service (Case\ B) .LP by establishing a packet\(hymode access connection to the packet handler (PH) of an ISDN. This connection may be initiated by the user or the ISDN. Both B\(hy and D\(hychannels may be used in this case. .PP The protocol and the text of \(sc\(sc 6.1 to 6.5 and Appendix II of Recommendation\ Q.931, and \(sc\(sc\ 6.1 to\ 6.5 and Appendix\ III of Recommendation\ X.31[14], are identical. .PP The term \*Quser\*U refers to the user equipment which may consist of an ISDN packet\(hymode terminal (TE1) or a combination of an existing data terminating equipment (DTE/TE2) attached to a terminal adaptor (TA). A DTE may not receive all of the information provided in Q.931\ signalling messages at the user\(hynetwork interface. .PP The ISDN TA/TE1 presents an S/T\(hyinterface towards the network and therefore the TA/TE1 implementation should embody the procedures described in Recommendation\ Q.921\ [3] and this Recommendation for B\(hy and D\(hychannel connection establishment and control. .PP For demand access connections, \(sc\(sc 6.1 through 6.4 apply. Example message flows for demand access connections are shown in Appendix\ II. .PP Two types of semi\(hypermanent connection on B\(hy and D\(hychannels are covered in this section: .RT .LP 1) physical layer semi\(hypermanently established between the terminal and the PH/AU, i.e.,\ the I.430/I.431 physical layer remains activated and the physical path through the ISDN is connected semi\(hypermanently; and .LP 2) data link and physical layers semi\(hypermanently established between the terminal and the PH/AU (in this type, the network shall keep the data link layer in the established state). .PP When a PVC is used, there must exist a type 2) semi\(hypermanent connection. .PP In semi\(hypermanent connection type 1), the procedures of \(sc\ 6.3 are followed for call establishment and release. .PP In semi\(hypermanent connection type 2), only the procedures of \(sc\ 6.3.2 are followed for call establishment and release. .PP When semi\(hypermanent connection type 2) is used for PVCs, none of the following procedures apply. .PP Semi\(hypermanent connections are established via a provisioning process without Q.931 procedures. .RT .sp 1P .LP 6.1 \fIOutgoing access\fR .sp 9p .RT .PP If the user selects an already established channel for the outgoing virtual call, then the procedures described in \(sc\ 6.3 apply. If the selected channel is not established to the AU/PH, then the procedures for activating a channel described in the following subsections are to be used before establishing the virtual call using the procedures of \(sc\ 6.3. .PP For outgoing data calls, the user first must decide whether the circuit\(hyswitched (Case\ A) or packet switched services (Case\ B) are desired from the network. For outgoing circuit calls, the user follows the procedures of \(sc\ 6.1.1. For outgoing packet calls, a user decides whether B\(hychannel or D\(hychannel is to be used for the packet call. If the user decides to use the B\(hychannel, then the procedures described in \(sc\ 6.1.2.1 are used. If the user decides to use the D\(hychannel, then the procedures described in \(sc\ 6.1.2.2 are used. .bp .PP \fINote\fR \ \(em\ Some networks may not support every type of access. In the case of B\(hychannel access, the network will clear a request for unsupported services by sending a RELEASE COMPLETE message with cause No.\ 65, \fIbearer\fR \fIcapability not implemented\fR . In the case of a request for D\(hychannel access (an SABME with SAPI=16), on a network port which does not support the service, no response is required of the network. .RT .sp 1P .LP 6.1.1 \fICircuit\(hyswitched access to PSPDN services\fR \fI(Case A)\fR .sp 9p .RT .PP The B\(hychannel connection between the user and the AU shall be controlled using the D\(hychannel signalling procedures for call establishment described in \(sc\ 5.1. The specific B\(hychannel to be used as a switched connection is selected using the channel selection procedures described in \(sc\ 5.1.2 and summarized in Table\ 6\(hy1/Q.931. .RT .ce \fBH.T. [T168.931]\fR .ce TABLE\ 6\(hy1/Q.931 .ce \fBUser requested channel and network response.\fR .ce \fBOutgoing access to either an AU or PH\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(54p) sw(54p) sw(54p) | cw(54p) , c | c | c | ^ . { Channel indicated in the SETUP message user to network direction } { Allowable network response (network\(hyuser) } Channel indication Preferred or exclusive D\(hychannel indication _ .T& cw(54p) | cw(54p) | cw(54p) | cw(54p) , ^ | c | c | c. Bi Exclusive No Bi Preferred No Bi, Bi` _ .T& cw(54p) | cw(54p) | cw(54p) | cw(54p) , ^ | c | c | c. Any (Ignore) No Bi` _ .T& cw(162p) | cw(54p) . (Absent) Bi` .TE .LP Bi the indicated (idle) B\(hychannel .LP Bi` any (other) idle B\(hychannel .LP \fINote\ 1\fR \ \(em\ All other encodings are invalid. .LP \fINote\ 2\fR \ \(em\ All columns under the heading \*QChannel indicated in the SETUP message\*U indicate possible user codings of the Channel identification information element contained in the SETUP message sent by the user to the network requesting a connection to an AU or PH (see \(sc\ 4.5.13). The column under \*QAllowable network response\*U refers to the allowable responses by the network to the user. .nr PS 9 .RT .ad r \fBTable 6\(hy1/Q.931 [T168.931], p.\fR .sp 1P .RT .ad b .RT .PP On the basis of the call set\(hyup information (e.g. Called party number identifying an AU, Transit network selection,\ etc.) and/or a subscription time agreement, the network provides a connection to the appropriate AU. The Bearer capability information element included in the SETUP message shall be coded with: .LP \(em information transfer capability set to either: .LP a) \fIunrestricted digital information\fR ; or .LP b) \fIrestricted digital information\fR ; .LP \(em transfer mode set to \fIcircuit mode\fR ; .LP \(em information rate set to \fI64 kbit/s\fR . .PP \fINote\fR \ \(em\ Bearer capability information element octets 4a and 4b shall not be included. .PP The user may also specify the layer\ 1 (e.g., rate adaption), layer\ 2 (i.e.,\ LAPB), and layer\ 3 (i.e.,\ X.25) information transfer protocols in the low layer compatibility information element in the SETUP message (see Annex\ L). .bp .RT .sp 2P .LP 6.1.2 \fIAccess to the ISDN virtual circuit service\fR \fI(Case B)\fR .sp 1P .RT .sp 1P .LP 6.1.2.1 \fIB\(hychannel\fR .sp 9p .RT .PP Demand access B\(hychannel connections are controlled using the D\(hychannel signalling procedures for call establishment described in \(sc\ 5.1 using the messages defined in \(sc\ 3.2 with the following exceptions: .RT .LP a) the procedures for overlap sending specified in \(sc\ 5.1.3 do not apply; .LP b) the procedures for call proceeding and overlap sending specified in \(sc\ 5.1.5.2 do not apply; .LP c) the procedures for notification of interworking at the origination interface specified in \(sc\ 5.1.6 do not apply; .LP d) the procedures for call confirmation indication specified in \(sc\ 5.1.7 do not apply; .LP e) the procedures for call connection specified in \(sc\ 5.1.8 apply as follows: .LP \(em upon accepting the access connection, the network shall send a CONNECT message across the user\(hynetwork interface to the calling user and enter the Active state; .LP \(em this message indicates to the calling user that an access connection to the packet handler has been established; .LP \(em on receipt of the CONNECT message, the calling user may optionally send a CONNECT ACKNOWLEDGE message, and shall enter the Active state; .LP f ) the procedures for call rejection specified in \(sc\ 5.1.9 apply as follows: .LP \(em when unable to accept the access connection, the network shall initiate call clearing at the originating user\(hynetwork interface as described in \(sc\ 5.3; .LP g) the procedures for transit network selection specified in \(sc\ 5.1.10 do not apply. .PP The specific B\(hychannel to be used as a demand connection is selected using the channel selection procedures described in \(sc\ 5.1.2 and summarized in Table\ 6\(hy1/Q.931. .PP For a demand connection to an ISDN PH, the Bearer capability information element included in the SETUP message shall be coded with: .RT .LP \(em information transfer capability set to \fIunrestricted digital\fR \fIinformation\fR ; .LP \(em transfer mode set to \fIpacket mode\fR ; .LP \(em information transfer rate set to 00000; .LP \(em user information layer 2 protocol set to \fIRecommendation X.25, link layer\fR ; .LP \(em user information layer 3 protocol set to \fIRecommendation\ X.25, packet layer\fR . .PP \fINote\fR \ \(em\ Octets 4a, 4b, 5a, 5b, 5c and 5d shall not be included. .PP The demand access connection can then be used to suport packet communications according to X.25 link layer and X.25 packet layer procedures as specified in \(sc\ 6.3. .RT .sp 1P .LP 6.1.2.2 \fID\(hychannel\fR .sp 9p .RT .PP The D\(hychannel provides a connection which enables the ISDN user terminal to access a PH function within the ISDN by establishing a link layer connection (SAPI=16) to that function which can then be used to support packet communications according to X.25 layer\ 3 procedures as defined in \(sc\ 6.3. The X.25 packet layer uses the acknowledged information transfer service (i.e.,\ I\(hyframes) provided by LAPD (see Recommendation\ Q.920\ [45]). Consequently, Q.931 procedures are not required to provide D\(hychannel access. .PP A number of packet mode user equipment can operate simultaneously over the D\(hychannel, each using a separate layer\ 2 data link identified by an appropriate address (see Recommendation\ Q.921) in frames transferred between the user and\ PH. .bp .RT .sp 2P .LP 6.2 \fIIncoming access\fR .sp 1P .RT .sp 1P .LP 6.2.1 \fIAccess from PSPDN services\fR \fI(Case A)\fR .sp 9p .RT .PP The ISDN signals the establishment of the circuit\(hymode connection using the procedures described in \(sc\ 5.2. The virtual calls are signalled between the user and the AU using the procedures described in \(sc\ 6.3. .RT .sp 1P .LP 6.2.1.1 \fIGeneral\fR .sp 9p .RT .PP The general procedures performed by the AU are those defined in Recommendation\ X.32. .RT .sp 1P .LP 6.2.1.2 \fIChannel selection\fR .sp 9p .RT .PP If the physical circuit desired by the AU does not exist between the terminal and the AU, the procedures for physical channel establishment described in the following sections apply. .PP The format of the SETUP message sent by the network to the user is in accordance with \(sc\ 3.1. .PP The bearer capability information element included in the SETUP message shall be coded with: .RT .LP \(em information transfer capability set to either: .LP a) \fIunrestricted digital information\fR ; or .LP b) \fIrestricted digital information\fR ; .LP \(em transfer mode set to \fIcircuit mode\fR ; .LP \(em information rate set to \fI64 kbit/s\fR . .PP \fINote\fR \ \(em\ Bearer capability information element octets 4a and 4b shall not be included. .PP The Channel identification information element shall be coded according to Table\ 6\(hy2/Q.931. .RT .ce \fBH.T. [T169.931]\fR .ce TABLE\ 6\(hy2/Q.931 .ce \fBNetwork requested channel and user response.\fR .ce \fBIncoming access from an AU\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(48p) sw(48p) sw(48p) | cw(48p) , c | c | c | ^ . { Channel indicated in the SETUP message network to user direction } { Allowable user response (user\(hynetwork) } Channel indication Preferred or exclusive D\(hychannel indication _ .T& cw(48p) | cw(48p) | cw(48p) | cw(48p) | lw(36p) . Bi Exclusive No Bi .T& cw(48p) | cw(48p) | cw(48p) | cw(48p) | lw(36p) . Bi Preferred No Bi, Bi` .TE .LP Note 1 Bi indicated (idle) B\(hychannel .LP Bi` any other idle B\(hychannel (not permitted for broadcast call offering) .LP \fINote\ 1\fR \ \(em\ This encoding is not used for broadcast call offering. .LP \fINote\ 2\fR \ \(em\ All other encodings are invalid. .RT .ad r \fBTable 6\(hy2/Q.931 [T169.931], p.\fR .sp 1P .RT .ad b .RT .PP The B\(hychannel connection to the called user shall be established by the network using the signalling procedures described in \(sc\ 5.2. The call is offered by sending the SETUP message on a point\(hyto\(hypoint data link or on the broadcast data link. .PP The user responds to the SETUP as specified in \(sc\ 5. .bp .RT .sp 1P .LP 6.2.2 \fIAccess from the ISDN virtual circuit service\fR \fI(Case B)\fR .sp 9p .RT .PP To offer an incoming call, the network must perform the following steps in sequence: .RT .LP 1) Channel selection \(em the physical channel/logical link to be used for the incoming call must be identified. The network may use customer profile information, network resources,\ etc., to choose the channel, or the procedures in Step\ 2 below. .LP 2) Physical channel/logical link establishment \(em if the physical B\(hychannel or the logical link of the D\(hychannel have not been determined by Step\ 1, the network may use the procedures in \(sc\ 6.2.2.3. The network may then proceed with Step\ 3. .LP 3) Virtual call establishment \(em the network establishes the virtual call using the procedures described in\ \(sc\ 6.3. .PP In the configuration for the ISDN virtual circuit service, the choice of channel type to be used for the delivery of a new \fIincoming call\fR packet shall be made by the network as described below. .LP a) A new \fIincoming call\fR | acket may be indicated to the ISDN customer by a call offering procedure between the network and all user packet mode terminals (see \(sc\(sc\ 3.2.3.2 and 3.2.3.3 of Recommendation\ X.31\ [14]). .LP b) An incoming virtual call directed to a terminal with an established connection to the PH may be offered directly to the terminal over the established access connection without the use of Q.931 call offering procedures (see \(sc\(sc\ 3.2.3.1 and 3.2.3.2 of Recommendation\ X.31\ [14]). .sp 1P .LP 6.2.2.1 \fIB\(hychannel\fR .sp 9p .RT .PP When calls are to be offered on the B\(hychannels without channel negotiation, the procedures described in \(sc\ 5.2 of Recommendation\ Q.931 using the messages of \(sc\ 3.2 of Recommendation\ Q.931 apply with the following exceptions: .RT .LP a) The procedures for overlap receiving specified in \(sc\ 5.2.4 of Recommendation\ Q.931 do not apply. .LP b) The procedures for receipt of CALL PROCEEDING and ALERTING specified in \(sc\ 5.2.5.2 apply with the following exception: .LP \(em The receipt of an ALERTING message shall not cause the network to send a corresponding ALERTING message to the calling user. .LP c) The procedures for call failure specified in \(sc 5.2.5.3 apply with the following note: .LP \(em The network clears the incoming X.25 virtual call towards the calling X.25 DTE using the appropriate cause from Table\ 6\(hy5/Q.931. .LP d) The procedures for notification of interworking at the terminating interface specified in \(sc\ 5.2.6 apply with the following exceptions: .LP \(em The case of the call entering an ISDN environment during call establishment is not applicable. .LP \(em In the case of a call leaving the ISDN environment within the called user's premises, no notification is sent to the calling party. .LP \(em The case of in\(hyband information/patterns is not applicable. .LP e) The procedures for active indication specified in \(sc\ 5.2.8 apply with the following exception: .LP \(em The network shall not initiate procedures to send a CONNECT message towards the calling user. .LP f ) The procedures for user notification specified in \(sc\ 5.2.10 do not apply. .PP Where an established B\(hychannel connection is to be used, the \fIincoming call\fR | acket will be delivered in accordance with \(sc\ 6.3. .PP Where a new B\(hychannel connection is to be established, the identity of the selected user will be associated with the Connection Endpoint Suffix (CES) from which the first CONNECT message has been received. .RT .sp 1P .LP 6.2.2.2 \fID\(hychannel\fR .sp 9p .RT .PP The D\(hychannel provides a connection which enables the ISDN PH to access an ISDN user terminal or vice versa. This access is accomplished by establishing a link layer connection (SAPI\ =\ 16) to the terminal or network which can then be used to support packet communications according to X.25[5] layer\ 3 procedures as defined in \(sc\ 6.3. .bp .PP The layer 2 procedures shall be in accordance with Recommendation\ Q.921[3]. The D\(hychannel provides a semi\(hypermanent connection for packet access since all layer\ 2 frames containing a packet mode SAPI (16) are routed automatically between the user and the PH function. .PP When an incoming call is offered to packet mode user equipment at the user interface, the channel selection procedures described in \(sc\ 6.2.2.3 shall be used. .PP A number of packet mode terminals can operate simultaneously over the D\(hychannel, each using a separate layer\ 2 link identified by an appropriate TE1 (see Recommendation\ Q.921) in frames transferred between the terminal and the network. .RT .sp 2P .LP 6.2.2.3 \fICall offering\fR .sp 1P .RT .sp 1P .LP 6.2.2.3.1 \fIChannel selection through call offering\fR .sp 9p .RT .PP The call offering procedure is performed using the layer\ 3 messages and procedures of \(sc\ 5. The call offering procedure is integrated into the circuit\(hyswitched call control procedures, signalled on the D\(hychannel, with the channel selection being accomplished by means of the channel selection procedure if offered as a network option. .PP As described in \(sc 5, the network selects the first user which responds to the call offering with a CONNECT message. When the selected user has requested that the X.25 call be set up over a new B\(hychannel, the network will indicate that the channel is acceptable by returning a CONNECT ACKNOWLEDGE message to the user. If multiple terminals have responded positively to the SETUP message, the network shall clear each of the non\(hyselected terminals with a RELEASE message containing cause No.\ 26, \fInon\(hyselected user clearing\fR . .PP When the selected user has requested that the X.25 call be set up over an established B\(hychannel or the D\(hychannel, the network shall respond to the CONNECT message with a RELEASE message containing cause No.\ 7, \fIcall awarded\fR \fIand being delivered in an established channel\fR . The network shall also return a RELEASE message containing cause No.\ 26, \fInon\(hyselected user clearing\fR to any other positively responding terminals. The network will then deliver the X.25\ call over the selected channel. .PP \fINote\ 1\fR \ \(em\ There is no time significance between the delivery of the RELEASE message and the \fIincoming call\fR | packet, i.e.,\ either may occur first. .PP \fINote\ 2\fR \ \(em\ The network shall send the RELEASE message(s) and the user(s) shall respond with RELEASE COMPLETE. .PP If the channel indicated by the first positively responding user is not available, the network will use Q.931 call clearing procedures to clear the call with cause No.\ 6, \fIchannel unacceptable\fR . If the channel indicated in the SETUP message is not acceptable to the user, the user will clear the call with a RELEASE message containing cause No.\ 34, \fIno circuit/channel available\fR , or cause No.\ 44, \fIrequested circuit/channel not available\fR . .PP On the basis of a network option or subscription agreement, the network may choose the access channel or access channel type (e.g.\ B or\ D) for a particular incoming packet call. .PP When the Channel indication information element indicates \fIChannel indication \(em No channel\fR , \fIExclusive\fR , and \fID\(hychannel indication\fR \fI\(em\ Yes\fR , then the Bearer capability information element should be encoded as follows: .RT .LP \(em information transfer capability set to either: .LP a) \fIunrestricted digital information\fR ; or .LP b) \fIrestricted digital information\fR ; .LP \(em transfer mode set to: \fIpacket mode\fR ; .LP \(em information rate set to: \fIpacket mode (00000)\fR ; .LP \(em layer 2 protocol set to: \fIRecommendation Q.921\fR ; .LP \(em Layer 3 protocol set to: \fIRecommendation X.25, packet layer\fR . .PP In all other cases, the Bearer capability information element should be encoded as follows: .LP \(em information transfer capability set to either: .LP a) \fIunrestricted digital information\fR ; or .LP b) \fIrestricted digital information\fR ; .LP \(em transfer mode set to: \fIpacket mode\fR ; .LP \(em information rate set to: \fIpacket mode (00000)\fR ; .LP \(em layer 2 protocol set to: \fIRecommendation X.25\ [5],\fR \fIlink layer\fR ; .LP \(em Layer 3 protocol set to: \fIRecommendation X.25, packet layer\fR . .bp .PP There exists an understanding that if the terminal responds with D\(hychannel indication set (see Table\ 6\(hy3/Q.931), the Layer\ 2 protocol to be used is Recommendation\ Q.921 (LAPD)[3]. .PP The channel selection procedure for incoming calls is independent of the type of channel selected at the calling end. In this respect, any combination of channel type used at each end is possible, provided the user rates and available bandwidth are compatible. .PP The channel selection principle to be used in the procedure is shown in Table 6\(hy3/Q.931. .PP \fINote\ 3\fR \ \(em\ When the incoming SETUP message is sent on a broadcast data link with a Channel identification information element which indicates an idle B\(hychannel and \fIpreferred\fR , the called user is not permitted to respond with a different idle B\(hychannel in the response. The option to respond with a different idle channel is restricted to point\(hyto\(hypoint call offerings. .PP \fINote\ 4\fR \ \(em\ Networks providing packet mode call offering shall provide Q.931 signalling procedures for packet mode calls on SAPI\ =\ 0. For an interim period, some networks, by subscription agreement, may offer SAPI\ =\ 16 broadcast call offering procedures for providing Q.931 signalling. This option shall use all Q.31 procedures for packet mode calls with the following restriction: all calls will be offered as \fID\(hychannel exclusive\fR and will not provide channel selection procedures. Terminals implementing SAPI\ =\ 16 procedures shall also implement SAPI\ =\ 0 procedures for portability. .RT .ce \fBH.T. [T170.931]\fR .ce TABLE\ 6\(hy3/Q.931 .ce \fBNetwork requested channel and user response.\fR .ce \fBIncoming access for packet mode\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(54p) sw(54p) sw(54p) | cw(54p) , c | c | c | ^ . { Channel indicated in the SETUP message network to user direction } { Allowable user response (user\(hynetwork) } Channel indication Preferred or exclusive D\(hychannel indication _ .T& cw(54p) | cw(54p) | cw(54p) | cw(54p) , ^ | ^ | c | c. Bi Exclusive No Bi Yes Bi, D _ .T& cw(54p) | cw(54p) | cw(54p) | cw(54p) , ^ | ^ | c | c. Bi Preferred No Bi, Bi`, Bj Yes Bi, Bi`, Bj, D _ .T& cw(54p) | cw(54p) | cw(54p) | cw(54p) , ^ | ^ | c | c ^ | c | c | c. No channel Preferred No Bj Yes Bj, D Exclusive Yes D .TE .LP Bi indicated (idle) B\(hychannel .LP Bi` any other idle B\(hychannel (not permitted in response to broadcast call offering) .LP Bj an established B\(hychannel under the user's control .LP D the D\(hychannel .LP \fINote\fR \ \(em\ All other encodings are invalid. .nr PS 9 .RT .ad r \fBTable 6\(hy3/Q.931 [T170.931], p.\fR .sp 1P .RT .ad b .RT .sp 1P .LP 6.2.2.3.2 \fIInformation element mapping\fR .sp 9p .RT .PP Some networks may choose to provide a service of mapping some or all of the information from the \fIincoming call\fR packet into the SETUP message (see \(sc\ 3.2.3 of Recommendation\ X.31). Table\ 6\(hy4/Q.931 shows the mapping of the X.25 incoming call elements to Q.931 information elements. The incoming call packet will still contain these fields when it is delivered. See \(sc\ 3.2.3 of Recommendation\ X.31 for mapping requirements. .bp .RT .ce \fBH.T. [T171.931]\fR .ce TABLE\ 6\(hy4/Q.931 .ce \fBMapping of X.25 information elements to corresponding Q.931 .ce SETUP\fR .ce \fBmessage information elements in packet\(hymode incoming .ce call\fR .ce (Note 1) .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; lw(36p) | cw(96p) | cw(96p) . { Information elements in X.25 incoming call packet } { Corresponding information element in Q.931 SETUP message } _ .T& lw(36p) | lw(96p) | lw(96p) , ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l. . Calling address Calling party number Called address Called party number User data (UD) { User\(hyuser information (Note 2) } A\(hybit (Note 3) For further study D\(hybit { Packet layer binary parameters } Modulus { Packet layer binary parameters } _ .T& lw(36p) | lw(96p) | lw(96p) , ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l. X.25 user facility { Flow control parameter negotiation } { Packet size Packet layer window size } Throughput class negotiation Information rate Fast select { Packet layer binary parameters } Reverse charging For further study Closed user group selection For further study { Closed user group with outgoing access selection } For further study Bilateral closed user group For further study { Transit delay selection and indication } { Transit delay selection and indication } { Call redirection and deflection notification } Redirecting number _ .T& lw(36p) | lw(96p) | lw(96p) , ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l ^ | l | l. DTE facility Calling address extension Calling party sub\(hyaddress Called address extension Called party sub\(hyaddress { End\(hyto\(hyend transit delay } { End\(hyto\(hyend transit delay } Minimum throughput class Information rate Expedited data negotiation { Packet layer binary parameters } .TE .LP \fINote\ 1\fR \ \(em\ Mapping is optional or required as indicated in \(sc 3.2.3 of Recommendation\ X.31. .LP \fINote\ 2\fR \ \(em\ The maximum length of the user data within the user\(hyuser information element is network dependent and is either 32\ or 128\ octets. .LP \fINote\ 3\fR \ \(em\ The need and procedures for A\(hybit mapping is for further study. .nr PS 9 .RT .ad r \fBTable 6\(hy4/Q931 [T171.931], p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 1P .LP 6.2.2.3.3 \fIChannel selection without call offering\fR .sp 9p .RT .PP Where the network and user have agreed beforehand, the network may route an incoming call to the called user over an established B\(hychannel connection or D\(hychannel link without the need for any signalling for channel selection. .RT .sp 1P .LP 6.3 \fIVirtual call establishment and release\fR .sp 9p .RT .PP In all cases, once the physical channel has been selected and, if necessary, connected to the PH or AU, the virtual call is established according to the procedures below. Some networks may require some of the terminal identification procedures of Recommendation\ X.32 as well. .RT .sp 1P .LP 6.3.1 \fILink layer establishment and release\fR .sp 9p .RT .PP Link layer (LAPB on the B\(hychannel or LAPD on the D\(hychannel) establishment shall be initiated by: .RT .LP \(em the calling terminal in the case of outgoing calls; .LP \(em the AU in the case of incoming calls in Case A; or .LP \(em the PH in the case of incoming calls in Case B. .PP Link layer release may be initiated by: .LP \(em the terminal; .LP \(em the AU in Case A; or .LP \(em the PH in Case B. .sp 1P .LP 6.3.2 \fIPacket layer virtual call set\(hyup and release\fR .sp 9p .RT .PP The packet layer procedures of X.25\ [5] will be used for layer 3 call set\(hyup and release. The packet layer procedure will additionally be able to control and monitor the established or released state of the link layer. .RT .PP In Case B, the PH may maintain a timer T320 (defined in Recommendation\ Q.931). T320, if implemented, is started: .LP a) upon clearance of the last virtual call; or .LP b) upon transmission of a CONNECT message by the network in case of an outgoing B\(hychannel access access connection; or .LP c) upon transmission of a CONNECT ACKNOWLEDGE message by the network in case of an incoming B\(hychannel access connection; or .LP d) upon establishment of the link layer for D\(hychannel access connections. .PP T320 is canceled upon: .LP 1) establishment of the first (next) virtual call; or .LP 2) receipt of Q.931 clearing message from the user; or .LP 3) disconnection of the SAPI\ =\ 16 link on the D\(hychannel. .PP Upon expiry of T320, the PH will release the link layer and, in the case of B\(hychannel access, initiate clearing of the B\(hychannel. .PP X.25 logical channels are associated with their underlying logical link. Specifically, in case of the use of the B\(hychannel for packet communication, there is an association between the logical channels and the LAPB logical link below them. Thus the same logical channel number may be used simultaneously on each different B\(hychannel. .RT .sp 2P .LP 6.4 \fICall clearing\fR .sp 1P .RT .sp 1P .LP 6.4.1 \fIB\(hychannel\fR .sp 9p .RT .PP The clearing of the switched connection shall be effected by using the D\(hychannel signalling procedures for call clearing as specified in \(sc\ 5.3. For access to PSPDN services, no exceptions apply. For the ISDN virtual circuit service, the messages of \(sc\ 3.2 are used, and the following exceptions apply: .RT .LP \(em The terms defined in \(sc\ 5.3.1 (Terminology) apply by replacing \*Qcircuit\(hyswitched ISDN connection\*U with \*Qdemand packet mode access connection\*U. .LP \(em The exception condition f ) specified in \(sc\ 5.3.2 does not apply. .LP \(em The procedures for clearing with tones and announcements provided in \(sc\ 5.3.4.1 do not apply. .bp .PP The B\(hychannel may be cleared at any time by the user though, in general, it will be cleared following the clearing of the last virtual call over that B\(hychannel. In the ISDN virtual circuit service, if the user clears the B\(hychannel access connection using a Q.931 clearing message while X.25\ [5] virtual calls still exist on the B\(hychannel, the network shall clear the X.25 virtual call(s) with cause No.\ 17, \fIremote procedure error\fR , and diagnostic No.\ 64, \fIcall set\(hyup, call clearing, or registration problem\fR . .PP In Case B, if a Q.931 RESTART message is received by the PH during the X.25 data transfer phase, the X.25 virtual calls shall be treated as follows: .RT .LP \(em For switched virtual circuits, an X.25 \fIclear indication\fR | packet shall be sent with cause No.\ 9, \fIout of order\fR , and diagnostic No.\ 0, \fIno additional information\fR . .LP \(em For permanent virtual circuits, an X.25 \fIreset\fR | packet shall be sent containing cause No.\ 9, \fIout of order\fR and diagnostic No.\ 0, \fIno additional information\fR . .PP At the expiration of timer T320, the network may disconnect the X.25 link layer and the access connection. B\(hychannel clearing is as described in \(sc\ 5.3 with the exceptions above, with cause No.\ 102, \fIrecovery on timer\fR \fIexpiry\fR . .sp 1P .LP 6.4.2 \fID\(hychannel\fR .sp 9p .RT .PP D\(hychannel access connections are cleared using the disconnect procedures as defined in \(sc\ 6.3. .RT .sp 1P .LP 6.4.3 \fIAdditional error handling information\fR .sp 9p .RT .PP When failure occurs, or the X.25 virtual call is cleared prematurely, the rules of \(sc\ 5.8 shall apply. In addition, the following rules for determining the appropriate cause to be used shall apply in order of decreasing priority: .RT .LP 1) If a Q.931 clearing message or RESTART message is received by the PH during the X.25 data transfer phase, \(sc\ 6.4.1 applies. .LP 2) If a call is required by the destination user using Q.931 messages, the X.25 virtual call shall be cleared using a \fIclear indication\fR packet and the appropriate cause from Table\ 6\(hy5/Q.931. .LP 3) If a condition exists that prevents the Q.931 SETUP message from being delivered at the user\(hynetwork interface, the X.25 virtual call shall be cleared using a \fIclear\fR \fIindication\fR packet and a cause shall be selected appropriate to the condition. Table\ 6\(hy5/Q.931 shall serve as a guide to selecting an appropriate cause, i.e.,\ the X.25 mapping of the Q.931 cause describing the interface condition shall be used. .LP 4) If the Q.931 SETUP message is sent across the user\(hynetwork interface, but no response is received to the second expiry of timer T303, rule No.\ 3 applies. .LP 5) If the Q.931 SETUP message is sent across the user\(hynetwork interface, and a response is received from a user which results in the clearing of the call at the user\(hynetwork interface, the X.25 virtual call shall be cleared using a clear indication packet containing the appropriate cause from Table\ 6\(hy5/Q.931 relative to the cause received/sent in the Q.931 clearing message. .LP 6) If an X.25 clear request packet is received from the originating user prior to the delivery of the X.25 incoming call packet to the called user (premature clearing), the PH shall send a clear confirmation packet to the calling user and the access connection shall be treated as follows: .LP \(em If the Q.931 SETUP message was associated with the Unconditional notification class of service (see \(sc\ 3.2.3 of Recommendation\ X.31[14]), the access connection, when and if established, shall be cleared. The Q.931 clearing message shall contain the appropriate cause as described in Table\ 6\(hy6/Q.931. .LP \(em If the Q.931 SETUP message was associated with the Conditional notification class of service (see \(sc\ 3.2.3 of Recommendation\ X.31) and there exists at least one terminal which responds positively to the Q.931 SETUP message, then two options are allowed: .LP a) the access connection is cleared as described for the Unconditional class of service; or .LP b) the access connection is established and timer T320 is started. Upon expiry of the timer T320, the access connection is cleared with cause No.\ 102, \fIrecovery on timer expiry\fR , and diagnostic indicating timer T320. .bp .ce \fBH.T. [1T172.931]\fR .ce TABLE\ 6\(hy5/Q.931 .ce \fBMapping of Q.931 cause fields to X.25 cause field\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(18p) | cw(36p) | cw(18p) | cw(45p) | cw(36p) | cw(18p) | cw(45p) | cw(12p) . Item Q.931 cause Code Q.931 diagnostic X.25 cause Code X.25 diagnostic Code _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 1 { Unallocated (unassigned) number } \ 1 { Condition: unknown, transient, permanent } Not obtainable 13 Invalid called address 67 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 2 No route to destination \ 3 { Condition: unknown, transient, permanent } Not obtainable 13 Invalid called address 67 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 3 Channel unacceptable \ 6 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 4 Normal call clearing 16 { Condition: unknown, transient, permanent } DTE originated \ 0 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 5 User busy 17 (None) Number busy \ 1 No logical channel available 71 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 6 No user responding 18 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 7 User alerting, no answer 19 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 8 Call rejected 21 { Condition: unknown, transient, permanent + user applied diagnostics } DTE originated \ 0 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . \ 9 Number changed 22 New destination address Not obtainable 13 Invalid called address 67 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 10 Destination out of order 27 (None) Out of order \ 9 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 11 { Invalid number format (incomplete number) } 28 (None) Local procedure error 19 Invalid called address 67 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 12 Normal, unspecified 31 (None) DTE originated \ 0 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 13 No circuit/channel available 34 (None) Number busy \ 1 No logical channel available 71 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 14 Network out of order 38 (None) Out of order \ 9 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 15 Temporary failure 41 Network identity Out of order \ 9 No additional information \ 0 _ .TE .nr PS 9 .RT .ad r \fBTableau 6\(hy5/Q.931 [1T172.931], p. 5\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [2T172.931]\fR .ce TABLE\ 6\(hy5/Q.931\ \fI(cont.)\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(18p) | cw(36p) | cw(18p) | cw(45p) | cw(36p) | cw(18p) | cw(45p) | cw(12p) . Item Q.931 cause Code Q.931 diagnostic X.25 cause Code X.25 diagnostic Code _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 16 { Switching equipment congestion } 42 Network identity Network congestion \ 5 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 17 { Requested circuit/channel not available } 44 (None) Number busy \ 1 No logical channel available 71 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 18 { Resources unavailable unspecified } 47 (None) Network congestion \ 5 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 19 { Quality of service unavailable } 49 { Condition: unknown, transient, permanent } Network congestion No additional information _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 20 { Bearer capability not authorized } 57 { Bearer capability information element identifier } Incompatible destination 33 No aditional Information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 21 { Bearer capability not presently available } 58 { Bearer capability information element identifier } Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 22 { Service or option not available, unspecified } 63 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 23 { Bearer service not implemented } 65 Attribute numbers Incompatible destination 33 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 24 Channel type not implemented 66 Channel type Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 25 { Service or option not implemented, unspecified } 79 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 26 Invalid call reference value 81 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 27 { Identified channel does not exist } 82 Channel identity Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .TE .nr PS 9 .RT .ad r \fBTableau 6\(hy5/Q.931 [2T172.931], p. 6\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [3T172.931]\fR .ce TABLE\ 6\(hy5/Q.931\ \fI(cont.)\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(18p) | cw(36p) | cw(18p) | cw(45p) | cw(36p) | cw(18p) | cw(45p) | cw(12p) . Item Q.931 cause Code Q.931 diagnostic X.25 cause Code X.25 diagnostic Code _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 28 Incompatible destination 88 Incompatible parameter Incompatible destination 33 No additional information \ 0 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 29 Invalid message, unspecified 95 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 30 { Mandatory information element is missing } 96 { Information element identifier(s) } Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 31 { Message type non\(hyexistent or not implemented } 97 Message type Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 32 { Message not compatible with call state or message type non\(hyexistent or not implemented } 98 Message type Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 33 { Information element non\(hyexistent or not implemented } 99 { Information element identifier(s) } Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 34 { Invalid information element contents } 100 { Information element identifier(s) } Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 35 { Message not compatible with call state } 101 Message type Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 36 Recovery on timer expiry 102 Timer number Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .TE .nr PS 9 .RT .ad r \fBTableau 6\(hy5/Q.931 [3T172.931], p. 7\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [4T172.931]\fR .ce TABLE\ 6\(hy5/Q.931\ \fI(end)\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(18p) | cw(36p) | cw(18p) | cw(45p) | cw(36p) | cw(18p) | cw(45p) | cw(12p) . Item Q.931 cause Code Q.931 diagnostic X.25 cause Code X.25 diagnostic Code _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 37 Protocol error, unspecified 111 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 _ .T& cw(18p) | lw(36p) | cw(18p) | lw(45p) | lw(36p) | cw(18p) | lw(45p) | cw(12p) . 38 Interworking unspecified 127 (None) Remote procedure error 17 { Call setup, call clearing or registration problem } 64 .TE .LP \fINote\ 1\fR \ \(em\ When clearing occurs during the X.25 data transfer phase, the procedure described in \(sc\ 6.4.1 should be used. .LP \fINote\ 2\fR \ \(em\ When a Q.931 RESTART message is received during the X.25 data transfer phase, switched virtual circuits shall be cleared with a \fIclear\fR \fIindication\fR packet containing cause No.\ 9, \fIOut of order\fR , with diagnostic No.\ 0, \fIno additional information\fR . Permanent virtual circuits shall have an\ X.25 \fIreset\fR packet sent with the same cause and diagnostic. .nr PS 9 .RT .ad r \fBTableau 6\(hy5/Q.931 [4T172.931], p. 8\fR .sp 1P .RT .ad b .RT .ce \fBH.T. [T173.931]\fR .ce TABLE\ 6\(hy6/Q.931 .ce \fBMapping of X.25 cause to Q.931\fR .ce \fBfor premature clearing of the incoming call\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; lw(18p) | cw(114p) | cw(96p) . { X.25 cause in clear indication packet } Q.931 error condition _ .TE .TS center box ; cw(18p) | cw(42p) | cw(12p) | cw(42p) | cw(18p) | cw(42p) | cw(12p) | cw(42p) . Item X.25/X.96 cause Code Diagnostic Code Q.931 cause Code Diagnostic _ .T& cw(18p) | lw(42p) | cw(12p) | lw(42p) . 1 DTE originated 0 No additional information .T& cw(18p) | cw(42p) | lw(12p) | cw(42p) . 0 1XX DTE specified XX .T& lw(18p) | cw(42p) | cw(12p) | cw(42p) . Normal call clearing 16 (None) _ .T& cw(18p) | lw(42p) | cw(12p) | lw(42p) | cw(18p) | lw(42p) | cw(12p) | cw(42p) . 2 Network congestion 5 No additional information 0 { Switching equipment congestion } 42 (None) _ .T& cw(18p) | lw(42p) | cw(12p) | lw(42p) | cw(18p) | lw(42p) | cw(12p) | cw(42p) . 3 Out of order 9 No additional information 0 Destination out of order 27 (None) _ .T& cw(18p) | lw(42p) | cw(12p) | lw(42p) | cw(18p) | lw(42p) | cw(12p) | cw(42p) . 4 Remote procedure error 17 (Any allowed) Procotol error, unspecified 111 (None) .TE .LP \fINote\fR \ \(em\ Instead of providing the above mapping of X.25 to Q.931 the PH, as a network option, may code the\ Q.931 cause information element to indicate \fICCITT Coding Standard\fR in octet\ 3, \fIX.25\fR in octet\ 3a, and code octets\ 4 and\ 5 according to Recommendation\ X.25, copying the cause from the\ X.25 \fIclear indication\fR packet rather than mapping it to a\ Q.931 cause. .nr PS 9 .RT .ad r \fBTableau 6\(hy6/Q.931 [T173.931], p. 9\fR .sp 1P .RT .ad b .RT .LP .bp .sp 2P .LP 6.4.4 \fICause mappings\fR .sp 1P .RT .sp 1P .LP 6.4.4.1 \fIAccess to/from PSPDN services (Case A)\fR .sp 9p .RT .PP The AU may choose to follow the procedures in \(sc\ 6.4.4.2 when mapping between causes delivered by the ISDN or the PSPDN. .RT .sp 1P .LP 6.4.4.2 \fIAccess to/from the ISDN virtual circuit service (Case B)\fR .sp 9p .RT .PP There are several cases where it is necessary to map causes between Q.931 and X.25\ [5]. Networks shall use Table\ 6\(hy5/Q.931 and Table\ 6\(hy6/Q.931 to map the causes between Q.931 and X.25 messages. The figures in Appendix\ II describe some example situations. .RT .sp 1P .LP 6.5 \fIAccess collision\fR .sp 9p .RT .PP When the network offers a packet mode call at the interface simultaneously with the user requesting a packet mode call, the network shall give priority to the completion of the incoming call. If the user determines that accepting the incoming call would meet the needs of its own outgoing call request, the user may clear the call request and accept the incoming call. .RT .LP \fB7\fR \fBUser\(hyto\(hyuser signalling procedures\fR .sp 1P .RT .sp 2P .LP 7.1 \fIProcedures for user\(hyto\(hyuser signalling associated with\fR \fIcircuit\(hyswitched calls\fR .sp 1P .RT .sp 1P .LP 7.1.1 \fIGeneral\fR .sp 9p .RT .PP The user\(hyto\(hyuser signalling supplementary service(s) provides a means of communication between two users by using as a basis the layer\ 3 protocol defined in \(sc\ 5. User\(hyto\(hyuser signalling is used to exchange information between two users to provide the services described in the I.257A Recommendations. The exchange of user\(hyto\(hyuser signalling is limited by flow control procedures provided by the network or the user. The exchange of user\(hyto\(hyuser information is not a network acknowledgement service. Any acknowledgement procedure shall be controlled at a higher layer between users. .PP Three user\(hyto\(hyuser signalling services associated with circuit\(hyswitched calls that may be provided by the network to users are: .RT .LP i) Service 1: .LP user\(hyto\(hyuser signalling exchanged during the set\(hyup and clearing phases of a call, within Q.931 call control messages. .LP ii) Service 2: .LP user\(hyto\(hyuser signalling exchanged during call establishment, between the ALERTING and CONNECT messages, within USER INFORMATION messages. .LP iii) Service 3: .LP user\(hyto\(hyuser signalling exchanged while a call is in the Active state, within USER INFORMATION messages. .PP All three services may be used separately or in any combination in association with a single call. As an option, at call set\(hyup, users may be able to specify that the requested user\(hyto\(hyuser signalling service(s) is (are) required for the call, i.e.,\ the call should not be completed if user\(hyto\(hyuser information cannot be passed. .sp 1P .LP 7.1.2 \fIExplicit invocation procedures for services 1, 2 and 3\fR .sp 9p .RT .PP Services 1, 2 and 3 listed above may be provided on a per call basis following an explicit request from a user. The standard explicit invocation procedure makes use of the Facility information element defined in \(sc\ 4. .PP In addition, or alternatively, some networks may support explicit invocation procedures making use of: .RT .LP \(em keypad facility information element; or .LP \(em feature activation information element. .bp .PP The exact operation of stimulus invocation procedures are network dependent but must follow the rules defined in \(sc\ 8 of this Recommendation. More detailed protocol aspects can also be found in \(sc\ 4 (for the keypad protocol invocation) and in \(sc\ 5 (for the feature management protocol invocation) of Recommendation\ Q.932. .PP When a network supports more than one invocation procedure, the following principles shall be followed: .RT .LP \(em for invocations using the Keypad facility information element, the network will convey the remote user's response using a Signal, a Display, or a Feature indication information element; .LP \(em for invocations using the Feature activation information element, the network will convey the remote user's response using a Feature information element; .LP \(em for invocations using the Facility information element, the network will convey the remote user's response using a Facility information element. .PP In the network\(hyto\(hyuser direction, explicit service 1 and service\ 2 requests may be indicated using the Facility information element. .PP In the network\(hyto\(hyuser direction, service 3 request may be indicated using: .RT .LP i) signal information element (see Note); .LP ii) display information element (see Note); .LP iii) feature indication information element (see Note); or .LP iv) facility information element. .PP For indications using the Facility information element, the user will respond with a Facility information element. No response is needed when any of the first three information elements are used. .PP \fINote\fR \ \(em\ These may be used only when the network has knowledge that the user receiving the notification has subscribed to the service. In this case, the network will generate the service confirmation to the originating user (i.e.,\ the user requesting the service) on behalf of the user who did not originate the service request. For service\ 3, invoked during the active state of a call, the message use is symmetric across the user\(hynetwork interface; i.e.,\ the FACILITY message is returned in response to a FACILITY message. .RT .sp 2P .LP 7.1.3 \fIUser\(hyto\(hyuser signalling service 1\fR .sp 1P .RT .sp 1P .LP 7.1.3.1 \fIGeneral characteristics\fR .sp 9p .RT .PP Service 1 allows the users to communicate by means of user\(hyto\(hyuser signalling by transferring user\(hyto\(hyuser information within Recommendation\ Q.931 call control messages during call establishment and clearing phases. .RT .sp 1P .LP 7.1.3.2 \fIUser\(hyto\(hyuser signalling \(em implicit service request (preferred,\fR \fIi.e. \(em not required)\fR .sp 9p .RT .PP Service 1 may be implicitly requested by including a User\(hyuser information element of variable length as specified in \(sc\ 4.5.29 in the SETUP message transferred across the user\(hynetwork interface at the calling side as described in \(sc\ 5.1.1. This information element is transported by the network and delivered unchanged in the User\(hyuser information element included in the SETUP message transferred across the user\(hynetwork interface at the called side as described in \(sc\ 5.2.1. For invocation purposes, this information element must be at least three octets long as defined in \(sc\ 4.5.29. .PP In the case where contention by users for the incoming call is not allowed (e.g.,\ when the SETUP message containing an implicit service invocation is delivered using a point\(hyto\(hypoint link at the data link layer or when the network, despite using broadcast capability at layer\ 2, knows based on the first response received from the user that no contention takes place), a User\(hyuser information element may be included in the ALERTING and/or CONNECT messages transferred across the user\(hynetwork interface at the called side as described in \(sc\ 5.2.5. The content of this information element is transported by the network and delivered in the User\(hyuser information element included in the corresponding message(s) transferred across the user\(hynetwork interface at the calling side as described in \(sc\(sc\ 5.1.7 and\ 5.1.8. .PP In the case where users are allowed to contend for an incoming call (e.g., when the SETUP message containing an implicit service invocation is delivered using the broadcast capability at the data link layer and the network is unable to determine based upon the first response received from the user that there is no contention), the User\(hyuser information element may be included in the CONNECT message transferred at the called side. The content of the User\(hyuser information element delivered to the calling user shall be that received from the selected terminal as described in \(sc\ 5.2.8. .bp .PP \fINote\ 1\fR \ \(em\ The user may not be able to interpret incoming user\(hyto\(hyuser information. In such situations, the user should discard this information without disrupting normal call handling. No specific signalling is provided by the network to accommodate this situation. .PP \fINote\ 2\fR \ \(em\ In accordance with Recommendation X.213, the called user may perform compatibility checking using the User\(hyuser information element contents (see Annex\ B). .RT .sp 1P .LP 7.1.3.3 \fIUser\(hyto\(hyuser signalling in the call establishment phase\fR \fI\(em\ explicit service request (preferred or required)\fR .sp 9p .RT .PP Procedures for call establishment are as described in \(sc\(sc\ 5.1 and 5.2 with the following modifications: .PP On call request, the SETUP message sent by the calling user shall contain a service\ 1 request. The SETUP message sent by the network at the called side shall also contain an explicit service\ 1 request. .PP In the case where contention by users for the incoming call is not allowed (e.g., when the SETUP is delivered using the point\(hyto\(hypoint data link layer or when the SETUP is delivered using the broadcast capability at the data link layer and the network is able to determine that no contention is occurring), and the called user can support the transfer of User\(hyuser information elements during the call, a service\ 1 acceptance shall be included in the ALERTING message. .PP This explicit service 1 acceptance will be forwarded by the network to the calling user in the ALERTING message. .PP A User\(hyuser information element may be included in the ALERTING message and/or CONNECT message transferred across the user\(hynetwork interface at the called side as described in \(sc\ 5.2.5. .PP In accordance with Recommendation X.213, the called user may perform compatibility checking using the User\(hyuser information element contents (see Annex\ B). .PP \fINote\fR \ \(em\ The use of the explicit service 1 request procedures in the case where contention by the users for the incoming call is allowed (e.g.\ the SETUP message is delivered using the broadcast capability at the data link layers and the network is unable to determine that there is no contention) is for further study. .RT .sp 1P .LP 7.1.3.4 \fIInterworking\fR .sp 9p .RT .PP In the case of interworking with a non\(hyISDN network, the return of a PROGRESS or an ALERTING message with the Progress indicator information element indicating No. 1, \fIcall is not end\(hyto\(hyend ISDN; further call progress\fR \fIinformation may be available in\(hyband\fR , to the calling user shall serve as indication that, in particular, the delivery of User\(hyuser information elements in call control messages cannot be guaranteed. .RT .sp 1P .LP 7.1.3.5 \fIRejection of implicit service requests\fR .sp 9p .RT .PP Networks that cannot provide the service requested will not return a rejection indication. .RT .sp 1P .LP 7.1.3.6 \fIRejection of explicit service requests\fR .sp 9p .RT .PP If the called user or network does not understand the service 1 request, then the ALERTING message returned to the calling party shall not include either a service\ 1 acceptance or rejection. This type of response will be taken as an implicit rejection of service\ 1. .PP If the network or called user cannot support service 1, and it was requested as preferred, a service\ 1 rejection is included in the ALERTING message. .PP If the service 1 request indicated as required and the called user or network cannot support it, a RELEASE COMPLETE is sent with cause No.\ 50, \fIrequested facility not subscribed\fR , or cause No.\ 69, \fIrequested facility not\fR \fIimplemented\fR , and a service\ 1 rejection. .PP If the called user does not include a service 1 acceptance or rejection in the ALERTING message, the network shall return an explicit rejection in the ALERTING message sent to the calling user. .bp .RT .sp 1P .LP 7.1.3.7 \fIUser\(hyto\(hyuser signalling in the call clearing phase\fR .sp 9p .RT .PP A User\(hyuser information element may be included in the first message used to initiate the normal call clearing phase (see \(sc\(sc\ 5.3.3 and\ 5.3.4). .PP The information contained in such an information element is transferred to the remote user in the first clearing message (see \(sc\(sc\ 5.3.3 and\ 5.3.4). Such a transfer is only performed if the information is received at the local exchange of the remote user before sending a clearing message to that user, otherwise, the information is discarded without sending any notification. .PP In addition, when a SETUP message has been delivered using the broadcast capability at the data link layer, and the network is unable to determine from the first response received from the user that there is no contention, only the following user\(hyto\(hyuser information transfer is allowed: .RT .LP i) in the network to called user direction: .LP in the case of premature clearing by the calling user, user\(hyto\(hyuser information is sent in the first clearing message to each called user that has already responded to the incoming SETUP message; .LP ii) in the called user\(hynetwork direction: .LP the user\(hyto\(hyuser information will only be accepted from a terminal which is selected. .PP If multiple clearing messages are received, the network may, as a network option, retain the User\(hyuser information element along with the cause retained according to \(sc\ 5.2.5.4. In the event that this cause is returned to to calling user, the associated User\(hyuser information element shall also be returned. If there are multiple clearing messages containing causes of equal priority and User\(hyuser information elements, the User\(hyuser information element contained in the first clearing message will be sent to the calling user. If any of the clearing messages with the highest priority causes do not contain User\(hyuser information elements and other clearing messages with causes of lower priority do contain User\(hyuser information elements, no User\(hyuser information element shall be sent back to the calling user. .PP In the case where contention by users for the incoming call is not allowed (e.g.,\ when the SETUP message is delivered using the point\(hyto\(hypoint data link layer or the network knows that a user responding to a SETUP sent using the broadcast capability at the data link layer is not contending for the call) a User\(hyuser information element may be included in the first clearing message sent by the called user prior to entering the Active state. .PP In the case where contention by users for the incoming call is not allowed, if the called user rejects the call with a RELEASE COMPLETE message containing user\(hyuser information, the network shall deliver the user\(hyuser information in the DISCONNECT message sent to the calling user. However, if the network is providing in\(hyband information to the calling user, and chooses not to initiate clearing procedures at that time, the network may deliver the user\(hyuser information in a PROGRESS message sent to the calling user. .PP If the network is providing in\(hyband information to the calling user, in conjunction with call clearing, the network shall include the User\(hyuser information element in the DISCONNECT message sent to the calling user. .PP \fINote\fR \ \(em\ It is intended that this capability may be used to provide the clearing data transfer described in Recommendation\ X.213. .RT .sp 1P .LP 7.1.3.8 \fIUnexpected user\(hyuser information in call control messages\fR .sp 9p .RT .PP The network shall discard the User\(hyuser information element if it is received from either user in an ALERTING, CONNECT, DISCONNECT, RELEASE or RELEASE COMPLETE message but a request for user\(hyuser signalling was not indicated (either explicitly or implicitly) in the SETUP message delivered to the user. If this occurs, the network shall take action on the remaining contents of the message received from the user and shall send a STATUS message to the user containing cause No.\ 43, \fIaccess information discarded\fR . .RT .sp 2P .LP 7.1.4 \fIUser\(hyto\(hyuser signalling service 2\fR .sp 1P .RT .sp 1P .LP 7.1.4.1 \fIGeneral characteristics\fR .sp 9p .RT .PP Service 2 allows the users to communicate by means of user\(hyto\(hyuser signalling by transferring two USER INFORMATION messages in each direction during the call establishment phase. This service allows either an implicit or explicit rejection (see \(sc\ 7.1.4.3). .PP Service 2 is only applicable when a SETUP message has been delivered using the point\(hyto\(hypoint data link layer at the user\(hynetwork interface at the called side. .bp .RT .sp 1P .LP 7.1.4.2 \fICall establishment\fR .sp 9p .RT .PP Procedures for call establishment are as described in \(sc\(sc\ 5.1 and 5.2 with the following modifications. .PP On call request, the SETUP message sent by the calling user will contain a service\ 2 request. The SETUP message sent by the network at the called side will also contain an explicit service\ 2 request. .PP If the called user can support USER INFORMATION messages during call establishment, a service\ 2 acceptance shall be included in the ALERTING message sent to the network. This explicit acceptance indication shall be forwarded in the ALERTING message sent by the network to the calling user. .RT .sp 1P .LP 7.1.4.3 \fIService rejection\fR .sp 9p .RT .PP If the called user or network does not understand the service\ 2 request, then the ALERTING message returned to the calling user will not include either a service\ 2 acceptance or rejection. This type of response shall be taken as an implicit rejection of service\ 2. Alternatively, if the network or called user cannot support USER INFORMATION messages during call establishment, and the request is indicated as preferred, a service\ 2 rejection is included in the ALERTING message. .PP If the service 2 request indicated is required, and the called user or network cannot support or provide the service, a RELEASE COMPLETE is sent with cause No.\ 50, \fIrequested facility not subscribed\fR , or cause No.\ 69, \fIrequested\fR \fIfacility not implemented\fR , and a service\ 2 rejection. .PP If the called user does not include a service 2 acceptance or rejection in the ALERTING message, the network shall return an explicit rejection in the ALERTING message sent to the calling user. .PP In the case of interworking with a non\(hyISDN network, a PROGRESS or ALERTING message with the progress indicator information element indicating No.\ 1, \fIcall is not end\(hyto\(hyend ISDN; further call progress information may be\fR \fIavailable in\(hyband\fR , is sent to the calling user to indicate that the full service cannot be guaranteed. .RT .sp 1P .LP 7.1.4.4 \fITransfer of USER INFORMATION messages\fR .sp 9p .RT .PP Once an ALERTING message has been received, both the involved users can transfer information between themselves by transferring USER INFORMATION messages across the user\(hynetwork interface. The network provides for the transfer of such messages from the calling to the called side and vice versa. .PP The USER INFORMATION message includes the Call reference, the Protocol discriminator, and the User\(hyuser information elements as defined in \(sc\ 3.1.23. The More data information element may also be included by the source user to indicate to the remote user that another USER INFORMATION message will follow, containing information belonging to the same block. The use of More data information element is not supervised by the network. .PP If the user\(hyto\(hyuser signalling facility is provided, no more than two USER INFORMATION messages may be transferred in each direction after the ALERTING message and before the CONNECT message. .PP Sending or receiving of USER INFORMATION messages does not change the state of the call. .RT .sp 2P .LP 7.1.5 \fIUser\(hyto\(hyuser signalling service 3\fR .sp 1P .RT .sp 1P .LP 7.1.5.1 \fIGeneral\fR .sp 9p .RT .PP Service 3 allows the users to communicate by means of transferring USER INFORMATION messages during the Active state of a call. This service allows either an implicit or explicit rejection (see \(sc\ 7.1.5.3). This service may be requested during call establishment or during the Active state of the call. .RT .sp 1P .LP 7.1.5.2 \fIService request during call establishment\fR .sp 9p .RT .PP Procedures for call establishment are as described in \(sc\(sc 5.1 and 5.2 with the following modifications: .RT .LP a) On call request, the SETUP message sent by the calling user will contain a service\ 3 request. The SETUP sent by the network at the called side will also contain a service\ 3 request. .LP b) If the called user can support USER INFORMATION message transfer during the Active state, a service\ 3 acceptance shall be included in the CONNECT message. .bp .sp 1P .LP 7.1.5.3 \fIRejection of service requested during call establishment\fR .sp 9p .RT .PP If the called user or network does not understand the service 3 request, then the CONNECT message returned to the calling user shall not include either a service\ 3 acceptance or rejection. This type of response will be taken as an implicit rejection of service\ 3. Alternatively, if the network or called user cannot support USER INFORMATION messages during the Active state, and the request is indicated as preferred, a service\ 3 rejection is included in the CONNECT message. If the service\ 3 request indicated required, and the called user or network cannot support or provide the service, a RELEASE COMPLETE is sent with cause No.\ 50, \fIrequested facility not subscribed\fR , or cause No.\ 69, \fIrequested facility not implemented\fR , and a service\ 3 rejection. .PP If the called user does not include a service 3 acceptance or rejection in the CONNECT message, the network shall return a service\ 3 rejection in the CONNECT message sent to the calling user. .PP When interworking with a non\(hyISDN network occurs, a PROGRESS or an ALERTING message with the Progress indicator information element indicating No.\ 1, \fIcall is not end\(hyto\(hyend ISDN; further call progress information may be\fR \fIavailable in\(hyband\fR , is sent to the calling user to indicate that the service cannot be guaranteed. .RT .sp 1P .LP 7.1.5.4 \fIService request after call establishment\fR .sp 9p .RT .PP During the Active state of a call, a user may request service 3 preferred only. A FACILITY message indicating a service\ 3 request is sent from the requesting user to the network. The network shall indicate the service\ 3 request to the user that did not request service\ 3 in the FACILITY message. .PP If the user that did not request service 3 can support the transfer of USER INFORMATION messages during the Active state, a service\ 3 acceptance is returned in the FACILITY message. This explicit acceptance indication shall be conveyed back to the requesting user in a FACILITY message. .RT .sp 1P .LP 7.1.5.5 \fIRejection of service request after call establishment\fR .sp 9p .RT .PP If the user that did not request service 3 or network does not understand the service\ 3 request, then no message is returned. This response shall be taken as an implicit rejection of the service request. Alternatively, if the requested user or network cannot support or provide the service requested, a service\ 3 rejection shall be returned in the FACILITY message. .PP If the requested user does not respond to the service 3 request, the network shall return a service\ 3 rejection to the calling user. .RT .sp 1P .LP 7.1.5.6 \fITransfer of USER INFORMATION messages\fR .sp 9p .RT .PP Once the call is established, both users can transfer information between themselves by transporting USER INFORMATION messages across the user\(hynetwork interface. The network provides for the transfer of such messages from the calling to the called side and vice versa. .PP The USER INFORMATION message includes the Call reference, the Protocol discriminator, and the User\(hyuser information elements. The More data information element may also be included by the source user to indicate to the remote user that another USER INFORMATION message will follow, containing information belonging to the same block. The use of the More data information element is not supervised by the network. .RT .sp 1P .LP 7.1.5.7 \fICongestion control of USER INFORMATION messages\fR .sp 9p .RT .PP The network or user will flow\(hycontrol, when needed, the transfer of USER INFORMATION messages from a user or network by means of a CONGESTION CONTROL message containing a congestion level information element. Two indications of congestion level are specified: \fIreceive not ready\fR and \fIreceive ready\fR . On receipt of the former, the user or network should suspend sending USER INFORMATION messages; on receipt of the latter, sending may recommence. After having sent a receive not ready indication, the network or user shall discard USER INFORMATION messages which are subsequently received. The network or user will send a CONGESTION CONTROL message with a receive not ready indication whenever a USER INFORMATION message is locally discarded, if it is possible. The CONGESTION CONTROL message shall also include a cause No.\ 43, \fIaccess information discarded\fR . .bp .PP The receipt of the receive ready indication shall be interpreted as an indication that no more than \fIn\fR USER INFORMATION messages may be sent before another receive ready indication is received. The value of \fIn\fR requires further study. .PP Congestion control procedure itself should be regarded as local. .RT .sp 2P .LP 7.1.6 \fIUnexpected USER INFORMATION messages\fR .sp 1P .RT .sp 1P .LP 7.1.6.1 \fIReceipt of USER INFORMATION messages in incompatible call\fR \fIstates\fR .sp 9p .RT .PP Whenever a USER INFORMATION message is received from the user and it is not allowed by an invoked service (e.g.,\ in any other state than Active where only service\ 3 is invoked), the message will be discarded by the network. The network will respond with a STATUS message with a cause No.\ 43, \fIaccess\fR \fIinformation discarded\fR . .RT .sp 1P .LP 7.1.6.2 \fIReceipt of unexpected USER INFORMATION messages\fR .sp 9p .RT .PP Whenever a USER INFORMATION message is received by the network from the calling or called user after the network has indicated that user\(hyto\(hyuser cannot be supported, that message shall be discarded without further action. .RT .sp 2P .LP 7.1.7 \fIRequesting user\(hyto\(hyuser signalling services 1, 2 and 3\fR .sp 1P .RT .sp 1P .LP 7.1.7.1 \fIGeneral\fR .sp 9p .RT .PP This section describes procedures for requesting services 1, 2 and 3 in the same SETUP message. These services are described in \(sc\(sc\ 7.1.3, 7.1.4 and\ 7.1.5, respectively. .PP \fINote\fR \ \(em\ User\(hyto\(hyuser service 1 implicit request/acceptance follows \(sc\ 7.1.3.2 procedures. Only explicit service\ 1 requests may follow the procedure in this section. .RT .sp 1P .LP 7.1.7.2 \fICall establishment\fR .sp 9p .RT .PP Procedures for call establishment are described in \(sc\(sc 7.1.3.3, 7.1.4.2, and 7.1.5.2 with the following modifications. On call request, the SETUP message sent by the calling user will contain independent service\ 1, 2, 3 requests. .PP The SETUP sent by the network at the called sides will also contain the same independent service requests. If the called user can support the indicated services, then specific services acceptances may all be indicated in the ALERTING message. Alternatively, the user may accept services\ 1 and\ 2 in the ALERTING message, as defined in \(sc\(sc\ 7.1.3.3 and 7.1.4.2, and service\ 3 in the CONNECT message, as defined in \(sc\ 7.1.5.2. .RT .sp 1P .LP 7.1.7.3 \fIService rejection\fR .sp 9p .RT .PP If the called user or network does not understand any of the services requested, then the ALERTING and CONNECT messages returned to the calling user will not include either a service acceptance or rejection. This type of response will be taken as an implicit rejection of all services. If the called user or network does not understand a specific service request, that specific service is implicitly rejected following the procedures defined in \(sc\(sc\ 7.1.3.6, 7.1.4.3 or\ 7.1.5.3. Alternatively, if the network or called user cannot support one or more services requested, and the service requests were indicated as preferred, the specific service rejection may be included in the ALERTING messages. The services may also be rejected following the procedures in \(sc\(sc\ 7.1.3.6, 7.1.4.3 or\ 7.1.5.3. .PP If the called user does not include a service 1, 2 or 3 acceptance or rejection in the ALERTING and/or CONNECT message, the network shall return a service\ 1, 2 or\ 3 rejection in the ALERTING and/or CONNECT message sent to the calling user. .PP When interworking with a non\(hyISDN network occurs, a PROGRESS or an ALERTING message with the Progress indicator information element indicating No.\ 1, \fIcall is not end\(hyto\(hyend ISDN; further call progress information may\fR \fIbe available in\(hyband\fR , is sent to the calling user to indicate that the service cannot be guaranteed. .bp .PP If any or all of the services requested is indicated as required, then the network or called user that cannot support or provide the request will send a RELEASE COMPLETE with cause No.\ 50, \fIrequested facility not subscribed\fR , or cause No.\ 69, \fIrequested facility not implemented\fR , and the service rejection associated with that service. .RT .sp 1P .LP 7.1.7.4 \fITransfer of USER INFORMATION messages\fR .sp 9p .RT .PP The transfer of USER INFORMATION messages is defined in \(sc\(sc 7.1.4.4 and 7.1.5.6. .RT .sp 1P .LP 7.1.8 \fISummary of actions to be taken by the called side and subsequent\fR \fInetwork action\fR .sp 9p .RT .PP Actions to be taken by the called side and the subsequent network actions are summarized in Table\ 7\(hy1/Q.931. .RT .ce \fBH.T. [T174.931]\fR .ce TABLE\ 7\(hy1/Q.931 .ce \fBActions to be taken at the called side\fR .ce (Note 1) .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(12p) | cw(42p) | cw(48p) | cw(66p) | cw(60p) . Case Called user's capability Requested service (Note 2) Called user action { Calling user network interface action } _ .T& cw(12p) | lw(42p) | lw(48p) | lw(66p) | lw(60p) . 1 { Can analyze the service and accepts the service } { Services 1, 2, 3 preferred or required } { Return appropriate ACK indication by the response message } { Pass ACK to the calling user in normal call control messages } _ .T& cw(12p) | lw(42p) | lw(48p) | lw(66p) | lw(60p) , ^ | ^ | l | l | l ^ | ^ | l | l | l. 2 { Can analyze the service but does not accept the service } Services 1, 2, 3 required { Clears the call with appropriate message and cause } { Pass same cause to the calling user in the normal call control clearing message } { Service 1 (explicit invocation), 2, 3 preferred } { Return appropriate NACK indication in the response message. The call is not cleared } { Pass NACK to the calling user in normal call control messages. The call is not cleared } { Service 1 (implicit invocation) preferred } { Ignore the request or return appropriate NACK indication by the response message, the call is not cleared } Pass NACK to the calling user _ .T& cw(12p) | lw(42p) | lw(48p) | lw(66p) | lw(60p) , ^ | ^ | l | l | l ^ | ^ | l | l | l. 3 { Cannot analyze the service request } Services 1, 2, 3 required { Treats as an unrecognized optional information element } { Clears the call with appropriate message and cause } Services 1, 2, 3 preferred { Treats as an unrecognized optional information element } { Passes back the implicit user responses to the calling node (Note\ 3) } .TE .LP \fINote\ 1\fR \ \(em\ This Table covers the point\(hyto\(hypoint case. In the point\(hyto\(hymultipoint case, it is applied only if no contention to a broadcast SETUP EXISTS. .LP \fINote\ 2\fR \ \(em\ When an implicit user\(hyto\(hyuser signalling invocation is received for service\ 1 (which means that the user\(hyto\(hyuser information element is included in the SETUP but the explicit invocation is not), the request is regarded as preferred. .LP \fINote\ 3\fR \ \(em\ When no indication of acceptance or rejection of requested service is received from the called user, then it is regarded an an implicit service rejection. Therefore, in service\ 1 the user\(hyuser information element carried by originating SETUP message is not guaranteed an acknowledgement. The action to be taken in this case is up to the calling user. .nr PS 9 .RT .ad r \fBTable 7\(hy1/Q.931 [T174.931], p.\fR .sp 1P .RT .ad b .RT .LP .bp .sp 2P .LP 7.2 \fIProcedures for user\(hyto\(hyuser signalling not associated with\fR \fIcircuit\(hyswitched calls\fR .sp 1P .RT .sp 1P .LP 7.2.1 \fIGeneral characteristics\fR .sp 9p .RT .PP This feature allows the users to communicate by means of user\(hyto\(hyuser signalling without setting up a circuit\(hyswitched connection. A temporary signalling connection is established and cleared in a manner similar to the control of a circuit\(hyswitched connection. .RT .sp 1P .LP 7.2.2 \fICall establishment\fR .sp 9p .RT .PP Procedures for call establishment are as described in \(sc\(sc 5.1 and 5.2 with the following modifications. .PP On call request, the calling user sends a SETUP message identifying, within the Bearer capability and Channel identification information elements, a temporary signalling connection to be established on SAPI\ =\ 0. The SETUP message is encoded to indicate: .RT .LP i) Bearer capability information element: .LP \(em Unrestricted digital information in the information transfer capability field; .LP \(em Packet mode in the transfer mode field; .LP \(em User information layer 2 protocol is Recommendation\ Q.921 and user information layer\ 3 protocol is Recommendation\ Q.931 in the layer and protocol identification field. .LP ii) Channel identification information element: .LP \(em Exclusive in the preferred/exclusive field; .LP \(em D\(hychannel in the D\(hychannel indicator field; .LP \(em No channel in the channel selection field. .PP If the network determines that the requested temporary signalling connection service is not authorized or is not available, the network shall initiate call clearing in accordance with \(sc\ 5.3.2 | ) or \(sc\ 5.3.2 | ) with one of the following causes: .LP a) No. 57 \fIbearer capability not authorized\fR ; .LP b) No. 58 \fIbearer capability not presently available\fR ; .LP c) No. 63 \fIservice or option not available, unspecified\fR ; or .LP d) No. 65 \fIbearer service not implemented\fR . .PP The called user accepts the temporary signalling connection request by sending a CONNECT message towards the calling user. After the called user has received a CONNECT ACKNOWLEDGE message, it may begin sending USER INFORMATION messages. Once the calling user receives a CONNECT message, it can begin sending USER INFORMATION messages. .sp 1P .LP 7.2.3 \fITransfer of\fR \fIUSER INFORMATION messages\fR .sp 9p .RT .PP Once a temporary signalling connection is established, both users can transfer information between themselves by transferring USER INFORMATION messages across the user\(hynetwork interface. The network provides for the transfer of such messages from the called to the calling side and vice versa. .PP The USER INFORMATION message includes the Call reference, the Protocol discriminator, and the User\(hyto\(hyuser information elements as defined in \(sc\ 3.3.13. The More data information element may also be sent by the source user to indicate to the remote user that another USER INFORMATION message will follow, containing information belonging to the same block. The use of the More data information element is not supervised by the network. .RT .sp 1P .LP 7.2.4 \fICongestion control of USER INFORMATION messages\fR .sp 9p .RT .PP Congestion control procedures are the same as those described in \(sc\ 7.1.5.7. .RT .sp 1P .LP 7.2.5 \fICall clearing\fR .sp 9p .RT .PP The clearing of an established temporary signalling connection can be initiated by the user or network by sending a RELEASE message towards the far end user. The clearing procedure followed and the timers involved are the same as those for clearing a circuit\(hyswitched connection as described in \(sc\(sc\ 5.3.3 and\ 5.3.4. .bp .RT .sp 2P .LP \fB8\fR \fBApplication of circuit\(hyswitched supplementary services to\fR \fBterminals using stimulus procedures\fR .sp 1P .RT .PP This section describes how stimulus procedures may be used by an ISDN terminal to invoke supplementary services. .PP Signalling messages sent by terminals using stimulus procedures to invoke network supplementary services are usually generated as a direct result of actions by the terminal user (e.g.\ feature key activation) and in general do little more than describe the event which has taken place at the man\(hymachine interface (MMI). For the establishment of supplementary services, such stimulus operations at the MMI will normally be conveyed in the keypad or feature activation information element within, for example, the INFORMATION message. The meaning of the keypad or feature activation information may be customer specific. Similarly, signalling messages sent by the network to terminals using stimulus procedures may contain explicit instructions regarding the operations to be performed by the terminals (e.g.\ feature indication, start alerting,\ etc.) .PP Terminals using stimulus procedures are not expected to maintain a record of the states of that service since they have a master\(hyslave relationship with the network. Such terminals may also support only a compatible subset of the call states defined in \(sc\ 2.1.1 and may only report that compatible subset in the call state information element as described in the procedures of \(sc\ 5. At a minimum, the user shall be able to report the call state when the call is active. .RT .sp 2P .LP \fB9\fR \fBList of system parameters\fR .sp 1P .RT .PP The description of timers in the following tables should be considered a brief summary. The precise details are found in \(sc\(sc\ 5 and\ 6, which should be considered the definitive descriptions. .RT .sp 1P .LP 9.1 \fITimers\fR \fIin the network side\fR .sp 9p .RT .PP The timers specified in Table 9\(hy1/Q.931 are maintained in the network side of the interface. .RT .sp 1P .LP 9.2 \fITimers in the user side\fR .sp 9p .RT .PP The timers specified in Table\ 9\(hy2/Q.931 are maintained in the user side of the interface. Timers\ T305, T308 and T313 are mandatory for all user side implementations. .RT .LP .rs .sp 23P .ad r Blanc .ad b .RT .LP .bp .ce \fBH.T. [1T175.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . TABLE\ 9\(hy1/Q.931 .T& cw(342p) . { \fBTimers in the network side\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T301 Minimum 3 min Call received ALERT received CONN received Clear call Timer is not restarted Note 2 _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T302 10\(hy15 s (Note 5) Overlap sending { SETUP ACK sent. Receipt of INFO, restarts T302 } { With sending complete indication, or network alert, or connect request received } { Clear if call information determined to be definitely incomplete; else send CALL PROC } Timer is not restarted Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T303 4 s (Note 1) Call present SETUP sent { ALERT, CONN, CALL PROC or SETUP ACK received, REL COMP received if SETUP sent on point\(hypoint data link } { Retransmit SETUP; restart T303. If REL COMP has been received, clear the call } { Clear network connection. Enter call abort state } Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T304 20 s (provisional values) Overlap receiving { SETUP ACK received. Sending of INFO restarts T304 } { Send INFO; receive CALL PROC, ALERT or CONN } Clear the call Timer is not restarted { Mandatory only if \(sc\ 5.2.4 implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T305 30 s Disconnect indication { DISC without progress indicator No.\ 8 sent } REL or DISC received Network sends REL Timer is not restarted Mandatory _ .TE .nr PS 9 .RT .ad r \fBTableau 9\(hy1/Q.931 [1T175.931], p. 11 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [2T175.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . { TABLE\ 9\(hy1/Q.931\fI(cont.)\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T306 30 s (Note 6) Disconnect indication { DISC with progress indicator No. 8 sent. } REL or DISC received { Stop the tone/announcement. Send REL } Timer is not restarted { Mandatory when in\(hyband tones/ announcements are provided; see \(sc\(sc\ 5.4, 5.3.4.1 and Rec. I.300 series } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T307 3 min Null SUSP ACK sent RES received { Clear the network connection. Release call identity } Timer is not restarted Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T308 4 s (Note 1) Release request REL sent REL COMP or REL received { Retransmit REL and restart T308 } { Place B\(hychannel in maintenance condition. Release call reference (Note 9) } Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T309 90 s Any stable state { Data link disconnection. Calls in stable states are not lost } Data link reconnected { Clear network connection. Release B\(hychannel and call reference } Timer is not restarted Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T310 10 s (Note 7) Incoming call proceeding CALL PROC received { ALERT, CONN or DISC received. If DISC, retain cause and continue timing } { Clear call in accordance with \(sc\ 5.2.5.3 } Timer is not restarted Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T312 T303 + 2 s { Call present, call abort, etc. } { SETUP sent or resent on broadcast data link } Timeout Note 4 Timer is not restarted Mandatory _ .TE .nr PS 9 .RT .ad r \fBTableau 9\(hy1/Q.931 [2T175.931], p. 12 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [3T175.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . { TABLE\ 9\(hy1/Q.931\ \fI(end)\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T314 4 s Receiving segmented message Message segment received Last message segment received Discard message Timer is not restarted Mandatory see Annex K _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T316 2 min Restart request REST sent REST ACK received { REST may be retransmitted several times } { REST may be retransmitted several times } { Mandatory when \(sc\ 5.5 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T317 (Note 3) Restart REST received { Internal clearing of call references } Maintenance notification Timer is not restarted { Mandatory when \(sc\ 5.5 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T320 30 s (Note 8) { a) For B\(hychannel access: active b) For D\(hychannel access: null } { a) For B\(hychannel access: CONN sent or received b) For D\(hychannel access: DL\(hyESTABLISH\(hyCONFIRM or DL\(hyESTABLISH\(hyINDICATION received c) Last logical channel, cleared } { Call request packet received; or incoming call packet delivered; or DISC received; or for D\(hychannel access DL\(hyRELEASE\(hyIND received } { a) For B\(hychannel access: disconnect link layer and initiate clearing b) For D\(hychannel access: send DL\(hyRELEASE\(hy REQ } Timer is not restarted Optional. See \(sc\ 6.3 _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T321 30 s Any call state D\(hychannel failure { Response to layer 3 message received } { Send DL\(hyESTABLISH\(hy REQ on both D\(hychannels } Timer is not restarted { Mandatory when ANNEX F is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T322 4 s Any call state STAT ENQ sent { STAT DISC REL or REL COM received } { STAT ENQ may be retransmitted several times } { STAT ENQ may be retransmitted several times } { Mandatory when \(sc\ 5.8.10 is implemented } _ .TE .nr PS 9 .RT .ad r \fBTableau 9\(hy1/Q.931 [3T175.931], p. 13 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [4T175.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .nr PS 9 .RT .ad r \fBTableau 9\(hy1/Q.931 [4T175.931], p. 14 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [1T176.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . TABLE\ 9\(hy2/Q.931 .T& cw(342p) . { \fBTimers in the user side\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T301 Minimum 3 min Call delivered ALERT received CONN received Clear call Timer is not restarted { Mandatory when Annex D is implemented. (Note\ 3) } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T302 15 s (provisional value) Overlap receiving { SETUP ACK sent. Restart when INFO received } { INFO received with sending complete indication; or internal alerting; or internal connection; or a determination that sufficient call information has been received } { Clear if call information determined to be incomplete; else, send CALL PROCeeding } Timer is not restarted { Mandatory only if \(sc\ 5.2.4 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T303 4 s (Note 1) Call initiated SETUP sent { ALERT (Annex\ D) CONN (Annex\ D) SETUP ACK, CALL PROC, or REL COMP received } { Retransmit SETUP; restart T303. If REL COMP was received, clear the call (Annex\ D) } { Clear internal connection. Send REL COMP. Enter null state } { Mandatory when Annex D is implemented; otherwise optional } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T304 15 s Overlap sending { INFO sent. Restarted when INFO sent again } { CALL PROC ALERT, CONN, or DISC received } DISC sent Timer is not restarted Optional _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T305 30 s Disconnect request DISC sent REL or DISC received REL sent Timer is not restarted Mandatory _ .TE .nr PS 9 .RT .ad r \fBTableau 9\(hy2/Q.931 [1T176.931], p. 15 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [2T176.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . { TABLE\ 9\(hy2/Q.931\ \fI(cont.)\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T308 4 s (Note 1) Release request REL sent REL COMP or REL received Retransmit REL; restart T308 { B\(hychannel placed in maintenance condition. Call reference released (Note 5) } Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T309 90 s Any stable state { Data link disconnection. Calls in stable states are not lost } Data link reconnected { Clear internal connection. Release B\(hychannel and call reference } Timer is not restarted Optional _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T310 (Note 4) 10 s Outgoing call proceeding CALL PROC received { ALERT, CONN, DISC, or PROG received } Send DISC Timer is not restarted { Mandatory when Annex D is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T313 4 s (Note 1) Connect request CONN sent CONNect ACKnowledge received Send DISCconnect Timer is not restarted Mandatory _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T314 4 s Receiving segmented message Message segment received Last message segment received Discard message Timer is not restarted Mandatory; see Annex L _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T316 2 m Restart request REST sent REST ACK received { REST may be retransmitted several times } { REST may be restransmitted several times } { Mandatory when \(sc\ 5.5 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T317 (Note 2) Restart REST received { Internal clearing of call references } Maintenance notification Timer is not restarted { Mandatory when \(sc\ 5.5 is implemented } _ .TE .nr PS 9 .RT .ad r \fBTableau 9\(hy2/Q.931 [2T176.931], p. 16 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp .ce \fBH.T. [3T176.931]\fR .ps 9 .vs 11 .nr VS 11 .nr PS 9 .TS center box; cw(342p) . { TABLE\ 9\(hy2/Q.931\ \fI(end)\fR } .TE .TS center box ; cw(39p) | cw(45p) | cw(45p) | cw(39p) | cw(45p) | cw(45p) | cw(45p) | cw(39p) . Timer number Default time\(hyout value State of call Cause for start Normal stop At the first expiry At the second expiry Cross\(hyreference _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T318 4 s Resume request RES sent RES ACK or RES REJ received { Clear internal connection. Release call reference. Enter null state } Timer is not restarted { Mandatory when \(sc\ 5.6 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T319 4 s Suspend request SUSP sent SUSP ACK or SUSP REJ received { Enter active state. Notify user application } Timer is not restarted { Mandatory when \(sc\ 5.6 is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T321 30 s Any call state D\(hychannel failure { Response to layer 3 message received } { Send DL\(hyESTABLISH\(hy REQ on both D\(hychannels } Timer is not restarted { Mandatory when Annex F is implemented } _ .T& cw(39p) | cw(45p) | lw(45p) | lw(39p) | lw(45p) | lw(45p) | lw(45p) | lw(39p) . T322 4 s Any call state STAT ENQ sent { STAT, DISC, REL or REL COMP received } { STAT ENQ may be retransmitted several times } { STAT ENQ may be retransmitted several times } { Mandatory when \(sc\ 5.8.10 is implemented } .TE .LP \fINote\ 1\fR \ \(em\ This default value assumes the use of default values at layer 2; i.e., (N200\ +\ 1) times\ T200. Whether these values should be modified when layer\ 2 default values are modified by an automatic negotiation procedure is for further study. .LP \fINote\ 2\fR \ \(em\ The value of this timer is implementation dependent, but should be less than the value of\ T316. .LP \fINote\ 3\fR \ \(em\ The user may already have applied an internal alerting supervision timing function; e.g., incorporated within call control. If such a function is known to be operating on the call, then timer\ T301 is not used. .LP \fINote\ 4\fR \ \(em\ T310 is not started if progress indictor 1 or 2 has been delivered in the CALL PROCEEDING message or in a prevous PROGRESS message. .LP \fINote\ 5\fR \ \(em\ The restart procedures contained in \(sc 5.5 may be used on B\(hychannels in the maintenance condition. .nr PS 9 .RT .ad r \fBTableau 9\(hy2/Q.931 [3T176.931], p. 17 \ \ \ A L'ITALIENNE\fR .sp 1P .RT .ad b .RT .LP .bp