Question 9/XI - Common Channel Signalling System No. 7 - Signalling
Connection Control Part

Considering

(a) the increasing use of signalling networks utilizing Signalling
System No. 7;

(b) that such a signalling network has the capability to serve as a
transfer system in an integrated services digital network (ISDN);

(c) that the CCITT has recommended Signalling System No. 7 for use at 64
kbits in digital networks;

(d) that the Signalling System is specified and structured into:

-the Message Transfer Part, common for all services and applications,

-the Signalling Connection Control Part, common for all non-circuit
related signalling between all types of nodes,

-the Transaction Capabilities Application Part,

-the User Parts.

(e) that the MTPSCCP interfaces have been specified;

(f) that the transfer capability provided by the MTP and the SCCP has
taken into account the requirements defined by the Open Systems
Interconnection layered model defined in Recommendation X.200 by
providing a standard OSI network layer service and a number of
additional features;

(g) that the CCITT has specified a digital access signalling system for
access to the ISDN and that its interaction with the SCCP for new
services and applications (e.g., for user-to-user signalling) may impose
some additional requirements in terms of flow and congestion control;

(h) that further study is required for SCCP to complete the
specifications for such items as:

- signalling network functions;

-SCCP sub-system congestion control, SCCP management procedures;

-signalling system performances, in particular. The effects of possible
uneven traffic distribution due to the load sharing mechanism (SLS) on
SCCP performance parameter values,

What additional functions and what enhancements to existing SCCP
Recommendations are necessary to meet the current and additional
requirements resulting from further study of their application to
support various services and capabilities in telephone networks
Integrated Service Digital Networks (ISDN) and PLMNs?

ANNEX 1

(to Question 9/XI)

Unresolved issues in SCCP Recommendations

This annex lists the topics in SCCP on which study is expected to
continue in the period. It is not an exhaustive list, but does indicate
where the Recommendations might change. In these areas, RPOAs may need
to supplement the Recommendations, but in such a way so as not to
conflict with on-going work; implementors should consider likely future
developments and, where possible, design to accommodate these.

The topics under study are listed below, the references are to the Blue
Book:

1) inter-nodal communication model with SCCP connectionless service
(1.3.3Q.711);

2) delivery confirmation service (N-DATA ACKNOWLEDGE primitive) (Table
1Q.711);

3) transitions caused by N-DATA ACK primitive (Figure 7Q.711);

4) facilities causing differences in the called and responding addresses
in N-CONNECT request and response (2.1.1.2.2Q.711);

5) the need for Receipt Confirmation Service in SCCP (2.1.1.2.2 and
4.1.1.2Q.711);

6) connection identification parameter inclusion in Request types 1 and
2, and reply primitives between SCCP and ISUP (2.1.1.3.2Q.711);

7) connection identification parameter inclusion in N-CONNECT, N-DATA,
N-EXPEDITED DATA, N-RESET, and N-DISCONNECT primitives (Tables 2, 3, 4,
5, 6, 7, 8Q.711);

8) the list of release reason parameter values (2.1.1.2Q.711);

9) QOS parameter set inclusion in N-INFORM (Table 7Q.711);

10) set up and release functions for permanent signalling connections
(2.1.2.1Q.711);

11) integrating sequence control and return option parameters into the
QOS set (Table 9Q.711);

12) sequence control parameter inclusion in the N-UNITDATA indication
primitive (Table 10Q.711);

13) SCCP response to MTP-STATUS and MTP-RESTART (3.2.4, 3.2.5Q.711);
14) difference in QOS between permanent and temporary signalling
connections (4.1.2.2Q.711);

15) SCCP management procedures for sub-system congestion (4.3Q.711;
3.11, 3.12, 3.15Q.713; 5.1, 5.3Q.714);

16) SCCP capabilities in OSI NSAP address translation (4.4Q.711);

17) possible need for diagnostic parameter (2.6Q.712);

18) constraints on order of optional parameter transmission (1.8Q.713);

19) destination local reference coded as all ones (3.2Q.713);

20) source local reference coded as all ones (3.3Q.713);

21) alignment with X.96 call progress information (3.11, 3.15Q.713);

22) inclusion of routing failure causes as for return cause in Q.713
3.12 (3.15Q.713);

23) data parameter maximum length for Unitdata and Unitdata Service
messages (4.10, 4.11Q.713; 1.1.2, 4Q.714);

24) need for Released message cause value 1110 "not obtainable" (Annex
AQ.713);

25) need for Reset Request message cause value 1011 "not obtainable"
(Annex AQ.713);

26) notification regarding unrecognized messagesparameters (1.14Q.714);

27) classification of SCCP routing failure causes (2.4Q.714);

28) management procedures for non-dominant mode nodessub-systems with
more than one backup (5.1Q.714);

29) receipt from a local originating sub-system of a message for a
prohibited sub-system (5.3.2.1Q.714);

30) possible introduction of a sub-system out of service denial message
(5.3.5.3Q.714);

31) mathematical analysis of SCCP performance;

32) Q.716 parameter values (section 3Q.716).