1) The word 'protocol' in the header of the template needs changing to 'part'; the individual layers are parts of the SS#7 protocol, not protocols in their own right - that's why P in the names of the layers stands for Part, not Protocol. Just because the datacoms world decide that any simple set of message formats deserves to be called a protocol, doesn't mean the telecoms world has to as well!
2) TCAP isn't really at the application layer; I'd say it was more at the session layer. It certainly doesn't provide any applications, on its own, to a telecoms network; it just provides dialogue capabilities to its users, which are the real application layers. 18.104.22.168 21:53, 26 March 2007 (UTC)
This "diagram" doesn't make it immediately obvious that TCAP and CAP are one layer below INAP and MAP. Perhaps we could put a message that said null between the Application and Network OSI Layers? Bostonvaulter (talk) 09:50, 7 October 2009 (UTC)
Changes to SS7 Protocol diagram
The following is the justification and citations for alterations made to the SS7 protocol stack diagram:
The SS7 stack is broken into Functional Levels not Layers (as in OSI).
- Level 1 is the Signalling Data Link Functional Level (Data Link Level).
- Level 2 is the Signalling Link Functional Level (Link Level).
- Level 3 is the Signalling Network Functional Level (Network Level).
- Level 4 is the MTP User and consists of SCCP, ISUP, TUP, or any MTP User.
The quintessential diagram for MTP levels is ITU-T Recommendation Q.700 (03/1993), Figure 3/Q.700, "SS No. 7 functional levels", p. 8.
- MTP and SCCP together are referred to as the Network Service Part (NSP). Some user parts making use of the services of the NSP may use MTP alone (e.g. TUP), or both MTP and SCCP in a Type A or Type B arrangement.
The quintessential diagram for SCCP levels is ITU-T Recommendation Q.711 (03/2001), Figure 1/Q.711, "Functional diagram for the SCCP in Signalling System No. 7", p. 2.
(Note that this diagram also depicts the Type A and Type B user part that use both MTP and SCCP. A user part that interfaces only to MTP can be termed a Type I user. A user part that interfaces to both MTP and SCCP can be termed a Type II user. Type II users can either by Type II (a) or Type A in that they use MTP, SCCP CONS and CLNS services; or Type II (b) or Type B in that they use MTP and SCCP CLNS (no CONS) services.)
Mapping of OSI Layers onto MTP Levels is described in ITU-T Recommendation Q.700 (03/1993), Clause 4, "OSI layering an SS No. 7", p. 9, and ITU-T Recommendation Q.1400 (03/1993), Clase 2.2, "OSI layering and SS No. 7", p.4.
- OSI layers 1, 2 and part of layer 3 map to the MTP.
- OSI layer 3 (the remainder of layer 3) is provided by SCCP or some part of another MTP User part.
- OSI layer 4, 5 and 6, are null.
- OSI layer 7 corresponds to the upper part of the MTP user, or the TC sublayer and TC-User.
A simple diagram for the mapping of OSI layers onto the SS7 architecture is given in ITU-T Recommendation Q.700 (03/1993), Figure 2/Q.700, "Architecture of SS No. 7", p. 7. A more detailed diagram for the mapping of OSI layers onto the SS7 architecture is given in ITU-T Recommendation Q.1400 (03/1993), Figure 1/Q.1400, "Relationship between SS No. 7 Functional Levels and OSI Layering", p. 5.
I have taken a first stab at it, but if someone could coerce the diagram to better reflect those of Q.700, Q.711 and Q.1400 I'm sure it would be appreciated as I have no skill in generating Wikipedia diagrams.