ISO/IEC ISP 10609 is applicable to end systems concerned with operating in the Open Systems Interconnection (OSI) environment. It specifies a combination of OSI standards, which collectively provide the connection-mode Transport Service using the conn ection-mode Network Service.
This part of ISO/IEC ISP 10609 defines the profile TC1231. The TC1231 profile is in the TC Group which supports Transport protocol classes 0 and 2.
1.2 Position within the taxonomy
The taxonomy of OSI profiles is defined in ISO/IEC TR 10000-2. This part of ISO/IEC ISP 10609 defines the profile:
TC1231 Connection-mode Transport Service over connection-mode Network Service - Switched access to a PSDN - ISDN B-channel case - Virtual Call (VC).
This profile may be combined with any A-profile at the A/T boundary.
Figure 1 illustrates the configuration of systems to which the TC1231 profile is applicable.
The reference end system communicates with the remote end system through an Integrated Services Digital Network (ISDN) and a Packet Switched Data Network (PSDN). The reference end system is directly attached to the ISDN at an S/T reference point.
This part of ISO/IEC ISP 10609 specifies the required functions from the supporting protocol stack shown in figure 2.
At layer 1, CCITT I.430 is used for ISDN basic rate access and CCITT I.431 is used for primary rate access. At layer 2, CCITT Q.921 provides the LAPD Data Link procedures for the D-channel and ISO 7776 provides the LAPB Data Link procedures for the B- channel. At layer 3, CCITT Q.931 signalling procedures are used on the D-channel, and ISO/IEC 8208 packet layer protocol is used in DTE/DCE mode on the B-channel. The provisions of ISO/IEC 8878 apply with regard to the mappings of the CONS primitives and parameters to and from the elements of the ISO/IEC 8208 packet layer protocol, subject to further provisions specified in ISO/IEC 9574.
The reference end system implements two protocol pillars below layer 4. One pillar is used over the ISDN D-channel for establishing, maintaining and clearing circuit switched B- channel connections. The other is used over the B-channel(s) for establishing, maintaining and clearing virtual calls, and for the information transfer itself.
Network Service connection establishment is, in general, a multi-stage process; the first stage is the establishment of a circuit switched B-channel connection using the D-channel call control procedures, the next is the establishment of the ISO 7776 Data Link layer, and finally the virtual call is established.
In general, Network Service connection release is also a multi- stage process, the first stage being the release of the virtual call. If the associated B-channel connection does not currently support any other Network Service connections, the system may release the ISO 7776 Data Link layer connection, and may then release the B-channel connection using the D-channel signalling procedure in conformity with CCITT Q.931.