1

Scope

1.1

General 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 connection-mode Network Service.

This part of ISO/IEC ISP 10609 specifies the definition of Profile TC4331. The TC4331 profile is in the TC group which supports Transport protocol classes 0 and 2.

1.2

Position of Profiles within the Taxonomy The taxonomy of profiles is defined in ISO/IEC TR 10000-2. This part of ISO/IEC ISP 10609 defines the profile: TC4331

Connection-mode Transport Service over Connection-mode Network Service over ISDN - Packet mode service - B-channel de mand access - Virtual Call (VC).

This profile may be combined with any A-profile at the A/T boundary.

1.3

Scenario Figure 1 illustrates the end system configurations to which TC4331 profile is applicable.

The reference End System is directly attached to the ISDN at an S/T reference point of a Basic or a Primary Rate Access.

This part of the 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 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 7 776 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 mo de on the B-channel. The provisions of ISO/IEC 8878 apply with regard to the mapping of the CONS primitives and parameters to and from the elements of the ISO/IEC 8208 packet layer protocol.

The reference end system implements two protocol pillars below layer 4. One pillar is used over the ISDN D-channel for establishment, maintaining and clearing B-channel access connection. The other is used over the B-channel(s) for establis hing, maintaining and clearing virtual calls, and for the information transfer itself.

In making a call, Network Service connection establishment is a multi-stage process; the first stage is the establishment of B- channel access connection using D-channel call control procedures, the next is establishment of ISO 7776 Data Link layer, and finally the virtual call is established.

In receiving a call, Network Service connection establishment is a multi-stage process; the first stage is the channel selection and establishment of B-channel access connection (if not established) using D-channel call control procedure, the next is the establishment of the ISO 7776 Data Link layer (if not established), finally the virtual call is established.

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.