TS Supplement (Includes RFC-1006 Support)

Changes in the Transport Layer When Using RFC-1006

Introduction to RFC-1006

107751 Tandem Computers Incorporated 1–15

Changes in the

Transport Layer When

Using RFC-1006

This section provides an overview of the following features of OSI/TS when using

RFC-1006:

Transport Layer protocols: OSI transport protocol class 0 is used along with

Transmission Control Protocol (TCP).

Transport service user data: Exchange of transport user data during connection

establishment is supported.

Transport expedited data: Transport expedited data service is supported.

Larger TPDU Size: A much larger TPDU size is supported.

OSI/TS TPDU and TCP/IP transport packet structure: Only six TPDUs are

supported when using RFC-1006. TPDUs are encapsulated into the transport

packet for transmission across the network.

Transport service procedures: Service primitives, mapping between the OSI and

TCP/IP services, and the available transport service procedures.

Transport Layer Protocols When TCP/IP is the NSP, OSI/TS uses OSI transport protocol class 0, which does not

provide error-recovery, error-detection, or multiplexing. However, TCP/IP uses the

TCP, which is very similar to the OSI transport protocol class 4. TCP provides error-

recovery, error-detection, and multiplexing, in addition to other services.

TCP and OSI Transport Class 4 Compared

The following table compares the services provided by the TCP transport protocol and

the OSI transport class 4 protocol.

Table 1-1. TCP and OSI Transport Class 4 Compared

Service TCP/IP Transport OSI Transport Class 4

Addressing 16 bit port number variable TSAP-ID

Data transfer streams blocks

Datagrams UDP ISO 8602

Disconnect graceful abrupt

Error detection checksum checksum

Flow control bytes segments

Interrupts urgent pointer expedited data

Precedence 3 bit IP field 16 TP, IP fields

Security 11 byte IP field variable TP, IP fields

The end result is that OSI applications using OSI/TS over TCP/IP receive reliable

transport service over a TCP/IP network. The fact that the application is connecting

over a TCP/IP network is transparent to the application.