About the X.25 Product

Transport Level (L4)

Transport Level (L4)

At the transport level (level 4), the X.25 link provides TCP (based on the DARPA standard) and UDP. These Transport level protocols are used by Internet/Berkeley Services, by NS, and by user application programs that access the TCP/UDP and IP protocols.

The TCP protocol is a connection-based protocol. TCP verifies that all data is delivered without duplication to its destination. The UDP protocol, unlike TCP, has no concept of a connection. Messages are sent as a unit with source and destination information in the header.

The X.25 link provides a BSD to PLP (Packet Level Protocol) translator to allow access to PLP at level 3 for user-written application programs via BSD IPC.

The X.25 link also provides an OTS to PLP translator to allow access to PLP at level 3 for OSI Services via Xport OSI.

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HP General IO Connectivity manual Transport Level L4