APN Configuration and Management Manual

Configuring for Token-Ring Support

SNAX/XF and SNAX/APN Configuration and Management Manual—425836-006

9-15

Types of Conversation

Transmissions over Token-Ring occur in one of two modes; they are either

connectionless or connection-oriented. Connectionless (or datagram) transmission

means that the Data Link Control component of a sending station does not keep any

state information about the data being sent and does not ensure that the data was

successfully received in the correct order by the destination station. In this mode, the

higher-level services must provide any required error recovery or frame sequencing.

This mode of data transfer uses a protocol called LLC1 (Logical Link Control type 1).

SNAX uses datagrams to send exchange IDs (XIDs) and set up the links. When the

links are set up, subsequent data exchanges are always handled by LLC2 protocol.

LLC2 protocol is connection-oriented and therefore verifies that sent data was

successfully received in the correct order by the destination station. This state

information is managed by the link station. IBM SNA components use LLC2 to ensure

that data transfer has occurred properly. The LLC type 2 services are summarized as:



Sequence numbering of data frames at the data link layer



Error detection and recovery



Flow control

Description of Frames

At the HP TRSA adapter, data and SDLC control information are encapsulated in a

data frame suitable for transport on the Token-Ring. SNAX/APN supplies the

information for the source and destination SAPs, and the destination MAC address.

The first part of the encapsulation is to create the link protocol data unit (LPDU), shown

in Figure 9-10 on page 9-16.