SNAX/XF and SNAX/APN Configuration and Management Manual

Configuring for Ethernet Support
SNAX/XF and SNAX/APN Configuration and Management Manual—425836-006
10-10
Types of Conversation
For a further discussion about SAPs, see Figure 10-11 on page 10-15 and Unique
Addressing on page 10-15.
Types of Conversation
Transmissions over Ethernet 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 error recovery and 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:

Sequence numbering of data frames at the data link layer

Error detection and recovery

Flow control
Figure 10-7. SAPs and LLC Connections
A1
Station A
Station B Station C
SAP
LLC
MAC
B1 B3 C2B2 C1
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