SNAX/XF and SNAX/APN Configuration and Management Manual

Configuring for Ethernet Support
SNAX/XF and SNAX/APN Configuration and Management Manual—425836-006
10-9
SAPs and Link-station Addresses
Figure 10-7 on page 10-10 shows three stations (A, B, and C) connected on an
Ethernet LAN. Station A has SAP A1 that is connected to SAP B1 of Station B. Station
B has three active SAPs. SAP B2 has two connections, one with SAP C1 and one with
SAP C2. SAP B3 also is connected to SAP C1.
What Figure 10-7 on page 10-10 does not show is multiple connections between the
same two MAC SAPs. For example, SAP B2 cannot have two sessions with SAP C1.
The inability of the same two MAC SAPs to have multiple connections is an architected
rule of Ethernet, because there is no way to identify an application’s conversation to
the lower layers other than the unique combination of MAC SAP to MAC SAP
connection.
The link-station serves approximately the same function as an SNA physical unit (PU).
The upper layers of SNA may be running parallel sessions within a single LU or
supporting multiple sessions, but all these conversations are channeled through the
same PU. In SNA, the architected restriction is 254 LUs for each PU.
Figure 10-6. SAPs and Link-stations
Protocol
Stack
#2
Protocol
Stack
#2
Protocol
Stack
#2
Protocol
Stack
#1
SAP 1 SAP 2
Link
Stations
Logical Link Control
Medium Access Control
Physical
User
Application
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