458 Chapter 12: SNA Technology
Figure 12-25
SDLC Multipoint
Secondary Link Station
The SLS is the slave. It receives commands and returns responses. The physical layer can be
full duplex or half duplex, and it can be leased or dialup. The frame type can be FID2 or FID4.
Because it is a slave, it waits for the line protocol to be initiated by the PLS. There are two types
of SLS operation:
·
Two-way simultaneous--This device can both transmit and receive at the same time.
·
Two-way alternate--This device can either send or receive data, but not both at the same
time. Two-way alternate can send data and wait while the other link station sends.
When you configure Cisco routers as the PLS, these options must match between the router and
the SDLC device.
Physical Layer Between Link Stations
The leased line can be full duplex or half duplex between the PLS and SLS. The four-wire full-
duplex circuit is more expensive but more efficient. It is a good design practice is to connect all
the FEPs with full duplex, and any connections from the FEP to cluster controllers should be
half duplex. Each drop is controlled by a line-sharing device (LSD).
NOTE
Full datamode is when the PLS is full duplex and the SLS is full duplex. Half datamode is when
the PLS is full duplex and the SLS is half duplex.
IBM 3720/25/45
IBM 3x74
IBM 3x74
IBM 3x74
PU 4
FEP - Primary link
station 3745
Spokes can not
communicate
Secondary link station
PU 2
3174
Secondary link station
PU 2
3174
Secondary link station
PU 2
3174
87200333.book Page 458 Wednesday, August 22, 2001 2:53 PM