25 CONFIGURING DLSW
This chapter contains information on the following topics:
■DLSw Protocol Overview
■Configuration of DLSw
■Display and Debug DLSw
■Typical DLSw Configuration Example
■Diagnosis and Troubleshooting of DLSw Fault

DLSw Protocol

Overview Data Link Switch Protocol (DLSw) is a method designed by Advanced Peer-to-Peer
Networking (APPN) Implementers Workshop (AIW) to load SNA through TCP/IP
(SNA is a network protocol introduced by IBM in 1970's and completely
correspondent with OSI reference model). DLSw technology is one of the solutions
for implementing the transmission across WANs via SNA protocol.
The operating principle of DLSw is shown in the following diagram:
Figure 138 DLSw principle diagram
From the above diagram, you may find out the router with DLSw transforms the
frame in format LLC2 on the local SNA equipment into SSP frame which can be
encapsulated into TCP messages. Then it sends SSP frame to the remote end
through TCP channel across WANs, and transforms SSP frame into the
corresponding frame in LLC2 format at the remote end site, finally sends the latter
to the next-hop SNA equipment. In another words, DLSw makes the local
terminating equipment “think” the remote equipment locates in the same
network. With the differences from transparent bridge, DLSw transforms the
original LLC2 protocol frame into SSP protocol frame instead of
transparent-transmitting to the next hop directly, so as to encapsulate the existing
data into TCP messages. It features local acknowledgement mechanism, thus
reducing unnecessary data transmission (confirming frame and maintaining alive
frame) and resolving the overtime problem of data link control.
With DLSw technology, the transmission across TCP/IP via SDLC link protocol can
also be implemented. The procedure is to transform the messages in SDLC format
into the messages in LLC2 format, then utilize DLSw to intercommunicate with the
remote end. DLSw also supports intercommunication of different media between
LAN and SDLC.
SSP
TCP/IP
LLC2LLC2
LANLAN
End System End SystemDLSwDLSw