RFC 2114 (rfc2114) - Page 2 of 22

Data Link Switching Client Access Protocol

RFC 2114                          DCAP                     February 1997


1.  Introduction

   Since the Data Link Switching Protocol, RFC 1795, was published, some
   software vendors have begun implementing DLSw on workstations. The
   implementation of DLSw on a large number of workstations raises
   several important issues that must be addressed. Scalability is the
   major concern. For example, the number of TCP sessions to the DLSw
   router increases in direct proportion to the number of workstations
   added. Another concern is efficiency. Since DLSw is a switch-to-
   switch protocol, it is not efficient when implemented on
   workstations.

   DCAP addresses the above issues. It introduces a hierarchical
   structure to resolve the scalability problems. All workstations are
   clients to the router (server) rather than peers to the router. This
   creates a client/server model. It also provides a more efficient
   protocol between the workstation (client) and the router (server).

2.  Overview

2.1.  DCAP Client/Server Model

      +-----------+              +-----------+       +---------+
      | Mainframe |              | IP Router +- ppp -+ DLSw    |
      +--+--------+              +-----+-----+       | Work    |
         |                             |             | Station |
         |                             |             +---------+
      +--+--+      +-------------+     |
      | FEP +- TR -+ DLSw Router +-- IP Backbone
      +-----+      +-------------+     |
                                       |
                                       |
                                 +-----------+       +---------+
                                 | IP Router +- ppp -+ DLSw    |
                                 +-----+-----+       | Work    |
                                                     | Station |
                                                     +---------+

                           |         DLSw Session          |
                           +-------------------------------+
  Figure 2-1. Running DLSw on a large number of workstations creates a
                         scalability problem.

   Figure 2-1 shows a typical DLSw implementation on a workstation. The
   workstations are connected to the central site DLSw router over the
   IP network.  As the network grows, scalability will become an issue
   as the number of TCP sessions increases due to the growing number of
   workstations.



Chiang, et. al.              Informational