Data Comm for Business, Inc.

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Product Application Note

Mix n Match:
Running Routers behind the DCB Multiplexer

Wide area networks that have been optimized for terminal type ASCII traffic are now being called upon to pass LAN based traffic for email and casual file transfers. At times, we also need to add a few PCs at a remote location LAN and connect that LAN to the host site for routed LAN traffic. If you are already using DCB multiplexers on the WAN, there is a quick, easy solution to this dilemma. DCB asynchronous routers work quite well when connected to a port on the DCB multiplexer. There are limitations on throughput... you would not want to do this if youre loading programs or large data files through the routed WAN, but for casual file transfer and email traffic, it works well. Figure one illustrates a typical system running over a 56 Kbps DDS line.

The remote LAN is connected to the host LAN with routers through the multiplexer. This insures adequate performance for terminal users while packet data such as email is transferred in the background.

Figure 1.

In this diagram, the local LAN and remote LAN are connected using BR-ASI01 routers running at 19.2 Kbps. Terminals are connected to all other ports of the multiplexer and vie for bandwidth. Since DCB multiplexers use statistical multiplexing techniques to optimize line utilization, all terminals receive their share of the bandwidth.... the router doesnt hog the line or seriously degrade terminal response. However, the routed traffic may take longer getting through. This isnt a problem for store-and-forward systems such as email, and some client-server systems with low data transfer requirements, but may cause problems for LAN based applications that are used over the WAN.

Ground Rules:

  1. Primary use is for terminal based (or PC terminal emulation) character traffic.
  2. LAN traffic is of low priority store-and-forward Email or occasional casual file transfer type.
  3. WAN link speed is 56 Kbps or greater. (It works on slower lines, but terminal response suffers).

Data Comm for Business, Inc. is a manufacturer and distributor of a diverse line of data communications and networking products. Their experts can help you connect remote sites with phone (1-800-4-dcbnet), email (, or personal (807 Pioneer, Champaign, Il. 61820) assistance. Check out their Web page at .