from the files of
Networking Unlimited, Inc.
14 Dogwood Lane, Tenafly, NJ 07670
Phone: +1 201 568-7810

Async Dialup to Support Remote Sites Waiting for Frame Relay and ISDN Installation

Copyright © 1999, Networking Unlimited, Inc. All Rights Reserved.

An expanding retail chain could not get the local RBOC to install frame relay and ISDN services to match their store opening schedules. Networking Unlimited, Inc. designed and implemented an asynchronous dial-in server and matching store router configurations to support all IP and IPX requirements over available POTS lines.


A retail chain was expanding and opening multiple new and acquired stores a week. Stores required IP and IPX communications with the HQ data center to support stocking and payroll while preparing to open as well as to support retail sales once open. The RBOC providing frame relay and ISDN services could not respond to last minute scheduling changes, nor could they install connections while construction was still in progress. The only way to support new stores was to use existing POTS services and configure the store routers to support an analog modem on the auxiliary port.

Technical Approach

Networking Unlimited, Inc. configured a Cisco 2511 access server to support dial in by store routers. Since there were normally no skilled personnel at the store site, it was essential that the configuration be one that could not only support store operations while connected via analog modem only, but also be compatible with frame and ISDN links configurations so that reconfiguration would not be required as proper services became available. It was also essential that the modem link require minimal skill to manually restore a connection when required.

By using a line rotary on the access server, a single phone number could serve multiple stores simultaneously. Stores were identified by IP number on the PPP dial in, with each store having a unique identifier, IP address, and authentication password. While IP support was simple, IPX support was problematic as the 2511 dialer and the async lines both wanted to control IPXWAN, but a functional configuration was found by trial and error.

For periods when there are not many stores on async dialup, an alternative access server configuration was developed to support dial in access from PC's. The number of lines devoted to each can be easily changed as required.

Bottom Line Results

Scheduling of frame relay and ISDN lines has been reduced from being a schedule breaker to simply a matter of reducing costs. Up to a dozen stores have been supported simultaneously, and the same configuration can be used in other stores requiring emergency communications restoral after major outages affecting both frame relay and ISDN communications.

Activating the analog backup merely requires plugging a modem into power and the auxiliary port on the router, and pinging a "magic" address from any system in the store. That act automatically dials out and makes the connection. The link will then stay up as long as it is in use, with network management traffic being adequate to keep the link up indefinitely. When either frame relay or ISDN is installed and takes over the traffic load, the analog call will automatically drop and the modem can be retrieved when convenient.

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Copyright 1999-2000 © Networking Unlimited Inc. All rights reserved.