The benefits and drawbacks of DLSw

As frame relay continues to mature in the marketplace, more and more users are feeling comfortable using the technology for their mission-critical applications. In this issue and the following, we will address the two major methods used by IT managers operating in SNA environments. Today's issue will address DLSw; the next article will tackle RFC 1490.

Data Link Switching is a technique for carrying SNA over or through an IP network, sometimes referred to as "tunneling." The SNA end devices are not aware of the IP transport between them. Frame relay enters the picture when the IP network uses frame relay as the wide-area transport solution for interconnecting the routers. In essence, the SNA traffic is transported over IP over frame relay. To increase overall frame relay network performance and efficiency, DLSw supports "spoofing" - terminating all sessions locally at the router. In essence, it emulates the typical responses that would be received from host devices instead of having them traverse the wide area.

Most often, DLSw is utilized in WAN environments that are already router/IP-based. These environments typically have a smaller percentage of SNA traffic; they are not SNA-centric. It would not be efficient in an SNA-centric solution to add IP to the environment just to support DLSw.

However, there are also some drawbacks to DLSw. For one, the amount of per-frame overhead caused by the two levels of encapsulation results in less efficient use of frame relay resources. There's also the issue of SNA and IP traffic being labled similarly. To the frame relay network, all traffic appears to be IP, making it difficult to distinguish the SNA traffic from the true IP traffic. This is a concern if the SNA traffic is mission critical and in need of prioritization.

TeleChoice is one of the leading telecommunications consultancies worldwide for the design, development, implementation, and migration of new and leading edge telecommunications hardware, software and services. Our focus is on public networking and value-added services for the telecommunications industry. You can contact TeleChoice at its corporate headquarters at (973) 239-0700 or visit our Web site for more information.

A more in depth look at DLSw from Gen2 Ventures, Inc.

New Cisco executive details aggressive SNA plans
Network World, 3/30/98.

Vendor adds Clever ways to watch SNA and TP/IP performance
Network World, 3/2/98.

A comprehensive DLSw resource from Cisco

TCP/IP-to-SNA Connectivity with Channel-Attached Gateways
White paper by Polaris Communications, Inc. and Microsoft.

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