Pulling the new switch-eroo - frame relay switched virtual circuits - Technology Information

SVCs may soon be the method of choice for delivering connectivity between remote locations.

Frame relay is only a half-realized technology in the communications marketplace today. While corporations and carriers understand that frame relay PVCs (permanent virtual circuits) are more cost-effective than leased lines, they also know that PVCs are unsuitable for the requirements of dynamic networking. Enter SVCs (switched virtual circuits).

Unlike PVCs, SVCs are any-to-any connections that are initiated by the user, then torn down after the required data has been sent. Corporations and service providers around the world are beginning to look at frame relay SVCs to meet user requests for on-demand and dynamic services such as voice over frame relay.

Frame relay can improve performance (response time) and reduce transmission costs dramatically for a number of network applications, including file transfer, Internet access, and other data-intensive applications.

Frame relay is most effective when used under the following conditions:

* The end devices must be running an intelligent higher-layer protocol:

* The transmission lines must be virtually error-free;

* The application must tolerate variable delay.

At the heart of a frame relay connection is a type of virtual circuit called a data link connection (DLC). In most frame relay equipment and services today, DLCs are PVCs that are predefined on both sides of the connection. Each DLC has an identifying number called a data link connection identifier (DLCI). Having local significance only, the DLCI of a frame relay connection is different at the local and distant ends.

The routing tables at each intervening frame relay switch--in the carrier or private network--route the frames to the proper destination, alternately reading and assigning DLCI values in the control portion of the frame as appropriate.

With SVCs, users establish calls over the frame relay network or service by requesting a destination based on either the X.121 or E.164 specification numbering plan. SVCs can provide an alternative to a large network infrastructure, usually resulting in cost savings for networks with infrequent communications among sites.

Although SVCs were defined in the initial frame relay specifications, not all vendors or carriers of frame relay have implemented this powerful switching capability.

More carriers are expected to offer the service within the next 12 months as the complex billing systems needed to support frame relay SVC service are devised and implemented.

Given time and the continued development of dynamic networking technologies such as voice over frame relay, SVCs will be the method of choice for delivering connectivity between remote locations. Why? Because:

* As connectivity requirements increase, and as the number of PVCs increase geometrically in a meshed environment, the cost burden of managing those PVCs ultimately falls on the end user, just as with leased lines. These are hidden in such costs as additional FRAD or router serial ports or PVC charges from the frame relay carrier. For a large, fully meshed company, the PVC and management charges can become significant. SVCs can provide a way to avoid building a large infrastructure that is not necessary for infrequent communications between sites.

* Any-to-any, connectivity for frame relay is enabled with SVCs, allowing on-demand connections to remote users and applications. Global carriers can use the X.121 or E.164 numbering plans to offer true end-to-end switched services via frame relay, in a manner similar to what X.25, ISDN, and IP services do today.

* SVCs provide a true bandwidth-on-demand service with throughput parameters (such as CIR) requested at call setup time. This is particularly useful for voice over frame relay. In this case, when the digits are dialed, the SVC is established across the network to the appropriate point in the network. This approach is important, as it ensures that each call takes the optimum path through the network at call set-up.

* SVCs provide an easy and relatively inexpensive solution for disaster recovery solutions. Not only can costs associated with dedicated PVCs be eliminated, but by using switched access connections to the network in conjunction with SVCs, inexpensive and regular transfers can take place (for example, to update a "mirror image" database residing on a disaster recovery server). With SVCs, frame relay users can establish calls over the network without pre-configuring PVCs.

COPYRIGHT 1998 Nelson Publishing
COPYRIGHT 2000 Gale Group