Optimize with SVCs - Technology Information

Communications News, June, 1999 by Abdul Noury, Praveen Goli

Frame Relay switched virtual circuits enable new customer services.

As service providers evolve their networks into the next generation, enhancing Frame Relay services by adding switched virtual circuits with Quality of Service (QoS) guarantees will enable them to offer customers services tailored to meet their business needs.

Frame Relay switched virtual circuits (SVCs) with QoS capability allow service providers to optimize network resources in ways not possible with permanent virtual circuits (PVCs). Bandwidth on demand is a case in point. With this capability, customers pay only for the bandwidth they actually use. For example, an organization might require a lot of network access during the day when most employees are at work but less bandwidth in the evening. The same organization may have more stringent delay requirements for videoconferencing than for normal Internet access. With Frame Relay SVCs and QoS, organizations can request the exact quantity and quality of bandwidth suitable for their applications and be charged accordingly.

SVCs can be established as needed on a call-by-call basis and connections can be released when there is no more information to send, thus reducing the cost to the end user. SVCs also use the network more efficiently and improve performance by allowing service providers to allocate unused bandwidth for other connections. SVCs enable statistical network usage similar to that of the voice telephone network. Because of this, with SVC support, networks designed to support thousands of circuits can scale up to support tens--or even hundreds of thousands--of connections.

Organizations with large numbers of sites are prime candidates for SVCs, which allow them to dynamically add users as needed, greatly reducing administrative time and costs. SVCs also are beneficial for remote-site access needs. This would include small office/home office (SOHO) users and telecommuters who generate low volumes of traffic and only need occasional and sporadic connectivity. SVCs also can provide as-needed connections for inter-enterprise communications between companies and their suppliers, partners, or customers, as well as for Internet access and applications.

In addition to these advantages of SVCs, PVC users also can benefit from SVCs by using them as a backup for highly intermittent applications such as disaster recovery, intra-company voice calls, and traffic overflow, among others. An organization with data requiring constant connectivity might opt for a combination of PVC and SVC services. For organizations with a wide range of traffic, SVCs might be more beneficial for certain aspects of their business, while users who have a more constant traffic flow may prefer PVC connections.

Two International Telecommunications Union (ITU) standards govern the specifications for enhancing Frame Relay service-provider equipment to provide SVCs with QoS. These are the X.146 standard, which provides QoS capability, and the X.36 standard for SVC signaling over Frame Relay. Frame Relay customer premises equipment (CPE) must comply with the X.36 standard and implement either the E. 164 standard (originally designed for telephony numbering) or the X.121 standard (originally designed for data numbering).

With ATM at the core and Frame Relay at the edge of so many networks today, service providers long have been interworking the two transports as outlined in the FRF.5 and FRF.8 standards. FRF.5 specifies Frame Relay-to-ATM network interworking, while FRE.8 specifies Frame Relay-to-ATM service interworking. Both standards originally were designed for PVCs. Now new standards efforts are underway (and expected to be complete this summer) to introduce SVC support to complement the existing FRF.5 and .8 standards.

Frame Relay-to-ATM service interworking will help service providers cater to their very large installed base of Frame Relay customers. It will give service providers the ability to extend SVC services in mixed environments (Frame Relay at the edge and ATM at the core) while extending QoS across the two environments. In any network, the level of the QoS service providers can offer is only as good as the weakest link (or switch) in the chain. By extending QoS to the Frame Relay switches at the edge of the network for the first time, the standard will strengthen these links and provide the flexibility to go from the originating to the destination CPE through the Frame Relay and ATM public network.

Although flat-rate billing for SVCs can serve as an interim solution, usage-based billing is more beneficial for customers. Unlike flat-rate billing which is a set monthly charge for a fixed number of calls of a certain bandwidth category and is not based on the actual amount of data sent, usage-based billing charges are based on the actual amount of packets or frames sent. To offer usage-based billing, service providers must tie their Frame Relay switches into the back-office management system that performs rating and invoicing based on call detail records.