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Frame relay

Frame your data

There are numerous technology options like leased lines, VSAT links or VPNs that offer high-speed, reliable and secure connectivity between multiple geographically distinct locations. Ivano Rondelli, Country Director, Tele Media International (TMI), suggests you use Frame Relay technology and have the service provider sweat it out, managing the backbone. He also tells us how the technology enables your enterprise to make use of its cost-effectiveness, reduce overheads, and increase ease-of-use. by Soutiman Das Gupta

What are the limitations of VSATs (Very Small Aperture Terminals), leased lines and VPNs (Virtual Private Networks)?
VSATs are characterized by very high latency due to a long path that the signal has to cross to reach its destination. The VSAT service provider may have promised high bandwidth with reliable connectivity, but the actual performance depends on transponder space and weather conditions. Leased lines have its fair share of downtime and bottlenecks. In case of IPLCs (International Private Leased Circuit), when data passes from one provider to another provider's gateway, there're chances of signal loss and outage. Each provider will ping-pong responsibilities delaying the network recovery. VPNs do not provide any guarantee of throughput amounts. And since there's strong encryption on both sides, transmission is slow. It requires very expensive equipment which also needs well-trained technical staff to manage the service.

In that case, what wide-area connectivity option does an enterprise have?
You can consider the option of using Frame Relay technology backbone to transmit your data and voice. Frame Relay is a popular service and technology used to link distant LANs and networks (see box for a detailed explanation). The Frame Relay WAN (Wide Area Network) backbone connects LAN switches, bridges, and routers to nodes that function as Frame Relay end points or PoPs (Point of Presence). Data can be transferred at usual speeds of 64 to 128 Kbps, and one can go for a maximum throughput of 2 Mbps.

Enterprises that have LANs scattered globally can be interconnected using PVCs. A PVC (Permanent Virtual Circuit) is a point-to-point connection established and defined during the start of the service. These also operate at speeds between 64 Kbps and 2 Mbps.

What are the advantages of a Frame Relay-based WAN backbone?
Frame Relay technology offers many inherent advantages to an enterprise user and is a strong contender among competing technologies for connecting corporate LANs. It scores over other technologies like IPLCs, VSATs and VPNs on counts of lower cost of ownership, well established standards and easy interfaces that allow plug-and-play service implementation, interoperability with a large variety of protocols, network scalability and disaster recovery.

At the time of signing up for services with a service provider, a user can decide on a CIR (Committed Information Rate) and port speed. The CIR is a pledge on the part of the service provider to provide a certain amount of transmission capacity. And if the company needs more bandwidth, it can simply call the service provider and request allocation of additional bandwidth or ports.

Frame Relay transmission is simple because it operates on the thumb rule, 'If a frame has a problem, discard it!’ This makes the job to control traffic congestion and handle corrupt frames very efficient and admirable. In such cases the faulty frames will be discarded and normal data transmission can resume. Do note that different service providers implement signaling mechanisms in different ways.

How does the customer connect to a service provider at his end?
The service provider will have its PoPs (Point of Presence) scattered worldwide, which has backbone switches and routers. Each PoP is connected to one or more PoPs in order to build a redundant network.

A hardware device called FRAD (Frame Relay Access Device) is required at the customer's location to access the network. A router can act as a FRAD, and actually it is the most widely used customer access device. The FRAD connects to a port on a Frame Relay switch in the PoP using an interface called UNI (User-to-Network Interface). This line or port can typically provide bandwidth in multiples of 64 Kbps. The entire traffic for each customer generally travels through the same port.

Why will an enterprise prefer this service to other options?
A big advantage of Frame Relay is its cost-effectiveness compared to leased lines and IPLCs. Frame Relay service providers take care and manage the entire service end-to-end. Maintenance of the backbone, backing up data, and disaster recovery can sometimes also be looked after by the provider. Leased line service providers can't do this.

The performance standards are generally high and connectivity more reliable than other options. PoPs are connected in a mesh, and if one breaks down; the geographically nearest PoP can take over. The network can introduce a number of features like congestion management, change management, and bandwidth scalability. It can support multiple protocols and allow a smooth migration to ATM services in future. A customer can use VoFR (Voice over Frame Relay) to transport voice between its locations. It also allows Web-based traffic and performance reports and the service provider can offer easier billing options.

Bandwidth on a single connection is limited to 2 Mbps. What happens when the enterprise needs more?
When an organization needs more than 2 Mbps, it can use second PVC and more that will branch out from within the access line. PVCs in their full capacity can handle peak hour demands, traffic bursts, and bandwidth-intensive applications like video conferencing. Each customer's CIR can be guaranteed and spare bandwidth made available to prevent any congestion on the network.

TMI (Tele Media International) Limited is a wholly owned subsidiary of Telecom Italia Group. It's the sixth largest telecommunications operator in the world. It started operations in 1982 and has been in India since 1994 in partnership with VSNL. It has 130 PoPs in 44 countries and is one of the largest private digital networks in the world.

The company's backbone connects the 44 countries uses Cisco/Stratacom for ATM, Frame Relay, IP and messaging services, Newbridge for the transport layer and Ericsson for Intelligent Voice services. In India, the company only provides Frame Relay services. Other services are expected to be launched soon.

You can contact Ivano Rondelli at: TMI India, 909-912, Maker Chambers V, Nariman Point, Mumbai - 400 021,
Tel. 022-282 4606, Fax 022-282 4590, Web: www.tminet.net

Frame Relay all the way
Frame Relay is a high-speed packet switching protocol used in WANs that can provide bandwidth up to 45 Mbps. It operates at the physical and data link layers of the OSI reference model and is popular for connecting LANs across large distances. Frame Relay transmission is much faster than a X.25 network which was the first packet-switching WAN standard. It's mostly used to route LAN protocols like IPX or TCP/IP and can also carry asynchronous traffic, voice, and SNA (Systems Network Architecture IBM's mainframe network standards).

Frame Relay provides permanent and switched logical connections, known as PVCs (Permanent Virtual Circuits) and SVC (Switched Virtual Circuits). These are logical connections provisioned ahead of time. The connections are identified by a DLCI (Data Link Connection Identifier) number that is significant to the local Frame Relay switch.

Frame Relay is cost effective mostly because the network buffering requirements are carefully optimized. It’s also much faster than X.25.

The last 2 bytes of the frame are always generated by a CRC (Cyclic Redundancy Check) of the rest of bytes between the flags. CRC is an error checking technique that can ensure the accuracy of transmitting digital data. The remaining components of the frame contain the user data.

Soutiman Das Gupta can be reached at soutimand@networkmagazineindia.co


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