THE INTERACTIVE NETWORK DESIGN MANUAL

Building a Frame Relay Network

Selecting Frame Relay Equipment

To connect to a frame relay network, you need a device that understands the interface protocol. The User-Network Interface (UNI) is simple, so most equipment and software is not expensive. There are two general approaches: use a standalone FRAD to connect equipment with leased-line interfaces, or obtain software for an existing bridge, router, front end processor or other WAN device.

Frame Relay Access Devices

Standalone FRADs provide very simple mapping of DCLIs to other addresses, such as IP subnets. They may also perform limited routing functions, but don't have the range of routing protocols that a router does. They typically connect small remote sites to a limited number of locations.

Frame Relay Routers

Frame relay routers offer more sophisticated protocol handling than most FRADs. They may be packaged specifically for frame relay use, or they may be general purpose routers with frame relay software. This software may sometimes be an additional cost over the basic router code.

What to look for in a FRAD or router

• RFC 1490 support. This describes an encapsulation method for carrying traffic across a frame relay network. Using RFC 1490 will allow you to mix vendor equipment.
  
• Traffic prioritization. While protocols such as FTP will fill a WAN link very efficiently, this may choke delay-sensitive traffic, such as SNA or DEC LAT. Access devices should fragment large packets and provide priority queuing to critical traffic. Prioritization should be available at both the network and application level. For example, IP telnet traffic may get priority over IP SNMP traffic.
  
• Remote configuration via telnet and SNMP
  
• Management statistics. Devices should at least provide simple counters of frame rates, errored frames, congestion notifications and DE bits.
  
• Data compression. This is mainly important at low speeds (around 56 Kbps), and when the data sent will not already be compressed. Most vendors can provide compression between their own devices. An interoperable standard has been published by the Frame Relay Forum as Implementation Agreement FRF.9; However, there are few devices supporting it at this writing.
  
• Encryption for high security environments. In most cases, you'll be locked into a single vendor's equipment and may suffer an additional latency penalty.
  
• Automatic DLCI detection. The unit should learn DLCIs during the installation process.
  

FRADs may also contain an integrated CSU/DSU and should be less costly than routers. Routers should contain protocol-specific link optimization features such as traffic filtering and protocol spoofing.