Frame Relay

Frame Relay supports QoS only through a preset committed information rate (CIR) that allows packets to be designated as either "committed" or "excess." Frame Relay QoS often is found supporting Voice applications; for example, Voice over Frame Relay (VoFr). QoS is achieved within a Frame Relay network by artificially creating a fixed data stream. Frame Relay is designed for bursty data traffic, with the length of Frame Relay frames varying up to 4095 bytes (4 KB). VoFr applications truncate this variable-length frame to a fixed size; for example, 2 KB, providing the ability for sending and receiving equipment to clock the signal at regular intervals.

NOTE

Clocking enables the sending and receiving devices to synchronize with each other, ensuring a smooth transition state from idle to active and vice versa. In a VoFr application, clocking provides a "smoothing" of the signal so that voice conversations aren't clipped. (Clipping in voice conversations results in words being cut off or conversations sounding choppy; that is, with a lot of starting and stopping.)

VoFr often is used within converged enterprise networks; for the most part, VoFr is used for point-to-point virtual tie lines within an organization. VoFr traffic is marked as CIR, assuring no throughput delays affect voice signal quality. FRF.13 (Frame Relay Forum Implementation Agreement #13 Service Level Definitions Implementation Agreement August 1998) specifies the range of QoS parameters and SLAs that can be measured. FRF.13 also details how delay, frame delivery, data delivery and service availability should be calculated.

NOTE

A converged network is one supporting multiple and diverse applications across a single backbone with the same technology, such as a network carrying voice and data with a single protocol; for example, IP or Frame Relay.



Network Sales and Services Handbook
Network Sales and Services Handbook (Cisco Press Networking Technology)
ISBN: 1587050900
EAN: 2147483647
Year: 2005
Pages: 269

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