Frame Relay Overview
The Frame Relay protocol allows network designers to reduce costs by using shared facilities that are managed by a Frame Relay service provider. Users pay fixed charges for the local connections from each site in the Frame Relay network to the first point of presence (POP) in which the provider maintains a Frame Relay switch. The portion of the network between the endpoint switches is shared by all the customers of the service provider, and individual data-link connection identifiers (DLCIs) are assigned to ensure that each customer receives only their own traffic.
Users contract with their providers for a specific minimum portion of the shared bandwidth committed information rate (CIR) and for a maximum allowable peak rate, burst information rate (BIR). Depending on the terms of the contract, traffic exceeding the CIR can be marked as eligible for discard, in the event of network congestion, or a best-effort term can apply up to the BIR rate.
Frame Relay does not require private and permanently connected wide area network facilities, unlike some older WAN protocols.
Frame Relay was developed as a replacement for the older and much slower X.25 protocol. It scales to much higher data rates because it does not require explicit acknowledgment of each frame of data.
You can configure the Frame Relay protocol on SONET/SDH, E1/E3, and T1/T3 physical router interfaces, and on the channelized DS3, channelized OC12, channelized T3 intelligent queuing (IQ), channelized OC12 IQ, and channelized E1 IQ interfaces.
Starting with Junos OS Release 11.2, multiple DLCIs are supported on a Frame Relay interface for End-to-End Multilink Frame Relay Implementation Agreement (FRF.15) bundles. Each DLCI should be part of a unique bundle and it is not possible to have more than one DLCI from the same Frame Relay interface in the same bundle. This feature enables you to have FRF.12 functionality over multiple DLCIs per Frame Relay interface.
 | Note: This capability is available on all M Series and MX Series routers supporting Layer 2 services. |
All Multiservices PICs and Multiservices Dense Port Concentrators support this feature. But Adaptive Services PICs (AS PICs) do not support the feature. DLCIs having different bandwidths that are part of the same bundle are also not supported.
