Some terms related specifically to Frame Relay are as follows:
Committed information rate (CIR): Specifies the maximum average data rate that the network undertakes to deliver under normal conditions. When subscribing to Frame Relay service, you will specify the local access rate (for example, 56 kbps or T1). Typically, you will also be asked to specify a CIR for each DLCI. If you send faster than the CIR on a given DLCI, the network will flag some frames with a discard eligible (DE) bit. The network will do its best to deliver all packets, but will discard any DE packets first if there is congestion. Many inexpensive Frame Relay services are based on a CIR of zero. A CIR of zero means that every frame is a DE frame, and the network will throw any frame away when it needs to. The DE bit is within the address field of the Frame Relay frame header.
Inverse Address Resolution Protocol (Inverse ARP): A method of dynamically associating the remote router network layer address with a local DLCI. Inverse ARP allows a router to automatically discover the network address of the remote DTE device associated with a VC.
LMI: A signaling standard between the router (DTE device) and the local Frame Relay switch (DCE device) that is responsible for managing the connection and maintaining status between the router and the Frame Relay switch.
Forward explicit congestion notification (FECN): A bit in the address field of the Frame Relay frame header. The FECN mechanism is initiated when a DTE device sends Frame Relay frames into the network. If the network is congested, DCE devices (Frame Relay switches) set the FECN bit value of the frames to one. When these frames reach the destination DTE device, the address field (with the FECN bit set) indicates that these frames experienced congestion in the path from source to destination. The DTE device can relay this information to a higher-layer protocol for processing. Depending on the implementation, flow control may be initiated or the indication may be ignored.
Backward explicit congestion notification (BECN): A bit in the address field of the Frame Relay frame header. DCE devices set the value of the BECN bit to 1 in frames that travel in the opposite direction of frames that have their FECN bit set. Setting BECN bits to 1 informs the receiving DTE device that a particular path through the network is congested. The DTE device can then relay this information to a higher-layer protocol for processing. Depending on the implementation, flow control may be initiated or the indication may be ignored.