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Frame Relay Protocols 531
Data terminal equipment (DTE)
DTEs are also known as data-circuit termination equipment. For
example, routers are DTEs when connected to a Frame Relay
service from a telecommunication company.
Data communications equipment
(DCE)
Frame Relay switches are DCE devices.
Access link
The access link is the leased line between DTE and DCE.
Access rate (AR)
The access rate is the speed at which the access link is clocked.
This choice affects the price of the connection.
Committed information rate
(CIR)
The CIR is the rate at which the DTE can send data for an
individual VC, for which the provider commits to deliver that
amount of data. The provider will send any data in excess of this
rate for this VC if its network has capacity at the time. This choice
typically affects the price of each VC.
Burst rate
The burst rate is the rate and length of time for which, for a
particular VC, the DTE can send faster than the CIR, and the
provider agrees to forward the data. This choice typically affects
the price of each VC.
Data link connection identifier
(DLCI)
A DLCI is a Frame Relay address and is used in Frame Relay
headers to identify the virtual circuit.
Forward explicit congestion
notification (FECN)
The FECN is the bit in the Frame Relay header that signals to
anyone receiving the frame (switches and DTEs) that congestion is
occurring in the same direction as the frame. Switches and DTEs
can react by slowing the rate by which data is sent in that direction.
Backward explicit congestion
notification (BECN)
The BECN is the bit in the Frame Relay header that signals to
anyone receiving the frame (switches and DTEs) that congestion is
occurring in the opposite (backward) direction as the frame.
Switches and DTEs can react by slowing the rate by which data is
sent in that direction.
Discard eligibility (DE)
The DE is the bit in the Frame Relay header that signals to a switch
to, if frames must be discarded, please choose this frame to discard
instead of another frame without the DE bit set.
Nonbroadcast multiaccess
(NBMA)
NBMA refers to a network in which broadcasts are not supported,
but more than two devices can be connected.
Local Management Interface
(LMI)
LMI is the protocol used between a DCE and DTE to manage the
connection. Signaling messages for SVCs, PVC status messages,
and keepalives are all LMI messages.
Link access procedure--frame
mode bearer services (LAPF)
LAPF is the basic Frame Relay header and trailer; it includes
DLCI, FECN, BECN, and DE bits.
Table 8-9
Frame Relay Terms and Concepts (Continued)
ch08.fm Page 531 Monday, March 20, 2000 5:17 PM