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Addressing
Encapsulation
PVC management
Frame Relay elements
18
increased interoperability as it complies with international standards
Each data packet contains a circuit number, also called a Data Link Connection
Identifier (DLCI), showing which logical channel that the information belongs
to. Frame Relay packets are routed to their destination on the basis of the circuit
numbers contained in the packet.
When using Frame Relay, ensure that your network provider allocates
Note
you the necessary DLCI values. DLCI values assigned during Frame
Relay connection, range from 16 up to 991.
Multiprotocol encapsulation according to FRF.3, specifying the protocol con-
tained in the current Information field (I-field). This encapsulation is also speci-
fied in RFC-1490 "Multiprotocol Interconnect over Frame Relay Data Terminal
Equipment", and is compatible with routers from other manufacturers.
Status information between Frame Relay network switches and user devices (for
example routers and bridges) is provided by signalling protocols defined by the
Frame Relay standards committees. These signalling protocols perform the fol-
lowing tasks:
providing a 'heartbeat' or 'keep-alive' message exchange to ensure that links
are available
informing about added and removed PVCs
providing status of existing PVCs
Frame Relay services may be broken down into three distinct elements:
Frame Relay access equipment
Frame Relay access equipment is customer premises equipment (CPE) which
sends information across the network. This may be, for example, a router, a
bridge, a host computer, and so on.
Frame Relay switching equipment
Frame Relay switching equipment is responsible for the transportation of infor-
mation across a WAN. This may be, for example, T1 (1.5 Mbps) and E1 (2 Mbps)
packet switches, and so on.
Public Frame Relay services
Public Frame Relay services see the deployment of Frame Relay switches via the
Public Data Network (PDN). If you do not make use of public services (sub-
scribed), private networks may be established. In this case, the private network
must have Frame Relay switching equipment installed.
Frame Relay can only be used on high-quality transmission lines dedi-
Note
cated to Frame Relay.
Frame Relay Services
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