Data Link Connection Identifier; Frame Relay Address Mapping; Lmi Protocol - HPE FlexNetwork MSR Series Comware 5 Layer 2 - Wan Access Configuration Manual

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Permanent virtual circuits (PVCs)—Preconfigured by network administrators and maintain
until being manually removed.
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Switched virtual circuits (SVCs)—Analogous to dialup connections. They are dynamically set
up or cleared on an as-needed basis through protocol negotiation.
PVCs are used far more than SVCs.

Data link connection identifier

A DLCI is a unique number assigned to a virtual circuit endpoint in a frame relay network for the
addressing purpose.
A DLCI uniquely identifies a particular virtual circuit on a physical link and has local significance only
to that link. A DLCI can be used on different physical ports to address different virtual circuits. A
virtual circuit between two DTE devices can be addressed with different DLCIs at the two ends, as
Figure
shown in
Because the virtual circuits in a frame relay network are connection oriented, each DLCI on a
physical port is destined for a distinct remote device. DLCIs can be regarded the frame relay
addresses of remote devices.
The maximum number of PVCs that can be created on a frame relay interface is 1024. The user
configurable DLCIs for the PVCs are in the range 16 to 1007. Other DLCIs are reserved for special
purposes. For example, DLCI 0 and DLCI 1023 are reserved for the LMI protocol to transfer control
messages.

Frame relay address mapping

Frame relay address mapping associates the protocol address of a remote device with its frame
relay address (local DLCI) so the upper layer protocol, IP for example, can locate the remote device.
Take delivering an IP packet across a frame relay network for example. After a DTE device receives
an IP packet, it looks up the IP routing table for the outgoing interface and next hop address. If the
outgoing interface is enabled with frame relay, the device must look up the frame relay address
mapping table based on the next hop IP address for the DLCI.
The address mappings can be static ones administratively created or dynamic ones created with the
InARP.
The following describes how frame relay uses InARP to create an address mapping:
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Once a new virtual circuit is created, InARP sends an InARP request over the circuit to request
the peer end for its protocol address. This request also conveys the local protocol address.
When the peer device receives the request, it creates an address mapping based on the
protocol address in the request and responds with its protocol address. When the local end
receives the response, it creates the address mapping for the peer.
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For virtual circuits with static address mappings, InARP will not be performed whether or not the
mappings are correct. In addition, the InARP request recipient does not create a mapping
based on the protocol address in the request if a static entry is already available for the address.
In an IPv6 network, address mappings are dynamically maintained by Inverse Neighbor Discovery
(IND). IND works in the same way InARP works.

LMI protocol

Frame relay uses the LMI protocol to set up virtual circuits and maintain their status between DTE
and DCE.
The system supports the following LMI standards:
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ITU-T Q.933 Annex A
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