Nortel Networks 8000 - Manual (Page 294)

8 Frame relay configuration
Nortel Secure Router 8000 Series
Configuration -WAN Access
Data link connection identifier
Frame relay is a statistically multiplexing protocol that provides multiple Virtual Circuits
(V Cs) on a single physical transmission line.
Data Link Connection Identifier (DLCI) differentiates VCs being valid only on the local
interface and its directly connected remote interfaces. In an FR network, the same DLCI on
different physical interfaces does not indicate the same virtual connection.
A user interface in the frame relay network supports up to 1024 VCs. The available DLCI
ranges from 16 to 1007.
As the FR VC is connection-oriented, you connect different local DLCIs to different remote
equipment making the local DLCI as the "FR address" of the remote equipment.
The FR address mapping connects the protocol address and the frame relay address (local
DLCL) of the remote device enabling the upper-layer protocol to locate the remote device.
When you transmit IP packets over frame relay links, the router searches for the next hop
address in the routing table first, and it finds the corresponding DLCl in the address mapping
table of frame relay. This table maintains the mapping information between remote IP address
and next hop DLCL. It can be configured manually or maintained through inverse ARP.
Virtual circuits
VCs divides into Permanent VC (PVC) and switching VC (SVC) on the basis of the
configuration method.
• PVC refers to the VC in manual mode.
• SVC is the VC that you can create or clear automatically in negotiation mode.
Frame relay use PVCs.
On DTE side, the DCE device determines the PVC status; On DCE side, the network
determines the PVC status.
If you connect the two networks directly, the administrator configures the VC status on DCE
side. In the system, you configure the number and the status of the VC at the same time when
configuring the address mapping. You can also configure it through the fr dlci command.
The PVC such as the Local Management Interface (LMI) protocol is used to test whether the
VC is available.
FR address mapping
In frame relay address mapping, you map the protocol address of the peer device to the local
DLCI which is the frame relay address of the peer device. Through FR address mapping, the
upper layer protocol identifies the peer device according to the protocol address of the peer
device.
Frame relay address mapping divides to the following two types:
• Dynamic frame relay address mapping
In dynamic mapping, you can generate automatically the protocol address of the peer
device, both IP addresses, and IPX address.
You generate the mapping between the protocol address of the peer device and the DLCI
without manual configuration.
• Static frame relay address mapping
8-4 Nortel Networks Inc. Issue 5.3 (30 March 2009)