R3303-HP HSR6800 Routers MPLS Configuration Guide

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VC types

A PE encapsulates a Layer 2 packet received from an AC according to the VC type. The VC type is

determined by the AC type, as shown in Table 3.

Table 3 Relationship betw

een AC types and VC types

AC type VC type

PPP PPP

HDLC HDLC

FR DLCI mode

FR port mode

Ethernet

VLAN

ATM ATM AAL5 transparent transport

VC type for PPP/HDLC links

If the AC type is PPP, the VC type is PPP. If the AC type is HDLC, the VC type is HDLC.

In PPP encapsulation or HDLC encapsulation mode, a PE processes a PPP or HDLC packet as follows:

1. After receiving a packet from an interface, the PE searches for the VC bound to the interface.

2. The PE encapsulates the packet and sends the packet to the peer PE through the VC.

3. The peer PE removes the outer encapsulation to get the original PPP or HDLC packet, and then

forwards the packet to the user network.

VC types for FR links

The following VC types are available for an FR link:

• FR DLCI mode—After a PE receives an FR packet from the user network, it searches for the VC

according to the DLCI of the packet, and then forwards the packet to the VC. The FR DLCI mode is

also called the "one-to-one mapping" mode, because one FR virtual circuit corresponds to one VC.

• FR port mode—A PE forwards all FR packets received from an interface to the VC bound to the

interface. The FR port mode is also called the "many-to-one mapping" mode, because many FR

virtual circuits correspond to one VC.

VC types for Ethernet links

The following VC types are available for an Ethernet link:

• Ethernet—P-Tag is not transferred on a VC.

{ If a packet from a CE contains a P-tag, the PE removes the P-tag before encapsulating the

packet.

{ If the packet contains no P-tag, the PE directly encapsulates the packet. Whether the PE adds a

P-tag into a packet sent to a CE depends on the access mode you have configured. However,

rewriting and removing existing tags are not allowed.

• VLAN—Packets transmitted over a VC must carry a P-Tag.

For a packet from a CE: