Vc Types - HP HSR6800 Configuration Manual

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 Relationship between AC types and VC types
AC type
PPP
HDLC
FR
Ethernet
ATM
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:
If the peer PE does not require the ingress to rewrite the P-tag:
The PE keeps the P-Tag unchanged for the packet and then encapsulates the packet. If the packet contains no
P-tag, the PE adds a null label (the label value is 0) into the packet, and then encapsulates the packet.
Table 3.
VC type
PPP
HDLC
FR DLCI mode
FR port mode
Ethernet
VLAN
ATM AAL5 transparent transport
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