Panasonic NN46240-710 - Manual (Page 162)

Nortel Secure Router 8000 Series
Troubleshooting - VPN___________ 5 VPLS troubleshooting
An AC can be either a physical link or a logical link. AC transfers frames between CE and PE.
You can specify a remote PE as the AC side of the local VPLS (upe often used). The specified
PE need not fully connect with other PEs or perform split horizon.
Similar to that in the distance vector (DV) routing protocol, the split horizon in VPLS can
reduce the bandwidth consumption and prevent the loop.
VSI
VSI implements the bridging function.
In VPLS, a VSI on the PE represents a VPN. A PE can have multiple VPNs. Therefore, a PE
can be configured with multiple VSIs. Each VSI provides separate VPLS service.
5.1.2 Encapsulation type
Packet encapsulation on the AC
Packet encapsulation on the AC is determined by the user access mode. Two user access modes
are available:
• VLAN access: In this mode, the Ethernet frame sent upstream from the CE or sent
downstream from the PE contains a VLAN tag in the frame header. This tag is a service
delimiter used by the Internet Service Provider (ISP) to differentiate users. This type of tag
is a P-tag.
• Ethernet access: In this mode, the Ethernet frame sent upstream by CE or sent
downstream by PE does not contain a P-tag. If the frame contains a VLAN tag in its header,
this tag is an internal VLAN tag and is of no significance for PE. This type of internal
VLAN tag is a U-tag.
You can specify the access mode of the user on the device.
Packet Encapsulation on the PW
Two types of packet encapsulation exist on the PW.
• Raw mode: In this mode, the P-tag is not transmitted over the PW.
If the upstream packets on CE contain the service delimiter, their service delimiter is
removed before they are sent upstream; two layers of MPLS labels are added before they
are forwarded. If the upstream packets on CE do not contain a service delimiter, they are
sent upstream directly; two layers of MPLS labels are added before they are forwarded.
For downstream packets on PE, the service delimiter is added as needed before they are
forwarded to CE. It is not allowed to rewrite or remove an existent tag.
• Tagged mode: In this mode the frame sent to the PW must contain a P-tag.
If the upstream packets on CE contain the service delimiter, they are sent upstream directly
without the P-tag removed; two layers of MPLS labels are added before they are
forwarded. If the upstream packets on CE do not contain the service delimiter, a null tag is
added and then sent upstream; two layers of MPLS labels are added before they are
forwarded.
For downstream packets on PE, their service delimiter is rewritten, removed, or retained as
needed before they are forwarded to CE.
Issue 5.3 (30 March 2009) Nortel Networks Inc. 5-3