Service Entities
Page 54 7705 SAR OS Services Guide
Table 7: IP Pseudowire Payload Packet Descriptions
Field Description
Eth The Layer 2 transport header
The only Layer 2 protocol supported is Ethernet
MTU size depends on the encapsulation type (14 bytes for null
encapsulation and 18 bytes for dot1q encapsulation)
IP Indicates the transport protocol
The only supported option is MPLS in IP (0x89)
The Ethertype is always set to IP (0x0800), and in case of a
mismatch, the unexpected or illegal Ethertype counters are
increased
(1)
PW header The pseudowire header identifies a service within the IP tunnel.
The pseudowire header is like an MPLS header that has context
only to the encapsulating and decapsulating LERs. This means
that the IP transport network has no knowledge about the
pseudowires that it carries. Only the edge LERs are aware of the
pseudowire because the IPv4 Protocol Number field is set to 137
(0x89), indicating an MPLS unicast packet.
CW (optional) The pseudowire control word (CW) is a 32-bit (4-byte) field that
is inserted between the VC label and the Layer 2 frame
For more information on the control word, see Pseudowire
Control Word on page 190
ATM Cell #1 to ATM
Cell #N
Indicates the payload of the service being encapsulated (ATM)
Note:
1. The only exception to the Ethertype is if the packets are address resolution protocol (ARP) packets. For
information on ARP, refer to the 7705 SAR OS Router Configuration Guide.
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