Service Entities
Page 52 7705 SAR OS Services Guide
Payload Packet
The payload encapsulation format for pseudowires over GRE is shown in Figure 6 and
described in Table 6.
Figure 6: GRE Pseudowire Payload Packet over Ethernet
Table 6: GRE Pseudowire Payload Packet Descriptions
Field Description
Eth The Layer 2 transport header
In Release 3.0, 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 Ethertype is always set to IP (0x800), and in case of a
mismatch, the unexpected or illegal Ethertype counters are
increased
(1)
GRE Indicates the encapsulation protocol
PW header The pseudowire header identifies a service within the GRE
tunnel
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
PW payload The PW payload is the payload of the service being
encapsulated (Ethernet, ATM, or TDM)
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.
19873
PW Payload
CW (optional)
PW Header
GRE
IP
Eth
4
4
4
20
14 or 18
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