BayRS Version 13.10 Document Change Notice
56
300020-C Rev. 00
Configuring Frame Relay Services
The following section is an amendment to Configuring Frame Relay Services.
Calculating the MTU Size for Frame Relay Connections
If your Bay Networks router communicates across a frame relay line, you need to
make an adjustment when you configure the maximum transmission unit (MTU).
You set the MTU value by configuring the MTU parameter.
When you enter a value for the MTU parameter, the router automatically reduces
this value to account for WAN Encryption Protocol (WEP) and WAN
Compression Protocol (WCP) header sizes. Consequently, the amount of data that
the router sends across the frame relay line is less than you configured. For
example, if you are running IP over frame relay and you set the MTU parameter to
1506, the router reduces this value to 1439.
WEP and WCP are dynamically configurable for each frame relay virtual circuit.
Therefore, regardless of whether you configure these protocols, the router
subtracts the WEP and WCP headers from the MTU.
When you configure WEP or WCP, the router automatically accounts for the WEP
and WCP headers, resulting in a maximum packet size that is equal to the
configured MTU.
If you do not configure WEP or WCP for frame relay, enter an MTU value that is
larger than necessary to account for the router’s adjustments. For example, if you
are running IP over frame relay and you want the MTU to be 1600, enter a value
of 1667.
For more information about the MTU parameter, see Configuring WAN Lines
Services.
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