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Header compression increases the throughput of IPX and NCP packets over low-speed serial lines. An IPX packet header is 30 bytes and is typically followed by an upper-layer protocol header, such as an SPX header. Header compression reduces the size of this combined packet header to just a few bytes.
Header compression is negotiated by the IPXWANTM protocol when a call is established over any WAN connection. Header compression is not used on the connection if IPXWAN detects that one of the end nodes does not support it.
When you enable header compression, you can also specify the number of compression slots . A compression slot is a location in router memory that stores packet header information. The compression algorithm uses this information to compress outgoing---and decompress incoming---packet headers.
By default, the number of allocated compression slots is 16. In general, a session between two end points uses one slot; routing information uses one or two. Each slot can contain an IPX or an NCP header. When no more slots are available, packet headers are sent uncompressed, or old slots are reused.
For more information about IPX and NCP header compression and related topics, refer to Header Compression.
IMPORTANT: To use header compression, the routers at each end of the connection must have header compression enabled and must allocate the same number of header compression slots . If the number of compression slots is different on each router, IPXWAN selects the lesser of the two.
This topic contains the following sections:
To configure IPX and NCP header compression on a WAN interface, complete the following steps:
Load NIASCFG, then select the following parameter path:
Select Configure NIAS > Protocols and Routing > Bindings > a WAN interface > Expert Bind Options
Select Header Compression .
This parameter enables or disables header compression for all IPX packets sent through this interface. By default, header compression is enabled on all WAN interfaces; if you want to disable it on the interface, select Disabled .
Select Compression Slots , then enter the number of slots you want to allocate to this interface.
The more concurrent IPX sessions you use over the interface, the more compression slots you should allocate.
IMPORTANT: Be careful not to allocate too many compression slots. Memory is required to store the headers, and the compression algorithm must scan through stored headers to find a match for each transmitted packet. An excessive number of slots results in a higher processing load and slower performance.
Press Esc and save your changes.
Press Esc to return to the Internetworking Configuration menu.
If you want these changes to take effect immediately, select Reinitialize System .
If you want to configure other parameters, do so now, then reinitialize the system when you are finished.
By default, header compression is enabled for all WAN connections. To configure header compression for a particular WAN call destination, complete the following steps:
Load NIASCFG, then select the following parameter path:
Select Configure NIAS > Protocols and Routing > Bindings > a WAN interface > WAN Call Destinations
Select a call destination.
If you are modifying a call that has already been configured, select one from the list.
If you are configuring a new call, press Ins and choose a call from the list of available calls.
Select Expert Options .
Select Header Compression .
The default state is Use Default . This means the call uses the compression state to which the interface is currently set.
If compression is enabled on the interface but you want to disable it only for this call, select Disabled.
If compression is disabled on the interface but you want to enable it only for this call, select Enabled.
Select Compression Slots , then enter the number of slots you want to allocate to this call.
IMPORTANT: Be careful not to allocate too many compression slots. Memory is required to store the headers, and the compression algorithm must scan through stored headers to find a match for each transmitted packet. An excessive number of slots results in a higher processing load and slower performance.
Press Esc and save your changes.
Press Esc to return to the Internetworking Configuration menu.
If you want these changes to take effect immediately, select Reinitialize System .
If you want to configure other parameters, do so now, then reinitialize the system when you are finished.
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