Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring Priority Queueing or Custom Queueing for X.25Configuring X.25 and LAPB• Configuring a Route to a CMNS HostEnabling CMNS on an InterfaceTo enable CMNS on a nonserial interface, use the following command in interface configuration mode:CommandRouter(config-if)# cmns enablePurposeEnables CMNS.For an example of enabling CMNS on an interface, see the section “CMNS Switching Example” later inthis chapter.Configuring a Route to a CMNS HostOnce CMNS is enabled on a nonserial interface, the router can forward calls over that medium byconfiguring x25 route commands that define the MAC address of each CMNS host that can be reached.To define routes to CMNS hosts, use the following command—plus pattern and character match optionsfor the x25 route command—in interface configuration mode:CommandRouter(config)# x25 route pattern-character match optionsinterface cmns-interface mac mac-addressPurposeDefines route to CMNS host.Configuring Priority Queueing or Custom Queueing for X.25Two types of output queueing are available for X.25:• Priority queueing—Classifies packets on the basis of certain criteria and then assigns the packets toone of four output queues, with high, medium, normal, or low priority.• Custom queueing—Classifies packets, assigns them to one of 16 output queues, and controls thepercentage of available bandwidth for an interface that is used for a queue.Output queueing for X.25 interfaces differs subtly from its use with other protocols because X.25 is astrongly flow-controlled protocol. Each X.25 VC has an authorized number of packets it can send beforeit must suspend transmission to await acknowledgment of one or more of the packets that were sent.Queue processing is also subject to a VC’s ability to send data; a high priority packet on a VC that cannotsend data will not stop other packets from being sent if they are queued for a VC that can send data. Inaddition, a datagram that is being fragmented and sent may have its priority artificially promoted ifhigher-priority traffic is blocked by the fragmentation operation.Both priority queueing and custom queueing can be defined, but only one method can be active on agiven interface.To configure priority queueing and custom queueing for X.25, perform the following steps:44