Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Configuring X.25 and LAPBX.25 Configuration Task ListTo configure flow control parameters, complete the tasks in the following sections. These tasks areoptional if your X.25 attachment uses the standard default values for maximum packet sizes (128 bytesincoming and outgoing) and window sizes (2 packets incoming and outgoing).• Setting Default Window Sizes• Setting Default Packet SizesNoteBecause X.25 requires the DTE and DCE devices to have identical default maximum packet sizes anddefault window sizes, changes made to the window and packet sizes when the interface is up are helduntil X.25 restarts the packet service.Setting Default Window SizesX.25 networks have a default input and output window size (the default is 2) that is defined by yournetwork administrator. You must set the Cisco IOS software default input and output window sizes tomatch those of the network. These defaults are the values that an SVC takes on if it is set up withoutexplicitly negotiating its window sizes. Any PVC also uses these default values unless different valuesare configured.To set the default window sizes, use the following commands in interface configuration mode:CommandPurposeStep 1 Router(config-if)# x25 win packets Sets input maximum window size.Step 2 Router(config-if)# x25 wout packets Sets output maximum window size.For an example of setting the default window sizes, see the sections “Typical X.25 ConfigurationExample” and “DDN X.25 Configuration Example” later in this chapter.Setting Default Packet SizesX.25 networks have a default maximum input and output packet size (the default is 128) that is definedby your network administrator. You must set the Cisco IOS software default input and output maximumpacket sizes to match those of the network. These defaults are the values that an SVC takes on if it is setup without explicit negotiatiation of its maximum packet sizes. Any PVC also uses these default valuesunless different values are configured.To set the default input and output maximum packet sizes, use the following commands in interfaceconfiguration mode:CommandPurposeStep 1 Router(config-if)# x25 ips bytes Sets input maximum packet size.Step 2 Router(config-if)# x25 ops bytes Sets output maximum packet size.To send a packet larger than the agreed-on X.25 packet size over an X.25 VC, the Cisco IOS softwaremust break the packet into two or more X.25 packets with the M-bit (“more data” bit) set. The receivingdevice collects all packets in the M-bit sequence and reassembles them into the original packet.13