Configuring basic X.25 datagram transmission functionality
Introduction to X.25 datagram transmission
X.25 service enables two remote X.25 hosts to communicate across an X.25 packet switching network. As shown in Figure 125, LAN 1 and LAN 2 communicate remotely across an X.25 packet switching network.
Figure 125: Interconnecting LANs through X.25
LAN 1 and LAN 2 communicate with each other by sending datagrams that use IP addresses, and X.25 uses X.121 addresses. To correctly tunnel IP datagrams across an X.25 network, the routers must have an IP-to-X.121 address mapping table. This section describes how to establish an IP-to-X.121 mapping.
Mapping a protocol address to an X.121 address
An X.25 interface has its own X.121 address and internetworking protocol (such as IP protocol) address. When X.25 initiates a call through this interface, the source address (calling DTE address) in the call request packet is the X.121 address of this interface.
Then, how can the router target the destination of the call, or how can the router determine the X.121 address for the IP address destination? For this purpose, the router will look up the protocol-address-to-X.121 address mappings that have been configured on the router. A direct call destination has its own protocol address and X.121 address. In this case, a destination protocol-address-to-X.121 address mapping must be created on the source. Through the mapping, X.25 can find the destination X.121 address according to the destination protocol address to initiate a call successfully. This is why the address mapping will be established for X.25.
Such a mapping should be created for every destination.
Creating a PVC
A PVC can be created for the data transmission which features large but stable traffic size and requires the service quality of a leased line. A PVC does not need any call process and will always exist once set up. Before creating a PVC, it is unnecessary to create an address mapping, because an address mapping is created implicitly when a PVC is created.
Configuration guidelines
Because the default two-way channel range (LTC=1, HTC=1024) does not support PVC configuration, specify a virtual circuit range by using the x25 vc-range command to create a PVC.
If a PVC has no related parameters configured, its traffic control parameters are the same as its X.25 interface set by using the x25 packet-size and x25 window-size commands.
Configuration procedure
To configure the basic X.25 datagram transmission functionality:
Step | Command | Remarks |
|---|---|---|
1. Enter system view. | system-view | N/A |
2. Enter interface view. | interface interface-type interface-number | N/A |
3. Create a mapping of the destination protocol address to X.121 address. | x25 map protocol-type protocol-address x121-address x.121-address [ option ] | Not created by default. |
4. Specify the virtual circuit range. | x25 vc-range { bi-channel ltc htc [ out-channel loc hoc ] | in-channel lic hic [ bi-channel ltc htc ] [ out-channel loc hoc ] | out-channel loc hoc } | Required for PVC creation. |
5. Create a PVC. | x25 pvc pvc-number protocol-type protocol-address x121-address x.121-address [ option ] | Not created by default. |