X.25

What is X.25? X.25 is a layer 3, packet based protocol typically run over a LAPB (Link Access Procedure Balanced) layer 2 protocol. It is generally a wide area network protocol. The protocol was originally designed for use over low speed analogue lines, which often created errors. The design of the protocol has a large amount of error correction and detection. This means the protocol guarantees delivery and integrity of data from one node to another.

What is X.25 used for?

With circuits now being carried by error free digital circuits the use of X.25 for WAN communications has diminished, since the overhead of X.25 is too large. However use of the protocol is expanding in areas where the guaranteed data integrity is mission critical. For this reason banks and credit card clearing companies use X.25 for financial transactions, as they can be confident that data will arrive complete at the destination. Financial transactions suit X.25 because the amount of data to be transferred is small in each transaction, but the data must be completely error free.

X.25 can also be used as a WAN protocol between routers, particularly where a point to point circuit would be prohibitively expensive, such as where one of the sites may be in a developing county where the communications infrastructure does not permit any other systems.

Why use X.25?

The X.25 protocol is normally used when use of its resilience and error checking capability is needed. In addition X.25 is supported in many developing countries where it may be the only feasible connection method. For these reasons X.25 is often used in low speed radio networks, financial transaction networks, or defense networks.

Typically where you have text based protocol with no inherent error correction that you wish to transfer error free, X.25 is used to carry that data. For this reason the protocol is often used in alarm and system monitoring.

What do I need?

The X.25 network is a circuit switched network. This means that circuits through the network are generally created and cleared as required. This means that a site can connect to many nodes on the network. Each circuit that is created on the network needs to be managed by an X.25 device.

In the most simple form an external PAD (Packet Assembler Disassembler) may be used to connect asynchronous lines to an X.25 network. The PAD can be used to carry asynchronous data over the X.25 network.

Whilst this configuration may be fine for the simplest of legacy applications, most modern applications use virtual asynchronous lines or TCP/IP sockets. It is also possible to configure systems to act as a virtual PAD whereby asynchronous data is carried via TCP/IP sockets, which are then converted for communication via the X.25 network. By using this application it is possible to give X.25 access to a host application without having to connect many TTY lines between the host and PADs but to program using TCP/IP sockets. This allows programmers to be able to write X.25 applications without having to get involved in complex legacy X.25.

In modern credit card clearing ISDN lines are used for speed of connection and bandwidth of connection. However since the data must not contain errors, X.25 is still used as the protocol to transfer the data. In this environment is is necessary to have an X.25 PAD operating over ISDN lines. GGR is able to provide both point of sale connectivity and central clearing equipment to support this communications environment.

With our in depth experience of X.25 and other networking technologies, GGR Communications can offer an unrivalled integration service on X.25 applications.

Talk to GGR about your X25 needs to find the best solution for your company.