Data communications services networks x

Data communications services networks x

• The X.25 network contains the standard protocols for packet switching across networks.

Basic aspects of the X.25 network:

• Packet switching.
• Information from many different users is combined into packets.
• Packets are sent to the Packet Data Network (PDN).
• Packet are routed through the network cloud to the destination.
• The user has a virtual connection instead of a dedicated connection as in circuit switching protocols.
• The circuit is shared by many different users.
• Packets switching results in cost savings compared to circuit switching.
• The X.25 was one of several protocols designed for secure transmission of voice traffic using analog lines.

The protocol specifies:

• How terminals talk to packet forming devices.
• How packet assemblers talk to packet switches.
• How packet switching nodes talk to one another.
• The X.25 network handles the assembly of packets, delivery, and the disassembly of packets.
• The Packet Assembler/Dissembler (PAD) in X.25 networks.
• Assembles asynchronous transmissions into a single, synchronous X.25 packet (up to 128 data bytes in length).
• The PAD is like a 56 Kbps statistical multiplexer which will send packets to an X.25 switch.
• The switch separates and routes packets to destination with a specified algorithm.
• Analog lines often see lots of errors.
• X.25 networks use a series of error checks to overcome the errors often experienced using analog lines.

• Where asynchronous communications is desired.
• Where the line quality poor, the X.25 networks can overcome poor line quality.
• Where data traffic is small and in bursts.
• Where a decrease in transmission expenses is desired.