Differences between an X.25 group exchange network and a DDN Digital Data Network

Differences between an X.25 group exchange network and a DDN Digital Data Network

Network Terminal work X.25 is a group-based exchange network. It has functions such as protocol conversion and speed matching and is transparent to users on high-level protocols. DDN does not have the switching function and is a fully transparent network. DDN is used to lease leased lines on a regular or irregular basis.

From the perspective of user fees, X.25 is charged by byte, while DDN is charged by fixed monthly rent. Therefore, DDN is suitable for data communication between LANs or between hosts that require frequent communication.

The data transmission rate provided by DDN is generally 2 Mbps, up to 45 Mbps or higher. DDN: Digital Data Network (DDN) is a transmission Network that uses Digital channels to provide Data communication. It mainly provides point-to-point and point-to-point Digital leased lines or private networks. DDN transmission media include optical fiber, digital microwave, and satellite channels. DDN uses computer-managed Data CrossConnection (DXC) technology to provide users with semi-permanent connection circuits, that is, the channel provided by DDN is a non-switched, user-exclusive permanent virtual circuit (PVC ). Once you submit an application, the network administrator can use software commands to change the route or private network structure of the user's leased line, without the need for physical line transformation and expansion projects. Therefore, DDN can easily meet user needs, connect the line with the required bandwidth within the agreed time.

X.25 X.25 is the interface between the DTE of the data terminal device and the DCE of the Data circuit device, which works in group mode on the public data network. According to the ISO/OSI architecture, X.25 corresponds to three layers under the OSI reference model, namely the physical layer, data link layer, and network layer. The network layer of X.25 describes the interaction between the host and the network. The network layer protocol handles problems such as grouping definition, addressing, traffic control, and congestion control. The main function of the network layer is to allow users to establish virtual circuits and then send data packets with a maximum length of 128 bytes on the established virtual circuits. Packets are reliable and arrive at the destination in order. The X.25 network layer uses the Packet level Protocol (PLP ). The X.25 network is developed when the transmission quality of the physical link is poor. To ensure the reliability of data transmission, it performs error checksum and error retransmission on each link. Although this complicated error verification mechanism limits its transmission efficiency, however, it does provide a good guarantee for secure transmission of user data. The X.25 Packet Exchange Network can communicate with terminals and computers, computers and computers, and LAN at different rates. The data transmission rate provided by the X.25 network is generally 64 Kbps.