Difference Between ATM and Frame Relay

ATM与框架继电器

OSI模型的数据链路层定义了封装数据以在两个端点之间传输的数据和传输帧的技术。异步传输模式（ATM）和帧继电器都是数据链路层技术，它们具有面向连接的协议。每种技术都有自己的应用程序依赖性优势和缺点。

异步传输模式（ATM）

ATM is a network switching technology that uses a cell based methodology to quantize data. ATM data communication consists of fixed size cells of 53 bytes. An ATM cell contains a 5 byte header and 48 bytes of ATM payload. This smaller size, fixed-length cells are good for transmitting voice, image and video data as the delay is minimized.

ATM是一个面向连接的协议，因此在发送点和接收点之间应建立虚拟电路。当数据传输启动时，它在两个点之间建立了固定的路线。

Another important aspect of ATM is its asynchronous operation in time division multiplexing. Therefore cells are transmitted only when data is available to be sent unlike in conventional time division multiplexing where synchronization bytes are transferred if there data is not available to be sent.

ATM旨在方便硬件实施，因此处理和切换变得更快。ATM网络上的比特率最高可达10 Gbps。ATM是ISDN的SONET/SDH主链上使用的核心协议。

ATM provides a good quality of service in networks where different types of information such as data, voice, and are supported. With ATM, each of these information types can pass through a single network connection.

框架继电器

Frame relay is a packet switching technology for connecting network points in Wide Area Networks (WAN). It is a connection oriented data service and establishes a virtual circuit between two end points. Data transfer is done in packets of data known as frames. These frames are variable in packet size and more efficient due to flexible transfers. Frame Relay was originally introduced for ISDN interfaces though it is currently used over a variety of other network interfaces as well.

In frame relay, connections are called as ‘Ports’. All the points which need to connect to the frame relay network needs to have a port. Every port has a unique Address. A frame is made of two parts which can be called as ‘actual data’ and the ‘frame relay header’. Frame architecture is same as defined for LAP-D (Link Access Procedures on the D channel) which has a variable length for information field. These frames are sent over Virtual Connections.

帧中继可以创建多个冗余connections among various routers, without having multiple physical links. Since frame relay is not specific for media, and provides means to buffer speed variations, it has the possibility to create a good interconnect medium between different types of network points with different speeds.

Difference between ATM and Frame Relay 1. Although both techniques are based on end to end delivery of quantized data, there are many differences in terms of sizes of the data quanta, application network types, controlling techniques etc. 2. Although ATM uses fixed size packets (53 bytes) for data communication, frame relay uses variable packet sizes depending on the type of information to be sent. Both information blocks have a header in addition to data block and transfer is connection oriented. 3. Frame Relay is used to connect Local Area Networks (LAN) and it is not implemented within a single area network contrast to ATM where data transfers are within a single LAN. 4. ATM is designed to be convenient for hardware implementation and therefore, cost is higher compared to frame relay, which is software controlled. Therefore frame relay is less expensive and upgrading is easier. 5. Frame relay has a variable packet size. Therefore it gives low overhead within the packet which results it an efficient method for transmitting data. Although fixed packet size in ATM, can be useful for handling video and image traffic at high speeds, it leaves a lot of overhead within the packet, particularly in short transactions.