Compare ATM and Gigabit Ethernet
1. Quick Ethernet blocks ATM to expand to desktop
In the seven-layer mode of the OSI network architecture, ATM and Gigabit Ethernet only relate to low second layers, while the third floor exchange technology, as the name suggests, of course, is a third layer. In low Layer 2 network technology, Ethernet is the most familiar technology. The Ethernet protocol based on Aloha principle is very simple, and the online node wants to send it. In order to improve efficiency, monitoring and collision detection is added. In order to meet the growing requirements of people, there is a swap Ethernet, which is much higher than the transmission efficiency of shared Ethernet, and when each port is only connected to a site, eliminate collision conflicts, can achieve full Duplex communication. With the development of network applications, 100Mbps fast Ethernet and Gigabit Ethernet. It can be said that the history of Ethernet represents the development history of computer network applications. It is also a huge inertia that meets people's growing demand. Cheap, simple, fast Ethernet technology blocked the expansion of the ATM to the desktop system, still firmly occupying the position of the LAN.
2. ATM has all characteristics of telecommunications network
WAN has a different feature of LAN. Since the WAN involves the region, its construction, maintenance and management is controlled by the telecommunications department or a few professional companies, forming a so-called public telecommunications network. While providing users with services, they try to avoid users involving and interfere with the interior of the telecommunications network. Typically, the administrator of the public telecommunications network hopes that the user will regard the telecommunications network as a black box, only provide a simple user interface to the user equipment, and the user can easily use the public telecommunications network, and the main functions are as concentrated as much as possible In telecommunications. The telephone system is the most successful model in this model. Unlike the landmark, manage, and use of LANs in the WAN, users are only the user, the administrator of the public telecommunications network is the service provider. This creates a number of features of WAN, for example, in order to billing, WAN is generally connected, and thus, before transmitting data, the connection process must be established first, with a complete full address. Call or dial, communicate with a simplified connection identifier in the data transfer phase. With the development of communication technology, in order to improve transmission efficiency, the path of transmitting data and transmission control information is currently separated, and the so-called extinction signaling is formed so that the transmission protocol inside the telecommunications network becomes quite complicated. ATM technology originated from B-ISDN with all characteristics of telecommunications network technology.
3. The complexity of ATM technology
ATM technology is very complicated, it is divided into three layers of AAL layers, ATM layers, and physical layers, each of which are divided into two sub-layers. In AAL layers, users typically have to run two protocols: one is used to transmit control information to network, referred to as a control surface; another is used to transmit data information, called user plane. The external signaling mechanism, the ITU and ATM forums are also used in the ATM network. ATM is a connection-oriented transmission technology, using a decimal number similar to a telephone number for call connections. Its call coding is currently four, has not been unified, up to 20 bits. On each ATM switch, the establishment of the connection process takes 10 to 30 ms time, which is too long relative to the fastest 10μs ATM switch speed, 10 ~ 30ms is too long. In addition, in order to ensure the resource reservation required for service quality, it is also possible to increase the time of establishing the connection. So now there is a lot of permanent virtual circuits in the ATM network (static route). This limits the telescopic ability of the ATM network. Among the 53 bytes of the ATM cell, there are 5 bytes of cell headers, and the coding efficiency is not high. When the data packet of other protocols should be transferred via the ATM network, it must be decomposed to the ATM cell stream in the network, and then restore the original packet. If the channel quality is not sufficiently high, or the cell discarding phenomenon occurs due to poor transmission control strategy, and a cell discard will result in retransmission of the entire packet. These processes increase system overhead, increase transmission delays, and reduce the transmission capacity of the ATM network. A wide range of superiority of ATM technology is made widely promoted. And don't mention expensive prices, as long as you think there is no connection, burst, users have existing right, and the use of ATM technology in the LAN of management, it is not difficult to understand why ATM technology cannot Extended to the LAN field. More: http://www.net130.com/search.asp
