Development and Application of ATM Technology

The ATM technology was proposed by ITU-T in late 1980s s to support broadband multimedia services for telecommunication networks. After nearly ten years of research, by the middle of 1990s, the ATM technology has been basically mature, and the relevant international standards developed by the ITU-T and ATM Forum are also basically complete, in addition, multiple telecom equipment manufacturers and computer network equipment manufacturers have launched commercial ATM devices. Since then, the construction of the ATM network has also been greatly developed, and many public or private networks around the world have been installed and used by the ATM network equipment. However, at the same time, the IP technology has also developed rapidly. The seamless integration of the IP technology and Ethernet technology makes the market prospect of ATM to desktop applications very gloomy. In addition, the IP technology is also actively expanding in the WAN field, the application combined with SDH/WDM Technology will greatly replace ATM and become the core technology of broadband communication networks in the future.
I. Influence of IP technology on ATM Technology
IP technology is the core of the Internet. For high-level protocols on the Internet, the layer 3 of the Unified IP protocol layer is used) it shields the differences between various low-layer protocols and physical network technologies, such as X.25, DDN, Ethernet, licensing ring, frame relay, ATM, SDH, and WDM, and achieves the goal of "IPovereverything. The key to successful IP technology is its concepts, methods, and ideas, such as the inclusiveness and openness of its hierarchy, as well as simple, practical, and effective principles. Another goal of the Internet is to achieve "everythingonIP". "everything" refers to all services, including data, images, and voice. These services are both real-time, there are also non-real-time. To achieve this goal, it is quite difficult for the current IP technology, and new technologies are needed to help solve the problem.
At present, the telecom industry holds that with the development of IP technology and the Internet, the future of telecommunication networks will be dominated by IP technology, while the ATM technology will exit the historical stage. In fact, as long as you carefully analyze and study the characteristics of the IP technology and ATM technology, it is not difficult to find this view is one-sided. For the construction of network telecommunication networks or computer networks, its development will not change with the emergence of new technologies), but it can only evolve gradually. The existing telecommunication network has formed a huge amount of resources, and it is impossible to disappear overnight. In addition, although existing IP networks use new technologies such as IPoverSDH or IPoverWDM to solve the bottleneck of transmission bandwidth to a certain extent, they still use traditional routers and leased lines for networking, there are problems such as hop-by-hop addressing and forwarding, and the service quality QoS cannot be guaranteed) and information security. The advantages of the ATM technology include end-to-end QoS Assurance, improved traffic control and congestion control, Flexible Dynamic Bandwidth Allocation and Management, support for multiple businesses, and comprehensive technical capabilities, at present, it is still far behind the IP technology.
One thing is certain. There is no omnipotent technology in the world. Because both IP and ATM are based on Packet Exchange Technology and have their own advantages, they will play a role in the integration and evolution of telecommunication networks and the Internet. At present, the advantage of IP technology lies in the provision of a unified data application platform, while the advantage of ATM technology lies in the provision of a unified network platform.
Ii. features, application scope and development trend of ATM Technology
1) features of ATM Technology
As a new technology of telecommunication networks, ATM is not only applicable to high-speed information transmission and QoS support for service quality, but also capable of integrating multiple services, and Dynamic Bandwidth Allocation and connection management capability and compatibility with existing technologies.
1. Support for QoS
1) ATM uses fixed short-length cells to transmit information. Information exchange is completed on the second layer, and the protocol simplifies the complexity of information storage management and processing on network nodes, it accelerates the information exchange rate, reduces the queuing latency and delay jitter of cells in the node buffer, and facilitates the time transparency of information transmission. It is especially suitable for information transmission in the core network.
2) virtual channel VP and virtual channel VC must be established before the ATM uses a connection-oriented communication method ), this avoids complicated cell sequence control, traffic control during user access, reasonable QoS and network resource management control, and various error control technologies, the cell loss rate can be reduced to the acceptable level for various businesses to meet the Semantic Transparency of various businesses.
3) in the ATM mode, the management function is supplemented by the necessary network management functions and signaling processing and connection control functions, and multiple priority connection priorities and cell priorities can be set, meet various requirements.
2. the comprehensive capabilities of ATM: the ability of ATM to transmit information in a trusted manner is independent of the characteristics and bit rate of the business. As long as the information of various businesses is converted into cells in a unified format when accessing the network, it can be transmitted and exchanged in the network. Therefore, the high flexibility gives it a variety of comprehensive capabilities.
3. Flexible Dynamic Bandwidth Allocation and connection management capabilities
1) ATM has the characteristics of statistical reuse. network resources can be allocated as needed, and the utilization of network resources is high.
2) In the ATM mode, the network supports multi-party connections, including broadcast and multicast connections.
4. compatibility of existing technologies ATM as an independent technology fully considers the integration with existing technologies. The compatibility of ATM is manifested in two aspects:
(1) compatibility with existing WAN technologies including group switching and circuit switching technology): ATM can be compatible with Frame Relay FR) business, leased line data business DDN), and support for PSTN and N-ISDN business.
2) compatibility with existing IP technologies: the compatibility between ATM and IP technologies includes Layer 2 data link layer, for example, LAN simulation-LANE) and Layer 3 network layer) such as CIPOA, MPOA, and MPLS ). Thanks to the above advantages of ATM technology, it has been widely valued by Telecom and computer networks. However, the two camps of research, development, and utilization of ATM technology clearly represent two different viewpoints and perspectives. The telecom industry expects that ATM can integrate its networks to achieve seamless integration of existing telecommunication networks and future networks, including IP networks and third-generation mobile communication networks, to protect investment in existing telecommunication networks; however, the computer wants to use ATM to better support IP addresses to achieve IP QoS. Of course, ATM also has its inherent defects. The main problems are high cell overhead and network complexity. For an ATM Cell itself, the overhead of the Cell Header exceeds 10%). If the overhead of the ATM adapter layer and higher-level protocols is taken into account, the overhead may exceed 5/48, this is unacceptable for some data services such as short group data such as E-mail. In addition, in order to support comprehensive services and ensure QoS, the traffic control functions such as CAC, UPC, and NPC introduced by the ATM network make the signaling and network management functions of SVC supported by the Network very complex, this not only increases network costs, but also increases network complexity.
2) Application of ATM
According to the characteristics of the ATM technology and the development of the telecommunication network technology, as far as the ATM technology itself is concerned, it is necessary to reposition its application fields. Due to the complexity of the ATM terminal and signaling, the idea of connecting the end-to-end ATM to the desktop has basically failed. The reason is that it is inferior to PSTN to support voice services on the user's resident network, data Services are not as good as Gigabit Ethernet. However, in the core network and edge access network, the ATM technology is still promising. Here, the advantages of ATM as a multi-service platform can be fully utilized. In addition, the combination of ATM and IP will increase the competitiveness of ATM. Therefore, the application of ATM mainly includes the following aspects:
1. Support the gradual evolution of existing telecommunication networks from traditional circuit switching technology to packet grouping technology.
1) support the evolution of existing telephone networks, such as PSTN/ISDN, and use them as their relay networks;
2) core exchange and transmission networks that support and serve as third-generation mobile communication networks that support mobile IP addresses;
3) supports the evolution of existing data network FR/DDN, as the core of the data network, and provides lease circuit, using ATM to achieve the interconnection between campus networks or enterprise networks.
2. It is the core router connecting the Backbone Transmission Network of the Internet and supports the continuous development of the IP network.
3. Work with IP technology to complement each other and serve as the core technology of future information networks. The IP and ATM technologies have their own advantages. They will play an important role in the integration and evolution of traditional telecommunication networks and the Internet. If these two technologies are combined, using the ATM network to provide high-speed and direct data links for IP users enables the ATM network operation department to make full use of the ATM network resources to develop the IP user services on the ATM network, it can also solve the bottlenecks encountered in the development of Internet networks and promote the further development of IP services, so that the potential of these two technologies can be fully realized and huge economic benefits can be achieved.
3) Development Trend of ATM Technology
1. in the future, the study of ATM voice support technology will take a dominant role in traditional telephone users from the perspective of the number of users. Therefore, ATM must consider how to support voice. ITU-T in September 1997 through the support for voice business and short packet business adaptation of the second type of ATM adapter layer protocol AAL2I. 363.2 recommendations in February 1999 through the voice business Recommendations I .htm.
2. The specific convergence sub-layer SSCS of the AAL service used for relay. On September 16, December 1999, the signaling protocol q.2630.1aal signaling protocol-capability set 1 was adopted ), the standardization of ATM support for voice services is basically completed. Using the AAL 2 protocol to support voice services is superior to IP phones in terms of efficiency and latency performance. The Application of AAL 2 technology mainly includes the following aspects:
1) supports voice and other real-time service transmission with low latency for PSTN or other network relay transmission;
(2) for the third generation mobile communication system IMT-2000), between BS and MSC to support low-speed voice and data transmission protocol;
(3) replacing the ATM layer with an AAL switch provides only the PVC cross-connection function) to provide end-to-end ATM voice and data services.
2. one of the disadvantages of simplifying the study of ATM technology is the complexity of the network. To promote the application of ATM technology, it is necessary to simplify and optimize the ATM technology to simplify the network, reduce network costs. At present, ITU-T and ATM forums are working on this, such as the ATM light signaling lightsignaling standard currently being developed by the ITU-T) is to simplify the original complex signaling standard to reduce network complexity. In addition, there is also a need for research in traffic control and network management.
3. Integration of ATM and IP technology
At present, the technology of Combining IP and ATM is mainly divided into two categories: overlapping technology and integration technology. When overlapping technology is used, the ATM endpoint is identified by the ATM address and the IP address or MAC address. The server is configured in the network to map the addresses of the ATM address and the IP address or MAC address, after the initiator obtains the receiver's ATM address, it establishes an ATMSVC connection and transmits IP packets on it. Typical technologies in this area include LANE, IPOA, MPOA, etc. The advantage of overlapping technologies is the adoption of standard signaling standards for ATM forums or ITU-T, and compatibility with standard ATM networks and services; the disadvantage is that the efficiency of IP packet transmission is low. When the integration technology is adopted, the ATM layer is regarded as the Peer layer of the IP layer. The ATM endpoint only needs to be identified by the IP address, and the non-standard ATM signaling protocol is used when the connection is established. When integrated technology is adopted, the Address Resolution Protocol is not required, but the complexity of the ATM switch is increased, making the ATM switch look more like a multi-protocol router. Typical technologies in this area include IP address exchange and Multi-Protocol Label exchange MPLS). The advantage of the integration technology is that the efficiency of IP packet transfer is relatively high, and address resolution protocols are not required; the disadvantage is that it is difficult to integrate with standard ATM technology. Over the past two years, we have concluded that overlapping technologies such as LANE, IPOA, and MPOA are more suitable for private networks or small-sized networks; integration technologies such as IP exchange and MPLS are more suitable for large-scale public networks. In March 2000, The ITU-T passed the recommended Y.1310 Public ATM network IP address to transmit IP information on a public ATM Network ), the recommendation clarifies that the recommended technical solution for IP information transmission over public networks using the ATM technology, including service provision networks and bearer networks, is Multi-Protocol Label exchange MPLS ), it is also clear that the target IP services supported by the Public ATM network are Differserv, Intserv, and PN ).