ATM is a transport mode in which information is organized into cells, which are asynchronous because the individual cells that contain information from a user do not need to appear periodically.
ATM is a new network technology, which uses the asynchronous transmission mode based on cell and the virtual circuit structure, which solves the real-time and bandwidth problem of multimedia fundamentally. Achieve point-to-point transmission towards virtual links, which typically provides 155Mbps of bandwidth. It not only absorbs the "connected" service and the service quality assurance of the circuit exchange in the traffic communication, but also maintains the flexibility of variable bandwidth in the traditional network such as Ethernet and FDDI, and is suitable for the sudden transmission, thus becoming the most widely used, the most advanced technology, the best transmission effect network interconnection means.
generation of 1.ATM
since Alexander Graham Bell invented the phone in 1870, the telephone exchange network was created to effectively connect with the increasing number of telephone subscribers. It has experienced the development of artificial exchange, electromechanical automatic switching system and Digital program control system, but the principle of circuit switching has not changed. With the popularization of the computer, the telephone network uses the modem to carry on the computer data transmission and the data information exchange, subsequently produces the public data network, Its representative is the X. Packet switching network, which is a technology based on packet switching, with the advantages of high reliability of the transmission, but due to the modem rate and the switching technology itself limited, x. Only processing medium and low speed data stream. Although LAN (LAN) technology has developed rapidly, such as Ethernet, Token Ring, token bus, and so on, the transmission rate is up to gigabit, but the nature of its local area network greatly restricts the large-scale LAN coverage and application, LAN is generally used for intra-enterprise data transmission, The size of the WAN cannot be formed.
It is not difficult to see that traditional networks generally have the following shortcomings: first, the business of dependence, general network can only be used for the exclusive service, public telephone network can not be used to transmit TV signals, X. No can be used to transmit high-bandwidth images and language signals with higher real-time requirements; second, there is no flexibility, that is, the possibility of business expansion, the quality of service of the original network, it is difficult to adapt to the emergence of new business; Thirdly, inefficient, one network resource is difficult to be shared by other networks.
with the continuous development of the society, the network services continue to diversify, people can use the network to do a lot of things, such as sending and receiving letters, Home Office, Video on demand, Internet telephony, which is more and more high demand for the network, some people cannot help but put forward such an idea: can these bandwidth, real-time, Transmission quality requirements are different network services by a unified multimedia network to achieve true first-line? The answer is yes, this is the ATM network. Fortunately, semiconductors and optical fiber technologies provide a solid guarantee for fast switching and transmission of ATM. CMOS processing capacity of two hundred or three hundred trillion, ecl up to 5 to 10G. SDH and SONET Technologies provide high-capacity reliable transmission with a stm-i standard of 155.52M. [1]
2.ATM Virtual Connection
ATM is a connection-oriented technology, and the logical connection of ATM is called Virtual connection (Visual Connection). Virtual connection is the basic Exchange unit in ATM network, and many operations in ATM (such as resource allocation, traffic control, service quality assurance, etc.) are based on virtual connection. When the ATM terminal is communicating, it must first establish a virtual connection between the terminals, and the user's data cells will be transmitted along the connection. This connection-oriented approach facilitates the high-speed processing of cells by Exchange nodes. In the case of no-connection, the switching node must complete some complex functions, such as destination address routing, which will undoubtedly affect the forwarding speed. In ATM connection-oriented way, each virtual connection has a unique identifier on a link to identify, recorded in the cell header. The switching node simply identifies the virtual connection in the cell header, which enables fast cell forwarding.
3.ATM Technology
ATM (asynchronous Transfer mode) as the name implies is the asynchronous transmission mode, is the International Telecommunication Union ITU-T set standards, in fact, in the 80 's mid-term, people have begun to conduct rapid packet exchange experiments, the establishment of a variety of named different models, Europe heavy in image communication the corresponding technology is called asynchronous time Division Multiplexing (ATD) The United States in the high-speed data communication to the corresponding technology called Fast Packet Switching (FPS), ITU coordinated research, formally named asynchronous Transfer Mode (ATM) technology in 1988 , it is recommended that it is the information transmission mode of broadband integrated Service data Network (B-ISDN). The
ATM cell is a fixed-length grouping of 53 bytes, divided into 2 parts. The first 5 bytes is the letterhead, the main completion of the addressing function, the following 48 bytes is the information section, used to load from different users, different business information. All digital information, such as voice, data, image, etc., is cut, encapsulated into a unified format of the cell in the network, and the receiver to restore the desired format. Because the ATM technology simplifies the exchange process, removes the unnecessary data verification, uses the easy-to-handle fixed cell format, so the ATM exchange rate is much higher than the traditional data network, such as X.25,DDN, Frame Relay and so on. In addition, for such a high-speed data network, ATM network adopts some effective traffic monitoring mechanism to monitor the online user data in real-time, minimizing the possibility of network congestion occurrence. Different services given different "privileges", such as the real-time voice of the highest privileges, general data file transmission of the correctness of the most privileged, the network of different services assigned to different network resources, so different business in the network to achieve "peaceful coexistence."
the general network mode of ATMThe
diagram on the left is the general access mode of ATM, which can be directly connected with the ATM router or the host with ATM card, or it can be an ATM subnet. On a physical link, you can simultaneously establish multiple virtual circuits that carry different services, such as voice, image, and file transfer. [1]
Asynchronous Transfer mode is an important milestone in the development of modern high-speed broadband information transmission and exchange technology. ATM technology is a unified broadband communication network service based on the technology advantages of various existing transmission and switching modes. As a result, ATM has actually designed the technology content of information reuse, exchange and transmission, and formed a series of advanced, strictly standardized but also very complex technology and protocol system. Theoretically, the advance of ATM technology makes it a kind of transmission mode which can be applied to the Network service and application information, but the complexity of the protocol leads to a great obstacle to the development and deployment of Terminal Services and applications. On the other hand, the development of ATM technology has played a significant role in the development of the Future broadband Communication network (especially the broadband Internet based on IP protocol). The basic principles of ATM, information reuse, quality of service (qos,quality of services) assurance, flow control and congestion control technology have been widely used in modern internet technology.
4.ATM Business Introduction
simplified protocol tiering for ATM
Let's take a look at ATM's streamlined protocol tiering
ATM uses AAL1, AAL2, AAL3/4, AAL5, a variety of adaptation layer to adapt to Class A, B, C, D level four different user business, business description is as follows:
class A-Fixed bit rate (CBR) Business: ATM Adaptation Layer 1 (AAL1), support for connection-oriented
business, its bit rate fixed, common business for 64KBIT/S voice service, fixed bit rate
Non-compressed video communications and leased circuits for dedicated data networks.
class B-Variable bit rate (VBR) service: ATM Adaptation Layer 2 (AAL2). Support for connection-oriented
business, its bit rate is variable. Common Business for compressed packet voice communication
and compressed video transmission. The service has transitive interface delay physical property, the reason is
the receiver needs to reassemble the original non-compressed voice and video information.
level C-connection-oriented data service: AAL3/4. The business is a connectivity-oriented business,
for file delivery and data network services, where the connection is established before data is transmitted
the. It is a variable bit rate, but it is not an interface delivery delay.
class D-No connected Data services: Common services are reported as business and data network services. In the
the connection is not established until the data is passed. This business is supported by AAL3/4 or AAL5.
Note: ⑴. Due to the complexity of the AAL3/4 protocol technology, AAL5 was proposed to support C-class business.
⑵. For each level of the business, we can also be subdivided, here do not repeat. [1]
5.ATM Application Examples
Lane refers to LAN Emulation over ATM, which is a LAN LAN simulation on an ATM network.
most data is transmitted over a LAN, such as a Ethernet network. In the ATM network Application Lane Technology, we can be distributed in different areas of the network interconnection, on the WAN to achieve the function of the LAN, for users, they are still in contact with the traditional LAN category, there is no sense of lane.
Lane is mainly used in lane server, which can exist in one or more switches, or in a separate workstation, Lane Server can be shortened to Les, the main function is to do MAC-TO-ATM address translation, Because Ethernet uses a MAC address, ATM uses its own address scheme, which can be used to connect lane clients distributed across the ATM edge via les address translation.
that's how lane works.
How Lane Works
1. LAN switch receives a frame from the Ethernet terminal, and the destination address of the frame is a Ethernet terminal at the other end of the ATM network. The LEC, Laneclient (which resides in LAN switch), sends a MAC-TO-ATM address translation request to the Les (Les resides in the ATM switch).
2. Les sends multipoint multicast to other LEC on the network. How Lane works
3. The LEC that contains the called MAC address in the Address table responds to the LEC.
4. The LEC then broadcasts the response to the other LEC.
5. The LEC that sends the address Translation request acknowledges this response and obtains the destination's ATM address, then establishes an SVC to the purpose LEC via the ATM network, transmitting the data with the ATM cell.
Five, Shanghai ATM backbone Network Node Introduction
the national ATM backbone network Shanghai node was built in April 1997, the network operation is stable after opening. The
network provides switching virtual circuit (SVC) and permanent virtual circuit business, the interface type supports BNC electric port and single, multimode fiber, physical access rate of 2M, 34M, 155M, can meet any business needs. [1]
6. Features
ATM is a kind of information transmission mode technology, its most prominent feature is its asynchronous way, ATM technology has some characteristics: [2]
(1) Group-oriented approach
a small grouping (cell) is used in ATM to host user data. The various operations of ATM are designed around the exchange and processing of cells.
(2) using asynchronous Time division Multiplexing method
an asynchronous time division multiplexing method is used in ATM. The user information is allocated dynamically when the bandwidth is occupied, and each user is statistically shared with the transmission bandwidth, so it is suitable for the burst service. In order to prevent resource access due to the asynchronous way of working ono within an individual, the ATM uses a large number of queues to swap out user information that is temporarily unavailable for service.
(3) error control and flow control without a link-by-segment
when errors occur on the link (including the internal link in the switching node), the ATM switch node does not perform any error recovery in any way. ATM assumes that the link quality in the network is very high, error control function implementation relies on the end-to-end protocol, which is the same as the circuit exchange. ATM switching nodes also do not support flow control on the link, the queue in the system may overflow due to information bursts, resulting in loss of cells. To prevent this loss, ATM provides preventative measures, which are connection-oriented and check and allocate resources when the connection is established, so that the probability of such cell loss is controlled in a very small range.
(4) Cell head function Simplification
because the error control and flow control are not required, the function of ATM cell head is very few, and the main function room identifies the virtual connection according to one identifier, and the other function room checks the error in the cell header, preventing the cell from being lost or mistakenly inserted due to incorrect routing. Due to the limited function of the cell head, the processing of the switching node is very simple and can be run at a very high rate (hundreds of megabits per second) with only a small processing and queueing delay.
(5) Small net charge length of cellIn order to reduce the capacity of the
internal buffer of the switching nodes, and to limit the queue delay of the information in these buffers, the net load (information field) in the ATM cell is relatively small, so as to guarantee the smaller delay and jitter in the service transmission.
7. Status Quo
the national ATM backbone network Shanghai node was built in April 1997, the network operation is stable after opening. has been with Beijing, Nanjing, Guangzhou, Hangzhou, Xian, Shenyang, Wuhan, the overall situation between the direct opening of the 155M circuit, in addition to a number of large-capacity circuit to other provincial capitals, the entire network has been all connected, the scale of the country, with high bandwidth, delay small, no bottleneck, etc., is the best choice for network multimedia applications. The
network provides switching virtual circuit (SVC) and permanent virtual circuit business, the interface type supports BNC electric port and single, multimode fiber, physical access rate of 2M, 34M, 155M, can meet any business needs.
Asynchronous transfer of ATM
