Atm lan technology

-- Abstract: The atm lan technology is currently a hot technology in the network field. This article discusses the background of the Application of ATM technology in Lan, the technical requirements for interconnection with traditional networks, the implementation scheme, and the principles and advantages and disadvantages of the existing atm lan technology.
-- ATM technology was initially designed for Wide Area Network broadband services, but it is currently moving forward in LAN applications. This development trend mainly stems from the following four application requirements:
-- ① A series of practical needs for broadband services, such as video on demand, video conferences, and multimedia services, have emerged on the traditional LAN;
(2) traditional LAN technologies, such as Ethernet and card rings, provide connectionless services based on TCP/IP protocol, which cannot meet the needs of real-time services. At the same time, as network users expand, the traditional LAN Based on the sharing method is no longer tolerable;
-- ③ With the development of chip technology, the performance of a single computer is greatly improved, and the computer port can even process data streams of up to 100 Mbit/s, making the Broadband LAN possible;
-- ④ As processing technology advances, users can lay broadband transmission media such as optical fiber on the LAN.
-- The difficulties faced by traditional local area networks have prompted people to consider applying ATM technology to local area networks. Because of the advantages of the ATM technology itself, that is, broadband exchange, connection-oriented and reliable service quality assurance, ATM naturally becomes the only technology that can solve the existing network difficulties.
-- At this stage, it is impossible for an atm lan to completely replace a traditional LAN. The interconnection technology must be developed to achieve a smooth transition from a traditional network to an atm lan. Therefore, when implementing interoperability with traditional LAN, the atm lan must implement the following functions:
-- ① Transparent support for existing protocols, applications and network services of traditional LAN;
-- ② Achieve connectionless services in traditional networks;
-- ③ Support the multicast/broadcast function;
-- ④ Resolution of IP or MAC address and ATM address is provided.
-- This article will discuss how to implement non-connection services on an atm lan. ATM supports application interfaces (APIS) of traditional network protocols and the technical principles and advantages and disadvantages of the existing atm lan.
1. connectionless services
-- ATM is a connection-oriented exchange and transmission technology and cannot directly support connectionless services. To this end, ITU-T defines two methods to achieve connectionless services on the ATM network, namely direct method and indirect method.
1. Direct Method
-- Whether the atm lan is configured with a connection server (CLSF: ConnectionLess Service Function ). The server can be plug-in or integrated into an ATM switch. When no-Connection Service is supported, both parties send packets to the unconnected server through the ATM virtual circuit connection (VCC, the server is responsible for distributing data packets to the destination terminal or its server. Servers and terminals are connected by an ATM virtual circuit to form an overlay network covering the ATM network.
-- In the direct method, you only need to establish a connection with the server without connecting the business host. The number of connections required for the business is small, and the network statistics gain is high. However, the emergence of unconnected servers makes the maintenance and management of the network complex, and the reliability of the network also decreases. When the business volume of the unconnected services increases, the server inevitably becomes a network bottleneck.
2. Indirect Method
-- In the indirect method, the connectionless service does not rely on the server's grouping and forwarding function, but uses the virtual circuit of the ATM Network to establish a direct connection between hosts to achieve the connectionless service. In this way, you need to establish a virtual circuit connection between any port. The result of this scheme is a great waste of bandwidth. In fact, not all contacts need to be connected to all other contacts in all business periods. Dynamic connections can be used to establish connections as needed to reduce network bandwidth usage.
-- The advantage of the indirect method is that no unconnected server is set in the network, which eliminates the server bottleneck effect. However, the network requires the technology of Route resolution and fast connection establishment, and too many virtual circuit connections in the network increase the network maintenance burden, and the bandwidth resource utilization is low.
2. Application interface (API)
-- Application interfaces of the atm lan technology must be compatible with traditional network protocols and be oriented to future ATM applications. Currently, two application interface technologies are available in the atm lan. One is the high-level application interface and the other is the low-layer application interface. The business capability of the lower-layer application interface is the same as that of the MAC Sub-layer of IEEE, because an atm mac Sub-layer is designed to simulate the MAC Sub-layer of IEEE in the atm lan. Therefore, the atm mac Sub-layer can be directly compatible with traditional LAN protocols and applications to achieve interoperability with traditional LAN.
-- In contrast, a higher-level application interface is more advantageous when it is required to support existing protocols. The function of high-level application interfaces can be from the network layer to the application layer, and can also support future ATM-oriented applications. The high-level application interface does not need to simulate the MAC Sub-layer, so it is more efficient. High-level application interface based on the network layer is already familiar to everyone, such as SOCKET and APPC. However, there are many protocols at the network layer, and each Protocol needs to define a direct application interface, large workload. To support traditional LAN and meet the needs of future ATM applications, these two application interfaces are required and will coexist in the atm lan.
Iii. atm lan technology
-- In order to introduce the ATM technology to the LAN, the ATM Forum and the Internet Engineering Task Group (IETF) have made unremitting efforts and launched several atm lan protocols with important practical significance. Among them, the LAN simulation and MPOA technologies of the ATM Forum are the most representative.
1. LAN simulation
-LAN simulation is a network solution that simulates traditional LAN services in an ATM network environment. In LAN simulation, the ATM network only uses the role of the network data link layer and is based on the simulation technology of the MAC Sub-layer, so the existing network layer protocols such as IP and IPX) it can run in the LAN simulation environment without any changes.
-- There are two types of network information in LAN simulation: one is the control information between the simulation customer and the simulation server, and the other is the control information between the simulation customer, and data information between the simulation customer and the broadcast server without a name. As shown in 3, when simulation CUSTOMER 1 wants to communicate with simulation Customer 2, simulation CUSTOMER 1 must first know the ATM address of simulation Customer 2. If the initiator of simulation CUSTOMER 1 contains the ATM address of simulation Customer 2, then simulation CUSTOMER 1 will use this address to establish a direct ATM virtual circuit connection with simulation Customer 2 to achieve communication such as e); otherwise, simulation CUSTOMER 1 sends an address resolution request group to the LAN simulation server such as a). The LAN simulation server uses the MAC address of simulation Customer 2 carried by this group to search in the cache, if the retrieval is successful, the LAN simulation server sends the ATM address of simulation Customer 2 to simulation CUSTOMER 1. Otherwise, the MAC address is sent to the Broadcast Server, such as B ), broadcast the MAC address to the entire network using the Broadcast Function of the unknown Broadcast Server. Simulation client 2 receives the broadcast information and sends the address back to the LAN simulation server, the LAN simulation server is then sent to simulation CUSTOMER 1. During the time when the LAN simulation server did not return feedback to the address of simulation Customer 2, simulation CUSTOMER 1 distributed the Data Group to the broadcast unnamed server, and the server sent the broadcast form to simulation Customer 2 such as c, d ).
-- From the above communication procedures, we can see that because LAN simulation is built on the MAC Sub-layer of the data link layer, it can transparently support various protocols at the traditional network layer, with good compatibility. The network implementation is simple, seamless connection between devices of different manufacturers. However, LAN simulation also has many defects:
-- ① The network is based on the Client/Server structure. Due to server restrictions, the number of network customers cannot be large, which limits the network size;
-- ② Because the backup server is not supported, the reliability of the server determines the reliability of the network. Once the server fails, the entire network will not work;
-- ③ When LAN simulation is used to implement inter-subnet communication, it still requires the participation of the router. In this way, the limited routing and packet forwarding functions of the router become the bottleneck of the network.
2. ATM multi-protocol procedure Technology
-- To solve the disadvantages of low communication capability of LAN simulation between subnets, the ATM Forum has introduced its Multi-Protocol (MPOA: Multi-Protocol Over ATM) technology. The basic goal of MPOA technology is to bind the LAN simulation technology with the next node interpretation protocol (NHRP) technology of the Internet Engineering Task Group, the purpose of this operation is to retain the high-efficiency communication advantage of LAN simulation in the subnet, and introduce the advantages of the next node protocol for effective communication between different subnets, the communication efficiency of the entire broadband network is greatly improved without the intervention of traditional routers.
-- Because MPOA supports the interconnection between the data link layer and the network layer, it can transparently support traditional network protocols to achieve large-scale interconnection networks. Communication between different subnets can interwork with traditional routers, establish direct connections to improve network efficiency; reduce physical devices involved in the routing connection process, thus reducing the complexity of network routing and improving efficiency. However, when MPOA technology implements optimal routing between subnets, it may bring about coordination between the ATM layer and the network layer routing and addressing. The network criteria for establishing optimal routing are as follows, the maintenance of optimal route connections still needs to be studied, and the network still requires the existence of Address Resolution servers. Therefore, the routing information databases between subnets must be synchronized, in this way, unnecessary latency is introduced when a connection is established, so that the complexity of network design and operations is not completely simplified.
Iv. Conclusion
-- After years of efforts, the application of the ATM technology in the LAN has made great progress. LAN simulation and MPOA technologies make the atm lan a reality. These protocols protect the existing investment of traditional network users, promote the development of the ATM network itself, and create conditions for the smooth transition to the ATM network. The existing ATM network interconnection technology has achieved effective interconnection with traditional networks to a large extent. The existing technical defects are also being studied, and many of them have been gradually solved. It is foreseeable that ATM will undoubtedly become the network technology of broadband networks including LAN and WAN in the future. In the near future, users will also enjoy high-quality network services of the ATM network.