ATM LANE concept
As the name implies, the function of LANE (Emulated LAN) is to emulate a LAN on an ATM network. The LANE protocol defines a mechanism to emulate IEEE 802.3 Ethernet or 802.5 token ring network. The LANE protocol defines the same interface as the service provided by the existing LAN to the network layer, and the data transmitted in the ATM network is encapsulated in the corresponding LAN MAC packet format.
Simulate the traditional local area network on the ATM network, and interconnect multiple traditional local area networks and terminal devices through the ATM network. Construct a new local area network on the ATM network, and the communication behavior between these local area network contacts is exactly the same as the traditional local area network. Local area network emulation hides the ATM switching structure from the local area network, and local area network terminals do not feel the existence of the ATM network, so they can take advantage of various advantages of the ATM network without modifying the hardware and software of the terminal equipment. As can be seen from the figure below, the simulation protocol is mainly implemented on the ATM host and the ATM LAN bridge. The ATM LAN bridge is a converter between the local area network and the ATM network. It uses the ALL5 protocol to adapt the local area network data to generate ATM cells, or reassemble ATM cells to restore the data frames of the local area network. The ATM host adds a LAN simulation function between the ATM adaptation layer and the high-level protocol, so that the ATM host simulates the behavior of the traditional LAN device and communicates with the LAN.
ATM LANE is specially designed for LAN access, which means ATM LAN Emulation (LAN EmulaTIon). For traditional IP terminals, the ATM network is like a local area network, which contains several IP subnets connected by routers.
LANE is based on the client / server model (Client / Server), a LANE server can be used for multiple LANE clients. LANE supports multiple protocol (MPOA: MulTI-Protocol over ATM) transmission, allowing the interconnection between different LANEs; LANE fully supports the connectionless feature in LAN; LANE supports unicast, multicast and broadcast transmission;
The advantages of ATM LAN:
Real-time information transmission, because the transmission and exchange delay of ATM is small, which can ensure the real-time transmission of information; with strong network processing capabilities, various services including voice, data, images, etc. can be uniformly converted into ATM cells in ATM Transmission and processing in the network; high transmission rate, easy to communicate between the local area network and the public network;
LAN simulation provides the functions of the lower two layers of the OSI-RM layer, that is, using the ATM network to simulate the functions of the LAN data link layer and the physical layer, and is independent of all high-level services, protocols, and applications. ATM switches do not directly participate in local area network simulation, but only provide virtual channels for ATM cells.
2. LAN simulation structure
The LAN simulation is logically composed of a server and a group of LAN simulation clients.
The LAN emulation server can be divided into three functions:
a. Broadcast & Unknown Server (BUS: Broadcast && Unknown Server) implements broadcast and multipoint communication functions, both emulating the traditional LAN broadcast mechanism, unicasting LEC data before the establishment of a direct link between LECs, and only one BUS in a LANE ;
b. The LAN emulation server (LES: LANE Server) is an address server, which stores the MAC address of each LEC in LANE
Correspondence table with ATM address to realize the conversion between MAC address and ATM address; (Provide registration and resolution of MAC address; respond to the above request of LEC; there is only one LES in a LANE;)
c. There can be multiple LANEs in the ATM network of the LAN emulation structure server (LECS: LANE ConfiguraTIon Server). The LECS saves the structure information of the LANE and configures the LEC into the LANE; LES and BUS configuration information; provide each LEC with the ATM address of the LES to which it belongs)
The LAN simulation client LEC can be implemented on ATM workstations and ATM bridges. Its main functions are: to realize the mutual conversion of MAC frames and ATM cells in the LAN; to save the correspondence table between MAC and ATM and VPI / VCI; and LAN simulation server Jointly complete the address resolution function; start signaling to establish an ATM virtual connection to provide a path for transmitting data; and implement management functions with the ATM layer management interface; (simulate Ethernet or token ring network nodes on the ATM terminal system, at least tied Set a MAC address, whose function is to encapsulate the IP datagram and send it to the ATM network, and at the same time translate the ATM packet to reconstruct the IP datagram.)
Each LANE consists of a group of LANE customers (LEC) and LANE services. LEC can also be a bridge and a router acting as an ATM host agent. LANE service consists of three different functional entities: LAN emulation configuration server (LECS), LAN server (LES) and BUS. These three service entities can exist separately, but they are usually located on the same device. For example: LES can be located on ATM switches, Routers, bridges and workstations.
LECS, LES and BUS are concentrated on the ATM workstation, LEC1 connects Ethernet to the ATM network, LEC2 connects the token ring network to the ATM network, LEC3 connects the FDDI network to the ATM network, and LEC4 is the ATM host. LUNI is a local network emulation user network interface, LEC and server are connected through LUNI and ATM network. Four LECs and servers form an emulated local area network LANE.
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