18. Atm technology

Asynchronous transfer mode (ATM) is a method of transmitting data using fixed length (53 bytes) data units, called cells, over circuits that can support not only traditional data requirements, but also voice and video. Since it operates at the MAC sublayer of the data link layer of the OSI model, which is above the physical layer, it can convert any type of packet into these fixed-length cells. Unlike other packet switching, ATM cells arrive at the destination point in the correct sequence.

• ATM is a high-speed data transmission technology that can be used for LANs and WANs. Primarily because of its bandwidth and quality of service capabilities, ATM could form the basis of a unified network. ATM is connection-oriented. Cell switching has many advantages over frame switching. ATM requires special ATM switches and interfaces to connect ATM switches to one another and to LANs. ATM is scalable. As an ATM network grows, more bandwidth can be added to handle more traffic.

ATM is independent of the transmission medium, though the medium can limit how fast ATM can operate. It is possible but still rare to have an all-ATM LAN. It is more common to connect an Ethernet network to an ATM backbone. LAN Emulation (LANE) specifies a way to do this. MPOA defines how to run IP and other Layer 3 transmission protocols over ATM. It enhances LANE, especially in the use of VLANs. But, ATM is still quite expensive and networks must have ATM devices that are interoperable. This requires new equipment

topology	creations of networks with frame switching
transfer rate	25 Mbps to 2.46 Gbps
access method	Cell switching
Transmission medium	Fiber optic
collision	no

19. Modems. Repeaters. Bridges. Routers. Gateways

A modem is a device that makes it possible for computers to communicate over a telephone line. When computers are too far apart to be joined by a standard computer cable, a modem can enable communication between them. Modems convert digital signals to analog waves, and convert analog waves to digital signals

Repeater enables signals to travel farther. It extends the distance of a Network run. Takes a weak Network signal in on one side, boosts the signal, and sends it out its other side. Operates at the physical layer of the OSI Networking model. It is only used to connect the same type of media. (they do not translate or filter signals). Can segment one of its connections from the other. Repeaters can move packets from one kind of physical media to another

A bridge can join segments or workgroup LANs and can divide a network to isolate traffic or problems. It is built-in switching. Bridges that can span different Networking systems and media are also available

Routers can determine the best path for sending data and filtering broadcast traffic to the local segment. They have routing tables. To determine the destination address for incoming data, the routing table includes: All known network addresses, Instructions for connection to other networks, The possible paths between routers, The costs of sending data over those paths. Routers operate at the network layer of the OSI Model. Routers can translate from any of the protocols at layers 1-3 to any other protocols at layers 1-3. They can connect similar and dissimilar networks. Routers become a node on a Network and have their own Network address. They can determine and use the shortest route to a location. They form the backbone of the Internet.

Gateways enable communication between different architectures and environments. They repackage and convert data going from one environment to another , so it`ll application program at the end. To process the data, the gateway:- Disassembles incoming data through the network's complete protocol stack.-Encapsulates the outgoing data in the complete protocol stack of the other network to allow transmission. Gateways are application-specific interfaces. They link the 7 layers of the OSI Model when they are dissimilar at any or all levels.