Packet-Switching Network, Frame Relay, and ATM

Packet Switching The name of the networks that can send packets from many different users over many different possible paths is Packet-switching networks because of the way they package and route data. The original data package is broken into packets and each packet is tagged with a desti-nation address and other information. This makes it possible to send each packet separately over the network.  In packet-switching, packets are relayed through stations in a computer network along the best route currently available between the source and the destination. Each packet is switched separately. Two packets from the same original data package may follow completely different paths to reach the same destination.  The data paths for individual packets depend on the best route open at any given instant. Even though each packet may travel along a different path, and the packets composing a message may arrive at different times or out of sequence, the receiving computer is still able to reassemble the original message. The switches direct the packets over the possible connections and pathways. These networks are sometimes called any-to-any connections. Exchanges in the network read packet and forward them along the best route available at that moment.

Network Introduction Network Cabling Wireless Network Network Interface Card OSI Model Protocols Ethernet - Network architecture Token Ring - Network architecture AppleTalk and ArcNet - Network architectures Repeaters, Bridges, Routers, and Gateways E-mail Standards Modem & Async Comm. T1, T3, and Switched 56 Digital Connectivities Packet-Switching Network,Frame Relay and ATM ISDN & FDDI

Many packet-switching networks use virtual circuits. These are circuits composed of a series of logical connections between the sending and the receiving computer. The circuit is not an actual cable, but bandwidth allocated on demand as opposed to a permanent, physical link between two stations. The connection is made after both computers exchange information and agree on communication parameters which establish and maintain the connection.

These parameters include the maximum message size and the path the data will take.

Virtual circuits incorporate communication parameters to ensure reliability.

These include: Acknowledgements, Flow control, and Error control. Virtual circuits can last either as long as the conversation (temporay) or as long as the two communicating computers are up and running (permanent).

Frame Relay & ATM

As network communications move toward digital and fiber-optic environment, new technologies will appear that require less error checking than earlier analog packet-switching method.

Frame relay is an advanced fast packet variable-length, digital, packet-swicthing tech-nology. With this technology designers have stripped away many of X.25?s accounting and checking functions that are not necessary in a reliable, secure, fiber-optic circuit environment.

Frame relay is a point-to-point system that uses a PVC (Permanent Virtual Circuit) to transmit variable length frames at the Data Link layer.

The data travels from a network over a digital leased line to a data switch into the frame relay network. It passes through the frame relay network and arrives at the destination network. Frame relay is much faster because it uses a PVC so the entire path from end-to-end is known.

Frame relay technology requires a frame-relay capable router or bridge to successfully transmit data over the network. A frame relay router will need at least one WAN port for a connection to the frame relay network and another port for the LAN.

Asynchronous Transfer Mode (ATM) is an advanced implementation of packet switching that provides high-speed data transmission rates to send fixed-size packets over broadband and baseband LANs or WANs.

ATM can accommodate voice, data, Fax, Real-time video, CD-quality audio, Imaging, and Multimegabit data transmission.

Because of the ATM?s power and versatility, it will influence the future of network communications. It is equally adaptable to both LAN and WAN environments, and it can transmit data at very high speeds (155 Mbps to 622 Mbps or more).

ATM is broadband call relay method that transmits data in 53-byte cells rather than in variable-length frames. These cells consist of 48 bytes of application information with five additional bytes of ATM header data. For example, ATM would divide a 1000-byte packet into 21 data frames and put each data frame into a cell. The result is a technology that transmits a consistent, uniform packet.

Theoritically, ATM can offer throughput rates up to 1.2 gigabits per second. Currently, however, ATM measures its speed against fiber-optic speeds that can reach as high as 622 Mbps. Most commercial ATM boards will transmit data at about 155 Mbps.

BACK TO MAIN PAGE