Establishing Communications Channels
Transmission path: point A point B
Networking Modes: connection-oriented; connectionless
Switching Modes: circuit switching; packet switching
Connection-Oriented: connection is established before information transfer occurs. All information from source follows the same path to the destination. The line is disconnected after the transmission is complete. No delay in transmission since the path is predetermined. NWs operate in circuit switching: Example: PSTN, SDH/SONET, DWDM; packet-switched NWs: X.25, Frame Relay, ATM NWs. PVCs (permanent virtual circuits)- connection established before transmission; SVCs (switched virtual circuits)- on demand. Connectionless Networking: No path is established. Data packets- source/destination in the header- are routed. Expect delays. Example: the Internet. •
Physically moving bits from node to node – source to destination - in a NW. Node = PBX, local exchange, mux, modem, computer/device. Switches contain tables/matrices with routing info. They simply look in table and pass the data to the next node. Switches do not change the data in a packet. Routers: more complex than switches. Routing involves determining the optimal path and transporting information through an internetwork. Need routing algorithms to determine the shortest path. Static router: knows only its routing table. Cannot communicate with other nodes/change the table. Simply transmits packets based on the info in the table/matrix. Dynamic router: can communicate with other nodes. Can adjust the routing table. Knows the entire NW/routing area. Has more intelligence than static router.
Circuit Switching (see Fig 3.1, p.88)
Basis of voice NWs. Circuit-switched NWs are analogous to the voice telephone systems. Can be used for data. Requires an end-to-end circuit for voice/data transmission. A fixed share of NW resources is reserved for the call;...
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