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Circuit Switching

Circuit Switching . Circuit-switched network direct physical connection between two devices ex) phones or computers shorter links (no, length) than point-to-point connection The circuit can not be shared by other devices. circuit switches. Packet Switching. Datagram Approach

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Circuit Switching

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  1. Circuit Switching • Circuit-switched network • direct physical connection between two devices • ex) phones or computers • shorter links (no, length) than point-to-point connection • The circuit can not be shared by other devices circuit switches

  2. Packet Switching • Datagram Approach • each packet is treated independently from all others • packet = datagram • datagrams may arrive at their destination out of order • Transport layer reorders the datagrams

  3. Packet Switching • SVC(Switched Virtual Circuit) • A virtual circuit is created whenever needed and exists only for the duration of the specific exchange • comparable conceptually to dial-up circuit switching

  4. Packet Switching • Circuit switching vs. Virtual Circuit • Path vs. Route physical path routing table

  5. Packet Switching • Circuit switching vs. Virtual Circuit (cont.) • Dedicated vs. Shared

  6. Frame Relay • Higher data rate at lower cost • the past WAN : leased line or X.25  low data rate • Solution : T-lines, mesh network, Frame relay • Data rate of Frame relay : 1.544Mbps (T-1) / 44.376Mbps (T-3) lower cost Pure mesh T-line network vs. Frame Relay

  7. Frame Relay • Less overhead due to improved transmission media • No need to have a WAN that spends time and resources checking and double checking potential errors • X.25 vs. Frame relay • X.25 • extensive error checking and flow control at the network layer • station-to-station frame checking at the data link layer • overhead for reliability eats up bandwidth • Frame Relay • does not provide error checking or require acknowledgment in the data link layer because network become reliable and less error • All error checking is left to network and transport layer protocols • Frame relay traffic : simplified transmission

  8. X.25 traffic Frame Relay traffic

  9. Frame Relay • Frame Relay is normally used as a WAN to connect LANs or mainframe computers. Frame Relay network

  10. Frame Relay • Virtual Circuits • Use a virtual circuit identifier (not physical address) • Virtual circuit identifiers in Frame Relay operate at the data link layer (cf. X.25: network layer) • data link connection identifier (DLCI) : local number • Two type of connections in Frame Relay • PVC(Permanent Virtual Circuit) Connection • SVC(Switched Virtual Circuit) Connection DLCIs

  11. Frame Relay Layers • Physical Layer • No specific protocol • Data Link Layer • A simplified version of HDLC called core LAPF • LAPF : LAP for frame mode • No extensive error and flow control fields frame priority for discard in bottleneck (1:high) a switch informs that congestion has occurred final(1)/more(0)

  12. ISDN Services Three categories network may change or process the content of data  layer 4-7 service provides additional functionality to the bearer services andTeleservices provides the means to transfer information (voice, data, video) between users without the network manipulating the content of that information Layer 1-3 services

  13. Subscriber Access to the ISDN • User Interfaces • BRI: Basic Rate Interface for home or small office • 2B+D = 192kbps • PRI: Primary rate Interface • 23B+D = 1.544Mbps (North America) = T1 • 30B+D = 2.048 Mbps (Europe) = E1 TP local loop T1

  14. Bit rates for different application Broadband ISDN (B-ISDN) • For the services beyond the capabilities of both the BRI and PRI

  15. ATM Architecture • Virtual Connection • Connection is accomplished through TP, VP, VC • Transmission Paths (TPs) • Physical connection (wire, cable, satellite and so on) • Virtual Paths (VPs) • A connection or a set of connection between Switches • Virtual Circuits (VCs) • All cells belonging to a single message follow the same VC TPs > VPs > VCs

  16. ATM Architecture TP Example of VPs and VCs

  17. ATM

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