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 SwitchingDatagram 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

Packet SwitchingSVC(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

Packet SwitchingCircuit switching vs. Virtual Circuit

Path vs. Route physical path

routing table

Packet SwitchingCircuit switching vs. Virtual Circuit (cont.)

Dedicated vs. Shared

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)

Pure mesh T-line network vs. Frame Relay

lower cost

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

X.25 traffic

Frame Relay traffic

Frame RelayFrame Relay is normally used as a WAN WAN to connect LANs or mainframe computers.

Frame Relay network

Frame RelayVirtual CircuitsVirtual 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

Frame Relay LayersPhysical LayerPhysical Layer

No specific protocolData Link LayerData Link Layer

A simplified version of HDLC called core LAPF LAPF : LAP for frame mode No extensive error and flow control fields

final(1)/more(0)

a switch informs that congestion has occurred

frame priority for discard

in bottleneck (1:high)

ISDN Services

provides the means to transfer information (voice, data, video) between users without the network manipulating the content of that information

provides additional functionality to the bearer services and Teleservices

network may change or process the content of data layer 4-7 service

Layer 1-3 services

Three categories

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

Subscriber Access to the ISDN

TP local loop

T1

Broadband ISDN (B-ISDN)

Bit rates for different application

For the services beyond the capabilities of both the BRI and PRI

ATM ArchitectureVirtual 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

Example of VPs and VCs

ATM ArchitectureTP

ATM