Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number. The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.) The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones. The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. Either of the users terminate the call by putting down a receiver. Telephone Office 1. Telephone Office 2. Telephone Office Telephone Office Telephone Office Telephone Office Figure 1.1

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Transportation Network Transportation City streets Highways Interstates Transport Vehicle Personal Automotives Cars Trucks Minivans Busses Tractor Trailers Transport Passengers Produce Freight Solid Liquid Specialty

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies The user clicks on a link to indicate which document is to be retrieved. The browser must determine the address that contains the document. It does this by sending a query to its local name server. Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections. The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle. The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format. The TCP connection is then closed and the user may view the document Figure 1.4

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Realplayer example Figure 1.5 Copyright © , RealNetworks, Inc. All rights reserved. RealPlayer is a trademark of RealNetworks, Inc.

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies t0t0 t1t1 Network Figure 1.6

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Network (a) A switch provides the network to a cluster of users (b) A multiplexer connects two access networks Access network Figure 1.7

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Metropolitan network A consists of access subnetworks a, b, c, d. National network consists of regional subnetworks . Metropolitan network A is part of regional subnetwork . A A Metropolitan 1* a c b d  (a) (b)   Figure 1.8

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Transmission capacity (bits/second) Printing telegraph Baudot multiplex T-1 carrier T-4 carrier SONET OC-48 DWDM Figure 1.9

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (a) A switch in the form of an operator with a patch cord panel (not shown) (b) Cords interconnect user sockets providing end-to-end connection Figure 1.10

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Tandem CO Toll CO Tandem Figure 1.11

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (a) Time-Shared Computers & Cables for Input Devices (b) Dial In C TT C T T T Modem Pool PSTN Modem T T = terminal Figure 1.12

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies C TTTT Response from terminal Poll to terminal Figure 1.13

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies T T Host T Address Info Mux Figure 1.14

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies T T T New York City San Francisco Chicago Atlanta Host Figure 1.15

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies UCLARANDTINKER USC NBS UCSB HARV SCD BBN STAN AMES McCLELLAN UTAHBOULDERGWCCASE CARN MITRE ETAC MIT ILL LINC RADC Figure 1.16

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies (a) (b) transceivers Figure 1.17

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies G G G G G net 1 net 2 net 3 net 4 net 5 G = gateway G Figure 1.18

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies Technology Regulation Market Standards Figure 1.19

Leon-Garcia & Widjaja: Communication Networks Copyright ©2000 The McGraw Hill Companies time Capability Initial class of invention Second type of invention Third type of invention time Capability (a)(b) Figure 1.20