Communications Networks: Fundamental Concepts and Key Architectures Leon-Garcia and Widjaja University of Toronto

Outline of Course C1 Networks and Services Survey Appendix A1 Queues Online tutorial Probability C2 Applications and Layered Architectures (Skip 2.4 Berkeley API) C3 Digital Transmission Fundamentals C4 Transmission Systems (Skip 4.4, 4.6, 4.7 on telephone details)

Course Outline Continued C5 Peer-Peer Protocols (C6 skip LANs) covered in CS487 C7 Packet Switching Nets C8 TCP/IP (Skip 8.8)

C1 Intro to Nets 1.1 Networks and Services 1.2 Approaches to Network Design 1.3 Internet and Packet Switching 1.4 Factors in Network Evolution

1.1 Networks and Services Definition of network TV Broadcasting Telephone Service PSTN POTS Cellular Phones Email Web Video on Demand

1.2 Approaches to Network Design Network Functions and Topology Terminals Connectivity Switches Access Network Multiplexers LANS, Metropolitan net, WANs Topologies Addressing (Flat vs. Hierarchical) Traffic Control Network Management

(a) A switch provides the network to a cluster of users Access network (b) A multiplexer connects two access networks Figure 1.7

Message, Packet and Circuit Switching Telegraph Network (Message) Internet (Packet) Telephone Network (Circuit) Table 1.1 Not Functions but rather dimensions of classifying nets

Telegraph Sam F. B. Morse Baltimore to DC 1837 Binary representation Relay Hardware, Relay, MD Message Switching Multiplexing Edison, Bell Teletype Networks

Telephone Alexander Graham Bell 1876 Boston Circuit Switching Hierarchy Analog Transmission Grafting of Digital Traffic Huge Investment, particularly local drops (last mile)

(b) Cords interconnect user sockets providing end-to-end connection (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

Fig. 1.11 Part of the Hierarchy for Telephone Switching Tandem CO Toll Fig. 1.11 Part of the Hierarchy for Telephone Switching Figure 1.11

1. Telephone Office The caller picks up the phone triggering the flow of current in wires that connect to the telephone office. 2. 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.) 3. Telephone Office 4. Telephone Office 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. 5. Telephone Office The ringing signals are discontinued when the destination phone is picked up and communication can then proceed. Telephone Office 6. Either of the users terminate the call by putting down a receiver. Telephone call set up Figure 1.1

Internet Packet Switching Taste of History SAGE, SABRE, ARPANET Terminal Oriented Nets Multiplexers LANs flat addressing Ethernets WAN Routers TCP/IP Protocol Suite

(a) Time-Shared Computers & Cables for Input Devices . T (b) Dial In T . C T T Modem Pool PSTN Modem T T = terminal Figure 1.12

Sharing a multidrop line Poll to terminal C Response from terminal T T T T Sharing a multidrop line Figure 1.13

Ethernet Local Area Network (LAN) transceivers       (a) Current star version Original bus version Figure 1.17

ARPANET about 1972 AMES McCLELLAN UTAH BOULDER GWC CASE RADC ILL LINC CARN AMES USC MIT MITRE UCSB STAN SCD ETAC UCLA RAND TINKER BBN HARV NBS ARPANET about 1972 Figure 1.16

An internetwork, not the Internet, necessarily G net 1 G G G net 5 net 2 G net 4 G G = gateway Figure 1.18

Retrieving a Web page over the Internet 1. 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. 2. 3. 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. 4. 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. 5. 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. 6. The TCP connection is then closed and the user may view the document. Figure 1.4

1.3 Key Factors in Network Evolution Rapid Improvement of Communications and Computer Performance – “Rapid Technology Push” “Market Pull” Regulation Standards

Evolution of network capacity DWDM SONET OC-48 T-4 carrier Transmission capacity (bits/second) T-1 carrier Baudot multiplex Printing telegraph Figure 1.9

Factors involved in success of a new service Technology Standards Market Regulation Figure 1.19