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

2. 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)

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

4. 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

5. 1.1 Networks and Services Definition of network TV Broadcasting
Telephone Service PSTN POTS
Cellular Phones
Web
Video on Demand

6. 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

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

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

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

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

12. (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

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

14. 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

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

16. (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

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

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

19. 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

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

21. Retrieving a Web page over the Internet1.
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

22. 1.3 Key Factors in Network Evolution
Rapid Improvement of Communications and Computer Performance – “Rapid Technology Push”
“Market Pull”
Regulation
Standards

23. 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

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