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

Network

(a) A switch provides the network to a cluster of users

(b) A multiplexer connects two access networks

Access network

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)

(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

Tandem

CO

Toll

CO COCO

CO

Tandem

Figure 1.11

Fig. 1.11 Part of the Hierarchy for Telephone Switching

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

3.

4.

Telephone Office

5.

6.

Telephone Office

Telephone Office

Figure 1.1

Telephone call set up

Internet

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

(

C...T T

C...

T

T

T

ModemPool

PSTN Modem T

T = terminal

Figure 1.12

(a) Time-Shared Computers & Cables for Input Devices

(b) Dial In

C

T T TT

Response from terminal

Poll to terminal

Figure 1.13

Sharing a multidrop line

(a)

transceivers

Figure 1.17

Ethernet Local Area Network (LAN)

Original bus version Current star version

UCLA RAND TINKER

USC

NBS

UCSB

HARV

SCD

BBN

STAN

AMES

AMES McCLELLAN UTAH BOULDER GWC CASE

CARN

MITRE

ETAC

MIT

ILL

LINC

RADC

Figure 1.16

ARPANET about 1972

G

G

G

G

G

net 1

net 2

net 3

net 4

net 5

G = gateway

G

Figure 1.18

An internetwork, not the Internet, necessarily

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.

1.

2.

3.

4.

5.

6.

Figure 1.4

Retrieving a Web page over the Internet

1.3 Key Factors in Network Evolution

• Rapid Improvement of Communications and Computer Performance – “Rapid Technology Push”

• “Market Pull”

• Regulation

• Standards

Tra

nsm

issi

on c

apac

ity

(bit

s/se

con

d)

1.0E+00

1.0E+02

1.0E+04

1.0E+06

1.0E+08

1.0E+10

1.0E+12

1.0E+14

1850 1875 1900 1925 1950 1975 2000

Printing telegraph

Baudot multiplex

T-1 carrier

T-4 carrier

SONET OC-48

DWDM

Figure 1.9

Evolution of network capacity

Technology

Regulation Market

Standards

Figure 1.19

Factors involved in success of a new service