ITEC350 Networks I Lecture 1 Hwajung Lee. What is Computer Networks? A collection of autonomous computers interconnected by a single technology Interconnected.

ITEC350 Networks ILecture 1

Hwajung Lee

What is Computer Networks?

A collection of autonomous computers interconnected by a single technology Interconnected via:

• Copper wire• Fiber optics• Microwaves• Infrared• Communication satellites, etc.

Why Computer Networks?

Business Applications [Goal1] Resource Sharing

• To connect isolated computer and information to be able to extract and correlate information about the entire company.

• To make all programs, equipment (ex: printers, scanners, and CD burners), and especially data available to anyone on the network without regard to the physical location of the resource an the user.

[Goal 2] Communication Medium• Electronic mail (e-mail)• Shared resources (ex: shared hard driver)• Videoconferencing, a shared virtual

blackboard

[Goal 3] Electronic Commerce (e-commerce)• To do business electronically with other

companies. (ex: order the parts of a product from a variety of suppliers)

• To do business with consumers over the Internet.

Home Applications [Goal 1] Access to remote information

• Newspapers, Digital library

[Goal 2] Person-to-person communication• Email, Instant messaging, Chat room,

Worldwide newsgroups• Peer-to-peer communication (ex: Napster)• Internet phone, Internet video phone,

Internet radio, Telelearning

Home Applications (cont.) [Goal 3] Interactive entertainment

• Video on demand, Interactive live television show, Multiperson real-time simulation games – possibly with worldwide shared virtual reality.

[Goal 4] Electronic commerce• Home shopping, Electric flea markets, On-

line auctions

Mobile Network Users [Goal] To have a portable office

• Cellular phone, PDA, Military use, Wireless sensor networks, Mobile-commerce, Wearable wireless computers

Combinations of wireless networks and mobile computing.

Network Types Based on Roles

Terminal Connection

Network Types Based on Roles

Client-server

Network Types Based on Roles

Peer-to-peer Computers act as both client and server

on the network There is no reliance on a centralized

server to provide access to data and other resources

Compared to a centralized client-server model, peer-to-peer is decentralized, meaning any host can communicate with any other host

Network Topologies

HYBRIDSOF THESE

RING

STAR

BUS

MESH

Comparison of Basic Topologies

Topology Bus Star Ring

Advantages Physical Broadcast

Inherent Security, Limited Delay

Reliability, Limited Delay

Disadvantages PoorSecurity – All stations see the data at onceInefficient – collisions when two or more stations send at once.

Poor Reliability (central controller is single point of failure)

Poor Security – All stations see the data as is travels around the ring

Classification of interconnected processors by scale.

Personal Area Network (PAN) A person’s body or desk area

Local Area Networks (1)

Local Area Network (LAN)

Limited geographical distance: home, office, building, campus, industrial part

Customer premises operation• User firm chooses technology• User firm needs to manage on ongoing basis

Low cost per bit transmitted• Companies can afford high speed• 100 Mbps to the desktop is typical

Local Area Networks (2)

Two broadcast networks(a) Bus (b) Ring

Local Area Networks (3)

Ethernet Most popular LAN

Architecture of the original Ethernet.

Metropolitan Area Networks

Metropolitan Area Network (MAN) Single urban area (city and its suburbs) Faster than long-distance WANs Still slower than LANs

Metropolitan Area Networks

A metropolitan area network based on cable TV.

WANWide Area Network (WAN) To link sites

• Long distances

Requires the use of carriers to provide service• Limited and complex choices but carrier manages

High cost per bit transmitted• Companies cannot afford high speeds• Usually low speed (56 kbps to a few megabits per

second)

Wide Area Networks (1)

Relation between hosts on LANs and the subnet.

Wide Area Networks (2)

A stream of packets from sender to receiver.

Wireless Networks

Categories of wireless networks: System interconnection Wireless LANs

• Speed: Upto about 50Mbps• Distance: Tens of meters

Wireless WANs (ex: cellular system)• Speed: below 1Mbps• Distance: Kilometers

Wireless Networks (2)

(a) Bluetooth configuration (b) Wireless LAN

Wireless LANs

(a) Wireless networking with a base station.(b) Ad hoc networking.

Standard for Wireless LANs

IEEE 802.11 network.

Network Software Protocol Hierarchies Design Issues for the Layers Connection-Oriented and

Connectionless Services Service Primitives The Relationship of Services to

Protocols

Network SoftwareProtocol Hierarchies

Layers, protocols, and interfaces.

Protocol Hierarchies

The philosopher-translator-secretary architecture.

The software used to maintain each protocol is often called a protocol stack

Transport layer protocols can be: Connectionless, or stateless, which sends

each packet without regard to whether any other packet was received by the destination computer (implementation: packet switching, UDP)

Connection-Oriented and Connectionless Services (1)

Connection oriented, or stateful, which maintains information about which packets have been correctly received by the destination computer (implm.:circuit-switching, TCP)

Connection-Oriented and Connectionless Services (2)

Connection-Oriented and Connectionless Services

Six different types of service.

Why Standard or Reference Model?

Consumer Easy to select a product which is

compatible with other equipments.Supplier

Minimize risk when it develops new technologies.

Reference Models

The OSI Reference Model ISO (International Organization for

Standardization) OSI (Open Systems Interconnection) Model

The TCP/IP Reference Model TCP (Transmission Control Protocol) IP (Internet Protocol)

A Critique of the OSI Model and Protocols A Critique of the TCP/IP Reference Model

OSI Reference Model

OSI Reference Model

The TCP/IP reference model

Conceptual Models of Networking(1)

AcronymsPOP (Post Office Protocol)FTP (File Transfer Protocol)UDP (User Datagram Protocol)TCP (Transmission Control Protocol)SMTP (Simple Mail Transport Protocol)HTTP (Hypertext Transport Protocol)DNS (Domain Name Service) ICMP (Internet Control Message Protocol)PPP (Point-to-Point Protocol)SATNET (Satellite Networks) IRC (Internet Relay Chat)

A Critique of the OSI Model and Protocols

Why OSI did not take over the world

Bad timing Bad implementations Bad politics

Bad Timing

The apocalypse of the two elephants.

A Critique of the TCP/IP Reference Model

Problems: Service, interface, and protocol not

distinguished Not a general model Host-to-network “layer” not really a

layer No mention of physical and data link

layers Minor protocols deeply entrenched,

hard to replace

Networking TechnologiesEthernet

Most widely used technology Three variation of Ethernet based on

transmission speed, or bandwidthToken-ring

Uses a token to identify which computer on the network has the right to transmit data

Not as fast as Ethernet, and may be more expensive

Networking Technologies

Network Standardization

Who’s Who in the Telecommunications World

Who’s Who in the International Standards World

Who’s Who in the Internet Standards World

ITU (International Telecommunication

Union)

Main sectors• Radiocommunications• Telecommunications Standardization• Development

Classes of Members• National governments• Sector members• Associate members• Regulatory agencies

IEEE 802 Standards

The 802 working groups. The important ones are marked with *. The ones marked with are hibernating. The one marked with † gave up.

Metric Units

The principal metric prefixes.