ITEC350 Networks I Lecture 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 ( ) 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 , 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 HYBRIDS OF THESE RING STAR BUS MESH

Comparison of Basic Topologies TopologyBusStarRing Advantages Physical Broadcast Inherent Security, Limited Delay Reliability, Limited Delay Disadvantages Poor Security – All stations see the data at once Inefficient – 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.

WAN Wide 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 network.

Network Software Protocol Hierarchies Design Issues for the Layers Connection-Oriented and Connectionless Services Service Primitives The Relationship of Services to Protocols

Network Software Protocol 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

The TCP/IP reference model

Conceptual Models of Networking (1)

Acronyms POP (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 Technologies Ethernet  Most widely used technology  Three variation of Ethernet based on transmission speed, or bandwidth Token-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.