Post on 27-Dec-2015
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
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
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
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
Metropolitan Area Networks
Metropolitan Area Network (MAN) Single urban area (city and its suburbs) Faster than long-distance WANs Still slower than LANs
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)
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
Network Software Protocol Hierarchies Design Issues for the Layers Connection-Oriented and
Connectionless Services Service Primitives The Relationship of Services to
Protocols
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)
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
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
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
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.