Session 1. Introduction to Communication Networks

Transcription

1 Session 1. Introduction to Communication Networks Networks 1 Network Services The Traditional Networks Postal mail Water supply networks Electricity power networks Transportation networks Cable and television broadcast networks Telephone Communication networks microwave, electronic and optical Wireless communication (cellular, satellite, ) Public networks (telephone, Internet, ) Private networks (bank, military, airlines, ) Networks 2

2 Radio and Television Broadcasting Multiple recipients Passive All user receives identical contents No user sends a message High quality required Tolerable delay Several seconds Not tolerable a variation of delay, though Networks 3 Telephone service-1 Real-time service A few hundred mili-seconds delay Peer-to-peer communication Reliable No automatic re-transmission Connection-oriented First,established a connection Networks 4

3 Telephone Service-2 Caller Access Networks Central Office Telecom Networks Central Office Access Networks Callee pickup dial tone dial the number route ring ring ring callee pick up the phone Connection established for bidirectional conversation hang-up terminating signals Networks 5 Cellular Telephone Service Mobility Shared medium Radio Transmission Hand-off Able to keep conversation when moving an area to another Roaming Able to carry a hand-set out of home base Radio transmission Low quality, low availability, and a security hole. Networks 6

4 Electronic mail Not a real-time at all Tolerable to large delays: possibly several days Forward a whole message at a time No need of connection-oriented Networks 7 World Wide Web Client-server model Remote document retrieval Text file Binary file - audio, image and application file Link specified with URL Interactive but not a real-time HyperText Transfer Protocol (HTTP) Networks 8

5 Video-on-demand (VOD) Integration of video rental store and video player Interactive STOP, PLAY, FF, REW, PAUSE No need of real-time Billing Copyright protect Networks 9 What is a protocol? A set of rules governing how two parties are to interact. Postal Mail Protocol Sender s address at the left -upper corner Recipient s address at the center Stamps at the right -upper corner Walkie-Talkie Protocol Listen Hear Over! or nothing Say a sentence and Over! while holding down the button Release the button Protocols in communication networks HTTP, FTP, TCP, IP, Ethernet, CDMA, ATM, SONET, PPP, ICMP, SNMP, SMTP, ARP, RARP, DHCP, RTP, UDP, HDLC, IGMP, RIP, OSFP, LCP, NHRP, RSVP, Networks 10

6 Direct Connection N hosts and N(N-1)/2 lines Fault tolerant Connectivity = N-1 Costs Networks 11 Star Networks Easy Need a switch Faults in the switch is intolerable Connectivity = 1 10/100BaseT Networks 12

7 Ring Networks Easy Single fault tolerable Connectivity = 2 Token Ring, FDDI, ADM Networks 13 Bus Networks Easy Scalability Resource starvation Radio transmission, 10Base5, 10Base2 Connectivity? Networks 14

8 Tree Scalability Bottle-neck at the top level POTS Connectivity? Networks 15 Daisy-chain Easy Arbitration and fairness SCSI, UUNET Scalable Ethernet hub (uplink) Connectivity? Networks 16

9 Network Topology Topology Pros Cons Direct Star Ring Bus Tree Daisy-chain Irregular Connectivity Affordable Affordable Affordable Scalability Affordable Flexibility Scalability Fault sensitivity Fault sensitivity Resource starvation Bottleneck Fairness Maintainability Networks 17 Hierarchical Network, 1 Communication networks grow so fast that a organization cannot control them alone. Need based topology Need based techniques Protocols and Standards Cost optimized Networks 18

10 Hierarchical Network, 2 To Chicago Switch Office in Indianapolis To Cleveland Switch Offiice in Hamilton County Multiplexer Multiplexer Switch Office Marion County Backbone Network Concentrator Concentrator Backbone Network Networks 19 Switching Methods Message switching Whole message passed to the next hop Storage Postal mail, telegraph Packet switching Packet size fixed, variable Routing for each packet Internet, ATM Circuit switching Resource is dedicated to a single conversation Connection established before communication Telephone Networks 20

11 Message Switching Sender Time SW 1 SW 2 Recipient Networks 21 Packet Switching Sender Time SW 1 SW Recipient Networks 22

12 Circuit Switching Sender SW 1 Connection Establishment Time Transfer SW 2 Recipient Networks 23