Communication Networks

Communication NetworksProf. Anish Goel

Communication Network ArchitectureNetwork architecture: the plan that specifies how the network is built and operatedArchitecture is driven by the network servicesOverall communication process is complexNetwork architecture partitions overall communication process into separate functional areas called layers2Basics of Communication Networks. Anish Goel

Network Architecture EvolutionTelegraph Networks Message switching & digital transmission Telephone Networks Circuit Switching Analog transmission -> digital transmission Mobile communications Internet Packet switching & computer applications Next-Generation Internet Multiservice packet switching network3Basics of Communication Networks. Anish Goel

Approaches to Long-DistanceCommunicationsCourier: physical transport of the message by messengers Messenger pigeons, pony express, FedExTelegraph: message is transmitted across a network using signals Drums, beacons, mirrors, smoke, flags, semaphores… Electricity, light Telegraph delivers message much sooner4Basics of Communication Networks. Anish Goel

Optical (Visual) TelegraphClaude Chappe invented optical telegraph in the 1790’sSemaphore mimicked a person with outstretched arms with flags in each handDifferent angle combinations of arms & hands generated hundreds of possible signalsCode for enciphering messages kept secretSignal could propagate 800 km in 3 minutes!5Basics of Communication Networks. Anish Goel

Message SwitchingNetwork nodes were created where several optical telegraph lines met (Paris and other sites)Store-and-Forward Operation: Messages arriving on each line were decoded Next-hop in route determined by destination address of a message Each message was carried by hand to next line, and stored until operator became available for next transmission6Basics of Communication Networks. Anish Goel

Electric TelegraphSamuel Morse telegraph system (1837) A text is encoded into sequences of dots and dashes Short and long pulses of electrical current over a copper wire to generate dots & dashes (Table 1.1) Experimental telegraph line (e.g., submarine cable) over 40 miles (1840) connecting two telegraph stations Sore-and-forward process at each station Precursor of the modern digital communication systemSignal propagates at the speed of light! Approximately 2 x 108 meters/second in cable7Basics of Communication Networks. Anish Goel

Electric Telegraph NetworksElectric telegraph networks exploded Message switching & Store-and-Forward operation Key elements: Addressing, Routing, ForwardingOptical telegraph networks disappeared Why? What is the limitation?8Basics of Communication Networks. Anish Goel

Baudot Telegraph Multiplexer (1874)Combine 4 signals in a single telegraph circuit by multiplexing Binary block code (ancestor of ASCII code) A character represented by 5 bit binary code Time division multiplexing Binary codes for characters are interleaved Framing is required to recover characters from the binary sequence in the multiplexed signal Keyboard converts characters to bitsUse a single line by multiple operators at the same time (increase transmission rate)9Basics of Communication Networks. Anish Goel

Elements of Telegraph Network Architecture Digital transmission Text messages converted into symbols (dots/dashes, zeros/ones) Transmission system designed to convey symbols Multiplexing Framing needed to recover text characters Message Switching Messages contain source & destination addresses Store-and-Forward: Messages forwarded hop-by-hop across networkMessage-switching node: a general purpose computer (or human operator node) with storage to buffer messages as they come in. It receives all bits of the message, waits for an opportunity to retransmit to the next node and send them if it gets the opportunity)Routing according to destination address10Basics of Communication Networks. Anish Goel

Telephone Networks and Circuit SwitchingSignal for “ae” as in catMicrophoneLoudspeakeranalogelectricalsignalsoundsoundAlexander Graham Bell (1875) working on harmonic telegraph to multiplex telegraph signalsDiscovered voice signals can be transmitted directlyMicrophone converts voice pressure variation (sound) into analogous electrical signalLoudspeaker converts electrical signal back into sound Telephone patent granted in 1876Bell Telephone Company founded in 187711Basics of Communication Networks. Anish Goel

The N2 Problem12N. . .34For N users to be fully connected directlyRequires N(N – 1)/2 connections Requires too much space for cablesInefficient & costly since connections not always onN = 1000N(N – 1)/2 = 49950012Basics of Communication Networks. Anish Goel

Early Telephone (Manual) SwitchingPatch cord panel switch invented in 1877Operators connect users on demandEstablish circuit to allow electrical current to flow from inlet to outletOnly N connections required to a central office13Basics of Communication Networks. Anish Goel

Digitization of Telephone NetworkPulse Code Modulation digital voice signalVoice gives 8 bits/sample x 8000 samples/sec = 64x103 bpsTime Division Multiplexing for digital voiceT-1 multiplexing (1961): 24 voice signals = 1.544x106 bpsDigital Switching (1980s)Switch TDM signals without conversion to analog formDigital Cellular Telephony (1990s)Optical Digital Transmission (1990s)One OC-192 optical signal = 10x109 bpsOne optical fiber carries 160 OC-192 signals = 1.6x1012 bps!All digital transmission, switching, and control14Basics of Communication Networks. Anish Goel

Computer Connection ControlComputerSwitch connectsInlets to Outlets. . .. . .VoiceA computer controls connection in telephone switchComputers exchange signaling messages to:Coordinate set up of telephone connectionsTo implement new services such as caller ID, voice mail, . . .To enable mobility and roaming in cellular networks“Intelligence” inside the networkA separate signaling network is required15Basics of Communication Networks. Anish Goel

Computer Network Evolution Overview1950s: SAGE (Semi-Automatic Ground Environment) – the first computer network for air defense system1960s: Dumb terminals access shared host computer SABRE airline reservation system1970s: Computers connect directly to each other ARPANET packet switching network TCP/IP internet protocols Ethernet local area network1980s & 1990s: New applications and Internet growth Commercialization of Internet E-mail, file transfer, web, streaming video, P2P, . . . Internet traffic surpasses voicetraffic16Basics of Communication Networks. Anish Goel

What is a protocol?Communications between computers requires very specific unambiguous rulesA protocol is a set of rules that governs how two or more communicating parties should interactInternet Protocol (IP)Transmission Control Protocol (TCP)HyperText Transfer Protocol (HTTP)Simple Mail Transfer Protocol (SMTP)17Basics of Communication Networks. Anish Goel

Terminal-Oriented NetworksEarly computer systems very expensiveTime-sharing methods allowed multiple terminals to share local computerRemote access via telephone modems18Basics of Communication Networks. Anish Goel

Computer-to-Computer NetworksAs cost of computing dropped, terminal-oriented networks viewed as too inflexible and costlyNeed to develop flexible computer networks Interconnect computers as required Support many applicationsApplication Examples File transfer between arbitrary computers Execution of a program on another computerMultiprocess operation over multiple computers19Basics of Communication Networks. Anish Goel

Packet SwitchingComputer network should support multiple applications Transfer arbitrary message size Low delay for interactive applications But in store-and-forward operation, long messages induce high delay on interactive messages Packet switching introduced Very much like message switching (no connection setup, no dedicated channel) Network transfers packets using store-and-forward Packets have maximum length (Massage switching systems accommodate far larger messages) Break long messages into multiple packets ARPANET testbed (70’s) led to many innovations What is the difference between packet switching and message switching?20Basics of Communication Networks. Anish Goel

Packet Switching21Basics of Communication Networks. Anish Goel

ARPANET Routing22Basics of Communication Networks. Anish Goel

Ethernet Local Area NetworkIn 1980s, low-cost workstations (individual computers) availableNeed for low-cost, high-speed networks To interconnect local workstations To access local shared resources (printers, storage, servers)Low cost, high-speed communications with low error rate possible using coaxial cableEthernet is the standard for high-speed wired access to computer networks23Basics of Communication Networks. Anish Goel

The InternetDifferent network types emerged for data transfer between computersARPA also explored packet switching using satellite and packet radio networksEach network has its protocols and is possibly built on different technologiesInternetworking protocols required to enable communications between computers attached to different networksInternet: a network of networks (interconnection of multiple network into a single large network)24Basics of Communication Networks. Anish Goel

Internet Protocol (IP)Internet Protocol (IP) was developed to provide for the connectionless transfer packets (datagram) across an internetworkRouters (gateways) interconnect different networks Host computers prepare IP packets and transmit them over their attached networkRouters forward IP packets across networksBest-effort IP transfer service, no retransmission25Basics of Communication Networks. Anish Goel

Thank You.. But Wait…26My Lectures are open source…You can Access them.. ( View or Download) at:www.discovermechatronics.blogspot.comYou can also:Brows my other projects.Basics of Communication Networks. Anish Goel

Communication Networks

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Communication Networks (20)

More from anishgoel (20)

Recently uploaded (20)

Communication Networks