EECS 122: Introduction to Communication Networks Unit 1: The question and history of the solutions… What do we use communication for ? • Exchanging Information !!! /Getting information… - Runners (marathon!), Flags, Mirrors…. Etc.. - E-mail, WWW… • Maintaining inter-human relations - Letters (of affection!) - Phone … - SMS, CHAT, SOCIAL NETWORKS…. • Entertainment - Passive Live Theater/Circus/Movies/Radio/TV/Videos (on demand?) - Active Games!!! – network games – virtual worlds AW: Unit 1 2 EE 122 Spring 2015 2 What to communicate: Information, data • Information - Facts, Concepts, Ideas Information - A Human – oriented term Facts, concepts, • Data (encapsulated in media) ideas, … - A formalized representation of facts, concepts, ideas - Example: text, speech, picture - A human interpretation of data, conferring meaning to data • In Engineering we are interested in Data - Capturing “information” in the form of Formalized data (recording videos, taking pictures, representation of recording voice) information - Delivering data quickly to proper persons in form of media with high fidelity and efficiency AW: Unit 1 3 EE 122 Spring 2015 How? Telecommunication • First solution: Couriers - Runners (a.k.a. the story of marathon). Horse courriers, e.t.c - The concept of Relay! • Telecommunication = moving information over long distances - Without moving a human.. - But to selected, intended partners… • But HOW to move quicker? - Using “life help” – pigeons... - Using “guided media” to carry the document containing data è - (e.g. the pneumatic post, see eg. https://about.usps.com/who-we- are/postal-history/pneumatic-tubes.pdf ) - Using SIGNALS, i.e. physical phenomena able to propagate with high speed: Light, electricity, radio waves… AW: Unit 1 4History of TelecommunicationEE 122 Spring 2015 4 AW: Unit 1 5 EE 122 Spring 2015 The early optical signals • Visual signals - Limited to the Line of sight (LOS) • Examples: - Mirrors, Smoke - Humans giving signs... signaling convention: seamen flags, n Hissed flags http://www.christinedemerchant.com/flag- alphabet.html n Flag semaphore, e.g. http://www.anbg.gov.au/flags/semaphore.html n The optical Telegraph • And, much , much later: the optical fiber transmission J AW: Unit 1 6 EE 122 Spring 2015 Optical Telegraph • Optical Telegraph (Chappe, 1793) - Need for fast information flow in time of French Revolution n Claude Chappe installed the first optical telegraph line in summer 1794 AW: Unit 1 7 EE 122 Spring 2015 7 Electricity made THE change… • Telegraph (Morse, 1837) - Digitally coded text information, hard copy option (see e.g http://morsecode.scphillips.com/morse2.html ) - Large distance covered with constant quality - Low speed, rather public than individual use • Telephone (Bell, 1876, many claims from others…) - Transmission of voice (analog information) - Analog (later digital! Information transmission) - Individual use, end-system (not person) addressed - Data transmission by telephone is possible - World’s largest unified technical system! • Broadcast Services (30ties in 20th Century) - Radio, TV AW: Unit 1 8 EE 122 Spring 2015 8 Telegraph (1) [Noll, op. cit)] • Diagram of Simplex Electromagnetic Telegraph n a) Single simplex link n b) Two simplex links cascaded by repeater AW: Unit 1 9 EE 122 Spring 2015 9 Telegraph (2) [Noll, op. cit)] • Simplified diagram of Morse's half-duplex telegraph AW: Unit 1 10 EE 122 Spring 2015 10 Telephones - The basic Idea (1) [Noll, op. cit)] Variable-resistance transmitter Bell's liquid transmitter AW: Unit 1 11 EE 122 Spring 2015 11 Telephones - The basic Idea (2) [Noll, op. cit)] Watson's electromagnetic receiver AW: Unit 1 12 EE 122 Spring 2015 12 Early Broadcasting… • Drummers, walking and announcing (acoustic) • Mr. Litfaß – 5. Dec. 1854 Berlin, Germany (visual!) • Much later: Megaphones… (Acoustic, now: rlectric amplification of the acoustic signal!) AW: Unit 1 13 EE 122 Spring 2015 13 Some fundamentals… before moving further • Non-Zero delay between sending and receiving of a given message… (propagation delay!) - The speed of light – the highest possible is c =300 000 km/s in vacuum!! - The speed of electricity and light in optical fiber is v = 2/3 c • A bounded amount of messages can be posted in a time unit... - Think in term of the speed of Morse´ing or typing… or… - Think in terms of the speed of your internet access…J • Loss/errors in data transmission è THIS ALL IS REALITY !!! AW: Unit 1 14 EE 122 Spring 2015 Realistic Transmission… • Propagation delay d: - Propagation speed v: - d = distance / v • Data rate r: How much SOT:Start of messages/sec or bits/second transmission can a sender transmit? - (EOT – SOT) = Data size / data rate EOT: End of Time • Error rate: What is the rate of transmission incorrect messages arriving at the receiver? Delay d - Corrupted messages are frequently deleted…… Distance AW: Unit 1 15 EE 122 Spring 2015 Transmission medium can store data • What happens during a transmission? Start of transmission - Bits propagate to the receiver - Sender keeps sending bits - First bit arrives after d seconds Delay d Time - In this time, sender has transmitted d*r bits - They are “stored in the wire” (or in the Air!) • d*r is the product of delay and data rate - Commonly called Example (transcontinental): bandwidth-delay product • Data rate 100 Mbit/s - Crucial network property • Delay 4000km/(2/3c) = 0.02 s • d*r = 2 Mbit (in the wire) AW: Unit 1 16 EE 122 Spring 2015 Challenges in using signals • The speed of the signal can hardly be influenced…# • The number of data block (groups of bits)/second which we can transmit, as well as the probability of them being in error can be influenced - This is issues of communications… (eg. EE121) - We will discuss these topics shortly to understand how we can use it …or suffer form them… AW: Unit 1 17 EE 122 Spring 2015 Just a line? [H.Karl, Paderborn] • Connecting many phones - the simple issue ? AW: Unit 1 18History of TelecommunicationEE 122 Spring 2015 18 Concepts: The Network, Switching • Choosing the recipient of your call… • It is NOT efficient to build a physically separate path for each pair of communicating end systems (left picture). • CONCEPT: The Network: There is a set of path sections (e.g. electrical cables) and switching points (right picture). • “End systems” vs.“switching elements” a.k.a routers/bridges NOTE THE SIMILARITY TO OTHER NETWORKS …. AW: Unit 1 19History of TelecommunicationEE 122 Spring 2015 19 Communication Networks…a lot of questions • How to move data to a desired destination ? - Path selection? • How to structure data? “Portions”? Flows? • Mixing streams of data in the switches …overload? Losses…variable delay? • Binding of communication in the end systems? Many, Many issues…. This is the main subject of THIS CLASS AW: Unit 1 20 EE 122 Spring 2015 Concepts: Names, Addresses, Routing… • Name: WHO (identifies the object) - Structured for simple reference by humans! - E.g. According to organizational structure? Mnemonics? • Address: WHERE TO FIND (the object) - Must be REACHABLE - The object can move (mobility) è change address … • Route: HOW TO GET THERE - Has to assure delivery. - It is nice, if the address structure helps.. (e.g. street blocks) ? How to find the Address of some object ? ? How to find the route ? AW: Unit 1 21 EE 122 Spring 2015 Some considerations • Which objects would one like to address - Humans? Devices? Processes? • An object might have many points of access - A building with entrance from 2 different streets? - A human has Phone, e-mail, post, … - A laptop with WLAN (university Network) and ATT cellular? • How can addresses be grouped to enhance routing ? - City – District - Street- house – apartment AW: Unit 1 22 EE 122 Spring 2015 Types of addresses • Unicast: A single destination • Multicast: Destination is a group (defined explicitly or implicitly – i.e. every entity knows if it belongs…) • Anycast: Whoever of the group members • Broadcast: everybody… AW: Unit 1 23 EE 122 Spring 2015 Computer Networks • User logged into a single computer (or a process started by this user!) can: - Access any of the machines and use its resources - Execute processes. - Cause moving data (e.g. files) • Some important gains - Resource utilization: processor cycles, printers, specialized programs. - The centralized management of programs and data (software versions, backups) - Increase of SYSTEM reliability (as whole!) • Sharing and exchanging DATA - collaborative activities (work, entertainment, …) AW: Unit 1 24History of TelecommunicationEE 122 Spring 2015 24 Computer Networks: Consecutive challenges • Challenge I: Interconnection of different computer/OS types • Challenge II: Transmission Speed/Transmission Distance/… - WAN - Wide Area Network n No limit in distance n Provides national and international connectivity - LAN - Local Area Network n Less than approx. 1 km in distance n Provides local connectivity typically within a building - And many more…. n Mobile Cellular Data Networks n BAN (Body Area Networks) n SAN (Storage Area Networks) n Desktop Area Networks… n Industrial Networks AW: Unit 1 25History of TelecommunicationEE 122 Spring 2015 25 Internet: Interoperability vs. Heterogeneity WAN MAN LAN Gateway See:The Brief History of the Internet AW: Unit 1 26History of TelecommunicationEE 122 Spring 2015 26 Recent tendencies • Challenge III: Multimedia Communication - Observation: The information is stored/exchanged in MEDIA n Voice, Video, Data… n Different requirements as for transmission!!! - Historically supported by different technologies