Lecture 21: Communications (cont.)AnnouncementsHW6/Lab6  ProjectReview: CommunicationsDigital CommunicationsPlan for TodayCommunications ParadigmsTransmission TechnologiesPacket CommunicationsWired vs. Wireless CommunicationWhy Different types of Wireless?Practical Network CommunicationRedundancyCommunication ConsiderationsDifferent Types of NetworksPictures of the Internet (Backbones)What do all these numbers mean?Ad Hoc NetworksCommunications Used Last WeekInternet/Wireless Impact on SocietyLecture 21: Communications (cont.)The Digital World of MultimediaProf. Mari OstendorfEE299 Lecture 2129 Feb 2008Announcements Lab next week: Video conferencing is working, so you will do your presentations next week by video Go to Sieg lab and you’ll split into two rooms. Bring your presentation on a memory stick. Upload presentation to CollectIt by Thursday Peer grading of presentation Mosaics are posted: Let me know if… You want a different name than “mosaic#” You want to be credited by name on the web page Reminders:  Send me anonymous email suggesting fundamentals that would be good to spend more time on Exam grade change requests due in writing by Monday next weekEE299 Lecture 2129 Feb 2008HW6/Lab6 Æ Project Choose a paper from  IEEE Spectrum, Signal Processing Magazine, Communications Magazine Put together a 10 min presentation Upload the presentation (ppt or pdf) to CollectIt by 3/7 Give the presentation via video conferencing in lab next week Give a stand-up presentation to whole class 3/14 (extended) or 3/20??? Write a 2-3 page summary due 3/15 to CollectItEE299 Lecture 2129 Feb 2008Review: Communications Challenges: noise, fading, interference Analog vs. digital:  At the lowest level, communication is analog Difference is whether the signal set is finiteEE299 Lecture 2129 Feb 2008Digital Communications Sending bits: ultimately the implementation is analog, e.g. 0 vs. 1:  Cos(100t) vs. cos(200t) Pulse vs. no pulse 000, 001, 010, … cos(2πkf0t) So what is the advantage of digital? Small problems can be recovered from perfectly Intermediate detection and retransmission to avoid big problemsEE299 Lecture 2129 Feb 2008Plan for Today Transmission technologies Digital: bit streams vs. packets Network communicationEE299 Lecture 2129 Feb 2008Communications ParadigmsPoint-to-point 2-way communicationsBroadcast communicationsIssues:• 1-way vs. 2-way• Wired vs. wireless• Number of usersFull mesh networkEE299 Lecture 2129 Feb 2008Transmission Technologies Point-to-point Wires, fiber-optic cables Reliable, sometimes dedicated, but expensive & slow installation  Broadcast  Radio, satellite Frequencies often assigned by FCC Antenna size depends on frequency Topography impacts antenna placement Inexpensive options, but shared and variableEE299 Lecture 2129 Feb 2008Packet Communications Standard phones, radio etc. Steady stream of data (though different sources may be interleaved) Data arrives in the order it was sent Internet communications Data grouped into packets with destination and order info Data may arrive in a different order Need extra layers of communication protocols to transmit and recover messageEE299 Lecture 2129 Feb 2008Wired vs. Wireless Communication Communication needs Long distance: general phone, cable TV, ISPs Medium distance: internetwork connections, cell phones Short distance: in the building Very short distance: mouse to computer, phone to headset Wired Cable, fiber: long, medium & short distances Wires for very short distances Wireless Long distance: Satellite broadcasting (GPS) Medium distance: WiMAX, terrestrial broadcasting (towers)  Short distance: WLAN (wireless local area network) Very short distance: BluetoothWireless allows access where cables can’t be run; reduced cost relative to cabling.EE299 Lecture 2129 Feb 2008Why Different types of Wireless? Medium distance: (WiMAX, WiMAN) 10Mbps, 10km Last mile alternative to cable, DSL; provides nomadic connectivity Operates at 2-11GHz, or 10-66 GHz High power, good quality of service, not yet widespread Local: (Wi-Fi) 25Mbps, 25-75m range Connect different computers in a home, lab, coffee shop, … Operates at: 2.4GHz or 5GHz (different versions) Global standard, reasonable encryption, economical, relatively high power consumption, variable quality of service Short range: (Bluetooth) <1Mbps, 10m range Connect cell phones, PCs, PDAs, digital cameras, mouse/keyboard, … Operates at unlicensed 2.4GHz, same as cordless phones, microwaves etc. but very different signalling strategy Low power, low cost,EE299 Lecture 2129 Feb 2008Practical Network CommunicationStar configuration: central relay pointMuliple relay pointsIssues:• cost of long lines• need for clever relays• congestion in shared linesEE299 Lecture 2129 Feb 2008Redundancy Large networks have some redundancy: multiple paths between two sites Why? Need alternatives if a relay node goes down (failure or routine maintenance) Need alternatives if a path is congestedEE299 Lecture 2129 Feb 2008Communication Considerations Challenges: multiple paths & congestion/failure Routing:  Computer addresses (e.g. 192.53.222.7) determine destination, help determine path Domain name server maps from numbers to names Options for dealing with congestion:  Store-and-forward (efficient, good if you can tolerate variable delay) Switching (low delay & reliable, more costly) Impact on coding: Message needs info about sender & receiver Long messages need to be broken into pieces (packets) Coding needs to account for variable delay, reordering of packets, lost chunks of information Variable rate coding allows for sending different bit rates, progressive transmissionEE299 Lecture 2129 Feb 2008Different Types of Networks Telephone network Cable network Cellular network Power grid Internet (world wide web) Backbone network Internet Service Provider (ISP) networks Local area networks Personal area networksEE299 Lecture 2129 Feb 2008Pictures of the Internet (Backbones)geog-www.sbs.ohio-state.edu/faculty/okelly/www.washington.edu/.../directions/highspeed.htmlEE299 Lecture 2129 Feb 2008What do all these numbers mean? 802.16, 802.11, 802.15, 2.5G, 3G, … Standards for