Lecture 22: Networks (cont.)AnnouncementsPlan for TodayNetwork ConfigurationsNetwork communicationsRelays: Switches vs. RoutersOSI* Seven LayersAcronym Alphabet Soup (Protocols)Network Performance IssuesAd Hoc NetworksTypes of Ad Hoc NetworksLecture 22: Networks (cont.)The Digital World of MultimediaProf. Mari OstendorfEE299 Lecture 223 March 2008Announcements Lab this week week: Video conferencing is working Go to Sieg lab and you’ll split into two rooms. Bring your presentation ***IN PPT FORMAT*** on a memory stick. Upload presentation to CollectIt by Thursday Peer grading of presentation No Ostendorf office hours this week, guest lectures Weds & Friday Reminders:  Send me anonymous email suggesting fundamentals that would be good to spend more time on Exam grade change requests due in writing todayEE299 Lecture 223 March 2008Plan for Today Network communications review Communications over the Internet Ad hoc networksEE299 Lecture 223 March 2008Network ConfigurationsStar configuration: central relay pointMultiple relay pointsIssues:• cost of long lines• need for clever relays• dedicated vs. shared lines• efficiency vs. congestion- related delayFull mesh networkrelaysEE299 Lecture 223 March 2008Network communications Break the message into packets Place address header info (used in routing) Transmit using several protocolsAt each relay need to: Determine destination Store in “queue” until ready to send Transmit At final destination, put messages back togetherEE299 Lecture 223 March 2008Relays: Switches vs. Routers Switches When low delay and reliable transmission are important Allocation of bandwidth guaranteed, route pre-specified Network designed for peak demands, often underutilized Used in telephone networks and interactive media Routers Route determined on the fly, depending on traffic etc. Store message in a queue until ready to forward it to final destination or another relay point Efficient use of network bandwidth Good for messages that can tolerate variable delayEE299 Lecture 223 March 2008OSI* Seven LayersFTP, HTTP, SMTPMIME, data compressionTCP, UDP, SCTP(image from http://wiki.go6.net/index.php?title=OSI_model)Point-to-point vs. packetsIPModem, fiber/cableSession establishment*Open Systems InterconnectionsEE299 Lecture 223 March 2008Acronym Alphabet Soup (Protocols) Finding computers in the internet URL: universal resource locator [192.53.222.7] DNS: domain name service Making connections (IP: Internet protocol) TCP: transport control protocol  UDP: user datagram protocol (faster, less reliable) SCTP: stream control transmission protocol Sending and receiving/retrieving… SMTP: simple mail transfer protocol MIME: multipurpose Internet mail extensions (for multimedia) HTTP: hypertext transfer protocol (for web pages) FTP: file transfer protocol (generic data files)EE299 Lecture 223 March 2008Network Performance Issues Quality of Service (QoS) Refers to resource control when there is congestion (not actual quality) Control for: bit rate (or, bandwidth), delay, jitter, bit error, packet loss Bandwidth: data rate in bits/sec (not the same as bandwidth in frequency domain in signal processing, but related) Delay: Processing + queuing + transmission + propagation Jitter: Difference in end-to-end delay |(R2 -R1 ) –(T2 -T1 )| -- R for received times, T for transmit timesEE299 Lecture 223 March 2008Ad Hoc Networks Wireless networks where… Nodes come and go, no fixed infrastructure Dedicated hardware services (routers, switches, hubs) performed by the computers in the network Self-configuring network, collaborative communication Individual nodes are not that powerful Æ collaborative signal processing Easy to set up, so good for situations where infrastructure is not available Challenge: vulnerability to attacksEE299 Lecture 223 March 2008Types of Ad Hoc Networks Mobile ad hoc networks Examples: military operations, emergency/rescue, disaster relief, education (One Laptop per Child program), … Node characteristics: mobile, so neighbors change (and hence network topology) Smart sensor networks Examples: surveillance, environmental change sensing, traffic monitoring, …. Node characteristics: large number of sensors, low power, node failures change network