Wireless Networks (CSC-7602) Lecture 1 (27 Aug 2007) Seung-Jong Park (Jay) http://www.csc.lsu.edu/~sjpark 1 Handouts Class information Schedule (check online frequently) 2 1
Goals Principles on Wireless Networks Topics Architecture Technologies Protocols MAC Routing Transport Simulation & Performance Evaluation 3 Requirements for Simulation Programming C/C++ Linux (just need to know how to use it and compile C) Linux server account? Passion 4 2
Administrative Information Seung-Jong Park Room 289, Coates Hall Email : sjpark at csc.lsu.edu Office hours: Mon. 5:10pm-8:00pm Class website http://www.csc.lsu.edu/~sjpark 5 Policies Lecture slides will be available on website before the day of class Lecture slides are NOT comprehensive students are expected to attend classes to fill in information Miss classes at your own risk. Professor will NOT be responsible for any information you might not have because of a missed class Zero tolerance policy toward cheating 6 3
Textbook Textbook NO Just Slides Additional reading list will be available on website 7 Grading Exam 1 final (1 x 30% = 35%) Paper Presentation 1 x 20% = 20% Project (Ns2 Simulation) 2 Projects 1 st project (20%) 2 nd project (20%) Class points Interaction in class (1 x 5% = 5%) Grades A if above 85 out of 100 B if above 70 out of 100 C if above 50 out of 100 F if below 50 or miss class more than 4 times 8 4
Introduction of Networks Communication Networks Broadcast networks Each station can hear every other station in the network (fully connected network) Switched networks Stations interconnected through a (non-fully) connected mesh Packet switched vs. Circuit switched What kind of a network is the Internet? 10 5
Communication Protocols Rules used in communication Monolithic vs. Layered Protocol data units used to exchange information between peer layers of protocol stack Examples of communication protocols? 11 OSI Open Systems Interconnection: ISO (International Standards Organization) s standard for communication protocols Also referred to as the OSI reference model or simply the OSI model 7 layer protocol stack 12 6
OSI Protocol Stack Physical Data link Network Transport Session Presentation Application 13 OSI (contd.) Physical: mechanical/electrical rules for transferring bits Data link: flow control error detection error recovery 14 7
OSI (contd.) Network Routing Congestion control Quality of service Transport End-to-end communication of data Reliability Sequencing Flow control Congestion control 15 OSI (contd.) Session Application specific functionality Still, generic to multiple applications (e.g. security) Presentation Data formatting Application 16 8
TCP/IP Protocol Suite Differences between OSI and TCP/IP? 5 layers: Physical Data link/mac (ARP, SLIP) Network (IP, ICMP, IGMP) Transport (TCP, UDP) Application (http, ftp, telnet, smtp) 17 Introduction of Wireless Communications 9
How Radio Works Electricity vs. Magnetic Field Sine Wave Frequency 19 How Communication Works AM (Amplititute Modulation) FM (Frequency Modulation) 20 10
Wireless Transmission The Electromagnetic Spectrum Radio Transmission Microwave Transmission Infrared and Millimeter Waves Lightwave Transmission 21 The Electromagnetic Spectrum The electromagnetic spectrum and its uses for communication. 22 11
Politics of the Electromagnetic Spectrum The ISM bands in the United States. 23 Voice Communication Sampling & Quantization x n n 24 12
Voice vs. Data Communication Past: analog voice communication which is the 1 st application of wireless networks, such as radio Current: digital voice communication (4 or 8 Kbps) and low speed digital data communication Future: high speed data communication for speech, video, and data 25 Wireless Networks from System Perspective Cellular networks Ad-hoc networks WLAN networks Sensor networks 26 13
Architecture of Cellular Networks 27 Evolution of Cellular Networks 28 14
Issues at Cellular Networks Multiple access technology Increase # of users in finite amount of frequency bandwidth Resource management Reduce redundant usage of resource Handoff 29 Multiple Access Technologies FDMA (Frequency Division Multiple Access) Each user has a private frequency AMPS TDMA (Time Division Multiple Access) Each user has a private time on a private frequency GSM, IS-54 CDMA (Code Division Multiple Access) Users share time and frequency with a private code IS-95 30 15
Frequency Division Multiplexing (a) The original bandwidths. (b) The bandwidths raised in frequency. (b) The multiplexed channel. 31 Advanced Mobile Phone System (a) Frequencies are not reused in adjacent cells. (b) To add more users, smaller cells can be used. 32 16
Time Division Multiplexing Multiplexing T1 streams into higher carriers. 43210 Large BW 33 Handoff How to find neighboring base stations How to connect BSs Hard handoff between different service providers or different systems Soft handoff between CDMA base stations 34 17
Wireless Local Area Networks LAN IEEE 802.11 WLAN 35 Ad-hoc Networks Multi-hop wireless networks No Infrastructure Typically used in military applications (where there is no infrastructure), or disaster relief (where infrastructure has been destroyed) Mobile stations double-up as forwarders/routers Can use existing WLAN technology (e.g. IEEE 802.11 supports a Distributed Coordination Function (DCF) mode of operation) Study on network layer and transport layers How to know paths between two remote nodes without coordination 36 18
Wireless Sensor Network Elements Sink : sends queries to collect data from sensors Sensor : monitors phenomenon and reports to sink Application Sink Sensors Field Object Tracking Environment Monitoring Medical Monitoring Indoor Control 37 Issues in 7602 course 19
Protocol Perspective Protocol: Rules used in communication Monolithic vs. Layered Protocol data units used to exchange information between peer layers of protocol stack 7 layers Open Systems Interconnection: ISO (International Standards Organization) s standard for communication protocols 39 Problems for Each Protocol Application Layer HTTP, FTP Transport Layer How to deliver data Variants of TCP Network Layer How to reach to a destination Mobile IP Link (MAC) Layer How to share a common media Ethernet (IEEE 802.3) WLAN (IEEE 802.11b) Physical Layer How to connect two nodes physically Physical Layer 40 20
Problems at MAC Layer Basic How to fairly share a medium Hidden Terminal Problem A talks to B C senses the channel C does not hear A s transmission (out of range) C talks to B Signals from A and B collide Collision A B C 41 Problems at Network Layer Mobile IP Problem The IP address associated with a mobile host is network dependent! When user connects to another network, IP address needs to change Packets belonging to ongoing connections somehow need to be delivered to the mobile host Post Office Solution Leave a forwarding address with your old postoffice! The old post-office forwards mails to your new post-office, which then forwards them to you 42 21
Problems at Transport Layer TCP over wireless networks TCP uses losses as indication of congestion Reduces congestion window by half (LIMD) when it experiences congestion Even when no congestion, if packets are dropped due to random losses, TCP will cut down its rate (is this right?) TCP will interpret hand-offs related losses also as congestion based losses Hence, it will reduce the congestion window every time handoffs related losses occur Split Connection Approach divide a path into two sub-paths WTCP: Use inter-packet delay (as opposed to losses) as indication of congestion 43 22