2-Chapter 7- part 1- Topdown approach.pptx

Engineering - Advanced networks

1. Section 1: Chapter 7 Wireless & mobile networks CC531: Advanced Networks

2. Chapter 7 Outline 7.1 Introduction 7.2 Wireless links, characteristics CDMA 7.3 IEEE 802.11 wireless LANs ( “ Wi-Fi ” ) 7.4 Cellular Internet Access architecture standards (e.g., GSM) 7.5 Principles: addressing and routing to mobile users 7.6 Mobile IP 7.7 Handling mobility in cellular networks 7 .8 Mobility and higher-layer protocols

3. Introduction Types of wireless and mobile networks A network that is wireless, but not mobile A network that is mobile, but not wireless A network that is both wireless and mobile Assumption: Users are connected into larger network infrastructure by a wireless link at the network’s edge. Wireless LANs as IEEE 802.11 Cellular networks as 3G network

4. Introduction Elements of a wireless network: Wireless hosts End devices / end systems. They run applications and initiate communication. Laptop Smartphone Desktop computer Wireless hosts may or not be mobile. network infrastructure

5. Introduction Elements of a wireless network: Wireless links: A host connects to a base station through wireless communication links. Wireless links connect wireless hosts that are located at the network’s edge. Wireless links may also be used to connect hosts within a network. network infrastructure

6. Introduction Elements of a wireless network: Wireless links: A host connects to a base station through wireless communication links. Wireless links connect wireless hosts that are located at the network’s edge. Wireless links may also be used to connect hosts within a network. network infrastructure

7. Introduction Elements of a wireless network: Base station: It is the key part of the wireless network infrastructure. It has no counterpart in a wired network. It is responsible for sending & receiving data packets. It is responsible for coordinating the transmission of multiple wireless hosts. network infrastructure

8. Introduction Elements of a wireless network: Hosts mode of operation: Infrastructure mode: Base station connects mobiles into wired network handoff: mobile changes base station providing connection into wired network Ad-hoc mode: no base stations nodes can only transmit to other nodes within link coverage network infrastructure

9. Introduction Categories of wireless networks Single-hop, infrastructure based: These networks has a single base station that is connected to the internet. IEEE 802.11 network in a classroom All data transmissions are one hop away from the base station. Single-hop, infrastructure-less: IEEE 802.11networks in ad-hoc mode Bluetooth devices

10. Introduction Categories of wireless networks Multi-hop, infrastructure based: Base station, located in a wireless network, is connected to a larger wired network. Data communications may be done through several relays. Wireless mesh network Multi-hop, infrastructure-less: Many nodes may be used to relay data until it reaches destination Nodes may be mobile MANETs ( Mobile Ad-hoc Networks) VANETs (Vehicular Ad-hoc Networks)

11. Wireless links & Network characteristics Important differences between wired links & wireless links: Decreasing signal strength: Radio signals attenuates as it passes through matter. In space, electro-magnetic radiations disperse as the distance between the sender and receiver increases (path-loss) Interference from all sources: Radio signals of the same frequencies will interfere with each other. 2.4 GHZ wireless phones & 802.11 b wireless LAN Multipath propagation: It occurs when a portion of the electromagnetic waves reflect-off objects, it take paths of different lengths between the sender and receiver.

12. Wireless links & Network characteristics Signal to noise ratio (SNR): It is the relative measure of the strength of the received signal and the noise. SNR is measured in dB. Large SNR makes it easier to extract the transmitted signal from the background noise. Bit error rate (BER): It is the probability that a transmitted bit is received in error at the receiver. The higher SNR, the lower BER Sender can increase SNR by increasing the transmission power, sender can decrease the probability that a frame is received in error by increasing the transmission power.

13. Wireless links & Network characteristics Hidden terminal problem: A physical obstruction is preventing A & C from hearing each other. However, their transmissions are interfering with each other. In one scenario, Station A can communicate with Station B. Station C can also communicate with Access Point Station B. However, Stations A and C cannot communicate with each other as they are out of range of each other, and thus start to transmit simultaneously preventing B from receiving messages intended for it. A B C

14. Wireless links & Network characteristics Fading / signal attenuation problem: An undetectable collision at the receiver that may result from fading of the signal’s strength in the wireless medium. Both A & C are placed at a distance where they can’t detect each other’s signal transmission. However, their signals are not string enough to interfere. A B C A ’ s signal strength space C ’ s signal strength

15. Wireless links & Network characteristics Managing multiple access is more complex in a wireless network. Categories / classes of medium access protocols: Channel partitioning This method divides the channels into smaller pieces (time slots, frequencies, code) Random access This method make use of the whole channel without any division, which allows collisions. Random access must implement collision recovery mechanisms. Taking turns Nodes take turns in accessing the channel. Nodes with more to send take longer turns.

16. Wireless links & Network characteristics Code division multiple access (CDMA): It is used in wireless LANs and cellular networks. Each bit is encoded by multiplying the bit by a code that changes at a fast rate (chipping rate) encoded signal = (original data) X (chipping sequence) decoding: inner-product of encoded signal and chipping sequence Assumptions: Each original data bit is transmitted in 1-bit time slot. : value of data bit of the ith bit slot. : when the original data bit contains a zero value. Each slot can be divided into M mini-slots. Encoding process: Decoding process:  

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