1 / 80

C. Rama Krishna Assistant Professor Dept. of CSE NITTTR, Chandigarh Email: rkc_97 at yahoo.com

Mobile Adhoc Networking & Challenges. C. Rama Krishna Assistant Professor Dept. of CSE NITTTR, Chandigarh Email: rkc_97 at yahoo.com. Outline. History and Introduction Brief overview to Physical Layer Issues in Medium Access Control (MAC) Issues in Routing and Transport Layers

adanna
Télécharger la présentation

C. Rama Krishna Assistant Professor Dept. of CSE NITTTR, Chandigarh Email: rkc_97 at yahoo.com

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Mobile Adhoc Networking & Challenges C. Rama Krishna Assistant Professor Dept. of CSE NITTTR, Chandigarh Email: rkc_97at yahoo.com

  2. Outline • History and Introduction • Brief overview to Physical Layer • Issues in Medium Access Control (MAC) • Issues in Routing and Transport Layers • Quality-of-Service Issues • Security Issues • Additional Resources

  3. Which Technology ? Wireless LAN Technology • 2.4 GHz Wireless LAN  • 5 GHz Wireless LAN • Ad-hoc Mode • Infrastructure Mode Cellular Technologies • 2G Systems  • 2.5G Systems  • 3G Systems • 4G Systems • Next G Systems Other Short-range Technologies • Home RF  • Bluetooth • ZigBee Long Range Technologies • Internet

  4. History and Introduction

  5. History • Packet Radio NETwork (PRNET) by DARPA - late 1960s • Military Communications • Disaster Management • Survivable Packet Radio Networks (SURAN) – 1980s • MANET group formed under Internet Engineering Task Force (IETF) – 1990s • IEEE released 802.11 PHY and MAC standard – 1995 (later updated versions evolved)

  6. traffic from A D is relayed by nodes B and C D A C B radio range of node A What is an Ad hoc Network ? • Network of wirelessnodes (may be static/mobile) • – No infrastructure (e.g. base stations, fixed links, routers, • centralized servers, etc.) • – Data can be relayed by intermediate nodes • – Routing infrastructure created dynamically

  7. Why an Ad hoc Network? • Does not depend on pre-existing infrastructure • Ease to deploy • Speed of deployment • Anytime-Anywhere-Any device-Anyone (A4) network paradigm

  8. Ad hoc Network Example • Communication between nodes may be in single/multi-hop • Each of the nodes acts as a host as well as a router

  9. Typical Applications • Military environments • soldiers, tanks, planes • Emergency operations • search-and-rescue • Personal area networking • cell phone, laptop, etc. • Civilian environments • meeting rooms, sports stadiums, hospitals, etc. • Education • virtual classrooms, conferences, etc. • Sensor networks • homes, environmental applications, etc. • And many more …

  10. Some Challenges • Limited wireless transmission range • Broadcast nature of the wireless medium • hidden terminal and exposed terminal problems – MAC problem • Packet losses due to: transmission errors and mobility • Mobility-induced route changes – routing problem • Battery constraints • Ease of snooping - security problem

  11. Physical Layer

  12. Sl.No Standard Specification 1 802.11 Physical Layer & MAC Layer 2 802.11a Physical Layer 3 802.11b Physical Layer 4 802.11c Support of 802.11 frames 5 802.11d New support for 802.11 frames 6 802.11e QoS enhancement in MAC 7 802.11f Inter Access Point Protocol 8 802.11g Physical Layer 9 802.11h Channel selection and power control 10 802.11i Security enhancement in MAC IEEE 802.11 WLAN standards

  13. IEEE 802.11 standard • Supports networking in two modes: • Infrastructure based WLAN using access points (APs) • Infrastructure-less ad hoc networks – widely used in simulation studies and testbeds of MANET

  14. PC IEEE 802.11 based infrastructure WLAN Wire line Access Point (AP) Laptop Basic Service Set (BSS)

  15. IEEE 802.11 based infrastructure-less Adhoc Network Independent Basic Service Set (IBSS) Laptop

  16. Standard Parameter 802.11 802.11a 802.11b Bandwidth 83.5MHz 300MHz 83.5MHz Frequency band 2.4-2.4835 GHz 5.15-5.35 GHz and 5.725 – 5.825 GHz 2.4-2.4835 GHz Channels 3 12 3 Data Rate ( in Mbps) 1, 2 6, 9, 12, 18, 24, 36, 48 and 54 1, 2, 5.5, and 11 Transmission Scheme FHSS, DSSS with QPSK OFDM (with PSK and QAM ) DSSS(with QPSK & CCK modulation) IEEE 802.11 PHY Layer Specification

  17. Physical Layer for high speed MANET • Present PHY Layer • IEEE 802.11, 11a, 802.11b and 802.11g • Supports 1/ 2 /11/ 22/ 54 Mbps data rate in static indoor environment • DSSS is not suitable for data rate more than 10Mbps • OFDM based PHY layer design for high data rate transmission up to 54 Mbps [ 802.11a & g]

  18. Medium Access Control (MAC) & Issues

  19. Need for a MAC Protocol • Wireless channel is a shared medium and bandwidth is a scarce resource • Need access control mechanism to avoid collision(s) • To maximize probability of successful transmissions by resolving contention among users • To avoid problems due to hidden and exposed nodes • To maintain fairness amongst all users • MAC protocol design has been an active area of research in recent years

  20. Classification of Wireless MAC Protocols Wireless MAC protocols Distributed Centralized Random Access Guaranteed Access Hybrid Access Random Access • Guaranteed Access and Hybrid Access protocols require infrastructure • such as Base Station or Access Point – Not suitable for MANETs • Random Access protocols can be operated in either architecture • – suitable for MANETS

  21. Distributed Random Access Protocols

  22. Pure ALOHA MAC Protocol • In pure ALOHA, frames are transmitted at completely arbitrary times.

  23. The throughput for pure ALOHA is S = G × e −2G The maximum throughput Smax = 0.184,when G = 0.5

  24. Slotted ALOHA MAC Protocol • In slotted ALOHA, frames are transmitted only at slot boundaries.

  25. The throughput for slotted ALOHA is S = G × e−G The maximum throughput Smax = 0.368, when G = 1

  26. Throughput versus offered load for pure and slotted ALOHA

  27. Carrier Sense Multiple Access (CSMA) Protocol • Max. throughput achievable by pure ALOHA is 0.184 and slotted ALOHA is 0.368 • CSMA gives improved throughput compared to ALOHA protocols • Listens to the channel before transmitting a packet (reduces collisions)

  28. Variants of CSMA Unslotted Nonpersistent CSMA Nonpersistent CSMA Slotted Nonpersistent CSMA CSMA Unslotted persistent CSMA Persistent CSMA Slotted persistent CSMA 1-persistent CSMA p-persistent CSMA

  29. Behavior of three persistence methods

  30. CSMA/CD • Adds collision detection capability to CSMA; greatly reduces time wasted due to collisions • Standardized as IEEE 802.3, most widespread LAN • Developed by Robert Metcalfe during early 1970s..... led to founding of “3COM” company. [later Metcalfe sold his company for $400M) • The name 3COM comes from the company's focus on "COMputers, COMmunication and COMmpatibility"

  31. Why can’t we use CSMA or CSMA/CD in a Wireless LAN or Adhoc Network?

  32. Carrier Sense Multiple Access (CSMA) • If the channel is idle, transmit • If the channel is busy, wait for a random time • Waiting time is calculated using Binary Exponential Backoff (BEB) algorithm • Limitations of carrier Sensing • - hidden terminals • - exposed terminals

  33. ! B Note:colored circles represent the Tx range of each node A C Hidden Terminal Problem • Node A can hear both B and C; but B and C cannot hear each other • When B transmits to A, C cannot detect this transmission using the carrier • sense mechanism • If C also transmits to A, collision will occur at node A • Increases data packet collisions and hence reduces throughput • Possible solution: RTS (request-to-Send)/ CTS (Clear-to-Send) handshake

  34. ? B C A D Exposed Terminal Problem • When A transmits to B, C detects this transmission using carrier sense • mechanism • C refrains from transmitting to D, hence C is exposed to A’s transmission • Reduces bandwidth utilization and hence reduces throughput • Possible solution: Directional Antennas, separate channels for control • and data

  35. Multiple Access Collision Avoidance (MACA) • Uses Request-To-Send (RTS) and Clear-To-Send (CTS) handshake to mitigate the effects of hidden terminals • Data transfer duration is included in RTS and CTS, which helps other nodes to be silent for this duration • If a RTS/CTS packet collides, nodes wait for a random time which is calculated using BEB algorithm • Drawback: • Cannot avoid RTS/CTS control packet collisions

  36. B E C A D RTS CTS DATA RTS-CTS Handshake in Action radio range of B radio range of A D C A B E • A is the source which is in the range of B, D and C • B is the destination which is in the range of A, D and E

  37. B E C A D RTS CTS DATA ACK MACA for Wireless LANs (MACAW) D C A B E • A is the source which is in the range of B, D and C • B is the destination which is in the range of A, D and E • B sends ACK after receiving one data packet • Improves link reliability using ACK

  38. IEEE 802.11 MAC Protocol • Has provision for two modes • - Point Coordination Function (PCF) • - Distributed Coordination Function (DCF) • Point Coordination Function • - Provides contention-free access • - Requires Access Point (AP) for coordination • - Not suitable for a MANET

  39. Distributed Coordination Function (DCF) • Two schemes: • Basic access scheme (CSMA/CA) • CSMA/CA with RTS (Request-to-Send)/CTS (Clear-to-Send) handshake (optional)

  40. Data packet Node X Node A Data packet Node B Data packet Node C Time DIFS (DCF Inter-Frame Space) Basic Access Scheme (CSMA/CA) -- Data packet -- Backoff slot

  41. CSMA/CA with RTS/CTS RTS A B C D E F RTS = Request-to-Send

  42. CSMA/CA with RTS/CTS (contd.) RTS A B C D E F NAV = 20 RTS = Request-to-Send NAV (Net Allocation Vector) = indicates remaining duration to keep silent

  43. CSMA/CA with RTS/CTS (contd.) CTS A B C D E F CTS = Clear-to-Send

  44. CSMA/CA with RTS/CTS (contd.) CTS A B C D E F NAV = 15 CTS = Clear-to-Send NAV (Net Allocation Vector) = indicates remaining duration to keep silent

  45. CSMA/CA with RTS/CTS (contd.) • DATA packet follows CTS. Successful data reception • acknowledged using ACK. DATA A B C D E F

  46. CSMA/CA with RTS/CTS (contd.) ACK A B C D E F ACK = Acknowledgement packet

  47. CSMA/CA with RTS/CTS (contd.) Reserved area for transmission between node C and D ACK A B C D E F

  48. Limitations of IEEE 802.11 DCF MAC • Performance of Basic Access Method (CSMA/CA) degrades due to • hidden and exposed node problems • CSMA/CA with RTS/CTS – consumes additional bandwidth for • control packets transmission • may introduce significant delay in data packet transmission if RTS/CTS • control packets experience frequent collisions and retransmissions (possible • in case of high node concentration)

  49. Example: RTS/CTS packet collisions E RTS RTS A B D RTS CTS CTS C • Node C (which is hidden from node A) misses the CTS packet • from node B due to a collision with an RTS packet from D

  50. Multi-Channel MAC • Divides bandwidth into multiple channels using frequency • division or by using orthogonal CDMA codes • Selects any one of the idle channels • Advantages: • Improves throughput performance in the network by distributing • traffic over time as well as over bandwidth • Disadvantages: • Increases hardware complexity

More Related