wireless ad hoc & sensor networks 3

Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP l WS 2010/2011 N etwor k P rotoco l Media Access Protocol Prof. Dr. Dieter Hogrefe Dr. Omar Alfandi Media Access Protocol Physical Channel (Radio) Dr. Omar Alfandi Physical Channel (Radio) Outline • Multiple Access Technique • Designing Issues of MAC protocols • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 2 Media Access Control (Intro.) • Wireless medium is shared • Many nodes may need to access the wireless medium to send or receive messages • Concurrent message transmissions may interfere with each other  collisions  message drops 3 Multiple Access Technique • Reservation-based (Recall: mobile communication 1) – FDMA : Frequency Division Multiple Access – TDMA : Time Division Multiple Access – CDMA : Code Division Multiple Access SDMA : Space Division Multiple Access – SDMA : Space Division Multiple Access • Random – ALOHA : University of Hawaii Protocol ALOHA : University of Hawaii Protocol – CSMA : Carrier Sense Multiple Access – MACA : Multiple Access with Collision Avoidance • Random with reservation – DAMA : Demand Assigned Multiple Access – PRMA : Packet Reservation Multiple Access 4 Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP l WS 2010/2011 N etwor k P rotoco l Media Access Protocol Prof. Dr. Dieter Hogrefe Dr. Omar Alfandi Media Access Protocol Physical Channel (Radio) Dr. Omar Alfandi Physical Channel (Radio) Outline • Multiple Access Technique • Designing Issues of MAC protocols • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 2 Media Access Control (Intro.) • Wireless medium is shared • Many nodes may need to access the wireless medium to send or receive messages • Concurrent message transmissions may interfere with each other  collisions  message drops 3 Multiple Access Technique • Reservation-based (Recall: mobile communication 1) – FDMA : Frequency Division Multiple Access – TDMA : Time Division Multiple Access – CDMA : Code Division Multiple Access SDMA : Space Division Multiple Access – SDMA : Space Division Multiple Access • Random – ALOHA : University of Hawaii Protocol ALOHA : University of Hawaii Protocol – CSMA : Carrier Sense Multiple Access – MACA : Multiple Access with Collision Avoidance • Random with reservation – DAMA : Demand Assigned Multiple Access – PRMA : Packet Reservation Multiple Access 4 Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP l WS 2010/2011 N etwor k P rotoco l Media Access Protocol Prof. Dr. Dieter Hogrefe Dr. Omar Alfandi Media Access Protocol Physical Channel (Radio) Dr. Omar Alfandi Physical Channel (Radio) Outline • Multiple Access Technique • Designing Issues of MAC protocols • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 2 Media Access Control (Intro.) • Wireless medium is shared • Many nodes may need to access the wireless medium to send or receive messages • Concurrent message transmissions may interfere with each other  collisions  message drops 3 Multiple Access Technique • Reservation-based (Recall: mobile communication 1) – FDMA : Frequency Division Multiple Access – TDMA : Time Division Multiple Access – CDMA : Code Division Multiple Access SDMA : Space Division Multiple Access – SDMA : Space Division Multiple Access • Random – ALOHA : University of Hawaii Protocol ALOHA : University of Hawaii Protocol – CSMA : Carrier Sense Multiple Access – MACA : Multiple Access with Collision Avoidance • Random with reservation – DAMA : Demand Assigned Multiple Access – PRMA : Packet Reservation Multiple Access 4 Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP l WS 2010/2011 N etwor k P rotoco l Media Access Protocol Prof. Dr. Dieter Hogrefe Dr. Omar Alfandi Media Access Protocol Physical Channel (Radio) Dr. Omar Alfandi Physical Channel (Radio) Outline • Multiple Access Technique • Designing Issues of MAC protocols • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 2 Media Access Control (Intro.) • Wireless medium is shared • Many nodes may need to access the wireless medium to send or receive messages • Concurrent message transmissions may interfere with each other  collisions  message drops 3 Multiple Access Technique • Reservation-based (Recall: mobile communication 1) – FDMA : Frequency Division Multiple Access – TDMA : Time Division Multiple Access – CDMA : Code Division Multiple Access SDMA : Space Division Multiple Access – SDMA : Space Division Multiple Access • Random – ALOHA : University of Hawaii Protocol ALOHA : University of Hawaii Protocol – CSMA : Carrier Sense Multiple Access – MACA : Multiple Access with Collision Avoidance • Random with reservation – DAMA : Demand Assigned Multiple Access – PRMA : Packet Reservation Multiple Access 4 Reservation-based • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel – permanent (radio broadcast), slow hopping (GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) • TDMA (Time Division Multiple Access) – assign a fixed sending frequency for a certain amount of time • CDMA (Code Division Multiple Access) CDMA (Code Division Multiple Access) • SDMA (Space Division Multiple Access) – se g ment s p ace into sectors , use directed antennas gp , – Use cells to reuse frequencies • Combinations 5 FDD and TDD • In case of tow communicating parties sharing the medium: – Simplex : one way communication from sender to receive r – Duplex : two way communication between two parties – Frequency division duplex (FDD) • Combination of two simplex channels with different carrier frequencies – Time division duplex (TDD) • Time sharing of a single channel achieves quasi - simultaneous Time sharing of a single channel achieves quasi simultaneous duplex transmission 6 Random Access • However, wireless communication is often much more ad-hoc – New terminals have to register with the network – Terminals request access to the medium spontaneously In many cases there is no central control – In many cases there is no central control Other access methods such as distributed and non - arbitrated = random access non arbitrated = random access 7 Multiple Access Characteristics: • Shared medium : radio channel is shared by an priori unknown number of stations • Broadcast medium: all stations within transmission range of a sender receive the signal Challenge: • Wireless communication channel is prone to errors and bl hidd / d d bl & i l pro bl ems, e.g., hidd en / expose d no d e pro bl ems & s i gna l attenuation 8 Reservation-based • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel – permanent (radio broadcast), slow hopping (GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) • TDMA (Time Division Multiple Access) – assign a fixed sending frequency for a certain amount of time • CDMA (Code Division Multiple Access) CDMA (Code Division Multiple Access) • SDMA (Space Division Multiple Access) – se g ment s p ace into sectors , use directed antennas gp , – Use cells to reuse frequencies • Combinations 5 FDD and TDD • In case of tow communicating parties sharing the medium: – Simplex : one way communication from sender to receive r – Duplex : two way communication between two parties – Frequency division duplex (FDD) • Combination of two simplex channels with different carrier frequencies – Time division duplex (TDD) • Time sharing of a single channel achieves quasi - simultaneous Time sharing of a single channel achieves quasi simultaneous duplex transmission 6 Random Access • However, wireless communication is often much more ad-hoc – New terminals have to register with the network – Terminals request access to the medium spontaneously In many cases there is no central control – In many cases there is no central control Other access methods such as distributed and non - arbitrated = random access non arbitrated = random access 7 Multiple Access Characteristics: • Shared medium : radio channel is shared by an priori unknown number of stations • Broadcast medium: all stations within transmission range of a sender receive the signal Challenge: • Wireless communication channel is prone to errors and bl hidd / d d bl & i l pro bl ems, e.g., hidd en / expose d no d e pro bl ems & s i gna l attenuation 8 Reservation-based • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel – permanent (radio broadcast), slow hopping (GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) • TDMA (Time Division Multiple Access) – assign a fixed sending frequency for a certain amount of time • CDMA (Code Division Multiple Access) CDMA (Code Division Multiple Access) • SDMA (Space Division Multiple Access) – se g ment s p ace into sectors , use directed antennas gp , – Use cells to reuse frequencies • Combinations 5 FDD and TDD • In case of tow communicating parties sharing the medium: – Simplex : one way communication from sender to receive r – Duplex : two way communication between two parties – Frequency division duplex (FDD) • Combination of two simplex channels with different carrier frequencies – Time division duplex (TDD) • Time sharing of a single channel achieves quasi - simultaneous Time sharing of a single channel achieves quasi simultaneous duplex transmission 6 Random Access • However, wireless communication is often much more ad-hoc – New terminals have to register with the network – Terminals request access to the medium spontaneously In many cases there is no central control – In many cases there is no central control Other access methods such as distributed and non - arbitrated = random access non arbitrated = random access 7 Multiple Access Characteristics: • Shared medium : radio channel is shared by an priori unknown number of stations • Broadcast medium: all stations within transmission range of a sender receive the signal Challenge: • Wireless communication channel is prone to errors and bl hidd / d d bl & i l pro bl ems, e.g., hidd en / expose d no d e pro bl ems & s i gna l attenuation 8 Reservation-based • FDMA (Frequency Division Multiple Access) – assign a certain frequency to a transmission channel – permanent (radio broadcast), slow hopping (GSM), fast hopping (FHSS, Frequency Hopping Spread Spectrum) • TDMA (Time Division Multiple Access) • TDMA (Time Division Multiple Access) – assign a fixed sending frequency for a certain amount of time • CDMA (Code Division Multiple Access) CDMA (Code Division Multiple Access) • SDMA (Space Division Multiple Access) – se g ment s p ace into sectors , use directed antennas gp , – Use cells to reuse frequencies • Combinations 5 FDD and TDD • In case of tow communicating parties sharing the medium: – Simplex : one way communication from sender to receive r – Duplex : two way communication between two parties – Frequency division duplex (FDD) • Combination of two simplex channels with different carrier frequencies – Time division duplex (TDD) • Time sharing of a single channel achieves quasi - simultaneous Time sharing of a single channel achieves quasi simultaneous duplex transmission 6 Random Access • However, wireless communication is often much more ad-hoc – New terminals have to register with the network – Terminals request access to the medium spontaneously In many cases there is no central control – In many cases there is no central control Other access methods such as distributed and non - arbitrated = random access non arbitrated = random access 7 Multiple Access Characteristics: • Shared medium : radio channel is shared by an priori unknown number of stations • Broadcast medium: all stations within transmission range of a sender receive the signal Challenge: • Wireless communication channel is prone to errors and bl hidd / d d bl & i l pro bl ems, e.g., hidd en / expose d no d e pro bl ems & s i gna l attenuation 8 Wired vs. Wireless • Ethernet uses 1-persistent CSMA/CD – carrier sense multiple access with collision detection • Sense if the medium is free and start sending as soon as it becomes free • While sending listen to the medium to detect other senders • In case of a collision immediately stop sending and wait for the random amount of time • Problems in wireless networks • Problems in wireless networks – signal strength decreases quickly with distance – senders a pp l y CS and CD , but the collisions ha pp en at receivers pp y , pp – Energy efficiency: having the radio turned on costs almost as much energy as transmitting, so to seriously save energy one needs to turn the radio off! needs to turn the radio off! 9 Outline • Multiple Access Technique •Desi g nin g Issues of MAC p rotocols gg p • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 10 Need for MAC Protocols ? • Popular CSMA/CD (Carrier Sense Multiple Access/Collision Detection) scheme is not applicable to wireless networks • CSMA suffers hidden terminal & exposed terminal problems Collision Detection is impossible in wireless • Collision Detection is impossible in wireless communication Specific MAC protocols for the access to the physical layer physical layer 11 Hidden Terminal Problem • A sends to B, C cannot receive A • C wants to send to B, C senses a “free” medium (CS fails) • collision at B, A cannot receive the collision (CD fails) • A is “hidden” for C B A C 12 Wired vs. Wireless • Ethernet uses 1-persistent CSMA/CD – carrier sense multiple access with collision detection • Sense if the medium is free and start sending as soon as it becomes free • While sending listen to the medium to detect other senders • In case of a collision immediately stop sending and wait for the random amount of time • Problems in wireless networks • Problems in wireless networks – signal strength decreases quickly with distance – senders a pp l y CS and CD , but the collisions ha pp en at receivers pp y , pp – Energy efficiency: having the radio turned on costs almost as much energy as transmitting, so to seriously save energy one needs to turn the radio off! needs to turn the radio off! 9 Outline • Multiple Access Technique •Desi g nin g Issues of MAC p rotocols gg p • Classification of MAC protocols Classification of MAC protocols • Protocols examples • Characteristics of Link layer protocols • Characteristics of Link layer protocols • The lower layers in detail • Summary 10 Need for MAC Protocols ? • Popular CSMA/CD (Carrier Sense Multiple Access/Collision Detection) scheme is not applicable to wireless networks • CSMA suffers hidden terminal & exposed terminal problems Collision Detection is impossible in wireless • Collision Detection is impossible in wireless communication Specific MAC protocols for the access to the physical layer physical layer 11 Hidden Terminal Problem • A sends to B, C cannot receive A • C wants to send to B, C senses a “free” medium (CS fails) • collision at B, A cannot receive the collision (CD fails) • A is “hidden” for C B A C 12 [...]... those time slots for which it has the highest priority t=0 Example: Priorities of node A and its two-hop neighbours B and C t=1 t=2 t =3 23 9 56 3 26 B 64 8 12 44 6 C 18 6 33 57 • The lower layers in detail t=4 A • Characteristics of Link layer protocols 2 • Summary 33 34 Link Layer Protocols Error control • Link Layer protocols cover the following topics • Error control has to ensure that data transport... those time slots for which it has the highest priority t=0 Example: Priorities of node A and its two-hop neighbours B and C t=1 t=2 t =3 23 9 56 3 26 B 64 8 12 44 6 C 18 6 33 57 • The lower layers in detail t=4 A • Characteristics of Link layer protocols 2 • Summary 33 34 Link Layer Protocols Error control • Link Layer protocols cover the following topics • Error control has to ensure that data transport... those time slots for which it has the highest priority t=0 Example: Priorities of node A and its two-hop neighbours B and C t=1 t=2 t =3 23 9 56 3 26 B 64 8 12 44 6 C 18 6 33 57 • The lower layers in detail t=4 A • Characteristics of Link layer protocols 2 • Summary 33 34 Link Layer Protocols Error control • Link Layer protocols cover the following topics • Error control has to ensure that data transport... those time slots for which it has the highest priority t=0 Example: Priorities of node A and its two-hop neighbours B and C t=1 t=2 t =3 23 9 56 3 26 B 64 8 12 44 6 C 18 6 33 57 • The lower layers in detail t=4 A • Characteristics of Link layer protocols 2 • Summary 33 34 Link Layer Protocols Error control • Link Layer protocols cover the following topics • Error control has to ensure that data transport... to wireless networks • CSMA suffers hidden terminal & exposed terminal problems • Collision Detection is impossible in wireless communication • A sends to B, C cannot receive A • C wants to send to B, C senses a “free” medium (CS fails) • collision at B, A cannot receive the collision (CD fails) • A is “hidden” for C Specific MAC protocols for the access to the physical layer A 11 B C 12 Wired vs Wireless. .. • Protocols examples • Problems in wireless networks • Characteristics of Link layer protocols – signal strength decreases quickly with distance – senders apply CS and CD, but the collisions happen at receivers pp y , pp – Energy efficiency: having the radio turned on costs almost as much energy as transmitting, so to seriously save energy one needs to turn the radio off! • The lower layers in detail... for MAC Protocols ? Hidden Terminal Problem • Popular CSMA/CD (Carrier Sense Multiple Access/Collision Detection) scheme is not applicable to wireless networks • CSMA suffers hidden terminal & exposed terminal problems • Collision Detection is impossible in wireless communication • A sends to B, C cannot receive A • C wants to send to B, C senses a “free” medium (CS fails) • collision at B, A cannot... • Protocols examples • Problems in wireless networks • Characteristics of Link layer protocols – signal strength decreases quickly with distance – senders apply CS and CD, but the collisions happen at receivers pp y , pp – Energy efficiency: having the radio turned on costs almost as much energy as transmitting, so to seriously save energy one needs to turn the radio off! • The lower layers in detail... • Contention-based with reservation – Wireless networks may need to support real-time traffic – R Reservation mechanisms f reserving b d idth a priori ti h i for i bandwidth i i – Such protocols can provide QoS support to time-sensitive traffic sessions 17 Outline 18 Multiple Access with Collision Avoidance (MACA) A • MACA uses a two step signaling procedure to address the hidden and exposed t d d terminal... • Contention-based with reservation – Wireless networks may need to support real-time traffic – R Reservation mechanisms f reserving b d idth a priori ti h i for i bandwidth i i – Such protocols can provide QoS support to time-sensitive traffic sessions 17 Outline 18 Multiple Access with Collision Avoidance (MACA) A • MACA uses a two step signaling procedure to address the hidden and exposed t d d terminal . Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP. Multiple Access – PRMA : Packet Reservation Multiple Access 4 Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP. Multiple Access – PRMA : Packet Reservation Multiple Access 4 Wireless Ad Hoc & Sensor Networks Wireless Ad Hoc & Sensor Networks Medium Access Control Application Transport Protocol NkP