CSE 3213 Computer Network I Medium Access Control
![CSE 3213 Computer Network I Medium Access Control Protocols (Ch. 6. 1 – 6. CSE 3213 Computer Network I Medium Access Control Protocols (Ch. 6. 1 – 6.](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-1.jpg)
![Chapter Overview • Broadcast Networks – All information sent to all users – No Chapter Overview • Broadcast Networks – All information sent to all users – No](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-2.jpg)
![Multiple Access Communications 3 Multiple Access Communications 3](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-3.jpg)
![Multiple Access Communications • Shared media basis for broadcast networks – Inexpensive: radio over Multiple Access Communications • Shared media basis for broadcast networks – Inexpensive: radio over](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-4.jpg)
![Approaches to Media Sharing Medium sharing techniques Static channelization • • Partition medium Dedicated Approaches to Media Sharing Medium sharing techniques Static channelization • • Partition medium Dedicated](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-5.jpg)
![Channelization: Satellite Channel uplink fin downlink fout 6 Channelization: Satellite Channel uplink fin downlink fout 6](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-6.jpg)
![Channelization: Cellular uplink f 1 ; downlink f 2 uplink f 3 ; downlink Channelization: Cellular uplink f 1 ; downlink f 2 uplink f 3 ; downlink](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-7.jpg)
![Scheduling: Polling Data from 1 from 2 Data Poll 1 Host computer Inbound line Scheduling: Polling Data from 1 from 2 Data Poll 1 Host computer Inbound line](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-8.jpg)
![Scheduling: Token-Passing Ring networks token Data to M token Station that holds token transmits Scheduling: Token-Passing Ring networks token Data to M token Station that holds token transmits](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-9.jpg)
![Random Access Multitapped Bus Crash!! Transmit when ready Transmissions can occur; need retransmission strategy Random Access Multitapped Bus Crash!! Transmit when ready Transmissions can occur; need retransmission strategy](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-10.jpg)
![Wireless LAN Ad. Hoc: station-to-station Infrastructure: stations to base station Random access & polling Wireless LAN Ad. Hoc: station-to-station Infrastructure: stations to base station Random access & polling](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-11.jpg)
![Selecting a Medium Access Control • Applications – – What type of traffic? Voice Selecting a Medium Access Control • Applications – – What type of traffic? Voice](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-12.jpg)
![Delay-Bandwidth Product • Delay-bandwidth product key parameter – Coordination in sharing medium involves using Delay-Bandwidth Product • Delay-bandwidth product key parameter – Coordination in sharing medium involves using](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-13.jpg)
![Two-Station MAC Example Two stations are trying to share a common medium A transmits Two-Station MAC Example Two stations are trying to share a common medium A transmits](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-14.jpg)
![Efficiency of Two-Station Example • Each frame transmission requires 2 tprop of quiet time Efficiency of Two-Station Example • Each frame transmission requires 2 tprop of quiet time](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-15.jpg)
![Typical MAC Efficiencies Two-Station Example: CSMA-CD (Ethernet) protocol: Token-ring network • If a<<1, then Typical MAC Efficiencies Two-Station Example: CSMA-CD (Ethernet) protocol: Token-ring network • If a<<1, then](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-16.jpg)
![Typical Delay-Bandwidth Products Distance 10 Mbps 1 m 3. 33 x 10 -02 100 Typical Delay-Bandwidth Products Distance 10 Mbps 1 m 3. 33 x 10 -02 100](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-17.jpg)
![MAC protocol features • • Delay-bandwidth product Efficiency Transfer delay Fairness Reliability Capability to MAC protocol features • • Delay-bandwidth product Efficiency Transfer delay Fairness Reliability Capability to](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-18.jpg)
![MAC Delay Performance • Frame transfer delay – From first bit of frame arrives MAC Delay Performance • Frame transfer delay – From first bit of frame arrives](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-19.jpg)
![Normalized Delay versus Load E[T]/X E[T] = average frame transfer delay • Transfer delay Normalized Delay versus Load E[T]/X E[T] = average frame transfer delay • Transfer delay](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-20.jpg)
![Dependence on Rtprop/L a > a E[T]/X a Transfer Delay a 1 r max Dependence on Rtprop/L a > a E[T]/X a Transfer Delay a 1 r max](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-21.jpg)
![Random Access 22 Random Access 22](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-22.jpg)
![ALOHA • Wireless link to provide data transfer between main campus & remote campuses ALOHA • Wireless link to provide data transfer between main campus & remote campuses](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-23.jpg)
![ALOHA Model • Definitions and assumptions – X frame transmission time (assume constant) – ALOHA Model • Definitions and assumptions – X frame transmission time (assume constant) –](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-24.jpg)
![Throughput of ALOHA • e-2 = 0. 184 • • Collisions are means for Throughput of ALOHA • e-2 = 0. 184 • • Collisions are means for](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-25.jpg)
![Slotted ALOHA • Time is slotted in X seconds slots • Stations synchronized to Slotted ALOHA • Time is slotted in X seconds slots • Stations synchronized to](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-26.jpg)
![Throughput of Slotted ALOHA 27 Throughput of Slotted ALOHA 27](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-27.jpg)
![Carrier Sensing Multiple Access (CSMA) • A station senses the channel before it starts Carrier Sensing Multiple Access (CSMA) • A station senses the channel before it starts](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-28.jpg)
![CSMA Options • Transmitter behavior when busy channel is sensed – 1 -persistent CSMA CSMA Options • Transmitter behavior when busy channel is sensed – 1 -persistent CSMA](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-29.jpg)
![1 -Persistent CSMA Throughput • Better than Aloha & slotted Aloha for small a 1 -Persistent CSMA Throughput • Better than Aloha & slotted Aloha for small a](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-30.jpg)
![Non-Persistent CSMA Throughput a = 0. 01 S 0. 81 0. 51 a = Non-Persistent CSMA Throughput a = 0. 01 S 0. 81 0. 51 a =](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-31.jpg)
![CSMA with Collision Detection (CSMA/CD) • Monitor for collisions & abort transmission – Stations CSMA with Collision Detection (CSMA/CD) • Monitor for collisions & abort transmission – Stations](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-32.jpg)
![CSMA/CD reaction time A begins to transmit at A t=0 B A detects collision CSMA/CD reaction time A begins to transmit at A t=0 B A detects collision](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-33.jpg)
![CSMA-CD Model • Assumptions – Collisions can be detected and resolved in 2 tprop CSMA-CD Model • Assumptions – Collisions can be detected and resolved in 2 tprop](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-34.jpg)
![CSMA/CD Throughput Busy Contention Busy Time • At maximum throughput, systems alternates between contention CSMA/CD Throughput Busy Contention Busy Time • At maximum throughput, systems alternates between contention](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-35.jpg)
![CSMA-CD Application: Ethernet • First Ethernet LAN standard used CSMA-CD – 1 -persistent Carrier CSMA-CD Application: Ethernet • First Ethernet LAN standard used CSMA-CD – 1 -persistent Carrier](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-36.jpg)
![Throughput for Random Access MACs CSMA/CD 1 -P CSMA max Non-P CSMA Slotted ALOHA Throughput for Random Access MACs CSMA/CD 1 -P CSMA max Non-P CSMA Slotted ALOHA](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-37.jpg)
![Carrier Sensing and Priority Transmission • Certain applications require faster response than others, e. Carrier Sensing and Priority Transmission • Certain applications require faster response than others, e.](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-38.jpg)
![Scheduling 39 Scheduling 39](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-39.jpg)
![Scheduling for Medium Access Control • Schedule frame transmissions to avoid collision in shared Scheduling for Medium Access Control • Schedule frame transmissions to avoid collision in shared](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-40.jpg)
![Reservations Systems • Centralized systems: A central controller accepts requests from stations and issues Reservations Systems • Centralized systems: A central controller accepts requests from stations and issues](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-41.jpg)
![Reservation Systems Reservation interval r d Frame transmissions d d r d Cycle n Reservation Systems Reservation interval r d Frame transmissions d d r d Cycle n](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-42.jpg)
![Reservation System Options • Centralized or distributed system – Centralized systems: A central controller Reservation System Options • Centralized or distributed system – Centralized systems: A central controller](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-43.jpg)
![Example • Initially stations 3 & 5 have reservations to transmit frames (a) r Example • Initially stations 3 & 5 have reservations to transmit frames (a) r](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-44.jpg)
![Example: GPRS • General Packet Radio Service – Packet data service in GSM cellular Example: GPRS • General Packet Radio Service – Packet data service in GSM cellular](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-45.jpg)
![Reservation Systems and Quality of Service • Different applications; different requirements – Immediate transfer Reservation Systems and Quality of Service • Different applications; different requirements – Immediate transfer](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-46.jpg)
![Polling Systems • Centralized polling systems: A central controller transmits polling messages to stations Polling Systems • Centralized polling systems: A central controller transmits polling messages to stations](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-47.jpg)
![Polling System Options • Service Limits: How much is a station allowed to transmit Polling System Options • Service Limits: How much is a station allowed to transmit](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-48.jpg)
![Application: Token-Passing Rings token Free Token = Poll Frame Delimiter is Token Free = Application: Token-Passing Rings token Free Token = Poll Frame Delimiter is Token Free =](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-49.jpg)
![Methods of Token Reinsertion • • Ring latency: number of bits that can be Methods of Token Reinsertion • • Ring latency: number of bits that can be](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-50.jpg)
![Application Examples • Single-frame reinsertion – IEEE 802. 5 Token Ring LAN @ 4 Application Examples • Single-frame reinsertion – IEEE 802. 5 Token Ring LAN @ 4](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-51.jpg)
![Comparison of MAC approaches • Aloha & Slotted Aloha – – Simple & quick Comparison of MAC approaches • Aloha & Slotted Aloha – – Simple & quick](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-52.jpg)
![Comparison of MAC approaches • Reservation – On-demand transmission of bursty or steady streams Comparison of MAC approaches • Reservation – On-demand transmission of bursty or steady streams](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-53.jpg)
- Slides: 53
![CSE 3213 Computer Network I Medium Access Control Protocols Ch 6 1 6 CSE 3213 Computer Network I Medium Access Control Protocols (Ch. 6. 1 – 6.](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-1.jpg)
CSE 3213 Computer Network I Medium Access Control Protocols (Ch. 6. 1 – 6. 3) Course page: http: //www. cse. yorku. ca/course/3213 Slides modified from Alberto Leon-Garcia and Indra Widjaja 1
![Chapter Overview Broadcast Networks All information sent to all users No Chapter Overview • Broadcast Networks – All information sent to all users – No](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-2.jpg)
Chapter Overview • Broadcast Networks – All information sent to all users – No routing – Shared media – Radio • Cellular telephony • Wireless LANs – Copper & Optical • Ethernet LANs • Cable Modem Access • Medium Access Control – To coordinate access to shared medium – Data link layer since direct transfer of frames • Local Area Networks – High-speed, low-cost communications between colocated computers – Typically based on broadcast networks – Simple & cheap – Limited number of users 2
![Multiple Access Communications 3 Multiple Access Communications 3](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-3.jpg)
Multiple Access Communications 3
![Multiple Access Communications Shared media basis for broadcast networks Inexpensive radio over Multiple Access Communications • Shared media basis for broadcast networks – Inexpensive: radio over](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-4.jpg)
Multiple Access Communications • Shared media basis for broadcast networks – Inexpensive: radio over air; copper or coaxial cable – M users communicate by broadcasting into medium • Key issue: How to share the medium? 3 1 2 4 Shared multiple access medium M 5 4
![Approaches to Media Sharing Medium sharing techniques Static channelization Partition medium Dedicated Approaches to Media Sharing Medium sharing techniques Static channelization • • Partition medium Dedicated](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-5.jpg)
Approaches to Media Sharing Medium sharing techniques Static channelization • • Partition medium Dedicated allocation to users Satellite transmission Cellular Telephone Dynamic medium access control Scheduling • • Random access Polling: take turns Request for slot in transmission schedule Token ring Wireless LANs • • Loose coordination Send, wait, retry if necessary Aloha Ethernet 5
![Channelization Satellite Channel uplink fin downlink fout 6 Channelization: Satellite Channel uplink fin downlink fout 6](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-6.jpg)
Channelization: Satellite Channel uplink fin downlink fout 6
![Channelization Cellular uplink f 1 downlink f 2 uplink f 3 downlink Channelization: Cellular uplink f 1 ; downlink f 2 uplink f 3 ; downlink](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-7.jpg)
Channelization: Cellular uplink f 1 ; downlink f 2 uplink f 3 ; downlink f 4 7
![Scheduling Polling Data from 1 from 2 Data Poll 1 Host computer Inbound line Scheduling: Polling Data from 1 from 2 Data Poll 1 Host computer Inbound line](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-8.jpg)
Scheduling: Polling Data from 1 from 2 Data Poll 1 Host computer Inbound line Data to M Poll 2 Outbound line 1 2 M 3 Stations 8
![Scheduling TokenPassing Ring networks token Data to M token Station that holds token transmits Scheduling: Token-Passing Ring networks token Data to M token Station that holds token transmits](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-9.jpg)
Scheduling: Token-Passing Ring networks token Data to M token Station that holds token transmits into ring 9
![Random Access Multitapped Bus Crash Transmit when ready Transmissions can occur need retransmission strategy Random Access Multitapped Bus Crash!! Transmit when ready Transmissions can occur; need retransmission strategy](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-10.jpg)
Random Access Multitapped Bus Crash!! Transmit when ready Transmissions can occur; need retransmission strategy 10
![Wireless LAN Ad Hoc stationtostation Infrastructure stations to base station Random access polling Wireless LAN Ad. Hoc: station-to-station Infrastructure: stations to base station Random access & polling](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-11.jpg)
Wireless LAN Ad. Hoc: station-to-station Infrastructure: stations to base station Random access & polling 11
![Selecting a Medium Access Control Applications What type of traffic Voice Selecting a Medium Access Control • Applications – – What type of traffic? Voice](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-12.jpg)
Selecting a Medium Access Control • Applications – – What type of traffic? Voice streams? Steady traffic, low delay/jitter Data? Short messages? Web page downloads? Enterprise or Consumer market? Reliability, cost • Scale – How much traffic can be carried? – How many users can be supported? • Current Examples: – Design MAC to provide wireless DSL-equivalent access to rural communities – Design MAC to provide Wireless-LAN-equivalent access to mobile users (user in car travelling at 130 km/hr) 12
![DelayBandwidth Product Delaybandwidth product key parameter Coordination in sharing medium involves using Delay-Bandwidth Product • Delay-bandwidth product key parameter – Coordination in sharing medium involves using](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-13.jpg)
Delay-Bandwidth Product • Delay-bandwidth product key parameter – Coordination in sharing medium involves using bandwidth (explicitly or implicitly) – Difficulty of coordination commensurate with delay -bandwidth product • Simple two-station example – Station with frame to send listens to medium and transmits if medium found idle – Station monitors medium to detect collision – If collision occurs, station that begin transmitting earlier retransmits (propagation time is known) 13
![TwoStation MAC Example Two stations are trying to share a common medium A transmits Two-Station MAC Example Two stations are trying to share a common medium A transmits](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-14.jpg)
Two-Station MAC Example Two stations are trying to share a common medium A transmits at t = 0 Distance d meters tprop = d / seconds A B Case 1 A B Case 2 A detects collision at t = 2 tprop A B B does not transmit before t = tprop & A captures channel B transmits before t = tprop and detects collision soon thereafter 14
![Efficiency of TwoStation Example Each frame transmission requires 2 tprop of quiet time Efficiency of Two-Station Example • Each frame transmission requires 2 tprop of quiet time](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-15.jpg)
Efficiency of Two-Station Example • Each frame transmission requires 2 tprop of quiet time – Station B needs to be quiet tprop before and after time when Station A transmits – R transmission bit rate – L bits/frame Normalized Delay. Bandwidth Product Propagation delay Time to transmit a frame 15
![Typical MAC Efficiencies TwoStation Example CSMACD Ethernet protocol Tokenring network If a1 then Typical MAC Efficiencies Two-Station Example: CSMA-CD (Ethernet) protocol: Token-ring network • If a<<1, then](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-16.jpg)
Typical MAC Efficiencies Two-Station Example: CSMA-CD (Ethernet) protocol: Token-ring network • If a<<1, then efficiency close to 100% • As a approaches 1, the efficiency becomes low a΄= latency of the ring (bits)/average frame length 16
![Typical DelayBandwidth Products Distance 10 Mbps 1 m 3 33 x 10 02 100 Typical Delay-Bandwidth Products Distance 10 Mbps 1 m 3. 33 x 10 -02 100](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-17.jpg)
Typical Delay-Bandwidth Products Distance 10 Mbps 1 m 3. 33 x 10 -02 100 Mbps 1 Gbps Network Type 3. 33 x 10 -01 3. 33 x 100 Desk area network 100 m 3. 33 x 1001 3. 33 x 1002 3. 33 x 1003 Local area network 10 km 3. 33 x 1002 3. 33 x 1003 3. 33 x 1004 Metropolitan area network 1000 km 3. 33 x 1004 3. 33 x 1005 3. 33 x 1006 Wide area network 100000 km 3. 33 x 1006 3. 33 x 1007 3. 33 x 1008 Global area network • Max size Ethernet frame: 1500 bytes = 12000 bits • Long and/or fat pipes give large a 17
![MAC protocol features Delaybandwidth product Efficiency Transfer delay Fairness Reliability Capability to MAC protocol features • • Delay-bandwidth product Efficiency Transfer delay Fairness Reliability Capability to](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-18.jpg)
MAC protocol features • • Delay-bandwidth product Efficiency Transfer delay Fairness Reliability Capability to carry different types of traffic Quality of service Cost 18
![MAC Delay Performance Frame transfer delay From first bit of frame arrives MAC Delay Performance • Frame transfer delay – From first bit of frame arrives](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-19.jpg)
MAC Delay Performance • Frame transfer delay – From first bit of frame arrives at source MAC – To last bit of frame delivered at destination MAC • Throughput – Actual transfer rate through the shared medium – Measured in frames/sec or bits/sec • Parameters R bits/sec & L bits/frame X=L/R seconds/frame l frames/second average arrival rate Load r = l X, rate at which “work” arrives Maximum throughput (@100% efficiency): R/L fr/sec 19
![Normalized Delay versus Load ETX ET average frame transfer delay Transfer delay Normalized Delay versus Load E[T]/X E[T] = average frame transfer delay • Transfer delay](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-20.jpg)
Normalized Delay versus Load E[T]/X E[T] = average frame transfer delay • Transfer delay X = average frame transmission time • • At low arrival rate, only frame transmission time At high arrival rates, increasingly longer waits to access channel Max efficiency typically less than 100% 1 Load rmax 1 r 20
![Dependence on RtpropL a a ETX a Transfer Delay a 1 r max Dependence on Rtprop/L a > a E[T]/X a Transfer Delay a 1 r max](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-21.jpg)
Dependence on Rtprop/L a > a E[T]/X a Transfer Delay a 1 r max Load rmax 1 r 21
![Random Access 22 Random Access 22](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-22.jpg)
Random Access 22
![ALOHA Wireless link to provide data transfer between main campus remote campuses ALOHA • Wireless link to provide data transfer between main campus & remote campuses](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-23.jpg)
ALOHA • Wireless link to provide data transfer between main campus & remote campuses of University of Hawaii • Simplest solution: just do it – A station transmits whenever it has data to transmit – If more than one frames are transmitted, they interfere with each other (collide) and are lost – If ACK not received within timeout, then a station picks random backoff time (to avoid repeated collision) – Station retransmits frame after backoff time First transmission t 0 -X t 0 Backoff period B Retransmission t t 0+X Vulnerable period t 0+X+2 tprop + B Time-out 23
![ALOHA Model Definitions and assumptions X frame transmission time assume constant ALOHA Model • Definitions and assumptions – X frame transmission time (assume constant) –](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-24.jpg)
ALOHA Model • Definitions and assumptions – X frame transmission time (assume constant) – S: throughput (average # successful frame transmissions per X seconds) – G: load (average # transmission attempts per X sec. ) – Psuccess : probability a frame transmission is successful • • X Prior interval X frame transmission Any transmission that begins during vulnerable period leads to collision Success if no arrivals during 2 X seconds 24
![Throughput of ALOHA e2 0 184 Collisions are means for Throughput of ALOHA • e-2 = 0. 184 • • Collisions are means for](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-25.jpg)
Throughput of ALOHA • e-2 = 0. 184 • • Collisions are means for coordinating access Max throughput is rmax= 1/2 e (18. 4%) Bimodal behavior: Small G, S≈G Large G, S↓ 0 • Collisions can snowball and drop throughput to zero 25
![Slotted ALOHA Time is slotted in X seconds slots Stations synchronized to Slotted ALOHA • Time is slotted in X seconds slots • Stations synchronized to](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-26.jpg)
Slotted ALOHA • Time is slotted in X seconds slots • Stations synchronized to frame times • Stations transmit frames in first slot after frame arrival • Backoff intervals in multiples of slots Backoff period k. X (k+1)X Vulnerabl eperiod t 0 +X+2 tprop B t t 0 +X+2 tprop+ B Time-out Only frames that arrive during prior X seconds collide 26
![Throughput of Slotted ALOHA 27 Throughput of Slotted ALOHA 27](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-27.jpg)
Throughput of Slotted ALOHA 27
![Carrier Sensing Multiple Access CSMA A station senses the channel before it starts Carrier Sensing Multiple Access (CSMA) • A station senses the channel before it starts](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-28.jpg)
Carrier Sensing Multiple Access (CSMA) • A station senses the channel before it starts transmission – – – If busy, either wait or schedule backoff (different options) If idle, start transmission Vulnerable period is reduced to tprop (due to channel capture effect) When collisions occur they involve entire frame transmission times If tprop >X (or if a>1), no gain compared to ALOHA or slotted ALOHA Station A begins transmission at t=0 Station A captures channel at t = tprop A A 28
![CSMA Options Transmitter behavior when busy channel is sensed 1 persistent CSMA CSMA Options • Transmitter behavior when busy channel is sensed – 1 -persistent CSMA](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-29.jpg)
CSMA Options • Transmitter behavior when busy channel is sensed – 1 -persistent CSMA (most greedy) • Start transmission as soon as the channel becomes idle • Low delay and low efficiency – Non-persistent CSMA (least greedy) • Wait a backoff period, then sense carrier again • High delay and high efficiency – p-persistent CSMA (adjustable greedy) • Wait till channel becomes idle, transmit with prob. p; or wait one mini-slot time & re-sense with probability 1 -p • Delay and efficiency can be balanced Sensing 29
![1 Persistent CSMA Throughput Better than Aloha slotted Aloha for small a 1 -Persistent CSMA Throughput • Better than Aloha & slotted Aloha for small a](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-30.jpg)
1 -Persistent CSMA Throughput • Better than Aloha & slotted Aloha for small a • Worse than Aloha for a > 1 30
![NonPersistent CSMA Throughput a 0 01 S 0 81 0 51 a Non-Persistent CSMA Throughput a = 0. 01 S 0. 81 0. 51 a =](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-31.jpg)
Non-Persistent CSMA Throughput a = 0. 01 S 0. 81 0. 51 a = 0. 14 • Higher maximum throughput than 1 persistent for small a • Worse than Aloha for a > 1 G a=1 31
![CSMA with Collision Detection CSMACD Monitor for collisions abort transmission Stations CSMA with Collision Detection (CSMA/CD) • Monitor for collisions & abort transmission – Stations](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-32.jpg)
CSMA with Collision Detection (CSMA/CD) • Monitor for collisions & abort transmission – Stations with frames to send, first do carrier sensing – After beginning transmissions, stations continue listening to the medium to detect collisions – If collisions detected, all stations involved stop transmission, reschedule random backoff times, and try again at scheduled times • In CSMA collisions result in wastage of X seconds spent transmitting an entire frame • CSMA-CD reduces wastage to time to detect collision and abort transmission 32
![CSMACD reaction time A begins to transmit at A t0 B A detects collision CSMA/CD reaction time A begins to transmit at A t=0 B A detects collision](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-33.jpg)
CSMA/CD reaction time A begins to transmit at A t=0 B A detects collision at A t= 2 tprop- B B begins to transmit at t = tprop ; B detects collision at t = tprop It takes 2 tprop to find out if channel has been captured 33
![CSMACD Model Assumptions Collisions can be detected and resolved in 2 tprop CSMA-CD Model • Assumptions – Collisions can be detected and resolved in 2 tprop](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-34.jpg)
CSMA-CD Model • Assumptions – Collisions can be detected and resolved in 2 tprop – Time slotted in 2 tprop slots during contention periods – Assume n busy stations, and each may transmit with probability p in each contention time slot – Once the contention period is over (a station successfully occupies the channel), it takes X seconds for a frame to be transmitted – It takes tprop before the next contention period starts. (a) Busy Contention Busy Idle Contention Busy Time 34
![CSMACD Throughput Busy Contention Busy Time At maximum throughput systems alternates between contention CSMA/CD Throughput Busy Contention Busy Time • At maximum throughput, systems alternates between contention](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-35.jpg)
CSMA/CD Throughput Busy Contention Busy Time • At maximum throughput, systems alternates between contention periods and frame transmission times • where: R bits/sec, L bits/frame, X=L/R seconds/frame a = tprop/X meters/sec. speed of light in medium d meters is diameter of system 2 e+1 = 6. 44 35
![CSMACD Application Ethernet First Ethernet LAN standard used CSMACD 1 persistent Carrier CSMA-CD Application: Ethernet • First Ethernet LAN standard used CSMA-CD – 1 -persistent Carrier](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-36.jpg)
CSMA-CD Application: Ethernet • First Ethernet LAN standard used CSMA-CD – 1 -persistent Carrier Sensing – R = 10 Mbps – tprop = 51. 2 microseconds • 512 bits = 64 byte slot • accommodates 2. 5 km + 4 repeaters – Truncated Binary Exponential Backoff • After nth collision, select backoff from {0, 1, …, 2 k – 1}, where k=min(n, 10) 36
![Throughput for Random Access MACs CSMACD 1 P CSMA max NonP CSMA Slotted ALOHA Throughput for Random Access MACs CSMA/CD 1 -P CSMA max Non-P CSMA Slotted ALOHA](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-37.jpg)
Throughput for Random Access MACs CSMA/CD 1 -P CSMA max Non-P CSMA Slotted ALOHA a • For small a: CSMA-CD has best throughput • For larger a: Aloha & slotted Aloha better throughput 37
![Carrier Sensing and Priority Transmission Certain applications require faster response than others e Carrier Sensing and Priority Transmission • Certain applications require faster response than others, e.](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-38.jpg)
Carrier Sensing and Priority Transmission • Certain applications require faster response than others, e. g. ACK messages • Impose different interframe times – High priority traffic sense channel for time t 1 – Low priority traffic sense channel for time t 2>t 1 – High priority traffic, if present, seizes channel first • This priority mechanism is used in IEEE 802. 11 wireless LAN 38
![Scheduling 39 Scheduling 39](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-39.jpg)
Scheduling 39
![Scheduling for Medium Access Control Schedule frame transmissions to avoid collision in shared Scheduling for Medium Access Control • Schedule frame transmissions to avoid collision in shared](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-40.jpg)
Scheduling for Medium Access Control • Schedule frame transmissions to avoid collision in shared medium ü More efficient channel utilization ü Less variability in delays ü Can provide fairness to stations û Increased computational or procedural complexity • Two main approaches – Reservation – Polling 40
![Reservations Systems Centralized systems A central controller accepts requests from stations and issues Reservations Systems • Centralized systems: A central controller accepts requests from stations and issues](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-41.jpg)
Reservations Systems • Centralized systems: A central controller accepts requests from stations and issues grants to transmit – Frequency Division Duplex (FDD): Separate frequency bands for uplink & downlink – Time-Division Duplex (TDD): Uplink & downlink time-share the same channel • Distributed systems: Stations implement a decentralized algorithm to determine transmission order Central Controller 41
![Reservation Systems Reservation interval r d Frame transmissions d d r d Cycle n Reservation Systems Reservation interval r d Frame transmissions d d r d Cycle n](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-42.jpg)
Reservation Systems Reservation interval r d Frame transmissions d d r d Cycle n r = 1 2 d d Time Cycle (n + 1) 3 M • Transmissions organized into cycles • Cycle: reservation interval + frame transmissions • Reservation interval has a minislot for each station to request reservations for frame transmissions 42
![Reservation System Options Centralized or distributed system Centralized systems A central controller Reservation System Options • Centralized or distributed system – Centralized systems: A central controller](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-43.jpg)
Reservation System Options • Centralized or distributed system – Centralized systems: A central controller listens to reservation information, decides order of transmission, issues grants – Distributed systems: Each station determines its slot for transmission from the reservation information • Single or Multiple Frames – Single frame reservation: Only one frame transmission can be reserved within a reservation cycle – Multiple frame reservation: More than one frame transmission can be reserved within a frame • Channelized or Random Access Reservations – Channelized (typically TDMA) reservation: Reservation messages from different stations are multiplexed without any risk of collision – Random access reservation: Each station transmits reservation message randomly until the message goes through 43
![Example Initially stations 3 5 have reservations to transmit frames a r Example • Initially stations 3 & 5 have reservations to transmit frames (a) r](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-44.jpg)
Example • Initially stations 3 & 5 have reservations to transmit frames (a) r 3 5 8 r 3 t • Station 8 becomes active and makes reservation • Cycle now also includes frame transmissions from station 8 (b) 8 r 3 5 8 r 3 t 44
![Example GPRS General Packet Radio Service Packet data service in GSM cellular Example: GPRS • General Packet Radio Service – Packet data service in GSM cellular](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-45.jpg)
Example: GPRS • General Packet Radio Service – Packet data service in GSM cellular radio – GPRS devices, e. g. cellphones or laptops, send packet data over radio and then to Internet – Slotted Aloha MAC used for reservations – Single & multi-slot reservations supported 45
![Reservation Systems and Quality of Service Different applications different requirements Immediate transfer Reservation Systems and Quality of Service • Different applications; different requirements – Immediate transfer](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-46.jpg)
Reservation Systems and Quality of Service • Different applications; different requirements – Immediate transfer for ACK frames – Low-delay transfer & steady bandwidth for voice – High-bandwidth for Web transfers • Reservation provide direct means for Qo. S – Stations makes requests per frame – Stations can request for persistent transmission access – Centralized controller issues grants • Preferred approach – Decentralized protocol allows stations to determine grants • Protocol must deal with error conditions when requests or grants are lost 46
![Polling Systems Centralized polling systems A central controller transmits polling messages to stations Polling Systems • Centralized polling systems: A central controller transmits polling messages to stations](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-47.jpg)
Polling Systems • Centralized polling systems: A central controller transmits polling messages to stations according to a certain order • Distributed polling systems: A permit for frame transmission is passed from station to station according to a certain order • A signaling procedure exists for setting up order Central Controller 47
![Polling System Options Service Limits How much is a station allowed to transmit Polling System Options • Service Limits: How much is a station allowed to transmit](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-48.jpg)
Polling System Options • Service Limits: How much is a station allowed to transmit per poll? – Exhaustive: until station’s data buffer is empty (including new frame arrivals) – Gated: all data in buffer when poll arrives – Frame-Limited: one frame per poll – Time-Limited: up to some maximum time • Priority mechanisms – More bandwidth & lower delay for stations that appear multiple times in the polling list – Issue polls for stations with message of priority k or higher 48
![Application TokenPassing Rings token Free Token Poll Frame Delimiter is Token Free Application: Token-Passing Rings token Free Token = Poll Frame Delimiter is Token Free =](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-49.jpg)
Application: Token-Passing Rings token Free Token = Poll Frame Delimiter is Token Free = 01111110 Busy = 01111111 Listen mode Input from ring Delay Transmit mode Output to ring Ready station looks for free token Flips bit to change free token to busy Delay From device To device Ready station inserts its frames Reinserts free token when done 50
![Methods of Token Reinsertion Ring latency number of bits that can be Methods of Token Reinsertion • • Ring latency: number of bits that can be](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-50.jpg)
Methods of Token Reinsertion • • Ring latency: number of bits that can be simultaneously in transit on ring Multi-token operation – Free token transmitted immediately after last bit of data frame • Single-token operation • Single-Frame operation Busy token Free token Frame Idle Fill – Free token inserted after last bit of the busy token is received back – Transmission time at least ring latency – If frame is longer than ring latency, equivalent to multi-token operation – Free token inserted after transmitting station has received last bit of its frame – Equivalent to attaching trailer equal to ring latency 51
![Application Examples Singleframe reinsertion IEEE 802 5 Token Ring LAN 4 Application Examples • Single-frame reinsertion – IEEE 802. 5 Token Ring LAN @ 4](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-51.jpg)
Application Examples • Single-frame reinsertion – IEEE 802. 5 Token Ring LAN @ 4 Mbps • Single token reinsertion – IBM Token Ring @ 4 Mbps • Multitoken reinsertion – IEEE 802. 5 and IBM Ring LANs @ 16 Mbps – FDDI Ring @ 50 Mbps • All of these LANs incorporate token priority mechanisms 52
![Comparison of MAC approaches Aloha Slotted Aloha Simple quick Comparison of MAC approaches • Aloha & Slotted Aloha – – Simple & quick](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-52.jpg)
Comparison of MAC approaches • Aloha & Slotted Aloha – – Simple & quick transfer at very low load Accommodates large number of low-traffic bursty users Highly variable delay at moderate loads Efficiency does not depend on a • CSMA-CD – Quick transfer and high efficiency for low delay-bandwidth product – Can accommodate large number of bursty users – Variable and unpredictable delay 53
![Comparison of MAC approaches Reservation Ondemand transmission of bursty or steady streams Comparison of MAC approaches • Reservation – On-demand transmission of bursty or steady streams](https://slidetodoc.com/presentation_image_h2/8a34741fb0b02add1a006c7da64ebb58/image-53.jpg)
Comparison of MAC approaches • Reservation – On-demand transmission of bursty or steady streams – Accommodates large number of low-traffic users with slotted Aloha reservations – Can incorporate Qo. S – Handles large delay-bandwidth product via delayed grants • Polling – – Generalization of time-division multiplexing Provides fairness through regular access opportunities Can provide bounds on access delay Performance deteriorates with large delay-bandwidth product 54
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