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Internet Technology NETW 902 Tutorial 2 CH2: LAN Medium Access Control

Mohamed Esam. Internet Technology NETW 902 Tutorial 2 CH2: LAN Medium Access Control. Outline . IEEE 802.x Standard MAC schemes ALOHA CSMA/CD Token Ring Token BUS Slotted Ring Register Insertion Ring DQDB Wireless LAN FDDI Modeling with IKR-Simlib. name. description. IEEE 802.1.

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Internet Technology NETW 902 Tutorial 2 CH2: LAN Medium Access Control

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  1. Mohamed Esam Internet TechnologyNETW 902Tutorial 2CH2: LAN Medium Access Control

  2. Outline • IEEE 802.x Standard • MAC schemes • ALOHA • CSMA/CD • Token Ring • Token BUS • Slotted Ring • Register Insertion Ring • DQDB • Wireless LAN • FDDI • Modeling with IKR-Simlib

  3. name description IEEE 802.1 Bridging (networking) and Network Management IEEE 802.2 Logical link control IEEE 802.3 Ethernet IEEE 802.4 Token bus IEEE 802.5 Defines the MAC layer for a Token Ring IEEE 802.6 Metropolitan Area Networks IEEE 802.7 Broadband LAN using Coaxial Cable IEEE 802.8 Fiber Optic IEEE 802.9 Integrated Services LAN IEEE 802.10 Interoperable LAN Security IEEE 802.11x Wireless LAN IEEE 802.12 demand priority IEEE 802.15 Wireless PAN IEEE 802.15.1 Bluetooth IEEE 802.15.4 ZigBee IEEE 802.16 Broadband Wireless Access (WiMAX)‏ 1. IEEE 802.x Standard • Standardization of shared medium systems is a classical task of (Institute of Electrical and Electronic Engineers), project group 802.x.

  4. 2. MAC Schemes (page 60)‏ • Distributed MAC: • Polling: • Token Ring • Token BUS • Slotted Ring • Register Insertion Ring • DQDB • FDDI • Contention based • Aloha • CSMA/CD • CSMA/CA • Centralized MAC: • Polling • HSLAN • Reservation • DQDB • FDDI

  5. 3. ALOHA Operation Collision No Collision Collision • ALOHA Operation • Messages transmitted once available • From time-to-time messages collide (treated as erroneous frames)‏ • The terminal knows that its messages was corrupted when it receives no acknowledgements (i.e., a timeout is used)‏ • Recovery by the use of retransmissions • Collision • Transmissions from two or more terminals overlap in time • SOLUTION: Retransmission after random intervals from timeouts (Backoff Algorithm)‏ • Vulnerable Period= 2* T Transmission  The longest Period of collision • T Transmission=Frame size / Data rate Terminal A Terminal A Terminal A Terminal B Terminal B Terminal B

  6. Exponential Backoff Algorithms FIRST COLLISION • Wait 0 or 1 transmission frames (chosen randomly) before trying again SECOND COLLISION • Wait 0, 1,2 or 3 transmission frames (chosen randomly) before trying again THIRD COLLISION • Wait 0, 1,2,… or 7 transmission frames (chosen randomly) before trying again GENERALLY: AFTER N COLLISIONS • Wait 0 to 2N-1 transmission frames if N≤10 before trying again. N>10, wait between 0 and 1023 (210-1)‏ • Give up at N=16

  7. ALOHA in our life • We daily use ALOHA for 2G or 3G mobile signaling.

  8. Slotted ALOHA • Objective • Reduce the probability of collisions • Operation • Transmission in synchronized slots • Avoid partial collisions (either full or no collision)‏ • Collision • If more than one station require transmission during a slot period. • SOLUTION: Retransmission after random intervals from timeouts (Backoff Algorithm)‏ • Vulnerable Period= T Transmission  The longest Period of collision C A B D A Collision B C D TS 2TS 3TS

  9. Carrier Sense Multiple Access/Collision Detection (CSMA/CD)‏ “Ethernet” • Sense before transmission, if the medium is idle  send. • If the medium is busy “check next slide” • If Collision occurs, go to back-off window • CSMA/CD: • Abort transmission when a collision is detected • Vulnerable Period= 2*TProp. • TProp.= length/speed C B A C A 1st bit TProp. Sense Transmit Vulnerable Period TProp.

  10. Classes of CSMA • CSMA schemes vary with the behavior when the terminal has something to send and channel is sensed to be busy 1-Persistent CSMA • If channel is busy continue to sense channel • As soon as channel is sensed idle transmit frame • In case of collisions, a backoff algorithm is used to set a time to re-sense the channel Non-Persistent CSMA • If channel is busy, immediately run the backoff algorithm to set a time to re-sense the channel p-Persistent CSMA • If channel is busy continue to sense channel • As soon as channel is sensed idle transmit frame with probability p. With probability (1-p) wait for tprop before sensing the channel again • In case of collisions, a backoff algorithm is used to set a time to re-sense the channel

  11. Exercise 2: Parts 1, 2 and 3

  12. Outline • Token Ring (single, multiple, timed and priority token) • Token BUS • Slotted Ring • Register Insertion Ring • DQDB • FDDI • Wireless LAN • IKR-Simlib installation bugs

  13. IEEE 802.5 1989 by 1. Token Ring Single Token Timed Token Priority Token Multiple Token

  14. 1.a) Single Token Ring • A Token is either • Free (No terminal is transmitting) • Busy (Some terminal is transmitting C A B D A Token Ring Operation D A A station that has something to send and sees a free token, changes the state of token to busy and inserts its address in the sender filed of the header Copy from Dr. Tallal’s lectures Free Token Busy Token Data Frame Sender Field in Header Dest. Field in Header

  15. 1.a) Single Token Ring C Token Ring Operation A station that sees the token as busy and its name is not in the sender or destination fields, simply acts as repeater than forwards the frame D A D A Free Token Busy Token Data Frame Sender Field in Header Dest. Field in Header D Token Ring Operation Send data frame to upper layer A station that sees the token as busy and its name is in the destination field, sends the data frame to the upper layer before acting as a repeater Copy from Dr. Tallal’s lectures D A D A Free Token Busy Token Data Frame Sender Field in Header Dest. Field in Header

  16. 1.a) Single Token Ring A Token Ring Operation A station that sees the token as busy, changes the state of the token to free and removes the frame from the ring D A Free Token Busy Token Data Frame Sender Field in Header Dest. Field in Header Copy from Dr. Tallal’s lectures

  17. Node Interface Node A Frame check Rx Buffer Ring To forward 0 0 0 1 0 1 0 1 1 To send new If this station Is the destination Tx Buffer

  18. a - factor • If a <=1: small LAN single frame • If a >>1: HSLAN or WANsingle token

  19. Single Token Only if a>1 • Check destination address field, then forward A Single Token Ring Operation A station that sees the token as busy, changes the state of the token to free and removes the frame from the ring D A Free Token Busy Token Time from 1st bit in your frame to 1st bit in next frame Data Frame Sender Field in Header Dest. Field in Header C A …0101 B D

  20. Single Frame • The station transmits and receive the same frame simultaneously. “a<1” C A …0101 B D A Single Frame Ring Operation A station that sees the token as busy and wait for whole frame to read sender address, changes the state of the token to free and removes the frame from the ring D A Free Token Busy Token Data Frame Sender Field in Header Dest. Field in Header Only if a<1

  21. 4.b) Timed Token Ring • Same to single token Ring, but each station can send for certain period. • During this period many frames can be transmitted Not only one frame.

  22. 4.c) Priority Token Ring • Priority header is added with n levels. • Higher priority station can issue more than one free token sequentially. • After completion of the frame cycle, the priority (n) is decremented. • Useful for real time applications

  23. 1.d) Multiple Token Ring If a-factor > 2,  means more than 1 frames can fill the ring  so 2 tokens A  B Then B  A Busy token Free token A B 0 1 0 1 0 C 1 0 1 0 1 1 1 One frame

  24. A  B Then B  A 1 1 0 1 0 1 0 1 0 1 0 A 1 B 1 C The channel is always busy but there is idle status (t) with the first frame “in previous slide” One frame A  B Then B  A A  B Then B  A 1 1 1 0 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 0 0 A A B B 0 0 0 1 0 C C 0 1 One frame One frame

  25. Example for Multiple Token In next slide, assume Station 2 sends to station 1 & Station 4 sends to station 1: • Station 2 waits for free token (transmission authorization). • Station 2 changes free token into an occupied one (occupied token = frame header). Afterwards, 2 sends the frame. (Station 2 may send further frames, if the token holding timer (default 10 ms) is not exceeded) • Station 2 terminates the frame and produces a new, free token • Station 1 copies the frame. Station 2 removes it from the ring.

  26. 2. Token Bus • Token Ring, but in BUS topology • Forwarding is based on logical (IP) address

  27. Ex.2 Part 4

  28. Elective course in 10th Semester • Information Storage and Management in Cloud Computing • Lecturers: • Prof. FarukBagci (MET) assisted by Mohamed Esam (IET) • Content: • Data Centers Storage Net’s Techniques (DAS, NAS, iSCSI, SAN, IPSAN, FCoE and CAS) + Cloud Computing • Link: http://met.guc.edu.eg/Courses/CourseEdition.aspx?crsEdId=293 • Why it’s useful: • Research: Cloud Computing • Industry: • vendors: EMC , IBM, hp, Cisco, Brocade, NetApp • Operators: Mobile Operators, Banks, Google, Yahoo, Apple …”data centers and cloud providers” • Supported by:

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