Multiple Access in Computer Network

Error Detection and correction: Types of Errors, Error Detection mechanism (Linear codes, CRC, Checksum), Error Correction mechanism: Hamming Encoding. Data Link Control and Protocols: Flow and Error Control, Stop-and-Wait ARQ. Go-Back-N ARQ,
Selective Repeat ARQ, HDLC and Point-to-Point Protocol
Multiple Access: Random Access (ALOHA, CSMA, CSMA/CD, CSMA/CA), Controlled Access (Polling, Reservation, Token Passing), Channelization (FDMA, TDMA, CDMA). Wired LANs (Ethernet): Traditional Ethernet, Fast Ethernet, Gigabit Ethernet.

1. Multiple Access
Hitesh Mohapatra
Class Note

2. Data link layer divided into two functionality-oriented sublayers

3. Taxonomy of multiple-access protocols discussed in
this chapter

4. ALOHA
Random Access
Frames in a pure ALOHA network

5. Importance Relevance Significance
•To maximize the
bandwidth
utilization
•ALOHA
•Carrier Sense
Multiple Access
•Carrier Sense
Multiple Access with
Collision Detection
•Carrier Sense
Multiple Access with
Collision Avoidance
•In random access or
contention methods, no
station is superior to
another station and none
is assigned the control
over another. No station
permits, or does not
permit, another station
to send. At each instance,
a station that has data to
send uses a procedure
defined by the protocol
to make a decision on
whether or not to send.

6. •No idle state
How to achieve the maximum utilization?
•Multiple send/receive
•Avoid Collision
•Avoid Trafficking
2
1
3
4

7. Procedure for pure ALOHA protocol

8. Vulnerable time for pure ALOHA protocol

9. Frames in a slotted ALOHA network

10. Vulnerable time for slotted ALOHA protocol

11. Space/time model of the collision in CSMA

12. Vulnerable time in CSMA

13. Behavior of three
persistence methods

14. Flow diagram for three
persistence methods

15. Collision of the first bit in CSMA/CD

16. Collision and abortion in CSMA/CD

17. Flow diagram for the
CSMA/CD

18. Energy level during transmission, idleness, or
collision

19. Timing in CSMA/CA

20. Note InCSMA/CA,ifthestation
findsthechannelbusy,it
doesnotrestartthetimer
ofthecontentionwindow;
itstopsthetimerand
restartsitwhenthe
channelbecomesidle.InCSMA/CA,the
IFScanalsobe
usedtodefinethe
priorityofa
stationoraframe.

21. Flow diagram for CSMA/CA

22. Controlled Access

23. Controlled Access
Incontrolledaccess,thestations
consultoneanothertofindwhich
stationhastherighttosend.Astation
cannotsendunlessithasbeen
authorizedbyotherstations.We
discussthreepopularcontrolled-
accessmethods.
1.Reservation
2.Polling
3.Token Passing

24. Reservation access method

25. Select and poll functions in polling access method

26. Logical ring and physical topology in token-passing
access method

27. Channelization

28. Channelization
Channelizationisamultiple-
accessmethodinwhichthe
availablebandwidthofalink
issharedintime,frequency,
orthroughcode,between
differentstations.Inthis
section,wediscussthree
channelizationprotocols.
1.Frequency-Division Multiple Access (FDMA)
2.Time-Division Multiple Access (TDMA)
3.Code-Division Multiple Access (CDMA)

29. FDMA
In FDMA, the
available
bandwidth
of the common
channel is divided
into bands that
are separated by
guard bands.

30. TDMA
In TDMA, the
bandwidth is just one
channel that is
timeshared between
different stations.

31. CDMA
In CDMA, one
channel carries
all transmissions
simultaneously.
Simple idea of communication with code

32. Chip sequences

33. Data representation in CDMA

34. Sharing channel in CDMA

35. Digital signal created by four stations in CDMA

36. Decoding of the composite signal for one in CDMA

37. General rule and
examples of creating
Walsh tables
The number of
sequences in a
Walsh table needs to
be N = 2
m
.

38. Reference
Author:Behrouz A. Forouzan
Publication:· Book
Data Communications and Networking (McGraw-Hill ForouzanNetworking)
McGraw-Hill Higher Education ©2007
ISBN:0072967757

39. Wired LANs: Ethernet

40. IEEE STANDARDS
In1985,theComputerSocietyofthe
IEEEstartedaproject,calledProject
802,tosetstandardstoenable
intercommunicationamongequipment
fromavarietyofmanufacturers.Project
802isawayofspecifyingfunctionsof
thephysicallayerandthedatalinklayer
ofmajorLANprotocols.
1.Data Link Layer
2.Physical Layer

41. STANDARD ETHERNET
TheoriginalEthernetwascreatedin1976atXerox’sPalo
AltoResearchCentre(PARC).Sincethen,ithasgone
throughfourgenerations.Webrieflydiscussthe
Standard(ortraditional)Ethernetinthissection.
1.MAC Sublayer
2.Physical Layer

42. Ethernet evolution through four generations

43. 802.3 MAC frame

44. Minimum and maximum lengths
Frame length:
Minimum: 64 bytes (512 bits)
Maximum: 1518 bytes (12,144 bits)

45. Example of an Ethernet address in
hexadecimal notation

46. Unicast and multicast addresses

47. Note
The least significant bit of the
first byte
defines the type of address.
If the bit is 0, the address is
unicast;
otherwise, it is multicast.
The broadcast
destination address is a
special case of the
multicast address in
which all bits are 1s.

48. Categories of Standard Ethernet

49. Encoding in a Standard Ethernet implementation

50. 10Base5 implementation

51. 10Base2 implementation

52. 10Base-T implementation

53. 10Base-F implementation

54. Summary of Standard Ethernet
implementations

55. CHANGES IN THE STANDARD

56. CHANGES IN THE STANDARD
The10-MbpsStandardEthernethas
gonethroughseveralchangesbefore
movingtothehigherdatarates.These
changesactuallyopenedtheroadtothe
evolutionoftheEthernettobecome
compatiblewithotherhigh-data-rate
LANs.
1.Bridged Ethernet
2.Switched Ethernet
3.Full-Duplex Ethernet

57. Sharing bandwidth

58. A network with and without a bridge

59. Collision domains in an unbridged network
and a bridged network

60. Switched Ethernet

61. Full-duplex switched Ethernet

62. AsK
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