This document discusses media access control and the evolution of Ethernet. It covers random access methods like ALOHA, CSMA, CSMA/CD, and CSMA/CA. It also discusses controlled access methods like reservation, polling, and token passing. The document then covers the evolution of Ethernet including standard Ethernet, Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet. It describes aspects like their addressing, access methods, frame formats, and physical layers.

1. COMPUTER COMMUNICATION
NETWORKS
Module-2
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2. CO-Identify the Media Access Control and Evolution of Ethernet
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Module-2
Media Access Control: Random Access: ALOHA, CSMA, CSMA/CD, CSMA/CA. Controlled
Access: Reservation, Polling, Token Passing.
Wired LANs: Ethernet: Ethernet Protocol: IEEE802, Ethernet Evolution, Standard Ethernet:
Characteristics, Addressing, Access Method, Efficiency, Implementation, Fast Ethernet: Access
Method, Physical Layer, Gigabit Ethernet: MAC Sublayer, Physical Layer, 10 Gigabit Ethernet.
Total lecture hours- 10

3. 2.1 RANDOM ACCESS
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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.
ALOHA
Carrier Sense Multiple Access
Carrier Sense Multiple Access with Collision Detection
Carrier Sense Multiple Access with Collision Avoidance

4. 2.1.1 ALOHA
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Pure ALOHA
Frames in a pure ALOHA network

5. 2.1.1 ALOHA
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Pure ALOHA
Procedure for pure ALOHA protocol

6. 2.1.1 ALOHA
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Pure ALOHA
Vulnerable time for pure ALOHA protocol

7. 2.1.1 ALOHA
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Slotted ALOHA
Frames in a slotted ALOHA network

8. 2.1.1 ALOHA
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Slotted ALOHA
Vulnerable time for slotted ALOHA protocol

9. 2.1.1 ALOHA
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Throughput
Where
G the average number of frames generated by the system during one
frame transmission time.

10. 2.1.2 CSMA
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Space/time model of the collision in CSMA

11. 2.1.2 CSMA
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Vulnerable time in CSMA

12. 2.1.2 CSMA
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Behaviour of three persistence methods

13. 2.1.2 CSMA
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14. 2.1.3 CSMS/CD
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Collision of the first bit in CSMA/CD

15. 2.1.3 CSMS/CD
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Collision and abortion in CSMA/CD

16. 2.1.3 CSMS/CD
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Flow diagram for the CSMA/CD

17. 2.1.3 CSMS/CA
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18. 2.1.3 CSMS/CA
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In CSMA/CA, the IFS can also be used to define the priority of a station or a frame.
In CSMA/CA, if the station finds the channel busy, it does not restart the timer
of the contention window;
it stops the timer and restarts it when the channel becomes idle.
Collision and abortion in CSMA/CD

19. 2.1.3 CSMS/CA
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CSMA/CA and NAV

20. 2.2 CONTROLLED ACCESS
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In controlled access, the stations consult one another to find which station has
the right to send. A station cannot send unless it has been authorized by other
stations. We discuss three popular controlled-access methods.
Reservation
Polling
Token Passing

21. 2.2.1 Reservation
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Reservation access method

22. 2.2.2 Polling
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Select and poll functions in polling-access method

23. 2.2.3 Token Passing
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Logical ring and physical topology in token-passing access method

24. 2.3 ETHERNET PROTOCOL
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2.3.1 IEEE Project 802
IEEE standard for LANs

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2.3.2 Ethernet Evolution

26. 2.4 STANDARD ETHERNET
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2.4.1 Characteristics
•Connectionless and Unreliable Service
•Frame format

27. 2.4.2 Addressing
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Each station on an Ethernet network (such as a PC, workstation, or printer) has its own
network interface card (NIC). The NIC fits inside the station and provides the
station with a link-layer address. The Ethernet address is 6 bytes (48 bits), normally
written in hexadecimal notation, with a colon between the bytes.
For example, the following shows an Ethernet MAC address:
4A:30:10:21:10:1A

28. 2.4.2 Addressing
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Implementation of standard Ethernet

29. 2.4.3 Access Method
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The standard Ethernet chose CSMA/CD with 1-persistent method
2.4.3 Efficiency of Standard Ethernet
The efficiency of the Ethernet is defined as the ratio of the time used by a station
to send data to the time the medium is occupied by this station. The practical
efficiency of standard Ethernet has been measured to be
Efficiency 5 1 / (1 1 6.4 3 a)
Where parameter “a” is the number of frames that can fit on
the medium.

30. 2.4.4 Implementation
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Encoding in a Standard Ethernet implementation

31. 2.4.4 Implementation
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10Base5 implementation
10Base2 implementation

32. 2.4.4 Implementation
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10Base-T implementation
10Base-F implementation

33. Changes in the Standard
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Bridged Ethernetn
Switched Ethernet

34. 2.5FAST ETHERNET (100 MBPS)
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The goals of Fast Ethernet can be summarized as follows:
1. Upgrade the data rate to 100 Mbps.
2. Make it compatible with Standard Ethernet.
3. Keep the same 48-bit address.
4. Keep the same frame format.

35. 2.5.1Access Method
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Autonegotiation
❑ To allow incompatible devices to connect to one another. For example, a
device with a maximum capacity of 10 Mbps can communicate with
a device with a 100 Mbps capacity (but which can work at a lower rate).
❑ To allow one device to have multiple capabilities.
❑ To allow a station to check a hub’s capabilities.

36. 2.5.2 Physical Layer
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37. 2.5 GIGABIT ETHERNET
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1. Upgrade the data rate to 1 Gbps.
2. Make it compatible with Standard or Fast Ethernet.
3. Use the same 48-bit address.
4. Use the same frame format.
5. Keep the same minimum and maximum frame lengths.
6. Support autonegotiation as defined in Fast Ethernet.

38. 2.5 GIGABIT ETHERNET
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2.5.1 MAC Sublayer
Full-Duplex Mode
In the full-duplex mode of Gigabit Ethernet, there is no collision; the maximum
length of the cable is determined by the signal attenuation in the cable.
Half-Duplex Mode
Traditional
Carrier Extension
Frame Bursting

39. 2.5 GIGABIT ETHERNET
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2.5.2 Physical Layer

40. 2.6 - 10GIGABIT ETHERNET
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2.6.1 Implementation

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Assignment-2
Problems on CSMA/CA, CSMA/CD