COMPUTER COMMUNICATION NETWORKS
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Module-2
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CO-Identify the Media Access Control and Evolution of Ethernet
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
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2.1 RANDOM ACCESS
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
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2.1.1 ALOHA
Pure ALOHA
Frames in a pure ALOHA network
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2.1.1 ALOHA
Pure ALOHA
Procedure for pure ALOHA protocol
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2.1.1 ALOHA
Pure ALOHA
Vulnerable time for pure ALOHA protocol
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2.1.1 ALOHA
Slotted ALOHA
Frames in a slotted ALOHA network
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2.1.1 ALOHA
Slotted ALOHA
Vulnerable time for slotted ALOHA protocol
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2.1.1 ALOHA
Throughput
Where
G the average number of frames generated by the system during one frame transmission time.
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2.1.2 CSMA
Space/time model of the collision in CSMA
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2.1.2 CSMA
Vulnerable time in CSMA
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2.1.2 CSMA
Behaviour of three persistence methods
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2.1.2 CSMA
Flow diagram for three persistence methods
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2.1.3 CSMS/CD
Collision of the first bit in CSMA/CD
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2.1.3 CSMS/CD
Collision and abortion in CSMA/CD
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2.1.3 CSMS/CD
Flow diagram for the CSMA/CD
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2.1.3 CSMS/CA
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2.1.3 CSMS/CA
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
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2.1.3 CSMS/CA
CSMA/CA and NAV
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2.2 CONTROLLED ACCESS
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
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2.2.1 Reservation
Reservation access method
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2.2.2 Polling
Select and poll functions in polling-access method
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2.2.3 Token Passing
Logical ring and physical topology in token-passing access method
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2.3 ETHERNET PROTOCOL
2.3.1 IEEE Project 802
IEEE standard for LANs
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2.3.2 Ethernet Evolution
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2.4 STANDARD ETHERNET
2.4.1 Characteristics
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2.4.2 Addressing
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
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2.4.2 Addressing
Implementation of standard Ethernet
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2.4.3 Access Method
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.
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2.4.4 Implementation
Encoding in a Standard Ethernet implementation
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2.4.4 Implementation
10Base5 implementation
10Base2 implementation
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2.4.4 Implementation
10Base-T implementation
10Base-F implementation
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Changes in the Standard
Bridged Ethernetn
Switched Ethernet
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2.5FAST ETHERNET (100 MBPS)
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.
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2.5.1Access Method
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.
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2.5.2 Physical Layer
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2.5 GIGABIT ETHERNET
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.
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2.5 GIGABIT ETHERNET
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
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2.5 GIGABIT ETHERNET
2.5.2 Physical Layer
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2.6 - 10GIGABIT ETHERNET
2.6.1 Implementation
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Assignment-2
Problems on CSMA/CA, CSMA/CD