Post on 08-Apr-2018
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 1/24
Lecture
09Data Communication & Networks
IEEE 802.3 (Ethernet)
Muhammad Yousaf
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 2/24
myousaf@ymail.com 2
LAN Standards:
IEEE has defined many standards for LANsInstitute of Electrical & Electronics Engineers
In the beginning of 1980s IEEE initiated the project802
Aim of this project was to develop standards foremerging LAN technologies
So that the equipment from different vendors can
work together
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 3/24
myousaf@ymail.com 3
LAN Standards: cont…
Following are some of many IEEE standardsIEEE 802.3 (Ethernet)
IEEE 802.4 (Token Bus)
IEEE 802.5 (Token Ring)
IEEE 802.11 (Wireless LAN)
IEEE 802.15 (Bluetooth)
IEEE 802.16 (WiMAX)
Most popular of these is 802.3
Base of 802.3 is CSMA/CD
Carrier Sense Multiple Access with Collision Detection
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 4/24
myousaf@ymail.com 4
Scope of LAN Technologies:
IETF = Internet Engineering Task Force IEEE = Institute of Electrical & Electronic Engineers
Physical
Data Link
IP
TCP UDP
Application
IEEE
IETF
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 5/24
myousaf@ymail.com 5
Bus/Star Configurations:
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 6/24
myousaf@ymail.com 6
Ethernet Transmission:
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 7/24
myousaf@ymail.com 7
Ethernet Card:
RJ=Registered Jack
UTP=Unshielded Twisted Pair
LED=Light Emitting Diode
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 8/24
myousaf@ymail.com 8
Media Access Control (MAC) Address:
Many levels of addressing are used in computer networksDomain Names (highest level of addressing)
IP addresses (for routing)
MAC addresses (lowest level of addressing)
MAC address is the physical Address of Network InterfaceCard (NIC)
It is 48-bit address, written in hexadecimal notation
First 24-bits are organizational identifier
Next 24-bits are network interface identifier
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 9/24
myousaf@ymail.com 9
MAC Addresses: cont…
C:\yousaf>ipconfig /all
Ethernet adapter Local Area Connection:
Media State . . . . . . . : Media disconnected
Description . . . . . . . .: Realtek RTL8139/810x Family Fast Ethernet NIC
Physical Address. . . .: 00-16-D3-03-0A-D4
Ethernet adapter Wireless Network Connection:
Media State . . . . . . . : Media disconnected
Description . . . . . . . .: Intel(R) PRO/Wireless 2200BG Network Connection
Physical Address. . . .: 00-16-6F-52-F3-8B
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 10/24
myousaf@ymail.com 10
802.3 Frame:
Header Trailer
SFD=Start Frame Delimiter MAC=Media Access Control
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 11/24
myousaf@ymail.com 11
802.3 Frame Fields:
Preamble + SFD:Used for synchronization
Start of Frame Delimiter
Destination & Source Addresses:
MAC addresses of receiver & sender
MAC = Media Access Control
Length:
Length of Frame in bytes
Type:
Type of next protocol header; e.g. ARP, IP, etc
Frame Check Sequence: (FCS)
CRC Value; used for error detection
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 12/24
myousaf@ymail.com 12
Media Access Control:
Two major types of protocols that control rights totransmit over the physical medium
Primary / Secondary Protocols:Primary station controls the access on media
Contention-Free protocolsMedia Access is simple and controlled
Peer-to-Peer Protocols:All stations have equal rights to send data
For transmission, node doesn’t need to take permissionfrom any other node
If more than one nodes try to send data simultaneously,then there will be collision
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 13/24
myousaf@ymail.com 13
CSMA/CD:
CSMA/CD is a peer-to-peer protocolAll nodes share a common transmission medium
Only one station can transmit at a time
But which station?
This is controlled by the CSMA/CD protocol
Multiple Access means this protocol is for multipoint links(shared links)
Carrier Sense means that nodes will sense the carrier(medium) before transmission
Collision Detection
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 14/24
myousaf@ymail.com 14
CSMA/CD: (look before you speak)
If some node is transmitting, it means that mediumis busy
Else medium is idle
Whenever a node needs to transmit, it senses the
medium before starting to transmit
If medium is idle then start transmitting
If medium is busy then wait
In this way we can avoid almost all collisions
Can collision still occur???
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 15/24
myousaf@ymail.com 15
CSMA/CD Transmissions:
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 16/24
myousaf@ymail.com 16
CSMA/CD: cont…
Yeah! Collision can still occur in followingconditions:
More than one nodes try to transmit at the same time
Time difference in transmitting from two nodes is less
than the propagation delay between themSo, we need a collision detection mechanism
Nodes sense the medium while transmission
In case of collision, voltage level on the medium willbe much greater than the valid voltage level
In this way, collision can easily be detected
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 17/24
myousaf@ymail.com 17
CSMA/CD: cont…
When a node detects the collision, it immediatelystops transmitting data & sends a jamming signal
Jamming signal is a short message, declaring emergencyon medium so that all nodes be aware of collision
Note: this collision happened due to the fact thatmore than one nodes were trying to transmitsimultaneously
Now competing nodes will again try to contend
We need a contention resolution mechanism
The most popular contention resolution algorithm isBinary Exponential Backoff (BEB)
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 18/24
myousaf@ymail.com 18
Transmission pattern:
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 19/24
myousaf@ymail.com 19
Binary Exponential Backoff:
Base of BEB is the contention window
Initially contending nodes randomly choose from 2-contention slots
Nodes wait for the time equal to the period of contentionslots
After this random time slot nodes again come and sense themedium and if found idle then they are allowed to transmit
If only one node picks the shortest slot then contention isresolved
Otherwise at every collision, contention window size isdoubled to 4, 8, 16, …
But there is maximum window limit e.g. 32 or 128-slots
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 20/24
myousaf@ymail.com 20
IP
TCP UDP
Application
Putting 802.3 in protocol stack:
Physical
Data Link
IEEE
IETF
Signal Tx / Rx
Data Encoding
Media Control
Data Encapsulation / Decapsulation
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 21/24
myousaf@ymail.com 21
Putting 802.3 in protocol stack: cont…
Data Encapsulation/ Decapsulation:Appends MAC header and trailer
Also appends the synchronization bits
Media Control:
Buffers the upper layer dataMakes decision according to CSMA/CD & BEB
Data Encoding:Conversion of data bits into voltage levels
Ethernet uses Manchester Encoding schemeSignal Transmission/Reception:
Transceivers actually send/receive the signals
Can also sense the medium
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 22/24
myousaf@ymail.com 22
Evolution of Ethernet:
Ethernet:10Mbps
Pioneering work done by Dr. Robert Metcalf in 1972
In 1979 Xerox, DEC & Intel formed a consortium for development ofEthernet
In 1983 IEEE standardized it
Implemented in Bus / star topology
Fast Ethernet:100Mbps
Approved by IEEE in 1995
Star topologyGigabit Ethernet:
1Gbps to 10Gbps
Standardized by IEEE in 1998
Star topology
8/6/2019 Ccnet Lec 09 Ethernet 3
http://slidepdf.com/reader/full/ccnet-lec-09-ethernet-3 23/24
myousaf@ymail.com 23
Typical Configuration of Ethernet: