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Ethernet Frame Format                        1
Objectives• Ethernet characteristics• Ethernet Frame Format                   9EC606A.35   2
Ethernet• Trade mark of Xerox Corporation• Invented at Xerox PARC in 1976• Standardised by IEEE in 1978• Popular for LAN• ...
Ethernet• Xerox PARC  • CSMA / CD  • 2.94 Mbps  • No length field in Packet Header• IEEE  • 1 – Persistent CSMA / CD  • 1 ...
Ethernet• Ether refers to the ‘Cable’. Its variants are       • 10 base 5       • 10 base 2       • 10 base T       • 10 b...
10 Base 5 – Called Thick Ethernet4• Resembles yellow garden hose• Marking for every 2.5 meters• Connections are made using...
10 Base 2 – Called Thin Ethernet• Bends easily• Connections can be made using BNC to for  T-junction• Can run over 100 met...
10 Base T – Twisted Pair• Easy maintenance• Can run over 100 meters• Can handle 1024 machines                             8
10 Base F – Fibre Optics• Best choice of using between two buildings or  widely separated Hubs• Run over 2000 meters• Can ...
ETHERNET CONNECTIONS      Fig.1                       10
Encoding• Is a way to determine the start, end, or middle of each bit• There are two approaches       • Manchester encodin...
Manchester Encoding• Each bit period is divided into two equal intervals• Binary 1 is sent by having the voltage set high ...
Differential Manchester Encoding• A binary 1 is indicated by the absence of a transition at  the start of the interval• A ...
IEEE 802.3 Frame Format                          14
Preamble• Length of the field is 7 bytes.• Each byte contain the bit pattern of 10101010.• Manchester encoding produces a ...
IEEE 802.3 Frame FormatPreamble   SFD    D Address   S Address•   Start of Frame delimiter          – Contains 10101011 to...
IEEE 802.3 Frame FormatPreamble     SFD   D Address   S Address   Length  Length           – Tells how many bytes are pres...
IEEE 802.3 Frame FormatPreamble   SFD   D Address   S Address   Length   Data   Pad   Checksum     • Pad field          If...
IEEE 802.3 Ethernet LANsWhen a computer wants to receive a frame it   • Listens to all frames traveling on the cable   • I...
SummaryIn this class, you have learnt about    • Different types of Ethernet cables    • Encoding    • All the fields of F...
Summary• Unicast a frame from one computer to any other  computer connected to the same cable• Broadcast a frame from one ...
Quiz1. In Ethernet the valid frame size is     (a) 64 bytes     (b) 16 bytes     (c) 46 bytes     (d) 32 bytes            ...
Quiz2. A frame containing all 1’s in the destination field  is for      (a) Unicasting      (b) Broadcasting      (c) Mult...
Frequently Asked Questions1. Explain Ethernet frame format?2. List the various types of Ethernet cables                   ...
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Ethernet frame format

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Ethernet frame format

  1. 1. Ethernet Frame Format 1
  2. 2. Objectives• Ethernet characteristics• Ethernet Frame Format 9EC606A.35 2
  3. 3. Ethernet• Trade mark of Xerox Corporation• Invented at Xerox PARC in 1976• Standardised by IEEE in 1978• Popular for LAN• Uses Packet Switching Technology 3
  4. 4. Ethernet• Xerox PARC • CSMA / CD • 2.94 Mbps • No length field in Packet Header• IEEE • 1 – Persistent CSMA / CD • 1 – 10 Mbps • Length field in Packet Header 4
  5. 5. Ethernet• Ether refers to the ‘Cable’. Its variants are • 10 base 5 • 10 base 2 • 10 base T • 10 base F 5
  6. 6. 10 Base 5 – Called Thick Ethernet4• Resembles yellow garden hose• Marking for every 2.5 meters• Connections are made using vampire taps• Can run for 500 meters• Can handle 100 machines 6
  7. 7. 10 Base 2 – Called Thin Ethernet• Bends easily• Connections can be made using BNC to for T-junction• Can run over 100 meters• Can handle 30 machines• Cheaper and Easier to install 9EC606A.35 7
  8. 8. 10 Base T – Twisted Pair• Easy maintenance• Can run over 100 meters• Can handle 1024 machines 8
  9. 9. 10 Base F – Fibre Optics• Best choice of using between two buildings or widely separated Hubs• Run over 2000 meters• Can handle 1024 machines• Excellent Noise Immunity• More Expensive 9
  10. 10. ETHERNET CONNECTIONS Fig.1 10
  11. 11. Encoding• Is a way to determine the start, end, or middle of each bit• There are two approaches • Manchester encoding • Differential Manchester encoding 11
  12. 12. Manchester Encoding• Each bit period is divided into two equal intervals• Binary 1 is sent by having the voltage set high during the first interval & low in the second interval• Binary 0 is just reverse Disadvantage – Requires twice the Band width than straight binary encoding 12
  13. 13. Differential Manchester Encoding• A binary 1 is indicated by the absence of a transition at the start of the interval• A binary 0 is indicated by the presence of transition at the start of the interval• Advantage – Better noise immunity• Disadvantage – Requires more complex equipment 13
  14. 14. IEEE 802.3 Frame Format 14
  15. 15. Preamble• Length of the field is 7 bytes.• Each byte contain the bit pattern of 10101010.• Manchester encoding produces a square wave for this bit pattern with.• Frequency of 10 MHz.• Time period of 5.6 µsec. 15
  16. 16. IEEE 802.3 Frame FormatPreamble SFD D Address S Address• Start of Frame delimiter – Contains 10101011 to indicate the start of Frame• Source Address – Contains either 2 bytes or 6 bytes• Destination Address – Contains either 2 bytes or 6 bytes – For ordinary addressing the higher order bit is 0 – For group addressing the higher order bit is 1 i.e Multicasting – For Broadcasting of the frame in the network all the bits are made as 1’s 16
  17. 17. IEEE 802.3 Frame FormatPreamble SFD D Address S Address Length Length – Tells how many bytes are present in the data field 0 to a maximum of 1500 – A data field of 0 bytes is legal, it causes a problem – When a computer detects a collision, it truncates the current frame which means that corrupted frames appear on the cable all the time – To make it easier to distinguish valid frames from corrupted frames (due to collisions), 802.3 states that valid frames to be at least 64 bytes long from destination address to checksum 17
  18. 18. IEEE 802.3 Frame FormatPreamble SFD D Address S Address Length Data Pad Checksum • Pad field If the data portion is less than 46 bytes, the pad field is used to fill out the frame to the minimum size of 64 bytes • Checksum The Checksum is used to detect if any data bits have been corrupted during transmission 18
  19. 19. IEEE 802.3 Ethernet LANsWhen a computer wants to receive a frame it • Listens to all frames traveling on the cable • If the frame address is the same as the computer’s address or the same as the group address of the computers of which it is a member, it copies the frame from the cable • Otherwise it just ignores the frame 19
  20. 20. SummaryIn this class, you have learnt about • Different types of Ethernet cables • Encoding • All the fields of Frame Format 20
  21. 21. Summary• Unicast a frame from one computer to any other computer connected to the same cable• Broadcast a frame from one computer to all other computers connected to the same cable• Multicast a frame from one computer to a subset of the computers connected to the same cable 21
  22. 22. Quiz1. In Ethernet the valid frame size is (a) 64 bytes (b) 16 bytes (c) 46 bytes (d) 32 bytes 22
  23. 23. Quiz2. A frame containing all 1’s in the destination field is for (a) Unicasting (b) Broadcasting (c) Multicasting 23
  24. 24. Frequently Asked Questions1. Explain Ethernet frame format?2. List the various types of Ethernet cables 24

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