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Underlying Technologies 
ET3003 Computer Networks 
4 
Tutun Juhana 
Telecommunication Engineering 
School of Electrical En...
Two types of networks 
at the data link layer 
– Broadcast Networks: All stations share a single 
communication channel 
–...
WIRED LOCAL AREA NETWORKS 
3
• A local area network (LAN) is a computer 
network that is designed for a limited 
geographic area such as a building or ...
FDDI 
Fiber Distributed Data Interface 
Token Ring 
Token Bus 
ATM LAN 
IEEE Standard Project 802, designed to 
regulate t...
IEEE Standards 
• Project 802 is a way of specifying 
functions of the physical layer and the data 
link layer of major LA...
The Ethernet 
• Robert Melancton 
"Bob" Metcalfe 
(born April 7,1946) 
is an electrical 
engineer from the 
United States ...
Frame Format 
‘Length” used by 
IEEE standard to 
define the number of 
bytes in the data field 
“Type” used by 
original ...
Frame Length 
• The minimum length restriction is required for the correct operation of CSMA/CD 
• If the upper-layer pack...
Addressing 
• Each station on an Ethernet network has its own 
network interface card (NIC) 
• The NIC provides the statio...
• Ethernet Address 
– The address normally is referred to as the 
data link address, physical address, or MAC 
address 
11
12 
Example: 
• 00-14-22 OUI for Dell 
• 00-04-DC for Nortel 
• 00-40-96 for Cisco 
• 00-30-BD for Belkin
• The address is sent left-to-right, byte by byte 
• For each byte, it is sent right-to-left, bit by bit 
• Example 
– Sho...
Unicast, Multicast, and Broadcast Addresses 
• A source address is always a unicast 
address 
– the frame comes from only ...
• The broadcast address is a special case of 
the multicast address; the recipients are all 
the stations on the LAN 
15
• Define the type of the following destination 
addresses 
– 4A:30:10:21:10:1A 
– 47:20:1B:2E:08:EE 
– FF:FF:FF:FF:FF:FF 
...
Ethernet Evolution 
17
STANDARD ETHERNET 
18
Access Method: CSMA/CD 
• The IEEE 802.3 standard defines carrier 
sense multiple access with collision 
detection (CSMA/C...
• Stations on a traditional Ethernet can be 
connected together using a physical bus or star 
topology, but the logical to...
• How can we be 
sure that two 
stations are not 
using the medium at 
the same time? 
• If they do, their 
frames will co...
22
• To minimize the chance of collision and, 
therefore, increase the performance, the 
CSMA method was developed 
23
• Carrier sense multiple access (CSMA) 
requires that each station first listen to the 
medium (or check the state of the ...
Space/time model of a collision in CSMA 
25
Collision of the first bit in CSMA/CD 
• A transmits for the duration t4 - t1; C transmits for the duration t3 - t2 
 for...
Minimum Frame Size 
27 
The worst collision on a shared bus 
http://cnp3book.info.ucl.ac.be/lan/lan/
• The frame transmission time Tfr must be at 
least two times the maximum propagation 
time Tp 
28
• Example 
– In the standard Ethernet, if the maximum 
propagation time is 25.6 μs, what is the 
minimum size of the frame...
CSMA/CD flow diagram 
The station transmits 
and receives 
continuously and 
simultaneously 
(using two different 
ports) ...
Implementation 
31
FAST ETHERNET 
32
• IEEE created Fast Ethernet under the name 802.3u 
• Fast Ethernet is backward-compatible with Standard 
Ethernet, but 10...
MAC Sublayer 
• Keep only the star topology 
– There are two choices: half duplex and full duplex 
– In the half-duplex ap...
Autonegotiation 
• Autonegotiation allows two 
devices to negotiate the mode 
or data rate of operation 
• It was designed...
Implementation 
36
GIGABIT ETHERNET 
37
• Gigabit Ethernet (IEEE 802.3z) 
• The goals of the Gigabit Ethernet: 
1. Upgrade the data rate to 1 Gbps 
2. Make it com...
MAC Sublayer 
• A main consideration: keep the MAC 
sublayer untouched  To achieve a data 
rate of 1 Gbps, this was no lo...
Full-Duplex Mode 
• There is a central switch connected to all 
computers or other switches 
– Each switch has buffers for...
Half-Duplex Mode 
• A switch can be replaced by a hub  a 
collision might occur  CSMA/CD is used 
 the maximum length o...
• Traditional approach 
– Keep the minimum frame length 512 bits 
– The maximum network length only 25 m 
(because the len...
• Carrier Extension 
– Increase the minimum frame length  512 bytes (4096 bits)  
8 times longer 
– It forces a station ...
Carrier Extension is very inefficient if we 
have a series of short frames to send (each 
frame carries redundant data) 
4...
• Frame Bursting 
– To improve efficiency, frame bursting was proposed 
– Instead of adding an extension to each frame, 
m...
Gigabit Ethernet Implementation 
46
TEN-GIGABIT ETHERNET 
47
• Ten-Gigabit Ethernet standard : IEEE802.3ae 
• The goals : 
1. Upgrade the data rate to 10 Gbps. 
2. Make it compatible ...
Implementation 
• Ten-Gigabit Ethernet operates only in full 
duplex mode  no need for contention  
CSMA/CD is not used ...
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Underlying Technologies Part I (Lecture #4 ET3003 Sem1 2014/2015)

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Underlying Technologies Part I (Lecture #4 ET3003 Sem1 2014/2015)

  1. 1. Underlying Technologies ET3003 Computer Networks 4 Tutun Juhana Telecommunication Engineering School of Electrical Engineering & Informatics Institut Teknologi Bandung
  2. 2. Two types of networks at the data link layer – Broadcast Networks: All stations share a single communication channel – Point-to-Point Networks: Pairs of hosts (or routers) are directly connected 2 Broadcast Network Point-to-Point Network • Typically, local area networks (LANs) are broadcast and wide area networks (WANs) are point-to-point
  3. 3. WIRED LOCAL AREA NETWORKS 3
  4. 4. • A local area network (LAN) is a computer network that is designed for a limited geographic area such as a building or a campus • Most LANs today are also linked to a wide area network (WAN) or the Internet 4
  5. 5. FDDI Fiber Distributed Data Interface Token Ring Token Bus ATM LAN IEEE Standard Project 802, designed to regulate the manufacturing and interconnectivity between different LANs 5
  6. 6. IEEE Standards • Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols 6
  7. 7. The Ethernet • Robert Melancton "Bob" Metcalfe (born April 7,1946) is an electrical engineer from the United States who co-invented Ethernet 7
  8. 8. Frame Format ‘Length” used by IEEE standard to define the number of bytes in the data field “Type” used by original Ethernet to define upper-layer protocol using the frame 8
  9. 9. Frame Length • The minimum length restriction is required for the correct operation of CSMA/CD • If the upper-layer packet is less than 46 bytes, padding is added to make up the difference Reason for the maximum length restriction: 1. To reduce the size of the buffer (memory was very expensive when Ethernet was designed) 2. It prevents one station from monopolizing the shared medium 9
  10. 10. Addressing • Each station on an Ethernet network has its own network interface card (NIC) • The NIC provides the station with a 6-byte physical address 10
  11. 11. • Ethernet Address – The address normally is referred to as the data link address, physical address, or MAC address 11
  12. 12. 12 Example: • 00-14-22 OUI for Dell • 00-04-DC for Nortel • 00-40-96 for Cisco • 00-30-BD for Belkin
  13. 13. • The address is sent left-to-right, byte by byte • For each byte, it is sent right-to-left, bit by bit • Example – Show how the address 47:20:1B:2E:08:EE is sent out on line 13
  14. 14. Unicast, Multicast, and Broadcast Addresses • A source address is always a unicast address – the frame comes from only one station • The destination address can be unicast, multicast, or broadcast 14
  15. 15. • The broadcast address is a special case of the multicast address; the recipients are all the stations on the LAN 15
  16. 16. • Define the type of the following destination addresses – 4A:30:10:21:10:1A – 47:20:1B:2E:08:EE – FF:FF:FF:FF:FF:FF 16
  17. 17. Ethernet Evolution 17
  18. 18. STANDARD ETHERNET 18
  19. 19. Access Method: CSMA/CD • The IEEE 802.3 standard defines carrier sense multiple access with collision detection (CSMA/CD) as the access method for traditional Ethernet 19
  20. 20. • Stations on a traditional Ethernet can be connected together using a physical bus or star topology, but the logical topology is always a bus Physical star, logically bus topology 20 Physical bus topology • The medium (channel) is shared between stations and only one station at a time can use it • All stations receive a frame sent by a station (broadcasting) • The real destination keeps the frame while the rest drop it
  21. 21. • How can we be sure that two stations are not using the medium at the same time? • If they do, their frames will collide with each other 21
  22. 22. 22
  23. 23. • To minimize the chance of collision and, therefore, increase the performance, the CSMA method was developed 23
  24. 24. • Carrier sense multiple access (CSMA) requires that each station first listen to the medium (or check the state of the medium) before sending – sense before transmit, or – listen before talk • CSMA can reduce the possibility of collision, but it cannot eliminate it – The possibility of collision still exists because of propagation delay 24
  25. 25. Space/time model of a collision in CSMA 25
  26. 26. Collision of the first bit in CSMA/CD • A transmits for the duration t4 - t1; C transmits for the duration t3 - t2  for the protocol to work, the length of any frame divided by the bit rate in this protocol must be more than either of these durations • Before sending the last bit of the frame, the sending station must detect a collision, if any, and abort the transmission  because, once the entire frame is sent, station does not keep a copy of the frame and does not monitor the line for collision detection 26
  27. 27. Minimum Frame Size 27 The worst collision on a shared bus http://cnp3book.info.ucl.ac.be/lan/lan/
  28. 28. • The frame transmission time Tfr must be at least two times the maximum propagation time Tp 28
  29. 29. • Example – In the standard Ethernet, if the maximum propagation time is 25.6 μs, what is the minimum size of the frame? 29
  30. 30. CSMA/CD flow diagram The station transmits and receives continuously and simultaneously (using two different ports) 30
  31. 31. Implementation 31
  32. 32. FAST ETHERNET 32
  33. 33. • IEEE created Fast Ethernet under the name 802.3u • Fast Ethernet is backward-compatible with Standard Ethernet, but 10 times faster (100 Mbps) • The goals of Fast Ethernet: 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. 5. Keep the same minimum and maximum frame lengths 33
  34. 34. MAC Sublayer • Keep only the star topology – There are two choices: half duplex and full duplex – In the half-duplex approach, the stations are connected via a hub – in the full-duplex approach, the connection is made via a switch with buffers at each port • The access method is the same (CSMA/CD) for the half-duplex approach • For full-duplex there is no need for CSMA/CD – The implementations keep CSMA/CD for backward compatibility with Standard Ethernet 34
  35. 35. Autonegotiation • Autonegotiation allows two devices to negotiate the mode or data rate of operation • It was designed particularly for the following purposes: – To allow incompatible devices to connect to one another – To allow one device to have multiple capabilities – To allow a station to check a hub’s capabilities. 35
  36. 36. Implementation 36
  37. 37. GIGABIT ETHERNET 37
  38. 38. • Gigabit Ethernet (IEEE 802.3z) • The goals of the 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. To support autonegotiation as defined in Fast Ethernet 38
  39. 39. MAC Sublayer • A main consideration: keep the MAC sublayer untouched  To achieve a data rate of 1 Gbps, this was no longer possible • Gigabit Ethernet has two distinctive approaches for medium access 1. Half-duplex 2. Full-duplex • Almost all implementations of Gigabit Ethernet follow the full-duplex approach 39
  40. 40. Full-Duplex Mode • There is a central switch connected to all computers or other switches – Each switch has buffers for each input port in which data are stored until they are transmitted • There is no collision in this mode  CSMA/CD is not used • The maximum length of the cable is determined by the signal attenuation in the cable, not by the collision detection process 40
  41. 41. Half-Duplex Mode • A switch can be replaced by a hub  a collision might occur  CSMA/CD is used  the maximum length of the network is totally dependent on the minimum frame size • Three solutions have been defined: 1. Traditional 2. Carrier extension 3. Frame bursting 41
  42. 42. • Traditional approach – Keep the minimum frame length 512 bits – The maximum network length only 25 m (because the length of a bit is 1/100 shorter than in standard Ethernet) • It may not even be long enough to connect the computers in one single office 42
  43. 43. • Carrier Extension – Increase the minimum frame length  512 bytes (4096 bits)  8 times longer – It forces a station to add extension bits (padding) to any frame that is less than 4096 bits – The maximum length of the network can be increased 8 times to a length of 200 m – This allows a length of 100 m from the hub to the station 43 Frame RRRRRRRRRRRRR Carrier Extension 512 bytes
  44. 44. Carrier Extension is very inefficient if we have a series of short frames to send (each frame carries redundant data) 44
  45. 45. • Frame Bursting – To improve efficiency, frame bursting was proposed – Instead of adding an extension to each frame, multiple frames are sent • To make these multiple frames look like one frame, padding is added between the frames (96 bits) so that the channel is not idle  The method deceives other stations into thinking that a very large frame has been transmitted 45 Frame Extension Frame Frame Frame 512 bytes Frame burst Maximum frame burst is 8192 bytes
  46. 46. Gigabit Ethernet Implementation 46
  47. 47. TEN-GIGABIT ETHERNET 47
  48. 48. • Ten-Gigabit Ethernet standard : IEEE802.3ae • The goals : 1. Upgrade the data rate to 10 Gbps. 2. Make it compatible with Standard, Fast, and Gigabit Ethernet. 3. Use the same 48-bit address. 4. Use the same frame format. 5. Keep the same minimum and maximum frame lengths. 6. Allow the interconnection of existing LANs into a metropolitan area network (MAN) or a wide area network (WAN) 7. Make Ethernet compatible with technologies such as Frame Relay and ATM. 48
  49. 49. Implementation • Ten-Gigabit Ethernet operates only in full duplex mode  no need for contention  CSMA/CD is not used 49

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