1. Underlying Technologies4
Underlying Technologies
Tutun Juhana
Telecommunication Engineering
School of Electrical Engineering & Informatics
Institut Teknologi Bandung
Computer Networks

2. 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 a campus
Most LANs today are also linked to a wide area network (WAN) or the Internet

4. Token Ring
ATM LAN
Token Bus
FDDI
Fiber Distributed Data Interface
Ethernet is the Winner!
IEEE Standard Project 802, designed to regulate the manufacturing and interconnectivity between different LANs

5. IEEE Standards
Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols

6. The Ethernet
Robert Melancton "Bob" Metcalfe (born April 7,1946) is an electrical engineer from the United States who co-invented Ethernet

7. 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. 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:
To reduce the size of the buffer (memory was very expensive when Ethernet was designed)
It prevents one station from monopolizing the shared medium

9. 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. Ethernet Address
The address normally is referred to as the data link address, physical address, or MAC address

11. Example:
OUI for Dell
00-04-DC for Nortel
for Cisco
00-30-BD for Belkin

12. 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. 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. 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

16. Ethernet Evolution

17. Standard Ethernet

18. Access Method: CSMA/CD
The IEEE standard defines carrier sense multiple access with collision detection (CSMA/CD) as the access method for traditional Ethernet

19. 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 bus topology
Physical star, logically 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

20. 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

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 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. 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 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. The worst collision on a shared bus
Minimum Frame Size
The worst collision on a shared bus

27. 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?

29. CSMA/CD flow diagram
The station transmits and receives continuously and simultaneously (using two different ports)

30. Implementation

31. Fast Ethernet

32. 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:
Upgrade the data rate to 100 Mbps
Make it compatible with Standard Ethernet
Keep the same 48-bit address.
Keep the same frame format.
Keep the same minimum and maximum frame lengths

33. 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. 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. Implementation

36. UTP Colour code

38. Gigabit Ethernet

39. Gigabit Ethernet (IEEE 802.3z) The goals of the Gigabit Ethernet:
Upgrade the data rate to 1 Gbps
Make it compatible with Standard or Fast Ethernet
Use the same 48-bit address
Use the same frame format
Keep the same minimum and maximum frame lengths.
To support autonegotiation as defined in Fast Ethernet

40. 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
Half-duplex
Full-duplex
Almost all implementations of Gigabit Ethernet follow the full-duplex approach

41. 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

42. 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:
Traditional
Carrier extension
Frame bursting

43. 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

44. 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
Frame
RRRRRRRRRRRRR
Carrier Extension
512 bytes

45. Carrier Extension is very inefficient if we have a series of short frames to send (each frame carries redundant data)

46. 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
Frame
Extension
Frame
Frame
Frame
512 bytes
Frame burst
Maximum frame burst is 8192 bytes

47. Gigabit Ethernet Implementation

48. Ten-Gigabit Ethernet

49. Ten-Gigabit Ethernet standard : IEEE802.3ae The goals :
Upgrade the data rate to 10 Gbps.
Make it compatible with Standard, Fast, and Gigabit Ethernet.
Use the same 48-bit address.
Use the same frame format.
Keep the same minimum and maximum frame lengths.
Allow the interconnection of existing LANs into a metropolitan area network (MAN) or a wide area network (WAN)
Make Ethernet compatible with technologies such as Frame Relay and ATM.

50. Implementation
Ten-Gigabit Ethernet operates only in full duplex mode  no need for contention  CSMA/CD is not used

51. Wireless LANs

52. Topics Discussed in the Section
IEEE
MAC Sublayer
Addressing Mechanism
Bluetooth

53. Basic service sets (BSSs)

54. Extended service sets (ESSs)

55. CSMA/CA flow diagram

56. CSMA/CA and NAV
2CTS

57. Hidden station problem

58. Note
The CTS frame in CSMA/CA handshake can prevent collision from a hidden station.

59. Use of handshaking to prevent hidden station problem

60. Exposed station problem

61. Use of handshaking in exposed station problem

62. Piconet

63. Scatternet

64. POINT-TO-POINT WANs

65. 65K Modems DSL Technology Cable Modem T Lines/E lines SONET/SDH PPP
Topics Discussed in the Section
65K Modems
DSL Technology
Cable Modem
T Lines/E lines
SONET/SDH
PPP

66. 56K modem

67. Note
ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

68. Bandwidth division

69. ADSL and DSLAM

70. Cable Modem

71. Cable modem configuration

72. T1/E1 Carrier System

73. SONET/SDH

74. PPP (point-to-point protocol)

75. Switched WANs

76. Topics Discussed in the Section
X.25
Frame Relay
ATM

77. X.25
Speed is about 64 kbps

78. Frame Relay
Speed 56Kbps to 1.544Mbps

79. ATM (Asynchronous Transfer Mode)
Note
A cell network uses the cell as the basic unit of data exchange.
A cell is defined as a small, fixed-size block of information.

80. ATM multiplexing

81. Architecture of an ATM network

82. Virtual circuit

83. Note
A virtual connection is defined by a pair of numbers: the VPI and the VCI.

84. ATM layers

85. Use of the layers

86. The IP protocol uses the AAL5 sublayer.
Note
The IP protocol uses the AAL5 sublayer.

87. CONNECTING DEVICES

88. Topics Discussed in the Section
Repeaters
Bridges
Routers

89. Connecting devices

90. Repeater or hub

91. A repeater forwards every bit; it has no filtering capability.
Note
A repeater forwards every bit; it has no filtering capability.

92. A bridge has a table used in filtering decisions.
Note
A bridge has a table used in filtering decisions.

93. A bridge does not change the physical (MAC) addresses in a frame.
Note
A bridge does not change the physical (MAC) addresses in a frame.

94. Bridge

95. Learning bridge M M M M

96. A router is a three-layer (physical, data link, and network) device.
Note
A router is a three-layer (physical, data link, and network) device.

97. A repeater or a bridge connects segments of a LAN.
Note
A repeater or a bridge connects segments of a LAN.
A router connects independent LANs or WANs to create an internetwork (internet).

98. Routing example

99. A router changes the physical addresses in a packet.
Note
A router changes the physical addresses in a packet.