4 Tutun Juhana Underlying Technologies Telecommunication Engineering School
- Slides: 99
4 Tutun Juhana Underlying Technologies Telecommunication Engineering School of Electrical Engineering & Informatics Institut Teknologi Bandung Computer Networks
WIRED LOCAL AREA NETWORKS 2
• 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 3
Token Ring FDDI ATM LAN Token Bus Fiber Distributed Data Interface IEEE Standard Project 802, designed to regulate the manufacturing and interconnectivity between different LANs 4
IEEE Standards • Project 802 is a way of specifying functions of the physical layer and the data link layer of major LAN protocols 5
The Ethernet • Robert Melancton "Bob" Metcalfe (born April 7, 1946) is an electrical engineer from the United States who co-invented Ethernet 6
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 7
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 8
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 9
• Ethernet Address – The address normally is referred to as the data link address, physical address, or MAC address 10
Example: • 00 -14 -22 OUI for Dell • 00 -04 -DC for Nortel • 00 -40 -96 for Cisco • 00 -30 -BD for Belkin 11
• The address is sent left-to-right, byte by byte • For each byte, it is sent right-to-left, bit by bit • Example – Show the address 47: 20: 1 B: 2 E: 08: EE is sent out on line 12
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 13
• The broadcast address is a special case of the multicast address; the recipients are all the stations on the LAN 14
• Define the type of the following destination addresses – 4 A: 30: 10: 21: 10: 1 A – 47: 20: 1 B: 2 E: 08: EE – FF: FF: FF: FF 15
Ethernet Evolution 16
STANDARD ETHERNET 17
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 18
• 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 19
• 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 20
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• To minimize the chance of collision and, therefore, increase the performance, the CSMA method was developed 22
• 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 23
Space/time model of a collision in CSMA 24
Collision of the first bit in CSMA/CD • A transmits for the duration t 4 - t 1; C transmits for the duration t 3 - t 2 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 25 does not monitor the line for collision detection
Minimum Frame Size The worst collision on a shared bus http: //cnp 3 book. info. ucl. ac. be/lan/ 26
• The frame transmission time Tfr must be at least two times the maximum propagation time Tp 27
• Example – In the standard Ethernet, if the maximum propagation time is 25. 6 μs, what is the minimum size of the frame? 28
CSMA/CD flow diagram The station transmits and receives continuously and simultaneously (using two different ports) 29
Implementation 30
FAST ETHERNET 31
• IEEE created Fast Ethernet under the name 802. 3 u • Fast Ethernet is backward-compatible with Standard Ethernet, but 10 times faster (100 Mbps) • The goals of Fast Ethernet: 1. 2. 3. 4. 5. 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 32
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 33
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. 34
Implementation 35
UTP Colour code 36
GIGABIT ETHERNET 38
• Gigabit Ethernet (IEEE 802. 3 z) • The goals of the Gigabit Ethernet: 1. 2. 3. 4. 5. 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. 6. To support autonegotiation as defined in Fast Ethernet 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 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 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 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 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 Frame RRRRRRR Carrier Extension 512 bytes 44
Carrier Extension is very inefficient if we have a series of short frames to send (each frame carries redundant data) 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 Frame Extension Frame 512 bytes Frame burst Maximum frame burst is 8192 bytes 46
Gigabit Ethernet Implementation 47
TEN-GIGABIT ETHERNET 48
• Ten-Gigabit Ethernet standard : IEEE 802. 3 ae • The goals : 1. 2. 3. 4. 5. 6. 7. 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. 49
Implementation • Ten-Gigabit Ethernet operates only in full duplex mode no need for contention CSMA/CD is not used 50
WIRELESS LANs 51
Topics Discussed in the Section • IEEE 802. 11 • MAC Sublayer • Addressing Mechanism • Bluetooth 52
Basic service sets (BSSs) 53
Extended service sets (ESSs) 54
CSMA/CA flow diagram
CSMA/CA and NAV 56
Hidden station problem 57
Note The CTS frame in CSMA/CA handshake can prevent collision from a hidden station. 58
Use of handshaking to prevent hidden station problem 59
Exposed station problem 60
Use of handshaking in exposed station problem 61
Piconet 62
Scatternet 63
POINT-TO-POINT WANs 64
Topics Discussed in the Section • 65 K Modems • DSL Technology • Cable Modem • T Lines/E lines • SONET/SDH • PPP 65
56 K modem 66
Note ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. 67
Bandwidth division 68
ADSL and DSLAM 69
Cable Modem 70
Cable modem configuration 71
T 1/E 1 Carrier System 72
SONET/SDH 73
PPP (point-to-point protocol) 74
SWITCHED WANs 75
Topics Discussed in the Section • X. 25 • Frame Relay • ATM 76
X. 25 Speed is about 64 kbps 77
Frame Relay Speed 56 Kbps to 1. 544 Mbps 78
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. 79
ATM multiplexing 80
Architecture of an ATM network 81
Virtual circuit 82
Note A virtual connection is defined by a pair of numbers: the VPI and the VCI. 83
ATM layers 84
Use of the layers 85
Note The IP protocol uses the AAL 5 sublayer. 86
CONNECTING DEVICES 87
Topics Discussed in the Section • Repeaters • Bridges • Routers 88
Connecting devices 89
Repeater or hub 90
Note A repeater forwards every bit; it has no filtering capability. 91
Note A bridge has a table used in filtering decisions. 92
Note A bridge does not change the physical (MAC) addresses in a frame. 93
Bridge 94
Learning bridge M M M 95 M
Note A router is a three-layer (physical, data link, and network) device. 96
Note A repeater or a bridge connects segments of a LAN. A router connects independent LANs or WANs to create an internetwork (internet). 97
Routing example 98
Note A router changes the physical addresses in a packet. 99
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