Ethernet and Wireless LANs: Multiple Access Control and Protocols, Study notes of Computer Systems Networking and Telecommunications

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ECE453 – Introduction toComputer Networks

Lecture 8 – Multiple Access Control (II)

LAN (IEEE 802.x)

Network Layer

Network Layer

IEEE 802.2 (logical link control sublayer) IEEE 802.3 (Ethernet) 802.11 (wireless LAN) IEEE 802.15 (Bluetooth)

802.16 (wireless MAN)

A story of Metcalfe^ Metcalfe is perhaps best known for his 1995 prediction that theinternet would suffer a

catastrophic collapse

the following year; he promised to

eat his words^ if it did not. During his key note

speech at the Sixth WWW International Conference in 1997, he took a printed copy of his column that predicted the collapse,took a printed copy of his column that predicted the collapse, put it in a blender with some liquid and then consumed thepulpy mass. This was after he tried to eat his words in the formof a very large cake, but the audience strongly protested; thecake was quite good and was eaten by some of the audienceafter the speech.

Ethernet^ Ethernet Cabling^ Ethernet framing and Manchester^ Encoding

Encoding The Ethernet MAC Sublayer Protocol^
^ CSMA/CD^
^ Binary Exponential Backoff

Ethernet Cabling – Wiring a Building

Ethernet Frame Structure^ Preamble:^ 7 bytes with pattern 10101010 followed by one

^ 7 bytes with pattern 10101010 followed by one^ byte with pattern 10101011
^ used to synchronize receiver, sender clock rates Type: upper layer protocol Data
^ maximum length 1500 bytes
^ Minimum length 64 bytes (from dest. to CRC)

Ethernet’s CSMA/CD – BinaryExponential Backoff^ Goal: adapt retransmission attempts^
^ heavy load: random wait will be longer^ first collision: choose K from {0,1}; delay is K^ x 512 bit transmission times

x 512 bit transmission times after second collision: choose K from{0,1,2,3}… after ten or more collisions, choose K from{0,1,2,3,4,…,1023}

The 802.11 Protocol Stack

Direct sequence spread spectrumTransmits at 2.4GHz

Orthogonal frequency-division multiplexingTransmits at 5GHz-6GHzData rate 54Mbps

The 802.11 MAC SublayerProtocol – CSMA/C

A

DCF mode (distributed coordination function^
^ RTS, CTS, NAV (network allocation vector) PCF mode (point coordination function)^ Polling frame (beacon frame)

^ Polling frame (beacon frame)

Broadband Wireless (802.16)^ Common points of 802.11 and 802.16:both provide high-bandwidth wirelesslinks.^ Difference:^ 802.16 provides services to fixed hosts (e.g.buildings) while 802.11 handles mobility^ 802.16 has larger coverage

PHY Layer

Bluetooth

Hub^ Repeaters with some network managementfunctionality^ Hub do not check 802 addresses.^ The use of backbone hub

^ Provides interdepartmental communication
^ Extends the maximum distance between any pair of nodes
^ Cannot interconnect various departments using differentEthernet technologies
^ Restrictions on the maximum allowable number of hostsconnected
^ Common collision domain

Bridges^ Examines the layer-2 destination address of the frame andattempts to forward the frame on the interface that leads to thedestination^ Each LAN segment is an isolated collision domain^ Can interconnect different LAN technologiesCan interconnect different LAN technologies^ No limit to how large a LAN can be