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OSI Model and Project 802

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Project 802

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802.1 Internetworking802.1 Internetworking

802.2 - Logical Link Control *802.2 - Logical Link Control * 802.3 - Ethernet or CSMA/CD, Carrier-Sense Multiple802.3 - Ethernet or CSMA/CD, Carrier-Sense Multiple

Access with Collision detection LAN *Access with Collision detection LAN *

802.4 - Token-Bus LAN *802.4 - Token-Bus LAN *

802.5 - Token Ring LAN *802.5 - Token Ring LAN * 802.6 - Metropolitan Area Network (MAN)802.6 - Metropolitan Area Network (MAN) 802.7 - Broadband Technical Advisory Group802.7 - Broadband Technical Advisory Group 802.8 - Fiber-Optic Technical Advisory Group802.8 - Fiber-Optic Technical Advisory Group

802.9 - Integrated Voice/Data Networks802.9 - Integrated Voice/Data Networks 802.10 - Network Security802.10 - Network Security 802.11 - Wireless Networks*802.11 - Wireless Networks* 802.12 - Demand Priority Access LAN, 100 Base VG-802.12 - Demand Priority Access LAN, 100 Base VG-

AnyLANAnyLAN

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PDU Format

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PDU Control Field

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Technology OptionsEthernet

Fast Ethernet

Gigabit Ethernet

10 Gig Ethernet

WLAN

LAN Technologies

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MAC Frame

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Ethernet Frame Structure

Preamble:

7 bytes with pattern 10101010 followed by one bytewith pattern 10101011

Used to synchronize receiver, sender clock rates

Addresses: 6 bytes, frame is received by all adapters ona LAN and dropped if address does not match

Length: 2 bytes, length of Data field

CRC: 4 bytes generated using CR-32, checked atreceiver, if error is detected, the frame is simply dropped

Data Payload: Maximum 1500 bytes, minimum 46 bytesIf data is less than 46 bytes, pad with zeros to 46 bytes

LAN Technologies

Length

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Ethernet AddressEnd nodes are identified by their EthernetAddresses (MAC Address or HardwareAddress) which is a unique 6 Byte address.

MAC Address is represented in HexaDecimal format e.g 00:05:5D:FE:10:0A

The first 3 bytes identify a vendor (alsocalled prefix) and the last 3 bytes are

unique for every host or device

LAN Technologies

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Ethernet10 Base 5 (Thicknet) (Bus Topology)

10 Base 2 (Thinnet) (Bus Topology)

10 Base T (UTP) (Star/Tree Topology)

10 Base FL (Fiber) (Star/Tree Topology)

LAN Technologies

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Ethernet

Physical Media :-

10 Base5 - Thick Co-axial Cable with Bus Topology

10 Base2 - Thin Co-axial Cable with Bus Topology

10 BaseT - UTP Cat 3/5 with Tree Topology

10 BaseFL - Multimode/Singlemode Fiber with Tree

Topology

Maximum Segment Length

10 Base5 - 500 m with at most 4 repeaters (Use Bridge to extendthe network)

10 Base2 - 185 m with at most 4 repeaters (Use Bridge to extend

the network)

10 BaseT - 100 m with at most 4 hubs (Use Switch to extend the

network)

LAN Technologies

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Ethernet BUS Topology

LAN Tehnologies

Repeater

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Ethernet STAR Topology

LAN Technologies

Hub

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Ethernet Segments

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10BASE5

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Transceiver

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10BASE2

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10BASET

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1BASE5

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LAN T h l i

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Fast Ethernet100 Mbps bandwidthUses same CSMA/CD media access protocol andpacket format as in Ethernet.

100BaseTX (UTP) and 100BaseFX (Fiber) standards

Physical media :-100 BaseTX - UTP Cat 5e

100 BaseFX - Multimode / Singlemode Fiber

Full Duplex/Half Duplex operations.

LAN Technologies

LAN T h l i

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Fast EthernetProvision for Auto-Negotiation of mediaspeed:10 Mbps or 100Mbps (popularly availablefor copper media only).

Maximum Segment Length100 Base TX - 100 m100 Base FX - 2 Km (Multimode Fiber)100 Base FX - 20 km (Singlemode Fiber)

LAN Technologies

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Gigabit Ethernet

1 Gbps bandwidth.

Uses same CSMA/CD media access protocol as inEthernet and is backward compatible (10/100/100modules are available).

1000BaseT (UTP), 1000BaseSX (Multimode Fiber)and 1000BaseLX (Multimode/Singlemode Fiber)standards.

Maximum Segment Length

1000 Base T - 100m (Cat 5e/6)1000 Base SX - 275 m (Multimode Fiber)

1000 Base LX - 512 m (Multimode Fiber)

1000 Base LX - 20 Km (Singlemode Fiber)

1000 Base LH - 80 Km (Singlemode Fiber)

LAN T h l i

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10 Gig Ethernet10 Gbps bandwidth.Uses same CSMA/CD media access protocol as in

Ethernet.

Propositioned for Metro-Ethernet

Maximum Segment Length

1000 Base-T - Not available

10GBase-LR - 10 Km (Singlemode Fiber)

10GBase-ER - 40 Km (Singlemode Fiber)

LAN Technologies

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Multiple Access

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Taxonomy of multiple-access protocols

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Random Access ProtocolsWhen node has packet to sendtransmit at full channel data rate R.no a priori coordination among nodes

two or more transmitting nodes collision,random access MAC protocol specifies:how to detect collisionshow to recover from collisions (e.g., via delayed

retransmissions)

Examples of random access MAC protocols:slotted ALOHAALOHACSMA, CSMA/CD, CSMA/CA

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Evolution of CSMA/CD

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ALOHA

The throughput for pure ALOHA is

S = G e 2G .

The maximum throughput

Smax = 0.184 when G= (1/2).

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Procedure for pure ALOHA protocol

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Vulnerable time for pure ALOHA protocol

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Slotted ALOHA:

The throughput for slottedALOHA is

S = G eG .

The maximum throughput

Smax = 0.368 when G = 1.

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Vulnerable time for slotted ALOHA protocol

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Carrier Sense Multiple Access

CSMA: listen before transmit:

If channel sensed idle: transmit entire frame

If channel sensed busy, defer transmission

Human analogy: dont interrupt others!

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collisions can still occur:propagation delay means

two nodes may not hear

each others transmission

collision:entire packet transmission

time wasted

note:role of distance & propagation delayin determining collision probability

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Vulnerable time in CSMA

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Behavior of three persistence methods

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Flow diagram for three persistence methods

LAN Technologies

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Ethernet CSMA/CD

CSMA/CD (carrier sense multiple accesswith collision detection) media accessprotocol is used.

Data is transmitted in the form of packets.

Sense channel prior to actual packet transmission.Transmit packet only if channel is sensed idle; else,defer the transmission until channel becomes idle.

After packet transmission is started, the nodemonitors its own transmission to see if the packet

has experienced a collision.If the packet is observed to be undergoing acollision, the transmission is aborted and thepacket is retransmitted after a random interval oftime using Binary Exponential Backoff algorithm.

LAN Technologies

CSMA/CD (Collision

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CSMA/CD (CollisionDetection)

CSMA/CD: carrier sensing, deferral as in CSMAcollisions detectedwithin short time

colliding transmissions aborted, reducing channelwastage

collision detection:easy in wired LANs: measure signal strengths, compare

transmitted, received signals

difficult in wireless LANs: receiver shut off while

transmittinghuman analogy: the polite conversationalist

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Flow diagram for the CSMA/CD

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CSMA/CA

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Flow diagram for CSMA/CA

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Controlled access method

Logical ring and physical topology in

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g g p y p gy

token-passing access method

Token Ring

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Token Ring

Token Passing

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Token Passing

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Token Passing

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Token Passing

Token Passing

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Token Passing

Token Passing

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Token Passing

Token Ring Frame

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Token Ring Frame