CSCI1412Lecture 18

Networks 4Topologies and Protocols

Dr John Cowell

phones off (please)

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OverviewNetwork topologies

ring, star, bus and mesh topologiescombined topologies

Communication protocolsmessage switchingLAN

Ethernet, Token RingMAN

FDDI, DQDBWAN

ATM, ISDN

Network Topologies

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Network TopologiesTopology means physical layout of a network

issues of: hardware

cabling, desking software

protocol, applications

Each workstation attached to network is known as a node

Types of Networksring, star, bus, mesh/distributedcombined

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Ring NetworksRing must be

maintained at all timesnetwork crashes if

break in cable ring

• Higher speeds available at cost• Can be inflexible in wiring• Addition/deletion cause problems

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Star Networks

Server dependent - often a mainframeGood central controlRobust - no problems if cable/node

breaks

• Large amounts of cable

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(Common) Bus Networks

Also known as multidropEach node has a feed to the busEasy to add new nodesCan be inflexible - limits to cable lengthCoax connectors cause problems – only used with 10

MHz Ethernet

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Mesh Networks

Fully connected networkUsed in WANs, not LANsNo competition for common lines

fast connectionsWasteful of connectivity potential

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Combined Topologies

Ethernet

Bridge

Router

File Server

Network PrinterMainframe

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Combined Topologies 2Combinations of topologies are common

‘dynamically grown’ networks

Common bus - backbone

LAN’s cope with most usersoccasional access to mainframe is sufficient

Bridges convert between protocols

Communication Protocols

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ProtocolsSet of rules governing communication issues

a standard IEEE define the 802 protocol standards

Different protocols exist for different geographical area topologies LANs

Ethernet (802.3), Token Bus (802.4), Token Ring (802.5), Wireless - WiFi (802.11[a|b|g|n])

MAN FDDI (802.5), DQDB (802.6)

WANs ATM, ISDN, Frame Relay

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Connection Strategies

Circuit switched ‘permanent’ circuit established for call duration

Message switched a message is sent from node to node message is stored temporarily at intermediate nodes

problem if message is too long for buffer security issues

Packet switched - 2 types datagram and virtual circuit

A

E

F

D

C

B

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Packet SwitchingPacket switched - 2 types

datagram each packet transmitted separately (e.g. TCP/IP) connectionless service

virtual circuit protocols establish a circuit, used for all packets (e.g. ATM) segments may be shared with other virtual circuits connection oriented

There are possible routes between A and Feach packet may have new route

packet 1: A B Fpacket 2: A C E F (could arrive last of three)packet 3: A C F

LAN ProtocolsEthernet and Token Ring

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EthernetNode connects to bus cable via a transceiverSending Network interface card receives a frame from

PCTransceiver says when cable clear

frame is put onto cable by transceivertransceiver listens for collision (CSMA/CD)if collision occurs, waits random time, then tries again

Receiving Transceiver monitors all trafficall incoming frames address field are readif for node, bits are sent to NICNIC does error checkPC executes network software to move frame from NIC

to memory for further processing

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Ethernet Cable SpecificationsThe 802.3 standard specifies limits

maximum backbone lengthmaximum number of nodes attachedcommon data rates

Max distanceCable Type Backbone between nodes Data Rate

10 BASE 5 50 ohm coax, 500 10 Mbps ‘Thick’10 mm diameter

10 BASE 2 50 ohm coax, 185 10 Mbps ‘Thin’5 mm diameter

10 BASE-T UTP 100 10 Mbps star topology

100 BASE-T UTP 100 100 Mbps ‘Fast’

1000 BASE-T UTP 100 1000 Mbps Gigabit Ethernet

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Distance limitations10 BASE 5 was limited to 500 metres

signals degrade in copper cable

Used repeaters (amplifiers) to join 500 meter sections together maximum of four repeaters (between two nodes) the limit comes from the collision detection protocol

if the transceiver hears a collision, it must still have part of frame to transmit, in order to abandon it

minimum frame size of 64 bytes maximum frame size to prevent network hogging

Faster Ethernet reduces cable lengthe.g. 100 base T limited to 100 metre cables from central

switch/hub

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Token RingUsed widely in industry

originally developed by IBMtime critical applications

Data rates of 1 Mbps, 4 Mbps, 16 Mbps

Nodes are connected in a ring topology

A token (special frame) is constantly circling

If network breaks, token disappears need to restart (reboot) networkavoid this with wire centre hub

‘star topology’, logical ring

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Sending Data on Token RingNode wishing to send frame waits

for token if token is ‘free’, it is replaced with

data frameFrame travels around ring

each node reads destination addressdestination node

copies frame resets status bits puts frame back on ring

transmitting node removes frame from ring creates a new token, and puts it on

ring waits a period before next grabbing

token prevents hogging

Token-ring

ServerWorkstation

Network Printer

Workstation

Workstation

Workstation

Workstation

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Token Ring FeaturesUnlike Ethernet, collisions cannot occur

a node must wait until the token is freeit is possible to calculate the maximum time that will

pass before any node will be able to transmitno wasted bandwidth from collisions

Token ring uses a sophisticated priority schemenodes can be assigned different prioritiesonly nodes with high priority can seize the token

If a sending device fails, its token may continue to circulate forever and lock the networkspecial monitor nodes can detect such a situation

MAN ProtocolsFDDI and DQDB

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Fibre Distributed Data InterfaceFDDI is essentially Token Ring over fibre

covered by the same IEEE 802.5 standard no electromagnetic interference better security faster data rates

100 Mbps around 200 Km ring with 200 nodes

Token is put back onto the ring immediately after a frame is transmitted

Capacity much greater than Token RingRecently a CDDI (Copper Distributed Data

Interface) standard has also emerged

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Distributed Queue Dual Bus

Attributed to the PhD thesis of Robert Newman (Uni. Western Australia)

IEEE 802.6 is an exampleHigh speed MAN (2 - 300 Mbps)Range up to 34 miles.Two parallel cables, if one breaks the signal can switch to

the other bus.Highly resistance to cable damage

Head

Sink Head

SinkBus A

Bus B

WAN ProtocolsISDN, ATM & 10GbE

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Integrated Services Digital NetworkNow largely replaced by broadband technologies

ISDN is digital network available over telephoneintegrates voice & non-voice transmission

Basic installation uses three separate channels2 B channels = 64 Kbps - data channelsD channel = 16 Kbps - control channel

can also used for telemetry remote (water/electricity) meter reading, alarm systems

the three channels share time on a cable time-division multiplexing

Industry installation uses thirty B channels + D

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Asynchronous Transfer ModeATM is a very fast packet-switched protocol

100 Mbps or greater, up to gigabits per second!Uses small fixed-size packets

53 octets (5 header, 48 payload) very similar to DQDB

Connection orientedevery packet with same destination travels same routevirtual circuit number in header

requires dedicated routers

CRC in header allows error checking at network nodesProtocol optimised for multimediaWill probably be replaced by Gigabit Ethernet technologies

for new implementations

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10 GbE 10 Gigabit Ethernet

10 times as fast as Gb Ethernet retains Ethernet frame format Over 1.2 million ports shipped in 2008

Different standards available E.g. 10 GBASE-SR short range, 26m-85m. Low cost. E.g. 10 GBASE-LR range up to 10km, but 25lm often achievable. Fibre

LAN PHY, etc Copper

10GBaseT, etc

Greatest distance between hosts currently 80 km (10GBASE-ZR), but this is a de-facto standard only (not part of IEEE802)

See http://en.wikipedia.org/wiki/10_gigabit_Ethernet http://www.ieee802.org/3/10GBT/public/nov03/10GBASE-T_tutorial.pdf

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SummaryNetwork topologies

ring, star, bus and mesh topologiescombined topologies

Communication protocolsmessage switchingLAN

Ethernet, Token RingMAN

FDDI, DQDBWAN

ATM, ISDN