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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
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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
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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
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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
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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
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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