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CSCI1412 Lecture 18

phones off (please). CSCI1412 Lecture 18. Networks 4 Topologies and Protocols Dr John Cowell. Overview. Network topologies ring, star, bus and mesh topologies combined topologies Communication protocols message switching LAN Ethernet, Token Ring MAN FDDI, DQDB WAN ATM, ISDN.

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CSCI1412 Lecture 18

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  1. phones off(please) CSCI1412Lecture 18 Networks 4 Topologies and Protocols Dr John Cowell

  2. Overview • Network topologies • ring, star, bus and mesh topologies • combined topologies • Communication protocols • message switching • LAN • Ethernet, Token Ring • MAN • FDDI, DQDB • WAN • ATM, ISDN

  3. Network Topologies

  4. Network Topologies • Topology 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 Networks • ring, star, bus, mesh/distributed • combined

  5. Ring Networks • Ring must be maintained at all times • network crashes if break in cable ring • Higher speeds available at cost • Can be inflexible in wiring • Addition/deletion cause problems

  6. Star Networks • Server dependent - often a mainframe • Good central control • Robust - no problems if cable/node breaks • Large amounts of cable

  7. (Common) Bus Networks • Also known as multidrop • Each node has a feed to the bus • Easy to add new nodes • Can be inflexible - limits to cable length • Coax connectors cause problems – only used with 10 MHz Ethernet

  8. Mesh Networks • Fully connected network • Used in WANs, not LANs • No competition for common lines • fast connections • Wasteful of connectivity potential

  9. Combined Topologies

  10. Combined Topologies 2 • Combinations of topologies are common • ‘dynamically grown’ networks • Common bus - backbone • LAN’s cope with most users • occasional access to mainframe is sufficient • Bridges convert between protocols

  11. Communication Protocols

  12. Protocols • Set 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

  13. 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

  14. Packet Switching • Packet 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 F • each 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

  15. LAN Protocols Ethernet and Token Ring

  16. Ethernet • Node connects to bus cable via a transceiver Sending Network interface card receives a frame from PC • Transceiver says when cable clear • frame is put onto cable by transceiver • transceiver listens for collision (CSMA/CD) • if collision occurs, waits random time, then tries again ReceivingTransceiver monitors all traffic • all incoming frames address field are read • if for node, bits are sent to NIC • NIC does error check • PC executes network software to move frame from NIC to memory for further processing

  17. Ethernet Cable Specifications • The 802.3 standard specifies limits • maximum backbone length • maximum number of nodes attached • common 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

  18. Distance limitations • 10 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 length • e.g. 100 base T limited to 100 metre cables from central switch/hub

  19. Token Ring • Used widely in industry • originally developed by IBM • time 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) network • avoid this with wire centre hub • ‘star topology’, logical ring

  20. Sending Data on Token Ring • Node wishing to send frame waits for token • if token is ‘free’, it is replaced with data frame • Frame travels around ring • each node reads destination address • destination 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

  21. Token Ring Features • Unlike Ethernet, collisions cannot occur • a node must wait until the token is free • it is possible to calculate the maximum time that will pass before any node will be able to transmit • no wasted bandwidth from collisions • Token ring uses a sophisticated priority scheme • nodes can be assigned different priorities • only nodes with high priority can seize the token • If a sending device fails, its token may continue to circulate forever and lock the network • special monitor nodes can detect such a situation

  22. MAN Protocols FDDI and DQDB

  23. Fibre Distributed Data Interface • FDDI 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 Ring • Recently a CDDI (Copper Distributed Data Interface) standard has also emerged

  24. Distributed Queue Dual Bus • Attributed to the PhD thesis of Robert Newman (Uni. Western Australia) • IEEE 802.6 is an example • High 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

  25. WAN Protocols ISDN, ATM & 10GbE

  26. Integrated Services Digital Network • Now largely replaced by broadband technologies • ISDN is digital network available over telephone • integrates voice & non-voice transmission • Basic installation uses three separate channels • 2 B channels = 64 Kbps - data channels • D 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

  27. Asynchronous Transfer Mode • ATM 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 oriented • every packet with same destination travels same route • virtual circuit number in header • requires dedicated routers • CRC in header allows error checking at network nodes • Protocol optimised for multimedia • Will probably be replaced by Gigabit Ethernet technologies for new implementations

  28. 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

  29. Summary • Network topologies • ring, star, bus and mesh topologies • combined topologies • Communication protocols • message switching • LAN • Ethernet, Token Ring • MAN • FDDI, DQDB • WAN • ATM, ISDN

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