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

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Presentation on theme: "Networks 4 Topologies and Protocols Dr John Cowell phones off (please) 1."— Presentation transcript:

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

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 2

3 3

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 4

5 Ring Networks Ring must be maintained at all times network crashes if break in cable ring 5 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 6 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 7

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

9 Combined Topologies 9

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

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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 12

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 13

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 F packet 2: A C E F(could arrive last of three) packet 3: A C F 14

15 Ethernet and Token Ring 15

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 Receiving Transceiver 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 16

17 Ethernet Cable Specifications The standard specifies limits maximum backbone length maximum number of nodes attached common data rates 17 Max distance Cable TypeBackbonebetween nodes Data Rate 10 BASE 550 ohm coax,50010 MbpsThick 10 mm diameter 10 BASE 250 ohm coax, MbpsThin 5 mm diameter 10 BASE-TUTP10010 Mbpsstar topology 100 BASE-TUTP MbpsFast 1000 BASE-TUTP MbpsGigabit 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 18

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 19

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 20

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 21

22 FDDI and DQDB 22

23 Fibre Distributed Data Interface FDDI is essentially Token Ring over fibre covered by the same IEEE 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 23

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

25 ISDN, ATM & 10GbE 25

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 26

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 27

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 28

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 29

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