Chapter 10 Networking Types

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1 Chapter 10 Networking Types Aims: Define the infrastructure of networks. Outline the differing networking topologies. Outline the main networking technologies.

2 Interconnection of networks LAN LAN B B BACKBONE2 BACKBONE1 Bridge Bridge or or router router LAN LAN A LAN LAN D LAN LAN C Local network LAN LAN E E LAN LAN F F Local network Local network Bridge Bridge or or router router Local network Local network BACKBONE3

3 Network topologies Central server Ring network Star network Bus network

4 Tree topologies Network backbone Concentrator (or hub) Concentrator (or hub)

5 Star topology Central server Star Star Network Network Since Since the the data data rate rate is is relatively relatively low low between between central central server server and and the the node, node, a a low-specification low-specification twisted-pair twisted-pair cable cable can can be be used used to to connect connect the the nodes nodes to to the the server. server. A fault fault on on one one of of the the nodes nodes will will not not affect affect the the rest rest of of the the network. network. Typically, Typically, mainframe mainframe computers computers use use a a central central server server with with terminals terminals connected connected to to it. it. Network Network is is highly highly dependent dependent upon upon the the operation operation of of the the central central server. server. If If it it were were to to slow slow significantly significantly then then the the network network becomes becomes slow. slow. In In addition, addition, if if it it were were to to become become un-operational un-operational then then the the complete complete network network would would shut shut down. down.

6 passing ring network Electronic token is passed from node to node Nodes can only transmit data when they capture the token Ring Ring Orderly Orderly access access to to ring. ring. Single Single electronic electronic token token passes passes from from one one computer computer to to the the next next around around the the ring. ring. Computer Computer can can only only transmit transmit data data when when it it captures captures the the token. token. Each Each link link between between nodes nodes is is a a point-to-point point-to-point link link and and allows allows the the usage usage of of almost almost any any type type of of transmission transmission medium. medium. All All nodes nodes on on the the network network have have an an equal equal chance chance of of transmitting transmitting data. data. If If one one of of the the nodes nodes goes goes down down then then the the whole whole network network may may go go down. down. may may get get lost, lost, or or many many tokens tokens are are generated. generated. Difficult Difficult to to add add and and delete delete nodes nodes to/from to/from the the ring. ring. Typically, Typically, twisted-pair twisted-pair cables cables allow allow a a bit bit rate rate of of up up to to Mbps, Mbps, but but coaxial coaxial and and fibre-optic fibre-optic cables cables are are normally normally used used for for extra extra reliability reliability and and higher higher data data rates. rates. A typical typical ring ring network network is is IBM IBM Ring Ring and and FDDI. FDDI.

7 Bus topology All computers have access to a common bus at the same time Common bus Ethernet hub Bus Bus network network Uses Uses a a multi-drop multi-drop transmission transmission medium. medium. All All nodes nodes on on the the network network share share a a common common bus bus and and all all share share communications. communications. This This allows allows only only one one device device to to communicate communicate at at a a time. time. A distributed distributed medium medium access access protocol protocol determines determines which which station station is is to to transmit. transmit. Data Data frames frames contain contain source source and and destination destination addresses, addresses, where where each each station station monitors monitors the the bus bus and and copies copies frames frames addressed addressed to to itself. itself. Twisted-pair Twisted-pair cables cables give give data data rates rates up up to to Mbps, Mbps, whereas, whereas, coaxial coaxial and and fibre-optic fibre-optic cables cables give give higher higher bit bit rates rates and and longer longer transmission transmission distances. distances. Gigabit Gigabit Ethernet Ethernet is is now now available available (1Gbps). (1Gbps). A typical typical bus bus network network is is Ethernet Ethernet Good Good compromise compromise over over the the other other two two topologies topologies as as it it allows allows relatively relatively high high data data rates. rates. If If a a node node goes goes down, down, it it does does not not affect affect the the rest rest of of the the network. network. Requires Requires a a network network protocol protocol to to detect detect when when two two nodes nodes are are transmitting transmitting at at the the same same time. time. Does Does not not cope cope well well with with heavy heavy traffic traffic rates. rates.

8 ring data exchange (a) Data Frame (b) (d) Ack. A D C B (c) (a) Data Frame (b) (d) (a) (a) Data Frame (b) Data Frame (b) (d) (d) Ack. A D C B (c) Ack. A D C B (c)

9 Ethernet Two nodes transmit at the same time Nodes detect there has been a collision Nodes transmit a jamming signal CSMA/CD CSMA/CD Ethernet Ethernet uses uses carrier carrier sense, sense, multiple multiple access access with with collision collision detection detection (CSMA/CD). (CSMA/CD). Nodes Nodes monitor monitor the the bus bus (or (or Ether) Ether) to to determine determine if if it it is is busy. busy. A node node wishing wishing to to send send data data waits waits for for an an idle idle condition condition then then transmits transmits its its message. message. Collisions Collisions can can occur occur when when two two nodes nodes transmit transmit at at the the same same time, time, thus thus nodes nodes must must monitor monitor the the cable cable when when they they transmit. transmit. When When a a collision collision occurs, occurs, both both nodes nodes stop stop transmitting transmitting frames frames and and transmit transmit a a jamming jamming signal. signal. This This informs informs all all nodes nodes on on the the network network that that a a collision collision has has occurred. occurred. Each Each of of the the nodes nodes involved involved in in the the collision collision then then waits waits a a random random period period of of time time before before attempting attempting a a retransmission. retransmission. As As each each node node has has a a random random delay delay time time then then there there can can be be a a prioritization prioritization of of the the nodes nodes on on the the network. network. 4 Nodes wait a random period before retransmitting All computers have access to a common bus at the same time Common bus

10 Repeaters, bridges and routers Network segment (repeater extends the network segment) Router only forwards if the network address is on another network. It does not forward broadcasts. Repeater Repeater Router Router Bridge Bridge Bridge only forwards if the station (or MAC) address is not on the connected network segment that it originated from. Broadcasts are also passed over. Network segment bounded by a router or a bridge

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD

Ethernet. Ethernet Frame Structure. Ethernet Frame Structure (more) Ethernet: uses CSMA/CD Ethernet dominant LAN technology: cheap -- $20 for 100Mbs! first widely used LAN technology Simpler, cheaper than token rings and ATM Kept up with speed race: 10, 100, 1000 Mbps Metcalfe s Etheret sketch