Computer Networks CSC225 Classification of Computer Networks Part 1 Classification of computer networks ► There is no generally accepted taxonomy into which all computer networks fit ► Two dimensions stand out: transmission technology and scale Classification of computer networks ► When classified by transmission technology, there are broadly two types networks ▪ Broadcast networks ▪ Point-to-point networks Broadcast networks Broadcast networks ► Broadcast systems have: ▪ A Single/Shared communication channel - shared by all the computers/hosts on the network. ▪ Packets sent by any host are received by all others. Broadcast networks Two broadcast networks (a) Bus (b) Ring Broadcast networks Ethernet Frame Broadcast networks ► Modes of communication • Unicast (one-to-one) communication: frame is received by only one host; Unicast address in the address field • Broadcast (one-to-all) communication: frame is received by all hosts:. Broadcast address (special code) in the address field Multicast (one-to-many) communication : frame is received by a subset of the hosts. Group address (different from the unicast address) is entered in the address field. A host can subscribe to any or all of the groups • Broadcast networks ► Addressing ▪ Upon receiving a packet ▪ Each host checks the address field if the destination address matches one of the three addresses: unicast, multicast, broadcast. ▪ ▪ How does each host determine whether an address is unicast, multicast or broadcast? If it matches, it is received else the packet is ignored (coz intended for some other host ) Broadcast networks • • Broadcast networks have some limitations ► Number of computers that can be attached to the shared medium is limited. ► The geographical area that can be covered by the network is often limited How then can we facilitate communication between hosts that are distant from one another? ► Point-to-point networks. ► Point to point networks are scalable and can grow to a large number of nodes. Point-to-point networks Point to point Networks • In point-to-point networks ► Individual pairs of computers are connected, not necessarily directly. ► They can be linked indirectly via a communications network (network of intermediate nodes connected using point-to-point links). ► A packet being transmitted may visit many intermediate nodes. Point to point Networks Relationship between hosts and subnet Point-to-point networks • Communication ► Data moves from source through the network of intermediate nodes to destination(s), switching from one p2p link to another. ► Multiple routes of different lengths possible between any two computers. Point-to-point networks • Modes of communication: ► Unicast communication: mostly point-to-point transmission with one sender and one receiver. ► Multicast or broadcast communication is possible but complex to achieve in point-to-point networks. Point-to-point networks ► A general rule: ▪ Smaller geographically localized networks tend to use broadcasting ▪ Larger networks tend to use point-topoint Classification of computer networks Broadcast networks Point to point networks A single communication channel that is shared by all the machines on the network Multiple communication channels. Pairs of computers are linked indirectly via a network of intermediate computers. Frames sent by any machine are received by all others. A frame is accepted by intended recipient(s) and discarded by others (non in tended recipients) Communication is received only by intended recipient(s). Communication is typically achieved by transmitting data from source to destination(s) through the network of intermediate nodes Often a single route between any two computers. Often multiple routes of different lengths are possible between any two computers. Unicast, multicast and broadcast communication are all possible. Unicast, multicast and broadcast communication are all possible. However it is difficult to achieve multicast and broadcast communication. Used in smaller geographically localized networks Used in larger networks Switching ► Switching: Connecting end nodes via network of transit nodes ► Each Node transmits data from one interface e.g. A to another interface e.g.B; ► Route: sequence of nodes on the path from the source to the destination nodes. ► E.g. route 2-1-5-4, switching Fig. 2.12. Switching via the network of transit nodes Switching ► Switching tasks: ► Determining information flow ► Source and destination addresses determine a single flow for each pair of end nodes. ► Routing of information flow – typically selects one route based on appropriate criteria ► Flow forwarding (local flow recognition and switching)► Transit nodes perform local interface switching. Requires switching table. ► Flow multiplexing and demultiplexing – merging and separating flows – mixed flow Fig. 2.14. Switch Questions?
