2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 1 Basic Concepts Link: Physical pathway between devices Line Configuration: Attachment of communications devices to a link –Point-to-point (dedicated link between 2 devices) –Multipoint (more than 2 devices can use) Link ≠ wire

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 2 Topology of Networks Topology defines logical or physical arrangement of links in a network Transmission control: –Peer-to-peer: All devices equal –Primary-secondary: One device controls traffic while others transmit through primary MeshStarTreeBusRing Topology

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 3 Topologies Mesh: –Dedicated point-to-point links to every other device –n(n-1)/2 links, n-1 interfaces per device Star: –Point-to-point link only to a central controller –n links, 1 interface per device Hub

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 4 Topologies Tree: –Star with secondary hubs –Hierarchical structure Bus: –Multipoint connection –Devices connected to the backbone over taps and drop lines Hub

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 5 Topologies Ring: –Point-to-point lines between two neighbors only –Physical or logical organization Hybrid topologies

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 6 Comparison of Topologies Mesh: –Pros Parallelism in communication  Higher capacity  Robustness High security (privacy) Easy fault identification and isolation –Cons High interface and device cost Hard to install/reconfigure Limited expandability

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 7 Comparison of Topologies Star: –Pros Easy installation/reconfiguration 1 interface/host needed (cheap) Robustness  Link failures affect only 1 host Relatively easy fault isolation –Cons Traffic goes over a bottleneck  Single point of failure  Diminishing capacity/node Limited expandability

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 8 Comparison of Topologies Tree: –Pros and cons similar to star topologies –Additional Pros Hierarchical Structure  Prioritization and isolation of traffic  Better expandability –Additional Cons More central nodes with lower vitality Link failures affect entire subtrees

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 9 Comparison of Topologies Bus: –Pros Very easy installation Can be used to connect other subnetworks –Cons Difficult fault isolation Single point of failure (consider reflections) Hard to reconfigure Diminishing capacity/node Decreasing signal strength with additional taps Bus length limited (signal strength and bus access)

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 10 Comparison of Topologies Ring: –Pros Easy installation/reconfiguration (move only 2 connections) Easy fault isolation –Cons Unbalanced delay due to unidirectional nature Link or node failures affect the entire topology (can be resolved with 2 rings or automatically closing switches)

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 11 Transmission Mode Direction of signal flow on link –Simplex (one directional) Keyboards, monitors, TV broadcast… –Half Duplex (one direction at a time) Walkie-Talkies, CB radios First Later

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 12 Transmission Mode –(Full) Duplex (bidirectional) Either sharing the same line or utilizing two simplex connections Telephone network

2 - Winter 2005 EE EE 766 Computer Interfacing and Protocols 13 Categories of Networks Local Area Networks –Limited geographic area (up to few km) –Privately owned and operated –Single type of topology Metropolitan Area Networks –Extends over an entire city –Stand-alone or interconnection of LANs –Public or private Wide Area Networks –Long distance communications –Public and private components –If entirely owned by a single company  Enterprise