© Oxford University Press 2011 Computer Networks Bhushan Trivedi, Director, MCA Programme, at the GLS Institute of Computer Technology, Ahmadabad

© Oxford University Press 2011 Chapter 2 Network Fundamentals Network Fundamentals

© Oxford University Press 2011 Definition A computer network can be defined as a collection of computing devices (nodes) interconnected by wires or wireless means and governed by a set of standards (protocols) in order to share data and resources.

© Oxford University Press 2011 Division based on scope PAN or Personal Area Network or the wireless version WPAN (Wireless PAN) LAN or Local Area Network which is usually confined to a moderately large building. MAN or Metropolitan Area Network which is confined to a city or a part of it. WAN or Wide Area Network which can span multiple countries.

© Oxford University Press 2011 Other Types Wired Wireless MANet Sensor Broadcast Point to point

© Oxford University Press 2011 Broadcast Networks

© Oxford University Press 2011 Point to point

© Oxford University Press 2011 Broadcast

© Oxford University Press 2011 Broadcasting Better when a very low probability of more than one user transmitting simultaneously It is useful when the network is inherently a broadcast network. Better when routing through neighbours or addressing each node of the network is not required Broadcasting helps when the topology is not fixed.

© Oxford University Press 2011 Point to point

© Oxford University Press 2011 P2P Issues P2P requires to know where the recipient is Sender must know where each router is Similarly each router must be aware of where other routers are located For inherently broadcast network P2P communication is not possible. Little advantage for high bandwidth case

© Oxford University Press 2011 Sensors and MANets Sensors are usually very large Sensor can be immobile. Size, power and memory Sensor may not be individually addressable. Power consumption is severe in Sensors Sensor nodes may captured

© Oxford University Press 2011 Home Networking Applications Refrigerator reminds about buying vegetables Stranger trying to break into your house Babysitter is sleeping TV has a serious problem and it conveys Electric bulb tells us if it is going down Lamp dims itself when you are asleep Night lamp automatically switches on and off

© Oxford University Press 2011 Home Networking Applications Smart spectacles helps old people Smart Keys A phone receiver transfers the call automatically Control house via Internet or phone. The shower adjusts the temperature Single remote control for many home devices

© Oxford University Press 2011 Home Networking issues Robustness Cost Security issues Regular upgrades Maintenance and availability Wired or Wireless Holding the vendor responsible

© Oxford University Press 2011 Network Components The Network Interface Card Cable for wired connection Frequency band for wireless transmission The servers and the nodes

© Oxford University Press 2011 Interconnecting devices Hub Switch Repeater Bridge Router

© Oxford University Press 2011 Repeaters

© Oxford University Press 2011 Bridge

© Oxford University Press 2011 Interconnection using multiple bridges

© Oxford University Press 2011 Other types of Connection Serial connection Parallel connection Connection using a modem Universal Serial Bus (USB) connection The Logical Connection

© Oxford University Press 2011 The Logical Connection Connection-Oriented connection Connectionless connection Connection-oriented connection on top of connectionless connection Connectionless connection on top of connectionless connection Addressing issues

© Oxford University Press 2011 Advantage of CO connection Order Quality of service Reliable data transfer

© Oxford University Press 2011 Layers and service Each layer, using the services of the layer immediately below it, interacts with its peers. Each layer sends and receives data in a format understood by the peer in the recipient. Ideally, there is no dependency among the layers Each layer, while talking to a peer, uses a specific protocol to communicate.

© Oxford University Press 2011 Service provider and user

© Oxford University Press 2011 Application level design issues API or GUI User Friendliness Concurrency control

© Oxford University Press 2011 All layers together

© Oxford University Press 2011 The protocols There are multiple parties involved. Usually there is only one sender and one receiver. The sender knows what to send and in which sequence. The receiver also expects the messages in a particular sequence. Two paths of communication, accepting or rejecting

© Oxford University Press 2011 Other issues The standardization bodies Connection and protocol Connectionless and Connection-Oriented Protocols

© Oxford University Press 2011 Layers and protocols Interfaces and protocols Need for peers to communicate Applications of computer networks – Home Networking Applications – Mobile Networking Applications – Wireless Networking Applications

© Oxford University Press 2011 Security issues Hidden Dangers – No priority to security measures – Design of Communication protocols – Features vs security – Mindset of users Policy issues User convenience vs. secure network Social Engineering