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Introduction Chapter 1
Computer network • computer network, often simply referred to as a network, is a collection of hardware components and computers interconnected by communication channels that allow sharing of resources and information.Where at least one process in one device is able to send/receive data to/from at least one process residing in a remote device.
Uses of Computer Networks • Business Applications • Home Applications • Mobile Users • Social Issues
Business Applications of Networks • A network with two clients and one server.
Business Applications of Networks (2) • The client-server model involves requests and replies.
Home Network Applications • Access to remote information • Person-to-person communication • Interactive entertainment • Electronic commerce
Home Network Applications (2) • In peer-to-peer system there are no fixed clients and servers.
Home Network Applications (3) • Some forms of e-commerce.
Mobile Network Users • Combinations of wireless networks and mobile computing.
Network Hardware • Local Area Networks • Metropolitan Area Networks • Wide Area Networks • Wireless Networks • Home Networks • Internetworks
Broadcast Networks • Types of transmission technology • Broadcast links • Point-to-point links
Broadcast Networks (2) • Classification of interconnected processors by scale.
Various topologies are possible for broadcast LANs. • Bus • Ring • Star • Mesh • Tree • Hybrid
Metropolitan Area Networks • A metropolitan area network based on cable TV.
Wide Area Networks • Relation between hosts on LANs and the subnet.
Wide Area Networks (2) • A stream of packets from sender to receiver.
Wireless Networks • Categories of wireless networks: • System interconnection • Wireless LANs • Wireless WANs
Wireless Networks (2) • (a) Bluetooth configuration • (b) Wireless LAN
Wireless Networks (3) • (a) Individual mobile computers • (b) A flying LAN
Home Network Categories • Computers (desktop PC, PDA, shared peripherals • Entertainment (TV, DVD, VCR, camera, stereo, MP3) • Telecomm (telephone, cell phone, intercom, fax) • Appliances (microwave, fridge, clock, furnace, airco) • Telemetry (utility meter, burglar alarm, babycam).
Internetworks • A collection of interconnected networks is called an internetwork and internet.
Network Software • Protocol Hierarchies • Design Issues for the Layers • Connection-Oriented and Connectionless Services • Service Primitives • The Relationship of Services to Protocols
Protocol Hierarchies • Most networks are designed as a stack of layers to reduce the design complexity. • The purpose of each layer is to offer certain services to the higher layers, shielding those layers from the details of how the offered services are actually implemented. • The fundamental idea is that a particular piece of software provides a service to its users but keeps the details of its internal state and algorithms hidden.
Layer n on one machine carries on a conversation with layer n on another machine. • The rules and conventions used in this conversation are collectively known as the layer n protocol. • Basically a protocol is an agreement between the communicating parties on how communications is to proceed.
Network SoftwareProtocol Hierarchies • Layers, protocols, and interfaces.
In reality, no data is directly transferred from layer n on one machine to layer n on another machine. • Instead each layer passes data and control information to the layer immediately below it, until the lowest layer is reached. • Below layer 1 is the physical medium through which actual transmission occurs. • The Interfaces defines which primitive operations and services the lower layer makes available to the upper one. • Each layer must perform a specific collection of well-understood functions.
Defining a clear cut interface makes it easy to replace an old implementation by a new one provided that it gives the same services as the older one. • A set of layers and protocols is called a network architecture. • Niether the details of the implementation nor the specification of the interfaces is a part of the architecture because they are kept hidden. • A protocol stack is a list of protocols used my a system.
Example information flow supporting virtual communication in layer 5.
Design Issues for the Layers • Addressing: A means is required for a process on one machine to specify with whom it wants to talk because of multiple destinations. • Data Transfer: It needs to be specified that how many logical connections can a system provide. For. Eg: some systems provide 2 logical connections: one for normal data and one for urgent data. • Error Control: Errors are bound to occur because the physical communication circuits are not perfect. Both the communicating parties need to decide on which error control technique needs to be used.
Flow Control: When the speed differs on the sender’s side and the receiver’s side, a mechanism is needed to assure the sending party that all the packets are being received. This can involve some kind of feedback from the receiver. Or they can decide the transmission speed before hand. • Message size: If the process insists on breaking an arbitrarily long message into very small packets which will be very inefficient to send individually, then a number of small packets that belong to different messages can be assembled that are going in the same direction/ destination, and furthur can be diassembled at the destination.
Multiplexing: When it is very expensive to set up a separate connection for different or unrelated conversations, then the same connection can be used • Routing: Choosing the best path when a number of paths are available.
Connection-oriented services • It is like a telephone system where to talk to someone, you have to pick up a phone, dial the number, talk and then hang up. • Similarly a user who wishes to communicate has to first set up a connection, use it and then terminate it. • Acts like a tube where the data is inserted at one end by the sender and extracted at the other end by the receiver. • In some cases after the connection is setup, both the parties can decide on the parameters like message size, quality of srevice etc.
Connectionless service • It is like a postal system where a post card contains the address of the receiver and is sent. • Each message is sent through the system independent of all the others.
Each service is characterized by quality of service • Could be reliable/Non reliable. • For a reliable service, acknowledgements can be used which introduces overhead and delays which are often worth it but sometimes undesirable, • A reliable connection-oriented service is appropriate in a file transfer situation. • Reliable connection oriented service has two variations- Message sequences and byte streams.
Where as the delays introduced by acknowledgements are not acceptable is case of digitized voice traffic. • Not all applications require setting up connections. For. Eg: e-mail. • Various other services are: • Datagram service: e.g. telegram service • Acknowledged datagram service.: sending a registered letter • Request-reply.: query to the local library
Connection-Oriented and Connectionless Services • Six different types of service.
Service Primitives • Five service primitives for implementing a simple connection-oriented service.
Service Primitives (2) • Packets sent in a simple client-server interaction on a connection-oriented network.
Services to Protocols Relationship • The relationship between a service and a protocol.
Reference Models • The OSI Reference Model • The TCP/IP Reference Model • A Comparison of OSI and TCP/IP • A Critique of the OSI Model and Protocols • A Critique of the TCP/IP Reference Model
Reference Models The OSI reference model.
Reference Models (2) • The TCP/IP reference model.
Reference Models (3) • Protocols and networks in the TCP/IP model initially.
