CHAPTER -1 Introduction to Computer Networks
PRELIMINARY DEFINITIONS computer network :: [Tanenbaum] a collection of autonomous computers interconnected by a single technology. communications network ::a set of equipment and facilities that provide a service. General definition : A network can consist of two or more computers directly connected by some medium such as physical or wireless medium.
USE OF COMPUTER NETWORKS (i) Business Applications : In business there is resource sharing of inventories, payroll etc. This can be done by computer networks, its main goal is to make all the programs, equipment and especially data available to all trough network.
A) USING CLIENT-SERVER APPLICATIONS
CLIENT-SERVER ARCHICTECTURE server: always-on host permanent IP address server farms for scaling clients: communicate with server may be periodically connected may have dynamic IP addresses do not communicate directly with each other 5
CLIENT SERVER MODEL :--
B) USING E-COMMERCE - Includes: Online business to business transactions Online business to consumer transactions Digital delivery of products and services Online merchandising(trading). Automated telephone transactions example phone banking etc.
(II) HOME APPLICATIONS : These applications are used by the people for their personal use. a) Access to remote information :- This application can be obtained by surfing WWW(World Wide Web), here the information is available at a particular location the user can connect through a network and access these information. For example : online information.
B) PERSON-TO-PERSON APPLICATIONS Figure :- In a peer-to-peer system there are no fixed clients and servers.
PEER-TO-PEER APPLICATIONS In Peer-to-Peer Applications all the end system of the computer network is known as peer, these peer communicate directly with each other to form a peer communication.
C) INTERACTIVE ENTERTAINMENT :- There are many applications which are used for entertainment, for example :- Video on Demand VoIP (Voice over Internet Protocol) Messages services etc.
(III) MOBILE NETWORK USERS :- Communication through wireless systems. Many mobile computers and personal digital assistant(pda) are very popular these days. These system uses WAP 1.0 (Wireless Application Protocol). This is known as m-commerce.(mobile commerce)
Figure :- Combinations of wireless networks and mobile computing.
NETWORK CLASSIFICATION BY SIZE Figure :- Classification of interconnected processors by scale.
NETWORK HARDWARE There are two types of transmission technology : Broadcast links Point to Point
BROADCAST LINKS In broadcast network there is a single communication channel which is shared by many system onto the network. The information in the network travel in the form of packets. A packet is short message, chunk of packets combine to form a information. When a packet is transmitted or received to all the machine on the network this mode of operation is called Broadcasting.
P2P ARCHITECTURE no always on server arbitrary end systems directly communicate peers are intermittently connected and change IP addresses example: Gnutella large peer-to-peer network which, at the time of its creation, was the first decentralized peer-to-peer network of its kind, leading to other, later networks adopting the model. Highly scalable But difficult to manage 18
CLASSIFICATION OF NETWORK : LANs {Local Area Networks} Wired LANs: typically physically broadcast at the MAC layer (e.g., Ethernet, Token Ring) Wireless LANs MANs {Metropolitan Area Networks} campus networks connecting LANs logically or physically. often have a backbone (e.g., FDDI fiber distribution data transfer and ATM asynchronous transfer mode)
WIRED LANS transceivers Ethernet bus Ethernet hub
WIRELESS LANS Figure : (a) Wireless networking with a base station. (b) Ad hoc networking.
METROPOLITAN AREA NETWORKS Figure : A metropolitan area network based on cable TV.
MAN 2 a 3 c 1* 4 A b d Metropolitan network A consists of access subnetworks a, b, c, d. Subnet : is a logically visible subdivision of an IP network. Hierarchical Network Topology A a National network consists of regional subnetworks a, b, g. b g Metropolitan network A is part of regional subnetwork a. Leon-Garcia & Widjaja: Communication Networks
WANS {WIDE AREA NETWORKS}ALSO to as point-to-point networks. ARPANET (Advanced Research Projects Agency Network (early internet) usually hierarchical with a backbone. Enterprise Networks, Autonomous Systems (ASs) VPNs (Virtual Private Networks).
WIDE AREA NETWORKS (WANS) Figure : A stream of packets from sender to receiver.
WIRELESS NETWORKS System Interconnection Wireless LAN Wireless WAN a)system Interconnection :- means interconnection of components of computer within short range, via infra-red, bluetooth etc
B) WIRELESS LAN Here every system of the network contains radio modem and antenna by which it communicate with each other. (Peripheral Component Interconnect) The standard for WLAN is IEEE 802.11, due to less distance between end system & base system, the speed is very high upto 50Mbps.
WIRELESS LANS: 802.11 IEEE 802.11 IS A SET OF STANDARDS FOR IMPLEMENTING WIRELESS LOCAL AREA NETWORK (WLAN) COMPUTER COMMUNICATION IN THE 2.4, 3.6 AND 5 GHZ FREQUENCY BANDS. THEY ARE CREATED AND MAINTAINED BY THE IEEE LAN/MAN STANDARDS NETWORKS. INSTITUTE OF ELECTRICAL AND ELECTRONICS ENGINEERS WI-FI : Wireless Fidelity Multipath fading
C) WIRELESS WAN
NETWORK SOFTWARE PROTOCOL HIERARCHIES
PROTOCOL HIERARCHIES Example information flow supporting virtual communication in layer 5.
Connection oriented : Direct path establishment between source and destination. Example : Telephone system Connection less : Indirect path establishment between source and destination. Example : Mailing service
CONNECTION-ORIENTED VERSUS CONNECTIONLESS SERVICE
SERVICE PRIMITIVES
THE OSI (OPEN SYSTEM INTERCONNECTION)REFERENCE MODEL Principles for the seven layers Layers created for different abstractions Each layer performs well-defined function Function of layer chosen with definition of international standard protocols in mind Minimize information flow across interfaces between boundaries Number of layers optimum
TASKS INVOLVED IN SENDING LETTER
LAYER 7 THE APPLICATION LAYER The top layer of the OSI model Provides a set of interfaces for sending and receiving applications to gain access to and use network services, such as: network file transfer, message handling and database query processing
LAYER 6 THE PRESENTATION LAYER Manages data-format information for network communications (the network s translator) For outgoing messages, it converts data into a generic format for network transmission; for incoming messages, it converts data from the generic network format to a format that the receiving application can understand This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression A special software facility called a redirector operates at this layer to determine if a request is network related on not and forward network-related requests to an appropriate network resource
LAYER 5 THE SESSION LAYER Enables two network resources to hold ongoing communications (called a session) across a network Applications on either end of the session are able to exhange data for the duration of the session This layer is:responsible for initiating, maintaining and terminating sessions Responsible for security and access control to session information (via session participant identification) Responsible for synchronization services, and for checkpoint services
LAYER 4 THE TRANSPORT LAYER Manages the transmission of data across a network Manages the flow of data between parties by segmenting long data streams into smaller data chunks (based on allowed packet size for a given transmission medium) Reassembles chunks into their original sequence at the receiving end Provides acknowledgements of successful transmissions and requests resends for packets which arrive with errors
LAYER 3 THE NETWORK LAYER Handles addressing messages for delivery, as well as translating logical network addresses and names into their physical counterparts Responsible for deciding how to route transmissions between computers This layer also handles the decisions needed to get data from one point to the next point along a network path This layer also handles packet switching and network congestion control
LAYER 2 THE DATA LINK LAYER Handles special data frames (packets) between the Network layer and the Physical layer At the receiving end, this layer packages raw data from the physical layer into data frames for delivery to the Network layer At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer
LAYER 1 THE PHYSICAL LAYER Converts bits into electronic signals for outgoing messages Converts electronic signals into bits for incoming messages This layer manages the interface between the the computer and the network medium (coaxial, twisted pair,etc.) This layer tells the driver software for the MAU (media attachment unit, ex. network interface cards (NICs, modems, etc.)) what needs to be sent across the medium The bottom layer of the OSI model
THE TCP/IP REFERENCE MODEL Simple Mail Transfer Protocol (SMTP) Real Time Transport Protocol(RTP) Internet Controlled Message Protocol(ICMP) Sychronous Optical Network (SONET) Digital Subscriber Link (DSL)
FRAME RELAY Frame Relay is a standardized wide area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network (ISDN) infrastructure, it may be used today in the context of many other network interfaces. Offers speeds of 64 kbps to about 40 Mbps; This covers the range of greatest corporate demand Most demand is at the low end of the range Priced aggressively Both reasons are critical
FRAME RELAY Low-Cost Service Packet-Switched Uses virtual circuits to cut costs Unreliable Relatively low speeds Dedicated Connections Always ready to send and receive
X.25 X.25 is an ITU-T (International Telecommunication Union)standard protocol suite for packet switched wide area network (WAN) communication. An X.25 WAN consists of packet-switching exchange (PSE) nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN(Integrated Service Digital Network) connections as physical links.
THE X.25 PROTOCOL The Model Network Has Multiple Nodes (DCEs-data communication equipments) Host Computers (DTEs-data terminal equipments) Outside Hosts Have Addresses Like Phone Numbers Virtual Call Setup Virtual Call Clear Data Transfer DCE X.25 DTE DTE X.25 DCE Intra-Network Protocol DCE DCE X.25 DCE DTE 49
THE X.25 PROTOCOL The X.25 Protocol Layers Layer Name Network Link Physical Description X.25 Packet Level X.25 Frame Level (LAPB) RS232, etc LAPB- Link Access Procedure, Balanced is a data link protocol that manages a communication session and controls the packet framing. 50
RS-232 CABLE AND CONNECTOR
Asynchronous Transfer Mode (ATM) "A transfer mode in which information is organized into cells; it is asynchronous in the sense that the recurrence of cells containing information from an individual user is not necessarily periodic".
BENEFITS OF ATM high performance via hardware switching dynamic bandwidth for bursty traffic class-of-service support for multimedia scalability in speed and network size common LAN/WAN architecture opportunities for simplification via VC(virtual circuits) architecture international standards compliance
Voice ATM Adaptation Layers A/D s 1, s 2 Digital voice samples AAL cells Video A/D picture frames Compression compressed frames AAL cells Data Bursty variable-length packets AAL cells Copyright 2000 The McGraw Hill Companies Leon-Garcia & Widjaja: Communication Networks Networks: ATM Figure 9.3
Asynchronous Transfer Mode(ATM) Voice Data packets Images MUX Wasted bandwidth TDM ATM 4 3 2 1 4 3 2 1 4 3 2 1 4 3 1 3 2 2 1 `