Computer Networks A network is a set of devices or nodes connected by communication links A node can be a computer, printer or any other device capable of sending and receiving data generated by other nodes in the network. A link can be a cable, air or optical fiber or any medium which can transmit signal carrying information It is a collection of hardware and software which can share information. Example: Sharing of printers

Computer Networks Distributed Processing A task is divided among multiple computers and processed Network Criteria Performance Measured in terms of transit time and response time Often evaluated by 2 metrics: Throughput and delay Reliability Accuracy of Delivery, Frequency of failure and time to recover Security Protecting data from unauthorized access, damage and development

Computer Networks Physical Structure Type of connection: In a network one or more devices are connected through links Point to point Multipoint or multi-drop connection Spatially shared: several devices uses the link simultaneously Timeshared: Devices takes turns Physical Topology: The way in which the network is laid out physically.

Classification of networks Based on the size of the network it is divided into (PAN)- Personal Area Network LAN- Local Area Networks WAN- Wide Area Networks MAN- Metropolitan Area Networks

Classification of networks Personal Area Network (PAN) The interconnection of devices within the range of an individual person, typically within a range of 10 meters. For example, a wireless network connecting a computer with its keyboard, mouse or printer is a PAN. Another example of PAN is a Bluetooth.

Classification of networks Local Area Network (LAN): Privately-owned networks covering a small geographic area, like a home, office, building or group of buildings (e.g. campus). They are widely used to connect computers in company offices and factories to share resources (e.g., printers) and exchange information. LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance. Knowing this bound makes it possible to use certain kinds of designs that would not otherwise be possible. It also simplifies network management. Traditional LANs run at speeds of 10 Mbps to 100 Mbps, have low delay (microseconds or nanoseconds), and make very few errors. Newer LANs operate at up to 10 Gbps. Early LAN (Local Area Network) networks were formed using coaxial cable, coax is an electric cable and it is used to carry radio signals. LAN (Local Area Network) setup is developed by connecting two or more than two computers with each other using a physical connection in order to share files and data overtime.

Classification of networks Metropolitan Area Network (MAN): Covers a larger geographical area than is a LAN, ranging from several blocks of buildings to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking of LANs. Metropolitan Area Networks can span up to 50km, devices used are modem and wire/cable. Most widely used technologies to develop a MAN (Metropolitan Area Network) network are FDDI (fiber distribution data interface), ATM (Asynchronous Transfer Mode) and SMDS (switched multi megabit data service).ATM (Asynchronous Transfer Mode) is the most frequently used of all. ATM (Asynchronous Transfer Mode) is a digital data transfer technology. It was developed in 1980 to improve the transportation of real time data over a single network. ATM (Asynchronous Transfer Mode) works just like cell relay system, where data is separated in the form of fixed equal sized packets and is transferred overtime. The purpose of ATM (Asynchronous Transfer Mode) was to access clear audio and video results during a video conferencing.

Classification of networks Wide Area Networks (WAN): Computer network that covers a large geographical area, often a country or continent. (Any network 1 whose communications links cross metropolitan, regional, national boundaries). Less formally, a network that uses routers and public communications links. Routers will be discussed later. WAN (Wide Area Network) networks are established often by seeking help from telecomm departments who provide the] facility of leased lines. Router is connected to the LAN at one side and a hub is attached at the other end.

Internet Interconnection of networks or internetwork When 2 or more networks are connected, it is called as internet. History of Internet ISP- Internet Service Provider

Internet History of Internet Mid 1960’s- Stand alone devices(multi-vendor systems that can not communicate with each other) ARPA- (Advanced Research Projects Agency) found a way to connect these computers to share information In 1967 ARPA introduced the idea of ARPANET Each host computer attached to a specialized computer called Interface Message Processor(IMP) and the IMPs are connected to one another In 1969 first physical network was construct

Internet History of Internet Software called NCP(Network Control Protocol) provided communication between hosts This is the first operational packet switching network In 1972 introduced the concept of protocols to achieve end to end delivery of packets and the first email program was created The TCP concept is developed During 1973 the development began on the protocol called TCP/IP

Internet Most end users who wants the internet connection use the services of ISP (Internet Service Providers) An Internet Service Provider (ISP) is a company that provides internet connectivity to home and business customers. It provides access to the internet through a variety of intermediaries Dial up modems Wireless modem Broadband Cable modem

Protocol For proper communication, entities in different systems must speak the same language there must be mutually acceptable conventions and rules about the content, timing and underlying mechanisms Those conventions and associated rules are referred as “PROTOCOLS”

Protocol A set of rules governing data Communications that defines What is Communicated How it is Communicated When it is Communicated Key elements are Syntax Semantics Timing

Protocol Syntax : Refers to structure or format of the data Data formats, Signal levels Semantics: Refers to meaning of each section of bits control information, error handling information Timing: When and how fast the data can be sent Speed matching and sequencing

Protocol STANDARS Enables national and international interoperability of data and telecommunication technology and process 2 Categories De-facto- Not approved by an organization but wide spread De jure- Standards approved by organizations like ISO, ITU-T, ANSI, IEEE

Protocol PROTOCOL ARCHITECTURE Data exchange between 2 devices is a complex task Protocol architecture is the layered structure of hardware and software that supports data exchange There are a number of tasks to be performed in a data transfer application These tasks are broken into subtasks and implemented separately The modules are arranged in a vertical stack Each layer in the stack performs a related subset of functions required to communicate with another system Each layer provides services to the next higher layer

Protocol PROTOCOL ARCHITECTURE Layers are designed in such a way that change in one layer do not affect the other layer To enable communication between 2 systems the same set of layered functions must exist in 2 systems. The corresponding layers are called peers.

Protocol LAYERED ARCHITECTURE

Protocol A BASIC 3 LAYER MODEL

Protocol PROTOCOL ARCHITECTURE- 3 layer model Network Access Layer Manages the exchange of data between the computer and network Sending computer provides the address of destination Dependent on the type of network used. This layer may need specific drivers and interface equipment depending on type of network used.

Protocol PROTOCOL ARCHITECTURE- 3 layer model Transport Layer reliable exchange of data To make sure that all the data packets arrived in the same order in which they are sent out Packets nor received or received in error are retransmitted Independent of the network being used Independent of the application

Protocol PROTOCOL ARCHITECTURE- 3 layer model Transport Layer reliable exchange of data To make sure that all the data packets arrived in the same order in which they are sent out Packets nor received or received in error are retransmitted Independent of the network being used Independent of the application Application Layer Provides support for different user applications. Example: Email, File Transfer

Protocol Protocol Data Units (PDU) User data is passed from layer to layer Control information is added/removed to/from user data at each layer Header (and sometimes trailer) each layer has a different header/trailer Data + header + trailer = PDU (Protocol Data Unit) This is basically what we call packet each layer has a different PDU

Protocol