By S.ESAKKI MUTHU UNIT -I FUNDAMENTALS AND LINK LAYERS Computer Networks Group of Computers are connected together in order to send and receive the data. Node The Computer are electron devises connected in the network that represent every thing is called node. Host If refers functional general purpose computer IP ADDRESS Internet protocol It is unique address to identify a computer in q quick manner Example: Understand what is computer network How to built a scalable network. Understand a computer network architecture. Application world wide web(WWW) Online Social Network Streaming Audio & Video File Sharing Instant Messaging Information Gathering Streaming The delivery of audio and video has some important difference from fetching a simple web page of text and image. Audio and Video download take mints to hours before watching the First scene Class of Application Text and Image Audio and Video Application Protocols We need 17 Messages for One URL Request URL Uniform Resource Locator HTTP Hyper Text Transfer Protocol TCP-Transmission Control Protocol IP-Internet Protocol 6 Messages to Find The IP Address. 3 Message for connection establishment of TCP 4Messages for HTTP request and acknowledgement 4 Messages for trained down TCP connection Requirement Prespectives 1 )Application programmer: List the services that his application needs. Example: A guaranty that each message the application sends will be deliver without error within certain amount of time. 2)Network Designer: Design a cost effective n/w with sharable resource Example: A n/w resourses are effectively utilize & fairly allocated to different uses. 3)NETWORK PROVIDER OR OPERATOR: List the characteristics of a system that is easy to manage. Example: In which fault can be easily isolated new devices can be added to the network and configured correctly. The network Must provide connectivity among a set of computers. Some times it is enough to built a limited network that connect only a few selected machines because or privacy and security A system that is design to support growth to a large size is said to be scale. Example: Internet. Scalable connectivity: Terminologies: Scale Link The net work can consists of two or more computers directly connected by some physical medium is called link. Example Coaxial cable, Optical fiber. Circuit switch Mainly used for telephone System. Packet Switch higher Efficiency. Mainly used in computer networks. Internetwork (Or) Internet A set of computers can be indirectly connected. A Set of independent network s( Clouds) or inter connected to form an internetwork (or) Internet. Host to Host Connectivity A node that is connected to two (or) More networks is commonly called Router (or) Gateway. The Main functionality of Router is forward Message from one network to another network. Router (or) Gateway Each node must be able to stay which are the other and network it wants to communicate with is called host to host connectivity. This is done by assigning and address to each node. Routing The process of determining systemeticaly to forward messages towards the destination node based on its address is called routing. Addressing: UniCast Broadcast Multicast Unicast: The source node wants to send a single destination node then broadcast. Broadcast: The source node want to broadcast the msg to all the nodes in the nodes in n/w. Multicast: The souce node wants to tell a msg to some subset of other nodes but not all of them. Multiplexing It Means a system resource is shared among multiple users. 2 Types Of Multiplexing: i)STDM (Synchronous Time Division Multiplexing) Divide the time into equal sized quanta (Path ) and in a round of information give each flow a chance to send. ii)FDM (Frequency Division Multiplexing) Transmit Each Flow Over The Physical Link At Difference Frequencies Like Difference Channel in Our TV. Drawbacks of STDM & FDM Sender 3 had to wait its turn behind s1 &s2 had nothing to send. Is not practical to resize the quantum (or) to add additional quanta incase of STDM and we cannot add new frequencies in the case of FDM. STATISTICAL MULTIPLEXING Statistical multiplexing defines an upper down on the size of block of data each flow is permitted to a given time. Packet: Limited block of data is called packet. packet to be send first that will be decided by switch independently but we have to decided fair manner by using 1.FIFO 2.Round QOS: Quality of service. A n/w that attempts to allocate bandwidth to particular flow is said to be quality of services. Congestion: When a switch run out of memory for the packet storage there will be a chance some packets will have to be dropped. When a switch is operating in the state is said to be congestion. N/W Types: LAN Less Than 1 km MAN-Less Than 10 km WAN-Geographically distant computer SAN-Single room connected with various components Support for common services A lot of complicated things must happened beyond sending a message from one host to another. Many application need common services. so we need to implement those common services to one. Process communicating over and abstract Channel like a pipe connecting two applications so we can send data at one end and receive the data at another end. CHANNEL Connecting one process to another in application level is called channel. Identifying common communication factors Process that requires access to the file is called client. Process that supports access to the file it is called server. Types of channels: 1) Request/Reply channel 2) Message stream channel Request Reply Channel Used for file transfer Protect privacy and integrity of data(PPI) Unauthorized party cannot access Every message send by one side is received by other side only one copy of each message is delivered Message stream channel This channel used by both video on demand &video conferencing Difficulties( go for channel ) Ensuring message is delivered (or) not Receive the message in the same order(or)not Ensure no third party in the channel (eavesdrop) Reliability failures 1. machine 2.Fiber are cut 3.Electrical 4.interference 5.Switch run out of 6.buffer space To avoid error we need to detect & correct the errors Types of error 1.bit error-single 2.burst error-several consecutive bit are corrupted 3.packet failure-switch has no memory than it discard the packet 4.node & link level Power failure System crash physical link is cut Manageability n/w grows then traffic increase so we need to troubleshoot with the n/w design Layering And Protocols Layering network designers have developed general blue print usually called network architecture.n/w architecture guides to design & implementation of n/w two standard n/w architecture OSI network Internet architecture Abstraction Hiding the details behind the well defined interface to manage the complexity Advantage of layer Decompose the problem of building n/w into a manageable compound Provides modular design Protocols Abstract object that makeup the layers of a n/w are called protocols Protocol define two different interfaces Service interface It defines the operations that local object can perform on the protocols Peer interface It defines the forward and meaning of message exchange between protocols peer to implement the communication service High level object protocol High level object protocol Host A Host B Protocol Graph Host 1 Host 2 Host -A Host B File transfer Digital image Video app RRPMSP HHP File transfer Digital image Video app RRP MSP HHP Protocol Specification It may be prose, pseudo code, state transition diagram The specification given by IETE(Internet Engineering Task Fource) Encapsulation HHP RRP Application programmer HHP RRP Application programmer HHP|RRP|DAT A Header It is a small data structure(few bytes) It is added in front of the message Payload: The rest of the message is called message body(or) payload Multiplexing & Demultiplexing Sender in RRP attaches as demux key to identify the correct application OSI ISO Seven Layer Model OSI Architecture Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer NL DL PL NL DL PL It is a reference model for a protocol graph Partitioning of n/w functionality into seven layers One or more protocol implement the functionality assign to each layer Physical Layer handles the transmission of raw over a communication link Data Link Layer Collects a stream of bits into a layer aggregate called frame Network Layer Handles routing among nodes within a packet switched n/w Transport Layer Implements process to process channel Session Layer It provides a name space that is used to combine different transport streams Presentation Layer Concerned about the format of data exchange between peers Application Layer Standardize common type of exchange Internet architecture FTP TCP LP NET -1 NET- 2 NET- 3 VDP TFTPHTTPNV It is an alternate view of internet architecture A n/w later shown here sometimes referred as sub n/w link layer Network protocols: It is the combination of H/W & S/W IP-internet protocol used to send to the exact destination ICP&UDP=END TO END PROTOCOLS Application: This is the real application Example HTTP,FTP,SMTP,TEINET(re mote login) Three main features of n/w Architecture 1)Does not strict layering 2)And Hourglass Shape 3)New Protocol Network & software: Most n/w protocols are implemented in s/w The interface in the n/w is called application programmer interface(API) Socket The point where a local application attaches to the n/w The interface defines operations for Creating a socket Attaching socket to the n/w Sending & receiving message through socket Closing the socket Socket Family: 1.PF-INE-for internet 2.PF-UNIX-Pipe facility 3.PF-PACKET-Direct access to the n/w interface Socket type: Sock-STREAM-Denotes bite STREAM SOCK-DGRAM-Message provided by UDP Creating Socket: Int socketfd=socket(PF-INE7,SOCK-STREAM,0); Int socketfd=socket(PF-INT7-DRAM,0); Client & server with TCP Server: The server is always passive Server invokes: Bind Listen Accept Client: It is active open by application Client invokes: Connect Practice Performance Bandwidth: It is a width of frequency band Latency: L=P(propagation)+T(transmit)+Q(queue) Propagation=distance/speed of light Transmit=size/bandwidth Delay vs Bandwidth For large file transfer the BW is increase For small message transfer the delay is increase Variance in latency is normally called jitter RTT(Round Trip Time) How long send the message from one end of a n/w to other and back Relation between latency & bandwidth Through put: through put=transfer for size/transfer for time Consider 1mb of data occupies 80 pipes full then it is transmitted through 1mbps link similarly the same 1mb of data occupies 1/12 pipes full if it is transmitted through 1gbps link Link Layer Different communication medium Link capacity C(capacity)=Blog2(H S/N) wave length WL=speed of light/frequency Modulation Modifying a signals in terms of their attitude frequency & phase Encoding The binary data send to the receiver as a signal using encoding Encoding techniques NRZ NRZI Manchester Network Adapter: Frames In a packet n/w the blocks of data called frames (or) exchange between nodes Node ANode B Adapter frames It enables the node to exchange frames Bits-flow b/w adapter Frame-flow b/w nodes Byte oriented protocols: To view each frame as a collection of byte(characters) BISYNC( Binary Synchronous Communication Pratocol) PPP(Point to Point Protocol) DDCMP(Digital Data Communication Message Protocol) Error Detection: Bit error are introduced into the frame because of electrical interference and thermal noise Common Techniques for Error Detection: Cyclic Redundancy Check id used in HDLC,DDCMP,CSMP/CD,Token,ring Redundant: It is a extra bit Two Dimentional Parity Algorithm : Based on simple Parity and adding one extra bit to seven bit code to balance the number of 1s in the byte. Cyclic Redundancy Check: Treat the message as a binary number anf divide the binary number byanother fixed binary number Reliability: To ensure the original message is received by the receiver without error. Stop and wait protocol: After transmitting one frame the sender waits for an ACK before transmitting the next frame.