This chapter focuses on basics of COMPUTER NETWORKING. This will help you to study higher levels of computer networking.
OSI – open system interconnection ( This is the very basic of computer networking. OSI 7 layers in chronological order –
- physical layer
- data link layer
- network layer
- transport layer
- session layer
- presentation layer
- application layer
physical layer concerns with bit-by-bit delivery. physical signalling sublayer of physical layer interfaces with the media access control sublayer of datalink layer. media access control layer depends up on type of medium
In asynchronous serial communication the physical layer provides start and stop signalling and flow control. physical layer translates logical communication requests into hardware specific operations. Functions of physical layer are hardware specification, encoding and signalling data transmission and reception, topology and network design
All issues of line coding, channel coding and modulation are concerned with physical layer, where binary phase shift keying is used to represent logic 1 and logic 0. No error corrections in physical layer, so probability of error is high. Transmission data rate depends on physical layer. Data link layer provide reliable transmission of packets
Header of a frame generally contains synchronization bytes, addresses and frame identifier. Automatic repeat request error management mechanism is provided by logical link control sublayer of data link layer. Burst error – two or more bits in a data has been changed during the transmission. data link protocol are Ethernet, point to point protocol, HDLC etc
CSMA/CD and CSMA/CA are multiple access protocol for channel access control. piggybacking is technique of temporarily delaying outgoing acknowledgements so that they can be hooked onto the next outgoing data frame
Data link layer functions
- Framing
- Acknowledgment
- Sequence numbering
- Error detection
- Retransmission
- Flow control
Error detection in data link layer is link to link base. Connection state is used to keep track of sending frame and which one requires retransmission. Best effort is the designing consideration of data link layer. Network layer transport layer interface is called interface between carrier and customer, that is the boundary of subnet. network layer concerns with packets
4 byte IP address consists of network address and host address. In virtual circuit network each packet contains VC number. Multidestination routing data is not sent by packets. Spanning tree a subset of a network that includes all the routers but contains no loops
Algorithms used for congestion control
- Traffic aware routing
- Admission control
- load shedding
Network layer protocol of internet is internet protocol. ICMP is used for error and diagnostic functions. Network layer should know about the topology of the network, so that it can find out idle path route for data transmission. No reliability in network layer
Functions of network layer
- Routing – process of transferring data from data link of source to data link of destination is called routing. For routing some kind of addressing is required which is different from MAC address. Routing is of three types
- Static – routes are based on the static tables that are “wired into” network and are rarely changed
- Dynamic – all packets of same application follow different routes
- Semi dynamic – route is determined initially then packet flow takes place
- Congestion control
- Internetworking
- Transfer layer functions
- Multiplexing/ demultiplexing
- Fragmentation / re assembly – data received from session is splited into fragments and sends to network layer, similarly data received from network layer is re assembled and send to session layer
- Selecting type of service
- Error control – end to end basis
- Flow control
- Connection establishment
- Transport layer provide process to process delivery
All UDP (user datagram protocol) packets are treated independently by transport layer, so it is connectionless. Datagram congestion control protocol is a version of UDP. TCP (Transmission control protocol) is connection oriented protocol. TCP uses a three way handshake to establish a connection. TCP receives data from application as a single stream. Port is a TCP name for a transport service access point
Stream control transmission protocol is a transport layer protocol. An endpoint of an inter-process communication flow across a computer network is socket. Socket-style API for windows is winsock. port address identifies a process on a host
Session layer provides synchronisation, Reestablishment, authentication of user and delimiting. Session layer controls dialogues in video conferencing. Presentation layer deals with syntax and semantics. Presentation layer makes the interconnection of two computers with different data structure possible, for that this layer converts data structure into abstract and encoded and exchanged with other computers network layer. Presentation layer also deals with compression, encryption and description
Boundary between application layer and presentation layer consist of protocols (HTTP, FTP etc.,). Physical, data link and network layers are network support layers and session, presentation and application layers are user support layers. TCP/IP model was first created and it is followed by OSI
The number of layers in Internet protocol stack is five. In Internet protocol stack, when data is sent from device A to device B, the 5th layer to receive data at B is application layer and in case of OSI layer it is session layer. In OSI model one layer may duplicate lower layer functionality
URL – universal resource locator
Application layer protocols
- TELNET – allows a user at one site to establish a connection to another site
- DNS – Domain name system, translates internet domain and host names to IP address
- SOAP – simple object access protocol
- SMTP – simple mail transfer protocol
- SIP- Session Initiation Protocol, controlling multimedia communication sessions
- SNMP – simple network management protocol, manages devices on IP network
- HTTP – hypertext transfer protocol
- TFTP – trivial file transfer protocol
- FTP – file transfer protocol
The ASCII encoding of binary data is base 64 encoding, E-Mail is an elastic application. Hostname has maximum 255 characters. DNS client is a resolver. Wildcard domain names start with a label *. Domain name system is maintained by distributed database system
Telnet protocol establish a connection to TCP port number 23. All telnet operations are sent as 8 bytes. AbsoluteTelnet is a telnet client for windows. Line mode of telnet is full duplex
TCP/IP model layers are
- Application (coding of packet data)
- Transport (monitors end to end path selections of packets)
- Internet (sending packet through different networks)
- Link (provides service to internet layer)
Comparison of TCP/IP and OSI
- TCP/IP designed after advent of internet and OSI before advent of internet
- TCP/IP supports internet working, where OSI doesn’t support
- TCP/IP is loosely layered, where OSI is strictly layered
- TCP/IP protocol dependant standard, OSI independent
- TCP/IP is more credible, OSI is less credible
- TCP reliably deliver packets and IP is not reliable, In OSI all packets are delivered reliably
Switch is a device that joins multiple computer using LAN. It is identical to hub, but only switch can inspect data packets. Switch conserves bandwidth hence have better performance than hub. Switch adopt daisy chaining method to increases number of devices connected to the LAN
Bridge is a box with usually two ports to LAN segments. It works in promiscuous mode at data link layer, Bridge reduces traffic and improves security. Router is a box with minimum two ports to connect dissimilar networks. It works in network level, that is the difference with the bridge. Gateway is packet switch, which usually used with devices which works above network layer and can perform translation between different protocols.
virtual private network extends a private network across public networksIn the layer hierarchy as the data packet moves from the upper to the lower layers, headers are added. The structure or format of data is called Syntax. MAC address is 48 bits. Multiport bridge is also called layer 2 switch. ARPANET is the first network. message travels through the physical path called medium. FCC have authority over interstate and international commerce in the communications field.
Contents