Data Communication Concepts and Internet

Unit-5

Introduction to Internet

• What is Internet ?– Network of Network– No owner of Internet– Community of Resources– Facilitate to Collaboration – Use of Protocol

• Key Milestones in Evolution– 1950 : Advanced Research Projects Agency– 1970 : ARPANET creates TCP : Transmission Control Protocol– 1971 : Telnet and FTP made available– 1972 : First Mail exchange– 1973 : Arpanet Connected to England and Norway– 1974 : Use of TCP for communication among network– 1982 : US Military created networks based on ARPANET– 1983 : ARPANET Splits into ARPANET and MILNET– 1983 : Internet is Established – TCP/IP standardised– 1986 : National Science Foundation implements NFSNET– 1991 : Archie and Gopher released – Search Engine for FTP – FTP catalogues – 1992 : Internet Links more then 33 countries and 17000 networks– 1993 : www launched– 1995 : Service providers came in market

Important Internet Applications

• Telnet• FTP• Electronic Mail• Gopher• Internet Relay Chat• WWW

• Request for Comments – Internet Standards

– Protocols

Notable RFC’s

• RFC 821 : Simple Mail Transfer Protocol – SMTP

• RFC 791 : Internet Protocol

• RFC 793 : Transmission Control Protocol

• RFC 2616 : Hyper Text Transmission Protocol

• RFC 2045 : MIME

Data Communication

• Source – Transmitter – Receiver – Destination

• Transmission Impairments and Channel Capacity– Attenuation– Bandwidth of Medium– Distortions : Delay and Time– Rate of Data Transmission– Nyquist Bit Rate– Baud Rate – Data and Signal Sending Capacity– Noise Sources

• Transmission Media– Guided– Unguided : Air/ Wireless ? – Radio, Microwave and Infrared

Conversion Techniques

• Digtial – Digital : Encoding– Line Coding : Polar and Unipolar and Bipolar

• Analog – Digital : Encoding– Pulse Code Modulation and Delta Modulation

• Analog – Analog : Modulation– Amplitude Modulation and Angle Modulation – Frequency and Phase Modulation

• Digital – Analog : Modulation– Fsk, psk, ask, qam

Error Detection and Correction

• Types of Error– Single Bit Error– Brust Error

• Error Detection Techniques– Parity Check– Two Dimensional Parity Check– Checksum– Cyclic Redundancy Checks

• Error Detection codes

• Flow Control Techniques– Stop and wait Flow Control and Sliding Window

• Performance of Control Techniques

• Backward Correction Techniques– Stop and wait, Go back and selective repeat

Data Communication

• Through LAN and WAN

• Issues with SWITCHING

• Cellular Techniques

• Satellite Communication

• Through Internet– Segmentation and reassembly– Connection Control– Addressing of IP– Multiplexing– Encapsulation– Data Compression– Data Encryption– Transmission Services

Layered Architecture

• Why/ What is layered approach

• Basic Principles

• Layers and Interfaces

• Entity and Protocols

• Service and service access points

• Types of Services

TCP/IP

• Set up by US Military

• Used as Standard

• All computers are connected through TCP/IP

• Layered Approach – Why– Changes are not affecting all layers– Interface Remain same– To allow structured development of software

• Seven Layer Approach – Old – Host to host

• Application- presentation- session – Transmission

– Point to Point• Network – Data Link – Physical

• Four Layer Approach– Application – Transport – Network - Datalink

TCP/IP

• Family of Protocols• Protocols are made on Connectionless Technology – Datagrams

– Datagrams are sent in sequence– Datagrams may follow different routes

• What Does IP do ?– IP transport datagrams

• Responsible for routing the packets• Segmentation of Packets• Unreliable service

– Packets may lost– Repetition of packets– Duplication of Packets

• What Does TCP do ?– Reliable Service source to destination

• Assemble the packets • Deliver the lost packets and reassemble at destination

– Interface with IP• Responsible for routing the packets to IP• Error Control done by TCP

TCP/IP

• What Does UDP ( User Datagram Protocol) do ?– Unreliable services– Does not care about size– Do not splits the datagram– Does not care about Error control

• Encapsulation ?– As data moves down the protocol hierarchy, Headers and trailers gets appended

to it– As data moves up the protocol hierarchy, Headers and trailers gets stripped off

• IP Layer– Source and Destination Address– Does not ensure delivery – Simply attempts to deliver– IP Layer Encapsulation – 20 bytes header

Format of IP Datagram

VER HLEN Service Type Total Length

Identification Flags Fragment Offset

Time to Live Protocol Header Check Sum

Source IP Address

Destination IP Address

Options

Data

• Ver – Version – 4 bits – IP6

• HLEN – Header Length – 4 Bits

• Total Length – 16 bits

• Service Type – For priority

• Time to Live – 8 bits – Packets to live for some time – till the value is not zero

• IP Address – 32 bits

• Header Checksum– Covers only Header– How Computed

• Header as sequence of 16 bits integer

• Integers are added as ones complement arithmetic

• Ones complement of final sum taken as Check sum

– Mismatch in Checksum discard the datagram

Questions

• With respect to speed which network is faster LAN or WAN

• Why Circuit Switching is not used for data transfer

• Steps for data communication

• What kind of switching is good for data communication

Data Link Layer • Line Access Control

– Two way simultaneous Point to Point– Two way simultaneous Multi Point– Two Way Alternate Point to Point and Multipoint

• Frame Synchronizations– Asynchronous and Synchronous

• Data Delimiting– Character Oriented– Byte Count– Bit Oriented

• Transparency• Error Detection and Recovery• Flow Control• Addressing• Connection Establishment and release

Congestion

• Receiver Capacity

• Network Capacity

• Congestion Avoidance– Multiplicative Algorithm– Slow Start

TCPIP

• Distributed Model or algorithm

• Domain Name System– Hierarchical Naming System– Proper Syntax and translation medium– High Level Symbolic names– Generic Names– Country Names

Connection Establishing

Host -1 Host - 2

Syn – Seq-X

Syn ( seq Y Ack = X+1

Syn (Seq = x+1) ack =Y+1

Connection Termination

Host -1 Host - 2

FIN– Seq-X

Ack = X+1

ack =Y+1

Fin ( Seq = y Ack X+1)

Reliable Communication

Host -1 Host - 2

4K – Seq

Ack

4k

8K

4K+3K+1K

4K +4K

3K + SEQ

Ack 7k