computer communication networks (sub., code : 10ec71)

1 01\08\2011 Unit-I introduction

Computer Communication Networks(Sub., Code : 10EC71)


Layered tasks

OSI Model

Layers in OSI model

TCP/IP Suite

Addressing

Telephone and cable networks for data transmission,

Telephone networks

Dial up modem

DSL

Cable TV for data transmission.

Unit - 1

Overview


Network Models


Layered Tasks

We use the concept of We use the concept of layerslayers in our daily life. As an example, let in our daily life. As an example, let us consider two friends who communicate through postal mail. us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if The process of sending a letter to a friend would be complex if there were no services available from the post office. there were no services available from the post office.

Sender, Receiver Sender, Receiver and, Carrier and, Carrier

Higher LayerHigher Layer

Middle LayerMiddle Layer

Lower layerLower layer

HierarchyHierarchy

Tasks must be Tasks must be done in the given done in the given orderorder


THE OSI MODEL

Established in 1947, the International Standards Established in 1947, the International Standards Organization (Organization (ISOISO) is a multinational body ) is a multinational body dedicated to worldwide agreement on international dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects standards. An ISO standard that covers all aspects of network communications is the Open Systems of network communications is the Open Systems Interconnection (Interconnection (OSIOSI) model. It was first introduced ) model. It was first introduced in the late 1970s. in the late 1970s.

ISO is the organization.OSI is the model.


Layers in the OSI Model

“Please Do Not Touch Steve’s Pet Alligators”


Layered networking model is advantageous because• Divides networking into less complex components• Enables programmers to specialize in a particular level• Allows upgrades to a specific layer without effecting other

layers• Encourages interoperability• Allows for standardized interfaces

Reasons For Layering


The interaction between layers in the OSI model


Layered Architecture

Peer to peer Process• The process on each machine that communicates at a given

layer are called peer-to-peer process.Interfaces Between Layers• Interface defines the information and services a layer

must provide for the layer above it.Organization of the layers (subgroups )• Layers 1,2, and 3 are the network support layers• 5,6, and 7 as a user support layers• Layer 4, Transport layer links the two subgroups

Reasons For Layering


The interaction between layers in the OSI model• The OSI model is composed of seven ordered layers.

• Within a single machine each layer calls upon the services of the layer just below it.

• Layer 3 uses the services of layer 2 and provide services to layer 4

• Between machines, layer x on the machine communicates with layer x on another machine.

• Communication is governed by an agreed upon series of rules and conventions called protocols. (A protocol is a rule which guides how an activity should be performed, especially in the field of diplomacy. In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints.)

• The process on each machine that communicates at a given layer are called peer-to-peer process.


Physical layer

• The physical layer is concerned with transmitting raw bits over a communication channel.

• It deals with the mechanical, electrical, and timing interfaces, and the physical transmission medium, which lies below the physical layer.

• Physical Characteristics of interfaces and media, Representation of bits, Date rate, Synchronization of bits, Physical topology, Transmission mode(eg., Simplex).


Physical characteristics of interfaces and medium• Cable• Connectors• Interfaces

• Transmission Medium• Cable/wire• Radio waves• Infrared• Fiber/glass

Representation of bits• Bits must be encoded into signals- electrical, optical.

Type of encoding (binary encoding as voltages (Manchester encoding method)

• Transmission of the signal on the mediumSynchronization of bits• Tx and Rx clocks must be synchonized.

Physical layer has the following responsibilities


Data Rate• Duration of the bit

Physical Topology• How device are connected• Ring, Bus, Mesh, star Topology

Transmission mode• Simplex, half duplex, duplex.

Physical layer has the following responsibilities


Physical layer


Data link layer

• Responsible for moving frames from one hop (node) to the next

• Framing: Divides the stream of bits received from network layer into manageable data units called frames.

• Physical addressing: Adds a header to the frame to define the sender and/or receiver of the frame.

• Flow Control: If the receiver is slower than the transmitter

• Error Control: Retransmit for damaged frames, recognition duplication

• Access Control:


Hop-to-hop delivery


Data Link sublayers

• Logical Link Control (LLC) layer

• Defines how data is packaged (frames)

• Provides the linking function between the Physical Layer and the higher layers

• Media Access Control (MAC) layer

• Media access method

• Provides a unique identifier for the NIC (Physical address)

Data link layer


Data link layer

• Type ipconfig/all at command prompt


Network layer

• Responsible for source to destination delivery of individual packet.

• Logical addressing: Physical address used only for locally

• Routing:


Source-to-destination delivery


Transport layer

• Responsible for process-to-process delivery of the entire message.

• A process is an application program running on a host.

• Transport layer ensures the whole message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level


Transport layer has the following responsibilitiesEnd-to-end error free transmission and delivery

Segmentation and reassembly: Divided into transmittable segments by sequence number for each segment.

Connection Control: Connectionless or connection oriented, In connection oriented it makes connection and terminates connections when data transfer completes

Flow control: End to end rather than single link

Error control: Performed between process to process rather than a single link

Transport layer


Transport layer


Session layer has the following responsibilities• Control for data exchange

• Data synchronization

• Failure recovery

• Communication setup and teardown

Enables two applications to have an ongoing conversation or dialog

Ability to interrupt and recover as session

SQL, RPC, X-Windows

Session layer


Session layer

• The session layer allows users on different machines to establish sessions between them.

• Sessions offer various services, including dialog control (keeping track of whose turn it is to transmit), token management (preventing two parties from attempting the same critical operation at the same time), and synchronization (check pointing long transmissions to allow them to continue from where they were after a crash).


Presentation has the following responsibilitiesTranslation: Data is of text, audio or video: changed to bit stream. Different computers use different encoding system.

• BMP, WAV, JPEG, MIDI, HTML, ASCII

Data encryption: To ensure privacy (Encryption, Decryption)

Data compression: To reduce the size of the file

Presentation layer


Presentation layer

• Presentation layers concerned with the syntax and semantics of the information transmitted.

• In order to make it possible for computers with different data representations to communicate, the data structures to be exchanged can be defined in an abstract way, along with a standard encoding to be used ''on the wire.''

• The presentation layer manages these abstract data structures and allows higher-level data structures (e.g., banking records), to be defined and exchanged.


The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include:

20 & 21: File Transfer Protocol (FTP)

22: Secure Shell (SSH)

23: Telnet remote login service

25: Simple Mail Transfer Protocol (SMTP)

53: Domain Name System (DNS) service

80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web

3128: Port used by some proxy servers, Web caches and the default for the Squid cache

110: Post Office Protocol (POP3)

119: Network News Transfer Protocol (NNTP)

143: Internet Message Access Protocol (IMAP)

161: Simple Network Management Protocol (SNMP)

443: HTTP Secure (HTTPS)

465: SMTP Secure (SMTPS)

Application layer


Application layer

• The application layer contains a variety of protocols that are commonly needed by users.

• HTTP (Hyper Text Transfer Protocol)

• Other application protocols are used for file transfer, electronic mail, and network news.


Application has the following responsibilities• Initiate request for network services

• Provides network services to applications such as e-mail and Web browsers

Protocols and utilities• Telnet

• FTP

• DNS

• SMTP

• SNMP

Application layer


HTTP Hypertext Transfer Protocol. The core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents.

Telnet A remote terminal emulation protocol that enables clients to log on to remote hosts on the network.

SNMP Simple Network Management Protocol. Used to remotely manage network devices. Stands for the Simple Network Management Protocol.

DNS Provides meaningful names like achilles.mycorp.com for computers to replace numerical addresses like 123.45.67.89. Stands for the Domain Name System.

SMTP Simple Mail Transfer Protocol which gives simple electronic mail facilities.

FTP File Transfer Protocol is the standard way to transfer files between different machines. Needs FTP client program on computer.

Associated TCP/IP Protocols & Services


• It is a process of adding a header to wrap the data that flows down the OSI model.

Encapsulation Process

• Wrapping up of data into a protocol is also known as encapsulation.

• The Application layer, Presentation layer and Session layer create data from user's input.

• Encapsulation actually starts at layer 4 of the OSI model where the Transport layer convert the data into segments by adding a header containing source and destination port numbers.

• The Network layer convert the segments into packets (or datagram) by adding a header containing source and destination IP address.

• The Data link layer convert the packets into Frames by adding a header containing source and destination MAC address and a trailer containing the Frame check sequence(FCS)used for verifying the data integrity.

• The Physical layer convert the frames to bits and it is transmitted through the physical medium which can be a UTP

Data Encapsulation


Data Encapsulation


Summary of layers


Some Data Comm. Standards

Layer Common Standards

5. Application layer HTTP, HTML (Web) MPEG, H.323 (audio/video)IMAP, POP (e-mail)

4. Transport layer TCP (Internet)SPX (Novell LANs)

3. Network layer IP (Internet)IPX (Novell LANs)

2. Data link layer Ethernet (LAN)Frame Relay (WAN)PPP (dial-up via modem for MAN)

1. Physical layer RS-232c cable (LAN)Category 5 twisted pair (LAN)V.92 (56 kbps modem)


TCP/IP PROTOCOL SUITETCP/IP PROTOCOL SUITE

• Developed prior to the OSI model.

• The layers in the TCP/IP protocol suite do not exactly match those in the OSI model.

• The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application.

• However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.


TCP/IP and OSI model


• Simple Mail Transfer Protocol (SMTP)

• File Transfer Protocol (FTP)

• Hypertext Transfer Protocol (HTTP)

• Domain Name System (DNS)

• Simple Network Management Protocol (SNMP)

• Stream Control Transmission Protocol (SCTP)

• Transmission Control Protocol (TCP)

• User Datagram Protocol (UDP)

• Internet Control Message Protocol (ICMP)

• Internet Group Management Protocol (IGMP)

• Internet Protocol (IP)

• Address Resolution Protocol (ARP)

• Reverse Address Resolution Protocol (RARP)

TCP/IP and OSI Model


Covers physical interface between PC or workstation and a transmission medium or network

At the physical and data link layers, TCP/IP does not define any specific protocol.

It supports all the standard and proprietary protocols.

A network in a TCP/IP internetwork can be a local-area network or a wide-area network.

Physical and Data Link Layers


Concerned with access to and routing data across a network for two end systems attached to the same network.

TCP/IP supports the Internetworking Protocol.

IP uses four supporting protocols : ARP, RARP, ICMP, and IGMP. IP (Internetworking Protocol) ARP (Address Resolution Protocol) RARP (Reverse Address Resolution Protocol) ICMP (Internet Control Message Protocol) IGMP (Internet Group Message Protocol)Internet Layer: IP provides the routing functions

across the multiple networks

Network Layer


IP (Internetworking Protocol)

• IP is the transmission mechanism by the TCP/IP protocol.

• It is unreliable connectionless protocol a best effort delivery service.

• It transports data in packets called datagrams.

ARP (Address Resolution Protocol)

• Is used to associate a logical address with a physical address. ARP is used to find the physical address of the node when its Internet address is known.

RARP (Reverse Address Resolution Protocol)

• It allows a host to discover its Internet address when it knows only physical address. It is used when a computer is connected for the first time.

Network Layer


ICMP (Internet Control Message Protocol)

• ICMP is mechanism used by host and gateways to send notification of datagram problems back to the sender.

IGMP (Internet Group Message Protocol)

• IGMP is used to facilitate the simultaneous transmission of message to a group of recipients.

Network Layer


Collection of mechanisms in a single and common layer

The transport layer was represented in TCP/IP by two protocols : TCP and UDP.

IP is a host-to-host protocol

TCP and UDP are transport level protocols responsible for delivery of a message from a process to another process.

UDP (User Datagram Protocol)

TCP (Transmission Control Protocol)

SCTP (Stream Control Transmission Protocol)

Transport Layer


UDP (User Datagram Protocol)

• UDP is the simper of the two standard TCP/IP transport protocol. It is a process to process protocol that adds only port address, checksum, error control.

TCP (Transmission Control Protocol) IP is a host-to-host protocol

• TCP is a reliable stream transport protocol (connection oriented)

• At the sending end message is divided into smaller units called segments.

SCTP (Stream Control Transmission Protocol)

• Supports for newer applications such as voice over IP. It combiners the best features of UDP and TCP.

Transport Layer


Transmission Control Protocol (TCP) – uses a set of rules to exchange messages with other Internet points at the information packet level

Internet Protocol (IP) – uses a set of rules to send and receive messages at the Internet address level

TCP/IP is a result of protocol research and development conducted on experimental packet switched network by ARPANET funded by the defense advanced research projects agency (DARPA).

TCP/IP used as internet standards by the internet architecture board (IAB).

What is TCP/IP?


Connectionless protocol (I.e. no established connection between the end points that are communicating.)

Responsible for delivery the independently treated packet !!!!

TCP responsible for reassembly.

IP


The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model.

Many protocols are defined at this layer.

Contains the logic needed to support the various user applications.

Separate module are required for each application

Application Layer


HTTP Hypertext Transfer Protocol. The core of the World Wide Web, facilitates retrieval and transfer of hypertext (mixed media) documents.

Telnet A remote terminal emulation protocol that enables clients to log on to remote hosts on the network.

SNMP Simple Network Management Protocol. Used to remotely manage network devices. Stands for the Simple Network Management Protocol.

DNS Provides meaningful names like achilles.mycorp.com for computers to replace numerical addresses like 123.45.67.89. Stands for the Domain Name System.

SMTP Simple Mail Transfer Protocol which gives simple electronic mail facilities.

FTP File Transfer Protocol is the standard way to transfer files between different machines. Needs FTP client program on computer.

Associated TCP/IP Protocols & Services


RS-232


RS-232

D-Type-9 pin no.

D-Type-25 pin no.

Pin outs Function

3 2 RD Receive Data (Serial data input)

2 3 TD Transmit Data (Serial data output)

7 4 RTS Request to send (acknowledge to modem that UART is ready to exchange data

8 5 CTS Clear to send (i.e.; modem is ready to exchange data)

6 6 DSR Data ready state (UART establishes a link)

5 7 SG Signal ground

1 8 DCD Data Carrier detect (This line is active when modem detects a carrier

4 20 DTR Data Terminal Ready.

9 22 RI Ring Indicator (Becomes active when modem detects ringing signal from PSTN


Max 232


Parallel Port


ADDRESSINGADDRESSING

Four levels of addresses are used in an internet Four levels of addresses are used in an internet employing the TCP/IP protocols: employing the TCP/IP protocols: physical, logical, port, physical, logical, port, and specificand specific..


Relationship of layers and addresses in TCP/IP


• A network adapter has a unique and permanent physical address.

• A Physical address is also called MAC address is a 48-bit flat address burned into the ROM of the NIC (Network Interface Card) card at the factory which is a Layer1 device of the OSI model.

• On a local area network, low-lying hardware-conscious protocols deliver data across the physical network using the adapter's physical address.

• On a basic ethernet network, for example, a computer sends messages directly onto the transmission medium.

• The network adapter of each computer listens to every transmission on the local network to determine whether a message is addressed to its own physical address.

Physical Addressing


Physical Addressing (Network Interface Card)


Physical Addressing


Physical addresses

A node with physical address 10 sends a frame to a node with physical address 87.

The two nodes are connected by a link (bus topology LAN).

The computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.


Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below:

07:01:02:01:2C:4B

A 6-byte (12 hexadecimal digits) physical address.


• Logical address is necessary for universal communication.

• A Logical address also called IP address is a 32- bit address assigned to each system in a network.

• No two publicly addressed and visible host on the Internet can have the same IP address.

• This works in Layer-3 of OSI Model.

• This would be generally the IP address.

Logical Addressing


Logical Addressing


Two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.

IP Addresses


IP Addresses


The physical addresses will change from hop to hop,

but the logical addresses usually remain the same.


Port AddressA single wire connects the network to the distant computer, but there may be many applications on that machine-a web server, an ftp server, a telnet server, etc.-waiting for somebody to connect.

So the question arises: How do you use one wire and one IP address to connect to the right application? The answer: Ports.

Port address is transport layer ID (simillar to IP in Network Layer) which identify the application on the host.

The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture.

MAC address is usually stored in ROM on the network adapter card and is unique.

Telnet Port 23

Mail (smtp, or send mail) Port 25

World Wide Web Port 80

Post Office (pop, or get mail)

Port 110

News (nntp) Port 119


A port address is a 16-bit address represented by one decimal number as shown.

753

A 16-bit port address represented as one single number.


The sending computer is running three processes at this time with port addresses a, b, and c.

The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer.

Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.

Port Address


Port addresses


The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include:

20 & 21: File Transfer Protocol (FTP)

22: Secure Shell (SSH)

23: Telnet remote login service

25: Simple Mail Transfer Protocol (SMTP)

53: Domain Name System (DNS) service

80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web

110: Post Office Protocol (POP3)

119: Network News Transfer Protocol (NNTP)

143: Internet Message Access Protocol (IMAP)

161: Simple Network Management Protocol (SNMP)

443: HTTP Secure (HTTPS)

465: SMTP Secure (SMTPS)

Application layer


Specific Address

Email address, [email protected] and the Universal Resource Locater (URL) ex: www.google.co.in

Application layer

computer communication networks (sub., code : 10ec71)

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