Computer Communication Networks

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Computer Communication Networks (Sub., Code
10EC71)
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Unit - 1
Overview

• 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.

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• Network Models

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Layered Tasks
We use the concept of layers in our daily life.
As an example, let us consider two friends who
communicate through postal mail. The process of
sending a letter to a friend would be complex if
there were no services available from the post
office.
Sender, Receiver and, Carrier Higher
Layer Middle Layer Lower layer Hierarchy Tasks
must be done in the given order
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THE OSI MODEL
Established in 1947, the International Standards
Organization (ISO) is a multinational body
dedicated to worldwide agreement on international
standards. An ISO standard that covers all
aspects of network communications is the Open
Systems Interconnection (OSI) model. It was first
introduced in the late 1970s.
ISO is the organization.OSI is the model.
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Layers in the OSI Model
Please Do Not Touch Steves Pet Alligators
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Reasons For Layering

• 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

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The interaction between layers in the OSI model
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Reasons For Layering

• 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

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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.

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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).

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Physical layer has the following responsibilities

• 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 medium
• Synchronization of bits
• Tx and Rx clocks must be synchonized.

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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.

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Physical layer
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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

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Hop-to-hop delivery
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Data link layer

• 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)

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Data link layer

• Type ipconfig/all at command prompt

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Network layer

• Responsible for source to destination delivery of
  individual packet.
• Logical addressing Physical address used only
  for locally
• Routing

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• Source-to-destination delivery

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• 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

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• Transport layer

• Transport layer has the following
  responsibilities
• End-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

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• Transport layer

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• Session 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

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• 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).

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• Presentation layer

• Presentation has the following responsibilities
• Translation 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

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• 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.

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• Application layer

• 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)

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• 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.

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• Application layer

• 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

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Associated TCP/IP Protocols Services
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.
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• Data Encapsulation

• 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

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• Data Encapsulation

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• Data Encapsulation

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• Summary of layers

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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)
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TCP/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.

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TCP/IP and OSI model
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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)

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Physical and Data Link Layers

• 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.

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Network Layer

• 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

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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.

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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.

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Transport 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)

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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.

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What is TCP/IP?

• 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).

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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.

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Application Layer

• 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

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Associated TCP/IP Protocols Services
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.
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RS-232
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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
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Max 232
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Parallel Port
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ADDRESSING
Four levels of addresses are used in an internet
employing the TCP/IP protocols physical,
logical, port, and specific.
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Relationship of layers and addresses in TCP/IP
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Physical Addressing

• 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.

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Physical Addressing (Network Interface Card)
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Physical Addressing
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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.
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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
070102012C4B A 6-byte (12 hexadecimal
digits) physical address.
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Logical Addressing

• 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.

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Logical Addressing
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Logical Addressing
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Logical Addressing
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Logical Addressing
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IP Addresses
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.
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IP Addresses
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The physical addresses will change from hop to
hop, but the logical addresses usually remain the
same.
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Port Address
A 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
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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.
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Port Address
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.
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Port addresses
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Port addresses
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• Application layer

• 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)

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• Application layer

• Specific Address
• Email address, manjup.jnnce_at_gmail.com and the
  Universal Resource Locater (URL) ex
  www.google.co.in