Transcript No Slide Title

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 Steve’s 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 email 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 D-Type-25 pin
pin no.
no.
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Pin outs
Function
3
2
RD
Receive Data (Serial data input)
2
3
TD
Transmit Data (Serial data output)
7
4
RTS
8
5
CTS
6
6
DSR
Request to send (acknowledge to modem that
UART is ready to exchange data
Clear to send (i.e.; modem is ready to exchange
data)
Data ready state (UART establishes a link)
5
7
SG
Signal ground
1
8
DCD
4
20
DTR
Data Carrier detect (This line is active when
modem detects a carrier
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 48bit 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:
07:01:02:01:2C:4B
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
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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, [email protected] and the Universal
Resource Locater (URL) ex: www.google.co.in
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