why and how Protocol layering is done in TCP/IP protocol suite, how multiplexing and demultiplexing can be done in different protocol layers in TCP\IP.

1. By
Jaji Nekkanti
Network Applications And Protocol Layering
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2. Agenda
 Applications
 Need for Multiple Protocols
 The Conceptual Layers of Protocol Software
 Functionality of the Layers
 ISO 7-Layer Reference Model
 X.25 And its Relation to the ISO Model
 The TCP/IP 5-Layer Reference Model
 The Protocol Layering Principle
 The Layering Principle Applied To A Network
 Layering in Mesh Networks
 Two Important Boundaries In The TCP/IP Model
 Cross-Layer Optimizations
 The Basic Idea Behind Multiplexing And Demultiplexing
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3. Applications
 The World Wide Web
 Email
 Online social networking
 Streaming audio and video,
 Instant messaging
 File-sharing
 Create the applications-powerful programming platforms and new devices
such as smartphones have created new opportunities to develop applications
quickly and to bring them to a large market.
 Who operate or manage networks—mostly a behind-the-scenes job, but a
critical one and often a very complex one-network operators.
 Finally, there are those who design and build the devices and protocols that
collectively make up the Internet.
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4. Classes of Applications
Web
 Presents simple interface
 Users view pages full of textual and graphical objects and click on objects that
they want to learn more about, and a corresponding new page appears.
 Uniform Resource Locator (URL),
For example,
http://www.cs.princeton.edu/˜llp/index.htm.
 Message exchange includes up to six messages to translate the server
name(www.cs.princeton.edu) IP address (128.112.136.35)
 Three messages to set up a Transmission Control Protocol (TCP) connection
between your browser and the server.
 Four messages for your browser to send the HTTP “GET”
request and the server to respond with the requested page.
 Four messages to tear down the TCP connection.
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5. Streaming audio and video
 Services such as video on demand and Internet radio use this technology.
 The delivery of audio and video has some important differences from
fetching a simple web page of text and images.
For example, No need to download an entire video file—a process that might
take minutes to hours—before watching the first scene.
 Streaming audio and video implies a more timely transfer of messages from
sender to receiver, and the receiver displays the video or plays the audio
pretty much as it arrives.
 Audio and video streams in a continuous ,skipped sounds or stalled video is
not acceptable.
 By contrast, a page of text can be delivered and read in bits and pieces.
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6. Real-time audio and video
 Tighter timing constraints than streaming applications.
 Ex: Skype™ or a videoconferencing application, the interactions among
the participants must be timely.
 Interactive applications usually entail audio and/or video flows in both
directions, while a streaming application is most likely sending video or
audio in only one direction.
 Videoconferencing tools that run over the Internet have since the early
1990s but have achieved much more widespread in the last 2 years.
 Fitting the video content into a relatively low bandwidth network, for
example, making sure that the video and audio remain in sync and arrive in
time.
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7. A multimedia application including videoconferencing
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8. Protocol layering
The Need For Multiple Protocols
 Protocols allow one to specify or understand communication without
knowing the details of a particular vendor’s network hardware.
 Network communication is a complex problem with many aspects:
 Hardware failure
 Hosts, routers
 Network congestion
 Networks have finite capacity
 Packet delay or Packet loss
 Data corruption
 Electrical, magnetic interferences
 HW failure
 Data duplication or Inverted Arrivals
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9.  Program translation has been partitioned into 4 sub problems identified with
software that handles each sub problem.
 Compiler, assembler, link editor and loader.
 Two things are clear here that:
1. It should be clear that pieces of translation software must agree on the exact
format of data passed between them.
2. The four parts of the translator form a linear sequence in which output from
the compiler becomes input to the assembler, and so on.
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10. The Conceptual Layers of Protocol
Software
Network
Layer n
…
Layer 2
Layer 1
Layer n
…
Layer 2
Layer 1
Sender Receiver
The modules of
Protocol SW
are on each
machine
stacked
vertically into
layers
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11. Functionality of the Layers
 How many layers should be created ?
 What functionality should reside in each layer ?
 The questions are not easy to answer for several reasons:
 Given a set of goals and constraints governing a particular communication
problem.
 Reliable transmission.
 The design of network architecture and the organization of the protocol software
are interrelated.
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12. ISO 7-Layer Reference Model
Service –says
what a layer
does.
Interface –says
how to access
the service.
Protocol –says
how the service
is implemented.
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13. X.25 And its Relation to the ISO Model
 International Telecommunications Union(ITU).
 In the X.25 view ,a network operates much like a telephone system.
 Layers of the protocol standard specify various aspects of the network as
follows:
 Physical layer:
*physical interconnection between computers and network packet
switches.
*Includes electrical characteristics of voltage and current.
 Data link layer:
*specifies how data travels b/w a computer & packet switch to which it
connects.
*unit of data-frame.
* includes error detection.
* includes timeout mechanism.
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14. 14
 Network layer:
*Unit of data-Packets.
* includes the concepts of destination addressing and forwarding.
 Transport layer:
* Unit of data-segments.
*provides end-to-end reliability.
 Session layer:
*How protocol software can be organized to handle all the functionality
needed by applications programs.
*Ex: login and passwords, session and connection coordination.
 Presentation layer:
* standardize the format of data that application programs send over a
network.
 Application layer:
* includes application programs.
*Ex: E-mail, File transfer programs.

15. The TCP/IP 5-Layer Reference Model
 Application
Transport
Internet
Network Interface
Physical
Messages or Streams
Transport Protocol Packets
IP Packets
Network-Specific Frames
Functionality
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16.  Layer 5: Application
 Users invoke application programs that access services available across a
TCP/IP.
 Application programs may send,sequence of individual messages or a
continuous stream of data.
 Layer 4: Transport
 Provide communication from one application to another.
 Provides reliable delivery of data.
 Layer 3: Internet
 Handles communication from one computer to another.
 Defines uniform format of packets forwarded across networks of different
technologies and rules for forwarding packets in routers.
 Layer 2: Network Interface
 Responsible for accepting IP packets and transmitting them over a specific
network.
 Defines formats for carrying packets in hardware frames
 Layer 1: Physical
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17. 17
Protocol 1
Protocol 2
Protocol 3
Interface 1
Interface 2
Interface3
IP Module
A realistic view of protocol software with multiple network interfaces and
multiple protocols
Software Organization
Application
Transport
Internet
Network
interface
Physical
Hardware
app1 app3 app4 app5 app6app2
Network3Network2Network1
Conceptual Layers

18.  Conceptual layers of protocols needed in computers and routers to
transfer a message from an application on computer A to an application
on computer B.
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Transpor
t
Internet
Net Iface
Transpor
t
Internet
Net Iface
Net1 Net2 Net3
Internet
Net Iface
Internet
Net Iface
Send
er
Receiv
er
Computer
A
Computer B
Router
1
Router
2

19. Locus of Intelligence
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 In the original telephone network , all the intelligence was located in phone
switches. Ex: a microphone , earpiece & a mechanism used to dial.
 By contrast, the TCP/IP protocols require attached computers to run transport
protocols and applications as well as layer 3 and layer2 protocols.
 The fundamental concept is:
* TCP/IP protocols place much of intelligence in hosts – routers in the
Internet forward packets , but do not participate in higher-layer services.

20. The Protocol Layering Principle
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 Layered protocols are designed so that layer N at the destination receives
exactly the same object sent by layer N at the source.
 The layering principle offers:
 Protocol design independence:
* A protocol designers can focus on the message exchange for a given layer
with the assurance that lower layers will not alter the message.
* The key idea is that a transport protocol can be designed independent of
other protocols.
 Definition of the end-to-end property:
* We say a protocol is end-to-end if and only if the layering principle applies
between the original source and ultimate destination.
* Other protocols are classified as machine-to-machine.

21. The Layering Principle Applied To A Network
Application
Transport
Internet
Network Interface
Host A Host B
Application
Transport
Internet
Network Interface
Physical net
Identica
l
messag
e
Identica
l
packet
Identical
IP packet
Identica
l
Frame
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22. Layering in a tcp/ip internet environment
Application
Transport
Internet
Network Interface
Host A Host B
Application
Transport
Internet
Network Interface
Physical net1
Identica
l
messag
eIdentica
l
packet
Identical
IP packet
Identica
l
Frame
22 Physical net2
Identica
l
Frame
Network Interface
Internet Identical
IP packet
Router R

23. Layering in Mesh Networks
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Protocol 1
Protocol 2
Protocol 3
Interface 1
Interface 2
Interface3
IP Module
Point-To-Point
forwarding
Transport
Internet
Network Interface
Intranet Sublayer
Conceptual Layers Software Organization
Application
Physical hardware
app1 app2
app3 app4 app5 app6
Network1 Network3

24. Two Important Boundaries In The TCP/IP Model
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Application
Transport
Internet
Network
interface
Physical
Hardware
Conceptual Layers
Software outside the operating system
Software inside the operating system
Only Internet addresses used
Physical addresses used
 Application programs and all protocol software from the internet layer
upward use only Internet addresses; addresses used by the network hardware
are isolated at lower layers.
Protocol
addresses
boundary
Operating
system
boundary

25. Cross-Layer Optimizations
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 Designer divides complex problem into subproblems and solve each one
independently. But the software that results from strict layering can be
extremely inefficient.
 To optimize transfer, the transport layer should choose the largest packet size
that will allow one packet to travel in one network frame.
 Strict layering will prevent the transport layer from optimizing transfers.
 Implementers relax the strict layering scheme when building protocol software.
 When allocating packet buffers, transport layer protocols can use the
information to optimize processing by leaving sufficient space for headers that
will be added by lower-layer protocols.
 Similarly, lower-layer protocols often retain all the headers on an incoming
frame when passing the frame to higher-layer protocols.

26. The Basic Idea Behind Multiplexing And Demultiplexing
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Demultiplexing
Based on Frame type
IP Module
ARP Module
RARP Module
Frame arrives
Illustration of frame demultiplexing that uses a type field in the frame
header .Demultiplexing is used with most networks,including Ethernet
and Wi-Fi.

27. Illustration of demultiplexing incoming IP packets based on the type field
in the IP header
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IP Module
Datagram arrives
TCP Protocol
UDP Protocol
ICMP Protocol