The document discusses the layered architecture of computer networks. It describes the five layers of the Internet protocol stack: physical, link, network, transport, and application layers. The physical layer defines how bits are encoded and transmitted. The link layer moves frames between connected nodes. The network layer routes datagrams from source to destination. The transport layer transports messages between endpoints, using protocols like TCP and UDP. The application layer provides user interfaces and services to applications. Layering provides modularity and allows each layer to focus on its own function.

1. Computer Networks
Chapter 1:Introduction
Computer Networking:
A Top Down Approach ,
4th edition.
Jim Kurose, Keith Ross

2. Today’s Lecture
 Layered Architecture
 Brief description of Five Layers

3. Protocol Layers
Networks are complex!
• many “pieces”:
– hosts
– routers
– links of various
media
– applications
– protocols
– hardware,
software
Question:
Is there any way of
organizing network
architecture?
Answer:
Yes possible with a
layered architecture

4. Layering of Airline Functionality
ticket (purchase)
ticket (complain)
ticket
baggage (check)
baggage (claim
baggage
gates (load)
gates (unload)
gate
runway (takeoff)
runway (land)
takeoff/landing
airplane routing
airplane routing
airplane routing
departure
airport
airplane routing
airplane routing
intermediate air-traffic
control centers
arrival
airport
Airline functionality can be divided into layers, providing a frame work in
which we can discuss air travel.
• At the ticketing layer and below
– Airline-counter-to-airline-counter transfer of a person.
• At the gate layer
– Departure-gate –to-arrival-gate transfer of a person is accomplished
Layers: each layer implements a service
– via its own internal-layer actions
– Combined with the services directly below it
•

5. Why layering?
Dealing with complex systems:
Discuss a well defined, specific part of a
large and complex system
Modularization eases maintenance,
updating of system
Change of implementation of layer’s
service transparent to rest of system
e.g. change in gate procedure doesn’t
affect rest of system

6. Internet Protocol Stack
 To provide structure to design of
network
protocols,
network
designers organize protocols in
layers
 Service – says what a layer does
 Protocol – says how the service is
implemented
 Advantages
 Drawbacks
 When
taken
together
the
protocols of various layers are
called the Protocol Stack.
 Internet Protocol Stack consists
of Five layers
 Physical,
Link,
Network,
Transport and Application layers .
 Organization of Book

7. Internet Protocol Stack
 To provide structure to design of
network
protocols,
network
designers organize protocols in
layers
 Service – says what a layer does
 Protocol – says how the service is
implemented
 Advantages
 Drawbacks
 When
taken
together
the
protocols of various layers are
called the Protocol Stack.
 Internet Protocol Stack consists
of Five layers
 Physical,
Link,
Network,
Transport and Application layers .
 Organization of Book

8. Internet Protocol Stack
• Application Layer:
 Network applications and their application layer protocols
reside.
 Provides user interfaces and support for services such as email, file transfer etc.
Hyper Text Transfer Protocol (HTTP)
File Transfer Protocol (FTP)
Session Initiation Protocol (SIP)
 An application layer protocol is distributed over multiple end
systems
 The packets of information at the application layer is called
as a message.

9. Internet Protocol Stack
• Transport Layer:
 Transports application-layer messages between application
end points.
 Transport layer packet is called as a segment
 Breaks long messages into shorter segments
 There are two Transport Layer Protocols
 Transmission Control Protocol (TCP)
 Connection Oriented service
 Guaranteed delivery of application layer messages
 Flow control
 Congestion Control
 User Datagram Protocol (UDP)
 Connectionless service
 No reliability, flow control and congestion control

10. Internet Protocol Stack
• Network Layer:
Responsible for moving network layer packets
known as datagrams from one host to another.
Transport layer passes a transport layer
segment and a destination address to the
network layer.
Network layer includes IP Protocol
Defines the fields in the datagram as well as
how end systems and routers act on these
fields
Commonly referred as IP layer.
Different routing protocols.
Determine the route that datagrams take
between source and destination

11. Internet Protocol Stack
• Link Layer:
Moves a packet from one node (host or router)
to the next node in the route.
Divide the stream of bits received from the
network layer into manageable data units called
frames.
Transforms a raw transmission facility to a
reliable link.
Mechanism to detect and retransmit damaged
or lost frames
Example of link layer protocols include WiFi,
Ethernet etc.

12. Internet Protocol Stack
• Physical Layer:
The job of this layer is to move the individual
bits with in frames from one node to next.
Representation of bits
Physical Layer data consists of a stream of
bits (0 or 1)
To be transmitted bits must be encoded into
signals. The physical layer defines the type of
encoding.
The protocol in this layer depend on the
actual transmission medium of the link.

13. Internet Protocol Stack
 Application: Provides user interfaces and
support for services such as e-mail, file
transfer etc.

FTP, HTTP
 Transport: Transports application-layer
messages between application end points.


Segmentation and reassembly
TCP, UDP
 Network: Routing of Datagrams from
source to destination

IP, routing protocols
 Link: Move a packet from one node (host or
router) to the next node in the route.
 Ethernet, WiFi
 Physical: Move the individual bits with in
frames from one node to next
Application
Transport
Network
Link
Physical