Layered Tasks

Data Communication &  The concept of

Networking layered tasks
is common in
our daily life,
Layered Network Models e.g. postal
service.

RQ 2

Standardized Protocol
Architectures The OSI Model
 Required for devices to communicate  International Standards Organization (ISO)
 Vendors have more marketable products  An organization dedicated to worldwide
 Customers can insist on standards based agreement on international standards.
equipment
 Open Systems Interconnection (OSI)
 Two widely referred standards:
 OSI Reference model  An ISO standard/model that covers all aspects
 TCP/IP protocol suite of network communications.
 Most widely used  An open system is a set of protocols that allows
any two different systems to communicate
regardless of their underlying architecture.
Visit the following page for an interesting history of OSI & TCP/IP models:
http://spectrum.ieee.org/computing/networks/osi-the-internet-that-wasnt
RQ 3 RQ 4

The OSI Model OSI Model

 The OSI model is not a protocol OSI model

consists of seven
 It is a layered framework for the design
separate but
of network systems that allows related layers,
communication between all types of each of which
computer systems. defines a part of
 It is a model for understanding and the process of
moving
designing a network architecture that
information
is flexible, robust, and interoperable. across a network
RQ 5 RQ 6

1
 OSI Model Organization of the Layers
 All Application  Aaj
 The upper OSI layers are
 People Presentation  Phir
almost always implemented
 Seems Session  Say in software
 To Transport  Tum
 Need Network  Nay  The lower OSI layers are a
 Data Data Link  Daal combination of hardware
 Processing Physical  Pakai and software, except for the
physical layer, which is
mostly hardware
RQ 7 RQ 8

Interaction between layers in Interaction between layers in

OSI model OSI model
 Within a single machine,
each layer calls upon
the services of the layer
just below it.

 Between machines,
layer N on one machine
communicates with
layer N on another
machine.

RQ 9 RQ 10

Encapsulation and
Decapsulation in OSI model Summary of OSI Layers

Header

Trailer

RQ 11 RQ 12

2
 TCP/IP Protocol Suite OSI
vs.
 The layers in the TCP/IP protocol suite do not
exactly match those in the OSI model. TCP/IP
 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 host-to-network layer is equivalent to
the combination of the physical and data link layers.
 Thus, TCP/IP protocol suite is considered to be
made of five layers: physical, data link, network,
transport, and application.
RQ 13 RQ 14

Internet (TCP/IP) Model Encapsulation and Decapsulation

PDU

RQ 15 RQ 16

Fragmentation and Assembly Internet Layers

PDU
Fragmentation
Assembly

RQ 17 RQ 18

3
 Physical Layer Data Link Layer
 It is responsible for transmitting  It is responsible for transmitting frames from
individual bits from one node to the one node to the next.
next.  Its major duties are …
 Framing
 It is mainly concerned with …  Physical Addressing
 Characteristics of transmission medium  Flow Control
 Signal levels  Error Control
 Data rates  Access
Control

RQ 19 RQ 20

Node to node delivery Node to node delivery

 A node with physical address 10 sends a frame to a node with
physical address 87. The two nodes are connected by a link.
 At the data link level this frame contains physical addresses in
the header. These are the only addresses needed.
 The rest of the header contains other information needed at
this level.
 The trailer usually contains extra bits needed for error
detection

RQ 21 RQ 22

Network Layer Source to destination delivery

 Responsible for the delivery of packets from the
original source to the final destination.
 Performs routing functions across multiple
networks
 Implemented in end systems and routers

RQ 23 RQ 24

4
Source to destination delivery Transport Layer
 It is responsible for delivery of a message
from one process to another.
 Its major functions are …
 Port Addressing
 Connection Control
 Flow Control
 Error Control

RQ 25 RQ 26

Process to process delivery Process to process delivery

RQ 27 RQ 28

Application Layer Summary of TCP/IP Layers

 It is responsible for providing services to the

user.

RQ 29 RQ 30

5
 Addresses Addresses

 Four levels of addresses are used in an

internet employing the TCP/IP protocols:

RQ 31 RQ 32

OSI model and TCP/IP

protocol suite

RQ 33 RQ 34

Summary

 Layered tasks
 The OSI model
 7 layers
 The Internet model
 TCP/IP model
 5 layers
 Addressing in Internet
RQ 35