Download ICN lecture1 - OSI & TCP_IP

Introduction to
Communications and Networks
ECI-2-830
Dr. Vincent Siyau
Text Books & References
• Text Books (Essential)
– Data Communications: From Basics to Broadband,
3rd Edition by William J. Beyda
or
– Data Communications and Networking, 3rd Edition,
Behrouz A. Forouzan
• Reference Books (not required)
– Computer Networks and Internets, with Internet Applications, 4th
Edition.
Douglas E. Comer & Ralph E. Droms, 2004 by Prentice Hall.
– Data and Computer Communications, 7th Edition,
William Stallings, by Prentice Hall.
Lecture Notes and Tutorials
• Please check the blackboard (BB) regularly for any updates
regarding the ICN lectures week by week.
• ALL Lecture Notes are available in the BB. (in Document)
• Pay attention and follow closely (Save your revision time)
• Very often exam questions are revealed in the lectures!
• Sometimes, tutorials will be mixed within the lectures or
immediately available after each lectures to help you to
refresh and revise the important parts of each lecture.
• Sometimes, mini-test & quizzes will be given to help your
understanding in this subject. So, do your revision
frequently!
The OSI Model
OSI MODEL (1)
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.
Layered Architecture based on services provided
Peer-to-Peer Processes
Transparency
Encapsulation
OSI MODEL (2)
• The role of the OSI model is to offer a design
template to enhance the development of
network protocols and technologies.
• Each layer of the model represents a subset of
the requirements for reliable source (application)
to destination (application) delivery of the user
message
• The process of data exchange over a network is
viewed as operations managed by nodes that
‘talk’ to each other over passive links. The links
are not included in the model.
OSI MODEL (3)
• The analysis of the data exchange is based on
identifying services that the network must provide at
each stage of the exchange.
• The ISO has identified seven groupings of services
that can constitute the layers of the model.
• Each layer to layer interface of the OSI model is
precisely defined. This allows freedom to developers
to evolve how the layers offer the specified services.
The layers are in this sense independent.
• There are many parallels between networking in
other areas such as the postal service and this my
be helpful on occasion to illustrate
telecommunication behaviour)
Seven layers of the OSI model
{
Application
Layers
7
User interface
6
Common format
5 Manages
Dialogue
Reliable message
Delivery
4
Unreliable Source to
destination delivery
3
{
Network
Layers
2
Reliable link delivery
1
Data to signal
The interaction between layers in
the OSI model
An exchange using the OSI model
PDU Protocol Data Unit
SDU Service Data Unit
Segment
Datagram
Frame
OSI layer Summary
Physical layer
Signal
The physical layer:
Defines the electrical, mechanical, procedural, and functional specifications for
activating, maintaining, and deactivating the physical link between
communicating network systems.
Define characteristics such as type of encoding or modulation, voltage levels,
synchronisation, timing of voltage changes, physical data rates, maximum
transmission distances, and physical connectors.
Data link layer
The data link layer provides framing which includes :
•Reliable transit of data across a physical network link.
•Physical addressing
•Error Control
•Sequencing of frames
•Flow control.
Hop-to-hop delivery –Role of
framing
Network layer
The network layer:
Defines the network (logical) address. This is used for source network layer to
destination network layer delivery.
This delivery is connectionless and unreliable. Although IP, which is a network layer
protocol offers ICMP - which gives the source notification when delivery is not
possible.
Source-to-destination delivery using the network
address
Transport layer
The transport layer:
Segments the data for transport across the network.
Responsible for making sure that the message is delivered error-free - reliable.
Reassembles data using sequence numbers – connection oriented.
Flow control generally occurs at the transport layer.
Reliable process-to-process delivery of a
message
Network Address
Application Address – port
number
Session layer
Sets up dialogue and may partition the process
Session layer allows two systems to enter into a dialog for communications.
(half or full duplex). e,g. real-time skype or Instant Messaging (IM).
It partition the process by adding the <syn> as the check point.
Presentation layer
Presentation layer is responsible for:
•Ensure Common Format, Translation, Data Compression, Encryption
Concern about syntax and semantic info exchange btw 2 sides.
Application layer
Responsible for providing services to user and enable user
to access the network
OSI layer Summary
EXTRA NOTES:
For understading basic
Communications and Networks
structure/format
TCP/IP
Protocol Suite
PROTOCOLS AND STANDARDS
Agreed rules form the basis of harmonious data exchange
between network nodes. These rules are referred to as
protocols in the telecoms world.
All telecommunications technologies are underpinned by
protocols that should be recognised internationally managed
by established standards bodies.
A protocol has three aspects:
Syntax
This is the format (the length and ordering of the fields)
Semantics
The purpose/meaning/interpretation of each field.
Timing
When and how fast the data should be sent
Eg.
Ethernet 100Base-T
Network Model
• Data exchange at the local, national and international
level is complex.
• Exchange requires, among other things;
user interface,
agreed formatting,
common language,
dialogue,
security,
reliability,
ability to reach the destination,
and recover from faults.
• A network model must reduce this complexity and at the same
time enabling a more flexible approach to network design that
can offer a differentiated approach to evolution and if we are
lucky revolution.
Model of Internetworking delivery
• Access Networks (LAN based)
• Interconnection/Transit Networks (WAN
based)
Source LAN
interconnection
world internet
Gateway
by multiple WANS.
Although in this schematic the
is only via one WAN a real
delivery would be
Transit WAN
(‘Backbone’)
Gateway
Destination
LAN
TCP/IP PROTOCOL SUITE
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: network attachment, internet,
transport, and application.
However, when TCP/IP is compared to OSI, we can
view the TCP/IP protocol suite as five layers:
physical,
data link,
network,
transport, and
application.
TCP/IP and OSI model
Relationship of layers and addresses in
TCP/IP
Not used in
this unit
ADDRESSING
Three levels of addresses are used in an
internet employing the TCP/IP protocols:
• Physical / MAC
• Logical / IP
• Port / TCP/UDP
– layer 2
– layer 3
– layer 4
MAC – Data link : Data Frame
IP – Network : Packet
TCP/UDP – Transport : Segment
The concept of TCP/UDP and
Port address
will be covered later in
Transport layer lecture
Figure 2.21 shows two computers communicating via the Internet. 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.
Extra Examples:
Example 2.1 from
Forouzan
In the diagram below 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). As the figure shows, the computer with physical
address 10 is the sender, and the computer with physical address 87 is
the receiver.
ignored
Example 2.3 from Forouzan The diagram shows a part of an internet with 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.
Tutorial/Quiz at:
http://highered.mcgrawhill.com/sites/0072967757/student_vie
w0/chapter2/multiple_choice_quiz.html
The END
See you next week