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Title: Introduction to Communications and Networks ECI-2-830


1
Introduction to Communications and
NetworksECI-2-830
  • Dr. Vincent Siyau

2
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.

3
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!

4
The OSI Model
5
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
providedPeer-to-Peer Processes Transparency Encap
sulation
6
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.

7
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)

8
Seven layers of the OSI model
7 User interface 6 Common format 5 Manages
Dialogue 4 Reliable message Delivery 3
Unreliable Source to destination delivery 2
Reliable link delivery 1 Data to signal

Application Layers

Network Layers
9
The interaction between layers in the OSI model
10
An exchange using the OSI model
PDU Protocol Data Unit
SDU Service Data Unit
Segment
Datagram
Frame
11
OSI layer Summary
12
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.
13
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.

14
Hop-to-hop delivery Role of framing
15
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.
16
Source-to-destination delivery using the network
address
17
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.
18
Reliable process-to-process delivery of a message
Network Address
Application Address port number
19
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 ltsyngt as the check point.
20
Presentation layer
  • Presentation layer is responsible for
  • Ensure Common Format, Translation, Data
    Compression, Encryption
  • Concern about syntax and semantic info exchange
    btw 2 sides.

21
Application layer
Responsible for providing services to user and
enable user to access the network
22
OSI layer Summary
23
EXTRA NOTES For understading basic
Communications and Networks structure/format
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31
TCP/IP Protocol Suite
32
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
33
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.

34
Model of Internetworking delivery
  • Access Networks (LAN based)
  • Interconnection/Transit Networks (WAN based)
  • Although in this schematic the
    interconnection is only via one WAN a real
    world internet delivery would be by multiple
    WANS.

Source LAN
Transit WAN (Backbone)
Gateway
Destination LAN
Gateway
35
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.
36
TCP/IP and OSI model
37
Relationship of layers and addresses in TCP/IP
Not used in this unit
38
ADDRESSING
Three levels of addresses are used in an internet
employing the TCP/IP protocols
  • Physical / MAC layer 2
  • Logical / IP layer 3
  • Port / TCP/UDP layer 4

MAC Data link Data Frame IP Network
Packet TCP/UDP Transport Segment
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The concept of TCP/UDP and Port address will be
covered later in Transport layer lecture
44
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.
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Extra Examples
50
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
51
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.
52
  • Quiz at
  • http//highered.mcgraw-hill.com/sites/0072967757/s
    tudent_view0/chapter2/multiple_choice_quiz.html

53
The END
  • See you next week
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