Transcript 1.TNS01%20Review%20of%20Network%20%26%20Communi..

TNS1 - Review of Network &
Communication System
Source:
Chapter 1 and 2
Data Communications & Networking
Behrouz A. Forouzan
Third Edition
McGraw Hill
1
Basic Networking Concepts
Focus on:
 COMPUTER NETWORKS
 NETWORK
MODELS
2
COMPUTER NETWORKS
 Distributed Processing
 Network Criteria
 Physical Structures
 Categories of Networks
 Protocols and Standards
3
Distributed Processing


A task is divided among multiple computers.
Instead of a single large machine being
responsible for all aspects of a process,
separate computers handle a subset.
4
Network Criteria (1)
(1) Performance
• Transit time is the amount of time required for a
message to travel from one device to another.
• Response time is the elapsed time between an
inquiry and a response.
• Depending on the number of users, the type of
transmission medium, the capabilities of the
connected hardware, and the efficiency of the
software.
5
Network Criteria (2)
(2) Reliability
• Measured by the frequency of failure, the
time it takes a link to recover from a failure,
and the network’s robustness in a
catastrophe.
(3) Security
• Protecting data from unauthorized access.
6
Physical Structures

Type of connections

Physical topology
7
Type of Connections (1)
Point-to-point connection
• A dedicated link between two devices.
8
Type of Connections (2)
Multipoint (or multidrop) connection
• More than two devices share a single link
either spatially or temporally.
9
Physical (Network) Topology

Geometric representation of the relationship
of all the links and linking devices (called
nodes) to one another.
10
Mesh Topology



Every device has dedicated point-to-point link to
every other device.
A fully connected mesh network has n(n-1)/2
physical channels to link n devices.
Every device must have n-1 input/output (I/O) ports.
Fully connected mesh topology
(for five devices with 10
physical channels)
11
Mesh Topology - Advantages




Eliminating the traffic problems as each
connection can carry its own data load.
It is robust. If one link fails, it does not
incapacitate the entire system.
Better security. Message can only be
accessed by the intended recipients.
Easy fault identification and fault isolation.
12
Mesh Topology - Disadvantages
 Installation and reconnection are difficult.
 Sheer bulk of the wiring can be greater than

the available space (in walls, ceilings, floors)
can accommodate.
Hardware required (I/O ports and cable) is
expensive.
13
Star Topology

Each device has a dedicated point-to-point
link only to a central controller, called a hub.
14
Star Topology - Advantages




Less expensive than mesh topology as each
device needs only one I/O and one link to
connect it to the hub.
Easy to install and reconfigure.
Robustness. If one link fails, only that link is
affected.
Easy fault identification and fault isolation.
15
Star Topology - Disadvantages



Single point of failure at the hub. If the hub
fails, then the whole network fails.
Bottlenecks can occur because all data must
pass through the hub.
More cabling is required than bus or ring
topologies.
16
Bus Topology

A multipoint connection. One long cable acts
as a backbone to link all the devices in a
network.
17
Bus Topology - Advantages


Ease of installation. Nodes are connected to
the nearest points on the backbone cable by
drop lines.
Less cabling than mesh or star topologies.
18
Bus Topology - Disadvantages



Difficult reconnection and fault isolation. The bus is
designed to be efficient at installation and it can be
difficult to add new devices.
Signal degradation caused by taps limits the number
and spacing of devices connected to a given
backbone cable.
A fault or break in the backbone cable causes the
whole system to fail.
19
Ring Topology



Each device has a dedicated point-to-point
connection only with the two devices on either side
of it.
A signal is passed along the ring in one direction
until it reaches the destination.
A device receives a signal intended for another
device, its repeater regenerates the bits and passes
them along.
20
Ring Topology - Advantages


Easy to install and reconfigure. To add or
delete a device requires changing only two
connections.
Fault isolation is simplified. As a signal is
circulating at all times, a device will issue an
alarm if it does not receive the signal within a
specified period.
21
Ring Topology - Disadvantage

A break in the ring can disable the entire
network. This weakness can be solved by
using a dual ring or a switch capable of
closing off the break.
22
Categories of Networks

A network is classified according to its size,
its ownership, the distance it covers, and its
physical architecture.
23
Local Area Network (LAN) - 1

Usually a privately owned and links the devices in a
single office, building, or campus (group of
buildings).
24
Local Area Network (LAN) - 2



Designed to allow resources (hardware, software,
data) to be shared between personal computers.
Usually use one type of transmission medium, and
most common topologies are bus, ring and star.
Data rates can reach 100 Mbps and even gigabit
ranges.
25
Metropolitan-Area Network (MAN) 1
26
Metropolitan-Area Network (MAN) 2



Designed to extend over an entire city.
May be wholly owned and operated by a
private company, or a public company (e.g.
telephone company).
A single network (e.g. a cable television
network) or a number of LANs connected into
a large network.
27
Wide Area Network (WAN) - 1
28
Wide Area Network (WAN) - 2



Provides long-distance transmission of data,
voice, image, and video information over
large geographic areas that may comprise a
country, a continent, or even the whole world.
Utilize public, leased, or private
communication equipment.
The largest WAN is the Internet.
29
Protocols (1)


A set of rules that governs data communications.
The key elements: syntax, semantics, timing.
Syntax
• The structure or format of data. For example, the
first 8 bits of data to be the address of sender,
the second 8 bits to be the address of the
receiver, and the rest to be the message itself.
30
Protocols (2)
Semantics (meaning)
• The meaning of each section of bits. How is a
particular pattern to be interpreted, and what action
is to be taken?
Timing
• When the data should be sent and how fast they
can be sent.
31
Standards (1)


Essential in creating and maintaining an open
and competitive market for equipment
manufacturers and in guaranteeing national
and international interoperability of data,
technology, and processes.
Data communication standards fall into two
categories: de facto and de jure.
32
Standards (2)
De facto (by fact or by convention)
• Standards that have not been approved by an
organized body but have been adopted as
standards through widespread use.
• Often established by manufacturers that seek to
define the functionality of a new product or
technology.
• Examples: Hayes command set for controlling
modems, PostScript page description language for
laser printers.
33
Standards (3)
De jure (by law or by regulation)
• Standards have been legislated by an
officially recognized body.
• Examples: International standards
established by the ISO and IEEE.
• Reference link:
http://docs.sun.com/db/doc/8016735/6i13eq5fo?a=view
34
Standards Organizations





International Organization for Standardization
(ISO)
International Telecommunication Union (ITU)
Consultative Committee for International
Telegraphy and Telephony (CCITT)
Institute of Electrical and Electronics Engineers
(IEEE)
Reference link:
http://www.webopedia.com/Standards/Standards
_Organizations/
35
NETWORK MODELS
 Layered Tasks
 Internet Model
 OSI Model
36
Layered Tasks
– Sending a letter
Hierarchy
Sender site:
3 different activities
Receiver site:
3 different activities
Carrier:
Transporting the letter
Services
Higher layer uses the
services of lower
layer
37
Internet Model





Five-layer Model
Peer-to-peer Communication
Interfaces between Layers
Organization of Layers
Functions of Layers
38
Five-layer Model


The five-layer model dominates data
communications and networking today, sometimes
called the TCP/IP protocol suite.
Related networking functions are collected into
discrete groups that become the layers.
Layer number
39
Peer-to-peer Communication (1)



Within a single machine, each layer calls upon the
services of the layer just below it.
Between each machines, layer x on one machine
communicates with layer x on another machine.
Each layer in the transmitting machine
communicates with its peer layer in the receiving
machine via a process called peer-to-peer
communication.
40
Peer-to-peer Communication (2)


This communication is governed by an agreed-upon
series of rules and conventions called protocols.
The processes on each machine that communicate
at a given layer are called peer-to-peer processes.
process = running program
41
Interfaces Between Layers (1)


The passing of the data down through the layers of
the sending device and back up through the layers
of the receiving device is made possible by an
interface between each pair of adjacent layers.
Each interface defines what information and
services a layer must provide for the layer above it.
42
Interfaces Between Layers (2)


With well-defined interfaces and layer
functions, the specific implementation of its
functions can be modified or replaced without
requiring changes to the surrounding layers.
They provide modularity to a network.
43
44
Organization of Layers (1)
Network support layers
Layers 1, 2, 3 – physical, data link, network layers
•
Deal with the physical aspects of moving data from one device to
another such as electrical specifications, physical connections,
physical addressing, transport timing and reliability.
User support layer
Layer 5 – application layer
•
Allows interoperability among unrelated software systems.
45
Organization of Layers (2)
Layer to link subgroups
Layer 4 – transport layer
• Links the two subgroups and ensures that what the
lower layers have transmitted is in a form that the
upper layers can use.
46
Organization of Layers (3)
Sender
Receiver
Electromagnetic signal
47
Organization of Layers (4)



The transmitting process starts at layer 5, then
moves down to lower layers in sequential order. (54-3-2-1)
At each layer, a header (Hx) is added to the data
unit. At layer 2, a trailer (T2) is added for error
control.
The physical layer converts the data unit into an
electromagnetic signal and transports it along the
physical link.
48
Organization of Layers (5)




At the receiver side, the signal passes into layer
1 and is transformed back into digital form (bit
stream).
The data unit then move back up through layers.
(1-2-3-4-5)
The headers and trailers attached to it at the
corresponding sending layer are removed, and
actions are taken.
At layer 5, the message is in a form appropriate
to the application and is made available to the
receiver.
49
Physical Layer (Layer 1) – (1)

Responsible for transmitting a bit stream over a
physical medium from one node to the next.
Major duties are as below:
Physical characteristics of interfaces and media
• Deals with the mechanical and electrical
specifications of interface and transmission media.
50
Physical Layer (Layer 1) – (2)
Representation of bits
• To be transmitted, bits must be encoded into
electromagnetic signal (electrical or optical).
Data rate
• The number of bits send each second.
Synchronization of bits
• The sender and the receiver clocks must be
synchronized.
51
Physical layer
52
Data Link Layer (Layer 2) – (1)

Responsible for transmitting frames from one node
to the next (node-to-node or hop-to-hop delivery) on
the same network.
Major duties:
Framing
• Divides the bit stream received from the network
layer into manageable data units called frames.
53
Data Link Layer (Layer 2) – (2)
Physical addressing
• Adds a header containing the addresses of
the sender and receiver of the frame.
Flow control
• Imposes flow control mechanism to prevent
overwhelming of the receiver.
54
Data Link Layer (Layer 2) – (3)
Error control
• Adds reliability to the physical layer by adding
trailer to detect and retransmit damaged or
lost frames.
Access control
• Determine which device has control over the
link at any given time. (e.g. CSMA/CD,
CSMA/CA)
55
Data Link Layer
56
Data Link Layer – Hop-to-hop (node-to-node) delivery
57
Example – Data Link Layer

Only physical addresses are needed to
transmit data within a network.
58
Network Layer (Layer 3) – (1)

Responsible for the source-to-destination (end-toend or host-to-host) delivery of a packet, not the
entire message, across multiple networks.
Major duties:
Logical addressing
• Add a header containing the logical addresses of
the sender and receiver.
59
Network Layer (Layer 3) – (2)
Routing
• Provides the function for routers to route or
switch the packets in an internetworking
(network of networks) environment.
60
Network Layer
61
Network Layer - Source-to-destination delivery
62
Example – Network Layer



Sending data from node with
physical address 10 and
network address A, to a node
with physical address 95 and
network address P located on
different network.
The logical addresses of
packet remain the same from
source to destination.
However, the physical
addresses will change as the
packet moves from one
network to another.
63
Transport Layer (Layer 4)– (1)

Responsible for process-to-process delivery of the
entire message, and guarantees it will reach the
destination process in another computer intact and
in order .
64
Reliable process-to-process delivery of a message
65
Transport Layer (Layer 4)– (2)
Major duties:
Port addressing
• Process-to-process delivery means delivery not only
from one computer to the next but also from a
specific process (e.g. a Web browser) on one
computer to a specific process (a Web server) on
the other.
• The header includes a type of address called a port
address. For example, port 80 for web Server.
66
Transport Layer (Layer 4)– (3)
Segmentation and reassembly
• Segmentation: A message is divided into
transmittable segments, each segment containing a
sequence number.
• Reassembly: The segment numbers enable the
transport layer to reassemble the message correctly
upon arrival at the destination, and to identify and
replace packets that were lost in the transmission.
67
Transport Layer (Layer 4)– (4)
Connection control
• Connectionless: Treats and delivers each segment
as an independent packet.
• Connection-oriented: Makes a connection with the
transport layer at the destination machine first
before transmission. Terminates the connection
after all the data are transferred.
68
Transport Layer (Layer 4)– (5)
Flow control
• Prevents overwhelming of the receiver in an endto-end manner.
Error control
• The sending transport layer makes sure that the
entire message arrives at the receiving transport
layer without error (damage, loss, or duplication).
• Error connection is usually achieved through
retransmission.
69
Example – Transport Layer
 Data coming from the upper layers have port
addresses j and k (j is the address of the sending
process, and k is the address of the receiving
process). Since the data size is larger than the
network layer can handle, the data are split into two
packets, each packet retaining the port addresses (j
and k). Then in the network layer, network
addresses (A and P) are added to each packet.
70
k: port address of receiving process
j: port address of sending process
Segmentation
(2 segments)
Reassembly
71
Application (Layer 5) – (1)

Enables the user, whether human or software, to
access the services of network.
Major duties
Mail Services (e.g. SMTP)
• Email forwarding and storage.
File transfer and access (e.g. FTP)
• Allows user to read, change, retrieve and to
manage files in a remote host.
72
Application (Layer 5) – (2)
Remote log-in (e.g. Telnet)
• Allows user to log into a remote computer
and access the resources of that computer.
World Wide Web (e.g. HTTP)
• Allow users to access the World Wide Web
(WWW) in the Internet.
73
Application Layer
74
OSI Model (1)


Open Systems Interconnection (OSI) model
was designed by the international
Organization for Standardization (ISO).
A seven-layer theoretical model designed to
show how a protocol stack should be
implemented.
75
OSI Model (2)
Two extra layers:
Session layer
•
Network dialog controller to establish, maintain, and
synchronize the interaction between communicating
systems.
Presentation layer
•
Handles the syntax and semantics of the information
exchanged between the two systems.
•
Designed for data translation, encryption, decryption,
and compression.
76
OSI Model (3)
77
Summary (1)



Today, the duties of the two extra layers
(session and presentation) are handled by
other layers.
For example, encryption and decryption occur
at several layers. Data are compression at the
application layer.
Therefore, we concentrate on the five-layer
Internet model.
78
Summary (2)
TCP/IP Reference Model
79