Data Communications and Networking

1
CSCS 311
Data Communications and Networking
Lecture 2
2
Lecture Focus
Data Communications and Networking
Lecture 2

• Networking
• Distributed Processing
• Network Criteria
• Physical Structures
• Categories of Networks

3
NETWORKING
Data Communications and Networking
Lecture 2
In its simplest form, data communication takes
place between two devices that are directly
connected by some form of point-to-point
transmission medium. Often, however, it is
impractical for two devices to be directly,
point-to-point connected due to the following
reasons

• The devices are very far apart. It would be
  expensive, for example, to string a dedicated
  link between two devices thousands of miles
  apart.
• There is a set of devices, each of which may
  require a link to many of the others at various
  times.
• Example
• All the telephones in the world
• All of the computers owned by a single
  organization.
• Except for the case of a very few devices, it is
  impractical to provide a dedicated wire between
  each pair of devices.

Solution to this problem is to attach each device
to a communications network.
4
NETWORKING
Data Communications and Networking
Lecture 2

• Network is a highway on which data can travel.

• A network is a set of devices (often referred to
  as nodes) connected by communication links.
• A node can be a computer, printer, or any other
  device capable of sending and/or receiving data
  generated by other nodes on the network.

• Interconnected nodes can share data, hardware and
  software. Links connecting the devices are often
  called communication channels.

5
NETWORKING
Data Communications and Networking
Lecture 2
Distributed Processing

• Most networks use distributed processing, in
  which a task is divided among multiple computers.
  Instead of one single large machine being
  responsible for all aspects of a process,
  separate computers (usually a personal computer
  or workstation) handle a subset.

6
NETWORKING
Data Communications and Networking
Lecture 2
Network Criteria

• A network must be able to meet a certain number
  of criteria. The most important of these are
  performance, reliability, and security.

7
Data Communications and Networking
Lecture 2
Network Criteria
Performance
Performance can be measured in many ways,
including transit time and response
time. 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. The
performance of a network depends on a number of
factors, including The number of users The
type of transmission medium The capabilities of
the connected hardware, and The efficiency of
the software.
8
Data Communications and Networking
Lecture 2
Network Criteria
Performance
Performance is often evaluated by two networking
metrics Throughput Delay We often need
more throughput and less delay. However, these
two criteria are often contradictory. If we try
to send more data to the network, we may increase
throughput but we increase the delay because of
traffic congestion in the network.
9
NETWORKING
Data Communications and Networking
Lecture 2
Network Criteria
Reliability
In addition to accuracy of delivery, network
reliability is 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.
Security
Network security issues include protecting data
from unauthorized access, protecting data from
damage, and implementing policies and procedures
for recovery from breaches and data losses.
10
NETWORKING
Data Communications and Networking
Lecture 2
Physical Structures
Type of connection

• A network is two or more devices connected
  through links.
• A link is a communications pathway that transfers
  data from one device to another.
• For visualization purposes, it is simplest to
  imagine any link as a line drawn between two
  points.
• For communication to occur, two devices must be
  connected in some way to the same link at the
  same time.

11
NETWORKING
Data Communications and Networking
Lecture 2
Physical Structures
Type of connection
There are two possible types of connections
point-to-point and multipoint.

1. Point-to-Point
2. Multipoint

12
Data Communications and Networking
Lecture 2
Point-to-point connection

• A point-to-point connection provides a dedicated
  link between two devices.
• The entire capacity of the link is reserved for
  transmission between those two devices.
• Most point-to-point connections use an actual
  wire or cable to connect the two ends, but other
  options, such as microwave or satellite links,
  are also possible.
• When you change television channels by infrared
  remote control, you are establishing a
  point-to-point connection between the remote
  control and the television's control system.

A transmission medium is point-to-point if,
first, it provides a direct link between two
devices and, second, those are the only two
devices sharing the medium.
13
Data Communications and Networking
Lecture 2
Point-to-point connection
There is no central server.
Used in small business, homes etc.
14
Data Communications and Networking
Lecture 2
Multi-point connection

• A multipoint (also called multidrop) connection
  is one in which more than two specific devices
  share a single link.
• More than two devices share the same medium
• In a multipoint environment, the capacity of the
  channel is shared spatially or temporally.
• If several devices can use the link
  simultaneously, it is a spatially shared
  connection.
• If users must take turns, it is a timeshared
  connection.

• A central computer acts as a server and remaining
  computers are called clients in the network.

15
Data Communications and Networking
Lecture 2
Multi-point connection
16
Figure 1.7 Categories of topology
Next Lecture
17
Figure 1.8 Fully connected mesh topology (for
five devices)
18
Figure 1.9 Star topology
19
Figure 1.10 Bus topology
20
Figure 1.11 Ring topology
21
Figure 1.12 Categories of networks
22
Figure 1.13 LAN
23
Figure 1.13 LAN (Continued)
24
Figure 1.14 MAN
25
Figure 1.15 WAN
26
1.3 The Internet
A Brief History The Internet Today
27
Figure 1.16 Internet today
28
1.4 Protocols and Standards
Protocols Standards Standards
Organizations Internet Standards