Computer Networks/Computer Engineering.pdf

1.1
Chapter 1
Introduction
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

1.2
1-1 DATA COMMUNICATIONS
• The term telecommunication means communication at
a distance.
• The word data refers to information presented in
whatever form is agreed upon by the parties creating
and using the data.
• Data communications are the exchange of data
between two devices via some form of transmission
medium such as a wire cable.

1.3
Characteristics of Effectiveness
• Delivery
• Accuracy
• Timeliness
• Jitter

1.4
Figure 1.1 Five components of data communication

1.5
Data Representation
• Text: represented using bit patterns
• ASCII: 7-bit (128 symbols)
• Extended ASCII: 8-bit (256 symbols)
• Unicode: 16-bit (65,536 symbols)
• ISO: 32-bit (4B symbols)
• Numbers: represented in binary
• Images: bit patterns for pixels and colors
• Audio: analog or digitized form
• Video: analog or digitized form

1.6
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

1.7
1-2 NETWORKS
• A network is a set of devices (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.

1.8
Network Criteria
• Performance
• Bit rate vs. packet rate vs. throughput
• Transit time (or propagation delay)
• Response time (round trip delay)
• Reliability
• Bit error rate vs. packet error rate
• Error detection and correction
• Link failure recovery time
• Robustness to disasters

1.9
Network Criteria
• Security
• Protect against unauthorized access
• Protect against alteration
• Validity of sender

1.10
Figure 1.3 Types of connections: point-to-point and multipoint

1.11
Figure 1.4 Categories of topology

1.12
Figure 1.5 A fully connected mesh topology (five devices)

1.13
Mesh Topology
• Point-to-point
• n(n-1)/2 dedicated links
• (n-1) I/O ports per device
• Advantages:
• Full capacity
• Robustness (one link failure does not fail whole network)
• Privacy and security
• Easy fault detection and isolation
• Disadvantages:
• Cabling (installation)
• I/O ports
• Space
• Cost

1.14
Figure 1.6 A star topology connecting four stations

1.15
Star Topology
• N dedicated point-to-point links to the hub
• Indirect connections among the nodes
• 1 I/O port per device
• Advantages:
• Robustness
• Disadvantages:
• Single point of failure at the hub
• Bottleneck at the hub.

1.16
Figure 1.7 A bus topology connecting three stations

1.17
Bus Topology
• Multi-point
• 1 backbone link
• 1 I/O port per device
• Advantages:
• Ease of installation
• Minimum cabling at installation
• Disadvantages:
• Limited taps and distance to node
• Limited node addition after initial installation
• Limited quality due to signal reflection at taps
• Difficult fault isolation

1.18
Figure 1.8 A ring topology connecting six stations

1.19
Ring Topology
• Point-to-point
• n dedicated links
• 2 I/O ports per device
• Advantages:
• Easy installation
• Disadvantages:
• Speed: store-and-forward at each node
• Ring length and number of nodes

1.20
Figure 1.9 A hybrid topology: a star backbone with three bus networks

1.21
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

1.22
Figure 1.11 WANs: a switched WAN and a point-to-point WAN

1.23
Figure 1.12 A heterogeneous network made of four WANs and two LANs

1.24
1-3 THE INTERNET
Definition
• An internet: two or more networks that can communicate
with each other.
• The Internet: the network of all networks
A Brief History
The Internet Today (ISPs)
Topics discussed in this section:

1.25
A brief history
• Mid 1960’s: ARPA (Advanced Research Projects Agency) of
DOD (Department of Defense)
• ARPANET was initiated in 1967 and done in 1969
• Interface Message Processors
• Network Control Protocol
• 4-node internetwork

1.26
A brief history
• 1973: TCP (Transmission Control Protocol)
• End-to-end packet delivery
• Encapsulation, datagram, segmentation, reassembly,
error detection, and gateway functionality
• 1973: IP (Internetworking Protocol)
• Datagram routing

1.27
Figure 1.13 Hierarchical organization of the Internet

1.28
1-4 PROTOCOLS AND STANDARDS
• A Protocol: a set of rules that governs data communications
• What? How? and When?
• Syntax: the structure or format of the data (e.g. how many
bits for each section)
• Semantics: the interpretation of the data bit patterns
• Timing: when and how fast the data should be sent

1.29
1-4 PROTOCOLS AND STANDARDS
• A Standard: a set of agreed-upon rules that govern data
communications
• Interoperability
• Open market for competition
• Guidelines to manufactures, vendors, government agencies,
and service providers

Computer Networks/Computer Engineering.pdf

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