Networking

Computer Network
Network Models

Learning Outcomes
Students are able to describe basic structures of network.

Outline
• Data Communications
• Networks
• Network Types
• The Internet
• Protocol Layering
• TCP/IP Protocol Suite
• OSI Model and TCP/IP Model
• Network Devices
• Virtual LANs

Data Communications
• Data communications is the exchange of data between two devices via some form
of transmission medium such as a wire cable. For data communications to occur,
the communicating devices must be part of a communications system made up of
a combination of hardware (physical equipment) and software (programs).
• The effectiveness of a data communications system depends on four fundamental
characteristics:
– Delivery
– Accuracy
– Timeliness, and
– Jitter.

Components
• The message is the information (data) to be communicated. Popular forms of
information include text, numbers, pictures, audio, and video.
• The sender is the device that sends the data message. It can be a computer, a
telephone handset, a video camera, and so on.
• The receiver is the device that receives the message. It can be a computer,
workstation, telephone handset, television, and so on.
• The transmission medium is the physical path by which a message travels from
sender to receiver.
• A protocol is a set of rules that govern data communications.
Pic 1.1. Five components of a data communications system
Source : Data Communications and Networking with TCP/IP Protocol Suite.
Forouzan, B. A.

Data Flow
Pic 1.2. Data flow (simplex, half-duplex, and full-duplex)
Forouzan, B. A.

Network
• Network is the interconnection of a set of devices capable of communication.
• A device can be a host, such as a large computer, desktop, laptop, workstation,
cellular phone, or security system.
• A device in this definition can also be a connecting device such as a router that
connects the network to other networks, a switch that connects devices together,
or a modem (modulator-demodulator) that changes the form of data.

Network Criteria
• A network must be able to meet a certain number of criteria. The most important
of these are :
– Performance
• Depends on Network Elements
• Measured in terms of Delay and Throughput
– Reliability
• Failure rate of network components
• Measured in terms of availability/robustness
– Security
• Data protection against corruption/loss of data due to:
– Errors
– Malicious users

Physical Structures
• Type of Connection
– Point to Point - single transmitter and receiver
– Multipoint - multiple recipients of single transmission
• Physical Topology
– Connection of devices
– The topology of a network

Types of connections
Pic 1.3. Types of connections: point-to-point and multipoint
Forouzan, B. A.

Physical Topology
Pic 1.4. Categories of topology)
Forouzan, B. A.

Mesh Topology
Pic 1.5. A fully connected mesh topology (five devices)
Forouzan, B. A.

Star Topology
Pic 1.6. A star topology connecting four stations
Forouzan, B. A.

Bus Topology
Pic 1.7. A bus topology connecting three stations
Forouzan, B. A.

Ring Topology
Pic 1.8. A ring topology connecting six stations
Forouzan, B. A.

Categories of Networks
• Local Area Networks (LANs)
– Short distances
– Designed to provide local interconnectivity
• Wide Area Networks (WANs)
– Long distances
– Provide connectivity over large areas
• Metropolitan Area Networks (MANs)
– Provide connectivity over areas such as a city, a campus

LAN
Pic 1.9. An isolated LAN in the past and today
Forouzan, B. A.

WAN
Pic 1.10. A point-to-point WAN
Forouzan, B. A.

WAN (cont)
Pic 1.11. A switched WAN
Forouzan, B. A.

WAN (cont)
Pic 1.12. An internetwork made of two LANs and one point-to-point WAN
Forouzan, B. A.

The Internet
• The Internet has revolutionized many aspects of our daily lives. It has affected the
way we do business as well as the way we spend our leisure time. The Internet is a
communication system that has brought a wealth of information to our fingertips
and organized it for our use.

The Internet (cont)
Pic 1.13. A heterogeneous internetwork made of four WANs and two LANs
Forouzan, B. A.

The Internet (cont)
Pic 1.14. The Internet today
Forouzan, B. A.

Accessing the Internet
• The Internet today is an internetwork that allows any user to become part of it.
The user, however, needs to be physically connected to an ISP.
• The physical connection is normally done through a point-to-point WAN (such as a
– Telephone network,
– Cable network,
– Wireless network, or
– Other types of networks).

Protocol Layering
• In data communications and networking, a protocol defines the rules
that both the sender and receiver and all intermediate devices need
to follow to be able to communicate effectively.
• Communication is simple, we may need only one simple protocol;
when the communication is complex, we may need to divide the task
between different layers, in which case we need a protocol at each
layer, or protocol layering.

Protocol Layering (cont)
Single-layer protocol
Three-layer protocol
Pic 1.16. A three-layer protocol
Source : Data Communications and
Networking with TCP/IP Protocol Suite.
Forouzan, B. A.
Pic 1.15. A single-layer protocol
Source : Data Communications and
Networking with TCP/IP Protocol Suite.
Forouzan, B. A.

TCP/IP Protocol Suite
• TCP/IP is a protocol suite (a set of protocols organized in different layers) used
in the Internet today. It is a hierarchical protocol made up of interactive
modules, each of which provides a specific functionality. The term hierarchical
means that each upper-level protocol is supported by the services provided
by one or more lower-level protocols. The TCP/IP protocol suite is defined as
five layers.
Pic 1.17. Layers in the TCP/IP protocol suite
Forouzan, B. A.

Layered Architecture
Pic 1.18. Communication through an internet
Forouzan, B. A.

Brief Description of Layers
Pic 1.19. Logical connections between layers of the TCP/IP protocol suite
Forouzan, B. A.

Brief Description of Layers (cont)
Pic 1.20. Identical objects in the TCP/IP protocol suite
Forouzan, B. A.

International Organization for Standardization (ISO)
• International Organization for Standardization (ISO) is a multinational body dedicated to worldwide agreement
on international standards.
• ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI)
model. It was first introduced in the late 1970s.
• OSI model is a layered framework for the design of network systems that allows communication between all
types of computer systems.
Pic 1.21. The OSI model
Forouzan, B. A.

OSI versus TCP/IP
Pic 1.22. TCP/IP and OSI model
Forouzan, B. A.

Lack of OSI Model’s Success
• OSI was completed when TCP/IP was fully in place and a lot of time and money had
been spent on the suite; changing it would cost a lot.
• Some layers in the OSI model were never fully defined.
• OSI was implemented by an organization in a different application, it did not show
a high enough level of performance to entice the Internet authority to switch from
the TCP/IP protocol suite to the OSI model.

Connecting Devices
• Hosts and networks do not normally operate in isolation. Connecting devices to connect hosts
together to make a network or to connect networks together to make an internet.
• three kinds of connecting devices:
– Hubs,
– Link-layer switches, and
– Routers.
Pic 1.23. Three categories of connecting devices
Forouzan, B. A.

• Hub is a device that operates only in the physical layer. Signals that carry information within a network
can travel a fixed distance before attenuation endangers the integrity of the data.
• Repeater receives a signal and, before it becomes too weak or corrupted, regenerates and retimes the
original bit pattern. The repeater then sends the refreshed signal.
• Repeater has no filtering capability.
Pic 1.24. A Hub
Forouzan, B. A.
Hubs

• Link-layer switch operates in both the physical and the data-link layers. As a physical-layer device, it
regenerates the signal it receives. As a link- layer device, the link-layer switch can check the MAC
addresses (source and destination) contained in the frame.
• A link-layer switch has a table used in filtering decisions.
• A link-layer switch does not change the link-layer (MAC) addresses in a frame.
Pic 1.25. Link-layer switch
Forouzan, B. A.
Link-Layer Switches

• A router is a three-layer (physical, data-link, and network) device.
• There are three major differences between a router and a repeater or a switch.
– A router has a link-layer and network-layer address for each of its interfaces.
– A router acts only on those packets in which the link-layer destination address matches the
address of the interface at which the packet arrives.
– A router changes the link-layer address of the packet (both source and destination) when it
forwards the packet.
• A router changes the link-layer addresses in a packet.
Pic 1.26. Routing example
Forouzan, B. A.
Routers

• A LAN can be divided into several logical LANs, called VLANs, Each VLAN is a work group in the
organization.
• The group membership in VLANs is defined by software, not hardware.
• What characteristic can be used to group stations in a VLAN? Vendors use different characteristics such
as :
– Interface number,
– MAC addresses or
– Combination(Interface Number and MAC Address).
• VLAN can configured in one of three ways:
– Manual,
– Automatic, and
– Semiautomatic.
Virtual LANs

• Communication among Switches, three methods have been devised for
this purpose: Table maintenance, Frame tagging, and Time-division
multiplexing.
• There are several advantages to using VLANs : Cost and Time Reduction,
Creating Virtual Work Groups, and Security.
Pic 1.27. A switch using VLAN software
Forouzan, B. A.
Virtual LANs (cont)

• Characteristic can be used to group stations in a VLAN
– Interface number
– MAC addresses
– Combination.
• To Grouped into different VLAN have three ways:
– Manual
– Automatic
– Semiautomatic.
• How to Communication among Switches have Three methods :
– table maintenance
– frame tagging
– Time-Division Multiplexing (TDM)
Virtual LANs (cont)

• There are several advantages to using VLANs.
– Cost and Time Reduction
– Creating Virtual Work Groups
– Security
Advantages using VLAN

Summary
• Data communications are the transfer of data from one device to another via some form of transmission
medium. A data communications system must transmit data to the correct destination in an accurate and
timely manner. The five components that make up a data communications system are the message, sender,
receiver, medium, and protocol. Text, numbers, images, audio, and video are different forms of information.
Data flow between two devices can occur in one of three ways: simplex, half-duplex, or full- duplex.
• A network can be categorized as a local area network or a wide area network. A LAN is a data communication
system within a building, plant, or campus, or between nearby buildings. A WAN is a data communication
system spanning states, countries, or the whole world. An internet is a network of networks. The Internet is a
collection of many separate networks.
• Another model that defines protocol layering is the Open Systems Interconnection (OSI) model. Two layers in
the OSI model, session and presentation, are missing from the TCP/IP protocol suite. These two layers were
not added to the TCP/IP protocol suite after the publication of the OSI model. The application layer in the
suite is usually considered to be the combination of three layers in the OSI model. The OSI model did not
replace the TCP/IP protocol suite because it was completed when TCP/IP was fully in place and because some
layers in the OSI model were never fully defined.

Summary
• A repeater is a connecting device that operates in the physical layer of the Internet model. A repeater
regenerates a signal, connects segments of a LAN, and has no filtering capability. A link-layer switch is a
connecting device that operates in the physical and data-link layers of the Internet model. A transparent
switch can forward and filter frames and automatically build its forwarding table. A switch can use the
spanning tree algorithm to create a loopless topology.
• A virtual local area network (VLAN) is configured by software, not by physical wiring. Membership in a VLAN
can be based on MAC addresses, IP addresses, IP multicast addresses, or a combination of these features.
VLANs are cost and time efficient, can reduce network traffic, and provide an extra measure of security.

References
• Forouzan, B. A. (2021). Data Communications and Networking with TCP/IP Protocol Suite. 6th Ed. New York: McGraw-Hill. ISBN:
978-1-26-436335-3. Chapter 1 and 6.
• https://www.tutorialspoint.com/data_communication_computer_network/index.htm
• https://ecomputernotes.com/computernetworkingnotes/communication-networks/what-is-data-communication
• https://beginnersbook.com/2019/03/computer-network-topology-mesh-star-bus-ring-and-hybrid/
• https://fcit.usf.edu/network/chap1/chap1.htm
• https://www.cl.cam.ac.uk/teaching/1011/PrincComm/slides/layering-11.pdf
• https://study-ccna.com/osi-tcp-ip-models/
• https://www.tutorialspoint.com/communication_technologies/communication_technologies_network_devices.htm
• https://www.youtube.com/watch?v=49jqn93x7go
• https://www.youtube.com/watch?v=kCuyS7ihr_E
• https://www.youtube.com/watch?v=Ilk7UXzV_Qc
• https://www.youtube.com/watch?v=2QGgEk20RXM
• https://www.youtube.com/watch?v=ez24W5oTU3U

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