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COS2626 Exam Notes 2022
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Exam of 77 pages for the course COS2626 - Computer Networks I at Unisa (COS2626 Exam Notes)
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lOMoARcPSD|11273720COS2626 EXAM NOTES
Chapter 1 Introduction to Networking
1. How Networks are Used
Network services: resources a network makes available to its users, include applications and
data provided by the applications.
a. Client Server Application
First computer is client, request info from second computer: server. Communicate
through protocols
Web service: serves up web pages to client. Primary protocol used is HTTP
(Hypertext Transfer Protocol) layer on top of SSL (Secure Sockets Layer) or TLS
(Transport Layer Security), it is HTTPS (HTTP Secure).give secure transmission.
Email services: client-server application that involves 2 servers the client uses
SMTP (Simple Mail Transfer Protocol) to send a mail to the first server, SMTP
server, first server sends message to receivers server, stored until recipient
request delivery. Receiver mail delivers message to receiver using POP3(Post
Office Protocol version 3) email is downloaded to client computer, or
IMAP4(Internet Message Access Protocol version 4) client application
manages email stored on server.
FTP service: client-server application that transfers files between 2 computers.
FTP is not secure does not provide encryption.
Telnet services: Telnet protocol used by Telnet client-server command line
application to allow an administrator to remote in or control a computer
remotely.
Remote Desktop: in Windows Remote Desktop application uses RDP
Remote applications is an application that is installed and executed on a
server and is presented to a user working at a client computer, client
computer require less computing power and desk side support.
b. File and Print Services
File services are server’s ability to share data files and disk storage space, such a
computer is a file server, serves data to users, users do not keep copies of data on
their workstations. Data stored at a central location is more secure, easier for network
administrator to take charge of it, make backups.
Print services Share printers across a network
c. Communications Services
Same network to deliver multiple types of communications (Video, voice, fax) is
convergence. Unified communications (UC) is centralized management of multiple
network-based communications. Use one software program to manage all the
applications.
- Conversational voice: (VoIP) allows voice conversation over network, use
point-to-point model, not client-server model, so each computer involved is
independent from the other computers. Conference call use point-to-
multipoint model with transmitter and multiple transceivers.
- Streaming live audio and video: video teleconference (VTC) like Skype or
Google Talk, point-to-point model. Watching live sport is client-server
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model,
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client server called multicast distribution. Session layer protocol to transmit
audio and video in conjunction with VoIP is RTP (Real-time Transport
Protocol)
- Streaming stored audio or video: like videos on YouTube, client server model.
Voice and video transmission are delay sensitive- don’t want to hear breaks in
conversation. Loss of data can be tolerated (skipping a frame) = loss tolerant.
QoS (Quality of Service) provided by network
2. Controlling Network Access
Topology = how parts of whole work together.
- Physical topology: hardware layout
- Logical topology: software and how network is controlled.
Operating system control how users and programs get access to resources on network using:
a. Peer-to-Peer Network Model
Without centralized control, computers are nodes/ hosts on network and form logical
group of computers that let users share resources.
Administration, resources and security on a computer is controlled by that computer.
Examples: Windows 7, Windows 8.1, Linux, Mac OS X, for mobile devices: iOS, Android
and Blackberry
How it works:
Each computer has its own local account that works on that computer, each computer
has a list of the users and their rights on that PC, windows then allows a user to access
local resources. Using a homegroup, each computer shares files, folders, libraries and
printers with other computer in that homegroup. The homegroup limits how sharing
can be controlled for individual users.
Less than 15 computers it is a good method, simple to configure, less expensive.
BUT they are not scalable, not very secure
b. Client-Server Network Model
Managed by NOS (Network Operating System) via centralized directory database.
Windows server controls network access to a group of computers called domain.
Centralized directory database with user account info and security is Active Directory
(AD). Each user has own domain-level account called global account/global
username/network ID, assigned by network administrator and stored in AD, process
managed by Active Directory Domain Services (AD DS).
Example: Windows Server 2012 R2, Ubuntu Server, Red Hat Linux.
- Managing data and other resources for many clients
- Ensuring that only authorized users access the network
- Controlling which types of files a user can open and read
- Restricting when and from where users can access the network.
- Dictating which rules computers will use to communicate
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Servers with NOS require more memory, processing power and storage
Advantages:
- User accounts and passwords are assigned in one place
- Access to share resources centrally granted to users
- Problems are monitored, diagnosed and fixed in one location
- Easily scalable.
3. Networking Hardware and Physical Topologies
a. LANs and their Hardware
Small space, office or building. A switch receives incoming data from one of its ports
and redirects it to another port that sends the data to its destination.
Uses star topology, switch is central device. .
Onboard network port is embedded in motherboard, plug network cable into it
NIC (Network Interface Card) or network adapter, installed in an expansion slot on
motherboard, type of port.
Backbone is central conduit that connects the segments of a network. Use higher
transmission speed and different cabling, bus topology, from where each switch is
connected to its computers with star topology. Combination of topologies are hybrid
topology.
Ring topology: one node is connected to its neighbouring nodes.
Router: used to connect LAN with other networks. Device that manages traffic
between 2 or more networks, finds the best path for traffic. Stands between LAN and
internet. Difference between switch and router: switch belongs only to its local
network, ‘n router belongs to 2 or more networks.
Host: a computer on a network that hosts a resource or application or data.
Node: computer or device on net work that can be addressed on the local network.
b. MANs and WANs
Group of LANs = MAN (Metropolitan Area Network) CAN (Campus Area Network), same
geographical area.
Wide geographical area = WAN
4. The Seven-Layer Model
OSI model developed to categorise layers of communication
All People Seem To Need Data Processing
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