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Summary COS2626 Summarised Study Notes
- Institution
- University Of South Africa (Unisa)
- Book
- Computer Networks
COS2626 summarized notes for exam preparation. for assistance. All the best on your exams!!
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COS2626NOTES
,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.
Page | 2 2
, - Streaming live audio and video: video teleconference (VTC) like Skype or
Google Talk, point-to-point model. Watching live sport is client-server
model, 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
Page | 3 3
, - 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
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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