Chapter 9: Communications & Networks
Communication is a process of sharing information, data, program between 2 or more computers.
There are 4 elements in communication system:
1) SENDING AND RECEIVING DEVICES
- sending device is a place that information will be send.
- receiving device is a place of receiving information sent from sending device.
2) CONNECTION CHANNEL
- channel connect and transfer information from sending to receiving devices.
- 2 types of channel:
i) Physical connection
Coaxial Cable
ii) Wireless connection
intangible connection element that we cannot touch and see
- Radio Frequency
- Radio waves connect wireless devices (mobile phone, PSP, laptop)
- Have the longest wavelengths
Wi-Fi (Wireless Fidelity)
- Wi-Fi uses radio waves to provide wireless high-speed internet and network connections
- Wi-Fi works with no physical wired connection between sender and receiver by using radio frequency (RF) technology, When an RF current is supplied to an antenna, an electromagnetic field is created that then is able to propagate through space
- the cornerstone of any wireless network is an access point (AP)
- the primary job of an access point is to broadcast a wireless signal that computers can detect and "tune" into
- to connect to an access point and join a wireless network, computers and devices must be equipped with wireless network adapters
- relies on radio frequency and the protocol software that enabling it to transmit date to other devices
- Microwave
- - high frequency radio waves
- - moving in straight lines thought the air
- can penetrate clouds, haze, light rain and snow, and smoke
- transmit information like telephone calls and data from one city to another
- Satellite
Global Positioning System (GPS)
- a system of satellites and receivers that allow people to pinpoint their precise location on the earth.
- relies on 24 satellites that orbit the earth twice per day.
- GPS equipment receive transmissions from at least a few of the satellites and are able to discern very precise positioning data.
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- Infrared
- Far infrared waves are thermal. Exp: heat feel from sunlight, fire
- the temperature-sensitive nerve endings in our skin can detect the difference between inside body temperature and outside skin temperature
- Near infrared waves are not hot at all. These shorter wavelengths are the ones used by TV's remote control
3) CONNECTION DEVICES
- Telephone
- Cable
- Digital Subscriber Line(DSL)
Connection Service
- Dial-up Service
- operates through a standard telephone line by running the telephone line to amodem device in the personal computer, and configuring the computer to dial a specific phone number, the computer is granted Internet access
- DSL
- a family of technologies that provides digital data transmission over the wires of a local telephone network
- Cable
- connect by using cable of TV in home
- provide faster speed than satellite
- Satellite
- faster than dial-up but slower that cable and DSL
- exp: Wi-Fi connection for intenet
- Cellular Service
- 3G cellular network for network connecting
- increase bandwidth, and support more diverse applications
Connection Devices Signal
· -electric signals which run through cables are called signals.
information is sent and received through transmission media, it has to be communicated to a desired terminal in some way.
information is sent and received through transmission media, it has to be communicated to a desired terminal in some way.
· - transmission system is a nsystem used when transmitting.
· - signals (electric signals) which run through conducting wires are divided into the following 2 categories :
1. Digital signals
- code 1 is transmitted when applying a specific voltage and code 0 is transmitted in the case of 0V.
- a system of transmitting digital signals is called baseband system.
2. Analog signals
- signals 0 and 1 are transmitted as electric waves.
- a system of transmitting analog signals is called broadband system.
- code 1 is transmitted when applying a specific voltage and code 0 is transmitted in the case of 0V.
- a system of transmitting digital signals is called baseband system.
2. Analog signals
- signals 0 and 1 are transmitted as electric waves.
- a system of transmitting analog signals is called broadband system.
Illusion of Digital and Analog Signals
Bandwidth
- measure capacity of the channel
- 4 categories:
- Voice band also known as low bandwidth
- enable digital terminal equipment to communicate over telephone channels, which are designed around the narrow bandwidth requirements of the human voice.
- cable modems, on the other hand, support the transmission of data over hybrid fibre-coaxial channels, which were originally designed to provide high-bandwidth television service
- cable modems, on the other hand, support the transmission of data over hybrid fibre-coaxial channels, which were originally designed to provide high-bandwidth television service
- Medium band
- medium-Band microwave digital radios are a natural evolution of the narrow-band series, offering many solutions to assorted path lengths and digital capacity wireless requirements
- Broadband
- telecommunication with wide band of frequencies to transmit information
- information can be multiplexed and sent on many different frequencies or channels within the band concurrently, allowing more information to be transmitted in a given amount of time (much as more lanes on a highway allow more cars to travel on it at the same time)
- Baseband
- information is carried in digital form on a single signal channel on the transmission medium. This usage pertains to a baseband network such as ethernet and local area networks.
Protocols
- is the method by which data is sent from one computer to another on the internet.
- each computer (known as a host) on the internet has at least one IP address that uniquely identifies it from all other computers on the internet
Computer Network
- is a system in which computers are connected to share information and resources
- the connection can be done as peer-to-peer or client
Network Types
• Local area networks
• Home networks
• Wireless LAN
• Personal Area networks
• Metropolitan area networks
• Wide area networks
Network Architecture
- arrangement is called topology
- types of arrangement / topology:
i) Star network
- each server and workstation connected into central hub that provides connection to another device connected to the hub and it shapes like a star
- easy to work with and can pin point problem location also isolate problem if it occours on workstation
ii) Bus network
- best use in small area of network
- the cable runs from computer to computer making each computer a link of a chain
- different types of cable determine way of network can be connected
iii) Ring network
- each user is connected to two other users, so as to create a ring
- not widely used because is inefficient compared to other topology because the data have to travel through more node
- advantages: each node have equal access and capable of high speed data transfer also can span larger than other topology
- disadvantage: very expensive technology and not efficient
iv) Tree network
- also known as hierarchical network, combination of star and bus networks
- advantages:
- divides the whole network into parts that are more easily manageable
- have a point to point network
- provides enough room for future expansion of a network
- Dependence of the entire network on one central hub is a point of vulnerability for this topology. A failure of the central hub or failure of the main data trunk cable, can cripple the whole network.
- With increase in size beyond a point, the management becomes difficult.
More information: http://www.buzzle.com/articles/tree-topology.html
v) Hybrid network
- combination of the best features of two or more different topologies
- provide a large number of connections and data transmission paths to users
vi) Mesh network
- is reliable and offers redundancy
- if one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes
- mesh networks work well when the nodes are located at scattered points that do not lie near a common line
Organization Networks
- Intranet
- a private network within organization
- only all the employees in the company can use
- Extranet
- connect organization with it suppliers, customers and other access
Network Security
- security is important to ensure that the process of communication is safe
- Firewalls
- filter incoming and outgoing traffic that flows through system
- firewall can use one or more sets of “rules” to inspect the network packets as they come in or go out of the network connections and either allows the traffic through or blocks it
- rules of a firewall can inspect one or more characteristics of the packets, including but not limited to the protocol type, the source or destination host address, and the source or destination port
- Intrusion detection systems (NIDS)
- monitors traffic on a network looking for suspicious activity, which could be an attack or unauthorized activity
- to monitoring incoming and outgoing network traffic, a NIDS server can scan system files looking for unauthorized activity and to maintain data and file integrity
- the NIDS server can also detect changes in the server core components
- Virtual private networks (VPN)
- a network that is constructed by using public wires to connect nodes
- use encryption and other security mechanisms to ensure that only authorized users can access the network and that the data cannot be intercepted
- example, there are a number of systems that enable users to create networks using the internet as the medium for transporting data
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