Unit 1 Communication Channel Wired Transmission....

 

Wired Transmission

What is it? 
Wired Transmission is a media that is used to transfer information over another network, such as a twisted pair cable, Coaxial cable and optic fibre.

Coaxial Cable

• It consists of two conductors, but is constructed differently to permit it to operate over a wider range of frequencies. These include the outer cylindrical conductor that surround a single wire conductor and an inner conductor which is held in place by either regularly spaced separating the rings.
  
• This cable can support between 10 to 100Mbps
• It can be cheaper for a physical bus topology because less cable will be needed.
• It can also support up to 370MHz
• The second layer of the cable or shield can help reduce the amount of outside interference. Covering this shield is the cable jacket.

Optic Fibre

What is optic fibre? 


A technology that uses glass or plastic fibers (threads) to transmit data. It is capable of transmitting messages modulated onto light waves. 

• Entry level fibre optic speed starts at 15 Mbps. For example, this means a 5 megabyte film will upload in 8 seconds, and a 10 megabyte film can upload in 16 seconds; or downloading 10 songs would take less than half a minute. This type of speed is typically 3 Mbps faster than the regular cable internet service

• Now with technology rapidly improving, the fastest fibre optic speed has approached around 100 Mbps. 

• Modern fibre cables can contain up to a thousand fibres in a single cable, with bandwidth potentially in terabytes per second. 

• Some companies are offering unlimited fibre optic broadband for around $300 a month with 100 Mbps speed…

• Fibre optics are known to be the most secure transmission media around as it uses light to transmit data rather than electricity currents.

• The reasons for its high security include: 
• that it’s immune to electronic interference, 
• it never loses signal 
• it can not be tapped into unless a person intercepts the cable physically. 

• A security issue relevant to fibre optics include fiber tapping- this is when the network is tapped into and signal is extracted from an optical fibre.

Telephone line ...

A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. This is the physical wire or other signaling medium connecting the user's telephone apparatus to the telecommunicationsnetwork, and usually also implies a single telephone number for billing purposes reserved for that user. Telephone lines are used to deliver landline telephone service and Digital subscriber line (DSL) phone cable service to the premises. Telephone overhead lines are connected to the public switched telephone network.

What is Leased Line?

Leased Libe, also called a dedicated line, is a telecommunications service provided to businesses by telcos and long distance carriers that provides a permanent direct connection between two geographically separate local area networks (LANs).

Leased Line Service

Leased lines are dedicated circuits that the telco reserves for the exclusive use of the customer. They are permanently available, always active, and secure, and they have consistent quality of service (QoS) and a flat monthly fee. However, they are very expensive compared to dial-up lines, and businesses rarely use their full bandwidth capabilities except in short bursts.

Leased lines are a form of point-to-point connection. Your LAN is connected by bridges, routers, modems, and terminal adapters to the telco’s central office (CO), which sets up dedicated switches to connect you to the destination LAN. The presence of dedicated switches is what makes leased lines so expensive. You would use a leased line to connect a Microsoft Exchange server to the Internet, for example. Since the leased line is always on, there is no connection delay when users try to access the server for their 

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Switched Line

Definition - What does Switched Line mean?

A switched line is a communications link established through the use of switching equipment which allows a connection to be established between two transmission devices. The switched line provides a temporary connection between two user terminals or machines and only lasts for a certain period. Switched lines minimize the line costs while maintaining the advantages of interconnected systems. They are less expensive compared to leased lines and are often appropriate when there is low traffic, as well as for connecting several remote sites.

Advantages of a switched line are:

• Low cost, especially if there is low usage or traffic between terminals
• Provides means to access and connect multiple distant machines
• Flexibility since many machines offering different services can be accessed
• Once a breakdown occurs on a connection to a facility, the user or machine can redial and obtain an alternative route to the facility.

What is broadband?

Broadband is a high-speed internet connection which allows you to enjoy everything the internet has to offer.

Before broadband, internet access was achieved with ‘narrowband’ dial-upconnections that were very slow by today’s standards. Broadband is much quicker and allows us to do more on the internet.

How fast is broadband?

What makes a connection fast enough to be called “broadband”? There is no standard definition, and what qualifies as a broadband service varies across the world.

In the UK we have access to a wide variety of services with different levels of performance. Almost every home and business can get access to a fixed-line connection of at least 2Mbps (megabits per second), but most can get speeds in excess of 24Mbps.

Not sure what speed you need, or want to know what you’re currently getting? Our guide to broadband speeds can help.

How does broadband work?

An internet service provider (ISP) supplies the service and equipment to get your home or business online. Some ISPs operate their own infrastructure, but this is a complex and expensive endeavour so most pay for wholesale access to a network which they can then resell.

Most of the home broadband services you’ll find on Broadband Genie come into your home via a fixed line, which will very likely be either an Openreach (BT) telephone line or a Virgin Media network connection.

Broadband service does not always require a line though. There is also mobile broadband using mobile phone networks, satellite internetwhich connects to orbiting relays, and wireless broadband providers using long-range Wi-Fi transmissions.