Telecommunications Overview Richard Selby

Local Access Network The link between the customer and the Local Exchange (or Switch) Sometimes called the Local Loop could be: –Copper Cable (Overhead or underground) –Coaxial cable (with cable TV) –Wire-less Local Loop (WLL)

Overhead Copper Cable Connected to customers from poles Drop Wires sometimes shared with other users eg: power companies Possible danger of electrocution to installers Quick and easy to install

Underground Copper Cable Usually installed when new development is built More secure Longer to connect a new line

Coaxial Cable Supplied with Cable TV, providing the Regulator permits it Overhead or underground coaxial cable from local distribution cabinet

Wire-less Local Loop Connection is through a centrally located Base Station at a high point in the area Customer must have Line of Sight to the Base Station Customer must have an antenna on his house, and additional equipment inside house No local cable to maintain - so cheaper

Local Exchange Digital –solid state - computer controlled Analogue –electro-mechanical

Junction Network Connects from Local Exchange to Trunk Exchange Usually Fibre Cable for Digital equipment Usually Coaxial Cable for Analogue

Trunk Network Connects trunk exchanges together Could be: –Coaxial Cable –Microwave Radio –Optical Fibre –Domestic Earth Stations

Coaxial Cable Copper centre conductor surrounded by copper tube. Each separated by an insulator Carries High Frequency Multiplexed signals over long distances. Requires Repeaters to amplify the signal Noise distortion introduced at each Repeater

Microwaves Frequency Range about 3GHz upwards Travel in straight lines (through a uniform medium) Can be reflected (eg: by water or flat metal roofs) CAN BE DANGEROUS! - remember your microwave oven!

Microwave Radio Can be Analogue or Digital Requires Line of Sight between antennae Dish antennae are very directional Antennae are usually fitted at high level (eg on a Tower, Mast or tall building)

Optical Fibres Only used with Digital systems - high bandwidth Made of very thin, pure glass - flexible Secure Low attenuation Can carry digital signals over long distances before Regeneration is required

Optical Fibres (2) Considerable traffic can be carried through each fibre - works out cheaper than copper Requires laser energy to produce optical signal. Laser energy used is not visible - AND CAN BURN! –remember the surgeon!

Satellite Communication Satellites in Geostationery Orbit (36000km) Large Antennae required Special rceiving equipment required Not secure Compliments Fibre & Coax Staffing issues Sun Interference