SCC 130 - Part 3

Bandwidth is used for sending voice where a great deal of interference can be accepted without loss of intelligibility and as a result, data applications used the telephone bandwidth.

If digitally transmitted, it will need a systme that needs to accomodate a bit rate of 52.8 kbps once sampled and coded using 8 bits per sample. The reason for this is that we sample a signal of bandwidth B at twice its highest freqeuncy as we need to take a minimum of 2 readings per cycle.

We can reproduce the wave form exactly by taking "infinite" samples or we can reproduce the barest generalisation of its direction of change by taking less samples.

To ensure a signal is accurately "reconstructed", a minimum of 2 samples need to be recorded per cycle and this will help us to "recnstruct" the signal back.

For 3300Hz, we need to take 3300 x 2 = 6600 readings or 6600 samples / second. If "each sample" is "coded / represented" by 8 bits, we would have a total bit rate of 52.8 kbps.

The bandwidth allocated for data is 2400Hz but the highest frequency is 3300Hz and if digitally transmitted it can have a rate of 48 kbps if each sample is represented by 8 bits and so it therefore needs a transmission bandwidth that can accomodate 48 kbps.

The sample rate must be at least 2 times the highest frequency contained in the signal.

To ensure the accurate reproduction of the signal, the sample rate "must be at least twice" the highest frequency of the orignial sound.

If we consider other mediums or channels such as fast ethernet network, we can say that its Bandwidth is 100 Mbps.

The mediums or channels that are used for wired data trnasmission are twisted pair, coaxial cable and fibre optic.

The measure of how fast we can actually send data through a network.

Remember, bandwidth and throughput sound the same but they're not.

A link may have a bandwidth of B bps but we can only send T bps throught that link and T is always less than B.

Think a motorway designed to transmit 1000 cars per minute but due to congestions this may be reduced to 100 cars per minnute so 1000 would be B but 100 would be T.

A group of computers and devices connected together over a network and they're all in the same location which is typically a single building such as an office building or home.

They extend over an entire city such as single network cable tv and several LANs connected into a larger network.

They are either owned and operated privately or publicly such as telecommunication providers.

A popular MAN service called SMDS (switched-megabit data services)

Provides long-distance transmission of data, voice, image and video data.

They are normally created and run by communication companies and leased to public or private institutions and span a town, a state, a country or even the world.

WANs which are wholly owned by a single company are referred to as an enterprise network and they can therefore span an unlimited number of miles.

A switched WAN is used in the backbone of global communication today

This is similar to several point to point WANs that are connected by switches

It's rare to see a LAN or WAN in isolation so we see an inter-network made of two LANs and one point-point WAN and this allows employees from each side to communicate with each other.

A leased WAN for private communication within an organisation. Notice that within a LAN the router will block the mesage since it is internal and the switch can handle this and if the message is destined for the other side, the router R1 routed the packet to R2.