Communication, Networking and Connection Technologies Cheat Sheet

In Computers

Communication, Networking and Connection Technologies Cheat Sheet

At school I used to very short notes (compared to the actual class explanation and notes) so before an exam I just study this and I’ll be ready to go.. which I must admit worked perfectly for me. So today I thought I’d help fellow students like me by sharing this cheat sheet (I’m not telling you to print it and take it with you during an exam.. or am I?) but it will help a lot to take a look at before an exam. Anyways, I modified it a little bit so it can be understood by the general public.

Circuit Switched Connection - The path is on until both parties disconnect. The path is created between the devices before the users can communicate; the lag is constant unlike Packet Switching. A perfect example of this is how the fixed line telephone system works.

Packet Switched Connection - The path can be used by more than one party. This will split all the data into packets and these packets will be transferred from one device to another. In packet switching packets travel through different routes and each route is available to many connections from different devices (because more than one party can use that route). The lag here varies depending on the flow of packets on the network. A perfect example of this is a simple home network with 2 or more computers connected through a router.

PSTN – Public Switch Telephone Network. This is the network of the world’s public circuit switched telephone networks. Pretty much this is the fixed line telephone network. This is used by the dialup and since this has only 1 channel, in the old days, you had to choose between browsing the internet or calling someone. To fix this issue ISDN comes in.

ISDN – Integrated Services Digital Network. This is a protocol (set of rules or standards) that enables the telephone network to transfer voice and data at the same time. A perfect example of this is the DSL connection at your house. You can use the phone to call whoever you want while from the same connection you are browsing the internet.

There are different types of ISDN, the BRI (Basic Rate Interface) and the PRI (Primary Rate Interface). ISDN has a B channel (used for voice and data) and D channel (used for controlling the connection, example keeping a connection alive)

ISDN can have up to 64kbps per B channel and for D channel, if it is BRI it can run at 16kbps and if it is PRI it can run at 64kbps.

In a BRI connection you have 2 B channels + 1 D channel. Total (2 B channels x 64kbps + 16kbps) = 144kbps

While in a PRI connection you have 30 B channels + 1 D channel. Total (30 B channels x 64kbps + 64kbps) = 1984kbps

DSL – Digital Subscriber Line. This uses the PSTN, it has 2 channels one for voice and one for data. Phone and internet can be used simultaneously and it has faster downloads and more bandwidth.

T1 and E1 connections are the basic backbones between ISPs

T1 is used in United States, Canada, hong kong etc…

E1 is used in Europe.

Multiplexing / Demultiplexing - This is the technology of sending multiple signals at the same time in a single complex signal.

FDM - Frequency Division Multiplexing. This is a scheme in which multiple signals are assigned different frequencies and transmitted on a single channel.

TDM - Time Division Multiplexing. This is a scheme in which multiple digital signals are broken down into many segments each of a very short duration and sent on a single channel.

WDM – Wave Division Multiplexing is a scheme that works like the FDM one.

Satellite - This is a transceiver that orbits around the world. There are 3 types of Satellites.

Propagation Delay – This is the time taken for any data received on the satellite to be transmitted to some other location.

GEO – Geographical Earth Orbit

Geostationary
Takes 24 hours to go around (moves with the earth)
Expensive to maintain
It has a 12 year lifetime
22,000 miles away from earth
Used in TV, Radio and weather forecast
The average ping is 2 to 5 seconds, which is too high for internet use
High propagation delay (which explains the high ping)

MEO – Medium Earth Orbit

Non-geo stationary
Elliptical orbit
Few thousand miles away from earth
Low propagation delay
The average ping is less than 1 second
It has a 6 to12 year lifetime
Commercial, Governmental and Military uses
Cheaper to maintain.

LEO – Low Earth Orbit

Non-geo stationary
Negligible propagation delay
Very low ping
Orbits at a few hundred miles away from earth
Cheapest type of satellite to maintain
It has a 5 year lifetime
Used for internet and cellular purposes
Takes only a few hours to go around

Network topologies and architectures

Computer networks can be classified in two major groups which are LAN and WAN.

LAN – Local Area Network. This is a network confined to one building with devices distributed in different rooms is known as a LAN, such as a simple office or home network.

WAN – Wide Area Network. This is a network distributed nationally or internationally making use of telephone lines, satellite links and in certain cases service providers.

A network topology defines how the different devices are connected together; a physical network topology describes how the network is wired up while the logical topologies describe how the devices communicate together.

There are different ways to connect devices with each other and they will be able to communicate. Here is a list of Network topologies, meaning, different designs of networks: