This course will introduce you to the basics of Computer Networking and how data transmission works.
Communication Links
It is a communication channel that connects two or more communicating devices. One of the most common means of communication links is a pair of wires, also known as cable. Other channel include Coaxial Cable, Fiber Optics, etc.
End System
End System is a node or a user device. In a nutshell, computers connected to a computer network are end systems. They are called so because they are the edge of the system. Other end systems are not accessed directly by the user, but do facilitate internet communications. This includes servers for data such as email and web pages
Dial Up Connection
“Hey Mom! Put the phone down, I’m on the computer thing”
We all remember that time when the user’s software used to dial an ISP’s ( Internet Service Provider ) phone number. Almost all residential users accessed the internet over ordinary phone lines using a dial-up modem. The PC was attached to a dial up modem which was in turn attached to the home’s analog phone line. The home modem converted the digital output of the PC into an analog format appropriate for transmission over the analog phone line. At the other end of the connection, a modem in the ISP used to convert the analog signal back into digital form for input to the ISP’s router.
Dial-Up connection has following disadvantages :
- Slow ( Max : 56 Kbps )
- Uses ordinary phone line – So you could either make a call or use the internet.
DSL
Digital Subscriber Line or the DSL dominates the broadband connections of the world. A user typically obtains DSL internet access from the same company that provides it wired local phone access. It provided high speed ( VDSL stands for Very High Speed DSL which is even faster ) connection with a major freedom of using phone and internet at the same time.
- High speed downstream channel
- Medium speed upstream channel
- Two way telephone channel
The Network Core
- Circuit Switching : The resources needed along a path ( buffer, link transmission rate ) to provide for communication between the end systems are reserved for that duration of the communication session between the end systems. Think of it like that, when you book a restaurant, you might have to go through the hassle of calling them before you leave home. But when you arrive at the restaurant, you communicate with the waiter and get your table to enjoy the meal.
Book a Restaurant > No Tension
- Packet Switching : Resources are not reserved, so one might get in queue. Now, you don’t need to bother about the reservations. But when you arrive at the restaurant, you might have to wait for the table.
No Tension > Restaurant Full
Multiplexing in Circuit Switched Networks
- Frequency Division Multiplexing : The frequency spectrum of a link is divided up among the connections established across the link like the FM Radio Bandwidth is, say, 88-108 MHz.
- Time Division Multiplexing : Time is divided into frames of fixed duration and each frame is divided into a number of slots. If the link transmission rate is 8000 frames / sec and each slot consists of 8 bits, then the transmission rate of the circuit is 64 Kbps.
Packet Switching
Most packet switches use store and forward transmission at the inputs to the links. It means that the switches must receive the entire packet before it can begin to transmit the first bit of the packet onto the bound link.
Circuit Switching Vs Packet Switching
- Packet Switching is not suitable for real time services.
- Packet Switching offers better sharing of Bandwidth than Circuit Switching.
- Packet Switching is simple and efficient, less costly.
Why is Packet Switching Efficient ?
Suppose users share 1 Mbps link and users generate data at a constant rate of 100 Kbps with periods of activity of 10% of time. With Circuit Switching, 100 Kbps must be reserved for each user but with Packet Switching, the probability that a user is active is 10% so more users can enter.
I hope you found this tutorial useful. If you have any doubt, feel free to ask.
