Physical layer transmits a raw bit string from one machine to another.
Various physical media used for the actual transmission are grouped into groups
- Guided media (copper wire, fiber optics)
- Unguided media (radio waves, laser etc)
A common way to transfer data from one computer to another is to write them into magnetic tape or floppy disk and physically transport the tapes or disks to the destination machines and read them again using hardware parts
- It is the oldest and still the most common transmission medium as far as networking is concerned.
- Twisted pair consists of 2 insulated copper wires typically about 1 mm in thickness.
- The wires are twisted together in a helical form just like a DNA molecule.
- He purpose of the twisting the copper wire is to reduce electrical interference from similar pairs close by. The most common application of a twisted pair is a telephone system.
- The twisted pair can run several kilometers without amplification but for longer distances repeaters may be needed.
- Twisted pair can be used either for analog or digital transmission.
- The bandwidth depends on the thickness of the wires its length and the distance traveled.
- But several megabytes can be achieved for a few kilometers in many cases.
Base band coaxial cable
- It is better than the twisted pair and hence can span longer distance at higher speed.
- It is a cable which is commonly used for digital transmission.
- A coaxial cable consists of a stiff copper wire as the core surrounded by an insulated material.
- The insulator is encased by a cylindrical conductor. The outer conductor is covered in a protective shield
Broadband coaxial cable
It is a cable used for analog transmission. It is called broadband. It means any cable network using analog transmission.
**The major difference between the base band and the broadband coaxial cable is that the later covers a bigger area and involves analog transmission. Hence requires analog amplifiers to strengthen this signal periodically.
This amplifier only transmits signals in one direction. So a computer sending a “packet” will not be able to reach computers upstream from it if an amplifier lies between them.
For minimizing this error there are 2 types of broadband system
- Dual cable system
- Single cable system
Dual Cable system
It has two identical wires running parallel to each other.
A computer sends the data into cable 1 which runs to a device called the head-end at the root of the cable tree. The head end then transfer the signal to the cable for transmission back down the tree. All computers transmit through cable1 and receive through cable 2.
Single cable system
In this case, there is just one cable through which the sending and receiving of the data is done. The differentiating factor is the bandwidth. The bandwidth through which the packet is sent is not the same in which it is received.
Generally low frequency bandwidth is used for communication from the computer to the head end which then shifts the signal to the higher frequency bandwidth for broadcasting.
There are basically 2 categories in single cable system that is the exchange of packets through the bandwidth range is done in two ways
- sub split system
In this case the inbound traffic bandwidth rang: 5-30 mhz
Outbound traffic range: 40-300 Mhz
- Mid split system
In this case the inbound traffic bandwidth rang: 5-116 mhz
Outbound traffic range: 168-300 Mhz
- What are the two types of media in transmission media?
- Explain in detail about guided media and its various parts
- Give a brief overview of twisted pair cables.
- what is the difference between base band and broadband cable system?
- what are the types of broadband system adopted for minimizing the errors?
- what is the difference between dual and single cable system in broadband coaxial cable?
Filed under: Data communication and Networking |