Understanding Network Cables, Data Transmission, and Modems

Posted on Aug 14, 2024 in Computers

1. Twisted Pair Cable

Twisted pair cable consists of two insulated copper wires twisted together. One wire carries the signal, while the other serves as the ground reference. Twisting the wires helps cancel electromagnetic interference, which can occur with parallel cables acting as antennas.

2. Types of Copper Twisted Pair Cable

There are two main types of twisted pair cable:

  • UTP (Unshielded Twisted Pair): Lacks shielding, making it more susceptible to interference.
  • STP (Shielded Twisted Pair): Includes shielding to reduce interference.

There are seven categories (CAT 1 to CAT 7) of twisted pair cable, each with different quality, thickness, and data transmission speeds. For instance:

  • CAT 1: Used for basic telephony with a speed of 1 Mbps.
  • CAT 3 and 4: Used for LANs with transmission speeds of 10 Mbps and 20 Mbps, respectively.

3. Optical Fiber Transmission

Optical fiber transmits data as light through a cable with a core and a cladding. The light beam travels through the core, bouncing off the cladding. If the angle of incidence is greater than the critical angle, the beam undergoes total internal reflection, ensuring efficient transmission. The numerical aperture defines the range of valid angles for the beam.

4. Fiber Types Based on Refractive Index

There are two main types of optical fiber:

  • Single-mode Fiber: Transmits a single light beam in a nearly straight path.
  • Multimode Fiber: Transmits multiple light rays at different angles. Rays outside the acceptable range are rejected.

5. Infrared Waves

Infrared waves have frequencies above 300 kHz, offering a large bandwidth suitable for high-speed data transmission. However, they have a limited range and cannot penetrate walls. This makes them ideal for short-range communication, such as connecting a wireless mouse or keyboard to a PC without interference from other rooms. Infrared transmission requires line of sight.

6. Circuit Switching

Circuit switching, operating at the physical layer, establishes a dedicated physical connection between devices using switches with multiple channels. It involves three phases:

  1. Establishment Phase: Resources are requested and reserved for the duration of the transmission.
  2. Data Transmission Phase: Data is transmitted between the connected devices.
  3. Release Phase: The sender requests to release the connection, and the receiver confirms the release.

7. Datagram Networks

Datagram networks transmit data in small packets called datagrams. Each datagram contains the destination address and data. Datagrams are independent and may arrive out of order or with varying delays. Datagram switching operates at the network layer and is also known as connectionless communication because there is no dedicated connection establishment or release phase. Data is sent without confirmation from the receiver.

8. Bandwidth for Voice and Data on a Telephone Line

. The bandwidth used for voice is between 300 Hz and 3300 Hz, 3000 Hz is the voice A pretty little interference affect (the distortion is very small) but the data signals need to be more precise, it is recommended then that is somewhat smaller than the cable is then removed some of the edges, leaving a bandwidth of 2400 Hz (from 600 Hz to 3000 Hz). MODEM means modulator / demodulator that is what the modem sends data when it converts the signal into analog ones and zeros on the line to send and when it receives the transformed again into ones and zeros for the computer to understand. 9. MODEM V.90: The download speed is 56 Kb and 33.6 Kb upstream (limit of Shannon’s capacity). The moden is to be used with a digital line. You can get to get this rate increase because the signal is sampled and quantified what makes you lose speed. In downloading data that is not done so this speed is reached. The provider of telephony sampled 8000 times per second and 8 bits are sent. As one is control the speed of data rate is 8000 x 7 = 56,000 or 56 Kb 10. Meaning of DSL and ADSL. + DSL (Digital Subscriber Line) DSL (Digital Subscriber Line asimetrical / asymmetric digital subscriber line) + When peaked modems came out the dsl speed. It has many variants ADSL, HDSL, VDSL, etc. + In line ADSL is asymmetric which means that as modems the download speed is greater than the load. + This is done so for residential users and not for businesses that need good upload speed also. + Allocate more bandwidth for data download speed is therefore greater. + ADSL local loop can reach speeds of 1.1 Mb of what happens to the telephony central filter which put a speed delimited to 4 kb which is sufficient for voice transmission.