Media are what the message is transmitted over.
Transmission media are divided into two categories:
- Cable media: have a central conductor enclosed in a plastic jacket. Used for small LANs. Cable media normally transmit signals using the lower end of the electromagnetic spectrum. Ex- Coaxial, Twisted pair, Fiber-optic
- Wireless media: employs the higher electromagnetic frequencies, such as radio wave, microwaves and infrared. It is used in mobile networks. They are prevalent in enterprise and global networks.
Factors of Medium’s characteristics:
- Cost: it should be weighed against the performance it provides and the available resources.
- Installation: Some types of media can be installed with simple tools and little training; others require more training and knowledge and may be better left to professionals.
- Bandwidth Capacity: In the world of networking, bandwidth is measured in terms of Mbps. A medium with high capacity has a high bandwidth. A high bandwidth normally increase the throughput and performance.
- Node Capacity: Each network cabling system has a natural number of computers that can be attached to the network.
- Attenuation: Electromagnetic signals tend to be weaken during transmission. The phenomenon imposes limits on the distance a signal can travel through a medium without unacceptable degradation.
- Electromagnetic Interference: EMI affects the signal that is sent through the transmission media. EMI is caused by outside electromagnetic waves affecting the desired signal. It is often referred to as noise.
Characteristics of Cable Media
Fiber-Optic Cable:
- Fiber-optic cable transmits light signals rather than electrical signals.
- Each fiber has an inner core of glass or plastic that conducts light.
- The inner core is surrounded by cladding, a layer of glass that reflects the light back into the core.
- Each fiber is surrounded by a plastic sheath.
- The sheath can be either tight or loose.
- A cable may contain a single fiber, but often fibers are bundled together in the center of the cable.
- Optical fiber may be multimode or single mode.
- Single mode fibers allow a single light path and are typically used with laser signaling.
- Single mode fiber can allow greater bandwidth than multimode and is more expensive.
- Multimode fibers use multiple light paths and use with LEDs.
- Optical interface devices convert computer signals into light for transmission through the fiber.
- Conversely, when light pulses come through the fiber, the optical interface converts them into computer signals.
