Question

Discussion Question 6.2: Discuss the various types of impairments for guided and unguided media. Pick an impairment and discuss strategies for overcoming that impairment. Discuss security considerations for guided and unguided media. Which is more secure? Why?

Answer 1

Transmission media means the medium used for sending the data from one device to another. In simple words, it’s the pathway through which information is send from sender to receiver. Transmission media is classified into two categories:

1. Guided or Wired media

Guided transmission media consists of cables that are tangible and have physical existence. That’s why it’s known as wired media also. This kind of transmission media is limited by physical geography.

Examples are:

1. Twisted pair cable

1. Shielded twisted pair cable
2. Unshielded twisted pair cable

1. Co-axial cable

1. Baseband co-axial cable
2. Broadband co-axial cable

1. Fiber optical cable

1. Unguided or Wireless media

Unguided transmission media consists of ways of transmitting the data without using any cables and therefore are also known as wireless media. This kind of media is not limited by physical geography.

Examples are:

1. Microwave
2. Radiowave
3. Infrared

Transmission impairments

During a transmission, the received signal is different from the one sent by the sender. In any communication system, it is recognized that received signal will be different form the sent signal and the reason is transmission impairments. For example in an analog signal, impairments can cause random signal modifications that degrades the quality of the signal. And in a digital signal, it’s possible that sent 1’s become 0 while receiving and vice versa because of impairments.

The main transmission impairments in both guided and unguided medias are:

1. Attenuation

Attenuation is the loss or reduction in the amplitude (strength) of a signal as it passes through a medium. As a signal travels through a copper wire some of the signal will be absorbed by the medium (this is called heat dissipation). The effect of attenuation is one of the reasons why there are cable standards that specify the maximum length of cable run for particular types of cable.

For guided media, this reduction in strength (attenuation), is generally logarithmic and is thus typically expressed as a constant number of decibels per unit distance.

For unguided media, attenuation is a more complex function of distance and atmosphere.

1. Distortion
2. any change in a signal that alters the basic waveform or the relationship between various frequency components; it is usually a degradation of the signal.

Delay distortion is a phenomenon peculiar to guided transmission media. The distortion is caused by the fact that the velocity of propagation of a signal through a guided medium varies with frequency.

1. Noise

Noise refers to any unwanted signal. For any data transmission event, the received signal will consist of the transmitted signal, modified by the various distortions imposed by the transmission system, plus additional unwanted signals that are inserted somewhere between transmission and reception; the latter, undesired signals are referred to as noise-a major limiting factor in communications system performance.

NOISE REDUCTION

Transmission media can and will be affected by the noise coming from inner and outer sources. That is when noise immunity factor kicks in. Since several types of media has greater or smaller affects by the noise it is necessary to choose type of media depending on situation. Noise is affecting data signals, but since fiber optic does not use electric current it is less affected type of media.

Several points that will help in avoiding or decreasing electromagnetic forces:

1. Wiring should be deployed far from powerful electromagnetic forces
2. Type of the transmission media should be the one that will help decreasing noise. Wireless signal is much more affected by noise than wired.
3. Anti-noise algorithms can be used for data protection and error avoiding.
4. External conduit for the wiring will protect data traveling over media, if the conduit is made of metal. The pipeline might be alternative option.

WHICH IS MORE SECURE: GUIDED OR UNGUIDED MEDIA?

On first thoughts we can say wired media is more secure as it is harder to access. Wired media needs to be accessed physically to tap and sniff the traffic. In wireless, we send point to point or well beyond the facility in all directions. Anyone can pick up the signal and might be able to sniff the passed information.

However we must consider one more thing while deciding the more secured media, that is physical and technical controls that have been implemented. Wireless can be made more secure by using WPA, encryption or 802.1x. A cabled network can be fully switched, use encryption and have implemented VLANS. So even a seemingly weaker systems can have controls implemented to make their security more robust. Therefore, deciding which media is more secure depends on the situations like which kind of data you are sending, best medium to use it etc.