41. What are the categories of Transmission media?
a. Guided Media
i. Twisted – Pair cable
1. Shielded TP
2. Unshielded TP
ii. Coaxial Cable
iii. Fiber-optic cable
b. Unguided Media
i. Terrestrial microwave
ii. Satellite Communication
42. What are the types of errors?
a. Single-Bit error
In a single-bit error, only one bit in the data unit has changed
b. Burst Error
A Burst error means that two or more bits in the data have changed.
43. What is Error Detection? What are its methods?
Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are
a. Vertical Redundancy Check (VRC)
b. Longitudinal Redundancy Check (VRC)
c. Cyclic Redundancy Check (VRC)
d. Checksum
44. What is Redundancy?
The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.
45. What is VRC?
It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.
46. What is LRC?
In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant data unit follows n data units.
47. What is CRC?
CRC, is the most powerful of the redundancy checking techniques, is based on binary division.
48. What is Checksum?
Checksum is used by the higher layer protocols (TCP/IP) for error detection
9. List the steps involved in creating the checksum.
a. Divide the data into sections
b. Add the sections together using 1’s complement arithmetic
c. Take the complement of the final sum, this is the checksum.
50. What are the Data link protocols?
Data link protocols are sets of specifications used to implement the data link layer. The categories of Data Link protocols are 1. Asynchronous Protocols
2. Synchronous Protocols
a. Character Oriented Protocols
b. Bit Oriented protocols
