Consider the grammar rule $$E \to {E_1} - {E_2}$$ for arithmetic expressions. The code generated is targeted to a CPU having a single user register. The subtraction operation requires the first operand to be in the register. If E₁ and E₂ do not have any common sub-expression, in order to get the shortest possible code.

Choose the best matching between Group 1 and Group 2 :

Group –1

P. Data link layer
Q. Network layer
R. Transport layer

Group – 2

1. Ensures reliable transport of data over a physical point-to-point link
2. Encodes/decodes data for physical transimission
3. Allows end-to-end communication between two processes
4. Routes data from one network node to the next

A and B are the only two stations on an Ethernet. Each has a steady queue of frames to send. Both A and B attempt to transmit a frame, collide, and A wins the first backoff race. At the end of this successful transmission by A, both A and B attempt to transmit and collide. The probability that A wins the second backoff race is

Which of the following is NOT true with respect to a transparent bridge and a router?