I need help with these Computer Network questions:

1 - What is the percent overhead on a T1 carrier; that is, what percent of the 1.544 Mbps are not delivered to the end user? Assume that the T1 is being used to deliver data.

2 - Given a channel with an intended capacity of 20Mbps. The bandwidth of the channel is 3 MHz. What SNR (in dB) is required in order to achieve this capacity?

3 - Compare cable modems with Asymmetric Digital Subscriber Line (ADSL) modems. Points of comparison should include how they work, data rates supported, cost factors, and advantages and disadvantages of each. Research online for points of comparison.

4 - Two neighboring nodes (A & B) are a sliding-window protocol with a 3-bit sequence #. As the ARQ mechanism, Go-back-n ARQ is used with a window size of 4. Assuming A is transmitting & B is receiving, show the window positions (for both A and B) for the following succession of events:

a) Before A sends any frames

b) After A sends frames 0, 1, 2 & B receives them and sends ACK 1 to A (which means B acknowledges frame 0 only) and A receives the ack.

c) After A sends frames 3, 4 & B receives them and sends ACK 3 to A and A receives the ack.