Set – 4
1. In the following diagram, what will be BDP between H1 and S1 and between L1 and S1? The values associated with each link show the link bandwidth (in mbps) and link delay (in ms). [Note: mb denotes megabits (106 bits) and MB denotes Megabytes (220 bytes). BDP = Bandwidth x one way latency]
A. 37.5MB and 37.5MB
B. 3.75MB and 37.5MB
C. 35.5MB and 41.5MB
D. 3.45MB and 9.8MB
E. None of these
Answer: E
Explanation:
BDP = Bandwidth Delay product For H1 to S1 delay is 10+20 = 30 ms. And effective bandwidth is 10mbps So, BDP for H1 to S1 is 10*106*30/1000 bits = 30000 bits = 30000/(8*1024) KB = 3.66 KB Similarly for H2 to S1, the BDP is 5*106*60/(1000*8*1024) KB = 3.66 KB
2. Which of the following is true regarding transport layer rate control?
A. Transport layer rate control sends data to the IP layer immediately after it receives data from the application.
B. Transport layer rate control stores data in a temporary buffer and sends the data to the IP layer periodically based on the transmission rate control algorithm.
C. Transport layer rate control tries to send the data to the IP layer, but discards the application data if it fails to send the data immediately after it receives the same from the application.
D. Transport layer rate control waits indefinitely until it can send the data to the IP layer.
Answer: B
3. What are the properties of a source buffer used at the sender side of the transport layer in a connection-oriented protocol?
A. Source buffer needs to be connection specific that is a buffer is maintained for every connection from the device
B. OS maintains a global source buffer for all the connections from the device.
C. Source buffer is finite.
D. Source buffer is infinite.
Answer: A & C
Explanation:
Every connection needs a separate buffer. There is no option for the global buffer. Also, the source buffer cannot be infinite due to the hardware limitation.
4. What is congestion avoidance?
A. Regulating sending rate based on network capacity.
B. Regulating receiving rate based on network capacity.
C. Regulating sending rate based on receiver’s feedback.
D. Regulating receiving rate based on sender’s feedback.
Answer: A
Explanation:
Congestion avoidance is controlling the sending rate based on the network capacity. Receiver feedback is used for flow control. The final sending rate is controlled based on the network capacity (comes from congestion control) and the receiver feedback (comes from flow control). That is why SWnd = min(CWnd, RWnd) where CWnd is the window based on network capacity and RWnd is the window based on receiver feedback. The question asks for congestion control, so the answer would be to regulate the sending rate based on network capacity.
5. How congestion in the network is detected in the transport layer?
A. By looking at packet loss in the network.
B. By looking at delay in the packet transmission.
C. By looking at ACK drop in the network.
D. All of the above
Answer: D
Explanation:
Congestion can be detected via packet loss, ACK drop or delay variance (which is jitter).
6. What is the action to be taken by the sender at the transport layer when congestion in the network is detected?
A. Sender should pause for a short time before it sends another packet.
B. Sender should reduce the sending rate.
C. Sender should retransmit lost packets multiple time.
D. Receiver should not acknowledge until network become congestion free.
Answer: B
Explanation:
Congestion can be reduced only if the sending rate is reduced. The receiver cannot take action as it is not the one who detects the congestion.
7. What is the standard procedure of controlling sending rate during congestion
avoidance phase ensuring both network utilization and fairness?
A. AIAD
B. AIMD
C. MIMD
D. MIAD
Answer: B
Explanation:
It is the standard. AIMD means Additive Increase Multiplicative Decrease. AIMD ensures both capacity utilization and fairness.
8. In a transport layer, a connection-oriented protocol creates an uniquely identified connection between two processes. Which of the following fields are used as identifier for such connections?
A. Source IP
B. Source MAC
C. Source Port
D. Source Initial Sequence Number
E. Destination IP
F. Destination MAC
G. Destination Port
H. Destination Initial Sequence Number
Answer: A, C, D, E, G & H
Explanation:
These are used for uniquely identifying a connection in a device. For more details: https://youtu.be/EqzDTO9tdqs?t=1294
9. Which is true for TCP connections?
A. TCP connection is a message stream, but it does not preserve message boundaries
B. TCP connection is byte stream and it preserves message boundaries
C. TCP connection is byte stream and it does not preserve message boundaries
D. TCP connection is message stream which preserves message boundaries
Answer: C
10. If maximum network layer payload size is 1480 bytes, what is the maximum TCP payload size?
A. 1500
B. 1460
C. 1440
D. 1456
Answer: B
Explanation:
TCP has mandatory header of 20 bytes. Every TCP packet has to include this header. So, the minimum header length for TCP is 20 bytes. Entire TCP packet is the payload to the network layer. The maximum TCP packet size is 1480 bytes. So the maximum TCP payload = 1480-20 = 1460 bytes.
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