Question

Question 1

a. NETSTAT is a TCP/IP networking utility. By using NETSTAT provide below:

   i. General NETSTAT output from your Windows machine using Windows Command Prompt (5marks)

   ii. Display active all TCP connections with process ID (PID) for each connection (5marks)

   iii. Display the contents of the IP routing table (5marks)

   iv. Display statistics by protocol (5marks)

   v. Display Ethernet statistics (5marks)

b. Explain flow control techniques in the transport layer to handle end-to-end connection (8marks)

Answer 1

Hi,

Question A1: General NETSTAT output from your Windows machine using Windows Command Prompt.

Answer: Go to start (the windows icon), click on it and type 'cmd'. right click and choose 'run as administrator' to open the highlighted application and enter 'netstat' at command prompt. Copy the output. This is the answer.

Question A2: Display active all TCP connections with process ID (PID) for each connection

Answer: Run the command 'netstat -o'. The output is your answer.

Question A3: Display the contents of the IP routing table

Answer: Run the command 'netstat -r'. The output is your answer.

Question A4: Display statistics by protocol.

Answer: Run the command 'netstat -p proto -s'. The output is your answer.

Question A5: Display Ethernet statistics

Answer: Run the command 'netstat -e -s'. The output is your answer.

Use this picture for reference:

Question B: Explain flow control techniques in the transport layer to handle end-to-end connection

Answer:

Flow Control basically means that TCP will ensure that a sender is not overwhelming a receiver by sending packets faster than it can consume. The idea is that a node receiving data will send some kind of feedback to the node sending the data to let it know about its current condition. It’s important to understand that this is not the same as Congestion Control. Although there’s some overlap between the mechanisms TCP uses to provide both services, they are distinct features. Congestion control is about preventing a node from overwhelming the network (i.e. the links between two nodes), while Flow Control is about the end-node.

How it works:

The sender application writes data to a socket, the transport layer (TCP) will wrap this data in a segment and hand it to the network layer (IP),
that will somehow route this packet to the receiving node. On the other side of this communication, the network layer will deliver this piece of data to TCP, that will make it available to the receiver application as an exact copy of the data sent, meaning if will not deliver packets out of order, and will wait for a retransmission in case it notices a gap in the byte stream.

TCP stores the data it needs to send in the send buffer, and the data it receives in the receive buffer. When the application is ready, it will then read data from the receive buffer. Flow Control is all about making sure we don’t send more packets when the receive buffer is already full, as the receiver wouldn’t be able to handle them and would need to drop these packets.

To control the amount of data that TCP can send, the receiver will advertise its Receive Window, that is, the spare room in the receive buffer. Every time TCP receives a packet, it needs to send an ack message to the sender, acknowledging it received that packet correctly, and with this ack message it sends the value of the current receive window, so the sender knows if it can keep sending data.

TCP use a sliding window protocol to make sure it never has more bytes in flight than the window advertised by the receiver.

When the window size is 0, TCP will stop transmitting data and will start the persist timer. It will then periodically send a small WindowProbe message to the receiver to check if it can start receiving data again; When it receives a non-zero window size, it resumes the transmission.