Using UDP sockets, you will write a client and server program that enables the client to determine the round-trip time (RTT) to the server. To determine the RTT delay, the client records the time on sending a ping request to the server, and then records the time on receiving a ping response from the server. The difference in the two times is the RTT.

The ping message contains 2 4-byte integers and must be encoded in network-byte order as follows[1]:

4-byte message typewith an integer value of 1 or 2

Message type = 1 for a ping request (message from client to server)

Message type =2 for a ping response (message from server to client)

4-bytesequence number with a unique integer value starting from 1[2]. In the ping response, the server should echo back the clients sequence number.

The client program should take the following input parameters:

IP address of server

IP port of server

The client program will read in the above input parameters, and send 10 ping requests consecutively, waiting for a response each time, to the server running at the specified IP address and port. After each response is received, the client calculates and prints the RTT for the message. If no response is received within a certain amount of time (one second)[3], the client notes that the request timed out and then sends the next request up to the maximum. The program output should print out trace information when data is sent and received, and account for error conditions. Trace output must include:

At start of output, print a message indicating the IP address and port of the server being pinged

For each ping response received, print RTT along with sequence number of ping message

For no ping response, print Message timed out along with sequence number of the ping message

After completion, print the following statistics (similar to output of UNIX ping utility);

Number of packets sent, received, lost (% loss rate)

Min, Max, Average RTT for all acknowledged ping packets

The server will wait in an infinite loop to receive ping requests from the client. On receiving a ping request, the server program will randomly[4]decide whether to respond to ping requests to simulate network packet loss. In the case that the server responds, it sends a ping response containing the appropriate message type, and client sequence number. In the case that the server decides not to respond, no ping response is sent, and the server waits for another ping request. To implement random loss, the server should generate a random integer between 0 and 10 and if the result is < 4, do not respond to the packet.

In a ping request, the application data has the following format:

0 1 2 3 4 (bytes)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Message Type (1= request) |

--------------------------------------------------------------------------------

| Message sequence number (e.g. 5) |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

In a ping response, the application data has the following format:

0 1 2 3 4 (bytes)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Message Type (2 = response) |

--------------------------------------------------------------------------------

| Message sequence number (e.g. 5) |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Examples of the client program trace output are as follows:

Pinging 127.0.0.1, 12000:

Ping message number 1 timed out

Ping message number 2 RTT: 0.002154 secs

.

Ping message number 10 RTT: 0.000194 secs

Examples of the server program trace output are as follows:

The server is ready to receive on port: 12000

Message with sequence number 1 dropped

Responding to ping request with sequence number 2

Responding to ping request with sequence number 10

Notes:

1.Timestamp Resolution:

When testing your program, especially when running client and server on the same host, you might find little difference in the timestamp values. The values will depend on the test environment, and timer resolution on your machine. If there are issues, you should simulate longer delays, by adding in a random "wait" or "sleep" function on the server before sending a ping response on receipt of a message.

2.Data structure Alignment and Padding

Compilers on modern processors will typically try to align data structures to that optimal for the machine. For example, 4-byte values are stored at addresses divisible by 4, and 8-byte values are stored at addresses divisible by 8. When sending multiple values of different sizes, you may find that in data structures, such as struct in C/C++, the compiler adds padding. For example, if you are sending values of different sizes using a C struct to store a 4-byte integer, followed by an 8-byte integer, 4-bytes of padding may be inserted between the 2 integers to ensure 64-bit alignment. Thus, a struct of 12 bytes may become a struct of 16 bytes with this padding. (You can determine the size of the structure and the relevant fields in the structure using the sizeof() operator, and also looking at the wireshark output). This type of padding is acceptable for this exercise; just make sure to note this information when submitting your assignment.

[1]See struct.pack() and struct.unpack() functions to encode integers into a sequence of bytes in network byte order in https://docs.python.org/3/library/struct.html

[2]A message sequence number is a unique identifier for the packet. Start numbering from 1, and increment the number by one for each message sent. For example, the sequence number of the first ping request sent from the client is 1, the second ping request has a sequence number of 2, and so on, up until the last ping request which should have a sequence number of 10.

[3]The socket library provides the ability to set a timeout value on a socket. An exception is raised if the timeout value expires before the socket operation has completed.

[4]A programming language will typically provide a random number generator in a random standard library. For example, in Python, this can be found using import random and random.int() function.