Starting from:
$29.99
Assignment 3: Developing a Reliable Transport Layer Protocol using Raw Sockets
Assignment 3: Developing a Reliable Transport
Layer Protocol using Raw Sockets
Objective:
The objective of this assignment is to develop a reliable transport layer protocol on the top of
the IP layer. Note that IP layer provides unreliable datagram delivery there
is no guarantee
that a packet transmitted using IP will be eventually delivered to the receiver, because of any
of the following reasons:
1. The packet may get lost during endtoend
delivery this
can happen due to many
reasons, like buffer overflow, forwarding error etc.
2. The packet is transmitted to the end host, but the content of the packet may get
corrupted.
The broad objective of this assignment is to develop a transport layer protocol with following
features,
a) Connection oriented packet delivery before
initiating a session, an endtoend
connection is established to ensure that an endtoend
path exists between the
source and the destination
b) Ensure endtoend
reliability Endtoend
reliability is ensured via explicit
acknowledgement of packet reception.
We call this protocol as Reliable Transport Layer Protocol (RTLP) . The unix socket
programming API provides a raw socket (SOCK_RAW) framework to directly access the IP
layer services. Your task is to develop RTLP on top of the IP layer services supported by raw
socket APIs.
Description:
First you need to define a header structure for RTLP. RTLP header is 16 bytes and it
contains following fields:
● Source port : 2 bytes
● Destination port: 2 bytes
● Sequence number: 4 bytes
● Acknowledgement number: 4 bytes
● Checksum: 4 bytes
Part A: Connection Establishment: RTLP uses a three way handshaking for connection
establishment at the beginning of a data transmission session.
1. The client sends a SYN packet to the server. The SYN packet contains an initial
sequence number, say s1, (which is a randomly generated integer).
2. The server sends back with an SYN+ACK packet indicating that it agrees with the
connection (ACK), and it also wants to open a connection (SYN) towards the client.
Therefore, it generates another sequence number, say s2. For this SYN+ACK
packet, sequence number = s2 and acknowledgement number = s1.
3. The client, on receiving the SYN+ACK packet, returns back another ACK packet
where acknowledgement number = s2.
In this part of the assignment, your task is to implement the three way handshake
mechanism.
Part B: Error Control through Explicit Acknowledgements: RTLP uses explicit
acknowledgement mechanism to inform the sender that the receiver has received the data
sent by the sender. This is done through the sequence number and acknowledgement
number. RTLP uses byte sequence number that indicates how many bytes have been
transmitted, whereas the acknowledgement number indicates how many bytes have been
acknowledged. Note that the receiver acknowledges every individual packets explicitly. The
initial sequence number for the server and the client is established during the connection
establishment procedure as discussed before.
Assume that in a RTLP session, the initial sequence number is 1224 for the client and 3342
for the server (s1=1224, and s2=3342). Here is an example of sequence of packet
transmissions.
1. Client sends a packet of 24 bytes. So, in the RTLP header of the data packet,
sequence number = (1224+24) = 1248, Acknowledgement number = 3342. The
sender also keeps this data in a buffer, called RTLP sender buffer, until it receives
the corresponding acknowledgement.
2. On receiving the packet, the server sends an acknowledgement (ACK), where
Acknowledgement number = 1248, indicating that it has received the 24 bytes of data
correctly. Note that the sequence number field for this ACK packet is 3342, as the
server is not sending any data. If it wants to send data with this packet, it can do so
by modifying the sequence number field appropriately.
3. Now there can be two options:
a. The client receives the acknowledgement. On receiving the
acknowledgement, the client understands that all 24 bytes of the packet has
been transmitted successfully, and it deletes the packet from RTLP sender
buffer. If the next packet is of size 100 bytes, then for that packet, sequence
number = (1248+100) = 1348.
b. The client does not receive the acknowledgement. Now, if the client does
not receive the acknowledgement within a timeout period (think of the value of
a suitable timeout period), it resends the packet from the RTLP packet buffer,
with sequence number = 1248.
So, here are your tasks for this part of the assignment.
1. Implement the explicit acknowledgement mechanism with byte sequence number.
2. Implement the timeout mechanism. Vary the timeout value to check its impact over
packet transmission. Note that if this timeout value is less, you’ll receive duplicate
packets. On the other hand, for a large timeout value, the packet transmission delay
may increase.
Part C: Checksum Computation: RTLP header contains a checksum value. Before
sending a RTLP packet, the sender computes the checksum over following fields (together):
I. Source port
II. Destination port
III. Sequence number
IV. Acknowledgement number
V. Data
You can use any simple hash function for the checksum computation. The sender includes
the checksum in the RTLP header. The receiver, on reception of the packet, first computes
the checksum over all the above five fields together, and matches with the received
checksum. If the checksum value matches, it accepts the packet, otherwise, it drops the
packet. The checksum ensures that the neither the header nor the data has been modified
during packet transmission.
In Part C, your task is to implement the checksum computation and matching procedure in
RTLP.
Part D: Connection Termination. The connection termination procedure at the end of a
RTLP session is similar to the connection establishment procedure and uses three way
handshaking. If the client wants to terminate the session, it sends a FIN packet to the server.
In response, the server sends back with a FIN+ACK packet (similar to the SIN+ACK one),
and finally the client replies with an ACK packet. This closes a RTLP session.
Your task is to implement the three way handshaking mechanism for terminating a RTLP
session.
Test Cases:
This is a simple test case that you can use to check the working of RTLP. However, this
does not cover all the possible test scenarios, and you should think of developing the test
scenarios accordingly.
1. Run a RTLP server and a RTLP client at two different physical machines.
2. RTLP client sends periodic ECHO_REQUEST messages, where the message data
is “ECHO REQ N” where N is the request number, N=1,2,3,...
3. RTLP server replies back with ECHO_RESPONSE messages, where the message
data is “ECHO RES N+1”. For example, in reply to “ECHO REQ 10”, the server
should send “ECHO RES 11”.
4. Vary the Acknowledgement timeout value and check for what value of the timeout,
you get duplicate messages.
5. Food for Thought: Can you see any relation between acknowledgement timeout
and message transmission/propagation delay?
Layer Protocol using Raw Sockets
Objective:
The objective of this assignment is to develop a reliable transport layer protocol on the top of
the IP layer. Note that IP layer provides unreliable datagram delivery there
is no guarantee
that a packet transmitted using IP will be eventually delivered to the receiver, because of any
of the following reasons:
1. The packet may get lost during endtoend
delivery this
can happen due to many
reasons, like buffer overflow, forwarding error etc.
2. The packet is transmitted to the end host, but the content of the packet may get
corrupted.
The broad objective of this assignment is to develop a transport layer protocol with following
features,
a) Connection oriented packet delivery before
initiating a session, an endtoend
connection is established to ensure that an endtoend
path exists between the
source and the destination
b) Ensure endtoend
reliability Endtoend
reliability is ensured via explicit
acknowledgement of packet reception.
We call this protocol as Reliable Transport Layer Protocol (RTLP) . The unix socket
programming API provides a raw socket (SOCK_RAW) framework to directly access the IP
layer services. Your task is to develop RTLP on top of the IP layer services supported by raw
socket APIs.
Description:
First you need to define a header structure for RTLP. RTLP header is 16 bytes and it
contains following fields:
● Source port : 2 bytes
● Destination port: 2 bytes
● Sequence number: 4 bytes
● Acknowledgement number: 4 bytes
● Checksum: 4 bytes
Part A: Connection Establishment: RTLP uses a three way handshaking for connection
establishment at the beginning of a data transmission session.
1. The client sends a SYN packet to the server. The SYN packet contains an initial
sequence number, say s1, (which is a randomly generated integer).
2. The server sends back with an SYN+ACK packet indicating that it agrees with the
connection (ACK), and it also wants to open a connection (SYN) towards the client.
Therefore, it generates another sequence number, say s2. For this SYN+ACK
packet, sequence number = s2 and acknowledgement number = s1.
3. The client, on receiving the SYN+ACK packet, returns back another ACK packet
where acknowledgement number = s2.
In this part of the assignment, your task is to implement the three way handshake
mechanism.
Part B: Error Control through Explicit Acknowledgements: RTLP uses explicit
acknowledgement mechanism to inform the sender that the receiver has received the data
sent by the sender. This is done through the sequence number and acknowledgement
number. RTLP uses byte sequence number that indicates how many bytes have been
transmitted, whereas the acknowledgement number indicates how many bytes have been
acknowledged. Note that the receiver acknowledges every individual packets explicitly. The
initial sequence number for the server and the client is established during the connection
establishment procedure as discussed before.
Assume that in a RTLP session, the initial sequence number is 1224 for the client and 3342
for the server (s1=1224, and s2=3342). Here is an example of sequence of packet
transmissions.
1. Client sends a packet of 24 bytes. So, in the RTLP header of the data packet,
sequence number = (1224+24) = 1248, Acknowledgement number = 3342. The
sender also keeps this data in a buffer, called RTLP sender buffer, until it receives
the corresponding acknowledgement.
2. On receiving the packet, the server sends an acknowledgement (ACK), where
Acknowledgement number = 1248, indicating that it has received the 24 bytes of data
correctly. Note that the sequence number field for this ACK packet is 3342, as the
server is not sending any data. If it wants to send data with this packet, it can do so
by modifying the sequence number field appropriately.
3. Now there can be two options:
a. The client receives the acknowledgement. On receiving the
acknowledgement, the client understands that all 24 bytes of the packet has
been transmitted successfully, and it deletes the packet from RTLP sender
buffer. If the next packet is of size 100 bytes, then for that packet, sequence
number = (1248+100) = 1348.
b. The client does not receive the acknowledgement. Now, if the client does
not receive the acknowledgement within a timeout period (think of the value of
a suitable timeout period), it resends the packet from the RTLP packet buffer,
with sequence number = 1248.
So, here are your tasks for this part of the assignment.
1. Implement the explicit acknowledgement mechanism with byte sequence number.
2. Implement the timeout mechanism. Vary the timeout value to check its impact over
packet transmission. Note that if this timeout value is less, you’ll receive duplicate
packets. On the other hand, for a large timeout value, the packet transmission delay
may increase.
Part C: Checksum Computation: RTLP header contains a checksum value. Before
sending a RTLP packet, the sender computes the checksum over following fields (together):
I. Source port
II. Destination port
III. Sequence number
IV. Acknowledgement number
V. Data
You can use any simple hash function for the checksum computation. The sender includes
the checksum in the RTLP header. The receiver, on reception of the packet, first computes
the checksum over all the above five fields together, and matches with the received
checksum. If the checksum value matches, it accepts the packet, otherwise, it drops the
packet. The checksum ensures that the neither the header nor the data has been modified
during packet transmission.
In Part C, your task is to implement the checksum computation and matching procedure in
RTLP.
Part D: Connection Termination. The connection termination procedure at the end of a
RTLP session is similar to the connection establishment procedure and uses three way
handshaking. If the client wants to terminate the session, it sends a FIN packet to the server.
In response, the server sends back with a FIN+ACK packet (similar to the SIN+ACK one),
and finally the client replies with an ACK packet. This closes a RTLP session.
Your task is to implement the three way handshaking mechanism for terminating a RTLP
session.
Test Cases:
This is a simple test case that you can use to check the working of RTLP. However, this
does not cover all the possible test scenarios, and you should think of developing the test
scenarios accordingly.
1. Run a RTLP server and a RTLP client at two different physical machines.
2. RTLP client sends periodic ECHO_REQUEST messages, where the message data
is “ECHO REQ N” where N is the request number, N=1,2,3,...
3. RTLP server replies back with ECHO_RESPONSE messages, where the message
data is “ECHO RES N+1”. For example, in reply to “ECHO REQ 10”, the server
should send “ECHO RES 11”.
4. Vary the Acknowledgement timeout value and check for what value of the timeout,
you get duplicate messages.
5. Food for Thought: Can you see any relation between acknowledgement timeout
and message transmission/propagation delay?
1 file (620.4KB)
