Consider the TCP multiple acknowledgement scheme. A base station (BS) may receive an out of sequence packet that was buffered at an earlier point in time. How can such a situation arise in the network? (3 marks) Actions taken by the BS will depend upon the sequence number of the received packet from the sender (in the wired segment) and sequence number of the last unacknowledged packet (at the BS). Based on these sequence number values, explain the different responses the BS can generate to bring the system to a consistent state. (6 marks) Solution Here TCP may be defined as the transmission control protocol where each nodes has to depend on acknowledgment and sequence number from sender to receiver. Basically as we look at the OSI model this TCP protocol lies in transport layer of OSI model, which is connection oriented protocol. In this type of connection every data is divided into segments and each segment is given a sequence number and on that basis data is being completely sent one by one in segments. Since this type of protocol waits for the acknowledgment from the receiver so it is considered a slow connection. But has got capability of fast data recovery and error control as well flow control and congestion control. In multiple acknowledgments we can denote that RTT would be for end to end round trip time and similarly RTT (w) would be denoted as the round trip for base station and wireless node. Here sender tries to re send the segments after waiting some time from end to end acknowledgement until it receives an acknowledgment from the receiver thus establishes a proper connection when a sender holds a ACK from the base station, then apparently sender gets to know that base station has received the packets until S-1 but has got a difficulty to send it to the wireless nodes/hosts, since it has not received the ACK from the wireless host even waiting for some time. When a base station receives a packet from the node sender, it keeps a timer and then again sends to the sender. If suppose the timer get over from the base station it then sends ACKp towards the sender and then next sequence number is being attached and sends back to the sender which further sends to the wireless hosts. Similarly if base station receives a packet which is out of sequence then it will send this packet to the wireless node and if it doesn’t get received within time given then, then it will send early packet to the sender by the base station upon which it sends ACKp to the sender..

1. Consider the TCP multiple acknowledgement scheme. A base station (BS) may receive an out of
sequence packet that was buffered at an earlier point in time. How can such a situation arise in
the network? (3 marks) Actions taken by the BS will depend upon the sequence number of the
received packet from the sender (in the wired segment) and sequence number of the last
unacknowledged packet (at the BS). Based on these sequence number values, explain the
different responses the BS can generate to bring the system to a consistent state. (6 marks)
Solution
Here TCP may be defined as the transmission control protocol where each nodes has to depend
on acknowledgment and sequence number from sender to receiver. Basically as we look at the
OSI model this TCP protocol lies in transport layer of OSI model, which is connection oriented
protocol. In this type of connection every data is divided into segments and each segment is
given a sequence number and on that basis data is being completely sent one by one in segments.
Since this type of protocol waits for the acknowledgment from the receiver so it is considered a
slow connection. But has got capability of fast data recovery and error control as well flow
control and congestion control.
In multiple acknowledgments we can denote that RTT would be for end to end round trip time
and similarly RTT (w) would be denoted as the round trip for base station and wireless node.
Here sender tries to re send the segments after waiting some time from end to end
acknowledgement until it receives an acknowledgment from the receiver thus establishes a
proper connection when a sender holds a ACK from the base station, then apparently sender gets
to know that base station has received the packets until S-1 but has got a difficulty to send it to
the wireless nodes/hosts, since it has not received the ACK from the wireless host even waiting
for some time.
When a base station receives a packet from the node sender, it keeps a timer and then again
sends to the sender. If suppose the timer get over from the base station it then sends ACKp
towards the sender and then next sequence number is being attached and sends back to the sender
which further sends to the wireless hosts.
Similarly if base station receives a packet which is out of sequence then it will send this packet to
the wireless node and if it doesn’t get received within time given then, then it will send early
packet to the sender by the base station upon which it sends ACKp to the sender.