Stack Processing
Algorithm for Go Back
N protocol
Team Members:
Vinti (vv2236)
Garvit Singh (gs2731)
Pramod Nayak (ppn2106)
Vidhatre Gathey (vvg2111)
Contents
 Introduction: Go back N protocol
 Algorithm
 Software Modules
 Terminating Conditions
 Go Back N EFSM
 Assumptions
Go Back N protocol
 Allow multiple packets in transmission so that the line
isn’t idle in networks with long delays
 Accept all packets in proper order
 If packet ‘i’ lost, Transmitter sends ‘i+1’ and receiver
receives ‘i+1’ out of order and rejects it
 After time out, Transmitter must go back and retransmit
the lost frame and subsequent frames
Stack Processing and
Probabilistic Search
 Form probabilistic search tree, create a push down pop
up
 Place state with lowest probability at the bottom of the
stack
 At each new step, pop the top most sequence
 If a low probability event leads to this state, increase
the probability by 1
Software Modules
 Modular approach used to develop the software for
portability to any EFSM.
 Software verified using ARQ protocol first.
 EFSM states and transition saved in the header file.
 For a new protocol, only the header file needs to be
updated.
 Implementation done in C++, <stack> class used to
implement the stack.
Algorithm Flow Chart
Terminating Conditions
 Check for incorrect service sequence, if there is one,
stop
 Check the probability of the top most element poped
from the stack.
 P = pow(0.0001, probability.top())
 If P < 10-16, stop
GBN Transmitter
Si
Sw
Timeout
T
T
nx<Nx
a<bi
F
F
T
SF
F
a>bi+
w
GBN Receiver
Si
Re = 0
Sw
F
Output = 0
M=Re
T
Re= Re+1
Output = Ack(Re)
Probabilistic Search
Assumptions
 If the receiver receives a message it is not expecting, it
does nothing
 Sender goes into state of failure if it receives Ack of a
packet less than the base address.
 The number of retransmissions by sender after timeout
is limited , once the limit is hit, it goes into a state of
failure
 A simplified sequencing of the analysis has been
considered
Thank You !