Reliable Data Transfer

Figure illustrate the  framework for reliable  transfer. The service  abstraction provided  to the upper  layer  entities is that  of a reliable channel  through  which data  can be  transferred. With a reliable channel  no transferred data  bits  are corrupted ( flipped  from o to 1or  vice  versa)  or lost  and all are  delivered in the order  in which  they  were  sent. This is  precisely the service model  offered by TCP  to the internet application that invoke it.

                                                Figure Reliable data transfer: Service model service implementation

It is  the responsibility  of a reliable  data transfer  protocol to implement  this servers  abstraction. This task  is made  difficult by the fact that the  layer below the  reliable data  transfer protocol  may be unreliable. For example  IP is a reliable data  transfer  protocols  that is  implemented on top of  an unreliable IP  end to end network  layer.

In this section we will incrementally develop the sender  and receiver sides of a reliable  data  transfer  protocols, considering  increasingly  complex models  of the  underlying  channel. Figure illustrates the interfaces for our  data transfer protocols.

a.When the  application wants  to send data, it  calls  rdit send  to activate teh transport  protocols.

b.The transport  protocols  builds a packet  and cells  udt send to send to  packet  over the lower  layer.

c.On the  receiving  side  when the  lower  layer  protocols has a packet  to deliver  it calls  rdt rcv .

d.The transport  protocols  extracts the data from  teh packet  and delivers the data  to the  applications  by calling  deliver  data.

e.This protocols  is called rdt 1.0.