This question is from Muhammad Hasanain Chaudary:
1. What is the Role of keyword “self” in the OTcl?
2. What is the instproc (and what is the associated class) used to compute the optimal route in NS2?
3. What’s the difference between Fast Retransmit and Fast Recovery? What is their relationship?
4.Is there any drawback of TCP?
1. What is the Role of keyword “self” in the OTcl?
2. What is the instproc (and what is the associated class) used to compute the optimal route in NS2?
3. What’s the difference between Fast Retransmit and Fast Recovery? What is their relationship?
4.Is there any drawback of TCP?
3 comments:
1)I am not exactly know about self but i think it invokes the instproc with the same name (i.e., init{...} of the parent class. where the constructor of the parent class needs to be called earlier.
2)The instproc compute-flat-routes{} of
class Simulator retrieves the associated route logic object (using instproc get-routelogic{}), computes the optimal route using the retrieved object(using instproc compute{}), and configures the classifiers in all the
Nodes according to the computed route (using the command populate-flatclassifiers{n}).
3)Fast Retransmit is the mechanism for the packet lost detection in which it expedites the packet loss detection by means of duplicated acknowledgement detection.
while the Fast Recovery is Window Decreasing Mechanism in which Upon detection of a packet loss, the fast recovery mechanism
sets both current window size and slow-start threshold to half of
the current congestion window size. Then, it increases the window size
by one for each incoming duplicated acknowledgement.
The relationship is that when fast retransmit detect packet loss the tcp consider this is due to congestion so fast recovery decrease the rate or window size to over come congestion.
4)The main draw back of Tcp in my opinion is that if even only one packet loss the tcp consider it as due to congestion so it retransmit the packet which cause duplication and the network will be get heavy loaded traffic.
Thein Tun Aung/st108032
instproc is to define a member function to an object class. Class inheritance is specified using the keyword -superclass.
In defining member functions, $self acts same as the "this" pointer in C++, and instvar checks if the following variable name is already declared in its class or in its superclass.
A routing module acts as an interface to the other routing components such as route logic (which is responsible for computing the optimal routes),and to the agent attachment/detachment instprocs of class Node.
Fast retransmit is a heuristic that sometimes triggers the retransmission of a droppped pcket sooner than the regular timeout mechanism.The fast retransmit mechanism does not replace regular timeouts;it just enhances that facility.
When the fast retransmit mechanism signals congestion,rather than drop the congestion window all the way back to one packet and run slow start,it is possible to use the ACKs that are still in the pipe to clock the sending of packets.
kita juga punya nih artikel mengenai 'packet loss recovery', silahkan dikunjungi dan dibaca , berikut linknya
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