How does Alternating Bit Protocol work?

From Wikipedia entry on ABP ( http://en.wikipedia.org/wiki/Alternating_bit_protocol ):

When A sends a message, it resends it continuously, with the same
sequence number, until it receives an acknowledgment from B that
contains the same sequence number. When that happens, A complements
(flips) the sequence number and starts transmitting the next message.

When B receives a message that is not corrupted and has sequence
number 0, it starts sending ACK0 and keeps doing so until it receives
a valid message with number 1. Then it starts sending ACK1, etc.

I simply do not get it.

I understand the pretext and the whole thing with acknowledgements, but the process itself is described differently in different publications (a

In particular:

1. What does it mean "...and keeps doing so"? Does it mean that the receiver can send two consecutive acks down the ack channel without any activity from the sender at all? I.e. at that point it is not synchronized with the sender at all?




2. What does it mean "resends continuously"? Same as above - is sender completely independent of the receiver during this resending?

There is an alternative coverage of the way it works here, but it gives a conflicting picture again: http://staff.science.uva.nl/~psf/specifications/abp.html

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