[ih] Why did congestion happen at all? Re: why did CC happen at all?

[Dave Crocker]

On 8/30/2014 7:04 PM, P Vixie wrote:
> It was not simply left out. The omission of flow control and retransmission at L2 was deliberate, and reflects IP's need to run on links that by their nature cannot support transmission state. Had the RFC 791 authors been willing to limit themselves to a known set of link layer protocols we would not today have any Internet at all.


Carrying this point a bit further:

1. The predecessor, the Arpanet, had /lots/ of flow control and
retransmission.  So the decision for IP was based on experience.

2. IP was intended to be an overlay to a wide array of different kinds
of networks.  (The "Inter" part of the name was/is significant.) To make
operation over that much heterogeneity work, the overlay needs to impose
a minimum of requirements.  Flow control and retransmission are a long
way from minimal.

3. In fact, sometimes flow control and retransmission are poor choices.

So those were made optional, depending upon the transport layer, or are
imposed locally be the layer below.

d/

-- 
Dave Crocker
Brandenburg InternetWorking
bbiw.net