On 1/21/2014 6:40 PM, Ross Callon wrote:
If the upper layers (the thing that runs over the tunnel) involves
applications over TCP over IP, or if it is otherwise responding to
congestion in the same way that we expect anything running over IP to
respond to congestion, then we don't want the tunnel to also
independently try to respond to congestion (two independent cooks
cooking the same meal does not necessarily lead to success).
That's true, but is an issue only if the tunnel congestion control is
dynamic over the same or shorter timescales than the
congestion-controlled traffic being tunneled.
If the upper layer does not respond to congestion, then perhaps it
shouldn't be running over the open Internet (with or without a tunnel),
unless the *total* bandwidth that could be used is inherently quite low.
Sure, but who would enforce that? If you're using MPLS, the only entity
in a position to know (whether the traffic is congestion controlled or
not) is the tunnel encapsulator.
On the other hand, it might want to run within a data center or
internally to a service provider network with appropriate provisioning.
All bets are always off for private networks; they need not comply with
any Internet standards or expectations, even when they leverage Internet
header formats and protocols.
But that's not a strict constraint of the proposed approach here.
Joe
Ross
-----Original Message-----
From: Joe Touch [mailto:touch@xxxxxxx]
Sent: Tuesday, January 21, 2014 8:12 PM
To: Ross Callon; Eggert, Lars
Cc: mpls@xxxxxxxx; IETF discussion list
Subject: Re: [mpls] Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating MPLS in UDP) to Proposed Standard
On 1/16/2014 2:32 PM, Ross Callon wrote:
These tunnels are stateless
yep. (But they don't have to be.)
The tunnels strictly speaking do not have to be stateless. However, if you want routers to actually implement them, and you want to scale in both forwarding speed and number of tunnels, then yes they do have to be stateless.
There's clearly a problem though:
- tunnels must be stateless to be efficiently implemented
- transport layer tunnels must have congestion control
Saying that the only way we can make tunnels cheap is to make them break
the Internet isn't a good solution.
Maybe it's time to expect something that's inherently costly to end up
being expensive?
Joe