Subject: [Diffserv] Bidirectional flows, Emergency Services

From: "Steve Silverman" <[email-masked]>
Date: Wed, 30 Jan 2002 13:44:17 -0500

In response to my question about bidirectional flows, Fred Baker didn’t want
to impose the requirement on the routers to mark return packets because that
would mean keeping state info on every flow.  I sympathize with the desire
to avoid complicating the switch but:

If the system is going to allow DSCP marking to affect packet treatment, the
access router is going to have to be a gatekeeper to ensure that such
markings aren’t abused.  Otherwise most spam will be sent at high priority.
One would assume that Service Providers will want to limit use of and/or
charge for high priority markings.  This creates a state-keeping burden that
can’t be avoided.  If UserA has premium service, and sends a packet to
ServerX, packets from ServerX to UserA should get that premium service but
not packets from ServerX to other users.  The only way for the network to
validate these service requests is to note the packet from UserA to ServerX,
keep this state, and allow ServerX to UserA traffic to use this Diffserv
marking.

If IP is to be the global data/voice network of the future, I think
emergency services (and bidirectional flows) are going to be an unavoidable
part of the package even though it complicates the switch.

As I remember, when the Diffserv WG was first set up, allowing SPs to create
a premium service was a major driver for the WG.  This was presumed to
include web browsing.  Web browsing with Diffserv only makes sense if
priority is given to the return packets.

Steve Silverman
Houston Associates
[email-masked]

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 31 Jan 2002 14:32:49 +0100

I believe the points you raise are all discussed in RFC 2475.

   Brian