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Triggers for Transport

Document Charter Triggers for Transport WG (trigtran)
Title Triggers for Transport
Last updated 2003-12-10
State Approved
WG State Concluded
IESG Responsible AD (None)
Charter edit AD (None)
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IETF transport protocol development has been based
on the assumption that two communicating endpoints
"know" more about characteristics of the paths
between these endpoints than any single device
within the network. This is implicit knowledge,
based on transport algorithm adaptations to
events in the paths.  Because IP datagram forwarding
can follow a variety of paths between two endpoints,
a device within the network in contrast has information
about one part of the path, but not what the transports
endpoints "know".

When transport protocols are deployed over paths
including one or more a wireless subnets, a wireless access
device now may have significant information about that
part of the path.  

End-to-end mechanisms continue to work (see
PILC and related specifications), but must rely
on communication over a subnetwork link that
experiences outages and degradation. The TRIGTRAN
BOF is investigating whether special knowledge
from wireless access devices can be useful to
endpoint transports.

It is possible that a wireless access device might
provide information about the path in a useful way

(a) the wireless access device has detailed
        knowledge of a subnetwork link, and

(b) it can still communicate with one endpoint
        when a problematic subnetwork link stops working,
        or starts working, or...

The goal here is that changes in path characteristics,
especially outages, RTT...can be explicitly signaled
without end-to-end blind retransmissions based on peer
transport retry timers.

If this goal is accepted, it may be broadened to include
changes in nominal subnetwork transmission rates or other
subnetwork events, if these subnetwork events are generic
in nature and accepted by the IETF community as a whole.

The Triggers for Transport (TRIGTRAN) BOF is being held
to understand

- The nature of generic "transport triggers"

- Possible uses of "transport triggers"

- Mechanisms for signaling transport triggers to
        accessible transport endpoints

- The architectural impact of this addition to
        the transport layer

Although the need for this change is more obvious in a
wireless environment, we're also soliciting input from
the rest of the Internet community in these areas:

- Whether there are "transport triggers" applicable to
        all (other?) subnetwork types, beyond link up/link down

- Whether the use of "transport triggers" is worth the
        effort of modifying existing transport protocols to
        make use of this information

This BOF is related to, but distinct from, similar
discussions on triggers in MOBILEIP and in IRTF's Routing
Research Group on micro-mobility. The primary difference
is this departs from the low latency and tight coupling of
those. It is possible that work products from a
TRIGTRAN working group would be reused with fast handoff
signaling. We'll explore this *briefly* in the BOF meeting.

TRIGTRAN will start with a scope limited to wireless
subnetworks, but it is also possible that non-wireless
subnetworks (for instance, SLOW) may also have events
that fit into the TRIGTRAN framework.