Options for preserving established communications

["marcelo bagnulo" <mbagnulo@ing.uc3m.es>]

This is an attempt to summarize the options that have came up in the
on-going thread about preserving established communications in order to
evaluate the different possibilities.

A mechanism for preserving established communications requires the following
mechanisms:

- A mechanism to detect outages in the currenlty used path
- A mechanism to identify alternative paths that are working
- A mechanism to change from the broken path to the new path

Explored possibilities for each of those mechanism include:

- Possible option for detecting outages in the currenlty used path

The timing requirement for preserving established communcations vary with
the considered application.

The different options cosidered are:
    - End-to-end keepalives with two flavors:
                 - fixed frequency
                 - frequency determined by the ULP
    - BGP detection mechanisms
    - ULP detection mechanisms
    - Churn detection mechanism
    - ICMP errors

- Possible options for identifing alternative paths that are working
    - ping bomb with three flavors:
           - ICMP
           - replicated data packets
           - new M6 message piggybacked in data packets
   - BGP plus rewriting source address
   - None, just blindly try with alternative ones

- A mechanism to change from the broken path to the new path
This depends on the type of failure.
One type of failure is related to the Destination address, so the option is
change the destiantion address.
The other type of failures is related to the exit ISP, so the options to
deal with this are:
   - Source address based routing
   - a bit in the header that informs the routing system that alternative
path is needed
   - Routing header
   - BGP routes injected in the site

Regards, marcelo