impact of UDLR on upper level protocols

[LOVRIC Ivan CNET/DSE/CAE <ivan.lovric@cnet.francetelecom.fr>]

> During the UDLR meeting at Minneapolis, it has been proposed that the
> issue described in this mail could be discussed within the UDLR mailing
> list.
> 
>                          ==O==
>       2Mb satellite Link/     \
>                       /         \
> Sibling1----Router1-(-           -)---Router2--128k Leased Link--Sibling2
>               |_____ISDN 64k Link______| |
>                                          | 
>                                         Cache
>                                          |
>                                          |
>                                         Client
> 
> When using the application level protocol Internet Cache Protocol, we
> desmontrate that the ICP reply always come from Sibling 2 even though the
> bandwidth is better over the satellite link. This means also that the
> satellite link should be used to transfer any file which has a size upper
> than 50K in that case, but ICP can't work properly due to the the
> unidirectionnal link.
> 
> This example shows that the asymetrical link and routing has a direct
> consequence on the well working of an upper level protocol.
> 
> No actual QoS routing protocol is able to solve this kind of issue, which
> means that it would be useful to define a common way to communicate
> information between the unidirectional link layer, routing layer, and
> application layer so that upper level protocols may work properly.
> 
>