Cell Relay Archive

[bannai@best.com (Vinay Bannai)]

In article <64uchc$lv3$1@dismay.ucs.indiana.edu>,
Nafez Aboulibda  <nafez@igdv.fh-darmstadt.de> wrote:
>My name is Nafez Aboulibda, I'm doing my MSc project.
>There is some thing relating to the TTL field in the Flow identifier in
>Ipsilon=92s publications
>"IP switching" that I couldn't understand.
>Since this field is not transmitted within the packet and their issue is=

>to retain the function of
>TTL.
>My question is : where is  the recovery procedure explicitly done to
>decrement the TTL field
>on each node .
>Ipsilon's words" the TTL field is not transmitted in the packet but it
>is recovered from the
>info. stored at the destination"
>
>with regards.
>Nafez Aboulibda
>
>

This is something of an issue for all IP switching and tag switching
folks. Since the packets (or the cells of the packets) are switched till
they hit the egress node, there cannot be any TTL decrements. Tag folks
want to check the TTL value at the ingress point and based on the tag fin=
d
out how many swithing nodes it has to traverse to the egress point and
decrement that value from the TTL at the ingress. I have not been keeping=

up with the MPLS for a while so I am not sure what their position is righ=
t
now. As far, the IFMP, I think what they do is somehow code the TTL value=

into the flow identifier and at the egress point of the switching core
network, they re-introduce the TTL value back into the IP header. I don't=

think they decrement the TTL value either at the ingress or the egress. =


Vinay



-- =

Vinay Bannai                     E-mail: bannai@best.com