[ih] TTL [was Exterior Gateway Protocol]

[vinton cerf]

i don't think traffic is discarded except for hop count or lack for
forwarding path unless RTP does something with timers?

v


On Sat, Sep 5, 2020 at 5:34 PM Jack Haverty via Internet-history <
internet-history at elists.isoc.org> wrote:

> Unfortunately I can't remember where or when that discussion happened.
> It might have been in some meeting not involved in RTP, but perhaps
> thinking about how to make the underlying gateway system more efficient
> by discarding useless datagrams as soon as possible.  The "meeting" I
> remember might even have been in a hotel bar or some restaurant.
>
> I remember that TCP was split apart to create TCP/IP, in order to permit
> the creation of UDP, which was done to provide application access to a
> more basic datagram service in addition to TCP's virtual circuit
> service, for scenarios such as packet voice.   That split motivated
> subsequent thinking about how to deal in the gateways with the different
> traffic requirements, using the information provided by IP fields such
> as TOS and TTL.
>
> E.g., if a gateway received a packet with a TTL that it knew, from its
> routing tables, could not be delivered to the ultimate destination "in
> time", then it was advantageous to throw it away right then, even though
> the TTL was still non-zero.   That kind of discussion may not have
> overlapped much with the RTP community.
>
> I wonder if today's routers behave that way...?
>
> /Jack
>
> On 9/5/20 2:06 PM, Stephen Casner wrote:
> > On Sat, 5 Sep 2020, Jack Haverty via Internet-history wrote:
> >
> >> 4/ TTL was also intended for use with different TOS values, by the
> >> systems sending voice over the Internet (Steve Casner may remember
> >> more).  The idea was that a packet containing voice data was useless if
> >> it didn't get to its destination in time, so TTL with a "fastest
> >> delivery" TOS enabled the sender to say "if you can't deliver this in
> >> 200 milliseconds, just throw it away and don't waste any more
> >> bandwidth".   That of course wouldn't work with "time" measured in hops,
> >> but we hoped to upgrade soon to time-based measurements.
> > I don't recall any discussion of that idea while we were developing
> > RTP.  As you say, the units being in hops rather than time would make
> > this mechanism imprecise, and the variability in the diameter of the
> > network would make it hard to use.  Multicast complicates that even
> > further.
> >
> >                                                         -- Steve
>
> --
> Internet-history mailing list
> Internet-history at elists.isoc.org
> https://elists.isoc.org/mailman/listinfo/internet-history
>