What frame relay switch is causing MCI/Worldcom such grief?

smd at clock.org smd at clock.org
Mon Aug 9 22:58:08 UTC 1999

Vijay -

| Traffic flows change faster than the topology in most cases.

So, in other words TE is a hack to make up for people's weaknesses
in forecasting that leads one into a connectivity graph where the
normally-selected logical path between two points is insufficient 
for the amount of traffic one wants to shuffle between ingress
and egress?

"Our forecast horizon is shorter than our planning cycle, so therefore
we need TE" is probably the most real argument I've run into so far
for doing TE, but it's so terribly sad that this is the case.  
Again, again, again, just like so many other times in the past.

The other "compelling reason" I've run into for TE/MPLS is that it allows
some people to close the book on the ATM-switch-in-the-middle-of-a-
cluster-of-7[05]xx-es hack that was done in response to another
famous underprediction of growth about which the people who seem most
in favour of MPLS seem the most unforgiving.

Ironic, isn't it?

| Traffic measurements from end to end (per city flows) are also
| easier to measure with the city to city pipe as it were.

Uhm, think about that carefully before you declare it a compelling
reason - step 1: sort traffic into categories that group together
combinations of the 5-tuple, step 2: count this traffic.

Possible implementation: add column to FIB table which is of the type

	struct counter { long long bytes; long long packets } *

When a packet matches the FIB row, forward according to directives
in the other columns, and then do:

	FIBLINE.counter->packets++; FIBLINE.counter->bytes += packet_length;

Add glue to allow the FIB-creation-system to assign a particular
counter per FIB entry, and some stuff to allow for the nice extraction
of this information.   One might even put it like this 
"show interface POS 0/1 quasi-vc <identifier>", which should show
you a pretty printed summary of what the relevant counter structure contains.

In other words, if extracting information about aggregate traffic
flows is the means by which someone justifies deploying a pseudo-
circuit-switched network like MPLS, I believe the problem lies in
poor communications skills when communicating one's needs to one's


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