ATM (was Re: too many routes)

Michael Dillon michael at
Fri Sep 12 17:00:56 UTC 1997

>> Lets see you allocate an ESF B8ZS Clear Channel T1 over
>> IP....
>PDH is dead.
>POTS is only alive because you can emulate PDH still, and
>extracting a single DS0 from SDH is easy, and because the
>POTS user interface is well understood by a very large
>installed user base.

PDH = Plesiochronous Digital Hierarchy
This refers to muxing up DS0's into DS1's into DS2's into DS3's, i.e. TDM
stuff over twisted copper pairs.

SDH = Synchronous Digital Hierarchy and refers to optical fiber links like
OC3, OC12 and OC48. In North America the SDH standard is called SONET
(Synchronous Optical Network).

>  However, there are neat
>plans for SS7 and neater plans for doing clever things
>with interpreting DTMF.

Signalling System Number 7 is the packet switched control protocol used by
the telephone networks to exchange control and billing and caller-id and
similar info. DTMF (Dual Tone Multi Frequency) is an in-band signalling
mechanism more commonly called "touch tones".

> on aggregating up local
>access lines into VC11/VC12, dropping that into a
>POP-in-a-box at STM-16 and pulling out STM-16c to a big
>crunchy IP router.

I don't know everything. Sean will have to translate VC11 and VC12.
STM means Synchronous Transfer Mode. An STM-1 has the same bandwidth of OC3
so an STM16 will have the same bandwidth as OC48. Therefore STM-16c will be
like OC48c in that the bandwith is "concatenated" into a single big pipe
rather than a bunch of smaller channels.

>All I ever did was sit down with pst and tli and hack and
>slash at the 10.2-viktor caching scheme to try to get
>traffic to avoid moving over to the stabler of the two
>lines between ICM-DC and RENATER.

Again, Sean will have to identify pst, but tli is Tony Li of Juniper
formerly of Cisco and 10.2-viktor is one of many IOS versions. I suppose
most people realize that ICM-DC is ICM in Washington DC and RENATER is a
large network in France.

>Oh that and helping beat on CEF/DFIB packet-by-packet load
>balancing before my last retirement.

Once again, I'm at a loss as ti what CEF/DFIB stands for.

>Points if you know who Leon and Viktor are.  Hint: they're
>both as dead as PDH.)

Thinking of dead philosophies made me think of Leon Trotskiy by Viktor
escapes me. Obviously not omniscient, eh? :-)

>Finally another ABR demon is in the decay of the rate at
>which a VS is allowed to send traffic, which in the face

ABR (Available Bit Rate) is another ATM service something like VBR with
flow control and guarantees. The VC is a bunch of concatenated
subconnections and a VS (Virtual Source) is the end point of one of these

>This gets talked about quite frequently on the NANOG
>list.  I suggest you investigate the archives.  I'm sure
>Michael Dillon can point you at them.  He's good at that.


Actually I *WAS* about to suggest this very thing.

You see folks, Sean packs a whole lot of information into these messages
and whether you agree with his conclusions or not it would pay off to
review the meanings of the various acronyms he uses and then head off to
the archives conveninetly located at and re-read his
recent postings. Even if he is wrong about some of these things he has
clearly done a lot of research and thinking about the problems we all face
in deploying a global ubiquitous always-on network.

Michael Dillon                    voice: +1-650-482-2840
Senior Systems Architect            fax: +1-650-482-2844

"The People You Know.  The People You Trust."

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