North American Network Operators Group

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Re: IP over SONET considered harmful?

  • From: Sean M. Doran
  • Date: Sun Mar 22 13:50:30 1998

| There's LQM in PPP.

I would prefer to eliminate PPP.

| Better yet,
| what i do with splicing traffic into many channels effectively
| provides IP-invisible restoration w/o loss of useful capacity.
| Just route those channels into diverse physical paths :)

Um, unfortunately I missed your presentation at NANOG and
there is as yet no sign of the real video archives that
I can find, so going by memory and your web pages,
what I remember is that you are planning on using interfaces
roughly comparable to STS-1 and STS-3c, and using
telco WAN gear to do the work of add/drop multiplexing.

I thought this was rather clever, actually, particularly
given the accuracy of the prediction that non-facilities-owners
would have trouble getting access to anything faster than DS3s
in the near run.

If you have changed your mind and are building your own
fibre muxes, that would be neat to know. :)

| > SDH/SONET is also a really keen way of sharing a network
| > among IP and other things on the wide-area side, and
| > an even keener way of having access to relatively low-speed
| > customer data on the more local side.
| On customer-access side even ATM seems to be fine :)   It
| definitely is a huge lot cheaper than SONET gear.

It is pretty easy to pluck out VCs/SPEs from SDH/SONET.
The general thought was to have the equivalent of a CT3
(cisco device, takes T3 in on BNC pair, pulls out DS1s)
that can extract from, say, an OC3 or OC12, DS3s, SPEs
containing T1s and E1s, and perhaps even individual DS0s.
(DS0s would be neat as with clever load-balancing 
that gives you a granularity that is competitive with the
use of ATM as a fine-grained TDM system).

Essentially, an ADM on a card.   I don't see that as
being prohibitively expensive to engineer, and ironically
I think it would be easier for you than for some of
your competitors to make switching work, since they 
may be forced to simulate a hierarchy of routers on the card.

| Ciena folks told me some other compelling reasons for dropping
| SONET, which i do not feel i'm at liberty to discuss here.

Interesting.  Aim them at me or Peter if it doesn't have to
do with SONET's speed ceilings.

| I also expect it :)  My current favourite for framing is
| 32-to-33 bit encoding, with flag being one of "malformed words",
| one word header (2 bytes for payload length, 2 bytes for tag), and
| 32-bit CRC at the end.  I.e. the per-packet overhead is 12 bytes + 3.1% +
| rounding to 4 bytes for odd-sized packets. Make all 1s and all 0s
| and chess patterns to be invalid words, and loss-of-carrier becomes
| easy to detect.

Well, I still prefer the idea of a synchronous byte stream
to a clever HDLC on steroids... :)