Muni fiber: L1 or L2?

Leo Bicknell bicknell at ufp.org
Thu Jan 31 03:10:33 UTC 2013


In a message written on Wed, Jan 30, 2013 at 10:00:47PM -0500, Jay Ashworth wrote:
> > That can be fixed in other ways. It would be easy to make a standard
> > SNMP mib or something that the service provider could poll from the
> > customer gateway, and service providers could require compatable
> > equipment. There are ethernet OAM specs.
> 
> "Customer gateway".  Isn't that the box you're denigrating? :-)
> 
> Or do you mean the "FSLAM"? 

No, there's an important distinction here, and we have a great example
today.

The Cable Modem.

The Cable Modem is in many ways very similar to a FTTH ONT.  It takes
one media (cable, fiber), does some processing, provides some security
and a test point to the provider, and then hands off ethernet to the
customer.  A majority of customers then plug in a Home Gateway (router,
one of those linksys/netgear/belkin things), although some plug in a
single device.

What goes wrong?  Well, the Home Gateway sees a 1000Mbps GigE to the
cable modem, and tries to send at that rate.  The cable modem is only
allowed to transmit to the plant at maybe 10Mbps though, and so it must
buffer and drop packets, at what appears to be L2.  At which point
virtually any ability the customer had to do QoS is gone!  I believe
some Verizon FIOS customers had similar issues with GigE to the ONT, and
then 100Mbps upstream service.

Havng the two separate devices significantly degrades the customer
experience in many cases, particularly where there is a speed mismatch.
I want to chuck the cable modem and/or ONT out the window never to be
seen again, and let the customer plug their home gateway in directly.
No middle box to buffer or drop packets, or otherwise mangle the data
stream in bad ways.

I have no issues with the Home Gateway responding to OAM testing from
the provider.  I have no issues with it learning part of its config
(like a maximum transmit speed) from the provider.

A Cable Modem or ONT is a glorified media converter which should not
exist.

-- 
       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
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