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[EFM] Active Architectures

On the topic of active architectures, one that seems attractive in
comparison to PON for some deployment scenarios could be called a
"half-PON." Below I give a proposal for this. Comments appreciated.

The half-PON is a hybrid active/passive architecture that preserves the
attractive features of PON and P2P while eliminating many of the
unattractive features of each.

Downstream, it would be the same as the PON downstream (15x0nm GbE from PoP
to splitter; dedicated fibers from splitter to each of 16 (for example)

And upstream would be in two pieces: 

The first would be from the ONUs to the active node (hardened Ethernet
switch in node; node also contains the downstream splitter) and has a
dedicated fiber per ONU, each to a separate port on the Ethernet switch in
the node enclosure (more details in a second).

The second part of the upstream would be a single-fiber 13x0nm GbE between
the node and the PoP (wavelength-muxed into the same fiber as the downstream
so only one fiber between node and PoP).


The key savings come from the use of low power 850nm transmitters between
the ONUs and the switch, using 100BaseSX (TIA/EIA 785) as the baseline. So
instead of 16 high power (in comparison) 13x0 laser sources (one per ONU)
for PON upstream, each capable of >10km reach thru a 16:1 splitter, you'd
have 16 low power, low cost 850nm sources (one per ONU) that only have to
reach about 300m to the active node, and 1 low power 13x0 (low because no
splitter to go thru) source from the switch back up to the PoP. There are a
couple options on the fiber between the node and the ONU but I'll leave that
discussion for later.

Perhaps more importantly though, in comparison to PON you lose the need for
developing and agreeing upon a TDMA protocol, a ranging protocol, a sync
protocol, and a contention protocol for requests. You also get uniform
transmit power back to the PoP since there is only 1 source rather than 16
time-multiplexed from different ONUs at different distances, and no concerns
about run-away transmitter operation bringing down the node. You also get a
management-capable intermediate network point which will allow greater
diagnostic, provisioning, and demarcation capabilities. 

So, ONUs would be significantly cheaper. On this point there is no question.
For reference, a 100BaseFX (13x0 laser, 15km reach) to 100BaseTX media
converter goes for about 3-4x the cost of a 100BaseSX (850nm, 300m) to 100TX
media converter. Essentially, this is the ONU's function for any of the
architectures. Multiply that cost differential by 16 then subtract off a
10km lower power (no splitter to go thru) 1000BaseLX , then add back in node
powering costs. It seems to be an attractive option as a first order
estimate (i.e. thousands of dollars in savings per node branch, serving 16
ONUs), and powered nodes are a mature technology with lots of cost reduction
tradeoffs that can be made.  

By the way, I am not presenting this as a replacement for PON, but as an
alternative that has not been discussed, and may be more attractive in
certain situations. It would also be much less development effort since all
the constituent pieces have a defined Ethernet heritage, which means shorter
time to market. Arguably it is more future proof than PON since it starts
out with 100Mb ports per user, which PON cannot achieve due to TDMA overhead
and guardbands. It also appears cheaper overall than PON, per user (at least
in the early going anyway).  

In any event it is an alternative FTTH architecture that is decoupled from
the development time required for PON. The primary development effort would
involve adding OA&M to 100Base SX (but there are a couple other integration
decisions to make). The rest of the architecture uses EFM P2P elements as I
envision it. 

Any interest?

--Dave Horne

-----Original Message-----
From: Sukanta ganguly [mailto:sganguly@xxxxxxxxx]
Sent: Sunday, August 19, 2001 9:06 AM
Subject: Re: [EFM] EFM Requirements

  A all Fiber architecture will be simpler in the
overall aspect but would be a extremely expensive
deployment. So wo should have some sort of E/O deliver
in the last/first half mile.

Rich, Vladimir,
  An active architecture within the field isn general
is not a good idea, but actual scenario may digress
from generality. Some switching is required, no doubt.
I haven't read any deeper discussion on the switching
complexity (Maybe I missed some of the discussions in
the past.) I also did not understand the assumption of
the last/first 0.5 mile being more scalable than PON.
What kind of scalability is required at the last/first
mile. If you are talking about 1000baseX being
distributed to the real consumer or to then the amount
of bandwidth that is to be switched is fairly small
(i.e. in comparison to the 10G portion). The switching
components as far as scaleability and complexity is
concerned will be very different and hence, atleast
from my point of view is a very different discussion. 
  I think, and you folks may help me understand it
better, it is not a good idea to come up with a
generic one switching logic which can be applied to
100base-X/1000base-X and 10G network. 
  I would be extremely interested in discussing the
active component network on different scale of
operation as opposed to a PON as far as cost/ease of
deployment and maintainence, complexity etc is

My two cents.

(Sukanta Ganguly, An independent view)   
--- ramu <ramu_raskan@xxxxxxxxxxxxx> wrote:
> Rich, not sure I understand the logic behind some of
> your points, but the simple answer appears to be
> that it requires new trenching for the new copper
> drops, which will never fly. If I misunderstand,
> please elaborate.
> I don't quite get you conclusion: 'since E/O is
> required, 1KBaseX is significantly more cost
> effective, scalable, and simpler than PON.'
> If E/O is required in the field it can't be PON.
> Whether it is significantly more cost effective
> cannot be judged without detailed designs of each.
> Whether it is more scalable I guess depends on your
> definition. Simpler is hard to imagine, but again
> may depend on definition. If you could elaborate
> your view I would be interested.
> Since you are suggesting an active architecture with
> new electronics in the field, I for one would
> welcome a discussion of such a network architecture
> that had fiber for the last thousand feet. No one
> has addressed that at all to my recollection. None
> of the architectues is perfect in all respects so an
> all-fiber active architecture undoubtedly has some
> advantages. 
> Vladimir,
> It would seem that the most cost effective approach
> for a 10 mile EFM
> solution would be to use standard point-to-point
> 1000BASE-X or 10GBASE-X
> for the first 9.5 miles and then a 0.5 mile copper
> tail for the
> first/last half mile. Since E/O conversion is
> required at the 9.5 mile
> mark, standard 1000BASE-X or 10GBASE-X technology
> would be significantly
> more cost effective, scalable and simpler that PON
> at that point. I
> expect that there will be switching equipment
> located at the upstream
> (10 miles away) side, negating any benefit of a PON
> split at that point. 
> Please tell me what's wrong with this picture?
> P.S. I understand that this does not address the
> rural market portrayed
> by Frank Miller in this thread, but neither does
> PON.
> --
> Best Regards,
> Rich
> Get 250 color business cards for FREE!

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