Subject: Re: [pa-comnet] AT&T WiMAX paper

From: Mark Heyer <[email-masked]>
Date: Fri, 20 Apr 2007 15:19:52 -0700

I couldn't resist jumping into this discussion. Some of you may  
recall that in 2003 I was involved as CTO/partner in a startup in  
Oregon to deliver 10Mbps residential fixed wireless using Soma  
Networks gear and licensed spectrum. The system is still running  
today, although the lack of ability to deliver CPEs stunted the  
growth, along with reticence of investors after the tech meltdown.  I  
sorted through the hype issues way back then by actually building a  
system.

Jeff's comments below are right on the money. Let me add a few more  
based on my experience:

1) Wimax is nothing more or less than a chip/software standard that  
Intel has been pushing to displace the multitudes of proprietary  
standards promoted by the small companies like Soma. It does nothing  
more  than any of those are theoretically capable of doing, given a  
big daddy like Intel.

2) There is ongoing confusion about the capabilities of Wimax. For  
example, "100 Mbps over 10 miles." Is that point to point,  
omnidirectional, licensed spectrum or wi-fi spectrum?
- Even a little Linksys wireless router can reach 10 miles with an  
appropriate directional antenna and a low noise environment
- In the commercial world there are dozens if not hundreds of systems  
for high bandwidth wireless point to point. Take a tour of the roof  
of the Sheridan building and you will see wireless point to point  
broadband delivery to PA business buildings, with wireless backhaul  
to Fremont. Wimax is just a newcomer to an already mature market.
- When one talks about licensed spectrum, one is talking about  
transmitters with 40 W of output, as opposed to the hundreds of  
milliwatts for wi-fi. Whether it is Soma, cell phones or Wimax, all  
of the RF and antenna technology comes right out of the same parts  
catalogs. Wimax is just another encoding standard, which is not  
inherently better or worse than other proprietary systems.

3) Licensed spectrum is bought and sold in a marketplace, like real  
estate. In metro markets like ours, there literally is no spectrum  
available to buy at any price - it is all tied up by the big guys.  
Even when the FCC recently opened up some additional spectrum, it was  
gobbled up in minutes by the ATTs and Quests of the world to feed  
their growing cell phone babies.  The reason we won't see on-demand  
mobil video any time soon is that the operators don't have the  
bandwidth to deliver it in metro markets, where the most customers are.

Where spectrum IS available and cheap is in rural markets, like  
Klamath Falls, where there is more spectrum than people to use it,  
which is why I went there to do my trial system. That's why Craig  
McCaw is also starting in the sticks, just like he did before. He  
could very well succeed, but not see licensed spectrum Wimax migrate  
to metro markets ever, or until the cellular operators convert to IP  
telephony, but lots of dinosaurs have to die before that happens.

4) Using a cell tower and licensed spectrum creates a highly  
asymmetrical system - the 40W downlink has no problem delivering  
better than 1mbps at 10 miles (for us, throttled from 10mbps  
possible). The real problem is getting the customer's little 500MW  
uplink transmitter back to the base station ten miles away - through  
their walls, trees, etc. Furthermore, although the various upstream  
talkers ignored one another, each one creates noise for all the  
others. As more customers are added, the noise floor rises and  
upstream performance dies, until people can no longer get reliable  
upstream. This is an issue for every wireless technology including  
Wimax, so treat their claims about speed and range with EXTREME  
SKEPTICISM until you know how it works in a real world installation  
with maximum customer load.

We found that the real limit was about 1,000 customers per antenna,  
regardless of the range. In a densely populated area, like Bend, we  
could only hope to serve about 20-30% or so of the potential  
customers before the bandwidth ran out. Cell phone operators solve  
this problem with much smaller cells, putting dozens of half-million  
dollar base stations within that 10 mile theoretical radius - not a  
cost model that is likely to be supported by cheap Internet access,  
Wimax or anything else.

I hope this adds a little meat to the discussion of ATT's hype.

Mark Heyer

On Apr 20, 2007, at 1:49 PM, Jeff Hoel wrote:

> Re Arthur Keller's message to PA-ComNet of 4-20-07, 9:06:
>
>> See attached from
>>
> <http://www.business.att.com/nx_resource.jsp? 
> repoid=Solution&repoitem=eb_enhancing_productivity&rtype=Article&rvalu 
> e=update_lessons_learned_from_wimax_trials&segment=ent_biz&pl_code=MAT 
> T10FC18942P531823B536038S0>
>
> Please keep in mind that AT&T has an interest in discouraging  
> competition,
> especially from FTTH.
>
> Further comments below.
>
>
> Jeff
>
> ---------------------------------------------------------------------- 
> --
>
>> Update: Latest Lessons Learned from WiMAX Trials
>>
>> Although the technology is still evolving, WiMAX is likely to play
>> an increasingly important role in business networking.
>
> I have serious doubts about that.
>
> As long as WiMAX security is "evolving," why would a business tolerate
> the lack of security?
>
> Perhaps AT&T is speaking only of businesses that don't have any way of
> getting wired, point-to-point connections.
>
> ...
>
>> WiMAX could add value to businesses by providing a reliable way to
>> offer alternative access methods.
>
> Wireless connections are typically less reliable than wired  
> connections.
>
> ...
>
>> Given the importance of WiMAX as a networking technology....
>
> I don't think it is a given that WiMAX is an important networking
> technology.
>
> ...
>
>> 2. Latency as a Function of Distance and Terrain
>>
>> WiMAX compares favorably to other access methods when evaluating
>> latency.  Typically when used within a 4-mile diameter of the tower,
>> latency (averaging 45 ms or less) is better than cellular (averaging
>> 400 ms), and is on a par with private lines (averaging 10-20 ms) and
>> DSL/Cable (averaging 35-45 ms).
>
> So although WiMAX claims it can work up to 30 miles (radius), we're  
> only
> talking about 2 miles (radius) (i.e., 4-mile diameter).
>
> I'm not sure what kind of latency is being described.  The latency due
> to a wireless signal traveling 2 miles would be about 11 microseconds.
> (Right?)  (So most of the cited latencies have nothing to with  
> distance,
> per se, right?)
>
> For technologies (like WiMAX, Wi-Fi, cellular, and "cable", i.e., HFC)
> that share the medium among lots of users , waiting for your turn  
> is an
> important contributor to latency.  (Since DSL is point-to-point, you'd
> think its latency would be less than HFC, but the article doesn't  
> report
> DSL and HFC latencies separately.)
>
> In its bid of Palo Alto's FTTH01 RFP,
> <http://www.cityofpaloalto.org/cityagenda/publish/cmrs/documents/ 
> RFP-FTTH01.pdf>
> which proposed a point-to-point citywide FTTH system, DynamicCity said
> it expected to see no more than 1 ms of latency due to switches in the
> network and no more than another 1 ms of latency due to propagation
> delay in fiber.  (I think light in fiber could go more than 100 miles
> in 1 ms, so that part of the specification seems pretty conservative.)
>
> ...
>
>> WiMAX can also support latency-sensitive applications like VoIP,
>> video, conferencing/collaboration and database access --
>
> TV-style "video" is not particularly latency-sensitive, although it  
> can
> jitter-sensitive if buffers aren't large enough.
>
> VoIP is both latency-sensitive and jitter-sensitive, but the bandwidth
> requirement is relatively modest.
>
> If "conferencing/collaboration" means video conferencing, then it's
> both latency-sensitive and jitter-sensitive, and bandwidth is
> substantial.
>
> I have no idea what's meant by "database access."  In particular, I
> have no idea why there should be a real-time requirement.
>
> If AT&T wants us to take seriously the idea of using WiMAX for video
> anything, it should say how much bandwidth each user needs and how
> many users it wants to support simultaneously on each WiMAX tower.
>
> I wanted to cite something definitive about how fast WiMAX is at a
> 2-mile radius, but I didn't find it.  This document says:
> <http://en.wikipedia.org/wiki/WiMAX>
>
>      In practice this means that in line-of-sight environments you
>      could deliver symmetrical speeds of 10Mbps at 10km but in urban
>      environments it is more likely that 30% of installations may be
>      non-line-of-sight and therefore users may only receive 10Mbps
>      over 2km and if the recipient is on the move the bps rates drop
>      significantly.
>
> I take it that the 10 Mb/s mentioned is what all users have to share.
>
> ...
>
>> ... as long as packet loss is appropriately managed.
>
> What can this possibly mean??  With applications like VoIP and video,
> every time you drop a packet, the user notices.  Is AT&T saying that
> you should manage the network so that for real-time applications you
> drop virtually NO packets?
>
> ...
>
>> 5. WiMAX Security Standards are Still Evolving
>
> Wake me when it's over.
>
> ...
>
>> 10. Hype or Reality
>
> Hype.
>
> ...
>
>> WiMAX ... offers comparable bandwidth to broadband....
>
> I suppose that by "broadband" AT&T is using the FCC's definition of
> at least 200 kb/s in at least one direction.  That's really slow.
>
> ...
>
>> WiMAX offers a solution for temporary locations that need to be  
>> brought
>> on-line quickly....
>
> In the US, WiMAX uses licensed spectrum.  You can't get licensed  
> quickly.
>
> ---------------------------------------------------------------------- 
> ---
>
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