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Sizing Up Xenpak

Light Reading
News Analysis
Light Reading
1/30/2002
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Yet another 10-gigabit Ethernet transceiver complying with the Xenpak multisource agreement was announced today by OpNext Inc., the components spinoff of Hitachi Ltd. (NYSE: HIT; Paris: PHA).

In the press release, Ed Cornejo, Opnext’s director of applications marketing, is quoted as saying: “Xenpak has broad industry support and is generating a lot of interest from our telecom, datacom and storage customers.” (See OpNext Intros 10-Gig Modules.)

True, or false?

There’s little doubt that component vendors are giving Xenpak their backing. A total of 24 of them have now signed the agreement, which ensures that system vendors will get a wide choice of module suppliers (see Agilent, Agere Drive 10-Gig Ethernet ). At least five of the module makers have already announced products. For the record, they’re Opnext, Agere Systems (NYSE: AGR), Agilent Technologies Inc. (NYSE: A), Blaze Network Products Inc., and Optillion AB.

But are system vendors actually going to buy Xenpak modules? The jury’s still out on that question.

For starters, 10-gigabit Ethernet is in its early days. But, assuming that it does take off, Xenpak could come up against issues with the size and "feel" of the packaging, according to industry watchers.

Drew Lanza, general partner at Morgenthaler doesn't mince his words. "Xenpak isn't going to work," he says. "It's too big."

Systems vendors need to drive costs down, and they need higher density optics to enable them to do this. But Xenpak, Lanza contends, doesn't go far enough in this respect. At 4.36 inches long by 1.4 inches wide and 0.46 inches high, the Xenpak package is actually smaller than a standard 300-pin OC192 Sonet transceiver, but it's still considerably larger than the typical packages that datacom companies use for Ethernet.

And the fact that it's something "in between" is another irritation. Systems vendors being the conservatives they are, Lanza figures that neither datacom guys nor Sonet guys will be comfortable with the new packaging.

But Agere, which put the original proposal together with Agilent, says that it was responding to customers' needs when it drew up the Xenpak design. "The first thing we did was shop around our data customers," says Julie Eng, a director of product development at Agere. "At the time they viewed it as fine. But since then some of them have come back and said they need something smaller, and we're looking into that."

Agere says that one of the key things vendors asked for was to make the module hot pluggable, so system cards could be stored without optics and populated at the last moment before shipping to a customer. But Agere went about this in a strange way, in Lanza's view, with a design that requires the systems vendor to cut a hole in the printed circuit board and then slide the Xenpak module in.

Agere says there is method in its madness. "The primary reason we did this was so you can flow air over the top and bottom of the module, so you would get a little break on the thermal problem," Eng explains.

But Lanza faults this logic. "Density should be dictated by form factor, not by heat or connectors," he says. "What we're seeing is that you don't need that much space to dissipate heat. The systems guys don't like it."

So can Xenpak be made smaller? Agere's Eng says the company is working on it. But, at the end of the day, it may come down to the fact that there is a lot of functionality and electronics inside the Xenpak package. And if people want to start using enterprise-style optics, such as the small form-factor pluggable (SFP), for 10-gigabit Ethernet, then some of the functionality will have to come out of the package and go back onto the board.

"Why is a Cadillac bigger than a mini?" says Lanza. "It's got more stuff crammed inside."

— Pauline Rigby, Senior Editor, Light Reading
http://www.lightreading.com

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let-there-be-light
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let-there-be-light,
User Rank: Light Beer
12/4/2012 | 11:00:30 PM
re: Sizing Up Xenpak
"It's too big"

"Why is a Cadillac bigger than a mini?"

Where in Heaven's Name do you get these "experts" from?
switchrus
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switchrus,
User Rank: Light Beer
12/4/2012 | 11:00:29 PM
re: Sizing Up Xenpak
Two words....


Cup holders !
photonsu
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photonsu,
User Rank: Light Beer
12/4/2012 | 11:00:29 PM
re: Sizing Up Xenpak
Raychem!
ajo2
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ajo2,
User Rank: Light Beer
12/4/2012 | 11:00:26 PM
re: Sizing Up Xenpak
I have to agree with others, Pauline. Where do you all come up with these people?

Quoting a VC, which likely has a vested interest in a particular outcome, as the only "expert" source for your article seems pretty weak.

And then when you look at what he says, you know it IS weak.

For example:
>But Lanza faults this logic. "Density should be
>dictated by form factor, not by heat or
>connectors," he says. "What we're seeing is that
>you don't need that much space to dissipate
>heat. The systems guys don't like it."

Quite simply, if solutions he is looking at don't have a heat problem, the port density of those solutions is too low. If he really knew what he was talking about, he'd know that heat, port density, and connectors all go hand in hand.

Did you find anyone ELSE besides this guy that didn't like Xenpak?
Drew Lanza
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Drew Lanza,
User Rank: Light Beer
12/4/2012 | 11:00:24 PM
re: Sizing Up Xenpak
Yeesh! You guys are strict!

I was only trying to make three pretty obvious points based on conversations I've had with folks in the industry:

1. Xenpak's about the same size as what's out there today. Xenpak's great at putting a standardized shell around what's available today. Hooray! I just think that for a lot of the shorter range applications, using newer 10Gbps transceivers, it's complete overkill. There's been this ongoing debate between Xenpak and XGP or whatever comes next. Maybe Xenpak will be great for medium and long reach metro applications. I hope so. But it's just too big and clunky for short haul (and maybe medium haul) applications.

2. Cutting large notches in a very large PCB is something my mechanical friends tell me is not something they're looking forward to doing. Maybe it really is necessary as a way to shed the heat, but that doesn't make it pretty, cheap, or easy to do.

3. All I meant by the 'form factor' remark was that we shouldn't penalize lower power, shorter reach transceivers by sticking them in big, bulky packages designed for stuff that drives a signal out 50 miles. You said it better than I did, Ajo2, when you said "heat, port density, and connectors all go hand in hand". The new shorter reach transceivers generate less heat than the old longer reach ones (60-80% less than the spec Xenpak was designed for)and that can be traded off for greater density, which is what systems companies say they live or die by. I really do think that Xenpak is a wasteful, inefficient form factor for well over half of the metro applications out there.

As for where Pauline came up with me, cut me some slack. I've been working in the photonics industry for over 15 years. I remember going to OFC shows when everybody knew everybody else who was there.

Drew Lanza
ajo2
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ajo2,
User Rank: Light Beer
12/4/2012 | 11:00:19 PM
re: Sizing Up Xenpak
> Yeesh! You guys are strict!

It's the nature of many engineers, I fear.

> 1. Xenpak's about the same size as what's out
> there today. Xenpak's great at putting a
> standardized shell around what's available
> today. Hooray! I just think that for a lot of
> the shorter range applications, using newer
> 10Gbps transceivers, it's complete overkill.

Now knowing the correct context, your statements make a bit more sense. Unfortunately Pauline left out any mention of reach.

> 2. Cutting large notches in a very large PCB is
> something my mechanical friends tell me is not
> something they're looking forward to doing.
> Maybe it really is necessary as a way to shed
> the heat, but that doesn't make it pretty,
> cheap, or easy to do.

I agree with you that cutting the PCB forces you to stay with a particular body size forever, and that may not be the most desirable outcome when power drops by a noticable amount annually. But I must take issue with any notion that it is hard or expensive to make a cutout in a PCB.

> The new shorter reach transceivers generate
> less heat than the old longer reach ones (60-
> 80% less than the spec Xenpak was designed for)
> and that can be traded off for greater density,
> which is what companies say they live or die
> by. I really do think that Xenpak is a
> wasteful, inefficient form factor for well over
> half of the metro applications out there.
>
> As for where Pauline came up with me, cut me
> some slack. I've been working in the photonics
> industry for over 15 years. I remember going to
> OFC shows when everybody knew everybody else
> who was there.

It's a real shame Pauline left out the main points of your discussion with her.
packaging-man
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packaging-man,
User Rank: Light Beer
12/4/2012 | 11:00:17 PM
re: Sizing Up Xenpak
While I am sure that I am in the minority, I want to thank LR for any article relative to device packaging issues.

I do think, however, that those interested should look at this issue from an alternate perspective.

First, the Xenpak solution was developed in response to a specific issue raised from those using SFF & SFP transceivers, namely that they did not provide as 'clean' of a packaging solution for the business side of the equipment. Packaging engineers were forced to develop custom solutions for the business side of these modules, especially since very high switching was located adjacent to these modules. The 'standard' proposed MSA packaging for the SFF & SFP was barely adequate to suppress the EMI radiating from the openings created. By enclosing more of the high speed switching within the component similar to the bulky OC-192 transponders, EMI radiation is effectively reduced.

While Zenpak does address many of the packaing engineers complaints in this realm, it creates even more alternate issues with it's solution. First, the new package is no more EMI 'tight' that the old SFF (in regards to the interface between the package and the chassis cut-out), and is arguably much worse! Second, the PCB cut-outs do create some headaches on the manufacturing side.

All of this aside, however, the Xenpak provides a solution to what is truly more important to equipment developers. That is, to be able to smooth-out the cost/price curve for selling mulit-port 10Gig line cards. To be able to sell the line card shell seperately from the optical transponders allows for customers to incrementally take on more cost burden as they require it, outlaying less $$$ initially. As it was suggested in earlier posts, if more components were removed from the Xenpak solution to make it smaller, they would just be moved to the PCB, thus increasing the initial cost of the board and reducing the incremental cost of the optics.

As a final note, I think it would also be important to remember that, while many component and systems vendors continue to tout higher density chassis with more ports (and inherently more power), the implementation issues at the central offices and other POPs related to the explosion in system power density is tremendous. Most COs allow only enough power generation/backup and HVAC cooling to allow 60-120 amps per 7' rack. At the same time, many equipment vendors have power densities equivalent to 240 amps + in a 7' rack. This typically results in either not populating racks fully, or in the case of single or multiple 'monster' rack solutions, adjacent racks are removed to allow for an equivalent power density that can be managed.

The end result, while it is true that higher density 10 Gig E modules may be able to be cooled on a chassis level, looking at the problem in the eyes of the person who is making the decision shows that it is much less of an issue, and that it is much more important for them to achieve less power draw per port or per GHz bandwith than to achieve more ports per rack U's.

Mr. Lanza's points are well put, however, I would disagree with his assertion that system companies live and die by port density (this is of course a generality as I am sure that there are many applications were power draw and cooling requirments are not a problem). One great example of the is (or was...) Avici Systems. No one ever bought that monsterous router because it offered superior port density. They bought it because it worked, the software was what the customer wanted, and they delivered what they promised. The same hollds true today. The only reason systems companies 'think' they live & die by these issues is that they are all going around touting their port densities, next time ask someone who should care about it if they really do.



Neal
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Neal,
User Rank: Light Beer
12/4/2012 | 11:00:17 PM
re: Sizing Up Xenpak
XENPAK is being widely accepted and will be rolled out in 2002. The form factor will allow up to 8x 10 Gig Ethernet ports per Switch/Router blade. I think this is reasonable density.
CRC_Check
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CRC_Check,
User Rank: Light Beer
12/4/2012 | 11:00:15 PM
re: Sizing Up Xenpak
Thinking about the XENPAK implications...

Too Big - or Too Small? We have see this played out before. First implimentations are big, later generations trend to small. The extra room afforded in a roomy package allows vendors to differentiate. Long reach, XLR, ITU lambda, even MEM/VCSEL Agile DWDM ready may become possible some day in the envelope if the RF and eyesafe topics can be managed.

Front Pluggable? Vendors will have a hard time manageing that. What prevents a customer buying a cheapo 1310 nm SR blade and popping in a 1550 nm XLR ITU grid version later on the QT? Where does that leave the vendor's FDA laser safety, ALS, EMI and heat story? Containing RF emissions on a terabit system with up to 8 XENPAKs per blade may prove a real feat with the double whammy of X band front access gasketting plus containing the laser's RF launch out the apreture.

Interfacing rates? Nextgen CMOS PHYs and MACs will likely have 10G CMOS I/Os that can interface directly to serial transceivers with integral CDRs.

Cutting board slots? Biggest deal is the manufacturing process for the socket. What kind of IR reflow and test implications arise. Routing out the slot is nothing to be afraid of. But cooling is a big deal. At 10G you have a lot of impact if you lose your link. Operating the laser junction at 3-5C lower temperature during its life can dramatically extend MTBF so its worth it. Especially if it helps you avoid the need for exotic 80 or 85C case limits.

In summary I say look beyond the package into the materials and system implications. There will be 10G materials for trunking and LANs and dense, dependable 10G materials for the big cores. One product won't likely fit all needs.

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