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Feature Article
June 2001

Chris Donner

You Can Call It CompactPCI


"You say 't-m-t', I say 't-mh-t', let's call the whole thing off." Or in this case, you say, "CompactPCI" and I say, "switched Ethernet fabric" or "StarGen fabric" or "Infiniband." But Ira Gershwin lyrics aside, hopefully we won't be calling the whole thing off anytime soon. In fact, CompactPCI, which began life as an industrial form factor back in 1994, has proven itself a serious player in the telecom market, and it is this seriousness that is redefining that form factor in a way that makes me wonder whether it will still even be called CompactPCI (cPCI) once the changes are complete.

Mass Market
Anyone familiar with the rise of cPCI over the past six years or so will know cPCI's value proposition: Take advantage of the mass market PCI form factor while improving its reliability for industrial-style applications, including telecom. Since 1994, telecommunications has arguably become the key space for cPCI deployments, with around a billion dollars worth of shipments in 2000 (depending on which figures you use).

But densities in the central office are rising to meet increasing traffic demands due to growth of the wireless market, longer connection times for dial-up Internet access, and development of enhanced services tying together voice and data applications. Correspondingly, cPCI must meet these density needs or see itself eclipsed by other form factors that are perhaps less open but that save carriers and other service provider valuable space.

The PCI Industrial Computer Manufacturers Group (PICMG) has several projects underway to address these issues of system density, and I recently had a chance to speak with Joe Pavlat, president and chairman of PICMG, about some of these initiatives and the future of cPCI in general. Afterwards, I also talked with John Peters, chairman of the PICMG 2.16 subcommittee, the working group focusing on the integration of switched Ethernet fabric into the CompactPCI backplane, creating what is known as the CompactPCI Packet Switched Backplane (CompactPCI/PSB, or CompactPSB).

Manifest Destiny
Rumors and realities of a threatened recession aside, carriers are mainly concerned with one thing: Density. More calls per shelf mean lower real estate costs and easier network management, among other things. As Joe Pavlat pointed out, a 6U cPCI board has 535 pins, only 220 of which are devoted to the existing PCI bus. This leaves 315 free pins to be used as a manufacturer sees fit. As a result of increased demand, many cPCI vendors have already begun experimenting with alternative data buses running in tandem with the H.110 bus in cPCI.

I was able to get an overview of progress being made in PICMG on three fronts to address issues of increased densities in the cPCI chassis. These initiatives include the aforementioned 2.16 workgroup, bringing an Ethernet pinout directly into the cPCI backplane; the StarGen workgroup, which utilizes a bridge chip to link the PCI bus to a switch fabric; and Intel's Infiniband architecture.

The introduction of Ethernet into the cPCI backplane is very much in keeping with the original philosophy behind the development of the cPCI form factor itself: Take existing technology and adapt it for industrial purposes. This philosophy has many advantages, including the ability to use off-the-shelf (OTS) components, to benefit from widespread implementation and debugging, and a familiarity on the part of users.

Ethernet is certainly a well-established technology, and it is also inherently hot-swappable, something that is absolutely required in high-availability telecom systems. Additionally, Ethernet is an open specification and allows for communication between systems running different operating systems, so it is possible to imagine a chassis containing multiple boards, each of which has its own memory, CPU, and OS -- all of which can still communicate with each other quickly and effectively using TCP or UDP or another protocol.

John Peters argued that these advantages are more important than the purely technical merits of a particular specification, and this is a powerful point. Ethernet is here and it's well known: It has already achieved critical mass. And its capacity is increasing as well, from 10/100 to gigabit and soon to 10 gigabit. As John put it, "We're simply putting the pieces together in a unique way."

Unique... and popular as well. Joe Pavlat informed me that in terms of the number of meetings and the number of participants, the PICMG 2.16 committee is the biggest PICMG committee so far. Many of these participants are also ready to support the spec with OTS components once it's ratified, which John Peters says should happen around the end of July of this year, perhaps a bit later. Notably, this is less than a year after the first meeting of the subcommittee, back on November 8, 2000.

Baby, I'm A Star...
So that's it then, right? When the dust settles, it's CompactPSB from now on? Well, not quite. StarGen and other members of the StarGen workgroup have implemented the StarGen point-to-point, high-speed switch fabric into the cPCI form factor in an attempt to support speeds up to OC48, and calls in the 10s-100s of thousands per chassis.

The system employs an H.110 bridge chip that integrates the H.110 backplane into StarGen's high-speed switch fabric. The bridge chip translates H.110 traffic into the StarProtocol, allowing full backwards compatibility with PCI and H.110 and allowing a flexible adoption rate on the part of carriers, but also supporting high-speed, QoS-based switching of voice and data traffic.

Systems can be linked directly, using only a bridge-only configuration, or can be linked through the StarGen switch for large configurations, using additional switches for redundancy and additional capacity. Connections can be made on a chassis-to-chassis or point-to-point basis, as well as allowing for segmentation of the bus into multiple independent buses. Joe assured me that the StarGen technology will be an open specification as well, again assuring rapid and widespread usage and deployment.

One of the real strong points of the StarGen solution is its ability to handle TDM and isochronous traffic, which is important for carriers looking for a current solution that will scale and allow them to move over to an IP-based network without obsoleting network equipment along the way. This is an important consideration when you remember that fully replacing the current PSTN with an all-IP network is estimated to be a 10-15 year process at the minimum.

Both Joe Pavlat and John Peters are also involved in the development of Intel's Infiniband architecture, but they both also expressed reservations about this process. Most prominent in their concerns was the newness of the technology and the length of time before it would be ready for deployment.

John specifically referred to the long gestation period required for a new technology, citing the example of flash memory versus rotating memory. Despite the availability of flash and its technical superiority, most of us still use rotating disk drives in our PCs and laptops. Also, John suggested that if you project where current technologies like Ethernet and StarGen are likely to be when Infiniband is ready for use, the benefits of Infiniband in a telecom environment are less clear. Again, this is similar to the flash situation, since you can now go to the local computer megastore and easily and cheaply pick up a 20GB drive using rotating memory -- something not necessarily expected when flash was initially developed.

Joe Pavlat also questioned whether Infiniband really solved any problems that won't already be solved by gigabit Ethernet or optical (10G) Ethernet. Without clear performance or time-to-market advantages, Joe suggested that Infiniband will be useful in the commercial server world but that it is somewhat less compelling in the telecom space. It will certainly be interesting to watch the advances made with Infiniband, both within and outside of the central office space, but John and Joe make strong points supporting both the StarGen fabric and the CompactPSB Ethernet alternative, and at the moment these two options appear to be the most promising.

Let's Call The Whole Thing...?
We've looked at options for significantly increasing cPCI densities over the next few years, but I'm an editor after all, and words are important to me. Much like they were to Ira Gershwin. Will the new cPCI still be called CompactPCI, or will some other name perhaps become more popular and appropriate? I asked Joe Pavlat to speculate along these lines, and he laughed a bit and then pointed out that the original working name for CompactPCI was actually "rugged PCI," but that for various reasons this name was changed during development.

Still, if traffic is eventually being carried over high-speed secondary buses, and the PCI bus becomes more of a command and control bus, then why preserve the PCI name? What's in a name, after all, right? Well, marketing for one. Familiarity also -- look at all the changes that have happened with Ethernet over the years, and yet it's still called Ethernet. If the next few years sees cPCI implementing all kinds of changes -- integration with both StarGen and Ethernet, perhaps integration with Infiniband, hybrid systems using two or three of these technologies or even proprietary solutions -- then perhaps the simplest thing is to continue using the CompactPCI name, even if it isn't 100-percent accurate any longer.

One certainty is that even the originators of the cPCI form factor have been pleasantly surprised at the speed and extent of its acceptance into the telecom market. And they are likely to agree that whatever the final name, there's no need to be calling anything off. Since we're on the subject of names and words, I'll steal a recently coined word from our bumbling president: Don't "misunderestimate" this technology. No matter how you say it, no matter how it achieves higher densities, CompactPCI is planning on being around for a long time.

Chris Donner is a contributing editor to Communications Solutions magazine and editorial director of eNews In Your Inbox.

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