Review: HP and Optical Backplanes

There were a lot of cool things at InterOp, but not much that was new from the big vendors. I was hoping for some big announcements or new toys but … nothing. For example, Cisco didn’t announce anything, probably waiting announce at Cisco Live in July where they can control the press and message much more tightly. However, HP announced the A10500 switch (action pictures ) which is a new campus switch and Gnodal arrived with new products (more on this later).

However in the centre of the HP stand there was something very cool – a prototype E8212 ProCurve switch with a fully optical backplane. Hp procurve optical backplane 1

The line cards project out of the unit because the prototype optoelectronics boards haven’t yet been commoditised into chips. That’s normal for these prototype projects. The next image shows a slightly different angle and I’ve marked up the pieces.

Prototype Procurve E8212 showing functions (Click for Larger)

But what does the backplane look like – I took a photo of that too. See that black vertical line there ?

Photo of the back of the chassis with the Optical Backplane Highlighted

And this is a photo showing the photo of the actual optical backplane assembly (I like the wooden ruler they used to show how big it is).

Optical Backplane Assembly

This element is a very low cost, Optical Backplane based on a passive optical multi-bus system architecture

  • 12 channel, 1:6 broadcast for 120Gbps per tap
  • Very low cost injection molding fabrication
  • Low cost MEMs non-polarizing beam splitters
  • Commercially available VCSEL based OE engines
  • Passive backplane that scales to terabits per tap using faster optoelectronics and CWDM

Backplanes – Active, Passive, Optical

The role of backplanes in chassis based switches is vital to their success. Most chassis switches used in networking 1 use a passive backplane. This is usually some type of complex and hard to manufacture PCB board with electrical traces on it, and a bunch of mechanical connectors. Passive backplanes are usually cheaper, and much more reliable than active backplanes. Modules simply connect to the backplane and all electronics is contained on the line cards. You can think of a passive backplane as a bunch of high performance cables.

It’s my understanding that the Catalyst 4500 is an passive backplane (although, the latest version 4500-R possibly is not).

Active backplanes are used when highest performance is required at a point in time. The electrical signal transmitted over the backplane degrades in performance at higher clock speeds. By adding electronics and chips to the backplane, better performance can be achieved be managing the signal and clocking more effectively. However, this is at the cost of lower reliability and atrocious MTTR for failure. That is, the backplane is normally fixed in the chassis casing, and a failure of the backplane components means replacing the entire chassis. Because switch chassis are almost impossible to replace, and take tens to hundreds of hours of downtime, active backplanes are a cause of concern. They also cost more to manufacture.

Examples of active backplanes are the C6500 and Nexus 7000. I’m not sure about other vendors as there is very little documentation, customers don’t ask these days so vendors aren’t talking about it.

Optical Backplanes

This images show the traces that have been laid down on the plastic substrate for the prototype backplane – I find this fascinating.

Waveguide details



This is the actual optical backplane piece of plastic. (Click for a larger image)

The advantage of optical backplanes is at several, rather separate levels:

Optical backplanes
Feature Description
High Performance Bandwidth can scale according to optical line driver performance and less limitations due to poor signal integrity because of electrical propagation
Scalability, investment protection Optical backplane is passive, so performance of the chassis can be upgraded by adding CWDM capable modules
Low Power consumption Energy efficiency and low thermal generation
High Volume manufacturing Manufacturing a suitable plastic is far less complex than precision PCB layout
Backplane performance independence Data transfer performance can scale according to CWDM drivers on the processor and switch line cards. Thus replacing line cards can continue to upgrade the switch performance for a longer time.

Multi-Bus not Crossbar

In this case, HP has implemented a multi-bus system architecture without a central crossbar fabric. This means that each line card performs the forwarding decision for the outbound destination. Although crossbar fabrics have been popular for a number of years, designs can return to distributed forwarding because there would be suffcient bandwidth in the backplane.

This means that

  • the up-front cost of the chassis is reduced because you don’t need the expensive and power hungry crossbar silicon fabric for the first line card. Chassis cost scales linearly as modules are added.
  • performance scales with each additional line card since they add “bandwidth” by having local forwarding across the backplane. Better planning and more predictable outcomes.
  • that there are less critical dependencies in the switch chassis for mechanical and electrical failure.
  • the management module acts to manage, not supervise and becomes lower cost.
  • optical backplanes are cheap to produce, and cheaper to maintain. Lower maintenance costs.

The EtherealMind View

There are several points of interest here.

  • these products are three to five years away according to Charles Clarke, Research Director of HP. It’s just manufacturing and marketing from here
  • these products are expected to be cheaper than current switches, a lot cheaper for more performance.
  • They will have significant levels of future proofing by allowing for up to 2Tbps per channel (compared to 120Gbps today)
  • they will be used in smaller devices at first, mainly access or aggregation switches.

It’s the first time I’ve seen HP start talking about future products without an NDA. Normally, HP says nothing about futures, and when they do, it’s involves lawyers and stringent controls. Here’s hoping to more openness that lets me plan my strategy more effectively. Does this presage a now HP who is willing to engage with customers ?

HP has demonstrated some serious research work in networking. I’m impressed. It’s a shame they are using the ProCurve software/hardware platform which has a poor reputation in industry around software reliability, so here’s hoping they decide to use this technology in the A-series switch running ComWare.


HP Networking have paid for my travel and accommodation for Interop so that I was able to attend their briefings, meet executives and have good quality discussions. I’d like to think that my opinions and views are my own. It’s great to get access to information and the chance to learn new things. I am not remunerated in any other way. I didn’t even take the tchotckes.

  1. backplanes are used in many electronic applications, including servers, aeropsace, control systems as more. There isn’t anything that’s unique about networking electronics except the higher speeds / performance.
  • shivlu jain

    hope to get something new in cisco live. Is new HP switches are supporting open flow?

    Shivlu Jain

    • IJdo Dijkstra


      I’m not sure when HP will start using it, but I’ve seen a few HP documents list it as something HP either supports or helps develop.


    • Nathan Farrington

      HP has implemented OpenFlow for a particular model of their ProCurve switches. They have made their OpenFlow implementation available to particular researchers, but I do not believe they currently offer OpenFlow as a supported product.

  • stretch

    My guess is some companies may need to invest heavily in training people not to slam in line cards as hard as they can anymore before these switches become a viable solution.

    Very cool though!

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  • Paul

    @ethereallmind: Just curious: in what way does ProCurve have “a poor reputation in industry around software reliability”? Those are kind of weasel words – how about some actual examples?

    • Ferro Greg

      Check out Jeremy Gaddis sites at – that’s about the normal experience for most people. And mine.

  • Pablo Carlier

    Sorry Greg, some correction needed:

    Catalyst 6500 with switching fabric sports a passive backplane –

    • Etherealmind

      Cisco claims that the C6500 backplane is passive, however, if you disassemble it you will find several chips and components that provide (I understand) clocking functions. Your backplane can fail electronically in addition to mechanically. This is quite rare, but the backplane is not completely passive – compared to the mid-plane in a HP C7000 blade server chassis which has no electronic components at all.

  • Sam Crooks

    article on Light Reading about the optical backplane:


  • Jiezheng5

    Does anyone know what the plastic grating does here? Is it for selective transimission, selective reflection, vertical light extraction or focusing light?

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