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Immenstar and the Quad OLT

ImmenstarI first came across Immenstar, a provider of GE-PON silicon, while researching The Future of FTTH in China. These are the most notable things about Immenstar.

  • R&D in China. Helps win Chinese business
  • Funding from UT Starcom, and likely their lead customer
  • They have a quad OLT chip

They were recently profiled in Lightreading and in the comments a short debate ensued on the merits of a quad OLT.

I think the advantages of having a Quad OLT arise from the ability to more efficiently do statistical multiplexing onto the uplink side. If you have four discrete OLT chips the indivisual GE uplinks from each device need to be fed into an L2 aggregation chip that will make drop decisions. Having four OLT’s on one chip let you merge the control plane and make better decisions on DBA and discards as you forward. Theoretically, you would get better QoS and utilization.

BUT – as of right now, fairness on the upload side isn’t that important. Few applications exist that push the envelope in the upload direction – Enterprise applications and circuit emulation are two that would, but neither have been deployed over PON’s in any volume.

In short, nothing extraordinary except for Chinese heritage and a Chinese partner invested in their success. The complementary products that PMC-Sierra (PMCS) and Conexant (CNXT) bring to the table short circuit the advantages of a quad OLT, unless applications that make upload bandwidth the bottleneck gain popularity.

Companies Mentioned:
Immenstar – Private
Conexant Systems – (CNXT)
PMC Sierra Inc – (PMCS)


Comments are disallowed for this post.

  1. Ultimately, uplinks from all OLTs in a shelf go to one aggregation device (either a switch in the same chassis or an external device). Statistical multiplexing across 4 OLTs may have some advantages, but it falls short to stat-muxing across all OLTs in a shelf. The latter is achieved by having a DBA with a fast response time to changes in instantaneous uplink bandwidth. This will work, whether the OLT are integrated or standalone.

    I think the main driver for quad OLT is cost reduction and increase in port density. This, however, should be approached as an optimization problem. Increasing OLT integration increases number of subscribers that would be affected by a blade mulfunction/replacement/reset.

    Posted by Glen K. | June 2, 2006, 5:48 PM
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