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What's the best way to build networks?

Posted: 01 Sep 2014     Print Version  Bookmark and Share

Keywords:Hot Interconnects  cloud computing  data centres 

"A typical suburban Wi-Fi router sees six signals, an urban apartment often sees 24, and my apartment in Paris sees 38," he said. "Who needs Gbit Wi-Fi if it knocks out your neighbour and they knock you out as well?"

He slammed the 802.11ac standard for squandering spectrum. It takes 19 available 5GHz channels and bonds them into groups of eight "so you only get three channels again," like 2.4GHz Wi-Fi. What's worse, it only supports two users so "if one user hits another, it's wasted energy of eight channels."

Cioffi advocated modifying the firmware of an 11ac link to support more virtual SSIDs, thus delivering a greater number of stable connections (see below).

 Break up 802.11ac networks

Cioffi suggests a better way to break up 802.11ac networks.

Here comes silicon photonics

Several talks highlighted silicon photonics, expected to debut soon, supporting 100Gbit/s aggregation switches in big data centres with 4x25G links. Several camps are rolling out competing products based on technologies from Intel, Mellanox, and others.

"The CLR4 [approach] seems to have best attributes of time-to-market, cost, and a lot of vendors signed up for it, but with the QSFP28 [connectors (see below)] we will use, we can plug in any of them," said Andy Bechtolsheim of Arista.

 Arista will ride the QSFP28 link to 100G switching interfaces

Arista will ride the QSFP28 link to 100G switching interfaces.

Data centres will use copper inside the rack, active optical cables between racks, and silicon photonics links for the kind of third-tier links Microsoft described in a talk about its data centres (see below), he said.

 Links to the second-tier spine require 100G interfaces

Links to the second-tier spine (centre of graph) require 100G interfaces, said Bechtolsheim. (Source: Microsoft/Arista)

To date, 100G optics have been too expensive for the tight budgets of big data centres. Bechtolsheim blamed IEEE standards efforts for failing to see the kind of distance, cost, and bandwidth needs of the big data centres.

Meanwhile, other efforts created too many competing standards for optical connectors. "100G got more form factors than ever proposed for 10G, which makes no sense because they are only shipping a thousand a quarter."

More players, problems

 Mellanox uses wavelength-division multiplexing

Mellanox uses wavelength-division multiplexing in its planned 25G silicon photonics products.

Mellanox will join the silicon photonics fray soon with a 4x25G 100G product with 100m reach and 3W power consumption, according to a talk here (see above). It will be the company's second product from the Kotura team it acquired in May 2013, following active optic cables offering a similar bandwidth but shorter reach.


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