Wednesday, May 10, 2017

Facebook dreams of better network connectivity platforms – Part 1


Facebook's decision to launch the Open Compute Project (OCP) six years ago was a good one. At the time, Facebook was in the process of opening its first data centre, having previously leased space in various third party colocation facilities. As it constructed this first facility in Prineville, Oregon the company realised that it was going to have to build faster, cheaper and smarter if this strategy were to succeed, and that to keep up with its phenomenal growth it would have to open massive data centres in multiple locations.

In 2016, Facebook kicked off the Telecom Infra Project (TIP) with a mission to take the principles of the Open Compute Project (OCP) model and apply them to software systems and components involved in access, backhaul and core networks. The first TIP design ideas look solid and have quickly gained industry support. Among these is Voyager, a 'white box' transponder and routing platform based on Open Packet DWDM. This open line system will include Yang software data models of each component in the system and an open northbound software interface (such as NETCONF or Thrift) to the control plane software, essentially allowing multiple applications to run on top of the open software layer. The DWDM transponder hardware includes DSP ASICs and complex optoelectronic components, and thus accounts for much of the cost of the system.

The hardware design leverages technologies implemented in Wedge 100, Facebook's top-of-rack switch, including the same Broadcom Tomahawk switching ASIC. It also uses the DSP ASIC and optics module (AC400) from Acacia Communications for the DWDM line side with their open development environment. Several carriers and data centre operators have already begun testing Voyager platforms from multiple vendors.

In November 2016, Facebook outline its next TIP plans including Open Packet DWDM for metro and long-haul optical transport networks. This idea is intended to enable a clean separation of software and hardware based on open specifications. Again, there is early support for a platform with real world possibilities, either within Facebook's global infrastructure or as an open source specification that is ultimately adopted by others.

What's cooking at Facebook's network connectivity labs

At its recent F8 Developer’s conference in San Jose, Facebook highlighted several other telecom-related R&D projects out of its network connectivity lab that seem to be more whimsical fancy than down-to-earth practicality. In the big picture, these applied research projects could be game-changers in the race to the billions of people worldwide currently without Internet access, or potential Facebook users of the future. Facebook said its goal here is to bring down the cost of connectivity by an 'order of magnitude', a pretty high bar considering the pace of improvement already seen in mobile networking technologies.

This article will focus on three projects mentioned at this year's F8 keynote, namely: Terragraph, a 60 GHz multi-node wireless system for dense urban areas that uses radios based on the WiGig standard; Aquila, a solar-powered drone for Internet delivery from the stratosphere; and Tether-tenna, a sort of helicopter drone with a base station. It is not clear if these three projects will eventually become part of the TIP of even if they will progress beyond lab trials.

Terragraph

Terragraph is Facebook's multi-node wireless system for delivering high-speed Internet connectivity to dense urban areas and capable of delivering gigabit speed to mobile handsets. The scheme, first announced at last year's F8 conference, calls for IPv6-only Terragraph nodes to be placed at 200-metre intervals. Terragraph will incorporate commercial off-the-shelf components and aim for high-volume, low-cost production. Facebook noted that up to 7 GHz of bandwidth is available in the unlicensed 60 GHz band in many countries, while U.S. regulators are considering expanding this to a total of 14 GHz. Terragraph will also leverage an SDN-like cloud compute controller and a new modular routing protocol that Facebook has optimised for fast route convergence and failure detection. The architecture also tweaks the MAC layer to solve shortcomings of TCP/IP over a wireless link. The company says the TDMA-TDD MAC layers delivers up to 6x improvement in network efficiency while being more predictable than the existing WiFi/WiGig standard.

At the 2017 F8 conference, Facebook talked about how Terragraph is being tested in downtown San Jose, California, a convenient location given that is right next door for Facebook. Weather will not be a significant factor since San Jose does not experience the rolling summer fog of nearby San Francisco, nor does it suffer torrential tropical downpours, whiteout blizzard conditions, scorching summer heat, or Beijing-style air pollution that could obscure line-of-sight.

While the trial location might be ideal, one should also consider in which cities would Terragraph be practical. First, there are plenty of WiFi hotspots throughout San Jose and smartphone penetration is pretty much universal and nearly everyone has 4G service. Heavy data users have the option on unlimited plans from the major carriers. So maybe San Jose only serves as the technical trial and the business case is more applicable to Mexico City or Manaus, Lagos, Nairobi, or other such dense urban areas.

At the F8 conference, Facebook showed an AI system being used to optimise small cell placement from a 3D map of the city centre. The 3D map included data for the heights of buildings, trees and other obstacles. The company said this AI system alone could be a game changer simply by eliminating the many hours of human engineering that would be needed to scope out good locations for small cells. However, the real world is more complicated. Just because the software identifies a particular light pole as an ideal femtocell placement does not mean that the city will approve it. There are also factors such as neighbour objections, pole ownership, electrical connections, etc., that will stop the process from being fully automated. If this Terragraph system is aimed at second or third tier cities in developing countries, there is also the issue of chaotic development all around. In the shanty towns surrounding these big conurbations, legal niceties such as property boundaries and rights-of-way can be quite murky. Terragraph could be quite useful in bringing low-cost Internet into these areas, but it probably does not need fancy AI to optimise each small cell placement.

Generally speaking, 3G and now 4G services have arrived in most cities worldwide. The presumption is that Facebook is not seeking to become its own mobile carrier in developing countries but that it would partner with existing operators to augment their networks. Meanwhile one suspects that the reason carriers have been slow to upgrade capacity is certain neighbourhoods or cities is more economic than technical. It is probably not a lack of spectrum that is holding them back, nor a lack of viable femtocell products or microwave backlinks, but simply a lack of financial capital or a weak return on investment, or red tape. One reason for this that is often cited is that over-the-top services, such as Facebook, suck all the value out of the network, leaving the mobile operator with very thin margins and little customer stickiness.


Part 2 of this article we will look at Facebook's Aquila and Tether-tenna concepts.

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