US fibre rollouts are driving Cablelabs standards in new directions
Broadcom explains DPoE to El Reg
Google's fibre initiatives haven't just prodded the US cable operators to respond in kind, gigabit for gigabit – it's also driving standards.
A good example was the August announcement by Broadcom of a chipset that helps cable companies (mostly in the USA for now) deploy EPON alongside their DOCSIS networks, so The Register's networking desk spoke with the company's Jim McKeon (director of product marketing) and Robin Grindley (senior product line manager) about the market shift driving the standards.
Grindley says the need from the cable companies is clear, because they're already deploying fibre services to real customers.
The extension of the fibre that now switches to coax copper all the way to the customer is happening where the cable companies “have fibre that is deep enough in the network, close to the customer premises”.
Google's (and others') brand-new fibre networks are driving the cable companies to launch services like Comcast's 2 Gbps symmetric offering, he said.
“The 10 G EPON is symmetric,”he noted, “so you can put multiple customers on a single fibre drop.”
The “new normal”, he said, is a 1 Gbps symmetric service, so EPON can support multiple customers on a single drop.
But there's a problem: the fibre service is being deployed in an environment that's not set up to manage it.
The cable community, McKeon said, wants to “integrate PON networks into their established frameworks”.
The cable operators don't want to replace their hybrid fibre-coax networks – at least not yet – “but in some cases, for example greenfields builds, they have an interested in deploying fibre,” he said.
Passive optical networks have “nice characteristics for long-term future-proofing of the network,” he said, and “a longer investment horizon”, but there's a problem in mixing the environments.
“The management framework of the PON network don't have a one-to-one mapping to DOCSIS,” McKeon said.
That's where the Cablelabs EPON work fits, he said: it lets operators use their Cablelabs provisioning tools on the fibre side as well.
Broadcom's 2010 acquisition of Teknovus was the foundation of its play into this field, McKeon said. Teknovus worked out the key challenges in DOCSIS provisioning over EPON, forming the basis of the chipset released in August.
“What they did was to work out the details of managing the virtual cable modem in the EPON network,” McKeon said. “That allows you to put the EPON into the DOCSIS network with minimum of disruption.”
And that, he said, means that cable operators can start to roll out the latest 10 Gbps of EPON.
DOCSIS is Layer 3, PON is Layer 2. The twain must meet
The problem is simple: the DOCSIS architecture assumes the operator is delivering a Layer 3 service, while passive optical networks deliver Layer 2 services.
Hence DPoE – DOCSIS Provisioning of EPON – the spec to unify them at the management layer.
Grindley, who joined Broadcom from the Teknovus acquisition, says the implementation is simple enough: the DPoE stack runs on Broadcom optical network units (ONUs), talking to middleware in the operator's central office.
“Historically, the management interfaces for EPON were defined by telcos”, Grindley said. China Telecom was a leader here, he added, but different regions defined their own management stacks.
“So there wasn't something that mapped to what the DOCSIS world wanted.”
“The telco world manages access as a Layer 2 service, DOCSIS manages … an IP service.”
The EPON definitions didn't include how to manage or configure IP services, because IP is left to retailers rather than infrastructure (a division that will be familiar to Australians with an interest in the National Broadband Network).
Without something like DPoE, Grindley said, cable companies would need either a new back end, or substantial changes to their back end.
If anyone was running a “hard cutover” from a cable network to an optical network, that wouldn't be a problem, but at this stage the cable companies are “keeping the bulk of the copper”, so they need to manage both copper and fibre.
+Comment: Australian readers won't be blind to the implications this holds for the National Broadband Network, which is embarking on a DOCSIS-fibre integration, but from the other way around.
The NBN's management models, developed for the fibre network (at Layer 2) are going to have to integrate two DOCSIS networks – those built by Telstra and Optus.
Broadcom didn't comment directly on NBN policy, but Grindley noted that working in the other direction, creating management standards presenting a DOCSIS network to a Layer 2 management environment, is not a “popular” development direction. ®
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