Data Centre


CableLabs, Cisco working on LTE-over-DOCSIS

Plan avoids the need for new fibre to connect a squillion small cells

By Richard Chirgwin


+COMMENT Cisco and CableLabs have put their heads together in the hope they can convince mobile network operators that with a bit of unicorn-dust, DOCSIS networks can support the LTE small-cell rollout.

Switchzilla's John Chapman blogs that “When small cells are deployed deep into the mobile network, DOCSIS will already be there. Fibre may not be” – but there's one important aspect in which a cable network can't support cell base stations: latency.

Most importantly, base stations need to ask the network for a data slot (the request-grant process). DOCSIS has a similar concept, but the two live at different paces. Cisco shared the slide below with LightReading to explain the problem.

The latency that Cisco and CableLabs worry about here isn't between the user and a server; rather, it's how incompatible timing stops the network from processing network capacity assignments efficiently.

Chapman notes the LTE request-grant time is 5 milliseconds, while in DOCSIS it's 15ms, so a process is needed that closes the gap and makes the two more compatible in the same channels.

Cisco's proposal, co-authored with CableLabs, is to create a message the LTE base station can use to schedule its grant request, so requests can be pipelined.

“Bandwidth Report”, or BWR, lets the LTE small-cell ask for bandwidth ahead of time; that way, the signalling gateway that manages both LTE and DOCSIS requests can respond to the two, within a couple of milliseconds of each other, providing fairer scheduling to the two connection types.

“The intent is to create an API-based method for LTE to 'pipeline' its upstream request messages to a DOCSIS CMTS in advance, so as to 'work ahead' of known timing,” Chapman writes.

“This will allow the CMTS to make QoS and granting decisions earlier than it normally would.”

Cisco and CableLabs presented their backhaul scheduling proposal at this week's SCTE Expo.

+Comment What's interesting about Cisco and CableLabs pitching DOCSIS to support small-cell LTE extension is that it signals something of a change in expectations for the future of cable networks.

CableLabs' roadmap envisages a world in which the copper portion of a cable network becomes obsolete. Back in 2015, the organisation crafted DPoE (DOCSIS Provisioning of EPON) standards to make EPON (Ethernet Passive Optical Networks) manageable in a cable network infrastructure.

Many operators have, since then, soft-pedalled on fibre-to-the-home - but cellular networks are paradoxically pulling fibre in a different direction.

It's become a common observation that as cellular networks push closer to the end user, their network topology gets close to “fibre past every home” (Deutsche Telekom, in July, said 5G networks will need “fibre networks in every street).

At least where hybrid fibre-coax cable networks are present and in good condition, the CableLabs/Cisco proposal tries to avoid that, instead using the copper – along the way, sidestepping the question of how a cell operator gets electricity to their micro-base-stations, since that's already available on the copper. ®

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