Dan Warne17 July 2007, 3:32 AM
Don't assume fibre is Australia's only broadband future: both Optus and Telstra are working on upgrades to the speed of their HFC cable networks.
 Eureka: there's bandwidth to be mined in them thar old cable networks. |
Don't assume fibre is Australia's only broadband future: both Optus and Telstra are working on upgrades to the speed of their HFC cable networks.
Optus has confirmed it is evaluating DOCSIS 3 -- a cable internet standard that can run at up to 160Mbit/s downstream and 120Mbit/s upstream -- as an upgrade for its existing hybrid fibre/cable network.
"We’re still investigating our deployment on DOCSIS 3 – we have nothing to announce but we are absolutely investigating that," Michael Smith, Group Marketing Director for Optus Consumer, told journalists at the launch of the Optus "Fusion" plans, which combine line rental, ADSL2+ or cable broadband, and unlimited calls to landlines nationwide and Optus GSM/3G mobiles.
Smith was responding to questions about the need for greater upstream bandwidth on the Optus cable broadband network, which is still pegged at 256Kbit/s, and increasingly becoming a bottleneck for customers who want to upload videos to YouTube, do video chat and share files over P2P networks.
"Upload is becoming increasingly important in the mind of the customer and we’ve got to facilitate that,” agreed Warren Hardy, Managing Director of Optus Consumer.
"As the internet has evolved, it used to be very much a one-way traffic exercise. People used to pull down content over the connection. We’ve now seen huge growth in interest in multimedia devices – so customers are creating and distributing their own content, so now it’s becoming much more of a two-way street."
A Telstra source who asked to remain anonymous said the telco was not yet looking at rolling out DOCSIS 3 on the BigPond Cable network, as it is a young standard with no modems commercially available yet (the DOCSIS 3.0 standard was only finalised in August 2006.)
However, BigPond will instead upgrade to what some vendors call "pre-three DOCSIS", "channel bonded DOCSIS" or simply "DOCSIS 2.0b" (though the latter label is frowned upon since the standardisation of channel-bonded DOCSIS has been abandoned by standards bodies in favour of encouraging the finalisation of the official DOCSIS 3.0 standard, which also includes channel bonding technology.)
 Inside the BCM3255: note the multiple downstream channels, but only one upstream channel. |
Under this system each customer will use up to three individual cable internet connections bonded together for a maximum 100Mbit/s downstream. The head-end equipment and customer modem would effectively have multiple modem circuits in one box for each customer. The most popular cable modem chip that can do this is from Broadcom -- the
BCM3255 (the
PDF specifications for this chip make for interesting reading).
It's important to note, though, that channel bonded DOCSIS 2.0 only increases the downstream bandwidth -- it doesn't do anything to increase upstream, which remains limited to around 10Mbit/s (this is the case on Telstra's current cable network, but because of the number of customers sharing the upstream bandwidth, Telstra limits the per-customer upstream to 256Kbit/s.)
The channel-bonded arrangement is likely to be made possible by the fact that Foxtel recently shut down its analogue TV channels on Telstra's HFC cable, freeing up an enormous amount of bandwidth on the cable.
 Lean, green 100Mbit/s machine: the Motorola SB6100 might look like any other modem, but it is a channel-bonded powerhouse inside. |
Although American cable networks have shunned channel-bonded DOCSIS 2.0b in favour of implementing the proper DOCSIS 3.0, several networks around the world have successfully rolled it out, including
Starhub in Singapore. (Starhub markets the service as DOCSIS 3.0, but it's really pre-3.0, with the promise of a future upgrade to true 3.0). Starhub is using the
Motorola SB6100 modems, which seems like the most likely candidate for Telstra's network upgrade.
The evolution of cable
Telstra's HFC network was originally built using the proprietary Motorola CDLP standard which included an even more proprietary extension called the "heartbeat" used only by two ISPs in the world -- Telstra and Roadrunner in the US. The heartbeat meant that every customer had to run software on their PC to log in, and their PC had to send a precisely-timed network pulse every six minutes or so in order to stay connected. As a result, the original BigPond network had compatibility problems with home routers, with networking companies having to go to great expense to program special firmware for Australian models.
Telstra later introduced standards-based DOCSIS 1.1 head-end equipment and ran the two networks in parallel over the same cable, with a mix of customers using Motorola's proprietary CyberSURFR modems and other customers using DOCSIS modems.
In 2004, it turned off Motorola CDLP entirely, taking a financial hit to replace all remaining customers' CDLP modems with DOCSIS 1.1 compliant models. (Curiously, though, it retained the heartbeat system, promising to switch it off later, and is still yet to do.)
Telstra has already demonstrated its will to continue squeezing value from its cable network investment, despite writing it off as almost worthless at one point in Telstra's history (it cost $1.81 billion to construct but was written down to a book value of $210 million in 1997 -- just 11.6% of its original value.)
In 2006, BigPond removed its artificial speed limits on the DOCSIS 1.1 standard for customers willing to pay extra to subscribe to its "Cable Extreme" service, with downstream rates of up to 17Mbit/s.
Optus' cable network has had a less tumultuous history. It was built using the DOCSIS standard to begin with and Optus hasn't adjusted downstream speed since its initial launch -- it has been up to 10Mbit/s since launch. Optus did recently increase the upstream speed from 128Kbit/s to 256Kbit/s.