By Rich Nesin, General Manager and Resident Philosopher, HomePNA
You’ve probably heard that Gigle Semiconductor has claimed the high ground; launching the “World's First Gigabit Home Networking Chip”. No doubt about it, they are good. So what’s Gigle’s all-important user throughput. I don’t know BUT I heard that Belkin adapters, the first products using the chip, are available so we’ll know soon. We’ll also know more about Gigle’s proprietary “mediaxtream”, the technology giving them the boost over Homeplug AV data rates.
The big question is whether Gigle will be able to convince large service providers to use proprietary technology (especially with all the service provider interest in ITU G.hn’s Gigabit standard). If they want it to be selected they really need an open standard. I remember way-back-when that Gigle proposed something to G.hn but it wasn’t included in the G.9960 PHY standard. There are other standards groups in the world so if they are willing then who knows.
On to the small print. Gigle claims speeds up to 1000Mbps but there’s an asterisk and a note that 1000Mbps is the “ideal physical data rate” and actual data throughput and distance will be lower, depending on interference, network traffic, building materials, and other conditions”.
OK, we all play marketing games. That’s why I use phrases like “up to” when I write about data rates. It’s not my fault. Editors and analysts make me do it. Speed sells and it’s a lot easier than trying to explain user throughput. So … what it means is that the chip produces Gigabit speeds in the lab and maybe on a tester. In the real world you start with the real data rate which is pretty much guaranteed to be lower than a Gigabit and then start subtracting off the overhead.
The overhead depends on the encoding technology – the ways the digital data bits are “encoded” for transmission. Usually some user data bits are encoded into more bits for transmission on the media; be it phone wire, coax, powerline, Ethernet cable or air. There are other transmission taxes related to the way the technology deals with interference and other real world nasties. And then you subtract the MAC overhead – the gaps, address fields, error correction etc. Some MACs (like HomePNA 3.1) are very efficient. Others aren’t. What you have left is the real data throughput. And if you are lucky it will be stable. If you are unlucky it will vary all over the place depending on interference etc.
So the devil is in the details. But this is old news – it’s the reason that major North American service providers prefer coax and phone wires over wireless Wi-Fi and powerline for distributing triple play services in the home. And while we’re on the subject, the ITU G.hn is meeting this week. What’s on the agenda? Cleaning up the draft and converging toward final consent in Geneva. Gigle is first but that may or may not be important in the long run.