Why your gigabit broadband lags like hell – blame Intel's chipset

Software fix coming after Puma 6 code bug hits Virgin Media, Comcast, Arris and other boxes


Intel's Puma 6 chipset, used in gigabit broadband modems around the world, suffers from latency jitter so bad it ruins online gaming and other real-time connections.

The semiconductor giant is preparing a firmware update to correct spikes of lag and bouts of packet loss that repeatedly flare up in home internet hubs in America, Canada, the UK and beyond. A software fix will be pushed to internet subscribers by their ISPs, so if you're affected, look out for a firmware update and modem reboot coming your way. Some people have already been given a beta version of the update to test.

"We are aware of an issue with the Puma 6 system-on-chip software that impacts latency and are working to address it," an Intel spokesman told The Register this week.

Modems powered by Intel's Puma 6 chipset that suffer from bursts of game-killing latency include the Arris Surfboard SB6190, the Hitron CGNV4, and the Compal CH7465-LG, and Puma 6-based modems rebadged by ISPs, such as Virgin Media's Hub 3 and Comcast's top-end Xfinity boxes. There are other brands, such as Linksys and Cisco, that use the system-on-chip that may also be affected.

The surges in lag are experienced by subscribers on various big ISPs, from Comcast, Charter and Cox in the US to Rogers in Canada and Virgin Media in the UK. You don't need a full 1Gbps connection to trigger the latency spikes – just at least a super-fast package and a buggy modem.

Intel bought the Puma family of chips from Texas Instruments in 2010. The latest in the series – the DOCSIS 3.0-compatible Puma 6 – includes an Atom x86 processor, and it's aimed at gigabit broadband boxes. It claims it can handle internet traffic at speeds of up to 1.6Gbps.

The problem appears to be that the x86 CPU in the modem is taking on too much work while processing network packets. Every couple of seconds or so, a high-priority maintenance task runs and it winds up momentarily hogging the processor, causing latency to increase by at least 200ms and, over time, about six per cent of packets to be dropped. It affects IPv4 and IPv6 – and it spoils internet gaming and other online real-time interaction that need fast response times.

The issue is best illustrated by these two graphs provided by a Register reader in Phoenix, Arizona, who switched to an Intel-powered SB6190 with his Cox cable internet and noticed slower page loads and unexpected lag in online first-person shooters. The blue lines represent the latency and red is packet loss; the graphs show an ICMP ping running 33 times a second over 30 minutes to his ISP's DNS server. His previous Broadcom-based Arris Surfboard modem shows consistent low latency with no packet loss, whereas the Intel-based Arris box is erratic on the same cable line.

Broadcom-based Arris SB6183

Intel-based Arris SB6190

In the graph below showing latency on a connection over one minute with an Arris SB6190 modem, you can clearly see the spikes in lag, almost like clockwork every few seconds, adding an extra 200ms to packet roundtrip times and wrecking the responsiveness of an online game.

Our tipster, an electronic engineer who posts online as xymox1, has chronicled his findings in this forum thread here. "The problem is extreme and, frankly, horrific," he said. "Gamers will lose games because of random 250ms spikes in latency every few seconds."

"I excitedly swapped out my Arris SB1683 Broadcom modem for the new SB6190 Intel one expecting gigabit performance and immediately noticed slower webpage loads," he told The Register. "During first-person gaming, I was getting killed way more often for no apparent reason. I looked at an eight-year graph of latency from my home logs, and was horrified. Swapping back to my SB6183 solved all the issues."

This problem has been snowballing over the past year or so, ever since Puma 6-powered modems started shipping in large numbers, but has mostly stayed under the radar. In the past few months, though, the number of people with ultra-fast lines, and new top-end modems to use them, has grown, blowing the lid on Intel's programming blunder.

There are discussions here and here on Virgin Media's customer support boards revealing how the Hub 3 is affected.

A spokeswoman for Arris confirmed its Puma 6-powered SB6190 modem is hit by spikes in lag, and that a software patch will be coming from Intel to address the issue. She declined to comment on whether any other Arris devices are affected – we know the biz manufactures the Puma 6-based Hub 3 for Virgin Media and Xfinity boxes for Comcast.

"Arris has been working actively with Intel to address the issue, which resulted in some SURFboard SB6190 users reporting latency concerns," a spokeswoman for Arris said.

"We plan to quickly issue Intel’s firmware updates to resolve any latency. We remain committed to providing the best broadband experience for all users of Arris devices and regret any inconvenience this issue caused."

This is more than a little embarrassing for Intel. Its wireless modem chip in the Apple iPhone 7 is allegedly just not as good as rival Qualcomm's chip – thus, Intel's debut in a mainstream smartphone hasn't quite gone to plan. Now its foray into DOCSIS 3.0 broadband modems has stumbled. Chipzilla has big plans for the Puma family, such as turning home boxes into virtual servers with the Puma 7, and it needs to get its Puma 6 migraine cured if internet home hub makers are going to trust future Puma silicon. ®


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