Wireless Jumbo Frames? / TiVo

Discussion in 'Tomato Firmware' started by jersully, Aug 14, 2008.

  1. jersully

    jersully LI Guru Member

    Please pardon my ignorance, but I've been researching a bit on how to optimize file transfer speeds between my two TiVos. Currently one is wired and the other wireless. I've read in some TiVo circles of various hacks that can be done, most of them would be easy if I were more Linux savvy, but the biggest impact (other than putting the TiVo in standby or tuning to a non-existent channel) seems to be from enabling jumbo frames. I know that can be done for wired Ethernet, but what about wireless?

    Also, any TiVo specific networking advice would be appreciated. Over a year ago I made the biggest difference by purchasing the TiVo branded adapter which offloads some processing from the TiVo CPU and by switching the other TiVo from wireless to wired to alleviate the "half-duplex" issue inherent in wireless networks. (Plus my Netgear WG111 adapters were very unstable with TiVo.)

    I'll probably replace my one wireless TiVo with wired eventually to speed up transfers in general and specifically for wireless TiVo to wireless PC, but I'm in no hurry to climb into my attic. It's HOT where I live. :)


    P.S. If anyone's wondering, there are no Gb adapters for TiVo.
  2. TexasFlood

    TexasFlood Network Guru Member

    I don't think Jumbo Frames are supported on anything less and than gigabit devices, and support is not guaranteed for devices that are Gb. Unless I'm missing something, this leaves out current wireless and/or fast ethernet routers.
  3. Maggard

    Maggard LI Guru Member

    USB transfers are handled by the CPU (unlike 1394/FireWire). TiVos are highly optimized for video recording & playback with few additional CPU cycles for to spare for USB overhead. Thus networking a TiVo via USB is highly constrained for both the USB connection & also the accompanying network stack.

    Therefore using a USB/Ethernet adapter on a TiVo you're getting lousy USB speeds and possibly lots of latency on the network stack. (Also your TiVo is busy encrypting the files it transfers, which adds yet another layer of overhead.) The end result is you're not nearly straining a 10Mb connection, not to mention a typical 100Mb connection or much more expensive Gb network.

    It's like having a super-highway with a single lane dirt road at one end.

    Adding more lanes to the superhighway, increasing it's speed, won't do a thing getting traffic over that dirt road. TiVo's USB connection is that dirt road, with addt'l potholes provided by the starved network stack & file encryption delays. And adding 802.11 overhead, oh dear.

    Jumbo frames are one work-around, the idea being that by sending larger blocks of data there's less handshaking overhead (percentage-wise). Continuing the trite highway analogy jumbo packets are like shipping data in large trucks instead of smaller vans, more gets through per shipment, with less paperwork required for the volume sent. This of course only works on a stable lightly-loaded network as re-transmits of jumbo frames quickly eat up any savings. However as you've discovered support for jumbo frames is pretty spotty and unlikely to show up in the home router class of hardware.

    As to TiVo's, their branded network adapter offers minimal network 'assistance'. Instead it was a response to device vendors not labeling their USB/Ethernet adapters in any useful way.

    TiVo's customers were unable to purchase USB/Ethernet adapters they could trust to work with the TiVo-supplied drivers. Even with identical packaging & parts numbers from big-name vendors like LinkSys the chipset used inside is unpredictable, indeed undeterminable, until actually plugged in. So TiVo came out with a branded adapter using a specified chipset they'd already supplied drivers for - win/win for everyone.

    So what can you do to improve your TiVo file transfers?

    Get a TiVo with built-in Ethernet (no USB overhead.) Use wired connections instead of wireless (less network overhead.) Set your TiVo to a solid unchanging screen, no playback, while transferring files (fewer CPU cycles used on competing priorities.) If transferring to a computer look into the non-TiVo-supplied file transfer applications - some are significantly faster.

    But Jumbo Frames on these hopped-up home routers - even if possible the time, effort, & complexity won't be worth the minor speed improvement. Better to just accept the slightly slower transfer speed.
  4. jersully

    jersully LI Guru Member

    It's important to note that the USB interface itself isn't the culprit, but the work that the TiVo has to do to run the USB and keep it fed. As you've said, the TiVo is highly optimized for video and not networking - at both the hardware and software levels. The CPU and chipset max out before it saturates USB or the network.

    Personally I saw a GREAT improvement in speed when I swapped my Netgear adapter for the Tivo brand adapter. It's more stable too (though the Netgear give me no problems when used with a PC.)

    You left one suggestion off your list for speeding up file transfers. Put both TiVos in standby! I don't have benchmark numbers, but it is definitely faster than setting the TiVos to non-existent channels.

    Sometime this winter I'll once again climb into my attic to run a network drop to my wireless Tivo and hook up a wired adapter. There are other hacks out there (backrev adapters, tweaked kernel, removing netfilter) but no more often than I copy shows I'll just throw two wired adapters at it.
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