TCP Window Scale: How to adjust this value?

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Created Dec ’17

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Hi all,

I am curious to understand if there is any way possible to adjust the TCP Window Scale value that the device uses similar to how it can be modified on Windows and Linux platforms.

The reason behind this for those curious, is that I work within the TCP Accelerator and Deep Packet Inspection world and have recently found a deficiency across satelite links specific to the iPhone. Speeds achieved with Android/Linux/Windows7|10 consistently reach ~12Mbps while the iPhone can only reach 1/4 (3Mbps) using all of the same network infrastructure. Wireshark traces point specifically at the Window Scale values (currently seen: 3; would like to adjust to 7 or 8 if possible).

Kind regards and thanks for any insight you are able to provide.

-Chris

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Answer 1

DTS Engineer OP

Apple

Dec ’17

I am curious to understand if there is any way possible to adjust the TCP Window Scale value …

Not on a system-wide basis (you can do this sort of thing on macOS via

sysctl

, but iOS doesn’t expose that functionality). My recommendations:

File a bug about the slow performance you’re seeing. iOS has automatic buffer scaling that’s supposed to handle all sorts of weird environments, and I’m sure that the TCP folks would be interested in why it’s not handling yours.
Make sure to include a sysdiagnose log (per our Bug Reporting > Profiles and Logs page) and a packet trace of the problem.
Please post your bug number, just for the record.
If you’d like iOS to provide support for manual intervention in cases like this, you can file an enhancement request for that as well.

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