Trace format proposals

[flyingzl]

This issue is created to collect proposals and suggestions for network-emulation trace format.

A document is probably needed to describe the trace format, just like LPP network trace format.

[sudeepdi]

Thanks. This one is key to ensure to the browser based tools like Network Emulation tools or other like Lighthouse, WebPageTest, Sitespeed can consume. The reference proposal is a good one to start with.