9P and VOIP

9P and VOIP

Plan9’s filesystem protocol is interesting. What would it look like to implement VOIP on top of it? A first draft.

A quick summary

The man-page does a better job of providing a technical description of 9P, but I’ll give a low-tech explanation for completeness.

9P is: - A protocol used by clients and servers to expose and make use of a filesystem hierarchy on a remote machine. - In the simplest case, it allows a client to navigate a filesystem on a remote host. - For example, WSL2 (Linux-on-Windows) has each Linux subsystem start a 9P server to expose the Linux filesystem. - The filesystem hierarchy exposed may be /virtual/. As in a server responding to a read request with generated data. - For example, the server may construct a filesystem-structure representating known-paths of a website. When clients read a ‘file’ in that path, the data returned comes not from a file, but from a process (i.e. python, nodejs, ruby).

Modelling VOIP as a filesystem (draft 1)

I have some interest in how VOIP could be implemented with 9P. SIP isn’t hierarchical, so representing calls in a hierarchy isn’t immediately obvious. The properties of a tree-structure representing a typical commercial VOIP service (with UACs, calls, and perhaps call recordings), would (I think) look a little like this:

  | |_2025_01_01
  |   |_1735689600_1000123456_033443443434.cdr
  | |_2025_01_01
  |   |_1735689600_1000123456_0787878787.opus
    | |_1000123456_0787878787
    |   |_metadata
    |   |_hep.sock
    |   |_rtp_src.sock
    |   |_rtp_dest.sock

A few notes on this: