Media, networks and telephony
Check each media direction and its codec. Do not diagnose from “connected” alone.
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The ideas to retain
Draw the path before choosing an acronym
Architecture discussions often collapse three different planes:
WebRTC: the route selected by ICE matters
WebRTC does not assume that two endpoints can send UDP directly to each other. ICE gathers candidates and tests connectivity pairs. RFC 8445 distinguishes host, server-reflexive, and…
Why TCP can sound worse even when bandwidth is sufficient
TCP delivers a reliable ordered byte stream. If a segment is lost, later data can wait for the missing segment to be retransmitted. That behavior is usually correct for a download. For…
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Connected does not guarantee audio
SIP establishes the session. A 200 OK confirms signalling, not two-way audio.
Here incoming packets arrive, but the outgoing media path is blocked.
Check each media direction and its codec. Do not diagnose from “connected” alone.
The actual path can change
ICE tests connectivity between candidates. A direct path may not cross the network.
TURN provides a relay when needed. That does not mean the call failed.
Record the selected path and its changes: the additional hop belongs in the diagnosis.
A missing packet holds back the rest
TCP delivers in order. When segment 2 is missing, later data can be held back.
Once retransmission arrives, the sequence is released. Audio has accumulated waiting.
UDP has no TCP-style ordered delivery; the receiver still needs a loss policy.
Smoothing arrivals adds waiting
Four packets arrive at 0, 20, 70 and 75 milliseconds: the intervals are irregular.
With 60 milliseconds of margin, this example plays them at 60, 80, 100 and 120.
The buffer avoids these gaps by adding delay. It does not remove all network variation.
More samples do not restore detail
A telephone leg can remove part of the spectrum before audio reaches the model.
Increasing the sample rate later adds samples of the already limited signal.
The lost information does not return. Codec, bandwidth and sampling are different boundaries.
Repair must arrive in time
Redundancy in a later packet can help reconstruct earlier missing audio.
It helps that playout only when repair arrives before its deadline.
Enabling FEC does not guarantee continuity. Network loss and audible damage are measured separately.
