MicroCell
™
Informational Document for
Technical, Operational, and Troubleshooting Issues v1.7
by Otto Pylot
Page 3 of 23
Unfortunately, the end user has no control over these issues and they can be
on-going or temporary.
Jitter – this is defined as a variation in the delay of received packets. Data packets
are sent as a continuous stream evenly spaced apart. Due to network congestion,
improper queing, or configuration issues, the steady stream may be interrupted
such that the delay between each packet can vary instead of remaining constant.
When the router receives the RTP (Real-Time Protocol) audio stream, it has to
compensate for any jitter that is encountered. This basically means that the RTP has
to be buffered and then put back together in a steady stream to be sent to the DSP
(Digital Signal Processor) and re-converted back to an analog signal. This buffer is
either called the playout delay buffer or the de-jitter buffer.
If the jitter is too large to be buffered adequately, packets are discarded which
results in audio dropouts. Sometimes the dropouts are not noticeable if the DSP can
insert packets that it thinks should be there (predictive insertion). If they are too
large, audio quality deteriorates or the connection is dropped.
Jitter can only be fixed by your ISP.
Packet Loss – this is simply data packets that just get lost in transit. Not an
uncommon event on the internet. Causes can include signal degradation, channel
congestion, corrupted packets being rejected in-transit, faulty network hardware,
faulty network drivers, or home network/wiring issues. Sometimes packet loss can
be intentional by your ISP for operational management purposes.
Excessive packet loss can result in voice dropouts or loss of connectivity. Packets
are transmitted using either TCP (Transmission Control Protocol) or UDP (User
Datagram Protocol) protocols on specific ports designated by AT&T. The exact
function of those protocols will not be discussed in this document.
Insufficient Bandwidth – it’s nice to have a 50Mbps download speed but that is
rarely a sustained speed (100% of the time). It will vary for lots of reasons and are
not guaranteed by your ISP (the term usually given is “up to”). Most of the time one
is close to that but variations will occur with sometimes very drastic speed
fluctuations. All of which can affect the MicroCell voice quality and connectivity.
You home network will also affect the bandwidth if you are sharing multiple devices
that can all connect to the internet.
There are various applications that you can use to test for latency, jitter, packet loss,
and speed. But these only take snapshots at that point in time. To get a more
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