In this lesson,
we're going to talk about VoIP issues.
Now, VoIP stands for the voiceover internet protocol,
and this is a set of protocols that we use to be able
to send streaming voice and video in real time.
Now, unlike traditional network protocols like HTTP, FTP
or email, when you're dealing with a real-time application,
being able to have a very low latency
and a very high quality of service is imperative
to having a good voice connection
or video connection when using real-time
protocols such as VoIP.
Now, when you're dealing with VoIP services,
traditionally this is used
to make phone calls over the internet.
If you have poor VoIP service,
you're going to have issues like dropouts in the calls, issues
where you hear echoing from the other end
or other kinds of glitches inside of the call.
Now, when you're sending ordinary data over the network,
you can have the packets delivered in any order,
and it can take longer or shorter,
and it really won't make a difference.
But if we're having a phone call, you need to make sure
that the things I'm saying are coming
to you in the proper order and at the proper time,
and this is why real time protocols like VoIP really have
to rely on a high quality of service level.
Now, if you don't have a very good quality of service,
you're going to see that you're going to get two major quality
issues that affect VoIP drastically.
This is known as latency and jitter.
Now, latency is the time it takes for a signal
to reach the intended client,
and this is measured in milliseconds.
Now, in general, milliseconds are very fast.
We're talking about 1/1000th
of a second is one millisecond.
But if we're talking using a VoIP connection
and the latency increases to over 100 to 200 milliseconds,
it's actually going to be noticeable in the
audio when you're listening to me.
For example, if you're using a satellite internet
connection, generally you're going to have somewhere
between 150 to 250 milliseconds added to every single thing
that you send because of the time it takes to go up
to the satellite, down from the satellite,
over across the internet, up to the satellite,
down from the satellite, and be able to send all that data.
Now, because of that, that means you have a higher latency,
and in most applications, this wouldn't be a big deal.
But with VoIP it is.
As you have a higher latency,
that means you may start hearing echoes inside
of your connections and you'll hear your own voice repeated
back to you as you're talking over a VoIP connection.
To be able to minimize this, we need
to ensure the latency stays low.
Generally, to have a high quality of service
when using a VoIP connection,
you want to make sure you keep your latency under about 50
to 100 milliseconds.
I can tell you from personal experience,
when I was using VoIP over a satellite connection
that was using a satellite out in geosynchronous orbit,
it was about a 500 millisecond round trip.
Now, because of that, once I said something, I would have
to wait about half a second
before the other person heard it, said something back,
and then I would receive that.
So we always had this delay in our conversation,
and it got to the point when we had significant latency up
to about 1000 milliseconds where I basically have to say
what I was going to say and then use some kind
of a keyword like "Over," so they knew that I was done in
that sentence and it was safe for them to start talking.
This a really unpleasant experience if you're using VoIP
over a high latency connection,
but in some cases you just don't have a choice
because you're dealing with something
like a satellite connection.
The second issue you may experience
with VoIP is what's known as jitter.
Now, jitter is a measurement
of the variation in delay over time,
and it's measured by sampling the elapsed time
between when the packets are arriving
and when they were originally sent.
Now, in general, most VoIP services are going to send their
data over a UDP connection.
Because of this, that data can arrive in any order
as it crosses the network,
and then the system tries to put it
back into the correct order.
So as your latency increases up around 30
to 50 milliseconds,
you're going to start having impacts on your call quality
and you're going to start hearing jitter.
Now, jitter can happen because of a high latency environment
or because your packets are taking different routes across
the internet and being reassembled in the incorrect order
because we're dealing with a real-time protocol.
For example, if I started talking to you
and instead of saying, "One, two, three,"
you heard those packets as "One, three, two," that means
that packet three got there before packet two.
Now generally, you're not going to hear the entire word like
"One, two, and three," in the wrong order,
but instead just pieces of the word.
And this is why you'll hear almost like a robotic static
inside of a VoIP conversation if you have a low
quality of service.
So how do you solve latency and jitter?
Well, there's two ways to do it.
First, you can increase the performance overall
of the entire network.
Now, that's pretty hard to do
because you have to consider every single piece
of the network from that VoIP handset all the way
through the network and your WAN connection.
The second thing you can do though,
is you can implement quality of service.
Now, quality of service is an important tool
inside of your network.
This is a mechanism that allows you
to prioritize certain traffic over others.
For example, in your small office home office network,
you can actually configure your devices
to prioritize your VoIP traffic
and make it the highest priority in your network.
Now, in most small office home office environments,
that would be a very true statement.
Your voice traffic should be the most important
because it is the most susceptible to high latency
and this effective jitter when packets arrive out of order.
So by configuring your network devices
to identify those Voice over IP packets,
you can prioritize those over everything else in your
network, and this will reduce your latency and your jitter
and give you a higher quality of service to your end user.
Now keep in mind the settings you set for quality
of service only affect things inside of your network.
Once it gets to a public network like the internet,
your quality of service rules no longer are going to be
applied, and then it's up to each
of those internet service providers across the internet on
whether or not they're going to prioritize your VoIP traffic
over other things that they're sending to be able
to give you that higher quality of service.
That said, it's still important to set up QoS
or quality of service inside of your own network
for your VoIP devices
because this will allow you to prioritize it inside
of your own network and at least get it a headstart
out and onto the internet.
So remember, when it comes to VoIP issues,
the two biggest issues you're going to experience are high
latency and jitter.
And the best way to solve these is by implementing a quality
of service policy inside of your own network
to prioritize your VoIP traffic.