Instructor: In this lesson,
we're going to talk about VoIP issues.
Now, VoIP stands for the Voice Over 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 being 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'd 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 is 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 1, 2, 3,
you heard those packets as 1, 3, 2,
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 (indistinct) 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 effect of 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 your own network and at least get it a head start
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.