When we deal with the quality
of service categorization, we first have to ask,
what is the purpose of quality of service?
Now, the purpose of quality of service
is all about categorizing your traffic
and putting it into buckets so we can apply a policy
to certain buckets based on those traffic categories,
and then we can prioritize them based on that.
I like to tell stories and use analogies in my classes
to help drive home points, and so since we're talking about
quality of service and traffic,
I think it's important to talk about real world traffic.
Now, to alleviate this, they applied the idea
of quality of service to their traffic system.
They have three different categories of cars.
They have the first car, which is general public, right?
Anybody who gets in the road and starts driving,
they are part of this group.
Then there's another category
called high-occupancy vehicles or HOV.
And so if I'm driving my car
and I have at least two other passengers with me,
I can get into special HOV-only lanes,
and I can go a little bit of faster.
Now, the third bucket is toll roads or pay roads,
and you have to pay to get on these roads.
And based on the time of day
and the amount of traffic there is,
they actually increase or decrease the price.
Now, if it's during rush hour, you might pay 5 or $10
to get in one of those special toll lanes,
but they're going to travel a whole lot faster
than the regular general commuter lanes or those HOV lanes.
Now, what does this mean in terms of quality of service?
Well, it's really the same thing.
We take our traffic and we go,
okay, this is web traffic and this is email traffic
and this is voice or video traffic.
And based on those buckets, we assign a priority to them.
And we let certain traffic go first,
and we let it get there faster.
Now, when we categorize this traffic,
we start to determine our network performance based on it.
We can start figuring out the requirements
based on the different traffic types,
and whether it's voice or video or data.
If we're starting to deal with voice or video,
because there are things like streaming media,
especially in real time like a Skype call
or voiceover IP service,
I want to have a very low delay,
and therefore, a higher priority.
This way, I can do this stuff for streaming media
and voice services and prevent those jitters and drops
and things like that that we talked about before.
Now, this is something that I want to make sure
has a good high priority so I can get it through.
Instead, if I have something with a low priority,
that might be something like web browsing
or non-mission critical data.
For instance, if my employees are surfing on Facebook,
that would be a very low priority,
or if I deal with email.
Email is generally a low priority
when it comes to quality of service.
Now, why is that?
Isn't email important to you?
Well, because most email is done as a store
and forward communication map.
This means when I send email,
it can sit on my server for 5 or 10 minutes
before it's actually sent out to the end user,
and they'll never realize it.
So that's okay.
It can be a low priority.
It'll still get there eventually.
But if I did the same thing with VoIP traffic,
even delaying it by half a second or a second,
you're going to hear jitters and bumps and echoes,
and that would be a horrible service.
So we want to make sure you get high quality of service
for VoIP and lower priority for email.
Now, that's just the way we have it set up.
You can have it set up however you want.
As long as you understand
what your quality of service policy is
and you understand it and your users understand it,
this is going to be okay.
The best way to do that is to document it
and share that with your users.
You want to make sure your users understand your policy
because this will help make sure
that they don't have problems
and start reporting that back to your service desk.
You can do this by posting it to your internal website.
You might post it as part of your indoctrination paperwork
or whatever method you want.
You want to make sure those users understand it
because they're the ones who are going to be there
surfing Facebook or watching YouTube.
If you've categorized it as a low priority,
they're going to think something's broken.
Or if they know it's a low priority,
they understand it's not broken,
it's just your corporate policy.
Now, if they're going to be surfing something on the web
that's mission critical, that's a higher priority,
and it's going to get preferential treatment
with your quality of service,
they should know that too.
This is the idea here.
We have to make sure that they understand
how we categorize our traffic
and what categories those get put into.
Now, what are some ways that we can categorize our traffic?
Well, there's really three different mechanisms you can use.
We have best effort, integrated services,
and differentiated services.
Now, when we deal with best effort,
this is when we don't have any quality of service at all.
And so traffic is just first in, first out,
every man for himself.
We're going to do our best and just try to get it there.
There's really no reordering of packets, there's no shaping.
It's just pretty much no quality of service.
First in, first out, best effort.
The second type is known as Integrated Services or IntServ.
This is also known as Hard QOS.
There are different names for it
depending on what company you're using
and what routers and switches you're using.
But the idea here is we're going to make strict
bandwidth reservations.
We might say that all web traffic
is going to get 50% of our bandwidth,
VoIP service is going to get 25%,
and video service is going to get the remaining 25%.
Now, by reserving bandwidth
for each of these signaling devices,
we now decide how much is going to be there
for each of those three categories.
Now, when we deal with DiffServ
or differentiated services, also known as Soft QoS,
those percentages become more of a suggestion.
There's going to be this differentiation
between different data types,
but for each of these packets,
it's going to be marked its own way.
The routers and switches can then make decisions
based on those markings, and they can fluctuate traffic
a little bit as they need to.
Now, this is referred to as Soft QoS
because even though we set web up as maybe 50%,
it's not as much web browsing going on right now,
we can actually take away some of that 50%
and give it over to VoIP and increase that from 25 to 35%.
This way, when somebody wants to browse the web,
we can then take back that extra from VoIP
and give it back to web,
back to that 50% it has originally had
based on those markings and based on those categories.
Now, if we're using hard QoS or that integrated services,
even if we allocated 50% for web browsing
and nobody's using web browsing,
we're still going to have 50% sitting there,
waiting to serve people for web browsing.
And that's why a lot of companies
prefer to use soft QoS instead.
Now, let's take a look at it like this,
because I like to use simple charts
and graphs to try to make it easy to understand.
With best effort at the top,
you have no strict policies at all.
And basically, you just make your best effort
at providing everyone a good quality of service.
Now, with DiffServ, you have less strict policies,
also known as soft QoS.
Now, it's better than the best effort approach,
but it's still not the most efficient
or effective method of providing a good quality of service
to those who really need it.
Now, with IntServ approaches,
you're going to have more of a hard QoS limit.
This is what we've talked about before.
Now, this is going to give you the highest level of service
to those within strict policies,
and if you need a really strong quality of service level,
then IntServ or hard QoS with its strict policies
can really ensure that you get it.
Now, the way I like to look at this
is as bundles of QoS options that we can choose from.
So which of these bundles is really the best?
Well, it depends.
It depends on your network and it depends on your needs,
but most of the time, it's not going to be a best effort,
because that's usually going to give you
not as much quality as you're really going to want here.
Now, when we start categorizing our traffic out there,
we're going to start using these different mechanisms,
either soft or hard QoS for doing that.
And we can do that using classification and marketing.
We can do it through congestion management
and congestion avoidance.
We can use policing and shaping,
and we can also use link efficiency.
All of these choices fall under a soft QoS or hard QoS,
depending on your configuration that you've set up
within your network appliances, firewalls, or routers.