-: When we deal with the quality of service categorization, 2 2
we first have to ask, 3 3
what is the purpose of quality of service? 4 4
Now, the purpose of quality of service is all about 5 5
categorizing your traffic and putting it into buckets 6 6
so we can apply a policy to certain buckets 7 7
based on those traffic categories 8 8
and then we can prioritize them based on that. 9 9
I like to tell stories and use analogies in my classes 10 10
to help drive home points. 11 11
And so, since we're talking about 12 12
quality of service and traffic, 13 13
I think it's important to talk about real-world traffic. 14 14
I live in the Baltimore, Washington D.C area. 15 15
This area is known for having 16 16
some really really bad traffic. 17 17
Now, to alleviate this they applied the idea 18 18
of quality of service to their traffic system. 19 19
They have three different categories of cars. 20 20
They have the first car, which is general public. 21 21
Anybody who gets in the road and starts driving, 22 22
they are part of this group. 23 23
Then there's another category 24 24
called high occupancy vehicles or HOV. 25 25
And so, if I'm driving my car 26 26
and I have at least two other passengers with me, 27 27
I can get into special HOV only lanes 28 28
and I can go a little bit faster. 29 29
Now the third bucket is toll roads or pay roads. 30 30
And you have to pay to get on these roads. 31 31
And based on the time of day 32 32
and the amount of traffic there is, 33 33
they actually increase or decrease the price. 34 34
Now, if it's during rush hour, you might pay 5 or $10 35 35
to get in one of those special toll lanes. 36 36
But, they're going to travel a whole lot faster 37 37
than the regular general commuter lanes or those HOV lanes. 38 38
Now, what does this mean in terms of quality of service? 39 39
Well, it's really the same thing. 40 40
We take our traffic and we go, okay, this is web traffic, 41 41
and this is email traffic, 42 42
and this is voice or video traffic. 43 43
And based on those buckets we assign a priority to them. 44 44
And we let certain traffic go first 45 45
and we let it get there faster. 46 46
Now, when we categorize this traffic 47 47
we start to determine our network performance based on it. 48 48
We can start figuring out the requirements 49 49
based on the different traffic types 50 50
and whether it's voice or video or data. 51 51
If we're starting to deal with voice or video 52 52
because there are things like streaming media 53 53
especially in real-time like a Skype call 54 54
or a Voice over IP service, 55 55
I want to have a very low delay 56 56
and therefore a higher priority. 57 57
This way I can do this stuff 58 58
for streaming media and voice services 59 59
and prevent those jitters and drops and things like that 60 60
that we talked about before. 61 61
Now, this is something that I want to make sure 62 62
has a good high priority so I can get it through. 63 63
Instead if I have something with a low priority 64 64
that might be something like web browsing 65 65
or non-mission critical data. 66 66
For instance, if my employees are surfing on Facebook, 67 67
that would be a very low priority. 68 68
Or if I deal with email, 69 69
email is generally a low priority 70 70
when it comes to quality of service. 71 71
Now why is that, isn't email important to you? 72 72
Well, because most email is done 73 73
as a store and forward communication method. 74 74
This means when I send email, 75 75
it can sit on my server for 5 or 10 minutes 76 76
before it's actually sent out to the end-user 77 77
and they'll never realize it. 78 78
So that's okay. 79 79
It can be a low priority, it'll still get there eventually. 80 80
But if I did the same thing with VoIP traffic, 81 81
even delaying it by half a second or a second, 82 82
you're going to hear jitters and bumps and echoes 83 83
and that would be a horrible service. 84 84
So, we want to make sure you get high quality of service 85 85
for VoIP and lower priority for email. 86 86
Now that's just the way we have it set up. 87 87
You can have it set up however you want 88 88
as long as you understand 89 89
what your quality of service policy is, 90 90
and you understand it, and your users understand it, 91 91
this is going to be okay. 92 92
The best way to do that is to document it 93 93
and share that with your users. 94 94
You want to make sure your users understand your policy 95 95
because this will help make sure 96 96
that they don't have problems 97 97
and start reporting that back to your service desk. 98 98
You can do this by posting it to your internal website. 99 99
You might post as part of your indoctrination paperwork 100 100
or whatever method you want. 101 101
You want to make sure those users understand it 102 102
because they're the ones who are going to be there 103 103
surfing Facebook or watching YouTube. 104 104
If you've categorized as a low priority, 105 105
they're going to think something's broken. 106 106
But if they know it's a low priority, 107 107
they understand it's not broken 108 108
it's just your corporate policy. 109 109
Now, if they're going to be surfing 110 110
something on the web that's mission critical, 111 111
that's a higher priority and it's going to get 112 112
preferential treatment with your quality of service, 113 113
they should know that too. 114 114
This is the idea here. 115 115
We have to make sure that they understand 116 116
how we categorize our traffic 117 117
and what categories those get put into. 118 118
Now, what are some ways that we can categorize our traffic? 119 119
Well, there's really three different mechanisms you can use. 120 120
We have best effort, integrated services, 121 121
and differentiated services. 122 122
Now, when we use best effort 123 123
this is when we don't have any quality of service at all 124 124
and so traffic is just first in, first out, 125 125
every man for himself. 126 126
We're going to do our best and just try to get it there. 127 127
There's really no reordering of packets. 128 128
There's no shaping. 129 129
It's just pretty much new quality of service. 130 130
First in, first out, best effort. 131 131
The second type is known as integrated services or IntServ. 132 132
This is also known as hard QoS. 133 133
There are different names for it 134 134
depending on what company you're using 135 135
and what routers and switches you're using. 136 136
But the idea here is, 137 137
we're going to make strict bandwidth reservations. 138 138
We might say that all web traffic 139 139
is going to get 50% of our bandwidth, 140 140
VoIP service is going to get 25%, 141 141
and video service is going to get the remaining 25%. 142 142
Now, by reserving bandwidth 143 143
for each of these signaling devices, 144 144
we now decide how much is going to be there 145 145
for each of those three categories. 146 146
Now, when we do a DiffServ or differentiated services, 147 147
also known as soft QoS, 148 148
those percentages become more of a suggestion. 149 149
There's going to be this differentiation 150 150
between different data types 151 151
but for each of these packets, 152 152
it's going to be marked its own way. 153 153
The routers and switches can then make decisions 154 154
based on those markings 155 155
and they can fluctuate traffic a little bit as they need to. 156 156
Now, this is referred to as soft QoS 157 157
because even though we set web up as maybe 50%, 158 158
it's not as much web browsing going on right now 159 159
we can actually take away some of that 50% 160 160
and give it over to VoIP and increase that from 25 to 35%. 161 161
This way, when somebody wants to browse the web, 162 162
we can then take back that extra from VoIP 163 163
and give it back to web back to that 50% was originally had 164 164
based on those markings and based on those categories. 165 165
Now, if we were using hard QoS or that integrated services, 166 166
even if we allocate 50% for web browsing 167 167
and nobody's using web browsing, 168 168
we're still going to have 50% sitting there 169 169
waiting to serve people for web browsing. 170 170
And that's why a lot of companies prefer to use soft QS. 171 171
Now, let's take a look at it like this 172 172
because I like to use simple charts and graphs 173 173
to try to make it easy to understand. 174 174
With best effort at the top, 175 175
you have no strict policies at all. 176 176
And basically, you just make your best effort 177 177
at providing everyone a good quality of service. 178 178
Now with DiffServ you have less strict policies, 179 179
also known as soft QS. 180 180
Now it's better than the best effort approach 181 181
but it's still not the most efficient 182 182
or effective method of providing a good quality of service 183 183
to those who really need it. 184 184
Now with IntServ approaches 185 185
you're going to have more of a hard QoS limit. 186 186
This is what we've talked about before. 187 187
Now, this is going to give you the highest level of service 188 188
to those within strict policies. 189 189
And if you need a really strong quality of service level 190 190
then IntServ or hard QoS with a strict policies 191 191
can really ensure that you get it. 192 192
Now, the way I like to look at this 193 193
is as bundles of QoS options that we can choose from. 194 194
So which of these bundles is really the best? 195 195
Well, it depends. 196 196
It depends on your network and it depends on your needs. 197 197
But most of the time, it's not going to be a best effort 198 198
because that's usually going to give you 199 199
not as much quality as you're really going to want here. 200 200
Now, when we start categorizing our traffic out there 201 201
we're going to start using these different mechanisms, 202 202
either soft or hard QS, for doing that. 203 203
And we can do that using classification and marking. 204 204
We can do it through congestion management 205 205
and congestion avoidance. 206 206
We can use policing and shaping. 207 207
And we can also use link efficiency. 208 208
All of these choices fall under a soft QoS or hard QoS 209 209
depending on your configuration that you've set up 210 210
within your network appliances, firewalls, or routers.