1
00:00:01,630 --> 00:00:08,400
A phone can indicate that its traffic is important by mocking traffic at least three now at least three

2
00:00:08,410 --> 00:00:14,140
we would be using an IP version for header or IP version 6 header in this course will concentrate on

3
00:00:14,140 --> 00:00:17,160
IP version 4 in an IP version 4 header.

4
00:00:17,160 --> 00:00:20,830
There is a field called type of service.

5
00:00:20,830 --> 00:00:30,330
It consists of eight binary values now in the old days we used to only look at the most significant

6
00:00:30,330 --> 00:00:31,540
three bits.

7
00:00:31,680 --> 00:00:38,670
So these three bits of the header were read by routers and networking devices to determine how important

8
00:00:38,670 --> 00:00:52,140
the traffic is and the same way as cause the valleys are from zero all the way up to 7 so 0 1 to follow

9
00:00:52,170 --> 00:00:53,100
up to 7.

10
00:00:53,280 --> 00:01:00,330
Voice once again would be marked with a cos value of 5 so a phone as an example would markets traffic

11
00:01:00,330 --> 00:01:06,450
at Layer 2 and then market at least 3 to indicate how important the traffic is.

12
00:01:06,450 --> 00:01:13,920
The problem with this mechanism is we only have 7 classes close to zero would be used for best effort.

13
00:01:13,920 --> 00:01:20,280
In other words you are not going to get a decent quality of service and often 6 or 7 or both are used

14
00:01:20,280 --> 00:01:26,830
for network protocols so you are limited in the number of classes that you can use for traffic.

15
00:01:26,840 --> 00:01:35,280
So voice maybe using 5 video maybe using 4 What are you going to use for ERP or business traffic vs.

16
00:01:35,730 --> 00:01:39,090
HDP traffic versus other traffic on your network.

17
00:01:39,150 --> 00:01:45,360
You're running out of classes and in addition the classes weren't standardized so any traffic could

18
00:01:45,360 --> 00:01:51,150
end up in any class so this was adjusted to use 6 binary bits.

19
00:01:51,420 --> 00:01:55,680
And this is known as DCP or differentiated services code points.

20
00:01:55,770 --> 00:01:59,130
It's the same field in the IP version 4 header.

21
00:01:59,580 --> 00:02:05,610
It's just the interpretation of the bits rather than using three bits six bits in the header are read

22
00:02:05,970 --> 00:02:13,090
and marked to determine how important the traffic is this is known as IP precedence.

23
00:02:13,210 --> 00:02:18,160
So when only three bits are used it's known as IP precedence when 6 bits are used.

24
00:02:18,160 --> 00:02:26,320
It's known as differentiated services code points or DCP now DCP is backward compatible to IP precedents.

25
00:02:26,320 --> 00:02:33,160
These values in DCP are known as class selector values or CSR values.

26
00:02:33,160 --> 00:02:41,090
So you may see someone talk about this being IP precedents 5 but they may also mention this as CLOs

27
00:02:41,130 --> 00:02:43,650
select a 5.

28
00:02:43,700 --> 00:02:52,400
It depends whether we're using the old naming convention of IP precedents or or the newer DCP descriptions.