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Re: [STDS-802-16] DSCP Mask and Range??????



Hello Phil:

 

The text you kindly provided here describes the per hop behavior that is typical for PHB routing but here we are extending it to the BS (MAC). Yes I assume the BS may be marking the uplink packets and maybe for that purpose range may make some marking sense.

 

In any event the packet marking is typically an edge function (not MAC based BS) as determined by the edge router (DL) or the MS (UL). However, the more important function for us is the classification of the marked packets arriving to the BS from the MS (uplink) or from the ASN-GW (DL) onto a specific service flow and for that a range makes absolutely zero sense.

 

As you know, we are creating e-2e consistent flow from the ASN-GW through the BS to the MS and for that we need to be exact as where to place the incoming packets.

 

More later,

 

Peretz Feder

 

 

 


From: Phillip Barber [mailto:pbarber@broadbandmobiletech.com]
Sent: Friday, October 10, 2008 3:18 PM
To: Feder, Peretz (Peretz); STDS-802-16@LISTSERV.IEEE.ORG
Subject: RE: [STDS-802-16] DSCP Mask and Range??????

 

Peretz,

 

I assumed from your statement:

 

Whoever brought this text in, can you provide the logic behind this section please?

 

that you were insinuating that this somehow had changed since originally incorporated in the standard. After all, it has been in there since at least IEEE 802.16-2001 (I did a little more research and found that the existing language goes back at least this far).

 

So, this is most certainly not a recent change. It has been in the standard for around eight years. So I really doubt that we are going to be able to track back to the original contributors and get them to validate the rationale behind the current text.

 

That being said, I have no idea how the current language is supposed to correlate to the Diffserv code point value assignments that the existing RFCs define.

 

FYI, here is some text that I use as reference for Diffserv code point. I can’t remember where I got this from, someplace on the internet, but it is not my original work:

IP Precedence and Differentiated Services (DiffServ)

 

DiffServ is concerned with classifying packets as they enter the local network. This classification then applies to Flow of traffic where a Flow is defined by 5 elements; Source IP address, Destination IP, Source port, Destination port and the transport protocol. A flow that has been classified or marked can then be acted upon by other QoS mechanisms. Multiple flows can therefore be dealt with in a multitude of ways depending on the requirements of each flow. Packets are first Classified according to their current DSCP. Then they are separated into queues where one queue may be routed via a marking mechanism and another queue may be examined more closely. After further examination additional packets may be sent for marking or be sent direct to the shaping/dropping mechanisms where all packets end up before leaving the interface.

 

The IP header has a field called the Type of Service (TOS) that sits between the Header Length field and the Total Length field. (Refer to IP Datagram TOS field for a view of the Type Of Service field in the IP header.) Traditionally, IP Precedence has used the first three bits of the TOS field to give 8 possible precedence values.

·         000 (0) - Routine

·         001 (1) - Priority

·         010 (2) - Immediate

·         011 (3) - Flash

·         100 (4) - Flash Override

·         101 (5) - Critical

·         110 (6) - Internetwork Control

·         111 (7) - Network Control

DiffServ introduces the concept of the DiffServ Code Point (DSCP) that uses the first 6 bits of the TOS field thereby giving 26 = 64 different values. RFC 2474 describes the Differentiated Services (DS) field and the DiffServ Code Point (DSCP).

 

 

 

With DiffServ each router handles each packet differently. The concept of Per-Hop Forwarding Behaviour (PHB) is introduced where classes are developed such as Business, Telecommuter, Residential etc. that can be offered by an ISP as different levels of service. A Per-Hop Behaviour is effectively a way of forwarding a particular flow or group of flows (Behaviour Aggregate) of traffic on a DiffServ node. A flow, or flows, of packets marked with a particular DSCP in the DS field will be subject to a particular method of forwarding and rules as encapsulated in the Behaviour Aggregate. This Aggregate has three elements to it (or three colours) which determine whether the router interface 1) Drops the datagram, 2) Sends the datagram or 3) reclassifies it. This three-colour marker is detailed in RFC 2697. For instance 5 flows can be treated as a Behaviour Aggregate so they are treated similarly as a group in most respects. Each flow is then distinguished by an additional Drop Probability and Forwarding Behaviour. Be aware that as the Drop Preference value increases, so the probability of being dropped increases!

 

The following table illustrates the DSCP values:

 

Per Hop Behaviour (PHB)

 

 

DiffServ Code Point (DSCP)

 

IP Precedence

Default

 

 

 

 

0

 

 

000000

 

 

 

Assured Forwarding

 

Low Drop Probability

Medium Drop Probability

High Drop Probability

 

 

Class 1

AF11

AF12

AF13

1

 

 

001010

001100

001110

 

 

Class 2

AF21

AF22

AF23

2

 

 

010010

010100

010110

 

 

Class 3

AF31

AF32

AF33

3

 

 

011010

011100

011110

 

 

Class 4

AF41

AF42

AF43

4

 

 

100010

100100

100110

 

Expedited Forwarding

 

EF

 

 

5

 

 

101110

 

 

 

 

The values in decimal are given in the following table:

DSCP

Binary

Decimal

Default

000000

0

CS1

001000

8

AF11

001010

10

AF12

001100

12

AF13

001110

14

CS2

010000

16

AF21

010010

18

AF22

010100

20

AF23

010110

22

CS3

011000

24

AF31

011010

26

AF32

011100

28

AF33

011110

30

CS4

100000

32

AF41

100010

34

AF42

100100

36

AF43

100110

38

CS5

101000

40

EF

101110

46

CS6

110000

48

CS7

111000

56

 

We can observe the construction of the DSCP values by taking the example for the Per Hop Behaviour AF32. AF32 is derived from the binary 011100. The red section is where the 3 comes from in AF32 and is the Behaviour Aggregate. The blue section is where the 2 comes from in AF32 and is the Drop Probability. The final green section with the 0 is ignored.

 

The decimal IP Precedence value is derived from the red portion and is also called the Class Selector (CS). Often the DSCPs are configured in decimal. The decimal value is derived from all 6 bits of the DiffServ field as you will see from the table.

 

Notice how the three Most Significant Bits (MSB) determine the Class and map directly to the IP Precedence bits. The Class Selector Code Points all have the form xxx000. The three LSBs determine the Drop Probabilities and are ignored by IP Precedence-only devices. Also notice that the LSB is always '0'.

 

Packets from different sources can have the same DSCP value and so can be grouped together as a Behaviour Aggregate and treated in the same manner. A packet with a DSCP not mapped to one of the above PHB i.e. different from the recommendations, will have its DSCP mapped to the Default PHB of 000000. Be aware that the table is recommending the values and different manufacturers could use different ones.

 

Expedited Forwarding within DiffServ is as close as you can get to IntServ as it provides low-loss, low-latency, low-jitter and guaranteed bandwidth.

 

Assured Forwarding is described in RFC 2597 and Expedited Forwarding is described in RFC 2598.

 

To manage the policies you need to use a Common Open Policy Service (COPS).

 

 

 

I can also recommend RFC 3086 and RFC 4594 for reference.

 

And I think you may be mistaken on using RFC 2457 as a reference.

 

Thanks,
Phillip Barber
Chief Scientist
Wireless Advanced Research and Standards
Huawei Technologies Co., LTD.

 


From: Feder, Peretz (Peretz) [mailto:pfeder@ALCATEL-LUCENT.COM]
Sent: Friday, October 10, 2008 1:04 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] DSCP Mask and Range??????

 

I know Phil it has been included from day one. I am missing the rational here; it makes little sense to specify a range for a value that it is very deterministic in all the relevant RFCs.

 

This old text needs a better rational 4 years later when applied to the RFCs mentioned below.

 

Peretz Feder

 


From: Phillip Barber [mailto:pbarber@BROADBANDMOBILETECH.COM]
Sent: Friday, October 10, 2008 1:11 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] DSCP Mask and Range??????

 

Peretz,

 

Nobody changed it. It is exactly as it appears in IEEE 802.16-2004. There has been no subsequent modification.

 

Thanks,
Phillip Barber
Chief Scientist
Wireless Advanced Research and Standards
Huawei Technologies Co., LTD.


From: Feder, Peretz (Peretz) [mailto:pfeder@ALCATEL-LUCENT.COM]
Sent: Thursday, October 09, 2008 10:22 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: Re: [STDS-802-16] DSCP Mask and Range??????

 

IEEE colleagues:

 

I assume no response and no interest means that nobody really cares if the strange ip-tos mask is removed, yes?

 

Peretz Feder

 

 


From: Feder, Peretz (Peretz)
Sent: Wednesday, October 08, 2008 4:43 PM
To: STDS-802-16@LISTSERV.IEEE.ORG
Subject: RE: [STDS-802-16] status of three drafts towards Sponsor Ballot

 

 

Dear IEEE 802.16 Colleagues,

 

Section 11.13.18.3.3.2 Type of Service/DSCP (differentiated services codepoint)Range and Mask field talks about ip-tos mask.

 

What it the idea behind the use of DSCP range and tos mask as described in that section?

 

These terms are not mentioned in RFC 2474.

 

In RFC2457 DiffServ, RFC2597 and RFC3246 AF and EF classes are defined and they all refer to discrete values for DiffServ, no mention of mask or a range.

 

The IANA registry for these DSCP values is not contiguous, how can a range or a mask be applied.

 

http://www.iana.org/assignments/dscp-registry/dscp-registry.xhtml

 

Whoever brought this text in, can you provide the logic behind this section please?

 

Thanks in advance, Peretz Feder