code points in diff serv

Products PMP
1

hello all i am still getting my head around code points and high priority channels

i want to enable high priority traffic on the sm’s and set code points for my viop traffic
we are using linksys voip phones and linksys ptp modules and how to we equate the code point from the linksys gear to the sm gear.

regards,

richard

2

The CPE device needs to be able to set the diffserve codepoint. Canopy will recognize the codepoint and assign the appropriate priority.

3

This is an excellent topic I had been hoping to start talking about. We also use Linksys VoIP adapters in our system and have been experiencing echo from the other (outside our system) called or calling party.

There is an Application Note for Canopy VoIP under the Documents Library/Application

Noteshttp://motorola.motowi4solutions.c … on=1&cat=7

On page 28 it states:

particular, DiffServ employs Expedited Forwarding for VoIP as it means “low delay”.
This is DSCP 46 (decimal). It is critical that any VoIP application or ATA or GW set
DSCP 46 marking into each IP packet carrying VoIP payload. Canopy APs and SMs look
for this marking to classify packets into their appropriate “high” or “low” priority queue.
ATA product user guides typically indicate that they set the DiffServ field to hexadecimal
0xb8. This is an 8-bit representation, so includes the two non-DSCP bits to the “right” of
the DSCP 6-bit field. These other 2-bits are IP’s Explicit Forward Congestion Notification
(EFCN) bits, and for VoIP (which uses UDP) these should both be set to binary “0”.
Consequently, the EF code is properly expressed as 0xb8 when consider all eight bits.

I have also been reading that the value for this codepoint for VoIP should be 6.

When I looked at the Linksys routers they had been set in the Line Network Settings to have a TRP TOS/Diff value of 0xb8 with a RTP CoS value of 6.

So from this I am guessing that in the Canopy Configuration page of each VoIP SM (and it’s AP’s and switches and BH’s) you need to set the Configuration/Diff Serv Codepoint 46 to a value of 6. I have tries this out on 2 customers and so far it seems to be working.

On advice of others I also did not Enable High Priority Channels for the CIR setting in the Quality of Service page and have Disabled Prioritize TCP ACK in the General Page of all AP’s and BH’s.

Does this make sense?

4

i just read the same doc and i follow you so far.

anyone implemented?

the doc does say to enable high priority in qos


richard

5

Hi all,
I also read the doc, but there is something that still don’t understand.

1) Why is Moto suggesting the use of CP46, when its priority is 4? (not 6 or 7 as voice should have)
Probably because the Canopy implementation of DSCP only differentiate between two levels (0-3 and 4-7)

2) I understand that I have to set the CodePoint on my customer’s ATA, so that the VoIP traffic generated from ATA and entering the SM will be recognized and handled correctly.
But what about the traffic coming from the SIP gateway?
If customer connects to an external SIP gateway, how can I mark the traffic with CP46 in order to have my network considering it “high-priority” ?
Do I have to configure my core router to recognize incoming SIP traffic and mark the DSCP field?

3) Do I necessarly have to configure CIR settings on my customer’s SM? If not, will priority work anyway?
I mean: if the AP is bandwitdh saturated, and there are 2 customers using VoIP, can I assume that they will have a preferential channel for packets generated by their ATA, even without setting CIR?

Thanks
Massimo

6

I can’t answer all your questions BigTrumpet but I do not see in the doc that the code points are only 2 levels. I see them as any digit from 0-7. I have set Code Point 46 to a value of 6 for some of my VoIP customers and it seems to make a difference.

I agree that this must occur right through your network, AP’s, BH’s, switches, routers, etc.

7
Dave Bradich wrote:
I can't answer all your questions BigTrumpet but I do not see in the doc that the code points are only 2 levels. I see them as any digit from 0-7.


hi Dave
I read on page 28 of the Motorola document:

While DiffServ has many levels of priority defined, Canopy implements only two levels of
priority queues. Therefore, a Canopy AP or SM maps DSCP CP codes into one of two
queues depending upon configuration. Note that Canopy is, therefore, unable to fully
comply with the above DSCP semantics.
However, administratively ,Canopy has eight settable levels of priority, namely 0 to 7.
Since Canopy supports two queues – “high” and “low” (meaning “ordinary”) – levels 0, 1,
2, and 3 map to “low” priority and levels 4, 5, 6, and 7 map to “high” priority. At some
future date, Canopy may implement additional levels of priority queues.


So, if I did understand correctly, there shouldn't be any difference between setting the priority to 4 or 6.
Thanks for your reply
Massimo
8

Ah I see. Then I wonder why they set Codepoint 48 to 6 and Codepoint 56 to 7?

9

I’m not an IP QoS geek, but perhaps to match some mapping standard or future compatibility? Or perhaps the flags are re-applied after the packet egresses the Canopy network?

10
salad wrote:
I'm not an IP QoS geek, but perhaps to match some mapping standard or future compatibility?


I think the same: they are supposed to fully implement DSCP priority in some future release...