QoS/Traffic Shaping to avoid Output Drops on ATM Interface

Unanswered Question
Jun 8th, 2009

Hi,

I have an ATM on 2800 Series, configured as follows:

Router#sh run interface atM 0/1/0.1

Building configuration...

Current configuration : 290 bytes

!

interface ATM0/1/0.1 point-to-point

mtu 1500

bandwidth 1200

ip address 10.100.0.22 255.255.255.252

ip helper-address 192.168.101.3

no snmp trap link-status

pvc 8/35

vbr-rt 576 288 36

tx-ring-limit 4

oam-pvc manage

encapsulation aal5snap

service-policy output QoS

!

end

The output of the command show dsl interface ATM 0/1/0 is as follows:

Router#show dsl interface ATM 0/1/0

ATM0/1/0

Alcatel 20150 chipset information

ATU-R (DS) ATU-C (US)

Modem Status: Showtime (DMTDSL_SHOWTIME)

DSL Mode: ITU G.992.1 (G.DMT) Annex A

ITU STD NUM: 0x01 0x1

Vendor ID: ' ' 'TSTC'

Vendor Specific: 0xDBB0 0x0000

Vendor Country: 0x04 0xB5

Capacity Used: 29% 78%

Noise Margin: 15.5 dB 15.0 dB

Output Power: 20.0 dBm 12.0 dBm

Attenuation: 37.5 dB 21.5 dB

Defect Status: None None

Last Fail Code: Handshake or init message invalid or had bad CRC

Watchdog Counter: 0x05

Watchdog Resets: 2

Selftest Result: 0x00

Subfunction: 0x15

Interrupts: 9048 (0 spurious)

PHY Access Err: 0

Activations: 138

LED Status: ON

LED On Time: 100

LED Off Time: 100

Init FW: ASW_init_3_8_131.bin

Operation FW: ASW_R3_8_131.bin

FW Source: embedded

FW Version: 3.8.131

Interleave Fast Interleave Fast

Speed (kbps): 1504 0 608 0

Cells: 4977248 0 80677883 0

Reed-Solomon EC: 192 0 38 0

CRC Errors: 2 0 0 0

Header Errors: 2 0 0 0

Bit Errors: 0 0

BER Valid sec: 0 0

BER Invalid sec: 0 0

LOM Monitoring : Disabled

DMT Bits Per Bin

000: 0 0 0 0 0 0 0 5 4 6 8 9 9 A A A

010: A A A A A 9 9 9 9 9 8 7 6 5 0 0

020: 0 0 0 0 0 0 0 0 2 2 2 2 2 3 2 3

030: 3 3 3 3 3 3 3 3 3 3 3 2 3 2 3 3

040: 0 3 3 3 3 3 3 3 3 3 4 3 4 4 4 4

050: 3 2 2 4 4 5 5 5 5 2 5 5 5 4 4 4

060: 4 4 4 4 4 3 2 4 4 4 5 5 5 5 4 4

070: 4 4 4 4 4 4 4 4 4 3 2 2 4 4 4 4

080: 4 4 4 4 4 4 4 4 4 4 4 4 2 0 0 0

090: 0 3 3 3 4 4 4 4 4 4 4 4 4 3 3 3

0A0: 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3

0B0: 3 2 2 2 0 0 0 0 0 0 0 2 2 2 2 2

0C0: 2 0 2 2 2 2 2 2 0 0 0 0 0 0 0 0

0D0: 0 2 2 2 2 2 2 2 2 2 2 0 0 0 0 0

0E0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0F0: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

DSL: Training log buffer capability is not enabled

Router#

The problem is that I continue to have an output drops on the interface:

Router#sh interfaces atM 0/1/0

ATM0/1/0 is up, line protocol is up

Hardware is DSLSAR (with Alcatel ADSL Module)

MTU 4470 bytes, sub MTU 4470, BW 1200 Kbit, DLY 840 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ATM, loopback not set

Encapsulation(s): AAL5 AAL2, PVC mode

23 maximum active VCs, 256 VCs per VP, 1 current VCCs

VC Auto Creation Disabled.

VC idle disconnect time: 300 seconds

Last input 00:00:00, output 00:00:00, output hang never

Last clearing of "show interface" counters 4d06h

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 1473

Queueing strategy: Per VC Queueing

30 second input rate 8000 bits/sec, 4 packets/sec

30 second output rate 9000 bits/sec, 6 packets/sec

3846354 packets input, 602702599 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

4623694 packets output, 571626291 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

Router#

How can I do? Do you have any suggestions? Maybe something wrong?

Thanks!

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Giuseppe Larosa Mon, 06/08/2009 - 07:10

Hello Paolo,

use

sh policy-map int atm0/1/0 to see statistics of the service policy.

You may need to use hierchical QoS:

a parent service-policy doing shaping in single class class-default that invokes a child policy where you implement CBWFQ.

Hope to help

Giuseppe

Paolo Bratti Mon, 06/08/2009 - 08:07

Hi,

in my runnig-config I have something like that:

class-map match-any Voice

match protocol rtp

match protocol skinny

match protocol h323

class-map match-any Dati-MCritical

match protocol citrix

!

!

policy-map QoS

class Voice

priority percent 50

class Dati-MCritical

priority percent 10

class class-default

fair-queue

!

and the output of the command sh policy-map int atm0/1/0.1 is:

Router#sh policy-map int atm0/1/0.1

ATM0/1/0.1: VC 8/35 -

Service-policy output: QoS

Class-map: Voice (match-any)

456492 packets, 36103289 bytes

30 second offered rate 28000 bps, drop rate 0 bps

Match: protocol rtp

418498 packets, 33557578 bytes

30 second rate 28000 bps

Match: protocol skinny

35541 packets, 2259419 bytes

30 second rate 0 bps

Match: protocol h323

2453 packets, 286292 bytes

30 second rate 0 bps

Queueing

Strict Priority

Output Queue: Conversation 40

Bandwidth 50 (%)

Bandwidth 144 (kbps) Burst 3600 (Bytes)

(pkts matched/bytes matched) 56433/4413302

(total drops/bytes drops) 191/39124

Class-map: Dati-MCritical (match-any)

127545 packets, 8654122 bytes

30 second offered rate 5000 bps, drop rate 0 bps

Match: protocol citrix

127545 packets, 8654122 bytes

30 second rate 5000 bps

Queueing

Strict Priority

Output Queue: Conversation 40

Bandwidth 10 (%)

Bandwidth 28 (kbps) Burst 700 (Bytes)

(pkts matched/bytes matched) 4593/393559

(total drops/bytes drops) 473/106266

Class-map: class-default (match-any)

1023857 packets, 171914476 bytes

30 second offered rate 8000 bps, drop rate 0 bps

Match: any

Queueing

Flow Based Fair Queueing

Maximum Number of Hashed Queues 32

(total queued/total drops/no-buffer drops) 0/714/0

Router#

Do you have any suggestions?

Giuseppe Larosa Mon, 06/08/2009 - 08:43

Hello Paolo,

you have one level of QoS with a CBWFQ + LLQ for voice (priority)

One important note is the following:

the pvc 8/35 is configured for

vbr-rt 576 288 36

tx-ring-limit 4

the physical atm interface has BW 1200 kbps.

As you can see a priority percent 50 is seen as 144 kbps that is 50% of 288 kbps the second parameter in vbr-rt command

The sh policy-map int atm0/1/0.1 shows that all classes have experienced drops.

if the PVC settings are correct and you want to be sure to respect these parameters you need a parent policy like

policy-map shape_all_at_288

class class-default

shape average 288

service-policy QoS

and you apply to atm0/1/0.1

int atm0/1/0.1

service-policy output shape_all_at_288

Hope to help

Giuseppe

Paolo Bevilacqua Mon, 06/08/2009 - 22:55

Why?

A PVC with SCR should not need L3 shaping or nested policies.

I'm not sure why there are drops in the PQ, perhaps there were a lot of calls at a given time.

Giuseppe Larosa Tue, 06/09/2009 - 02:07

Hello Paolo,

I agree with you I was concerned with the fact that there are drops in all classes.

So you think that it can be a problem of call admission control that allows too many concurrent voice calls?

Best Regards

Giuseppe

Paolo Bratti Thu, 06/11/2009 - 23:21

Hi,

I have read this guide http://www.cisco.com/en/US/tech/tk39/tk824/technologies_tech_note09186a00800d76b5.shtml

I think, that QoS shaping is not supported in my WIC-1ADSL on Cisco 2801; infact when I try to apply my parent policy-map Prova on the VC I don't show it in my running-config.

class-map match-any Voice

match protocol rtp

match protocol skinny

match protocol h323

class-map match-any Dati-MCritical

match protocol citrix

!

!

policy-map QoS

class Voice

priority percent 50

class Dati-MCritical

priority percent 10

class class-default

fair-queue

policy-map Prova

class class-default

shape average 576000

service-policy QoS

How can I do? Do you have any suggestions? Maybe something wrong?

Thanks!

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