Checking the Bandwidth on IMA Interface

[vinod.thathamath]

I have a physical IMA interface which has 4 E1s bundled together and one PVC built on it. The VBR NRT setting on the PVc is

6000 6000. Iam experiencing packet drops on the link.

I have verified the PCR, SCR amd MBS settings with the Ckt vendor as 17960,15625 and 1000.

BUt when i execute the " sh atm int ATM0/IMA0 ", i get the available BW as 1680.

Is this BW in KBPS. Why am i getting the BW as 1680 when it should be the speed of 4 E1s.

Also can we change the setting on the physical IMA interface to match with the Ckt vendor?

IAm pasting the configs and the output of the show command for your reference.

interface ATM0/IMA0

description *** 4 Bounded E-1's ATT via d58-536 ***

bandwidth 8000

no ip address

no ip route-cache cef

no ip route-cache

no atm ilmi-keepalive

!

interface ATM0/IMA0.537 point-to-point

description *** 6M vc to SNSRBMUSCINGH03 via d58-537 ***

bandwidth 6000

ip address x.x.x.x 255.255.255.252

no ip route-cache

pvc 1/63

protocol ip x.x.x.x broadcast

vbr-nrt 6000 6000

oam-pvc manage

oam retry 3 3 3

encapsulation aal5snap

xxxxxxxxxxx#sh atm int ATM0/IMA0

Interface ATM0/IMA0:

AAL enabled: AAL5 , Maximum VCs: 255, Current VCCs: 1

VCIs per VPI: 256,

Max. Datagram Size: 4528

PLIM Type: E1 IMA, TX clocking: LINE

15549 input, 9571 output, 9866526 IN fast, 8507194 OUT fast, 0 out dropVBR-NRT : 6000

Avail bw = 1680

Config. is ACTIVE

xxxxxxxxxxxxxxx#

Awaiting your reply

[vinod.thathamath]

Would really appreciate if someone replies to this.

Thanx in advnace

[SCOTT JORDAN]

My experience is with IMA circuits are with T-1s but you have to create a ima group under ATM interfaces

interface ATM0/0

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

!

interface ATM0/1

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

!

interface ATM0/2

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

sho interface ATM0/IMA0

BW 4608

[vinod.thathamath]

Thats right..Here we have 4 E1s that are grouped to the IMA.

interface ATM0/0/1

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

interface ATM0/2/1

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

!

interface ATM0/3/0

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

!

interface ATM0/3/1

no ip address

no scrambling-payload

ima-group 0

no atm ilmi-keepalive

[wochanda]

Hey, i'm having a little trouble figuring out exactly what you're telco gave you for PCR, SCR, and MBS. Is 17960,15625 and 1000 in cells, bits, bytes, kb, etc? If its in cells, you're looking at 828kbps sustained rate for your IMA group, which isn't right, cause you're wasting 3 of your T1's.

Chances are if your telco sold you 4 T1's, it was so you could keep a 6mbps sustained rate, so the only shaping you need to set up is vbr-nrt 6000 6000.

If they actually are policing your traffic to 15625 cells for your SCR, its a mistake on their part, and thats the reason for your packet drops in the cloud.

[vinod.thathamath]

It is in cells. But when we convert it to kbps, it should be 15625 * 53 *8 bits = 6625 kbps right? I am confused on why you had mentioned 828 kbps?

[wochanda]

Good eye, forgot the bits/bytes.

Either way, shaping to 6000 6000 should be fine for you. Are you seeing CRC errors on the other side? This would be a sign that the cloud is dropping cells, and incorrectly policing you.

Are all of your counters clean on 'show interface' and 'show controllers t1'/'show controllers atm'?