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Beginner

MLPPP, 5 T1s, Interleave/Fragment or not?

Hi I have an old Cisco 3640 with 5 T1s in a MLPPP bundle.

I've been reading around that with the BW of 5 T1s, I don't need to turn on Interleaving and Fragmentation.

However, there is VoIP traffic going over this bundle as well, I do notice that occasionally I'm seeing jitter on VoIP calls.

Though the jitter seems to manifest itself when the out usage approaches 3-4Mb while the in usage is around 6Mb.

Could this be a CPU issue? Or is it most likely large packets delaying the small voip packets.

I was having more jitter when interleaving and fragmentation were turned on...

Here are relevant parts of the current config:

policy-map voip_policy

class voice

  priority 850

class voice-signaling

  bandwidth 64

class class-default

  fair-queue

interface Multilink13701

ip unnumbered Loopback0

ppp multilink

ppp multilink fragment disable

ppp multilink group 13701

ppp multilink endpoint ip 10.1.1.1

service-policy output voip_policy

interface Serial0/0

no ip address

encapsulation ppp

ppp multilink

ppp multilink group 13701

etc...

6 REPLIES 6
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Hall of Fame Master

5x T1 in MLPPP on an old tired 3640 is betting on luck  anough already, add interleaving and fragmenation, chances or success with some performance left are next to zero.

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Yeah, I was afraid of that.

What can handle 5 T1s that's fairly current short of going to a 7200 chassis?

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Upgrade to ethernet-based services, you will save money and trouble.

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Yes of course that's optimal, but at this location I cannot at the present time.

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Then keep struggling, because no matter the platform, MLPPP is the worst WAN technology of any.

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VIP Expert

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Posting

You shouldn't need interleaving/fragmentation if link bandwidth > half T1.

Try setting tx-ring-limit to minimal value on all your serial interfaces.