MLPPP, 5 T1s, Interleave/Fragment or not?

[jlamanna1]

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...

[paolo bevilacqua]

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.

[jlamanna1]

Yeah, I was afraid of that.

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

[paolo bevilacqua]

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

[jlamanna1]

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

[paolo bevilacqua]

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

[Joseph W. Doherty]

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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.