[c-nsp] Multilink PPP throughput instable

[tony kam]

Hello,

The topology is:

1. 2610XM connects to 2650XM with 2xE1 links with PPP multilink.
2. Same 2650XM connects with another 2610XM with another pair of E1 links.

Results:
1. Single FTP session in either direction can pump the bundle to a stable throughput around 3.9M.
2. Dual FTP sessions in mixed direction (put and get together) can only get a variable throughput from 3.1M to 3.9M.

All routers CPU are below 30%.

Any idea why it can't get stable throughput in mixed direction? 
Is it due to MLPPP overhead?
Is "no ppp multilink fragmentation" helpful in this case?

Thanks,
Tony



Below is the extract of the config.

2610XM (both the same)
----------------------
interface Multilink1
 ip address 15.63.232.1 255.255.255.252
 load-interval 30
 no cdp enable
 ppp multilink
 ppp multilink group 1
!
interface Serial0/0
 bandwidth 1984
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 load-interval 30
 no fair-queue
 no cdp enable
 ppp multilink
 ppp multilink group 1
!
interface Serial0/1
 bandwidth 1984
 no ip address
 no ip redirects
 no ip proxy-arp
 encapsulation ppp
 load-interval 30
 no fair-queue
 no cdp enable
 ppp multilink
 ppp multilink group 1
!

2650XM
------
interface Multilink1
 ip address 15.63.231.2 255.255.255.252
 load-interval 30
 ppp multilink
 ppp multilink group 1
!
interface Multilink2
 ip address 15.63.232.2 255.255.255.252
 load-interval 30
 ppp multilink
 ppp multilink group 2
!
interface Serial0/0:0
 bandwidth 1984
 no ip address
 encapsulation ppp
 load-interval 30
 no fair-queue
 ppp multilink
 ppp multilink group 1
!
interface Serial0/1:0
 bandwidth 1984
 no ip address
 encapsulation ppp
 load-interval 30
 no fair-queue
 ppp multilink
 ppp multilink group 1
!
interface Serial1/0:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 2
!
interface Serial1/1:0
 no ip address
 encapsulation ppp
 no fair-queue
 ppp multilink
 ppp multilink group 2
!