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PPP Multilink over ISDN multi BRI

PPP Multilink over ISDN multi BRI

PPP Multilink over ISDN multi BRI


It s been a while since using isdn dialers in a router config.
I have a point to point ip-link, encapsulated in PPP, that runs from one router to the other over 4 BRI.
I configured the multilink as to reduce latency while providing a bigger BW to the dataflow from one router to the other and vice versa.
The call setup is always from Router 1 to Router 2, configuration is pretty standard, no ip addr on the BRI being members of a dialer-pool, isdn point to point setup etc...

a pice of config:

mulitilink bundle-name authenticated
interface BRI0/0/0
no ip address
no ip redirects
no ip proxy-arp
encapsulation HDLC
dialer-pool member 1
dialer idle-timeout 0
isdn switch-type basic-net3
isdn point-to-point setup

interface BRI0/0/1 , 0/0/2 and 0/0/3 have the same config.

interface dialer1
ip address
mo ip redirects
no ip proxy-arp
encapsulation ppp
load-interval 30
dialer pool1
dialer idle-timeout 0
dialer string number1
dialer string number2
dialer string number3
dialer string number4
dialer load-threshold 1 either
dialer-group 1
no cdp enable
ppp multilink
ppp timeout multilink remove 1200

This conf works fine, each B-channel per BRI is opened and call setup (q931) is flawless.
ping with size 1400 Bytes and a repetition of 20 is around 1000 to 1100 msec average roundtrip and stable up to 4 channels(BW 256Kbps)
showing the dialer interface dialer 1 looks good, no drops etc...
Once the third BRI opens up, the roundtrip stays the same but there is some packet loss showing up.
As soon as the fourth BRI opens up the roundtrip gets higher and climbs up to 1300 to 1500 msec roundtrip and an averge packet loss of 10-15 %.
Though adding up to 512Kbps, the link is too slow to let the distant end user work comfy with enterprise mail etc...

We are looking to migrate to other media for this router combination I still am very intrigued by why this is happening.
Any thoughts out there?

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