SRX110 VDSL Configuration pp0.0 down inet

Hi,

I'm new to configuring Juniper products, I know my way around Cisco products reasonably well, certainly not a pro but not a beginner. 

I've brought an SRX110H-VA to get into Juniper and I'm attempting to replace my Cisco router on my VDSL line with the SRX.

I've followed the VDSL configuration guide for what I believe is the correct settings:

https://www.juniper.net/documentation/en_US/junos/topics/example/vdsl2-pim-security-interface-configuring.html

CHAP authentication and negotiated IP.  The Cisco and talktalk supplied router both use chap and negotiate the IP address so I believe this is correct.

However when I use the show interfaces terse command the pp0.0 interface is showing as "up down inet"

pp0.0                   up    down inet

Can anyone point me in the right kind of direction?

Below are the vdsp commands I've configured:

pt-1/0/0 {
vdsl-options {
vdsl-profile auto;
}
unit 0 {
encapsulation ppp-over-ether;
}
}
pp0 {
unit 0 {
ppp-options {
chap {
default-chap-secret "xxxxxxxxxxxxxxxxxxxxx"; ## SECRET-DATA
local-name "xxx@yyy.com";
}
}
pppoe-options {
underlying-interface pt-1/0/0.0;
auto-reconnect 10;
client;
}
family inet {
negotiate-address;
}
}
}

Any assistance would be greatly appreciated

Many Thanks,

Tom