Multiple drops similar spacing

I have another broadband connection that I am monitoring, it has a strange pattern to it with evenly spaced drops Tues 12/02/13, every day is the same as this.

This is a connection at one of the companies shops, we sometimes have trouble dialing into the tills at this shop.

What could cause this? I do believe that the wiring in this building is rather old.
Thanks

Which ISP and router is involved?

Looks most like something every 15 minutes happens, e.g. a short burst of noise from some bit of kit, or you are receiving/sending a small file at regular intervals,

Hi,

The ISP is ZEN and it is a Draytek 2800 Series router. I do not believe there is any files being sent, the connection is mainly for the shop staff to send there sales info at the end of the day and for the head office to update the tills.

Thanks

The ISP has nothing that would create that sort of regular blip.

On the Draytek 2800 it does not ring any alarm bells, do you use the same router elesewhere and not have this issue?

I have checked one of the other shops that uses the same router and it does not have this issue, it is only 200m along the road from the other shop and it has a very stable connection.
Other Shop

Could bad internal wiring cause a fault with blips?

Bad internal wiring would not cause such a regular pattern.

It is something that is working on a timer basis.

my first guess would have been fridge/ freezer

Do you have a shop alarm system with a phone line connection not connected via a filter?
Every 15 or so mins, it connects, pulls the line down.
I had a neighbour with a home alarm system doing something similar... took me a couple of hours to narrow it down.

Failing that, make a local (free??) call on the line for 20-25mins just after a failure and listen for any 'obvious' noise or clicks. Won't be any good if it's noise outside audible, but you should be able to detect something.

15mins is too long a time constant to be a capacitive type effect...

Look for all things in the shop that are on timers or cyclic.
(Someone suggested a freezer) but that wouldn't be perfectly 15mins on/off (at least one would hope not).

Definitely an interesting one... rather you than me !!!
You'll be chuffed when you find it.

Chris

have you checked the dial on demand settings and changed them to 0

In reply to a post by myst12:

What could cause this?

How did you get on with this problem?
The engineer in me is curious as to what you possibly found out?
Hope it's all fixed now !!