unexpected ISDN Dialup from 801 to 2620

[pnoo]

Configuration: several 801's dialing in on 2620 with PRI module.
Problem: With no expected traffic, 801's dialup every 15 minutes during 23 minutes with interval of 2 minutes.
So let's say unexpected dialup starts at 13:00 until 13:23 (2 minutes up, two minutes down).
Unexpected dialup starts again at 13:38 until 14:01 (2 minutes up, two minutes down).
Does anyone have a solution to quit this dialup.
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Configuration 801:
Using 1500 out of 8077 bytes
!
version 12.1
no service pad
service timestamps debug uptime
service timestamps log uptime
service password-encryption
!
hostname XXXXXX
!
enable password 7 XXXXXX
!
username XXXXXX password 7 XXXXXX
!
!
!
!
ip subnet-zero
!
ip dhcp pool 1
network 192.168.3.0 255.255.255.0
default-router 192.168.3.1
!
no ip domain-lookup
isdn switch-type basic-net3
!
!
!
interface Ethernet0
description connected to EthernetLAN_3
ip address 192.168.3.1 255.255.255.0
!
interface BRI0
description connected to Cisco2620
no ip address
encapsulation ppp
dialer rotary-group 1
isdn switch-type basic-net3
no cdp enable
!
interface Dialer1
description connected to Cisco2620
ip address 172.1.0.2 255.255.0.0
encapsulation ppp
no ip split-horizon
dialer in-band
dialer idle-timeout 300
dialer map snapshot 1 name Cisco2620 broadcast telnumber
dialer map ip 172.1.0.1 name Cisco2620 broadcast telnumber
dialer hold-queue 10
dialer-group 1
snapshot client 15 360 suppress-statechange-update dialer
no cdp enable
ppp authentication chap
!
no ip http server
ip classless
ip route 10.48.87.0 255.255.255.0 172.1.0.1 permanent
!
dialer-list 1 protocol ip permit
snmp-server engineID local 00000009020000021765156F
snmp-server location xxxx
snmp-server contact xxxx
snmp-server chassis-id JAD060100ZH
!
line con 0
exec-timeout 0 0
password 7 xxxx
login
transport input none
stopbits 1
line vty 0 4
password 7 xxxx
login
!
no rcapi server
!
!
end