Cisco CUCM NTP documentation/requirements

Question

Hello all,
Just wondering about the "actual" NTP clock Stratum version requirements when
installing Cisco CUCM. As the three sources below show varying results;
So first we have the install guides;
Note
Cisco   recommends that you use an external NTP server to ensure accurate   system time on the first node. Ensure the external NTP server is stratum   9 or higher (meaning stratums 1-9). Subsequent nodes in the cluster   will get their time from the first node.When you are installing   Cisco Unity Connection on a virtual machine, you must specify an   external NTP server.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/install/8_6_1/install/cmins861.html#wp804989
Then the SRND;
Unified CM automatically synchronizes the NTP time  of  all subscribers in the cluster to the publisher. During  installation,  each subscriber is automatically configured to point to an  NTP server  running on the publisher. The publisher considers itself to  be a master  server and provides time for the cluster based on its  internal  hardware clock unless it is configured to synchronize from an  external  server. Cisco highly recommends configuring the publisher to  point to a  Stratum-1, Stratum-2, or Stratum-3 NTP server to ensure that  the  cluster time is synchronized with an external time source.
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/netstruc.html#wpxref14097
And finally the NTP  White Paper;
For Cisco Unified CallManager Versions 5.0 and later:
– Manual configuration of the ntpd.conf file is not allowed.
– Cisco  Unified CallManager prompts the administrator to specify the  external  NTP server at publisher installation and automatically  populates the  ntpd.conf file on the publisher server.
– The ntpd.conf files of all other cluster servers are automatically configured to point to the publisher as the NTP source.
• Configure the publisher to point to a traceable stratum 1 clock source.
•   Configure network latency between the publisher and the dedicated  clock  source so that it is within 40 milliseconds round-trip time  (RTT).
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/vcallcon/ps556/prod_white_paper0900aecd8037fdb5.html
Thanks for any light you can shed on this.
Cheers!
Rob
"Spend your life waiting,
for a moment that just don't come,
Well, don't waste your time waiting" 
-Springsteen

Answer 1

Leo, 
Do you have reference for this. 
Still murky waters:
In 9.1 release Stratum 5 no longer enforced. 
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/rel_notes/9_1_1/CUCM_BK_RD7D4696_00_cucm-release-notes-911a/CUCM_BK_RD7D4696_00_release-notes-for-cisco-unified_chapter_0110.html
External NTP Server Requirements
The procedure "Set up first node" has been updated to remove the requirement that the external NTP server be Stratum 5 or higher. When you configure the first node, Cisco recommends configuring the publisher to point to a Stratum 1, Stratum 2, or Stratum 3 NTP server to ensure that the cluster time is synchronized with an external time source.