I have various customers running Cisco 7940's, 7911, 7942 and 7962 phones.  If I send an extended ping to the phone for more than 5 packets at a time, they start to drop.  There is no problems being reported with phone quality or phones dropping, its just something I noticed when running some ping tests to various phones checking for any network issues.  Is this normal?

I'm looking for Cisco documented reason for this.  Thanks!