Initially the Internet has been going down once a month toward the end of the month. Now it is happening more frequently but still during the 5 pm hour. Most recently was today (10/3/11). It progresses to a crawl by 5:15pm but the VOIP is still functioning. Then by around 6:45 ish it starts getting progressively better. The entire network becomes pretty much inoperable - not specific to a computer, etc. - everything is affected including VPN.
I have checked with the ISP - no downages. They did say that they would change our Channel (WAN).
FW logs - dumped its logs but was previously OK.
Server logs - OK.
Dedicated Wireless T3 (3MB up/down)
SonicWALL TZ 170 STD OS - one OS release back.
Microsoft Small Business Server 2003 - all patched
MS Windows XP - all patched.
Any ideas...I'm lost on this one.