We recently upgraded to the new Cisco CallManager Express (CME) version 8.8 so that we could try out the new 8945 phones for point to point video.  Immediately after the upgrade Exchange no longer answered calls to voicemail or auto-attendants and instead gave us a busy signal.  In reviewing the Exchange logs I found the following error:

Event ID: 1021
Source: MSExchange Unified Messaging
Task Category: UMCore

The Unified Messaging server rejected an incoming call with the ID “2ACCC6EF-E2F911E0-9286A0ED-1857E3E@10.1.1.22“. Reason: “The Unified Messaging server received “INVITE” request with an invalid SIP header “USER-AGENT” with value “”.”

That seemed strange that the USER-AGENT field would be “. so I created a sip-profile and modified the header to be “CME” instead.

router(config)#
router(config)#voice class sip-profiles 1
router(config)#request INVITE sip-header User-Agent modify “.” “CME”

then I applied the profile under “voice service voip”

router(config)#voice service voip
router(config)#sip
router(config)#sip-profiles 1

Now the calls go through.  Here is the entire SIP config:

voice service voip
cti csta mode basic
no cti shutdown
allow-connections sip to sip
no supplementary-service sip moved-temporarily
no supplementary-service sip refer
fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback none
sip
session transport tcp
header-passing
registrar server expires max 300 min 60
sip-profiles 1
!
voice class sip-profiles 1
request INVITE sip-header User-Agent modify “.” “CME”