I detect an echo problem in my voice network and after the TAC's diagnosis, they suggested me to upgrade the IOS version of my 2 Cisco Gateways 3825 because the dsp firmware was too old (4.4.708) and have echo problems. The older IOS version is 12.3(14)T7 and is in deffered state, they suggested me to upgrade my gateways to the 12.4(21) version which bring a new firmware. After the change I find that the new dsp firmware version is 4.4.29 and according to the evidence some echo troubles have been corrected. But I have a question, if the new dsp firmware version is apparently older than the initial one, does that new version have old already corrected caveats that I have to keep in mind? Should I look for another IOS version? Thanks for your answer.