Is it not possible to sent Imessage from both devices "simultaneously"?
Perfectly possible (if you use both hands :-).
Seriously, I occasionally have the same conversation going on an iPhone, an iPad, and a Mac. They all receive the incoming messages, and I can type on any of them, switching at will.
I'm sorry. Your constellation of symptoms confuses me. You said the iPad cannot send when the Mac is turned off, then you said the iPad cannot send messages at the same time the Mac is sending and does not receive the Mac's messages. When can the iPad send messages? Only when the Mac is powered on but not running the Messages app?
Using FaceTime http://support.apple.com/kb/ht4319
Troubleshooting FaceTime http://support.apple.com/kb/TS3367
The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting
Troubleshooting FaceTime and iMessage activation
iOS: FaceTime is 'Unable to verify email because it is in use'
Using FaceTime and iMessage behind a firewall
iOS: About Messages
Set up iMessage
iOS 6 and OS X Mountain Lion: Link your phone number and Apple ID for use with FaceTime and iMessage
How to Set Up & Use iMessage on iPhone, iPad, & iPod touch with iOS
Troubleshooting iMessage Issues: Some Useful Tips You Should Try
Setting Up Multiple iOS Devices for iMessage and Facetime
FaceTime and iMessage not accepting Apple ID password
Unable to use FaceTime and iMessage with my apple ID
FaceTime, Game Center, Messages: Troubleshooting sign in issues
How to Block Someone on FaceTime
My Facetime Doesn't Ring
To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8
How to Send SMS from iPad
You can check the status of the FaceTime/iMessage servers at this link.
Here is the whole story for clarification!
On Friday I upgraded the Mac to iosx 10.8.4.
Then I had to buy a new airport as this new version would not recognize old devices.
New airport was bought and installed
On Tuesday Ipad would not send imessage (mac was turned off )
On Wednesday I happenend to have both devices turned on and this is when I noticed taht I could not uses Imesssage from both devices, only from mac.
On thursday Ipad would not send messages when mac was turned off, then I turned Mac on and I was able to send messages.
Thanks for your patience!
Try working through the applicable articles among those Texas Mac Man posted. Maybe one of those will help.
If they don't help, here are some observations/questions based on your time line:
* Your old AirPort base station should have continued to work as it had even if you could no longer configure it with the new version of AirPort Utility. However, you may find you like the new base station better.
? Was Tuesday the first time you tried sending iMessages after installing the new base station?
? Was there any time between installation of the base station (over the weekend?) and turning the Mac off on Thursday that the iPad was able to send iMessages?
* I am mystified as to why turning on the Mac or sending iMessages from it should have an adverse effect on the iPad. I suspect an unrelated cause that just happened at the same time.
? Does turning the Mac back on cause the iPad to stop being able to send iMessages?
I will look in details into the links provides by texas man.
So far it did not help.
The apple store i went to explained me the new version installed on the mac - iosx 18.8.4- does not recognize the old airport this is the reason why i bought a new one.
and the new one works.
At least one problem solved but now this new one!
The installation done i have sent an imessage from the ipad and the mac was turned on.
Tuesday was indeed the first time then when the mac was turned off.
Imessage has never worked since the the network with the old airport was not recognized!
I have just tried again and i still face the issue!
I thought it might also have been due to the installation of the new version. No upgrade for the ipad is offered when connecting to itunes!
Thanks for your time!