Since I had, or sometimes still have, issues with Handoff between my Mac and iPhone I investigated a lot in this drama. Their are many parts involved in getting it work which made it really hard to pinpoint where the problem is at the beginning.
So I like to share the knowledge I have now, about the involved processes and for what they are responsible for:
cloudpaird -> Daemon responsible to registers your device for Handoff and Continuity after signing in to iCloud. If you encounter one-way problems and never got the other direction working, killing this process may help it could be your device failed to register at all.
identityservicesd -> When you are logged in to iCloud this daemon enables your registered device of the current session for Handoff and Continuity. This info was obtained from my logs. Which was:
identityservicesd[2765]: [Warning] Broadcasting no devices for account IDSDAccount: 0x7f881a62ab70 [Service: IDSDService: 0x7f881a412290 [Identifier: com.apple.private.alloy.continuity.auth Display Name: Continuity Auth Topic: com.apple.private.alloy.continuity.auth Service: com.apple.private.alloy.continuity.auth Protocol: com.apple.private.alloy] Login: XXX@XXX UniqueID: XXXXX-C5XX-XXXX-A6XX-DFXXXXDF569 Account Type: Apple ID Registration: (null) Registered: YES Linked Accounts: (null)] even though we have some.
identityservicesd[2765]: [Warning] Broadcasting no devices for account IDSDAccount: 0x7f881a520470 [Service: IDSDService: 0x7f881a412bb0 [Identifier: com.apple.private.alloy.icloudpairing Display Name: iCloudPairing Topic: com.apple.private.alloy.icloudpairing Service: com.apple.private.alloy.icloudpairing Protocol: com.apple.private.alloy] Login: XXX@XXX UniqueID: XXXXX-C5XX-XXXX-A6XX-DFXXXXDF569 Account Type: Apple ID Registration: (null) Registered: YES Linked Accounts: (null)] even though we have some.
There were some other interesting reverse-DNS style names I ommit here for the sake of cleanliness.
So killing this one can also help. My problems with identityservicesd have been resolved after resetting my login keychain.
sharingd -> Responsible for Handoff advertising and scanning. Check your logs for "Starting Handoff advertising" if you only see "Stopping Handoff advertising" Re-enable "Allow Handoff between your Mac and iDevices" in System Settings. If that doesn't help. Kill it. It is also responsible for AirDrop between iOS and OS X aka BTLE sharing. If AirDrop doesn't work this is almost the failing process.
imagent -> Agent responsible for SMS relaying. If you have problems receiving the code on your Mac. Then you probably see this in your log
imagent[587]: [Warning] ********** We received an imcomming pin code alert from a non SMS Device
right after tapping on your iPhone to activate message forwarding which is a great error. Thanks Apple for being so specific and saying an iPhone is a non SMS device. But killing this process and trying again a few times should fix your problem.
So hopefully you have some luck and get your features working until Apple fixes all of that and stability improves which each new release of OS X and iOS.