# Revision history [back]

### Sessionless signals and About

There's something that puzzles me on the way About and the sessionless signals work :

The AboutServer uses sessionsless signals to announce metadata about an Alljoyn application. This announce signal is only 'sent' on startup and when adding / removing a bus object, yet an AboutClient that comes after the announcing application still see the announcement.

As far as I understand, that means :

• that sessionless signal are not really sent but also somehow cached (probably for the duration of the TTL, and on the emitting side) so that late joiners can still receive them.
• that the actual discovery of the alljoyn node is not made with about but with other mecanisms in the core (mdns / NGNS / findAdvertiseName) and that an alljoyn node fetches existing sessionless signals on any nodes it discovers.

Is that correct ?

Now in the docs, I read :

Each sessionless signal will replace the previous one. If the receiving side has not had a chance to pull the data, it will be lost and not transmitted to the other side.

Does that mean that any sessionless signal my application emits will replace the annouce signal, and thus make my application non-discoverable (unless and until I manually call annouce again) ?

I've some stanges issues with applications that stop being visible with About and I cannot figure out the exact condition that makes this happens. Any information about the underlying mecanism and especially sessionless signals (documention is really missing here) would be appreciated !

thanks