Failed to subscribe a node on other XMPP server over s2s communication

Hello, I am enjoying to use openfire. Thanks for the effort of developers/community.

My question is, is it possible to subscribe a pubsub node on other XMPP server ?

I succeeded to federate two XMPP servers (both openfire). However, I cannot subscribe a pubsub node  over s2s communication.

Here is test environment:

Two xmpp servers (namely server1.com and server2.com) are federated.

There is a pubsub node namely nodeOnServer2 on server2.com.

I tried to subscribe nodeOnServer2 via a JID and connection on server1.com, namely user@server1.com. But no published data received.

I succeeded to publish a data nodeOnServer2 via server1.com, and also succeeded to retrieve a data by getItem() method (smack's method).

However, I could not succeed subscribe.

I am very happy if anyone can help me. Thank you !