# Revision history [back]

When messages are being transmitted on a topic , is it necessary that all these messages are of same message type

Yes.

When messages are being transmitted on a topic , is it necessary that all these messages are of same message type

Yes.Yes. In fact, it's enforced.

When messages are being transmitted on a topic , is it necessary that all these messages are of same message type

Yes. In fact, it's enforced.

Edit:

will md5 sum remain same on a topic ?

yes.

or does it change with each message although they are of same type?

The MD5 of a message is calculated as follows (from wiki/ROS/Technical Overview - Message serialization and msg MD5 sums):

For reference, this MD5 sum is calculated from the MD5 text of the .msg file, where the MD5 text is the .msg text with: