Hi Krishna,
There is a slight difference between the meaning of the words triggered and incremental.
The word triggered explains when are the updates sent. In particular, triggered updates are sent as a response to an event in the network - whenever some router, link or network comes up or down. Regular updates, as opposed to triggered updates, would be updates sent in regular intervals, without reacting to any changes in the network.
The word incremental explains what do the updates contain. An incremental update contains only the change or difference from the previous update. A full update contain the entire set of routing information, including networks or elements of network that have not changed at all.
There is a special meaning for the term "triggered update" when speaking specially about RIPv2 - but that was an optional extension concerned dialup circuits, not entirely related to your question, and I don't want to cover it here.
In OSPF, the regular 30-minute refreshes of all LSAs are actually "regular" updates, at least to the meaning I have explained so far. They do not react to any network change, rather they are performed to prevent the aging of LSAs. But apart from these refreshes, in OSPF, the updates are both triggered and incremental - because the OSPF sends new LSAs when a change in the network occurs, and the information sent covers only the change, not the entire set of everything that is reachable in the network.
Please feel welcome to ask further!
Best regards,
Peter
