Periodic update comprehension of CSNP messages on ISIS protocol

Why ISIS Protocol of the CSNP messages in MA In the network environment is with the cycle update however in Peer update only once in the network environment?

The individual learns through videos and materials:

We know that ISIS's CSNP message is similar to the DBD message in OSPF, which is used to confirm whether the LSDB between each other (neighbor) is synchronized, and when the neighbor router learns from the CSNP message (OSPF-DBD) which LSP is missing from the local LSDB, At this point the router will send me a local PSNP request message, at this time my local router through the PSNP message that the neighbor is missing which LSP then I will update the missing LSP to the neighbor, but my local router update the LSP after the neighbor will not give me confirmation, and there is no confirmation mechanism. We recall that this is not the case in OSPF, and when the neighbor route sends me an LSR request, I pass the information in the LSR request to the neighbor's missing LSU, and when the neighbor receives my LSU, it returns me a lsack message. This time I was locally able to confirm that my neighbor had received my LSU message, But this is not the case in the ISIS Protocol's MA network environment, and we can understand that it is unreliable to update the LSP in ISIS, in order to increase reliability in the ISIS protocol through the CSNP cycle update.

CSNP function is to be able to or know each other's lsdn in the LSP is synchronized, through the first interaction CSNP message then my local router to you updated the LSP this time normally each other's lsdb should be synchronized, If the cycle update csnp in the process I found that we still did not reach the synchronization state, we think just now I gave you the LSP you did not successfully receive this time I will send you resend.

This is not the case in the peer-to network environment, when you send the LSP after the successful reception of the neighbor will be a confirmation through the PSNP. So there's no cycle update for CSNP.

The above theory can be analyzed by grasping packet

Periodic update comprehension of CSNP messages on ISIS protocol