# Sequencer-Committee Interaction

To use the Committee to post a batch of transaction data, the Sanko sequencer sends the batch and an expiration time via RPC to all Committee members simultaneously. Each Committee member stores the data in its backing store, indexed by the data's hash. Then the member signs the (hash, expiration time) pair using its BLS key, and returns the signature with a success indicator to the sequencer.

Upon collecting the necessary number of signatures, the sequencer aggregates them and creates a valid DACert for the (hash, expiration time) pair. The Sequencer then posts that DACert to Arbitrum, making it available to the Sanko software at L3.

If the Sequencer fails to collect enough signatures within a few minutes, it will abandon the attempt to use the Committee, and will "fall back to rollup" by posting the full data directly to Arbitrum. Sanko can understand both data posting formats (via DACert or via full data) and will handle each one correctly.

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