Enterprise Administration > Implementing Windchill ESI > Implementing Windchill ESI in an SAP Environment > Performance Planning > Analyzing Message Numbers and Sizes > Rendezvous Interface
  
Rendezvous Interface
For the Rendezvous interface, the number of messages per transaction is the sum of:
API calls per business object or subtransaction (approximately 3) multiplied by the number of business objects or subtransactions in the ESIResponse message.
ERP API results (approximately 3) multiplied by the number of business objects or subtransactions in the ESIResponse message.
The size of each API message is typically quite small, containing attribute data for a single business object.
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Windchill ESI services will create as many transactions as there are ERP instances in a given release. Thus, the number of messages per release (or publish operation) will equal the number of messages per transaction multiplied by the number of transactions that are created for the release.