This object contains a count of the number of transactions that are in progress and transactions that have reached the 'Terminated' state. It is not applicable to stateless SIP Proxy Servers. A SIP transaction occurs between a client and a server, and comprises all messages from the first request sent from the client to the server, up to a final (non-1xx) response sent from the server to the client. If the request is INVITE and the final response is a non-2xx, the transaction also include an ACK to the response. The ACK for a 2xx response to an INVITE request is a separate transaction. The branch ID parameter in the Via header field values serves as a transaction identifier. A transaction is identified by the CSeq sequence number within a single call leg. The ACK request has the same CSeq number as the corresponding INVITE request, but comprises a transaction of its own. In the case of a forked request, each branch counts as a single transaction. For a transaction stateless Proxy Server, this counter is always 0. Discontinuities in the value of this counter can occur at re-initialization of the SIP entity or service. A Management Station can detect discontinuities in this counter by monitoring the sipCommonSummaryDisconTime object in the same row.