[Home](./index.md) > [sip.js](./sip.js.md) > [ClientTransactionUser](./sip.js.clienttransactionuser.md) ## ClientTransactionUser interface UAC Core Transaction User. Signature: ```typescript export interface ClientTransactionUser extends TransactionUser ``` ## Properties | Property | Type | Description | | --- | --- | --- | | [onRequestTimeout](./sip.js.clienttransactionuser.onrequesttimeout.md) | () => void | Callback for request timeout error.When a timeout error is received from the transaction layer, it MUST be treated as if a 408 (Request Timeout) status code has been received. https://tools.ietf.org/html/rfc3261\#section-8.1.3.1 TU MUST be informed of a timeout. https://tools.ietf.org/html/rfc3261\#section-17.1.2.2 | | [receiveResponse](./sip.js.clienttransactionuser.receiveresponse.md) | (response: IncomingResponseMessage) => void | Callback for delegation of valid response handling.Valid responses are passed up to the TU from the client transaction. https://tools.ietf.org/html/rfc3261\#section-17.1 |