HP-UX C SIP Stack Programmer's Guide (Novembery 2007)

312 HP-UX C SIP Stack Programmer’s Guide
Using TCP Transport
The application can use the SIP Stack Transport and Resolver APIs to authorize
a connection. You can see an example of connection authorization in the
simpleConnectionReuse sample application in the the Sample Applications
chapter.
USING TCP
T
RANSPORT
RFC 3261 defines the use of TCP transport by using the transport=TCP
parameter in a SIP URL address that indicates the destination of the message.
When working with transactions or register-clients, the next hop is determined
by the Request-URI of the message. Therefore, to send a message with TCP, you
need to set the transport=TCP parameter in the Request-URI parameter of the
object.
For connection-oriented operations, the SIP Stack uses non-blocking sockets.
The result of using non-blocking sockets is that the sending of a message can be
completed after an API call has returned. For example, the call for
RvSipTransactionRequest() using TCP may return before the request message is
sent. The SIP Stack will manage the sending operation until it is completed.
USING TLS
T
RANSPORT
TLS is a security mechanism that operates on the Transport layer, on top of TCP
transport. By using TLS as a connection transport, a SIP entity can send and
receive data in a secure authenticated manner.
TLS, together with the commonly used Public Key Infrastructure certification
distribution mechanism achieves the following goals:
 Guarantees the identity of a remote computer
 Transmits messages to that remote computer in a secure
encrypted manner.
TLS uses pairs of asymmetrical encryptions keys to guarantee the identity of a
remote computer. The public key of each remote computer is published in a
certificate.
A certificate is a document digitally signed by a certificate authority that both
sides of the connection agreed to trust before the TLS connection establishment
has started. (VeriSign and Thawte are examples of such certificate authorities).
In the TLS connection establishment process, the certificate of the remote
computer is retrieved and verified and a new key and encryption algorithm is
negotiated for the specific connection.
TLS CONNECTION
ESTABLISHMENT
TLS connection establishment requires the completion of the following three
phases: