Porting the Session Initiation Protocol to IPv6

class IpAddress. • SIP messages. Socket connections receive SIP messages, which must be parsed to identify each message’s corresponding elements. The JSIP library provides several classes (SipMessage, SipUri, and SipVia, for example) that perform such parsing, but we enhanced these classes to allow parsing of strings of any IPv6 addresses included in SIP messages. • Enhanced SDP support. The original SdpMessage class can manage IPv4 addresses only when they are included in the SDP body. We modified such classes to allow them to manage IPv6 classes as well. In this case, we reused the IpAddress class instead of the original String attribute of the SdpMessage class (see Figure 1). • UA support. The classes JSIP provides for supporting UA creation must also manage IP addresses. The same code might work over different IP stacks, so the UA must identify which IP address to use depending on the underlying network; it then fills in the corresponding field with this information. We modified the class SipClient by adding code for detecting the stack type and generating the proper IP address for completing the connection. These modifications concentrate on a few classes (SipUri, IpAddress, and SdpMessage) and the code that deals with the type of IP network inside the JSIP library. Deploying SIP Over Heterogeneous Networks To validate our approach with the modified JSIP library’s IPv4 and IPv6 capabilities, we created a test scenario (shown in Figure 2) with a simple audio-stream application that sent previously captured audio over both IPv4 and IPv6 networks using RTP packets. This let us test the feasibility of our proposed approach without dealing with the complexity of full-flagged multimedia applications. Using the JSIP library to build SIP elements facilitated this task because the SIP elements created with this library work in both network types. Nevertheless, when SIP elements are located on different types of networks, we need a suitable gateway mechanism to allow UAs to interconnect that cannot connect directly due to the underlying networks’ incompatibility. Figure 2 illustrates the test scenario, in which the streaming application client located in an IPv6 network connects to a server in an IPv4 network. IEEE INTERNET COMPUTING http://computer.org/internet/ MAY • JUNE 2003 47 Session Initiation Protocol Table 1. Code structure and effect. Element Internal Classes Methods Lines of code Effort Comments