Linksys Voice System Administration Guide 39
3
About LVS and SIP
Configuring the SPA9000 for ITSP Interoperability
Configuring the SPA9000 for ITSP
Interoperability
This chapter provides configuration details for the purpose of helping you to ensure that your
infrastructure properly supports the LVS.
• ”About LVS and SIP,” on page 39
• ”Network Address Translation (NAT) and Voice over IP (VoIP),” on page 40
• ”Firewalls and SIP,” on page 43
• ”Configuring SIP Timer Values,” on page 44
About LVS and SIP
The LVS is implemented using open standards, such as Session Initiation Protocol (SIP), to help
ensure interoperation with all ITSPs that support SIP. This section provides information about
the SIP requests and the settings that you may need to adjust on your network or your SPA9000
to help ensure interoperability.
The VoIP telephone service is coordinated by SIP requests and responses, whether the calls are
internal or external. Figure 3-1 illustrates the SIP requests and responses between client
stations in the LVS. The SPA9000 acts as a SIP proxy and establishes a session. After the session
is established, Real Time Protocol (RTP) traffic flows directly between the two client stations.
Figure 3-1 SIP Requests and Responses for Internal Calls
Likewise, SIP requests and responses are exchanged to support outbound and inbound calls
that are handled through the ITSP service. In Figure 3-2, UserA and UserB are client stations that
are registered to the SPA9000. When UserA calls UserC, the SPA9000 directs the request to the
SIP proxy at the ITSP, which is then responsible for routing the request to UserC. After the
session is established, RTP is anchored by the SPA9000.
SIP UA
SIP UA
SIP Proxy
SIP Proxy
RTP
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SIP Proxy
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