Cisco Systems manual SPA9000 Media Proxy, SPA9000 as a SIP Proxy

Advanced Topics in SPA9000 Administration

Technology Background

Figure 2 SPA9000 as a SIP Proxy

A

UserC

UserA

UserB

Hub/switch	IP Router (firewall)
	Broadband modem

ISP

Internet (WAN)

Interface

Internet

SPA9000

SIP Proxy with

media proxy enabled

ITSP

When a user picks up the handset in an SPA9000 Voice System, the SPA9000 collects DTMF digits from a touchtone analog telephone or the locally connected SPA900 Series IP phones. Unless the call is for a local client station, the SPA9000 system sends the full number in a SIP INVITE message to another SIP proxy server for further call processing.

To minimize dialing delay, a dial plan is maintained that is matched against the cumulative number entered by the user. Invalid phone numbers that are not compatible with the dial plan are detected and the user is alerted using a configurable tone (reorder) or announcement.

The figure also illustrates connectivity between the SPA9000 and the ITSP over the Internet. 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. Even after the SIP session is established, the SPA9000 continues to direct RTP packets between UserA and the ITSP.

SPA9000 Media Proxy

To address this possible security issue, the SPA9000 can also function as a media (RTP) proxy. This option forces RTP traffic destined for the Internet (or IP WAN) to be directed to the SPA9000, which then directs it to the remote UA. This configuration may simplify firewall configuration because the client stations do not require direct access to the Internet through the firewall.

SPA9000 Voice System Administration Guide 167