Information Technology Reference
In-Depth Information
To understand the benefits of H.450.3, you must first understand what happens with typi-
cal VoIP forwarding. When a call enters the network and hits a forwarded device, that de-
vice takes responsibility for the call and becomes a tandem hop in the call flow. That
means that the voice traffic now forwards through the IP phone that forwarded the call.
This can cause quality problems if the device that forwarded the call is a large geographi-
cal distance away from the phone receiving the forwarding call. The H.450.3 standard rep-
resents a method that allows the CME router to redirect the call directly to the final
destination instead of acting as a tandem hop. Figure 7-8 illustrates this concept.
Call Forwarding without H.450.3
Key
To p i c
x1002
California
IP WAN
x1001
Texas
x1003
Florida
Call Forwarding with H.450.3
x1002
California
IP WAN
x1001
Texas
x1003
Florida
Figure 7-8
Forwarding Calls With and Without H.450.3 Standards
In Figure 7-8, the IP phone with x1002 is forwarded to the IP phone with x1003. The top
part shows the VoIP call flow without H.450.3 when x1001 places a call to x1002. Notice
that the VoIP traffic must pass through the California CME router to reach Florida. This
can cause intense quality of service (QoS) problems with the call, such as audio clipping,
distortion, and even call drops. This symptom is commonly called
hairpinning
the call.
