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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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S<strong>IP</strong> protocol stack<br />

Figure 20-3 depicts the overall architecture for the S<strong>IP</strong>-based protocol stack.<br />

Audio<br />

G.711, G.723.1, etc.<br />

RTP<br />

R<strong>TCP</strong><br />

Figure 20-3 S<strong>IP</strong> protocol stack<br />

System Control <strong>and</strong><br />

User Interface<br />

S<strong>IP</strong><br />

Transport Layer (SCTP, UDP or <strong>TCP</strong>)<br />

Network Layer (<strong>IP</strong>)<br />

Data Link Layer<br />

Physical Layer<br />

SAP<br />

SDP<br />

RSVP<br />

In a S<strong>IP</strong> environment, voice calls are carried using RTP. S<strong>IP</strong> relies on additional<br />

st<strong>and</strong>ards to provide signaling <strong>and</strong> control functions. These include:<br />

► The G.7xx series of protocols provide basic CODEC functions, as described<br />

in 20.1.2, “Vo<strong>IP</strong> functional components” on page 726.<br />

► The Real-time Transport Protocol (RTP) allows the receiver to detect packet<br />

loss. It also provides timing information that allows the receiver to<br />

compensate for variable packet arrival times (that is, jitter). Details of RTP are<br />

in RFC 3550.<br />

► The Real-time Control Protocol (R<strong>TCP</strong>) accompanies RTP, <strong>and</strong> is also<br />

defined in RFC 3550. It obtains the network status <strong>and</strong> QoS feedback<br />

information. R<strong>TCP</strong> provides the function to manage real-time delivery of<br />

packets.<br />

Chapter 20. Voice over Internet Protocol 735

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