Compressed RTP
RTP includes a abstracts allocation and a attack portion. The abstracts allocation of RTP is a attenuate protocol
that provides abutment for the real-time backdrop of applications, such as continuous
media, including timing reconstruction, accident detection, and agreeable identification. The
header allocation of RTP is appreciably beyond than the abstracts portion. The attack portion
consists of the IP segment, the UDP segment, and the RTP segment. Given the admeasurement of the
IP/UDP/RTP articulation combinations, it is inefficient to accelerate the IP/UDP/RTP attack without
compressing it. Figure 1-7 illustrates application RTP attack cRTP over a almost lowspeed
WAN articulation (such as a T1 link), which could account from the bandwidth freed up by
compressing the IP/UDP/RTP header.
18 Authorized Self-Study Guide: Cisco Voice over IP (CVOICE)
RTP Stream
GW1
S0/0
S0/0
V GW2 V
cRTP on
Slow-Speed
Serial Links
Figure 1-7 RTP Attack Compression
The IP attack allocation consists of an IP segment, a UDP segment, and an RTP segment.
The basal 20 bytes of the IP segment, accumulated with the 8 bytes of the UDP segment
and the 12 bytes of the RTP segment, actualize a 40-byte IP/UDP/RTP header. The RTP
packet has a burden of about 20 to 150 bytes for audio applications that use
compressed payloads.
The RTP attack compression affection compresses the IP/UDP/RTP attack in an RTP data
packet from 40 bytes to about 2 to 4 bytes.
cRTP, authentic in RFCs 2508, 2509, and 3545, was developed to abatement the admeasurement of the
IP, UDP, and RTP headers.
■ RFC 2508: Compressing IP/UDP/RTP Headers for Low-Speed Consecutive Links
■ RFC 2509: IP Attack Compression over PPP
■ RFC 3545: Enhanced Compressed RTP (ECRTP) for Links with High Delay, Packet
Loss and Reordering
RFC 2509 was advised to assignment with reliable and fast point-to-point links. In beneath than
optimal circumstances, area there ability be continued delays, packet loss, and out-ofsequence
packets, cRTP doesn’t action able-bodied for VoIP applications. Another adaptation,
ECRPT, was authentic in a consecutive Internet abstract certificate to affected that problem.
RTP attack compression is accurate on consecutive curve application Frame Relay, HDLC, or PPP
encapsulation. It is additionally accurate over ISDN interfaces