Study Group 15 has approved a new recommendation G.769 (IP-CME; Circuit
multiplexing equipment optimised for IP-based network) in order to ensure interoperability of the IP-based CME (IP-CME) and its wide applicability.
We inform the IETF SIGTRAN Working
Group that the start of discussion
regarding schemes in order to realize the transmission of call
signaling messages over IP-based networks in G.769.
1. Circuit
Multiplication Equipment optimised for IP-based networks
A technique of multiplexing a plurality of voice signals of
GSTN into a single IP packet stream can be used for a route that
is shared by the voice streams. It can be recognized that the IP-based voice
transmission technique can be applied to realize a new type of CME, namely, IP-CME as shown in figure 1.
Note: The SS7
signaling is transmitted via SS7 networks in GSTN in this configuration.
Fig.1 Simplified view of
configuration of the IP-CME
2. Advantages of IP-CME
IP-CME solution has following advantages for example.
1) Reducing overhead in VoIP packet headers
Typical VoIP packets
have IP/UDP/RTP header
followed by a payload. It should be noted in this context that the IP/UDP/RTP
header is normally 40 bytes long and thus, when transporting a small payload, the
efficiency of the bandwidth used for the voice stream becomes very low.
2) Reducing processing loads of IP packet routing devices
The packetizing voice streams on a frame-by-frame
basis leads to generating a large number of shorter packets and may result in an
undesired processing load stress on the IP routing devices in the network.
3) Minimizing the
degradation in voice quality
The interleaving effect based on multiplication processing of
IP-CME makes no attempt to
replace a lost portion of the voice signal. Instead it attempts to hide it by
reducing the impact. For example, divide 200 byte portion into four 50 byte
quarters and rearrange as shown in figure
2. If one gets lost we still have 3/4 of each
portion. The lost part signal is unlikely to be noticed and there is no
additional traffic.
Fig.
2 Interleaving of
the voice signals by IP-CME
3. Transmission schemes of SS7 signal over IP-based network for IP-CME
Following two options in order to transmit the SS7 signalling messages are provided at chapter 8.6
in G.769.
Option 1: SIGTRAN transmission -IETF RFC 2719, IETF RFC 2960
Option 2: Clear channel (64kbit/s) transmission
In this liaison, we provide following three protocol
configurations based on the SIGTRAN implementation that is Option 1. There are several alternatives for
transmission schemes of SS7 signalling for IP-CME. The connection configuration
of the system is shown in figure 3.
Fig.3
Connection
configuration of IP-CME
1) Configuration 1
2) Configuration 2
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MTP3
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MTP2
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M2PA
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MTP1
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SCTP
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IP
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MTP3
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M2PA
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MTP2
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SCTP
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MTP1
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IP
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Note:
IWF: Interworking Function.
M2UA: It provides the
services of MTP2 in a client-server situation.
M2PA: It provides the services of MTP2 in a peer-to-peer situation.
Attachment: COM 15 – D 711 –
E “Transmission schemes of SS7 Signaling optimised for IP-CME”.
Attention: Some or all of
the material attached to this liaison statement may be subject to ITU
copyright. In such a case, this will be indicated in the individual document.
Such a
copyright does not prevent the use of the material for its intended purpose,
but it prevents the reproduction of all or part of it in a publication without
the authorization of ITU.
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