ND SatCom SKYWAN IDU 7000, Manual

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2010-10-26 Network Design and Engineering Guide 21
General Carrier Design
Data and Voice Networking Overview
On the receiving station the whole procedure is reversed:
- Demodulation and decoding,
- Reassembly of fragments into SLL frames,
- Replacing of SLL by Ethernet headers (for IP packets),
- Forwarding of Ethernet (or FR frames) over the Ethernet (or serial) port.
Voice connections
The requirement for data traffic is generally specified in terms of a required data rate. For voice
traffic usually the required number of (bidirectional) voice connections is specified. To translate
that into a data rate requirement it is necessary to know the data rate per voice call. This rate
depends on the codec rate of the used voice codec (typically in the range 6-64 kbps) and the
additional overhead due to the applied network protocol. In
Sky WAN
®
networks two different
network technologies are used:
- Voice over IP using IP/UDP/RTP encapsulation of the voice payload (VoIP).
- Voice over Sky WAN
®
FAD using the Frame Relay functionality (VoFR).
The data networking overhead for both options is quite different, leading to a higher bandwidth
consumption for VoIP calls compared to VoFR calls: The VoIP overhead (IP/UDP/RTP) sum-
marizes to 40 Bytes whereas the VoFR overhead is 8 Bytes.
Since the typical voice payload per packet is in the range of 10-40 Byte, the VoIP overhead
represents a large fraction of the required data rate. This may be reduced by the Robust Head-
er Compression (ROHC) technique. A detailed description of this procedure will be given in a
subsequent section of this Guide.
Figure 2-3 Voice over SkyWAN
®