SHAPING THE FUTURE OF SATELLITE COMMUNICATIONS
8.4.1 Processing Mode 1 – Eth (IP) -> Air(TS)
The processing mode “Eth(IP)<->Air(TS)” is typically used when compatibility with
legacy receiver products or interoperability with low cost IP receivers or set top
boxes are necessary. It is also the only processing mode that can be used in
DVB-S. The interoperability comes at a cost of lower bandwidth efficiency due to
the overhead of the encapsulation of the IP packets into an MPEG transport
stream.
Typical applications of this mode of operation are the distribution or primary
distribution of IPTV, the distribution of multicast content, or the forward link of
satellite broadband access systems. It is also used when the IP content needs to
be multiplexed with traditional MPEG video content at some point in the network.
The characteristics of this processing mode are:
• Support of DVB-S and DVB-S2 single-stream modulation (multi-stream not
possible);
• The following schemes are supported depend on the Multi Encapsulation
Protocol.
MPE supports no L2 Ethernet bridge. All other protocols support all routing
schemes: L2 Ethernet bridge, L3 IP bridge and IP routing;
• Flex ACM is supported in combination with XPE encapsulation.
8.4.1.1 Multi Protocol Encapsulation
Data casting technology is available using a variety of protocols that include Multi
Protocol Encapsulation (MPE). MPE is based on the ETSI EN 301 192 standard.
The hub equipment used to perform the MPE function is referred to as an Internet
Protocol (IP) to Digital Video Broadcasting (DVB) decoder. The IP to DVB encoder
acts as a router, a gateway, an encapsulator and, in some cases, a Quality-of
Service (QoS) engine and a statistics logging device for billing purposes. The
resulting output of the IP to DVB encoding is an MPEG transport stream that is fully
compatible with the open DVB standards. Thus, the IP to DVB encoder can be
used directly, or multiplexed together with other MPEG transport streams.
MPE supports unicast, multicast and broadcast data transmissions. It offers
exceptional bandwidth efficiency in the multicast and broadcast modes of
transmission because the data is only transmitted one time to a host of receiving
clients. MPE systems can support one-way “pushing” of data, or two-way
communications.
To transmit IP Packets over DVB-DSNG or DVB-S2, the Protocol Data Units
(PDUs, i.e. IP packets) need to be processed by a device known as an
encapsulator. The encapsulator can perform the function of either a bridge or
router.
The variable-sized PDUs are first encapsulated by adding encapsulation overhead
to form a SubNetwork Data Unit (SNDU). The overhead includes a field to indicate
the length of the subnetwork data unit and an AIRMAC address to associate the
protocol data units with a link-layer flow.
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