ASI-IP-GTW User's Manual
5.3 Overview of Video over IP
5.3.1 Protocol mapping
One of the core functions in the ASI-IP-GTW is the IP encapsulation of the MPEG-2 transport streams. The task is basically to encapsulate video packets into IP frames, using the right headers.
Figure 34 shows how the transport can be separated into various layers.
Figure 34. Protocol mapping
The MPEG-2/DVB layer is specified in ISO/IEC 13818-1.
The ASI-IP-GTW is able to handle both Multi-Program Transport Streams (MPTS) and Single-Program Transport Streams (SPTS). In the current version, the ASI-IP-GTW operates in a transparent mode. The unit will encapsulate and de-capsulate complete transport streams without changing the streams. This means that no insertion or removal of NULL packets is performed and PCR is sent transparently through the unit.
Control data are handled differently from transport stream data on the next layer. RTP as defined in RFC1889 is applied for the MPEG-2 transport stream data. Three types of protocols are used for control data. HTTP is used when the unit is configured and monitored via the internal WEB server. SNMP is used for alarm traps and simple status polling. Telnet is used for development purposes.
The transport stream data are handled according to RFC768 on the UDP layer. The operator can configure destination port for the MPEG-2 transports stream. The MTU for Ethernet is usually 1500 bytes. This limits the number of transport stream packets to embed into the outgoing Ethernet/IP frames to be between 1 and 7.
TCP is used for control data.
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