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MPEG Layer
The MPEG-2/DVB layer is specified in ISO/IEC IS 13818 “Generic Coding of Moving Pictures and Associated Audio”. The main
functionality of this layer is to transform MPTS (Multi-Program Transport Streams) into a number of SPTS (Single-Program Transport
Streams). A transport stream carrying multiple programs is in this way split into a number of ‘mini’ transport streams, each carrying
a single program. This ensures that the video can be passed through limited bandwidth links such as ADSL further down the
transmission path.
RTP Layer
The RTP layer is optional, and will add an 8-byte RTP header to the new packet. This header contains a sequence number and a time
stamp.
UDP Layer
The UDP layer is according to RFC768 “User Datagram Protocol”. The user can control the target UDP port number for the MPEG-2
stream. A configurable number of 188-byte long MPEG-2 TS packets are mapped straight into an UDP frame with no additional
overhead. The MTU for Ethernet is usually 1500 bytes. This limits the number of MPEG-2 TS packets per UDP frame to lie within 1 to
7. The following illustration shows the mapping of MPEG-2 transport streams into UDP packets.
IP Layer
The IP layer is according to RFC791 “Internet Protocol Specification”. The user is allowed access to the following IP header fields: IP
source address, IP destination address, Time-To-Live field, Type-Of-Service field. Performing static mapping between class-D IP
addresses and the corresponding Ethernet multicast MAC addresses supports limited IP Multicasting (Type 1).
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