MT92210 Zarlink Semiconductor, MT92210 Datasheet - Page 76

• Manufacturer Part Number: MT92210
• Description: 1023 Channel Voice Over ip (VoIP) Processor
• Manufacturer: Zarlink Semiconductor

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7.4
In the case of an connection carrying PCM or ADPCM, the packet assembly module uses the TX connection
structure to determine how the bytes should be assembled, as well as all the different headers needed by the
multiple protocols (Link, IP, UDP, RTP). The two fields that will determine the shape and size of the packet payload
are the Total number of frames, that determines how many payload samples per channel will be carried by the
packet, and the Number of Bearers, which tells how many xxPCM bearers will be included in the packet.
The total amount of payload samples in the packet will be Total number of frames multiplied by Number of Bearers.
This is converted into bytes according to the compression rate.
7.4.1
The first word of the structure contains the Next TDM write pointer on which the next packet can be assembled.
This is used when receiving a packet assembly event from the queue to determine if the packet assembly
requested is valid or not. If the current TDM pointer is greater or equal to this value, then the event is valid;
otherwise, it is ignored. The Initialized bit is used to detect the start-up of the connection: when a packet assembly
event is read and the Initialized bit is '0', the first packet will be discarded, and the Next TDM write pointer will be
initialized to the current TDM pointer + Next TDM write pointer. This means that this field should be initialized as an
Packet Type
UDP Header Start
Header Length
Minimum Total Packet
Length
Link Header Length
8P
802.3 Length Adjust
802.3 Length Position
ID v6 Position
PCM Packets
Next TDM Write Pointer
Field
Table 27 - Fields and Description (continued)
This field indicates the type of the first header present in the packet. This field
is only used when the RTD is set to sent packets to the packet identifier.
“0000” = LLC Header;
“0001” = PPP Header;
“0010” = IP Header;
“0011” = MPLS Unicast Header;
“0100” = MPLS Multicast Header;
“0101” = MPOA Tag;
“0110” = LANEv1-Ethernet/802.3 Header;
“0111” = UDP payload (with or without RTP contained in payload);
others = reserved.
Points to the first dword of the UDP header, relative to header word 0.
Header length in dwords, includes all Header Words.
Minimum desired packet length including headers+48, in bytes. Hardware will
pad the payload with 0’s up to this length as required, e.g. if a minimum
Ethernet encapsulated packet of 46 bytes is desired, and the Link Header is
14 Bytes, this value should be set to 46+14+48=108. When no minimum
packet length is desired, this field should be set to 0.
This field is the byte counter of all Header words, less the initial padding bytes
if there were any.
802.3 Present. When ‘1’, an 802.3 header requiring a Length is present.
This value is subtracted from hardware calculated packet length to obtain
correct 802.3 length. The hardware calculated packet length = Payload +
Header Words - Padding.
Position in bytes of the first byte of the 802.3 Ethertype/Length with respect to
Header word 0.
Points to the dword of the IPv6 header, relative to Header Word 0, in which the
packet identification field will be written.
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