MT92210 Zarlink Semiconductor, MT92210 Datasheet - Page 70

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

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boundary. The padding bytes will be ignored when the packet is transmitted on the bus. The Header Length is in
dword, including the padding octets.
7.3.3
The Packet Type indicates with which header packets on the connection begin. The values are: “0000” = LLC,
“0001” = PPP, “0010” = IP, “0011” = MPLS Unicast, “0100” = MPLS Broadcast, “0101” = MPOA, “0110” =
LANEv1/Ethernet, “0111” = Application data. The most exceptional type is 7, because in this mode no IP or UDP
headers are contained in the packet, meaning that several fields calculated by the chip, like IP lengths, UDP
checksum, and others, do not need to be calculated.
7.3.4
The Identification Counter Source Address field is used when a valid Identification value must be generated in the
IP header. This is always the case in IPv4 and sometimes the case in IPv6 to allow transparent conversion between
IPv6/IPv4 networks. The Identification value must be incremented for each packet that is transmitted. However,
because CPU-generated packets must also use the same pool of identification values, a mechanism is put in place
to allow the two to share it. Up to 2
connection, when it transmits a packet, uses the current value of the identification indicated by Identification
Counter Source Address and increments it by 1 after having transmitted the packet. The CPU may also access
these values in an uninterrupted way to seize values for its own packets (see the identification_seize registers for
more information on this mechanism). The IDentification Enable bit indicates if these identification values should be
generated. The ID v6 Position points, in a relative way to header dword 0 within the header structure, to the dword
in which the identification field is contained.
7.3.5
The UDP Header Start indicates how long the IP header is (in dword) and where the UDP checksum must be
inserted in the packet. In the word that would contain the UDP checksum, a partial checksum must be written that
contains the one's complement sum of the IP source and destination addresses, as well as the protocol (11h,
meaning UDP). This is necessary because, in IPv6, the UDP checksum is not calculated on the IP destination
address as indicated in the IP header, but on the final destination address, which may be contained in extension
headers.
7.3.6
The Timestamp Offset is a value that must be added to the generated RTP timestamp in the packet. Timestamps
are generated differently in PCM, HDLC and CPU packets. This offset ensures that an outside observer cannot
predict the timestamp; this offset should be set to a random value when the connection is initialized.
7.3.7
The Sequence Number is incremental and is incremented and generated for all packets regardless of their source.
This means that HDLC and CPU packets that generate an RTP header will have their Sequence Number thrown
out and replaced by the one generated by this structure. The Sequence Number Insert bit indicates whether or not
the sequence number will be inserted by the chip for HDLC and CPU-sourced packets. If this bit is '0', then the
sequence number coming from the packets will be kept. Note that in this case, no PCM packets can be generated
on this connection (i.e. ALL sequence numbers will be externally generated).
7.3.8
The Transmitted Packet Count is a 16-bit counter indicating the number of packets that have been generated on
this connection since its startup. The Transmitted Octet Count is a 32-bit counter of the number of payload bytes
generated in packets on this connection. This only includes payload, but it will also include any RTP headers
present in CPU or HDLC packets that are seen by the system as payload. These two fields allow good diagnostic of
the connection’s bandwidth on IP.
For RTCP support and diagnostics, each time a packet is transmitted, the first 12 bytes of the packet payload (in
the case of HDLC/CPU packets), or the first 12 bytes of RTP header for PCM packets, are copied into external
memory. For HDLC/CPU channel carrying RTP, the first 12 bytes will represent the mandatory fields of the RTP
Packet Type
Identification Counter Source Address
UDP Header Start
Timestamp Offset
Sequence Number
Transmitted Packet Count
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identification values can be contained in external memory, and each
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