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____________________________________________________ DS34T101, DS34T102, DS34T104, DS34T108
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Figure 10-62. Structure of Packets with Trailer
The CRC is calculated over all packet bytes including over the trailer bytes. The transmitted bytes counter and the
received bytes counter (section
11.4.3.3) do not count the trailer bytes.
10.6.15 Counters and Status Registers
For information about counters and registers in the TDMoP block, see section
11.4.
10.6.16 Connection Level Redundancy
The TDMoP block provides optional connection level redundancy for AAL1, SAToP and CESoPSN bundles. In the
TDM-to-Ethernet direction, on a bundle basis, each packet may be transmitted once with certain headers, or twice,
each time with different headers. When transmitted twice, the packets have the same payload, same control word
and same RTP header (if used) but may have different packet headers (including layer 2, 3 and 4 headers).
For example, the chip can duplicate a bundle’s packets on transmission where the only difference between the
duplicated packets is their bundle number or their VLAN ID.
On the receive side, when two redundant streams use different bundle numbers, the chip can be configured to
receive only the packets with the first bundle number or the packets with the second bundle number.
To enable this feature, CPU software must initialize the transmit buffers of a bundle with both headers. The second
header must be located at offset 0x782 from start of the buffer and its length (in bytes) is indicated by the buffer
descriptor
Hdr2_length field (not including the RTP header length neither the control word length). By changing the
Protection_mode configuration field of the bundle, the user can choose (per bundle) whether to transmit each of the
packets once with the first or the second header, or twice, each time with a different header.
On the receive side, only the packets with their bundle number configured in the
Rx_bundle_identifier field of a
specific bundle, are forwarded. The CPU may change this value dynamically, in order to switch to the redundant
connection at any time.
On the receive side, when both streams use the same bundle number, switching from one stream to another is
almost seamless. No software intervention is needed as the payload-type machine discards the duplicated packets.
During this process the end-to-end delay may change because of different route delays and 1–2 packet of packet
loss may occur.