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IXP1200 Network Processor Family ATM OC-3/12/Ethernet IP Router Example Design
40 Application Note
Modified on: 3/20/02,
4.4.2 DRAM Data Buffer Format
Packet payloads are stored in DRAM data buffers. Depending on if the data was received on an
ATM or Ethernet port, the payload will land in a different place within the data buffer..
Figure 29. Buffer Descriptor Format for Ethernet Transmit Destination Port
3
1
3
0
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9
2
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2
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2
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0
9876543210
0
1 RCV_PORT FL_ID START_BYTE END_BYTE ELE_COUNT
2-1
3
Entry Description
RCV_PORT Receive Port
FL_ID Free list ID
START_BYTE Frame start location in the buffer (zero-based)
END_BYTE
Number of bytes in the last MPKT - minus 1 (e.g. 0 means 1 byte)
ELE_COUNT Number of 64-byte MPKTs in packet
Figure 30. DRAM Data Buffer Format - 12 Byte Offset (Received by ATM)
0123456789
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0
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1
1
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1
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1
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1
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1
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1
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1
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1
9
2
0
... Bytes ->
ATM
Header
LLC/SNAP IP ... IP Pad AAL5 Trailer
Figure 31. DRAM Data Buffer Format - 6 Byte Offset (Received by ATM, Transmitted by
Ethernet)
0123456789
1
0
1
1
1
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1
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1
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1
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1
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1
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1
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1
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0
... Bytes ->
Enet Dest Addr Enet Src Addr Typ IP ... IP
Figure 32. DRAM Data Buffer Format - 6 Byte Offset (Received by Ethernet, Transmitted by
ATM)
0123456789
1
0
1
1
1
2
1
3
1
4
1
5
... Bytes ->
LLC/SNAP IP ... IP Pad AAL5 Trailer
Figure 33. DRAM Data Buffer Received by Ethernet
0123456789
1
0
1
1
1
2
1
3
1
4
... Bytes ->
Enet DstAdr Enet SrcAdr TYP IP ... IP