
IBM3206K0424
Preliminary
IBM Processor for Network Resources
pnr25.chapt05.01
August 14, 2000
Cell/Packet Re-assembly (REASM)
Page 323 of 676
used (that is, F4 End-to-end). There is a 16-bit mask field in the receive LCD. A description of each bit is in 
the table below:
When an OAM cell is processed, the configuration information from the gpmtagE is used to make reassembly 
decisions like which buffer pool or receive queue to use. 
TCP/IP Receive Checksum Verification
When enabled, the IBM3206K0424 is able to perform verification of the IP header checksum and the associ-
ated protocol checksum for the user. The final checksum status is raised to the user in the packet header 
flags. This function is accomplished by the RXCRC entity using the CRC nano-program. 
To enable and use the function, several things must be done: 
 TCP/IP checksum function must be enabled in the REASM Mode Register. This enables the overall func-
tion and includes the checksum state words in the receive portion of the LCD. 
 Specify a frame type in the frameType field of the receive LCD. This field specifies an entry point into the 
checksum verification nano-code. The entry point points to a piece of code that understands how to 
locate the IP header based on the current frame type. For example, a connection might be native IP over 
ATM or LANE ETH. For the currently supported types, see the crc.txt file provided with the RXCRC code 
load. 
Note:  
Other types can be added if needed. 
Once properly enabled, TCP/IP checksums are verified as packets arrive. The status is raised to the user in 
the packet header using four bits of status (two bits for IP and two bits for protocol). The format and meanings 
of the bits are specified in Packet Header. For connections that have mixed traffic, the checksum operation is 
only run on packets that are recognized as TCP/IP. For example, on a LANE ETH connection packets of 
different protocols can be interleaved. 
Bit
Description
15
Reserved
14
F4 segment
13
F4 End to End
12
F5 Segment
11
F5 End to End
10
Rm Forward Cell
9
Rm Backward Cell
8
Pti Reserved Cell
7
End to End Alarm
6
Segment Alarm
5
End to End Loopback
4
Segment Loopback
3
End to End Pm Cell
2
Segment Pm Cell
1
End to End Activate/Deactivate Cell
0
Segment Activate/Deactivate Cell