ibm3206k0424 ETC-unknow, ibm3206k0424 Datasheet - Page 327

• Manufacturer Part Number: ibm3206k0424
• Description: Ibm Processor For Network Resources
• Manufacturer: ETC-unknow

IBM3206K0424
Preliminary
IBM Processor for Network Resources
enabled in the cut through configuration. This buffer is referred to as the optional header page and uses its
own page size and receive queue to allow for better storage utilization. When enabled, the second entry in
the DMA list becomes the optional header page entry, and should be treated accordingly for page recovery.
In split header mode, the header bytes are DMAed as soon as they are all received. This mode is useful if the
user environment requires the header bytes to be in a separate buffer from the packet header and DMA list.
Another optional feature is to DMA the header only. This feature is enabled in the cut through configuration.
When enabled, only the packet header, DMA list, and header bytes are DMAed. Either a single DMA or two
DMAs occur based on if the optional header feature is enabled. This feature can be useful when a routing
decision needs to be made for a packet and the entire packet does not need to be brought into host storage.
Another possible scenario is the header bytes may determine how the user wants to DMA the packet data to
the host.
For smaller packet sizes, it may be more efficient to perform a single DMA and keep the packet header, DMA
list, and packet data in a single buffer. To do this, single page mode should be enabled in the cut through
configuration. When enabled, the header page size is used to determine the DMA behavior. If a packet
completes and the total length of the packet and headers will fit in the header page size, then a single DMA is
performed. If the data length exceeds the single page size as it is being received, the data is scattered using
the normal options (might need to catch up). This feature can be useful for optimizing user processing for
smaller packets. For example, all packets less than 2K might be a candidate for this feature.
Head Bytes
There are two ways to set the number of head bytes. They are set on a per connection basis in the receive
LCD using the numHeadbytes and useCrcNumHead fields. When the useCrcNumHead field is set to ’0’, the
numHeadbytes field provides a fixed number of bytes that is used as the number of header bytes. When
useCrcNumHead field is set to ’1’, then the RXCRC nano code will calculate the number of header bytes
using the frameType field to index an IP procedure. Currently, RXCRC will only set the number of header
bytes for recognized TCP/IP headers. Other headers can be recognized. Contact IBM technical support to
discuss requirements.
pnr25.chapt05.01
Cell/Packet Re-assembly (REASM)
August 14, 2000
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