Detailed Description of LRH

Refer to Figure 25-3 on this page. The LRH is the first field in every data packet and is required. It consists of the sub-fields shown in the illustration. The sections that follow provide a description of each subfield within the LRH.

Figure 25-3. Local Route Header

SL and VL Fields

These two LRH fields are each 4 bits wide.

SL Indicates Desired QoS and Is Specified by Software

The Service Level (SL) defines the desired QoS for a message's transit through the local subnet from the source CA port to the destination port within the same subnet. Software obtains the SL to be used for a given source/destination port pair ...

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