Raw EtherType Datagrams
General
Using the raw EtherType message transfer mechanism, software associated with a CA can support (as in the Ethernet environment) standard protocols, including TCP and UDP as well as IPv4.
Raw EtherType Datagram Format
Figure 21-3 on page 546 illustrates the format of a Raw EtherType request packet (there are no response packets). The packet contains the following elements:
LRH:
- LRH:DLID is used to guide the packet through the IBA subnet to a router ingress port.
- LRH:SL defines the desired QoS for the packet's travel through this IBA subnet.
Raw Header (RWH) contains the EtherType field. It defines what type of protocol the encapsulated non-IBA packet adheres to (and therefore, the presence or absence of other Transport Headers specific to that protocol). If there are other Transport Headers present, their type is defined by the protocol identified by the value in the EtherType field.
Figure 21-3. Raw Ethernet Packet Format
IEEE Assigns the EtherType Value
The EtherType values are assigned by the IEEE EtherType Field Registration Authority (see http://standards.ieee.org/regauth/ethertype/). Some example EtherTypes are:
0400h is assigned to the Nixdorf company.
0800h through 0803h are assigned to Xerox Corp.
8861h and 8862h are assigned to Intel Corp.
EtherType Message Format in Memory
In preparation for sending a message, software builds the message in local memory. For an EtherType message, the message in memory consists of:
Any protocol-specific Transport Headers defined by the EtherType specified in the WR that is subsequently posted to the SQ.
The packet's actual data payload.
EtherType Value Is Specified in the WR
When the message transfer request is posted to the raw EtherType QP's SQ, the 16-bit EtherType is specified as one of the input parameters.
Raw EtherType QP's Processing of the SQ WQE
When the raw EtherType QP's SQ Logic processes the WQE:
It forms the packet's LRH from the information supplied in the WQE (i.e., the WR).
It inserts the EtherType specified in the WR.
It then reads the message from local memory, generates the VCRC, and transmits the packet.