The DTM Host / Network Interface — Hardware Overview, Software Design and Protocol Layering

The DTM host/network adapter uses a dual-ported shared buffer memory on the interface board as in the Van Jacobson “Witless” interface [9]. The host operating system, SunOS, performs all protocol processing in the shared buffer memory and can therefore minimize the number of times data have to be transferred over the host system bus. We give an overview of the DTM host/network adapter hardware design emphasizing on the software visible parts. These parts include the dual-ported shared memory, the interrupt mechanism, control and status registers, and the FIFO queues used for managing buffers in the shared memory. The software controlling the hardware adapter constitutes a network interface driver in the SunOS operating system kernel. This driver implements the DTM service specification [7]. We describe how the adapter is managed by the driver and the operating system. In particular, we describe the modifications to the buffer system (mbufs) and socket layer that is necessary to use the on-board buffer memory in an efficient way. One modification for out-bound data is that the socket layer must know which particular network interface the data is destined for, at the time when the data is copied from the user application buffers into the mbuf buffers, so that the mbufs can be allocated in the on-board memory. We also describe the protocol layering on top of DTM and the design of the socket application interface to the DTM packet service. We introduce a DTM “link layer” protocol for addressing and encapsulating IP and other higher level protocols. Markus Hidell [email protected] Telecommunication System Laboratory Dept. of Teleinformatics Royal Institute of Technology S 164 40 KISTA Sweden Bengt Ahlgren [email protected] Swedish Institute of Computer Science Box 1263 S 164 28 KISTA Sweden