TUB - Medusa SMT Project

Medusa[12] is the name of a LAN card designed for Hewlett Packard (HP) workstations in 1992 by the HP Laboratories in Bristol. The card attaches to the SGC1 slot of the machine and connectes to another Medusa card using a point-to-point connection topologie. The SGC interface provides access to the 1MB board buffer memory, the on board FIFO buffers and to the FDDI chipset register. The intention for the card design was to build up a LAN interface able to support the Single Copy network architecture. Using Single Copy any user data to be transmitted via LAN becomes not buffered in the kernel space of the machine. Instead the data are directly copied between physical on board memory and the user space of the workstation. This saves the time needed to allocate kernel memory and to move the data into the kernel space. However this mechanism requires basic changes in the network kernel architecture. Supporting modifications were made in the LAN driver, the kernel memorymanagement and along the whole protocol stack up to the Socket-layer. Data received at the LAN interface have to be kept in the card memory as long as they are copied into the user space. Overlying network and transport-protocols perform their data processing and pass afterwards the buffer descriptor up to the Socket (or another API), that copies the data out in the user space and frees the corresponding receive-buffer on the card. During data output the Socket-layer allocates already a transmittbuffer on the card avoiding the allocation of kernel memory. 1. Standard Graphic Connection Medusa additionally provides support for IP checksum generation and includes a PAL for multicast reception. Contrary to ordinary LAN cards using the conventional network architecture the Single Copy mechanism provides significantly higher performance and lesser delay in transfering data between workstations via LAN. This paper gives the final account of the Medusa-SMT project performed by the TUB. We list the intention and describe our new Medusa FDDI LAN driver. Medusa is now able to connect into an ordinary FDDI ring. It is working according to the FDDI standard and can communicate to a variety of machines from different manufacturers. It supports Single Copy and provides high performance in transfering data via FDDI. Multicast support and the ability to run as conventional LAN card are also provided by Medusa. 1. Project and Development Goals The Medusa hardware has been designed using FDDI technologie. However the first Medusa LAN driver does not use the FDDI protocol. Instead it has got its own protocol for the data transmission on Data Link Level. The card is attached to the operating system as Ethernet interface and is using Ethernet address notation, Ethernet attributes and mechanisms. FDDI cards from other manufacturers do not interwork with Medusa. Since no real ring management mechanisms were implemented in the Medusa communication protocol only two cards should be connected to each other. This saves a reliable configuration. A real ring topologie including a set of machines communicating to each other is not supported in