ATM and Fast Ethernet Network Interfaces for User-level Communication Presented by Sagwon Seo 2000/4/13 Matt Welsh, Anindya Basu, and Thorsten von Eicken Cornell University

Introduction Interconnecting workstation clusters for parallel and distributed computing U-Net communication architecture to provide low-latency and high-bandwidth communication Detailed performance analysis of U-Net for Fast Ethernet and ATM

What is U-Net architecture? A user-level network interface architecture Provides low-latency and high-bandwidth communication over commodity networks for workstations and PCs. Virtualizing the network interface such that every aplication can send and receive messages without operating system intervention

Main Idea Remove the kernel from the critical path of sending and receiving messages –Kernel overhead - System call, buffer management –Require message mux/demux device for the purpose of enforcing protection boundaries Incorporate mux/demux directly into the NI Move all buffer management and protocol processing to user-level

U-Net building blocks(1/2) End points- application ’ s handle into the network Buffer area- hold message data Message queues- hold descriptors for messages that are to be sent or that have been received.

U-Net building blocks(2/2)

U-Net communication(1/3) Each process that wishes to access the network first creates one or more endpoints. Communication between endpoints occurs through communication channels. An application registers message tags with U- Net when it creates a communication channel.

U-Net communication(2/3) To send a message 1.A user process composes the data in the endpoint buffer area and pushes a descriptor for the message onto the send queue. 2.The NI then transmits the message after marking it with the appropriate message tag.

U-Net communication(3/3) To receive a message 1.Incoming messages are demultiplexed based on the message tag. 2.The data is then transferred into one or more free buffers provided by the application. 3.A message descriptor with pointers to the buffers is pushed onto the appropriate receive queue.

ATM vs. Fast Ethernet The size and granularity of network data units Multiplexing Connection-oriented vs. connection-less Switched vs. shared medium

Experimental Setup U-Net/ATM –NI; Fore Systems PCA-200(25MHz intel i960, 256KB memory, a DMA-capable PCI-bus interface) –Switch; Fore Systems ASX-200 U-Net/FE –NI; DECchip Fast Ethernet controller –Switch; Bay Networks 100BaseTX hub, Bay Networks port switch, Cabletron FN100 8-port switch

U-Net/ATM Implementation Use custom firmware to implement U-Net Main memory- buffer areas, receive queues PCA-200 memory- send and free queues

U-Net/FE Implementation Due to the lack of a programmable co- processor, the U-Net implementation is placed in the kernel. Send a message; User processes can issue a fast trap into Kernel space. Receive a message; An interrupt is generated by the DC21140