ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation By Ursula Sinkewicz, Chran-Ham Chang, Lawrence G. Palmer, Craig Smelser, and Fred L. Templin Abstract The ULTRIX operating The ULTRIX operating system supports Digital's system, Digital's version first implementation of of the UNIX operating an FDDI host networking system, supports the subsystem. A key decision first implementation of in the ULTRIX FDDI program a host networking subsystem was to design an adapter with a fiber distributed for reduced instruction data interface (FDDI) set computer (RISC)-based network adapter. Digital's workstations. Consequently, FDDIcontroller 700 adapter the DEC FDDIcontroller provides a single FDDI 700 network adapter was attachment for the reduced designed to support an FDDI instruction set computer single attachment for the (RISC)-based, DECstation DECstation 5000 model 200, 5000 model 200 platform. RISC-based workstation. Combined with the ULTRIX This support covers the networking subsystem, this Defense Advanced Research adapter brings high-speed Projects Agency (DARPA) communication directly to internet network protocols the workstation. designed for the ARPANET packet-switched network. Introduction The DARPA internet network Digital made the decision protocols include the to adopt fiber distributed internet protocol (IP), data interface (FDDI) the transmission control local area network (LAN) protocol (TCP), and the technology to follow user datagram protocol Ethernet. With the (UDP). FDDI system, Digital is This paper begins with an developing products to overview of the ULTRIX support improved network operating system. The performance such as the sections that follow high-speed interconnection present the implementation of workstations. details of the network and communication driver, review specific issues in the ULTRIX FDDI implementation, and discuss Digital Technical Journal Vol. 3 No. 2 Spring 1991 1 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation both performance and future system to associate data directions. with specific clients and servers. When executing in Overview of the ULTRIX kernel mode, the socket Operating System system calls perform the memory management, The ULTRIX operating the security checking, system is based on the 4.3 and the state management BSD system. (BSD refers common to all protocols. to Berkeley Software When the protocol-common Distribution, a popular processing is complete, the version of the UNIX operating system accesses operating system.) As in a protocol switch table other systems based on the containing vectors to UNIX system, the ULTRIX protocol-specific modules. operating system operates These modules, in turn, in user and kernel modes. access communications A process running in user drivers through the network mode can be preempted. interface table. Interrupts are run in the context of the current process. A process running in kernel mode voluntarily relinquishes control of the CPU. ULTRIX networks and communications device drivers run in kernel mode. The ULTRIX operating system supports network activity through a well-defined, layered hierarchy including user applications, system calls, and compile- time entry points to the protocols and communication device drivers. The layered hierarchy is illustrated in Figure 1. The user layer consists of applications (e.g., electronic mail) that use specific system calls to support network activity. These interprocess- communication system calls incorporate the notion of a socket and, hence, are referred to as socket system calls. Sockets are endpoints of communication containing information used by the operating 2 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation The ULTRIX environment However, the ULTRIX is characterized by a operating system running large number of servers, network applications on e.g., SUN's NFS system, RISC workstations was which allows remote already saturating the access to entire file Ethernet. The ULTRIX systems, and many network engineering group advocated applications. The servers FDDI adapters, not only for support a diverse range RISC-based servers but also of activities such as for the increasing number managing mail and ensuring of high-end, RISC-based that X Window System workstations. managers are available ULTRIX and VMS engineering to remote workstations. The groups began architectural underlying protocols for discussions with the FDDI most of these servers are development groups to TCP, IP, and UDP. write requirements for FDDI adapters for both RISC and ULTRIX Support for the FDDI VAX processors. Due to the System-Development Strategies evolving ULTRIX emphasis on and Issues RISC-based solutions, the ULTRIX engineering group Presentations by Digital's represented data structure, networking architects virtual addressing, and in May 1988 brought the performance requirements earliest news that Digital for RISC processors, was pursuing a timed token while the VMS engineering ring topology (i.e., FDDI) group represented the in contrast to Ethernet, same requirements which employs a carrier for VAX processors. sense multiple access with Approximately ten collision detection (CSMA months after the initial /CD) data link protocol. network architecture Digital's FDDI engineering presentations, the FDDI program began with product program team drafted requirements for a wiring product requirements for concentrator, a bridge the ULTRIX implementation, to link Ethernet and including support for an FDDI networks, and an FDDI workstation adapter. FDDI adapter to the VAX To provide a workstation computer. The FDDI program solution, members of the team planned only high-end ULTRIX engineering group system direct connectivity had already begun to work to the ring. Workstations with the Low End Network would be connected through Systems (LENS) Group on the existing Ethernet an advanced development across a bridge. project to define a workstation-based FDDI adapter. The team discussed alternatives for FDDI workstation connections, including the emerging Digital Technical Journal Vol. 3 No. 2 Spring 1991 3 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation DECstation 5000 model 200 TURBOchannel bus, the DECstation 3100 plug-in option, and the industry- standard small computer systems interface (SCSI) bus. Six months into the adapter advanced development project, the internet community confirmed interest in TCP/IP implementations for FDDI requirements by issuing a draft of the request for comment, RFC 1103 (recently renamed RFC 1188), which defines the encapsulation of internet packets on FDDI networks. Members of the FDDI engineering team were instrumental in providing direction for the internet FDDI task force meetings on RFC 1103 and the FDDI network management information base (MIB). The draft of RFC 1103 prompted internet vendors to hastily implement FDDI workstation- based products and the LENS group to publish plans for FDDI connectivity to RISC- based workstations with ULTRIX support. In October, at the Interop '89 Conference in San Jose, California, several internet vendors showcased FDDI products. Although Digital did not show FDDI products at the conference, this event prompted Digital to design an architecturally sound, high-quality, FDDI solution to gain a competitive edge. 4 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Soon after the conference, of the ULTRIX and adapter the FDDI Data Link combination to nearly 40 Specification and the percent of the entire FDDI project plan for ULTRIX bandwidth-a factor of four support for the FDDI system times greater than existing were released. Subsequent Ethernet implementations. ULTRIX development efforts At its trade show, DECWORLD to support the FDDI system 1990, Digital announced produced new networking the availability of its code for the TURBOchannel FDDI product offerings. device driver, the data These included the link layer, and the network DECconcentrator 500 and layer. These efforts DECbridge 500 products, paralleled the TURBOchannel and the DEC FDDIcontroller adapter development 700 adapter, which runs efforts. under the ULTRIX operating A prototype ULTRIX system. implementation successfully passed 802.2 frames over ULTRIX Internals an Ethernet connection, as required by the American The implementation of National Standards FDDI support in the ULTRIX Institute (ANSI) FDDI operating system required standard, to exercise the development of a the data link and network link-level architecture layer changes necessary for and a network device FDDI support. The product driver. Operating system announcement for the changes to improve the TURBOchannel FDDI adapter performance of the network assigned the official name were made later. The next DEC FDDIcontroller 700 to two sections describe the the adapter. Prototypes implementation of the link- were delivered in May 1990; level architecture and the firmware integration was device driver. Performance completed; and the first changes are discussed address resolution protocol in the ULTRIX Network (ARP) broadcast packet was Performance section. sent over an FDDI ring from Data Link Support an ULTRIX host. Device driver and The ULTRIX operating adapter interoperability system implements both problems such as timing the internet protocols (TCP considerations, data /UDP/IP) and the Digital corruption, and performance Network Architecture issues were solved promptly (DNA) model, including the by close cooperation Digital data link interface between the software and (DLI). In both the internet hardware groups. Several and DNA models, the data additional performance link defines services enhancements were added known as the logical link to the operating system, control (LLC) and the media bringing the performance access control (MAC). A Digital Technical Journal Vol. 3 No. 2 Spring 1991 5 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation major challenge in the implementation of ULTRIX FDDI support was defining a set of common data link encapsulation as required routines to satisfy the by RFC 1188. frame format requirements of both internet and DNA net_output() Function. models in a heterogeneous The net_output() function LAN environment. prepares packets for Prior to the introduction transmission by ULTRIX of the FDDI system, network communication all ULTRIX internet device drivers. If a driver networking for LANs ran requires 802.2 LLC support, over Ethernet networks the net_output() function using Ethernet V2 frame supplies the necessary formats, even though ULTRIX header, prefixes the MAC DLI networking supported header, and enqueues the both Ethernet V2 and 802.2 packet to the appropriate LLC frame formats. Figure 2 communication driver illustrates the differences for transmission.[2] among the V2 Ethernet and The function, while 802.2 Ethernet and the supporting 802.2 LLC FDDI frame formats. V2 encapsulation, does not and 802.2 frames include preclude protocol modules Ethernet encapsulation; from supporting their 802.2 frames consist of own LLC formatting. The the MAC, the LLC, and data encapsulation is switch- segments. When the 802.2 driven so implementors can frame is sent over the FDDI add special routines to the system, the FDDI framing switch to either replace adds the FDDI-specific or bypass the 802.2 LLC encapsulation, as shown encapsulation. in Figure 2. In order to net_read() Function. The conform to the ANSI FDDI net_read() function is standards, which require called by the communication 802.2 LLC frame formatting, drivers and prepares members of the Internet received packets for Network Working Group wrote delivery to protocol Internet RFC 1188.[1] This modules. This function RFC specifies the rules first identifies the for 802.2 LLC encapsulation protocol type from of internet frames on an information contained in FDDI network. To meet the the MAC and LLC headers, needs of both Ethernet and places the packet on FDDI networks, we designed the corresponding queue, and integrated a set of and finally schedules a network-common routines. software interrupt to alert These routines, the net_ the appropriate protocol output() and the net_read() module of the arriving functions, support 802.2 packet. 6 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Communication Driver driver data structures, and the driver data buffers, as The FDDIcontroller 700 shown in Figure 3. adapter connects directly Each port register is with the DECstation 5000 represented by 16 bits model 200 TURBOchannel bus. in adapter packet memory. The FDDIcontroller 700 is These registers are a 100-megabit (Mb)-per- described in Table 1. second, timed token ring adapter that supports an The adapter uses six FDDI single attachment for queues, called port memory the DECstation 5000 model rings, to exchange data, 200. The adapter provides a events, and commands with host interface with the the driver. These port following features: a memory rings, represented packet memory interface as circular lists of (PMI) gate array for descriptors, are described receive direct memory in Table 2. Each descriptor access (DMA) data transfer; is associated with a data a packet memory subsystem buffer in adapter packet that contains one megabyte memory or in driver memory. (MB) of dynamic random- access memory (DRAM) for packet store and forward; and the ability to handle FDDI ring initialization, recovery, and SMT frame processing. (SMT refers to the ANSI-specified FDDI station management.[3]) The adapter is controlled by a microprocessor and uses Digital's FDDI chip set, which includes ring memory control (RMC), media access control, and the elasticity buffer and physical link manager (ELM). The ULTRIX communication driver interfaces to the adapter's port architecture. The port architecture defines the mechanisms to transfer FDDI frames and control or status information between the communication driver and the port. The ULTRIX communication driver interfaces to the adapter through six port registers, six port memory rings, the Digital Technical Journal Vol. 3 No. 2 Spring 1991 7 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Table 1 Adapter Port Register ___________________________________________________________________ Register_Name____Written_by__Purpose_______________________________ Port Reset Driver Forces the adapter to reset Port Control A Driver Controls adapter operations Port Control B Driver Indicates that the driver is active Port Interrupt Adapter Notifies the driver of important Event events Port Status Adapter Indicates the adapter status Port Interrupt Driver Masks the adapter interrupt events Mask_______________________________________________________________ 8 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Table 2 Port Memory Rings ___________________________________________________________________ Ring_Name________Purpose___Description_____________________________ Host Receive Data Identifies driver data buffers to Ring Flow receive incoming packets RMC Transmit Data Identifies adapter data buffers Ring Flow containing packets to transmit SMT Receive Data Used by the driver to route SMT frames Ring Flow to the adapter for processing SMT Transmit Data Used by the driver to route SMT frames Ring Flow to the adapter for processing Command Ring Control Used by the port driver to initialize, configure, and monitor adapter operations Unsolicited Control Used by the adapter to notify the Events_Ring________________driver_of_unsolicited_events____________ The packet data flow SMT receive ring, and then between the adapter and the adapter queues the the ULTRIX communication packet to the SMT transmit driver is also shown in ring after processing. The Figure 3. For incoming driver is then notified FDDI packets, the adapter by the adapter to move uses a direct memory access this packet from the SMT engine to move the packets transmit queue to the from the adapter memory to RMC transmit ring for the receive data buffers transmission. When the net_ of the driver. These output() function requests buffers are allocated as to transmit packets, the 4-kilobyte (KB) pages in driver copies the packets kernel memory. Each host from driver memory to the receive ring descriptor is RMC transit ring, signaling associated with two receive the adapter to transmit the buffers to handle the packets. maximum FDDI frame (4500 The communication driver bytes). To achieve the controls and requests maximum receive throughput, information from the the driver performs packet adapter by issuing commands filtering. If the incoming through the command ring. packet is an LLC frame, These commands initialize the driver processes it the adapter, change the and calls the net_read() adapter state, modify and function. Otherwise, read the packet filter the driver forwards the address table, read data packet to the adapter's Digital Technical Journal Vol. 3 No. 2 Spring 1991 9 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation link counters, and read We expect FDDI performance data link status. In to develop similarly to addition, due to the that of Ethernet. Early evolving state of the Ethernet hosts were ANSI SMT specification, unable to utilize more the driver function now than 20 percent of the allows the on-line upgrade available network bandwidth of adapter firmware.[3] because of the limited Finally, the driver throughput capability of supports the ability to existing processors. The recognize unsolicited graph shown in Figure 4 adapter events communicated illustrates the historical through the unsolicited performance of several events ring. When received, different processors using these events are logged Ethernet adapters. Note and reported through the that since 1983, network console. throughput has increased significantly. At some time ULTRIX Network Performance after the middle of the decade, it was possible to Performance is a key factor reach a throughput of 10Mb in the success of Digital's per second, a rate high workstation FDDI offering. enough to saturate Ethernet A great effort was made to with a single host. characterize the DECstation 5000 machine performance by using the earlier DECstation 3100 workstation performance results to help set realistic goals. Both the characterization and the measurements were essential to predict the performance goals. This section discusses the level of performance achieved by the DECstation 5000 model 200 running the ULTRIX operating system with FDDI support. We present details of the historical precedence for predicting FDDI performance, the evolution of the ULTRIX networking code, and the performance of applications with the FDDI system. Historical Precedence 10 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Figure 4 also shows that, internet networking code in nearly all cases, the was updated to incorporate achievable throughput performance enhancements is limited by the speed available from a recent of the processor. In BSD release. Later, ULTRIX addition, an experimental network performance was constant of 1 mips/Mb is further improved to include measured in cases where the implementation of a the processor is saturated. dynamic buffer allocation (1 mips equals one million policy to replace the instructions per second.) inefficient static This constant means that 1 allocations. With FDDI mips of processor speed systems, the challenge then is needed to generate became adapting the code to 1Mb of network traffic. effectively use the higher For example, the 1-mips network throughput. VAX-11/780 processor is We attacked this problem able to generate about 1Mb by isolating and optimizing of network traffic. The each networking subsystem. data presented in Figure The ULTRIX networking 4 shows that a processor code is divided into follows the 1 mips/Mb ratio three major subsystems: unless the adapter becomes sockets, protocols, and a limiting factor, as in drivers. Each of these the case of the DECstation subsystems can be further 3100 system. The 1 mips/Mb subdivided: sockets into ratio allows us to predict the system call interface that a 100-mips processor and the socket-to-protocol is required to saturate interface; protocols the FDDI system. Thus, the into the IP and UDP FDDI system satisfies the components; and drivers throughput requirements of into the ARP, buffer available processors and management, and driver allows for the growth of interrupt components. We faster processors. Finally, used kernel profiling, a if the present trend of means for making run-time doubling processor speed measurements of time spent every two to three years in system-level routine continues, the FDDI graph calls, and known benchmarks will resemble the Ethernet to track progress. graph of the 1980s, with Using an unreliable the saturation of the FDDI protocol without error system possible in 1996 or recovery, such as UDP, 1997. instead of TCP with Evolution of the ULTRIX reliability and packet Internet Code sequencing features, the The early implementations packet-per-second (pps) of ULTRIX internet rate of each component networking code were based can be easily determined. on robust BSD networking Figure 5 shows the sizable code. In 1987, the ULTRIX packet rate measured on the DECstation 5000 Digital Technical Journal Vol. 3 No. 2 Spring 1991 11 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation model 200 for both the nonoptimized and the optimized ULTRIX network, i.e., before and after performance improvements are incorporated. Note that the pps rate of each layer reflects improvements in the layers below. 12 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Packet rate values for the The greatest long-term system call through the ARP benefit of end-node access components are determined to FDDI will probably by processor speed and come to those utilizing code. Rates below the ARP a distributed computing depend on adapter speed and environment since this not processor speed. The paradigm relies heavily packet rate value for the on the performance of ARP is the maximum packet the underlying network. rate for a processor. While Ethernet currently With an optimized packet serves this growing set rate, Figure 5 shows a of applications well, it maximum rate of 1230 pps is expected that as the for the DECstation 5000 application demand for workstation. Since each network service increases, test packet contains so will the total network 4096 bytes, this rate is bandwidth and performance equivalent to 40Mb per requirements of the second, which is a 40 participating end node. percent FDDI bandwidth Even today, some users utilization. of distributed network A significant amount of file systems (e.g., NFS) work is performed at the will notice a significant socket-to-protocol, IP, performance improvement as and driver start layers a direct result of using because in each case, an FDDI. This improvement effective copy of the data is particularly evident is performed. The socket on cached file reads and layer copies data from writes, where no disk the user into the kernel, access is required but the IP layer checksums the the aggregate bandwidth data, and the driver start advantage of FDDI is routine copies the data to beneficial. However, the adapter. We focused our overall NFS performance efforts on the socket-to- is currently limited by protocol layer and found CPU speed and disk write that considerable processor capabilities; so we expect time was spent allocating that with improvements in kernel buffers to hold processor performance, disk the data. Reworking this access, and data caching, code to buffer the data network performance at the more efficiently resulted level provided by FDDI will in the performance change soon be essential. between the optimized and Table 3 contains FDDI nonoptimized columns shown performance measurements in Figure 5. with respect to Ethernet for various applications and transports at the Application of the FDDI application layer. The System spray application is most often used to measure how an unreliable transport Digital Technical Journal Vol. 3 No. 2 Spring 1991 13 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation performs. Applications such as the BSD rcp (the remote file copy program over TCP/IP protocols), the file transfer protocol (FTP), and the test TCP (TTCP) program all measure performance of a reliable transport protocol. An NFS test is used to measure how FDDI performs as a file server. Note that, in all cases except FTP, performance improves by at least a factor of two. FTP does not take advantage of the larger buffering gained by using the FDDI system and, thus, shows no performance change over Ethernet. 14 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation Table 3 Application Performance in Relation to Ethernet ___________________________________________________________________ Rate (Megabits) RATE (Megabots) (UDP Checksum (UDP Checksum Transport___Application_on)______________Off)_____________Change___ TCP rcp 18 18 2X TCP FTP 5 5 1X UDP/NFS NFS Read 20 30 2X (3X) UDP Spray 22 35 2.5X (3.3X) TCP TTCP 18 18 2X UDP TTCP 22 38 2.5X __________________________________________________________(4X)_____ Another aspect of network serving as an FDDI router performance is the routing because we expect this function. Using the DEC product feature to be FDDIcontroller 700 adapter, popular. Table 4 shows the DECstation 5000 model the performance results 200 can perform FDDI-to- for a DECstation 5000 FDDI routing, FDDI-to- workstation performing Ethernet routing, or both, FDDI-to-FDDI routing and for internet traffic. With FDDI-to-Ethernet routing, a built-in Ethernet port both under minimal system and the ability to accept and network load. Note that up to three additional the data presented for the TURBOchannel adapters, TCP-based applications a 5000 model 200 can shows that throughput connect to as many as four is limited by the way different networks. TCP calculates its flow The performance of control window when data such a host-based is destined for a remote router is difficult to network. All current TCP characterize. A wide range implementations have this of factors influences this same limitation because all performance, including nonlocal connections must the protocols routed, the have a small flow control efficiency of the routing window size of 576 bytes algorithms, the system to avoid the saturation load, and the available of intermediate gateways. data link bandwidth. Since both Ethernet and Nonetheless, it is useful FDDI systems can transmit to consider the performance frames larger than this of the 5000 model 200 flow control window, the advantage of transmitting Digital Technical Journal Vol. 3 No. 2 Spring 1991 15 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation maximum-sized frames is lost. UDP does not have this limitation; thus, throughput numbers are only slightly lower than in the nonrouting case. Table 4 FDDI Routing for a DECstation 5000 Workstation ___________________________________________________________________ Ethernet-to-FDDI FDDI-to-FDDI Rate Transport_____Application___Rate_(Megabits)_____(megabits)_________ TCP rcp 4.8 4.8 TCP FTP 2.7 2.7 UDP/NFS NFS Read 8.0 16.8 UDP Spray 9.0 18.0 TCP___________TTCP__________6.4_________________6.4________________ Futures Stanford University.[4] This section describes VMTP demonstrates that some areas of research that a reliable transport is may impact the use of the achievable with no greater FDDI system. Included are overhead than existing discussions on protocol unreliable transports. alternatives, future VMTP, therefore, represents performance work, and how an alternative to TCP this system will facilitate that would nearly double new software technologies. the throughput of some remote procedure call New Protocols (RPC) applications. Also, As illustrated in Figure 4, knowledge gained from the processor speed is the VMTP research may influence current bottleneck in future internet or open FDDI throughput. While systems interconnection processor speed continues (OSI) directions. to increase, emerging Future ULTRIX Network protocols are making Performance Work efficient use of available In addition to examining processing power and are new protocols, performance yielding additional gains work is continuing with our in network performance. existing ULTRIX protocols. A development relevant One area being studied is to this discussion of data copy. Currently, user protocol alternatives data is copied twice as is the versatile message it traverses the internet transport protocol (VMTP) protocol stack. One copy research project from occurs in the socket 16 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation subsystem, and the other video application is one takes place in the the requirement of at device driver. Data copies least a 1-MB, continuous account for 50 percent of network connection, CPU utilization time when enough to easily saturate large amounts of data are Ethernet. Even a live audio transferred. Eliminating application will require one copy can yield a 200- to 300-KB-per- increased performance, second network connection. with savings of at least Clearly, with applications 25 percent of the total that demand these data processing time. rates, FDDI bandwidth is An FDDI adapter optimized necessary. for the internet protocol The DEC FDDIcontroller stack may also provide 700 adapter brings FDDI to improved performance. This the desktop. The adapter decrease in processing time is well matched to the may result from calculating DECstation 5000 model internet checksums in the 200, joining a 25-mips adapter or from moving the processor to a 100-Mb-per- complete protocol stack to second data link. As the the adapter. For example, next generation of LAN, researchers have proposed FDDI extends the base for protocol engine chips that network applications by would off-load all protocol allowing those applications processing to customized that run on Ethernet to run chips. With such real- faster and by providing the time protocol engines, bandwidth for a whole new existing processors could generation of applications. easily outpace current FDDI FDDI is the network of the speeds. '90s, as Ethernet was the network of the '80s. Conclusions Digital brought FDDI to Acknowledgments the ULTRIX workstation to We would like to thank satisfy the growing network Kathy Wilde for her early demands of its customers. participation on the The number of network- project, Kent Ferson intensive applications for general support and that run on ULTRIX encouragement, and Fred workstations is growing Glover for his help in at a fast pace. Graphics reviewing the document. and imaging applications Nolan Ring patiently edited have the potential of the early draft. Julia Fey generating megabytes helped with the collection of network data. Also, of performance data and multimedia applications with the data analysis. can strain FDDI networks We would especially like and are not practical to thank the staff of the using Ethernet. The best Digital Technical Journal scenario for a live motion for their help and support. Digital Technical Journal Vol. 3 No. 2 Spring 1991 17 ULTRIX Fiber Distributed Data Interface Networking Subsystem Implementation o W. Mason, "VMTP: A High Performance Transport Protocol," Connexions, vol. 4, no. 6 (June References 1990): 2-10. o A Proposed Standard General References for the Transmission of IP Datagrams over A Standard for the FDDI Networks, Internet Transmission of IP Network Working Group, Datagrams over IEEE 802 RFC 1188 (October 1990). Networks, Internet Network o Fiber Distributed Data Working Group, RFC 1042 Interface (FDDI) - (February 1988). Token Ring Media Access ANSI/IEEE Standards for Control (MAC), ANSI Local Area Networks: X3.139-1987. Logical Link Control, ANSI o ANSI FDDI Station /IEEE Standard 802.2-1985 Management Standard, (New York: The Institute of ANSI X3T9.5, Revision Electrical and Electronics 5.1 (September 1989). Engineers, Inc., 1985). 18 Digital Technical Journal Vol. 3 No. 2 Spring 1991 ============================================================================= Copyright 1991 Digital Equipment Corporation. Forwarding and copying of this article is permitted for personal and educational purposes without fee provided that Digital Equipment Corporation's copyright is retained with the article and that the content is not modified. This article is not to be distributed for commercial advantage. Abstracting with credit of Digital Equipment Corporation's authorship is permitted. All rights reserved. =============================================================================