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/Times-Bold-ISOLatin1 F 2400 o f
(FDDI: Meeting the Interoperability Challenge) h
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n 0.583 o f
(Dave Benson Paul Ciarfella Peter Hayden) h
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(Digital Equipment Corporation) h
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(153 Taylor Street) h
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(Littleton, MA 01460) h
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(ABSTRACT) h
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277.1 0 32 (The advent of the Fiber Distributed Data Interface) W
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279.0 0 32 (\(FDDI\) standard promises a multivendor 100 Mbps) W
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14.8 0 32 (LAN solution. The realization of that solution rests on) W
300 -8200 M
259.4 0 32 (the consistent interpretation and implementation of) W
300 -9600 M
149.3 0 32 (the distributed algorithms specified by the standard.) W
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467.8 0 32 (In addition, value added algorithms, utilizing the) W
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159.6 0 32 (SMT frame protocols, will rely on each vendor's con\255) W
300 -13800 M
(sistent interpretation of the standard.) h
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535.5 0 32 (Comprehensive interoperability testing among the) W
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31.3 0 32 (vendors both reinforces the 'normal' interpretations of) W
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23.1 0 32 (the standard, and performs the most immediate goal \255) W
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183.2 0 32 (that of verifying the correctness of implementations.) W
300 -21800 M
31.3 0 32 (This paper explores what Digital has observed to date) W
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406.4 0 32 (in the area of interoperability testing so that the) W
300 -24600 M
20.4 0 32 (FDDI community may continue to meet the interoper\255) W
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(ability challenge.) h
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/Helvetica-Bold-ISOLatin1 F 1200 o f
(INTRODUCTION) h
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/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
349.3 0 32 (The FDDI \(Fiber Distributed Data Interface\) stan\255) W
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87.1 0 32 (dards define a 100 Mbps fiber\255based token ring local) W
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59.9 0 32 (area network which can support up to 500 stations at) W
300 -37200 M
86.8 0 32 (a maximum distance of 2 kilometers apart. The stan\255) W
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109.2 0 32 (dard specifications [1],[2],[3],[4] define the FDDI pro\255) W
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67.3 0 32 (tocols for the Physical and Datalink layers of the OSI) W
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316.0 0 32 (model. The SMT \(Station Management\) draft stan\255) W
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300.0 0 32 (dard defines the protocols necessary to control and) W
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23.2 0 32 (monitor the FDDI layers in a network. The MAC \(Me\255) W
300 -45600 M
160.1 0 32 (dia Access Control\) standard defines the token pass\255) W
300 -47000 M
4.1 0 32 (ing and media access mechanisms. The PHY \(Physical) W
300 -48400 M
191.9 0 32 (Layer\) standard defines the rules for data encoding,) W
300 -49800 M
353.2 0 32 (decoding, and clocking while PMD \(Physical Layer) W
300 -51200 M
415.6 0 32 (Medium Dependent\) defines the optical connectors) W
300 -52600 M
297.8 0 32 (and media characteristics. [5],[6],[7] provide a good) W
300 -54000 M
(introduction to the technology.) h
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77.3 0 32 (Since FDDI defines a ring topology rather than a bus) W
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29.1 0 32 (topology, each station has a responsibility to establish) W
300 -59200 M
410.6 0 32 (and maintain physical connections and to repeat) W
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40.9 0 32 (frames without error. If frames are not repeated by a) W
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35.2 0 32 (single station, connectivity is lost \255 unlike a bus topol\255) W
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230.2 0 32 (ogy where a fault like this would likely not disrupt) W
300 -4000 M
217.1 0 32 (the network. On FDDI, faults which prevent proper) W
300 -5400 M
378.6 0 32 (ring operation have been anticipated by the X3T9) W
300 -6800 M
238.2 0 32 (standards committee, and algorithms have been de\255) W
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(vised to deterministically resolve such conditions.) h
300 -10600 M
344.4 0 32 (The addition of fault recovery schemes devised for) W
300 -12000 M
97.8 0 32 (FDDI, while necessary to guarantee proper operation) W
300 -13400 M
125.1 0 32 (of the network, has introduced much additional com\255) W
300 -14800 M
364.3 0 32 (plexity to the standard. Correct implementation of) W
300 -16200 M
86.7 0 32 (these complex protocols and distributed algorithms is) W
300 -17600 M
97.3 0 32 (essential to guarantee that one vendor's implementa\255) W
300 -19000 M
18.2 0 32 (tion will operate correctly on the same ring with other) W
300 -20400 M
97.8 0 32 (vendor's implementations \255 especially in the presence) W
300 -21800 M
(of fault conditions. ) h
300 -24200 M
42.8 0 32 (The issue of interoperability in FDDI is of greater im\255) W
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206.8 0 32 (portance than in other LANs for many reasons. For) W
300 -27000 M
264.7 0 32 (example, Ethernet was introduced by a few compa\255) W
300 -28400 M
35.4 0 32 (nies at a time when the number of operating commer\255) W
300 -29800 M
20.3 0 32 (cial networks was small. As networking grew in popu\255) W
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1015.6 0 32 (larity and more vendors introduced products,) W
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179.8 0 32 (Ethernet evolved into an interoperating multivendor) W
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119.7 0 32 (solution. Today, so many vendors are simultaneously) W
300 -35400 M
168.3 0 32 (introducing FDDI products into existing network ar\255) W
300 -36800 M
68.6 0 32 (chitectures and customer installations that interoper\255) W
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(ability must be assured right from the start.) h
300 -40600 M
15.2 0 32 (This paper discusses FDDI multivendor interoperabil\255) W
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28.6 0 32 (ity history, the stage where we, the FDDI community,) W
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48.5 0 32 (currently are, and presents a common set of problems) W
300 -44800 M
189.6 0 32 (as observed by Digital while testing with other ven\255) W
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(dors' FDDI products.) h
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/Helvetica-Bold-ISOLatin1 F 1200 o f
(INTEROPERABILITY HISTORY) h
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/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
442.0 0 32 (Efforts to achieve interoperability among different) W
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82.4 0 32 (vendors began very early in the history of FDDI with) W
300 -56000 M
366.3 0 32 (the work of the Physical Media Dependent \(PMD\)) W
300 -57400 M
210.6 0 32 (working group of ANSI X3T9.5. This working group) W
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283.0 0 32 (was responsible for developing physical layer inter\255) W
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201.7 0 32 (face specifications and models of optical components) W
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112.0 0 32 (Copyright 1990 IEEE, Reprinted, with permission, from ) W
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/Times-Italic & P
/Times-Italic-ISOLatin1 F 1200 o f
112.0 0 32 (Proceedings of the 15th Conference on Local Computer Networks\(LCN\);) W
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/Times-Roman-ISOLatin1 F 1200 o f
(Minneapolis, Minnesota October 1990; to be published.) h
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n 0.833 o f
52.3 0 32 (Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the) W
300 -5450 M
72.3 0 32 (IEEE copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Institute of Electrical and) W
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(Electronics Engineers. To copy otherwise, or to republish, requires a fee and specific permission.) h
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197.7 0 32 (and fiber media [8],[9],[10],[11]. Their work was im\255) W
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115.6 0 32 (portant to the development of FDDI because interop\255) W
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144.0 0 32 (erable physical connections to a common fiber media) W
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306.3 0 32 (were needed before higher layer functions, such as) W
300 -6800 M
(Media Access Control \(MAC\) could be tried.) h
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241.4 0 32 (The specifications and models allowed interoperable) W
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331.4 0 32 (designs and exhaustive testing [8] of many vendor) W
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663.5 0 32 (components, verifying physical interoperability of) W
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220.1 0 32 (FDDI standard components. As a result, the optical) W
300 -14800 M
315.6 0 32 (components developed by one vendor can be seam\255) W
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112.4 0 32 (lessly integrated with the physical layer circuitry de\255) W
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408.3 0 32 (veloped by others. This allows interoperability be\255) W
300 -19000 M
271.8 0 32 (tween the optical transmitters, receivers, fiber, and) W
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298.2 0 32 (fiber connectors produced by multiple vendors. The) W
300 -21800 M
74.3 0 32 (end result is that interoperable physical layer compo\255) W
300 -23200 M
267.1 0 32 (nents are now available, making it easy for FDDI) W
300 -24600 M
138.7 0 32 (equipment vendors to achieve physical layer interop\255) W
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(erability. ) h
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179.3 0 32 (As development of the higher layer standards \(MAC) W
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297.8 0 32 (and SMT\) progressed, the marketplace expressed a) W
300 -31200 M
325.4 0 32 (growing interest in FDDI network products. In re\255) W
300 -32600 M
238.8 0 32 (sponse, many vendors have shipped products before) W
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305.9 0 32 (the SMT draft was fully developed. Consequently,) W
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204.3 0 32 (many of the these early systems utilized incomplete) W
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(or proprietary FDDI SMT solutions. ) h
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14.8 0 32 (As a result, the level of interoperability testing among) W
300 -40600 M
79.8 0 32 (vendors during this period primarily centered around) W
300 -42000 M
261.4 0 32 (verifying that a stable physical connection could be) W
300 -43400 M
185.0 0 32 (achieved between stations and that the ring became) W
300 -44800 M
172.0 0 32 (operational, ie., the MAC level protocols successfully) W
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119.3 0 32 (completed and a token was created. While this form) W
300 -47600 M
6.7 0 32 (of testing fulfilled the needs of the time, it is no longer) W
300 -49000 M
32.7 0 32 (sufficient. Now that the SMT document has stabilized) W
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11.9 0 32 (and is being voted on for approval, more complete im\255) W
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267.8 0 32 (plementations exist in the market. The opportunity) W
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55.4 0 32 (now exists for us to perform complete interoperability) W
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200.4 0 32 (testing. The 'plug and play' testing was adequate to) W
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31.3 0 32 (verify the basic functionality required to interconnect,) W
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67.4 0 32 (but it is inadequate to measure the degree of interop\255) W
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(erability to expect over time. ) h
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80.4 0 32 (Full mandatory functionality as specified in the stan\255) W
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173.9 0 32 (dard must be verified in order to guarantee not just) W
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114.8 0 32 (peaceful coexistence on a faultless network, but also) W
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43.1 0 32 (the proper operation of the members of the FDDI net\255) W
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359.5 0 32 (work in the presence of ring fault conditions. The) W
300 -68200 M
139.2 0 32 (proper operation of all stations in the network in re\255) W
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(sponse to fault conditions is a necessity if the commer\255) h
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(cial marketplace is to fully accept FDDI. ) h
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(WHERE TESTING IS NOW) h
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175.6 0 32 (Some vendors are taking the initiative and have be\255) W
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295.2 0 32 (gun their own interoperability testing. Independent) W
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87.0 0 32 (testing consortiums have recently been formed where) W
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1.4 0 32 (vendors have tested their products against each other.) W
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67.5 0 32 (In addition, many customers have taken an active in\255) W
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16.9 0 32 (terest in FDDI interoperability issues and have begun) W
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(their own testing programs.) h
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6.0 0 32 (Multivendor interoperability within FDDI networks is) W
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465.0 0 32 (a major concern to Digital. The success of FDDI) W
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254.9 0 32 (hinges on the stability of a seamless heterogeneous) W
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338.8 0 32 (network environment in which all vendor products) W
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(completely interoperate with all others. ) h
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191.3 0 32 (To that end, extensive interoperability testing is be\255) W
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36.9 0 32 (ing carried out by Digital engineers between its FDDI) W
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43.2 0 32 (product set and those of a number of other FDDI ven\255) W
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75.2 0 32 (dors. The current results of the testing show that, for) W
300 -21400 M
39.3 0 32 (many vendors, a high degree of interoperability exists) W
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(among the products that have been examined. ) h
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61.1 0 32 (Testing is being performed at Digital's FDDI develop\255) W
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116.2 0 32 (ment center in Littleton, Massachusetts, at customer) W
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214.0 0 32 (sites, and at other vendors' locations. Many product) W
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138.7 0 32 (types have been tested, including bridges, concentra\255) W
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261.6 0 32 (tors, end station adapters, and routers. Included in) W
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412.4 0 32 (the products tested have been three of the major) W
300 -33600 M
13.7 0 32 (FDDI chipsets: the chipset developed by Digital which) W
300 -35000 M
48.5 0 32 (is being licensed to Motorola and Advanced Micro De\255) W
300 -36400 M
313.0 0 32 (vices, Advanced Micro Devices' SUPERNET family,) W
300 -37800 M
387.6 0 32 (and National Semiconductor's DP83200 FDDI chip) W
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(set.) h
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249.1 0 32 (A number of problems have been discovered during) W
300 -43000 M
39.8 0 32 (testing and most have already been fixed. Many prob\255) W
300 -44400 M
169.7 0 32 (lems discovered do not affect interoperability or net\255) W
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429.4 0 32 (work operation and stability, but others do. With) W
300 -47200 M
67.2 0 32 (FDDI in its early stages, these problems are to be ex\255) W
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138.7 0 32 (pected. Cooperation between vendors has been excel\255) W
300 -50000 M
254.9 0 32 (lent and many of these problems were immediately) W
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(resolved.) h
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/Helvetica-Bold-ISOLatin1 F 1200 o f
(TEST METHODOLOGY) h
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134.6 0 32 (A testplan was developed originally for design verifi\255) W
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167.8 0 32 (cation, and later for interoperability testing between) W
300 -61200 M
245.9 0 32 (Digital's FDDI product set and products from other) W
300 -62600 M
128.3 0 32 (vendors. The testplan concentrates mainly on the in\255) W
300 -64000 M
289.7 0 32 (teroperability of the FDDI datalink, defined by the) W
300 -65400 M
78.8 0 32 (FDDI PHY, MAC, and proposed PMD and SMT stan\255) W
300 -66800 M
95.3 0 32 (dards and is based upon both SMT 5.1 and 6.2 draft) W
300 -68200 M
(standards.) h
300 -70600 M
116.9 0 32 (The plan covers all of the FDDI SMT draft including) W
300 -72000 M
347.0 0 32 (Connection Management \(CMT\), Ring Management) W
300 -73400 M
105.3 0 32 (\(RMT\), and SMT frame\255based services and functions. ) W
300 -74800 M
186.5 0 32 (The intent of the plan is not just to verify plug and) W
300 -76200 M
45.5 0 32 (play capability but also to verify correct operation un\255) W
300 -77600 M
(der both normal and aberrant network conditions.) h
300 -80000 M
6.4 0 32 (Testing of Connection Management extensively covers) W
300 -81400 M
548.6 0 32 (the Physical Connection Management \(PCM\) and) W
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453.0 0 32 (Configuration Management \(CFM\) processes. PCM) W
300 -2600 M
366.3 0 32 (testing covers the bit signaling and connection in\255) W
300 -4000 M
614.6 0 32 (itialization algorithms, the Link Confidence Test) W
300 -5400 M
252.6 0 32 (\(LCT\) and Link Error Monitor \(LEM\), and verifica\255) W
300 -6800 M
392.9 0 32 (tion of the connection matrix defined in the SMT) W
300 -8200 M
32.1 0 32 (draft. CFM testing verifies correct operation of the re\255) W
300 -9600 M
(configuration scrub and MAC insertion functions.) h
300 -12000 M
157.0 0 32 (RMT testing covers both pre and post\255RingOp dupli\255) W
300 -13400 M
149.8 0 32 (cate address detection, including stuck beacon detec\255) W
300 -14800 M
17.0 0 32 (tion and recovery, Directed and Jam Beacon initiation) W
300 -16200 M
293.3 0 32 (and reception, and PC Trace initiation and conver\255) W
300 -17600 M
212.8 0 32 (gence. Other miscellaneous testing centers on moni\255) W
300 -19000 M
262.4 0 32 (toring for abusive use of Restricted tokens and Ex\255) W
300 -20400 M
(tended Service Frames.) h
300 -22800 M
245.8 0 32 (Frame\255based testing covers all required SMT frame) W
300 -24200 M
374.8 0 32 (protocols. The Neighbor Notification \(NIF\), Station) W
300 -25600 M
580.4 0 32 (Information \(SIF\), Echo \(ECF\), Extended Service) W
300 -27000 M
23.3 0 32 (\(ESF\), and Request Denied \(RDF\) protocols are all ex\255) W
300 -28400 M
76.0 0 32 (tensively tested for compliance to the SMT draft. The) W
300 -29800 M
90.8 0 32 (Neighbor Notification protocol's duplicate address de\255) W
300 -31200 M
195.3 0 32 (tection is tested as part of RMT. Parameters within) W
300 -32600 M
99.9 0 32 (the frames are all examined for consistency and cor\255) W
300 -34000 M
194.7 0 32 (rectness. For example, all timer values presented in) W
300 -35400 M
245.4 0 32 (SMT frames are verified to be in two's complement) W
300 -36800 M
190.8 0 32 (form and all canonical addresses correctly converted) W
300 -38200 M
(to FDDI MSB.) h
300 -40600 M
12.0 0 32 (A tool, herein called the 'DVT Monitor', was developed) W
300 -42000 M
75.3 0 32 (with the capabilities needed to perform interoperabil\255) W
300 -43400 M
216.9 0 32 (ity testing. Based on the diagnostic dispatcher built) W
300 -44800 M
296.3 0 32 (into each of Digital's FDDI products and originally) W
300 -46200 M
45.5 0 32 (used for our design verification testing, it was quickly) W
300 -47600 M
(expanded to suit the interoperability testing needs.) h
300 -50000 M
123.3 0 32 (The DVT Monitor has two components, a UART con\255) W
300 -51400 M
46.4 0 32 (nection which provides serial communication between) W
300 -52800 M
78.8 0 32 (the product and a display terminal, and monitor soft\255) W
300 -54200 M
225.6 0 32 (ware which is layered on top of the SMT firmware.) W
300 -55600 M
50.9 0 32 (The monitoring and managing of the SMT software is) W
300 -57000 M
290.0 0 32 (thus achieved by out\255of\255band access via the UART.) W
300 -58400 M
87.6 0 32 (This is necessary to perform testing of ring fault con\255) W
300 -59800 M
92.2 0 32 (ditions. The monitor software is run at a lower prior\255) W
300 -61200 M
65.0 0 32 (ity than all other components in the system so that it) W
300 -62600 M
62.8 0 32 (does not affect the system timing or operation. It pro\255) W
300 -64000 M
371.8 0 32 (vides both nonintrusive \(peek\) and invasive \(poke\)) W
300 -65400 M
321.2 0 32 (management capabilities. Password protection on a) W
300 -66800 M
109.3 0 32 (login screen prevents unsophisticated users from dis\255) W
300 -68200 M
267.4 0 32 (rupting the network. To use the tool, one must log) W
300 -69600 M
(onto an FDDI product running the test software. ) h
300 -72000 M
106.8 0 32 (As a nonintrusive tool, the DVT Monitor provides for) W
300 -73400 M
50.9 0 32 (passive monitoring of the network status and related) W
300 -74800 M
179.1 0 32 (events. The tool provides for real\255time monitoring of) W
300 -76200 M
242.7 0 32 (all physical \(Port\) and logical \(MAC\) connections in) W
300 -77600 M
68.0 0 32 (the product. Status windows continuously display the) W
300 -79000 M
339.8 0 32 (state of all physical and logical connections to the) W
300 -80400 M
(ring. ) h
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/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
289.7 0 32 (As an invasive tool, it can be used for purposes of) W
300 -2600 M
144.1 0 32 (fault insertion and exercising the ring. The tool can) W
300 -4000 M
109.0 0 32 (be used to easily change Station parameters, such as) W
300 -5400 M
407.4 0 32 (the MAC T_REQ timer and the station's address.) W
300 -6800 M
86.8 0 32 (Configuration hardware within each product can also) W
300 -8200 M
94.7 0 32 (be changed to affect the operational state of the ring.) W
300 -9600 M
33.1 0 32 (This is especially helpful for introducing duplicate ad\255) W
300 -11000 M
872.6 0 32 (dressed stations, stuck beacon conditions, bea\255) W
300 -12400 M
204.8 0 32 (con/claim ring oscillations, and other anomalies into) W
300 -13800 M
417.4 0 32 (an operational ring for the purposes of exercising) W
300 -15200 M
339.9 0 32 (RMT and the PC Trace function. To analyze SMT) W
300 -16600 M
366.1 0 32 (frames, an SMT frame agent exists in the tool to) W
300 -18000 M
550.4 0 32 (source and sink any SMT frame type, including) W
300 -19400 M
(frames not defined by the standard.) h
8871 -23600 M
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300 -26400 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
163.4 0 32 (The testing performed has discovered and helped fix) W
300 -27800 M
201.6 0 32 (problems in many vendors' implementations, includ\255) W
300 -29200 M
140.9 0 32 (ing Digital's. Many problems discovered were the re\255) W
300 -30600 M
58.4 0 32 (sult of inconsistent interpretations of the SMT drafts.) W
300 -32000 M
157.0 0 32 (Other problems were due to incomplete implementa\255) W
300 -33400 M
56.9 0 32 (tions which did not support some functions defined in) W
300 -34800 M
176.1 0 32 (the SMT draft. Still other problems were a result of) W
300 -36200 M
176.1 0 32 (changes in the SMT draft which were overlooked by) W
300 -37600 M
(some implementations.) h
300 -40000 M
23.8 0 32 (Each section below briefly summarizes the functional\255) W
300 -41400 M
215.4 0 32 (ity that was tested, followed by a description of the) W
300 -42800 M
286.8 0 32 (types of interoperability problems observed. Wher\255) W
300 -44200 M
175.8 0 32 (ever possible, suggestions are made on how to avoid) W
300 -45600 M
(these problems.) h
300 -49300 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(Connection Management \(CMT\)) h
300 -51600 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
348.4 0 32 (The Physical Connection Management \(PCM\) state) W
300 -53000 M
198.0 0 32 (machine governs the initialization of the full duplex) W
300 -54400 M
131.5 0 32 (connection between adjacent PHYs in the ring. This) W
300 -55800 M
231.0 0 32 (initialization involves the transfer of control symbol) W
300 -57200 M
227.3 0 32 (streams between the connecting PHYs. A particular) W
300 -58600 M
49.6 0 32 ('line state' is said to have been received when the cor\255) W
300 -60000 M
331.7 0 32 (responding control stream has been recognized per) W
300 -61400 M
265.0 0 32 (the requirements put forth in the ANSI PHY stan\255) W
300 -62800 M
326.3 0 32 (dard and SMT draft. The reception of specific line) W
300 -64200 M
134.5 0 32 (states is the mechanism used to control the synchro\255) W
300 -65600 M
(nization of state transitions in each PCM.) h
300 -68000 M
62.0 0 32 (The level of interoperability of PCM has already been) W
300 -69400 M
220.8 0 32 (demonstrated to be very high through the efforts of) W
300 -70800 M
198.0 0 32 (early testing between vendors at the Advanced Net\255) W
300 -72200 M
26.1 0 32 (working Test Center \(ANTC\) and trade shows such as) W
300 -73600 M
198.3 0 32 (INTEROP '89. A large number of vendors have suc\255) W
300 -75000 M
446.3 0 32 (cessfully connected with each other and exercised) W
300 -76400 M
71.0 0 32 (PCM and its parameters. However, we have observed) W
300 -77800 M
238.0 0 32 (two interesting interoperability problems in a small) W
300 -79200 M
168.2 0 32 (number of PCM implementations which bear discus\255) W
300 -80600 M
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300 -2600 M
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93.8 0 32 (First, we have observed implementations which dem\255) W
300 -4000 M
575.4 0 32 (onstrate a sensitivity to low values of TL_MIN.) W
300 -5400 M
284.4 0 32 (TL_MIN is a parameter in PCM which defines the) W
300 -6800 M
12.1 0 32 (minimum required time to continue to transmit a con\255) W
300 -8200 M
273.3 0 32 (trol stream after the incoming line state which en\255) W
300 -9600 M
134.1 0 32 (ables a state transition has been recognized. The de\255) W
300 -11000 M
225.3 0 32 (fault value of TL_MIN, as specified in the SMT 6.2) W
300 -12400 M
182.0 0 32 (draft, is 30 microseconds. This requirement places a) W
300 -13800 M
18.6 0 32 (lower limit on how long a line state will be visible at a) W
300 -15200 M
15.4 0 32 (PHY when it begins to transmit a new control stream.) W
300 -16600 M
302.6 0 32 (If an implementation cannot observe the line state) W
300 -18000 M
77.1 0 32 (change within TL_MIN, it will miss a line state tran\255) W
300 -19400 M
272.6 0 32 (sition. If this occurs, one or both PHY's PCMs will) W
300 -20800 M
156.6 0 32 (time out and the connection will be retried. Depend\255) W
300 -22200 M
201.0 0 32 (ing on the relative delays of the respective systems,) W
300 -23600 M
408.7 0 32 (this condition may repeat indefinitely, although it) W
300 -25000 M
115.1 0 32 (usually does not, ie. most implementations which ex\255) W
300 -26400 M
308.8 0 32 (hibit this behavior eventually complete the connec\255) W
300 -27800 M
(tion. ) h
300 -30200 M
185.3 0 32 (The first implementations of the PHY \(both discrete) W
300 -31600 M
198.4 0 32 (logic as well as VLSI\) relegated the PCM portion of) W
300 -33000 M
152.9 0 32 (the implementation to software. This was a 'natural') W
300 -34400 M
168.6 0 32 (decision due to the volatility of the standard at that) W
300 -35800 M
78.4 0 32 (time. As a result of this partitioning, it was not read\255) W
300 -37200 M
34.2 0 32 (ily apparent that some implementations exhibited the) W
300 -38600 M
99.6 0 32 (problem we describe here, since nearly all implemen\255) W
300 -40000 M
304.7 0 32 (tations had an artificially high equivalent TL_MIN) W
300 -41400 M
195.5 0 32 (due to the processor handling all responsibilities of) W
300 -42800 M
364.0 0 32 (PCM. As more implementations take advantage of) W
300 -44200 M
173.0 0 32 (FDDI chips with hardware assisted PCM, it will be\255) W
300 -45600 M
183.8 0 32 (come increasingly necessary that an implementation) W
300 -47000 M
(be able to operate with the specified value of TL_MIN.) h
300 -50200 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(TPC Timer) h
300 -51600 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
50.2 0 32 (Another problem observed in the area of PCM was an) W
300 -53000 M
150.0 0 32 (implementation failing to reload the TPC timer with) W
300 -54400 M
274.4 0 32 (C_Min after recognizing Halt line state when PCM) W
300 -55800 M
426.3 0 32 (was in CONNECT. Although this doesn't cause a) W
300 -57200 M
242.4 0 32 (problem with violating the acquisition time of a re\255) W
300 -58600 M
171.6 0 32 (ceiver \(except possibly for the first insertion of a ca\255) W
300 -60000 M
167.3 0 32 (ble\), it is outside of the specification and as a result) W
300 -61400 M
321.6 0 32 (some other implementations may fail to detect the) W
300 -62800 M
464.4 0 32 (halt line state sourced while in CONNECT. This) W
300 -64200 M
153.7 0 32 (would occur if the other implementation began sour\255) W
300 -65600 M
32.0 0 32 (cing halts prior to checking for the input line state. In) W
300 -67000 M
321.8 0 32 (this case, if the other PHY had already timed out) W
300 -68400 M
153.1 0 32 (TPC, it would transition to NEXT immediately upon) W
300 -69800 M
55.2 0 32 (reception of Halt line state \255 and begin sourcing idles.) W
300 -71200 M
125.9 0 32 (If the other implementation failed to sample the line) W
300 -72600 M
91.8 0 32 (state prior to the reception of idle line state, it would) W
300 -74000 M
82.8 0 32 (see idles instead of halts which would cause it to exit) W
300 -75400 M
124.6 0 32 (CONNECT and return to the BREAK state \255 and re\255) W
300 -76800 M
(try the connection.) h
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(Configuration and Topologies) h
300 -2600 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
142.5 0 32 (In the SMT draft, topology management may be dis\255) W
300 -4000 M
185.4 0 32 (tributed between the PCM pseudocode and the Con\255) W
300 -5400 M
20.0 0 32 (figuration Management state machine \(CFM\). As part) W
300 -6800 M
225.8 0 32 (of the PCM pseudocode, the decision is made to ac\255) W
300 -8200 M
58.6 0 32 (cept/reject a connection based on the station's connec\255) W
300 -9600 M
84.0 0 32 (tion rules. These rules determine which physical con\255) W
300 -11000 M
74.3 0 32 (nection types are allowed, such as M to M rejected, B) W
300 -12400 M
54.2 0 32 (to M allowed, etc. If a PHY is rejected, the connection) W
300 -13800 M
169.6 0 32 (is restarted. This process repeats until the condition) W
300 -15200 M
3.9 0 32 (is corrected. The CFM state machine controls the data) W
300 -16600 M
95.3 0 32 (path between the stations PHY and MAC entities. In) W
300 -18000 M
279.8 0 32 (certain cases, it may alter the data path to render) W
300 -19400 M
(some topologies harmless.) h
300 -21800 M
170.4 0 32 (To illustrate this, consider the application of the de\255) W
300 -23200 M
192.6 0 32 (fault connection rules matrix shown in the SMT 6.2) W
300 -24600 M
134.4 0 32 (draft. They allow nearly any connection type to form) W
300 -26000 M
121.9 0 32 (and relegate the disarming of particularly nasty con\255) W
300 -27400 M
60.1 0 32 (figurations to the CFM. For example, if we consider a) W
300 -28800 M
25.3 0 32 (topology when one of the attachment PHYs \(A or B\) is) W
300 -30200 M
187.8 0 32 (connected in peer mode \(to another A or B\) and the) W
300 -31600 M
167.9 0 32 (other attachment PHY is connected in tree mode \(to) W
300 -33000 M
101.3 0 32 (an M\), the connection rules would allow both connec\255) W
300 -34400 M
149.2 0 32 (tions to form, but CFM would be prevented from go\255) W
300 -35800 M
750.1 0 32 (ing to THRU and would instead transition to) W
300 -37200 M
126.8 0 32 (WRAP_B, such that the A PHY would be unused ie.,) W
300 -38600 M
(looped back on itself.) h
300 -41000 M
467.7 0 32 (As an alternate method, topology control may be) W
300 -42400 M
190.3 0 32 (achieved by the PCM pseudocode refusing to form a) W
300 -43800 M
76.3 0 32 (connection based on the peer/tree mode of the attach\255) W
300 -45200 M
101.9 0 32 (ment PHYs. In the above example, the A PHY would) W
300 -46600 M
20.8 0 32 (never form a connection; it would be rejected based on) W
300 -48000 M
78.5 0 32 (the fact that a B to M connection already exists. This) W
300 -49400 M
98.9 0 32 (illustrates a tree preference. Either tree or peer pref\255) W
300 -50800 M
131.8 0 32 (erence is allowed by the SMT draft. In this scenario,) W
300 -52200 M
81.9 0 32 (the CFM need not be concerned with topology control) W
300 -53600 M
(at all.) h
300 -56000 M
4.3 0 32 (Some examples of problems seen with topology control) W
300 -57400 M
308.9 0 32 (distributed between CFM and PCM are as follows.) W
300 -58800 M
22.9 0 32 (Some implementations accept both A to M and B to M) W
300 -60200 M
267.9 0 32 (connections and their CFM fails to go to WRAP_B,) W
300 -61600 M
49.6 0 32 (but remains in THRU. This causes the ring to be par\255) W
300 -63000 M
17.5 0 32 (titioned into two disjoint rings. We have also observed) W
300 -64400 M
201.1 0 32 (a case where the order of operations caused a prob\255) W
300 -65800 M
208.2 0 32 (lem. If we connected A to M then B to M, the DAS) W
300 -67200 M
303.4 0 32 (CFM correctly transitioned to WRAP_B. If we con\255) W
300 -68600 M
80.5 0 32 (nected B to M then A to M, the DAS CFM would cor\255) W
300 -70000 M
398.4 0 32 (rectly remain in WRAP_B, but the ring would go) W
300 -71400 M
128.4 0 32 (down and eventually the DAS would initiate a trace.) W
300 -72800 M
386.2 0 32 (This symptom implies that the DAS inadvertently) W
300 -74200 M
340.6 0 32 (blocked its MAC input. These examples show that) W
300 -75600 M
176.1 0 32 (even careful designs may miss certain cases and ex\255) W
300 -77000 M
283.0 0 32 (haustive testing of all configuration and connection) W
300 -78400 M
(types is indicated.) h
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(Ring Management \(RMT\) ) h
300 -3500 M
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13.7 0 32 (The RMT state machine has two primary responsibili\255) W
300 -4900 M
50.1 0 32 (ties, both having to do with handling ring fault condi\255) W
300 -6300 M
60.8 0 32 (tions. The first is to respond to a Stuck Beacon condi\255) W
300 -7700 M
715.6 0 32 (tion, the second is to detect duplicate address) W
300 -9100 M
39.7 0 32 (conditions which prevent the ring from completing in\255) W
300 -10500 M
212.2 0 32 (itialization. The RMT state machine also represents) W
300 -11900 M
270.3 0 32 (the state of the frame based duplicate address test) W
300 -13300 M
(when the ring is operational.) h
300 -16500 M
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(PC_Trace) h
300 -17900 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
56.5 0 32 (In a ring free of faults, a beaconing MAC would even\255) W
300 -19300 M
209.3 0 32 (tually receive its own beacon and continue with the) W
300 -20700 M
505.2 0 32 (initialization process, or it would receive another) W
300 -22100 M
128.9 0 32 (MAC's beacon and yield \(ie repeat the other beacon\).) W
300 -23500 M
328.8 0 32 (A MAC which is stuck beaconing indicates a fault) W
300 -24900 M
71.1 0 32 (situation where the ring has a logical break in it. If a) W
300 -26300 M
372.7 0 32 (station's MAC is stuck beaconing for greater than) W
300 -27700 M
39.4 0 32 (T_Stuck \(8 seconds\), then corrective actions are taken) W
300 -29100 M
114.2 0 32 (by RMT. A burst of directed beacons are first sent to) W
300 -30500 M
103.0 0 32 (indicate ownership of the stuck condition after which) W
300 -31900 M
87.1 0 32 (a PC_Trace is initiated. The directed beacon is a spe\255) W
300 -33300 M
139.1 0 32 (cial beacon frame which is addressed to a dedicated) W
300 -34700 M
170.2 0 32 (multicast address. The PC_Trace propagates against) W
300 -36100 M
53.8 0 32 (the token flow \(utilizing the full duplex physical links) W
300 -37500 M
259.4 0 32 (to signal status\) until another MAC is reached. All) W
300 -38900 M
109.1 0 32 (stations involved then do a 'path test'. This path test) W
300 -40300 M
16.3 0 32 (is a full test of the involved components \255 many imple\255) W
300 -41700 M
250.8 0 32 (mentations do a full powerup test. The intention is) W
300 -43100 M
52.6 0 32 (that the defective station will detect the fault and not) W
300 -44500 M
(rejoin the ring.) h
300 -46900 M
141.4 0 32 (In stations with more than a single PHY, the propa\255) W
300 -48300 M
106.6 0 32 (gation of PC_Trace from the MAC which is initiating) W
300 -49700 M
247.9 0 32 (the trace is dependent on the PCM state and CFM) W
300 -51100 M
6.5 0 32 (state of the PHYs in the station, ie., the trace signal is) W
300 -52500 M
255.2 0 32 (sent out on the next upstream PHY whose PCM is) W
300 -53900 M
233.1 0 32 (ACTIVE. The determination of who is upstream re\255) W
300 -55300 M
114.6 0 32 (quires knowledge of the CFM state or some other in\255) W
300 -56700 M
(ternal representation of the data path. ) h
300 -59100 M
78.8 0 32 (Some implementations have been observed which fail) W
300 -60500 M
105.7 0 32 (to propagate trace out of the station if the CFM is in) W
300 -61900 M
181.3 0 32 (WRAP_B. The effect of this error is that the station) W
300 -63300 M
15.4 0 32 (which is stuck beaconing fails to initiate the trace and) W
300 -64700 M
123.0 0 32 (send the HQ symbol stream to the upstream station.) W
300 -66100 M
179.3 0 32 (It, however, does \(usually\) remember to perform the) W
300 -67500 M
11.8 0 32 (path test. If the path test is sufficiently quick, the sta\255) W
300 -68900 M
188.6 0 32 (tion will complete its test and rejoin the ring before) W
300 -70300 M
490.0 0 32 (the NEXT downstream station would become the) W
300 -71700 M
251.9 0 32 (stuck beaconer and REALLY initiate the trace \(eg.,) W
300 -73100 M
160.8 0 32 (test and rejoin in less than 10 seconds\). The end re\255) W
300 -74500 M
265.0 0 32 (sult is that the ring will stay down with the stuck) W
300 -75900 M
185.0 0 32 (beaconer alternately being the station which fails to) W
300 -77300 M
156.3 0 32 (initiate trace and the next downstream station. This) W
300 -78700 M
94.7 0 32 (scenario renders the PC_Trace process completely in\255) W
300 -80100 M
(effective.) h
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268.4 0 32 (One implementation was observed which misunder\255) W
300 -2600 M
7.6 0 32 (stood the operation of trace. In this case, the trace sig\255) W
300 -4000 M
67.6 0 32 (nal would always propagate, never terminate. The ef\255) W
300 -5400 M
213.2 0 32 (fect of this was that the trace would extend beyond) W
300 -6800 M
115.4 0 32 (the true fault domain. Another implementation mis\255) W
300 -8200 M
223.6 0 32 (understood the operation of the stuck beacon timer. ) W
300 -9600 M
248.1 0 32 (The station would declare 'stuck beacon' if the ring) W
300 -11000 M
309.1 0 32 (was down for 10 seconds, whether the station was) W
300 -12400 M
36.4 0 32 (beaconing or not. The result of this error was that the) W
300 -13800 M
245.8 0 32 (station would frequently declare stuck beacon, even) W
300 -15200 M
51.7 0 32 (when outside the actual fault domain \255 so it would in\255) W
300 -16600 M
429.4 0 32 (itiate another trace, causing stations to path test) W
300 -18000 M
203.3 0 32 (which had nothing to do with the fault condition. A) W
300 -19400 M
56.8 0 32 (similar effect was observed in implementations which) W
300 -20800 M
98.6 0 32 (use a short value of T_Stuck. In older versions of the) W
300 -22200 M
228.6 0 32 (standard, the T_Stuck timer was specified at 2 sec\255) W
300 -23600 M
104.6 0 32 (onds and later was changed to 10 seconds. The effect) W
300 -25000 M
0.8 0 32 (of this error would likely cause a secondary trace to be) W
300 -26400 M
(initiated while the first one was trying to complete.) h
300 -29600 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(Directed Beacons) h
300 -31000 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
184.4 0 32 (Recall that the directed beacon frame is intended to) W
300 -32400 M
220.0 0 32 (allow network management to identify the fault do\255) W
300 -33800 M
15.8 0 32 (main of a PC_Trace process. The directed beacon is is\255) W
300 -35200 M
341.8 0 32 (sued to a dedicated multicast address immediately) W
300 -36600 M
116.4 0 32 (prior to the initiation of the trace process by the sta\255) W
300 -38000 M
175.6 0 32 (tion which is stuck beaconing. Optionally, the frame) W
300 -39400 M
191.4 0 32 (may contain the stations UNA, which MAY indicate) W
300 -40800 M
(the upstream extreme of the fault domain.) h
300 -43200 M
210.2 0 32 (Several implementations tested had minor problems) W
300 -44600 M
6.6 0 32 (in this area. We saw incorrect destination address \(eg.) W
300 -46000 M
83.2 0 32 (Upstream Neighbor Address \(UNA\) or Broadcast, not) W
300 -47400 M
49.8 0 32 (the dedicated multicast address\) and incorrect beacon) W
300 -48800 M
70.3 0 32 (type format. The optional UNA, while useful to imply) W
300 -50200 M
173.1 0 32 (the extent of the fault domain, was frequently miss\255) W
300 -51600 M
242.6 0 32 (ing. The directed beacon is not specifically required) W
300 -53000 M
109.4 0 32 (for stations to interoperate, but the correct transmis\255) W
300 -54400 M
186.5 0 32 (sion of the frame prior to a trace fault will be quite) W
300 -55800 M
267.6 0 32 (useful to network management to debug a network) W
300 -57200 M
194.0 0 32 (which experiences frequent trace processes \(presum\255) W
300 -58600 M
(ably due to an ineffective path test\).) h
300 -61800 M
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(Duplicate Addresses) h
300 -63200 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
139.2 0 32 (The RMT portion of the SMT draft which deals with) W
300 -64600 M
15.6 0 32 (pre\255ringop duplicate address detection was introduced) W
300 -66000 M
167.5 0 32 (relatively late in the standards process and many of) W
300 -67400 M
223.0 0 32 (the implementations tested had either a partial im\255) W
300 -68800 M
186.0 0 32 (plementation of RMT or none at all. Of those which) W
300 -70200 M
360.7 0 32 (fully implemented RMT, most appeared to operate) W
300 -71600 M
260.0 0 32 (quite well. Almost all implementations tested, how\255) W
300 -73000 M
3.6 0 32 (ever, chose to take leave actions rather than jamming.) W
300 -74400 M
47.8 0 32 (The optional jamming is done to inform the other sta\255) W
300 -75800 M
81.3 0 32 (tions with the same address that they are duplicates.) W
300 -77200 M
101.6 0 32 (By taking leave actions, the 'bad' station \(i.e. the one) W
300 -78600 M
52.7 0 32 (with the erroneous address\) can be unaware that it is) W
300 -80000 M
428.5 0 32 (a duplicate and the 'good' victim leaves the ring.) W
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361.2 0 32 (Many implementations will likely include jamming) W
300 -2600 M
(actions as time permits.) h
300 -5000 M
35.4 0 32 (The SMT 5.1 draft did not specify a post\255ringop dupli\255) W
300 -6400 M
230.7 0 32 (cate address test. Some implementations supplied a) W
300 -7800 M
391.7 0 32 (proprietary scheme in lieu of a standard solution. ) W
300 -9200 M
45.1 0 32 (Many omitted any test and waited for one to be speci\255) W
300 -10600 M
2.5 0 32 (fied in a later draft. The SMT 6.2 draft now specifies a) W
300 -12000 M
(request/response test based on NIF frames.) h
300 -14400 M
112.0 0 32 (The only difficulty observed when using the SMT 6.2) W
300 -15800 M
601.4 0 32 (request/response test is that one implementation) W
300 -17200 M
126.7 0 32 (failed to receive a NSA NIF request to the broadcast) W
300 -18600 M
329.2 0 32 (address if the source address was the same as its) W
300 -20000 M
(MAC address.) h
300 -23700 M
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300 -26000 M
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112.8 0 32 (Problems with Connection Management may prevent) W
300 -27400 M
112.1 0 32 (a station from joining the ring and disrupt ring per\255) W
300 -28800 M
52.6 0 32 (formance and stability. It is hard to determine at this) W
300 -30200 M
274.0 0 32 (point what effect implementations will have on the) W
300 -31600 M
15.1 0 32 (network if their SMT frame\255based services do not con\255) W
300 -33000 M
458.3 0 32 (form to the proposed standard. Despite a limited) W
300 -34400 M
115.7 0 32 (number of user applications which utilize these serv\255) W
300 -35800 M
25.6 0 32 (ices, it is crucial that all vendors thoroughly test their) W
300 -37200 M
(implementations in this respect.) h
300 -39600 M
9.3 0 32 (One application which does commonly exist is the net\255) W
300 -41000 M
26.4 0 32 (work management Ring Map application. A Ring Map) W
300 -42400 M
528.0 0 32 (is a graphical representation of both logical and) W
300 -43800 M
264.3 0 32 (physical FDDI topologies, showing a 'street map' of) W
300 -45200 M
171.7 0 32 (the network, token flow, and miscellaneous informa\255) W
300 -46600 M
191.4 0 32 (tion about each node. Station Information \(SIF\) and) W
300 -48000 M
118.9 0 32 (Neighbor Information \(NIF\) frames are used to build) W
300 -49400 M
518.0 0 32 (these maps. Incorrectly formatted information re\255) W
300 -50800 M
175.9 0 32 (ported by SMT frame\255based services will affect Ring) W
300 -52200 M
252.0 0 32 (Map applications, causing incorrect maps to be dis\255) W
300 -53600 M
(played.) h
300 -56800 M
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(Path Descriptors) h
300 -58200 M
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175.9 0 32 (The Path Descriptor parameter in the Station Infor\255) W
300 -59600 M
261.4 0 32 (mation response frame is probably the most impor\255) W
300 -61000 M
67.6 0 32 (tant piece of information used when building a physi\255) W
300 -62400 M
321.6 0 32 (cal ring map. Path Descriptors describe a station's) W
300 -63800 M
9.3 0 32 (internal topology, ie., how the MAC and PORT compo\255) W
300 -65200 M
161.4 0 32 (nents are arranged inside a device such as a Wiring) W
300 -66600 M
190.2 0 32 (Concentrator or Dual Attachment Station. The SMT) W
300 -68000 M
195.6 0 32 (draft does not stipulate the rules for reporting Path) W
300 -69400 M
27.3 0 32 (Descriptor information but presents "a possible index\255) W
300 -70800 M
90.3 0 32 (ing scheme" \([1],p.145\). This indexing scheme reports) W
300 -72200 M
76.0 0 32 (how the components inside a station are connected to) W
300 -73600 M
115.8 0 32 (each other \(eg., the output of M PORT 2 is the input) W
300 -75000 M
81.6 0 32 (to the MAC and the MAC's output is the input to the) W
300 -76400 M
23.1 0 32 (B PORT\). If a Ring Map application follows the guide\255) W
300 -77800 M
195.6 0 32 (line presented in the SMT draft when decoding this) W
300 -79200 M
87.0 0 32 (information then an incorrect map will be built when) W
300 -80600 M
282.8 0 32 (an implementation reports its Path Descriptors an\255) W
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289.7 0 32 (other way. All implementations seen to date follow) W
300 -2600 M
(the guidelines presented in the SMT draft. ) h
300 -5000 M
212.0 0 32 (A possible problem may appear in Ring Map imple\255) W
300 -6400 M
73.0 0 32 (mentations that aren't careful how they use Path De\255) W
300 -7800 M
308.2 0 32 (scriptor information. Not all implementations clean) W
300 -9200 M
261.7 0 32 (up the Path Descriptor fields when connections are) W
300 -10600 M
153.3 0 32 (lost. For example, the RemotePORTType field in the) W
300 -12000 M
8.6 0 32 (Path Descriptor PORT Record gives the type of the re\255) W
300 -13400 M
294.8 0 32 (motely connected PORT. Some implementations set) W
300 -14800 M
148.0 0 32 (RemotePORTType to UNKNOWN when the physical) W
300 -16200 M
134.6 0 32 (connection terminates, while others do not modify it.) W
300 -17600 M
461.0 0 32 (Likewise, similar action is taken with the Remo\255) W
300 -19000 M
15.9 0 32 (teMAC information. There is no right or wrong way to) W
300 -20400 M
312.6 0 32 (report these fields after the connection breaks; the) W
300 -21800 M
67.3 0 32 (SMT draft does not say what to do with it. Therefore,) W
300 -23200 M
185.1 0 32 (applications which use the data must determine the) W
300 -24600 M
85.5 0 32 (state it is being presented in and whether or not it is) W
300 -26000 M
(valid before referencing it.) h
300 -29200 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(Timer Representation) h
300 -30600 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
356.1 0 32 (The standard states that all timer values in SMT) W
300 -32000 M
148.0 0 32 (frames shall be reported in two's complement 80 na\255) W
300 -33400 M
53.9 0 32 (nosecond form. It was observed that some implemen\255) W
300 -34800 M
315.7 0 32 (tations were not presenting timers correctly in the) W
300 -36200 M
570.8 0 32 (Station Information response frames \(SIF\). Some) W
300 -37600 M
67.5 0 32 (were not in two's complement, others were 'almost' in) W
300 -39000 M
210.7 0 32 (two's complement. In one instance, the MAC Status) W
300 -40400 M
315.4 0 32 (parameter's 32 bit T_REQ field was incorrectly re\255) W
300 -41800 M
292.3 0 32 (ported as X'00FE7A00' instead of X'FFFE7A00'. A) W
300 -43200 M
424.0 0 32 (network management application collecting station) W
300 -44600 M
77.7 0 32 (statistics, for example, would report the correct timer) W
300 -46000 M
51.6 0 32 (value as 7.99 milliseconds. The erroneous timer value) W
300 -47400 M
(would be reported as 2960.78 milliseconds.) h
300 -50600 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(Omissions and Discrepancies) h
300 -52000 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
306.3 0 32 (Many other problems were seen which could affect) W
300 -53400 M
10.4 0 32 (network management and interoperability. A common) W
300 -54800 M
303.4 0 32 (problem with incomplete implementations was that) W
300 -56200 M
80.1 0 32 (place holders \(zero fill or F's\) were used where actual) W
300 -57600 M
138.0 0 32 (parameters should have been. Others reported erro\255) W
300 -59000 M
145.5 0 32 (neous information field lengths in the SMT headers) W
300 -60400 M
137.4 0 32 (of their frames, the PORT LER Status Ler_Estimate) W
300 -61800 M
343.9 0 32 (value out of range, the Path Latency Contribution) W
300 -63200 M
347.4 0 32 (with unreasonable values, or reported zero for the) W
300 -64600 M
96.3 0 32 (MsgTimeStamp station timestamp parameter. Errors) W
300 -66000 M
147.9 0 32 (in the Topology byte from the Station State parame\255) W
300 -67400 M
11.1 0 32 (ter were popular, such as failing to report WRAP_B or) W
300 -68800 M
203.3 0 32 (Twisted Ring \(A to A or B to B connections\) topolo\255) W
300 -70200 M
147.1 0 32 (gies. These errors obviously can make network man\255) W
300 -71600 M
17.1 0 32 (agement difficult and such erroneous data casts doubt) W
300 -73000 M
109.3 0 32 (on the reliability of the remaining information in the) W
300 -74400 M
290.5 0 32 (frame. Similarly, many incomplete implementations) W
300 -75800 M
508.8 0 32 (failed to accurately reflect unusual configurations) W
300 -77200 M
193.7 0 32 (which can cause instability in network management) W
300 -78600 M
(applications such as the Ring Map. ) h
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(Exception Handling) h
300 -2600 M
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317.2 0 32 (Implementations must also handle exception condi\255) W
300 -4000 M
440.1 0 32 (tions with the correct use of the Request Denied) W
300 -5400 M
77.3 0 32 (Frame \(RDF\) protocol. RDF frames are sent by a sta\255) W
300 -6800 M
239.9 0 32 (tion in response to an unsupported or unrecognized) W
300 -8200 M
93.3 0 32 (received request. Our testing shows that some imple\255) W
300 -9600 M
344.0 0 32 (mentations do not source RDFs while some others) W
300 -11000 M
250.0 0 32 (source incorrectly formatted ones. For example, one) W
300 -12400 M
151.3 0 32 (test sends a 1000 byte Echo request with Version Id) W
300 -13800 M
168.9 0 32 (not equal to the current SMT Version Id. To comply) W
300 -15200 M
31.4 0 32 (with the SMT 6.2 draft, the implementation which re\255) W
300 -16600 M
203.8 0 32 (ceives this request must respond with an RDF with) W
300 -18000 M
194.9 0 32 (Reason Code 2 \(Frame Version Not Supported\). The) W
300 -19400 M
151.3 0 32 (RDF will report which versions are supported in the) W
300 -20800 M
186.8 0 32 (SMT Supported Versions parameter and include the) W
300 -22200 M
331.2 0 32 (maximum length fragment from the request which) W
300 -23600 M
161.4 0 32 (can fit into the response in its Refused Frame Frag\255) W
300 -25000 M
(ment.) h
300 -27400 M
42.9 0 32 (In most cases a correctly formatted RDF was received) W
300 -28800 M
4.0 0 32 (as specified. Some implementations based on the SMT) W
300 -30200 M
171.2 0 32 (6.2 draft failed to include the Refused Frame Frag\255) W
300 -31600 M
15.6 0 32 (ment \(SMT 5.1 did not require it\) and SMT Supported) W
300 -33000 M
366.4 0 32 (Versions parameters. Some received responses had) W
300 -34400 M
14.0 0 32 (fragments containing only the MAC and SMT headers) W
300 -35800 M
238.9 0 32 (while some implementations didn't send an RDF at) W
300 -37200 M
(all.) h
300 -40400 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(Next Station Addressing \(NSA\)) h
300 -41800 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
99.3 0 32 (In one instance, it was observed that a station would) W
300 -43200 M
149.7 0 32 (enter the ring without broadcast recognition enabled) W
300 -44600 M
121.6 0 32 (in its MAC. The implementation at fault in this case) W
300 -46000 M
166.1 0 32 (was incomplete and required manual insertion of its) W
300 -47400 M
181.3 0 32 (MAC into the ring. If this appeared in complete im\255) W
300 -48800 M
638.2 0 32 (plementations it could have implications on the) W
300 -50200 M
304.4 0 32 (Neighbor Information protocol where stations could) W
300 -51600 M
159.7 0 32 (possibly fail to detect a Duplicate Address condition.) W
300 -53000 M
212.3 0 32 (Without enabling broadcast recognition while in the) W
300 -54400 M
103.6 0 32 (ring, a station could possibly remain invisible or con\255) W
300 -55800 M
10.3 0 32 (fuse network management. This station would only be) W
300 -57200 M
68.0 0 32 (participating in half of the Neighbor Information pro\255) W
300 -58600 M
84.9 0 32 (tocol. It would be announcing its presence via the pe\255) W
300 -60000 M
471.8 0 32 (riodic NIF announcement so that its downstream) W
300 -61400 M
188.8 0 32 (neighbor's Upstream Neighbor Address \(UNA\) infor\255) W
300 -62800 M
89.9 0 32 (mation would be correct. The station upstream of the) W
300 -64200 M
64.5 0 32 (broadcast disabled station would not know of its exis\255) W
300 -65600 M
50.2 0 32 (tence if it was sending out periodic NIF requests. The ) W
300 -67000 M
331.0 0 32 (downstream station would receive the NIF request) W
300 -68400 M
362.1 0 32 (and send its response back. When the station up\255) W
300 -69800 M
124.9 0 32 (stream of the broadcast disabled station received the) W
300 -71200 M
417.9 0 32 (response it would falsely record the source as its) W
300 -72600 M
(Downstream Neighbor Address \(DNA\).) h
300 -76300 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(FDDI Datalink Clients) h
300 -78600 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
391.6 0 32 (Introduction of the FDDI datalink has exposed at) W
300 -80000 M
94.8 0 32 (least one flaw in higher layer protocols which are cli\255) W
300 -81400 M
220.0 0 32 (ents of the FDDI datalink. The problem was antici\255) W
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100.8 0 32 (pated by, and a solution proposed in, the appropriate) W
300 -2600 M
90.2 0 32 (standards committee. However, until the problem be\255) W
300 -4000 M
207.3 0 32 (comes 'common knowledge', the solution may not be) W
300 -5400 M
(broadly implemented.) h
300 -7800 M
36.7 0 32 (The problem occurs in ARP \(Address Recognition Pro\255) W
300 -9200 M
306.9 0 32 (tocol\) [12] which includes a field for specifying the) W
300 -10600 M
156.5 0 32 (Hardware Type of the originating station in an ARP) W
300 -12000 M
74.4 0 32 (request. Hardware Type 1 specifies Ethernet type de\255) W
300 -13400 M
142.6 0 32 (vices, and Hardware Type 6 specifies IEEE 802 type) W
300 -14800 M
69.0 0 32 (devices. Unfortunately, numerous implementations of) W
300 -16200 M
134.8 0 32 (ARP currently in use check the Hardware Type field) W
300 -17600 M
72.6 0 32 (and discard the ARP request if the Hardware Type is) W
300 -19000 M
323.3 0 32 (anything other than 1. ARP implementation which) W
300 -20400 M
553.3 0 32 (supported FDDI devices sent ARP requests with) W
300 -21800 M
201.4 0 32 (Hardware Type 6, and of course accepted Hardware) W
300 -23200 M
(Type 6 as well.) h
300 -25600 M
490.1 0 32 (The problem occurred when an FDDI station at\255) W
300 -27000 M
334.7 0 32 (tempted to communicate with an Ethernet station.) W
300 -28400 M
225.8 0 32 (The FDDI station would send its ARP request with) W
300 -29800 M
62.1 0 32 (Hardware Type 6, and the Ethernet station would re\255) W
300 -31200 M
195.6 0 32 (ceive the request and discard it since the Hardware) W
300 -32600 M
82.4 0 32 (Type was not 1. The solution was to have all stations) W
300 -34000 M
119.2 0 32 (send ARP requests with Hardware type 1, and as an) W
300 -35400 M
309.0 0 32 (added precaution, stations should ignore the Hard\255) W
300 -36800 M
(ware Type Field on receipt of a request.) h
10938 -41000 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(CONCLUSIONS) h
300 -43800 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
160.8 0 32 (Continued growth of the FDDI marketplace requires) W
300 -45200 M
235.8 0 32 (ongoing demonstration of multivendor interoperabil\255) W
300 -46600 M
37.8 0 32 (ity. Products which exist in the market today must be) W
300 -48000 M
90.7 0 32 (capable of interoperating with products introduced in) W
300 -49400 M
427.1 0 32 (the future, and products introduced in the future) W
300 -50800 M
48.9 0 32 (must interoperate with each other. The exemplary in\255) W
300 -52200 M
209.4 0 32 (itiative and efforts of FDDI vendors in testing their) W
300 -53600 M
313.2 0 32 (products and quickly resolving discovered problems) W
300 -55000 M
408.7 0 32 (proves that the interoperability challenge is being) W
300 -56400 M
(met today.) h
300 -58800 M
293.1 0 32 (This paper hopefully will assist vendors to address) W
300 -60200 M
449.1 0 32 (and correct the described problems early in their) W
300 -61600 M
127.8 0 32 (product design and test process. Continued exchange) W
300 -63000 M
28.8 0 32 (of such information will enable and promote the ongo\255) W
300 -64400 M
3.1 0 32 (ing success of all vendors at continuing to meet the in\255) W
300 -65800 M
(teroperability challenge.) h
8839 -70000 M
/Helvetica-Bold-ISOLatin1 F 1200 o f
(ACKNOWLEDGMENTS) h
300 -72800 M
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65.3 0 32 (Our thanks go to Bill Cronin and Jerry Hutchison for) W
300 -74200 M
(their comments and suggestions.) h
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/Helvetica-Bold-ISOLatin1 F 1200 o f
(REFERENCES) h
2100 -4000 M
/NewCenturySchlbk-Roman-ISOLatin1 $
/NewCenturySchlbk-Roman & P
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
521.6 0 32 ([1] FDDI Station Management Draft Proposed) W
300 -5400 M
1116.2 0 32 (American National Standard, May 18, 1990,) W
300 -6800 M
(X3T9.5/94\25589 REV 6.2.) h
2100 -8200 M
446.2 0 32 ([2] FDDI Media Access Control, American Na\255) W
300 -9600 M
(tional Standard, ANSI X3.139\2551987.) h
2100 -11000 M
253.2 0 32 ([3] FDDI Physical Layer Protocol, American Na\255) W
300 -12400 M
(tional Standard, ANSI X3\255148\2551988.) h
2100 -13800 M
628.4 0 32 ([4] FDDI Physical Layer Medium Dependent,) W
300 -15200 M
206.2 0 32 (Draft Proposed American National Standard, March) W
300 -16600 M
(1, 1989, X3T9/86\25571, X3T9.5/84\25548 REV 9.) h
2100 -18000 M
12.9 0 32 ([5] Ross, F. \(1986, May\), "FDDI \255 a Tutorial", IEEE) W
300 -19400 M
(Communications Magazine, Vol. 24, No. 5.) h
2100 -20800 M
3.8 0 32 ([6] Hutchison, J. \(1989, October\), "The Role of Con\255) W
300 -22200 M
48.6 0 32 (centrators in FDDI Rings", IEEE 14th Conference on) W
300 -23600 M
(Local Computer Networks.) h
2100 -25000 M
118.9 0 32 ([7] Kuenzel, J. et al \(1989, October\), "FDDI Dual) W
300 -26400 M
416.0 0 32 (Ring of Trees Topology", p 75\25578, Telecommunica\255) W
300 -27800 M
(tions.) h
2100 -29200 M
159.6 0 32 ([8] Hutchison, J., & Knudson, D. \(1986, October\),) W
300 -30600 M
29.4 0 32 ("Developing Standards for a Fiber Optic LAN \255FDDI",) W
-7198 7169 T
R
S
40971 -7153 T
N
0 G
300 -1200 M
/NewCenturySchlbk-Roman-ISOLatin1 F 1200 o f
112.6 0 32 (Proceedings of the SPIE \(Society of Photo\255Optical In\255) W
300 -2600 M
(strumentation Engineers\), SPIE #71522, Volume 715.) h
2100 -4000 M
153.0 0 32 ([9] Miller, R.D. \(1986, October\), "Optical Require\255) W
300 -5400 M
708.8 0 32 (ments for the Fiber Distributed Data Interface) W
300 -6800 M
242.7 0 32 (\(FDDI\)", Proceedings of the SPIE \(Society of Photo\255) W
300 -8200 M
479.5 0 32 (Optical Instrumentation Engineers\), SPIE #71522,) W
300 -9600 M
(Volume 715.) h
2100 -11000 M
391.1 0 32 ([10] Hanson, D., & Hutchison, J. \(1987\), "LED) W
300 -12400 M
195.6 0 32 (Source and Fiber Specification Issues for the FDDI) W
300 -13800 M
353.0 0 32 (Network", COMPCON 87, Proceedings of the 32nd) W
300 -15200 M
(IEEE Computer Society International Conference. ) h
28800 -15200 M
2100 -16600 M
64.0 0 32 ([11] Schicketanz, D., & Jackman, W.S. \(1986, Sep\255) W
300 -18000 M
316.2 0 32 (tember\), "Effective Fiber Bandwidth in LED Based) W
300 -19400 M
187.6 0 32 (Systems", National Bureau of Standards Publication) W
300 -20800 M
543.4 0 32 (720, Symposium on Optical Fiber Measurements,) W
300 -22200 M
(Boulder, CO.) h
2100 -23600 M
254.6 0 32 ([12] Plummer, D.C. \(1982, November\), "Ethernet) W
300 -25000 M
264.4 0 32 (Address Resolution Protocol: Or converting network) W
300 -26400 M
538.7 0 32 (protocol addresses to 48.bit Ethernet address for) W
300 -27800 M
224.4 0 32 (transmission on Ethernet hardware", Internet Engi\255) W
300 -29200 M
(neering Task Force RFC 826. ) h
300 -30638 M
-40971 7153 T
R
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