Internet Draft GSMP Working Group Constantin M. Adam Internet Draft Aurel A. Lazar Document: <draft-adam-gsmp-sr-00.txt> Mahesan Nandikesan Xbind, Inc. October 21, 1999 A Quality of Service Extension to the Minimal Resource Set <draft-adam-gsmp-sr-00.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at: http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at: http://www.ietf.org/shadow.html. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. Abstract The present document introduces an extension to the minimal resource set [1] for guaranteeing quality of service based on the concept of a schedulable region. The schedulable region is an abstraction that captures the capacity of a multiplexer. The draft also provides GSMP messages to support the extension. Table of Contents 1. Introduction .................................................. 2 2. Admission control model ....................................... 2 3. Realizing the admission control model ......................... 3 Adam, Lazar, Nandikesan Expires March 2000 1 A QOS Extension to the Minimal Resource Set October 1999 4. Message set ................................................... 4 4.1 Traffic classes and QOS messages .......................... 5 4.2 Schedulable region estimation policy messages ............. 9 4.3 Schedulable region estimate messages ...................... 11 A. Schedulable region representation ............................. 12 B. Measure of change of schedulable region ....................... 13 1. Introduction In reference [1], a minimal resource model of an ATM switch was presented along with a message set for exposing and controlling those resources. The basic feature captured by that model was cell switching from the input to the output ports. The present document introduces an extension for guaranteeing quality of service while switching cells, and provides GSMP messages to support the extension. 2. Admission control model The present section lays down the foundations for a quality of service extension to the minimal resource model. The extension is based on a capacity concept known as the schedulable region, which characterizes the capacity of a multiplexer, the same way the capacity characterizes the capacity of a link. The concept is based on the auxiliary concept of traffic classes, which is used here with a different meaning than that used by the ATM Forum. In the context of the present quality of service model, a traffic class is a statistical model for the bit-rate of an information stream. For practical purposes it is characterized by two types of parameters: (i) A qualitative parameter describing its type, e.g., video, voice, audio. (ii) A quantitative parameter giving a bound on the peak cell rate - PCR (as defined in [5]). This description may optionally be complemented with bounds on additional quantitative parameters such as the maximum burst size - MBS. A list of presently used qualitative traffic characterizations is given below: o CBR Arbitrary statistics o Video Real-time video statistics o Voice Real-time voice statistics o Audio Real-time audio statistics With each traffic class, a set of quality of service constraints is Adam, Lazar, Nandikesan Expires March 2000 2 A QOS Extension to the Minimal Resource Set October 1999 attached. The quality of service constraints take the form of bounds on quantitative parameters such as the maximum cell transfer delay (defined in [5]). A set of traffic classes is associated with each output port multiplexer of an ATM switch. Given such a set of traffic classes and a multiplexer, the operating point is defined as the vector consisting of the number of calls of each class that the multiplexer currently accommodates. An operating point is said to be admissible if the multiplexer can provide the requisite quality of service guarantees to all the calls. The set of all admissible operating points is said to be the schedulable region of the multiplexer. Figure 1 gives an illustration of a schedulable region with two traffic classes. Number of class II calls ^ | | | |\ |.\ |..- |...\ |....-- |.......\ |........\ |.........---- |.............\ --------------------------> Number of class I calls Figure 1: A schedulable region of a multiplexer supporting two traffic classes. 3. Realizing the Admission Control Model The main task in realizing the admission control model is to determine the boundaries of the schedulable region. Once this has been determined, the admission control procedure reduces to checking whether the operating point of the multiplexer lies within the schedulable region. This can be performed easily by an external switch controller. Thus, the present section focuses on the definition and the representation of the schedulable region. A trivial approximation of the schedulable region is given by (See Appendix A) A = (C/p_1, C/p_2, ..., C/p_n) (i.e., k = 1), B = Null matrix (i.e., m = 0), Adam, Lazar, Nandikesan Expires March 2000 3 A QOS Extension to the Minimal Resource Set October 1999 where C is the capacity of the output line and p_1,p_2,...,p_n are the peak cell rate bounds of the n traffic classes. The above will be referred to as the "peak-rate-based estimator". This schedulable region approximation can be evaluated directly on the switch hardware or by an external switch controller. But some other estimation methods, including those based on real-time measurements, cannot be realized on the external switch controller. Thus, these must be implemented on the switch itself, just as with scheduling and buffer management policies. As a result, the minimal resource model shown in Figure 2 must be extended to include schedulable region estimators as shown in Figure 3. Although only one estimator is shown in the figure, there is one estimator per multiplexer. +---------------+ |Switching Table| +---------------+ Input Output Ports +=====================+ +-----------+ Ports -------->| |--|Multiplexer|---------> | Switch Fabric | +-----------+ ... | | +-----------+ -------->| |--|Multiplexer|---------> +=====================+ +-----------+ Figure 2: Minimal resource model +---------------+ |Switching Table| +---------+ +---------------+ |Estimator| Input +---------+ Output Ports +=====================+ +-----------+ Ports -------->| |--|Multiplexer|---------> | | +-----------+ | | | | ... | Switch Fabric | ... | | +---------+ | | |Estimator| | | +---------+ | | +-----------+ -------->| |--|Multiplexer|---------> +=====================+ +-----------+ Figure 3: Extended resource model 4. Message Set This section presents a set of messages to realize the QOS extension Adam, Lazar, Nandikesan Expires March 2000 4 A QOS Extension to the Minimal Resource Set October 1999 presented above. These messages are intended to be used in conjunction with the messages provided with the minimal resource model in [1]. The message set has been subdivided into three logical groups. However, the order in which they are supposed to be executed is not reflected by the order in which they are listed. The typical order of execution of these messages is as follows: At initialization (after adjacency, but before any connections are setup): 1. Get estimation policy support message 2. Get traffic and QOS parameter support message 3. Set traffic classes and QOS message 4. Set schedulable region estimator message After initialization: 1. Get schedulable region estimate message The message to set the schedulable region may be used at any time to re-initialize the schedulable region estimate. The messages that allow to set the traffic classes, the QOS parameters and schedulable region estimation policies on the switch must be issued after the adjacency protocol has been established, and before any connections are set up on the switch. 4.1 Traffic classes and Quality of Service 4.1.1 Get Traffic and QOS Parameter Support Message Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Message Type | Result | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Partition ID | Transaction Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SR-E | Reserved | Qualitative Traffic Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Quantitative Traffic Mask | QOS Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Purpose Query the set of traffic and QOS parameter types supported by a given schedulable region estimation policy. Message Type 220 Adam, Lazar, Nandikesan Expires March 2000 5 A QOS Extension to the Minimal Resource Set October 1999 Request Fields SR-E. Response Fields Qualitative Traffic Mask, Quantitative Traffic Mask, QOS Mask. Field Descriptions SR-E Code for the schedulable region estimation policy. Qualitative Traffic Mask Mask of supported qualitative traffic characterizations. Definitions are given in Section 2. Bit 0: Constant bit-rate (CBR) Bit 1: Video Bit 2: Voice Bit 3: Audio Bit 4 - 15: Reserved Quantitative Traffic Mask Mask of supported quantitative traffic parameters. All parameters that are given abbreviations are defined in [5]. Bit 0: Peak Cell Rate (PCR) Bit 1: Sustained Cell Rate (SCR) Bit 2: Maximum Burst Size (MBS) Bit 3: Cell Delay Variation Tolerance (CDVT) Bit 4 - 15: Reserved QOS mask Mask of supported QOS parameters. All parameters that are given abbreviations are defined in [5]. Bit 0: Maximum Cell Transfer Delay (Max CTD) Bit 1: Average Cell Transfer Delay (Ave CTD) Bit 2: Cell Loss Ratio (CLR) Bit 3: Average Gap Loss [citation] Bit 4: Cell Delay Variation (CDV) Bit 5 - 15: Reserved 4.1.2 Set Traffic Classes and QOS Message Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Adam, Lazar, Nandikesan Expires March 2000 6 A QOS Extension to the Minimal Resource Set October 1999 | Version | Message Type | Result | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Partition ID | Transaction Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port Session Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A| Reserved |Classes| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Traffic Class 1 Block ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ Traffic Class 2 Block ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | ~ ... ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The traffic class block has the following structure: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Buffer ID |Qualitat.| Quantitative Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | QOS Mask | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Parameter 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Traffic Parameter 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | QOS Parameter 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | QOS Parameter 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Purpose Set the number of traffic classes and the traffic and quality of service parameters for each traffic class. Message Type 221 Request Fields Port, Port Session Number, classes, Adam, Lazar, Nandikesan Expires March 2000 7 A QOS Extension to the Minimal Resource Set October 1999 Traffic Class Blocks. Response Fields None Field Description A 1 = Set all the other ports with the same set of traffic and quality of service parameters (in addition to the port given in the field Port). 0 = Set the traffic and quality of service parameters only for the specified Port. Classes Number of traffic classes. Buffer ID The buffer of the multiplexer to which the the traffic class is mapped. Only one traffic class may be mapped to a buffer. Qualitat. Code for the qualitative traffic description (See Section 3.1) Quantitative Mask Mask of quantitative traffic class characteristics. Every Quantitative Traffic Characteristic selected in the mask is specified using 2 bytes. The following list specifies the unit for each parameter that is listed in Section 4.1.1: Parameter unit ---------------------- PCR cells/s SCR cells/s MBS cell CDVT microsecond The peak cell rate is a mandatory quantitative parameter, i.e., bit 0 of the field 'Quantitative' must always be set to 1. QOS Mask mask of QOS parameters. Every QOS parameter selected in the mask is specified using 2 bytes. The following list specifies the unit and the range of each parameter: Parameter unit ---------------------- Max CTD microsecond Ave CTD microsecond CLR --- Adam, Lazar, Nandikesan Expires March 2000 8 A QOS Extension to the Minimal Resource Set October 1999 Ave Gap 10^-6 cells CDV microsecond The parameter CLR is represented as an order of magnitude. Thus, a value of n represents a CLR of 10^-n. Notes: This message must be issued by the GSMP controller to the switch after adjacency has been established but before any connections are set up on the switch. 4.1.3 Get Traffic Classes and QOS Message Message Format Same as in Section 4.1.3. Purpose Get the number of traffic classes and the traffic and quality of service parameters for each traffic class. Message Type 222 Request Fields Port, Port Session Number. Response Fields A, Classes, Traffic Class Blocks 4.2 Schedulable Region Estimation Policies 4.2.1 Get Schedulable Region Estimation Policy Support Message Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Message Type | Result | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Partition ID | Transaction Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SR Estimator Mask | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Purpose Query schedulable region estimation support available on a port. Message Type 223 Request Fields None Response Fields SR Estimator Mask Field Descriptions Adam, Lazar, Nandikesan Expires March 2000 9 A QOS Extension to the Minimal Resource Set October 1999 SR Estimator Mask Mask of supported schedulable region estimators. Bit 0: Peak rate based estimator Bit 1 - 14: Reserved Bit 15: Proprietary 4.2.2 Set Schedulable Region Estimation Policy Message Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Message Type | Result | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Partition ID | Transaction Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port Session Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |A| Reserved | SR-E | Res | SR Update Threshold | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Estimator Parameters ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Purpose Select a schedulable region estimation algorithm and update threshold on a specific port. Message Type 224 Request Fields A, SR-E, SR Update Threshold, Parameters. Response Fields None. A 1 = Set all the other ports with the same schedulable region estimator code, update threshold, and parameters (in addition to the port given in the field Port). 0 = Set the parameters only for the specified Port. SR Update Threshold specified in units of 0.01%, resulting in a maximum possible value of 20%. See Chapter 3 for definition. SR-E Code of the estimator. (See section 4.2.1.) Estimator Parameters Adam, Lazar, Nandikesan Expires March 2000 10 A QOS Extension to the Minimal Resource Set October 1999 specific to each estimator. The proprietary estimation policy and the peak rate based estimation policy do not take any parameters. Notes: This message is must be issued by the GSMP controller to the switch after adjacency has been established but before any connections are set up on the switch. 4.2.3 Get Schedulable Region Estimation Policy Message Message Format Same as in Section 4.2.2. Purpose Retrieve the schedulable region estimator code, parameters, and update threshold on a specific port. Message Type 225 Request Fields None. Response Fields A, SR-E, SR Update Threshold, Estimator Parameters. 4.3 Schedulable Region Estimates 4.3.1 Set Schedulable Region Message Message Format 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | Message Type | Result | Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Partition ID | Transaction Identifier | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Port Session Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | Dimen | Planes-A | Planes-B | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Coefficients a_ij ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Coefficients b_ij ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Purpose Set the schedulable region on a specific port. This message can be used to give the schedulable region estimator an initial estimate. The estimator is not required to use this initial estimate. Message Type 226 Adam, Lazar, Nandikesan Expires March 2000 11 A QOS Extension to the Minimal Resource Set October 1999 Request Fields Dimen, Planes-A, Planes-B, Coefficients a_ij, Coefficients b_ij. Response Fields None. Dimen The dimension of the Schedulable Region (the number of columns of the matrix A - see Appendix A). Planes-A The number of rows of the matrix A (See Appendix A). Planes-B The number of rows of the matrix B (See Appendix A). Coefficients a_ij The elements of the matrix A = (a_ij), listed row by row and represented using four bytes per element. (see Appendix A). Coefficients b_ij The elements of the matrix B = (b_ij), listed row by row and represented using four bytes per element. (see Appendix A). 4.3.2 Get Schedulable Region Message Message Format Same as the Set Schedulable Region Message. Purpose Query the present schedulable region estimate on a specific port. Message Type 227 Request Fields None. Response Fields Dimen, Planes-A, Planes-B, Coefficients a_ij, Coefficients b_ij. Appendices A. Schedulable Region Representation A n-dimensional schedulable region is represented using two matrices A = (a_ij) and B = (b_ij), each with n columns and an arbitrary number of rows. The entries of A and B are non-negative. Denote the number of columns of A and B by k and m, respectively. Each row of A represents a region H_i = { x in N^n| x_1/a_i1 + x_2/a_i2 + ... + x_n/a_in <= 1}, Adam, Lazar, Nandikesan Expires March 2000 12 A QOS Extension to the Minimal Resource Set October 1999 where N is the set of non-negative integers. In other words, H_i is the region bound by the coordinate axes (in the n-dimensional space N^n), and the hyper-plane whose intercepts are a_i1, a_i2, ..., a_in. Similarly, each row of the matrix B defines a region G_i in the n-dimensional space N^n. The schedulable region represented by the pair of matrices A, B is then given by S = S1 union S2, where S1 = union of H_1, H_2,..., H_k, S2 = intersection of G_1, G_2,..., G_m. B. Measure of Change of a Schedulable Region Suppose that the schedulable region of a multiplexer changes from S to S' (but both have the same dimension n). Let t_i be the largest number of calls of traffic class i that schedulable region S can accommodate if there are no calls of any other traffic class. Similarly, let t'_i be the largest number of calls of traffic class i that schedulable region S' can accommodate if there are no calls of any other traffic class. Then, the percentage change from S to S' is defined as max { |t_1 - t'_1|/t_1, ..., |t_n - t'_n|/t_n }. References [1] GSMP Working Group, T. Worster Editor, "General Switch Management Protocol V3", draft-ietf-gsmp-00.txt, June, 1999 [2] GSMP Working Group, A. Doria, F. Hellstrand, C. Adam, "Support Structure for Optional Abstract or Resource Models", draft-doria-gsmp-option-arm-00.txt, Feb 1999 [3] IEEE/WG 1520, C. Adam, A. A. Lazar, M. Nandikesan, "Proposal for Standaridizing the qGSMP protocol", P1520/TS/ATM-002, http://comet.columbia.edu/pin-atm/docs/P1520-TS-ATM-002R1.pdf, Jan 1999. [4] IEEE/WG 1520, C. Adam, A. A. Lazar, M. Nandikesan, "Switch abstractions for designing open interfaces", P1520/TS/ATM-016, http://comet.columbia.edu/pin-atm/docs/P1520-TS-ATM-016R1.pdf, March 1999. Adam, Lazar, Nandikesan Expires March 2000 13 A QOS Extension to the Minimal Resource Set October 1999 [5] ATM Forum, "Traffic Management Specification, Version 4.0", April 1996. Authors' Address Constantin M. Adam Xbind, Inc. 55 Broad Street, 23C New York, NY 10004 USA Telephone: 212-809-3303, ext. 102 email: Aurel A. Lazar Xbind, Inc. 55 Broad Street, 23C New York, NY 10004 m USA Telephone: 212-809-3303, ext. 101 email: aurel@xbind.com Mahesan Nandikesan Xbind, Inc. 55 Broad Street, 23C New York, NY 10004 USA Telephone: 212-809-3303, ext. 106 email: mahesan@xbind.com Adam, Lazar, Nandikesan Expires March 2000 14