Distributed management process for queued arbitrated traffic in a DQDB MAN Stefan Covaci

Tiffs paper addresses the problem of fairness for the queued arbitrated traffic in DQDB MANs. A solution to this problem in the form of a distributed management process called fairness management is proposed. The OSI management and the DQDB specific management functionality are over- viewed, and alternative management architectures based on standardized OSI concepts are subsequently specified. The functional description of the fairness management distributed process is given, and the flexibility and potential of this solution are discussed. The paper also presents ongoing implementation work, along ~4th a schedule of related simulation experiments within the framework of the BERKOM project activities.

Kep, vords: metropolitan area networks, distributed manage- ment, fairness

Management of the real-time operation of large heterogenous networks is an active research topic. Today available management tools are supplied by network element providers and confine their applic- ability to the specific network portion they span. Integrated management of the entire heterogenous network to provide end-to-end management through all logical and physical levels requires cooperation between these element management systems. In an effort to set the necessary grounds for devising solutions to such a complex problem, the ISO is currently developing a set ofstandards for OSI to build a common base concept "for realizing management systems.

GMD FOKUS. Hardenbergplatz 2. W-1000 Berlin 12. Germany

0140-3664/93/010013-06 © 1993 Butterworth-Heinemann ktd computer communications volume 16 number 1 january 1993

Related to the types oftraffic and services it supports, the currently standardized DQDB MAN I raises specific management tasks associated with its Physical Layer and DQDB sublayer resources. Tile mixed traffic the DQDB protocol supports raises the problem of capacity sharing between the Queued Arbitrated (QA) traffic and the Pre Arbitrated (PA) traffic z 3. Subsequent to the allocation of a certain amount of the total capacity to the QA traffic, the question of fair sharing of this capacity between the nodes and between the different types of bandwidth-demanding applications has to be addressed.

Extensive modelling and simulation have shown that the DQDB access scheme leads to significant throughput unfairness under heavy load, high speed or long distances. Among the already proposed improve- ments, a particular potential is shown by the Bandwidth Balancing (BWB) mechanism, which in a simplified form is already part of the IEEE 802.6 standard. A higher degree of fairness, along with provision of flexibility to respond to changes in load and type of traffic, calls for management activities.

OSI M A N A G E M E N T O V E R V I E W

OSI management provides the means to achieve control, coordination and monitoring of all resources in an OSI environment. Figure 1 shows a possible incarnation of the OSI management structure. OSI management is a distributed application where locally- stored information is accessed and interchanged between participating systems.

The OSI management information model is based upon object-oriented design principles, whereby the management view of physical and logical resources in

13

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an OSI environment is provided by managed objects (MO). MOs are organized into classes according to common features. MO classes are specified in a structured way to allow for interoperability, and registered by assignment of globally unique identifiers. There are inheritance and containment relationships between MO classes, according to which MO classes are ordered in hierarchical tree structures.

The ISO-OSI identifies five functional fields of management described as specific managementfimctional areas. Within each area, a set of management fimctions provide the user with a set of management sen'ices, i.e. Management Specific Application Service Elements, which accomplish subtasks and ensure overall functionality as a whole.

Depending on the roles assumed during the inter- change of management information, the applications (users of the management system) are described as

S Covaci

managers and agents. To interchange management information, managers and agents use a communication service. OSI systems management defines the Common Management Information Service (CMIS) provided to the management process by a Systems Management Application Entity (SMAE). The SMAE also contains a protocol machine that supports communication of management information with peer entities according to the Common Management Information Protocol (CMIP). The communication between two peer SMAEs follows an association phase first using the Association Control Service Element (ACSE) service, and after association establishment, management information is transmitted by use of the Remote Operation Serive Element (ROSE) service.

M A N A G E M E N T VIEW O F D Q D B MAN L O W E R LAYERS

The IEEE 802.6 standard identifies a number of management functions related to the resources within the DQDB Sublayer and the Physical Layer, to be invoked by a local management process at the MO's boundary. Functional elements and facilities subject to management within the two lower layers are described as instances of MO classes. Figure 2 shows an inheritance tree for MAC Layer MO classes derived from preliminary definitions 4.

P E E R - T O - P E E R M A N A G E M E N T VIA O S I LAYER M A N A G E M E N T

In the cases when the Physical Layer to DQDB Layer service is not guaranteed, or when the DQDB Layer is temporarily Out___Of__Service, management of communication activities to maintain the DQDB subnetwork operational is realized by the" Physical Layer Management Entities (Phy.LMEs). Processes intern to a Phy.LME communicate with their peers at the adjacent Phy.LME via the physical layer manage-

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14 computer communications volume 16 number 1 january 1993

Distributed management process for queued arbitrated traffic: S Covaci

merit protocol to monitor the status of the duplex transmission link between the nodes and the error performance of communication over this path.

When the DQDB layer service to LLC cannot be guaranteed, management of the communication activities within the DQDB layer is realized by the DQDB Layer Management Entities (DQDB LMEs) in a cooperative manner. Management processes within e a c h DQDB LME communicate with their peer processes at the other nodes using a specialized protocol, the DQDB layer management protocol The management information is carried by two octets, each of them generated by the Physical Layer at the active Head Of Bus (HOB) node with a frequencyof64 kbit/s.

The two management processes intern to the DQDB LME are the sub/zetwork configuration control fitnction and the MID page allocationfimction which communi- cate with their peers at the other nodes using the co#~guration contkol protocol, and the MID page allocation protocol. Both functions operate upon resources in a 'hardwired' manner using a number of state machines. Figure 3 shows the architecture of this distributed management processes.

For the management of resources within the Physical Layer and the DQDB Layer Subsystems, the two LMEs offer layer management hiterface services, and act as 'local agents' in providing fimctionality of the MOs to local management processes. It is to be remembered

that as long as the LLC service is not available, no remote management can be performed on these MOs.

R E M O T E M A N A G E M E N T ISSUES

Remote management of all resources within the Data Link Layer and the Physical Layer in an IEEE 802 LAN/MAN environment is specified in the IEEE 802.1 B Draft Standard 5. The functionality ofthe LAN/MAN management is complementary to that of OSI systems management. Communication of management information is supported by the connectionless mode LAN/MAN Management Protocol (LMMP). A management process, called LAN/MAN Management User (LMMU), exchanges management information with its peer process making use of the LAN/MAN Management Service (LMMS) provided by the LMMP Entity.

To assure the provision of logical association between LMMUs (called affiliation), and to reliably maintain it in the connectionless LAN/MAN environ- ment, several convergence functions were devised and are provided by the convelgence protocol entity. LMMS and LMMP are realized by making use of the services, PDUs and procedures defined in" CMIS and CMIP.

In networks where some stations have the full seven layer OSI protocol stack and some have only the two

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computer communications volume 16 number 1 january 1993 15

Distributed management process for queued arbitrated traffic: S Covaci

lower protocol layers (QMAN short stack protocol suite), distributed management can be achieved by cooperation between systems management and L A N / M A N management. Figure 4 presents one possible architecture. Coordination between the two processes can be done at the user level. Another alternative - the proxy manager - is to implement both protocols in the same station and to provide a relay function that enables the same management process, to interoperate with CMIP- based stations and with LMMP-based stations.

Management communication makes use of the CL service functionalities provided by the MAN MAC Layer. The management PDUs are uniquely identified by using the Protocol Identifier field (000010) in the IMPDU. Management communication uses the LLC type 3 service.

FAIRNESS M A N A G E M E N T P R O C E S S

The implementation of the fairness management process proposed in this paper is based on the BWB mech- anisms. From the control theory perspective, BWB mechanisms are self-regulated feedback processes in that they circulate an error quantity (i.e. the amount of unused bandwidth) over a feedback channel (a 'time channel') that acts upon the general distributed queue to counteract propagation delays on the request channel 6. The mechanism limits the station's through- put to a multiple of the unused capacity 7 and thus 'gives time" (introduces a time window) to other requests to attain the general queue that will accordingly better approximate the FIFO behaviour.

Based on imposed optimum criteria, several strategies of choosing the feedback factor to limit the nodal throughput to a multiple of the unused capacity have been proposed s-t°.

Functional description

The following description refers only to the manage- ment activities for the QA traffic on one bus. The same activity, for the management of the BWB machines, is carried on the other bus.

ThefahTwss management process has two subprocesses, each of them based on remote management:

• the Fairness__monitor, that continuously monitors the carried QA traffic on the subnetwork and decides when overload approaches

• the BWB__management, which is activated when the Fairness__monitor declares an overload condition.

The Fairness__monitor has two modules, each installed at the HOB nodes, that count the empty QA slots which arrive on each bus within a cycle time. The cycle time is a parameter set as a function of traffic load. When the total number of empty QA slots becomes less than an imposed threshold an overload condition is declared. An alternative approach to this task is + based on counting the REQs arriving within a cycle at each HOB on the reverse bus.

Besides this statistic, the Fairness__monitor can also derive the bus capacity not used by messages of equal

Figure 4 Parallel LAN/MAN management and systems manage- ment processes. ACSE: Association control service element: CMIP: common management information protocol: CMIS: common manage- ment information service: CPE: convergence protocol entity: LMMP: LAN/MAN management protocol: LMMPE: LAN/MAN management protocol entity; LMMS: LAN/MAN management service: MSASE: management specific application service element: ROSE: remote operation service element: SMAE: systems management application entity

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16 computer communicat ions volume 16 number 1 january 1993

Distributed management process for queued arbitrated traffic: S Covaci

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or greater priority than priority p (p = 0,1,2). This would be made possible by the addition of priority information in the slot header about the data in the payload field (the RESERVED bit could be used for this purpose).

The overload event is notified to the BWB manage- ment process to activate it. This distributed process has one BWB__manager subprocess installed at one node, and BWB agent subprocesses installed at every node in the subnetwork.

The BWB__agent at a node activates/deactivates the BWB machine and operates on a cycle basis to evaluate the local offered load (per priority and per CL/CO segment type). For this purpose extra counters must be implemented.

The BWB__manager remotely reads these values from each node and decides the new BWB__MOD values to be used by nodes in the next cycle.

Figure 5 shows the functional architecture of this distributed management process.

The management information described in terms of MO classes with their packages and attributes is presented in Table 1. For remote management, the

communication architectures presented above are used.

Implementation and evaluation of the potential

For ongoing development of management applications for DQDB subnetworks and their integration in a heterogeneous environment, the OSl-based platform available at GMD FOKUS It is used. For the fairness management several strategies are currently under investigation based on available proposals. Most of them use the same Value of the BWB__MOD system parameter for all nodes. Dynamic modification of this value is performed by the BWB__manager following one of the proposed strategies.

Inspired by the proportional allocation scheme ~°, the idea to individually set for each node the BWB__MOD value in a dynamic manner was adopted for the BWB__manager. This degree of freedom permits one to devise new flexible optimum criteria for the BWB mechanism in order to accommodate the changes in the QA offered load, QoS, and network

Table i MO classes and related packages with attributes

MO class Packages Attributes

bandwidthBalancingProcess

distributedQueueProcess

manDQDBsap

manCLrap

segmentlleaderProcessing

hnpduTransmissionProcess

bandwidthBalancingProcessPackage

bwbActivePackage distributedQueueProcessPackage localRequestQueueCounterPackage multiPointPackage

manDQDBsapPackage

manCLsapPackage

discardedIMPDUsCounterPackage impduFlowPackage

segmentHeaderProcessingPackage

impduTransmissionProcessPackage

band,,~idthBalancingld bwbBusldentifier bwbModulus bwbCounter dist ributcdQueueProcessld locaIRequestQueueCounter busIdentifier requestCounter countDownCounter manDQDBsapld manDQDBsapNumber manDQDBsapStatus manCLsapAddress discardedlMPDUsThreshold discardedlMPDUsCounter received IMPDUsCou nter sentlMPDUsCounter segmentHeaderProcessingld clVCIList impduTransmissionProcessld qosMap

computer communications volume 16 number 1 january 1993 17

Distributed management process for queued arbitrated traffic: S Covaci

elements. It also permits a fine tuning o f the BWB mechan i sm ' s behaviour .

The cycle period of the B W B _ m a n a g e r is general ly greater than the settle t ime needed by the BWB mechan i sm to reach steady-state, and is es t imated via simulation. This pa rame te r is also directly related to the capaci ty loss introduced by the m a n a g e m e n t traffic that occurs at every cycle beginning.

Values ofparameters associated with fairness schemes already proposed, as well as behav iour of the BWB mechan i sm with new o p t i m u m criteria, are issues o f ongoing work based on this m a n a g e m e n t architecture.

The relat ionship between the activity o f the Band- width M a n a g e r & VCI server and the fairness manage- ment process to dynamica l ly select the adequate fairness strategy is ano ther topic o f research at G M D - FOKUS, and results will be publ ished in future.

C O N C L U S I O N S

Based on the functionali ty offered by the D Q D B L M E and by the Phy.LME, m a n a g e m e n t processes may cooperate via L M M S / L M M P or via C M I S / C M I P . Coexistence o f these two protocols within a station enables interworking with peer stations implemen t ing only one of them. Based on this m a n a g e m e n t archi- tecture, the fairness m a n a g e m e n t distr ibuted process offers an accurate and flexible solution to the p rob lem of fairness for the bandwid th -demand ing QA traffic in a D Q D B MAN.

A C K N O W L E D G E M E N T S

The.frui t ful discussions with my colleagues at G M D F O K U S Berlin are hereby kindly appreciated.

R E F E R E N C E S

i Distributed Queue Dual Bus (DQDB) Subnetwork of a Metropolitan Area Network (~tblN). IEEE 802.6 Draft 15 (1990)

2 Potter, P G and Zuckerman, 1~1 'Cyclic rcquest control for provision of guaranteed bandwidth within the DQDB frame- work', Proc. 1SS'90, Stockholm, Sweden (1990)

3 Filip|ak, J "Shaping interworking MANs into an evolving B-ISDN', Comput. Networks & ISDN Syst.. Vol 20 (1990) pp 343-349

4 MAN AblC Layer Management (Draft), ETSI/NA5 WP MAN Management, Lisbon. Portugal (March 1992)

5 l..rlN/AfANManagement. IEEE DIS 802.1B/D 18 (May 1991) 6 Covaci, S and Mateescu, M Tile DQDB MAN State of the Art,

GMD Internal Res. Report, Berlin, Germany (June 1991) 7 Jaffe, J 'Bottleneck flow control', IEEE Trans. Commun.. Vo129.

No 7 (July 1981) pp 954-962 8 ilahne, E L and Maxemchuk, N F "Improving the fairness of

DQDB networks', Proc. hlfocom '90. San Francisco, CA (1990)

9 Hahne, E L and Maxemehuk, N ,F 'Fair access of multi-priority traffic to distributed queue dual bus networks'. Proc. hlfocom "91, USA (1991)

10 Mukherjee, B and Banerjee, S "Alternative strategies for improving the fairness in and an analytical model of DQDB networks', Proc. htfocom "91, USA (1991)

i 1 Tshlchholz, Met aL Guide to the Basic Management Sapport System (BMSS). Arbeitspapiere der GMD 509. Berlin. Germany (February 1991)

18 computer communications volume 16 number 1 january 1993