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8. Service Performance

EuroView will strive to provide the levels of service determined in D3.1 User Requirements Report. Performance levels will vary, and are dependent on a number of parameters:

1. Connection bandwidth between client and server.

2. Connection bandwidth between EuroView DSAs, central and local.

3. Level of chaining required to satisfy a request.

4. Need for intermediate gateways.

In the simple case of a user accessing a central EuroView DSA directly via a fast Internet connection the service can be expected to match up to requirements. A less optimal situation would be that of a user in the UK on a local network connecting via public X.25 to a gateway machine in another country (possibly Germany), and then looking up data held on a server running on a local site back in the UK. This is a complex and patently inefficient scenario, unfortunately one for which rapid response times cannot be enforced within limits of available resource. However some guarantees can be made (e.g. availability of central services), and some specific actions can be taken to monitor and maintain the X.500 service.

8.1 Server Availability

EuroView plans for central DSAs to be accessible 24 hours a day and 7 days a week. Totally uninterrupted service is probably not possible, as software faults are always likely to occur. To counter this DSAs will be run in "auto start" mode. This means that if a DSA crashes, a wrapper program will restart the server automatically. This will minimize down time in individual servers. Use of replication between EuroView DSAs should ensure that the system is tolerant to failure of a single server. In this case, though the service is still online, performance levels may well be reduced.

8.2 Network Availability

Although "best efforts" will be made to maximize network availability in practice this will be difficult. The UK DSA running at Brunel University is a good example. The UK Academic network has no quality of service agreements for availability, and, as a result, EuroView can offer no service agreements for service availability. In practise, however, the network is nearly always accessible and availability should be near 100%.

8.3 Service Management and Monitoring

The server software provided by EuroView has support for the SNMP network management protocol. The EuroView partners do not make use of SNMP for service management and monitoring are unlikely to do so during the course of the project, as the gain in service assessment is unlikely to match or exceed the cost of setting up and maintaining management, especially if performed on a one-off basis.

SNMP may well be used to generate statistics on DSA usage. At present the following aspects of DSA usage can be monitored:

• Number of anonymous connections made.

• Number of unauthenticated connections made.

• Number of connections made using simple authentication.

• Number of connections that have been rejected for security reasons.

• Total number of operations forwarded to this DSA from other DSAs or DUAs.

• Number of individual user operations of any type handled by this DSA.

• Number of referrals returned by this DSA.

• Number of errors (security or otherwise) returned by this DSA.

• Current number of incoming and outgoing associations.

The figures outlined above can give a good overview of DSA usage, but they will not give any strong indication of DSA performance. The best way to do this is with a DSA probe. A probe is a piece of software that sends requests to a DSA at regular intervals. The requests sent can be something as simple as a connection request (is the DSA up?), or else some random timed query (how quickly does the DSA satisfy real world requests and does it find an appropriate answer?). Probes can provide a good measure of how well a DSA (and indeed the service overall) responds to the kinds of requests that users are likely to make.

Probes are often difficult to set up and maintain. An even better solution may be to analyse the log files of a central DUA service. A possibility here is the proposed central Web/X.500 gateway. All requests and responses made via this route are logged, with the log file containing the exact query made, response time and success or otherwise of requests.

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Title: EuroView Service Design
Issue: 1.1
Date: 17