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Overview
signz
was designed to allow several different multi-site configurations. Each has different advantages and disadvantages. This document is designed to highlight the available options and discuss the pros and cons of each solution.
These are summarised in the table at the end of this document. You
can also download a copy of this
information in Word.
Single Database, Web or WAN Access
Where a number of different users in different physical locations all need access to the SAME data and that data needs to be consistent, the best solution may be a single database implementation.
Users at the same site as the database server have full access to the system. Remote users will have restrictions based upon them by the slower rate of access provided by Wide Area Network (WAN) or Internet access speed. Each of the solutions presented below requires a connection from the user’s PC to the central site whilst the
For higher speed, permanent WAN connections, SIGNZ can be fully access by users in remote offices. In this situation the users all connect to the central database directly. This ensures that all data is consistent, with no possibility to have double-bookings, no time delays between new data being added and it being available to all users. The negative is that this solution is primarily designed for higher speed connections only and is may suffer from interruptions to business if WAN connections fail.
- WAN – Direct Access via Internet VPN
As high-speed internet connections (Jetstream ADSL, for example) become more affordable and available the use of Virtual Private Networks (VPN) for accessing SIGNZ directly is workable – even for home workers or small offices. Using a VPN, data is encrypted and sent across the Internet to the main office. By using a VPN, users have full access to the SIGNZ system from remote locations and, as above, no data synchronisation issues.
Where large numbers of remote sites are involved, distribution of program updates may be an issue (though this can be addressed using automatic installation tools such as Microsoft SMS or Windows 2000’s Installer). VPN reliability may also be an issue. Security is a large issue and the purchase of high-end hardware or software VPN technology is recommended.
- WAN – Windows Terminal Server
/ Citrix
Windows Terminal Server and Citrix Metaframe allow a single-site solution to be expanded to many different sites without requiring high-speed connections. Rather than using native data connections from programs running at the remote site (as with the above solutions), Terminal Server runs the SIGNZ application programs on a dedicated server at the central site. Users at remote sites access a session running on this machine using special software to allow them to ‘remote control’ the application running centrally.
This solution means that users access the system can be connected via slower speed WAN links (down to 19.2K), dial-in links, lower speed Internet connections. As with all of the above solutions, one database means no synchronisation issues. The main negatives with this solution are the reliability of the links, high hardware and software costs for the Terminal Server and possible performance problems on slower links.
This solution may also be used from non-PC users (Macintosh, for example)
The SIGNZ Web software can provide remote users with access to data stored on a central server. Users connect via WAN or Internet connections using a standard Web browser such as Microsoft Internet Explorer or Netscape Navigator.
As web browsers cannot provide all of the features of a LAN based application, SIGNZ Web provides a sub-set of the full SIGNZ features and may not be suitable for full time users. The plus side is that this can be accessed from any user, across slow Internet connections and does not require any software to be installed on the users PC.
This solution suits a wide variety of non-PC users (such as Macintosh).
Multiple Database Setup
The Microsoft SQL Server database used by SIGNZ supports many options for building multi-site database configurations. Different configurations of SQL Server apply to different companies but each shares one common limitation: they all require a full-time or dial-up WAN / VPN connection.
In addition to the SQL Server replication, SIS offers it’s own email-based replication technology. For some sites this provides a cost-effective solution, particularly for laptops or small sites.
Each replication configuration has it’s own pros and cons and these are summarised below.
Microsoft has two basic replication models that are useful for a SIGNZ implementation:
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Transactional Replication (with Immediate Update)
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Merge Replication
i) Transactional Replication
The first, Transactional, allows two or more sites to hold identical copies of the database. When a user retrieves data from SIGNZ the system uses the local copy of the data. However, when updates are required the system will always update both the local copy and the central / head-office copy (the ‘publisher’). As 90% of the work required is lookup, this can provide a faster solution for those that have a full-time WAN / VPN connection between head-office and branches. Effectively there is only one database (at the ‘publisher’) with local copies for read-only access, improving performance.
The biggest negative, as with many of the single-database solutions, is line speed and reliability. Although line-speed can be much lower than with the single-database solutions, too low a line (or a heavily utilised line) may result in un-acceptable delays during updates. Reliability is also key. If the WAN / VPN link from branch office to head-office is down the branch office will not be able to process any updates. Data lookups will still be possible, which is a significant advantage over a single database solution.
Transactional Replication (with Updating Subscribers) requires a full-time WAN / VPN connection.
ii) Merge Replication
Unlike Transactional replication, Merge is designed to let the two sites run completely independent of each other. Merge does not require a full-time WAN / VPN connection, instead using scheduled updates that may run other a fixed or dial-up WAN / VPN connection. These updates may happen on-demand, daily, hourly or ‘ASAP’.
Merge replication permits each site to function completely independently, allowing changes to data at each site without requiring any on-line connection between sites.
This has the obvious benefit of lowering communications requirements and cost, decreasing the impact of a communications failure, maximising performance (both lookup and updates) and increasing flexibility.
The biggest drawback is obvious: what if two users update the same data on different servers? To eliminate booking clashes and other possible double-entry situations, SIGNZ data would be ‘partitioned’. This partitioning would occur along one or both of two different lines: geographic or functional. All data would be held at both locations but security would limit what functions could be performed at each location.
Geographic partitioning would involve splitting sites across geographic boundaries. Only the site responsible for a site could make bookings against that site. This would ensure that no double-booking of a site could be performed.
Functional partitioning with split the system across departmental boundaries. For example, accounting and sales at one location with maintenance and installation services at another.
Similar to the Merge Replication discussed above, SIS’ email based replication solution allows each site to run fully independently. Partitioning will still be required along the same lines (geographic or functional) to avoid data conflicts.
The advantage of this solution is that no WAN / VPN connection is required. Instead, standard email packages (Lotus Notes, Microsoft Exchange or Internet-based) are used to transfer data between sites. This lowers cost and eliminates the risk associated with full-time Internet connections required by SIGNZ Web or Internet based VPN solutions.
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