LAN ? WAN ? VPN

[CHUNN]

It would be nice for someone to explain ( In laymans terms ) the advantages and disadvantages of different network configurations. LAN versus WAN Michael

[jcole]

Here is a stab.A LAN (Local Area Network) consist of computers and computer like equipment, connected via a high speed dataline, such as cat 5 ethernet (10Mb/s or 100Mb/s).A WAN (Wide Area Network) operates just like a LAN, however the connections are made by slow speed connections, such as a modem or ISDN line (33.6Kb/s or 128Kb/s)Both networks operate in a similar fashion, however, the dramatic speed difference means that things that work well on a LAN do not perform well (or at all) over a WAN. An example is a Microsoft Network Shared Drive. Over a LAN, you can use the network neiborhood to view and transfer files easily and quickly. Over a WAN, the same protocol works, but doesn't perform as well as a FTP file transfer.Note that typically, LANs and WANs are private networks, in other words, each machine is connected only to machines you own, not each machine connected to the internet. You open up a different can of worms when you throw the internet in!I'll post more later...------------------John ColeSolarsoftwww.gosolarsoft.com

[jcole]

Here is some follow up info...If you have more than one computer a single location, you probobly have a LAN connecting them. WANs typically connect several LANs together (hence the term Wide Area Network), the WAN is still private, it just has slow links to other LANs.When you connect to an unsecure network, such as the Internet, it is usually not called a WAN, since you normally would not allow public access to your network. This despite the fact that the Internet is in essence one very large WAN!There are methods of creating a WAN through the internet, by encrypting your data as it leaves one location and decrypting it when it arrives at the other, this is known as a Virtual Private Network (VPN). A VPN allows you to use the Internet as an inexpensive WAN, since you do not need dedicated lines between locations.There are a lot of networking terms being tossed about now that everyone needs a multi-salon solution . Some vendors use the term WAN, others Network. The questions you need to ask are does the product require a constant connection between stores (not just dedicated lines, but that the network connection needs to be up all the time), and can you use the public Internet or do you need a private network (which can also be done through the Internet via a VPN).These two questions will be the primary factor driving the cost of implmenting a solution to connect your stores POS systems.------------------John ColeSolarsoftwww.gosolarsoft.com

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[CHUNN]

bump

[Andy]

Why did Solarsoft choose to implement replication via batches


Early in 2000 Solarsoft spent a lot of time evaluating the different methods of replication. We choose to implement the batch update process because it's by far the smartest method and has less points of failure. It was simply the best choice! Below is an outline of the methods with advantages and disadvantages.


Wide Area Networks can be implemented in 3 ways. The goals of all three are to combine data from multiple locations and redistribute that information back to the locations.


1 - Client-Server Model

Here a network Database system is used as the server. The clients connect to the server over a TCP/IP connection. This is usually a low bandwidth solution , but there are cases where it has quite a bit of overhead.

Advantages:

Central data point, managment (backups, users, permissions) easier

Data at stores is realtime, changed at one location, it's avaliable at another


Disadvantages

Single point of failure at Database server (server crashes or has hardware failure)

Single point of failure at server network connection (hub, modems, telephone lines, etc)

Critical failure point on unreliable communications link at stores

Larger Database queries require greater bandwidth (hit F2 in helios, that will take 10-30 seconds)

Performance is an issue. Database load and network load can slow point of sale terminal down.

Adding workstations at a store divides the bandwidth for that store (2 workstations only go half as fast, 3 only a third)


2 - Terminal Server (Widnows 2000 Terminal Server, Citrix WinFram)


Here a Terminal Server allows clients to connect via TCP/IP and run a graphical user interface. The difference between a Terminal Server and Client-Server approach is that the application always runs entirely on the Server, where a Client-Server shares the load between two machines (the client providing the GUI, and the server providing the DB). Terminal Server was not intended to be used as proposed by Helios. Terminal Server was intended to ease managment for over 50 to 100 thin client machines on a high speed network connection (100MB-1000MB). Distributed applications over slow network connections is a side benifit of Terminal Server, and not it's main focus. Extremely good network reliablity is assumed for general Terminal Server use. Dialup and low speed (1.5MB) connections are intended only for periodic use, not always on use.


Advantages:

Central data point

Central applications managment (you only need to update helios at one place)

Data is realtime

Easier administration for user machines (install MS Office at one location, it's available anywhere)

Large database queries do not require additional bandwidth to return results (only what will display in the window is returned, unlike client-server which has to ship the entire results set back, so hitting F2 will only take a second with Terminal Server)


Disadvantages

Single point of failure at Database server

Single point of failure at Terminal Server (note the Terminal Server can be a different machine than the DB Server)

Single point of failure at Server network connection

Critical point of failure on unreliable communications link at stores

Complex perphiral connections. Managing remote serial and parallel ports is complex, time consuming and unreliable.

RDP (the protocol that Windows Terminal Server uses) packets reqire larger bandwidth than a client-server database connection. You are sending images instead of text.

Adding workstations reduces available bandwidth by a larger factor, due to the larger volume of data being transfered.

Adding workstations impacts server performance more than adding client-server applications.

Does not reduce the number of licences necessary for software use. You will still need database licences for each workstation, office licences for everyone using office, etc... (MSDN the free MS SQL server only allows 5 connections, so you would have to use a full copy of MS SQL Server, plus licences for each workstation)
Bandwidth requirements preclude using phone lines, making internet connections more expensive.
Server hardware requirements are higher than Client-Server or batch method.


3 - Batch Update system (this is the method Salon Net uses).


With this method, client computers collect changes to local database and transmit those to a central server. The central server processes those in batches and collects changes to be sent back to the stores. The store retrieve changes and integrate them into local databases.


Advantages

Central Data point
Data is near realtime (you can update on a continual basis, every 30min or so)

Complete data sets are located at each store, providing multiple backups

Processing is distributed at all locations

Can use low speed dialup connections

Network conneciton not manditory for application to run (you can still operate your store without your network connection).

System can remain idle while any single point of failure is repaired, without affecting store operations.

No additional databse licences are requried, uses a single connection.

Runs on standard Windows operating systems, and does not require additional software licences

Easier to administer than Terminal Server or multi user Database system

Integration of store data is a natural part of the system. No external application is needed to import data into system.


Disadvantages

Data is not realtime

Data collisions are possible with width windows of replications.

Both of the above disadvantages are minimal and are mostly elimated if the batch system is updated in a real-time mode.


_________________

Andy Thompson
ACT Business Solutions
Toll-Free 877-777-6717
andy@atso.ca
ACT Help Center [ This Message was edited by: Andy @ ATSO.ca on 2002-08-29 10:50 ]

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