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Broadband and the POS – June 2003 – Paul Burton                                                       10

So we have now set up the system we can describe how it works using the IP addresses

shown in the diagram.

Under normal conditions when the POS is connected on a LAN the PC asks the POS for Data

and the POS sends it or the PC can ask the POS can it send preset data, the POS

acknowledges this and the PC sends it.

We must also consider that every IP address has many “sockets” sockets are individual

connections within 1 IP address. The best way to visualize this is to consider a cable with

many strands of wire in. Each strand represents one socket. This means on one IP address

many different communications can be made at one time.

From the above diagram we are looking at a single IP address, on it we can communicate

World Wide Web pages along with POS and FTP. All at the same time, and without

interference.

Firstly lets look at the PC asking for sales data.

1.  The PC software as it would do on a LAN sends the enquiry to the POS the address of the

POS is set in this software. In the example the address is set to 81.24.193.102. So the PC

asks address 81.24.193.102 on socket 49152 for the sales data.

2.  The enquiry passes to IP address 81.24.193.102, which in this case is the router. The

router is not a POS and therefore does not understand the request. However the “Port

Redirection” states that if ANY data is received on any IP address on port 49152 send it

IP address 192.168.0.1. This is does

3.  Address 192.168.0.1 receives the data. We can see that IP address 192.168.0.1 is the

POS and the data is received and processed.

Socket 21 (FTP)

Internet FTP

Socket 80

(WWW)

Socket 49152

Broadband and the POS – June 2003 – Paul Burton                                                       11

4.  After processing the POS needs to send the data back to the PC. To do this it uses the

MWS (Manager Workstation) address. This is the address that all data from the POS will

be sent. In this case it is 62.136.7.167. If the POS sent the data to this address the data

would not arrive. The reason for this is because looking at the diagram, all IP addresses
around the POS begin with 192.168.0.n The POS is 192.168.0.1 and the router is

192.168.0.100.

5.  To enable the POS to speak with the PC VIA the router we have to tell the POS to send

the data VIA  another address. This is called the gateway address, and in this case is the

internal address of the router 192.168.0.100. So the POS sends the data to

192.168.0.100 for sending to 62.136.7.167

6.  The router receives the data and sends it to the PC who then receives the data

Broadband and the POS – June 2003 – Paul Burton                                                       11

4.  After processing the POS needs to send the data back to the PC. To do this it uses the

MWS (Manager Workstation) address. This is the address that all data from the POS will

be sent. In this case it is 62.136.7.167. If the POS sent the data to this address the data

would not arrive. The reason for this is because looking at the diagram, all IP addresses
around the POS begin with 192.168.0.n The POS is 192.168.0.1 and the router is

192.168.0.100.

5.  To enable the POS to speak with the PC VIA the router we have to tell the POS to send

the data VIA  another address. This is called the gateway address, and in this case is the

internal address of the router 192.168.0.100. So the POS sends the data to

192.168.0.100 for sending to 62.136.7.167

6.  The router receives the data and sends it to the PC who then receives the data