Specifications

58 Rockwell Automation Publication AG-SG001G-EN-P - April 2015
Chapter 3 Choosing Data Communication Equipment
While it may seem that using the TCP mechanism should be the obvious choice,
this is not always true. TCP gives room to a lot of network overhead as it initiates
packet retransmissions and Acknowledgement packets whenever it detect a loss
in data receipt. Several applications employ their own data delivery integrity
validation procedures and do not require the network to validate data delivery for
it. In this case, the use of UDP may be encouraged as UDP has much less network
overhead compared to TCP. Hence, a choice of transport protocol to use to needs
to be made based on the application. A good choice of protocol can prove to be
cost beneficial.
Determining Monthly Cost for Data Usage
Monthly Circuit Switch data cost consists of a fixed data rate charge for a certain
amount of data per month, with additional data typically costing about US$0.05/
Megabyte. Roaming data charges are applicable if the equipment is used outside
the coverage area.
Monthly Packet data cost is charged to the nearest Kilobyte transferred. Cellular
providers have different plans (which could range from a set minimum to an
‘unlimited’ maximum); each consisting of a minimum block of Kilobytes. If the
monthly Kilobytes transferred figure is exceeded, the balance is billed as extra
charges. Site costs typically range from US$30…70 per month (including the
Kilobyte transfer).
Below is an example from a Rockwell Automation Encompass Partner, Prosoft
who is cellular modem provider.
Prosoft offers their modems bundled with data service plans from AT&T and
Verizon. Once a user selects a preferred carrier, Prosoft provides pricing and other
order related information. The list price for a Prosoft cellular modem device with
a two year service contract is approximately US$575. The Data Service charge for
the period of two years is an additional US$900 with a US$100 activation fee.
Prosoft also provides a plan where you can buy an already activated modem. This
plan costs about US$575 for the modem with a $100 Monthly ‘Try Before You
Buy’ Prosoft Data service plan. The customer is also charged a two year data
service plan with a two year activation plan. But, if the customer decides to return
the modem, Prosoft accepts the device back without a restocking fee and will not
invoice the Data Service plan and Activation charge. The trial period permitted is
60 days.
Other providers have similar products and services as well that can be used when
setting up a cellular network.