User's Manual

3-6 July 10, 2002
Integration Overview CreataLink2 XT Hardware Integrator’s Guide
Wireline and Wireless Communications
Wireline and Wireless Communications
Consider the similarities and differences between wireline and wireless
communications: Wireline data communications involve two data transceivers that
use a dial-up telephone link to send and receive data. This type of communication
is known as "full duplex, circuit-switched communications." Full duplex indicates
both sides can send and receive simultaneously. Circuit-switched indicates the
sender and receiver have access to the entire communications line at all times
without sharing with other users. The wireline method of communications wastes
air time in a wireless setting because, typically, one side does most of the
transmitting while the other side is listening.
In wireless packet communications, the sender and receiver can share the
communication media with other users by sending packets, or bursts of data. This
method of communication enables other users to send their packets between the
gaps. To reduce data transmission cost, the communications are usually sent half
duplex; the sender does not listen while it transmits.
Some data communications protocols (XMODEM and YMODEM) are designed to
be used on a full duplex, circuit-switched connection. The user pays for the number
of minutes the circuit is open, regardless of the amount of data sent. Short timers,
numerous link level acknowledgments, and error correction help speed the data
transfer. With wireless packet data, the user is billed only for the data actually sent.
It makes more sense to consider communications in terms of datagrams (similar to
what is used in IP). Much of the error correction and acknowledgment information
sent in wireline communications becomes an extra cost burden because the packet
data protocol already provides for forward error correction and link level
acknowledgments.
Determine which applications are best suited for wireless and which applications
need to be modified before you use wireless. Message-based applications such as
database lookup, e-mail without attachments, and point-of-sale transactions are
suited to wireless communication, often without modification. Applications that
send handshaking messages or applications with timers that resend too quickly are
unsuitable for wireless communications because of the unnecessary overhead traffic
they generate.
Power Conservation
For installations that require power conservation (battery or solar cell powered),
consider data transceiver power consumption in the various operating states and
how data transceiver configuration affects power consumption. The data
transceiver uses the ReFLEX protocol battery-save cycle configuration, a customer-
ordered option, for low power consumption. To reduce average power consumption
further, activate the data transceiver only when needed (see Table 2-3, "Power
Connection" section, and "Power Supply Circuit Details" section).
Network Communication
There are two ways to communicate with a network:
• Connection
• Connectionless
Most packet communication is connectionless and does not require call setup and
teardown for communications. For the most efficient airtime solution, SmartSynch,
Inc. recommends a connectionless communications model.