Image Processing Reference
In-Depth Information
10
9
8
7
6
5
4
3
2
1
0
0
2,000
4,000
6,000
8,000
10,000
Index
FIGURE .
Illustration of overhead delay associated with OPC over a Mb/s switched Ethernet network.
Mean
=
. ms with standard deviation
=
. ms; for comparison purposes the mean UDP round-trip time over
the same network is . ms.
TABLE .
High-Level Description of Common Wireless
Technologies Illustrating Trade-Offs
Characteristic
.
Bluetooth
ZigBee
Range
High
Medium, depends on class
Low
Power consumption
High
Medium
Low
Data rate
Very high
High
Low
Optimal data size
High
Medium
Low
Redundancy
Low
Low
High
23.3.6 Wireless Networks
The move to wireless has resulted in yet another explosion of protocol technologies due to the fact
that the change in the media from a wire to air has resulted in the need for higher level of consid-
eration of many external issues (e.g., noise, coexistence, and security) as well as the opportunity for
development of more elaborate protocols to address these issues (e.g., frequency hopping, dynamic
transmission power algorithms, and new CA and backoff-style algorithms) []. Table . provides a
high-level comparison of three technologies that are utilized in manufacturing that offer somewhat
complementary capabilities. From the table it is clear that, at least at this time, one size does not
it all when it comes to matching a wireless protocol to application requirements. In the remainder
of this section, . and Bluetooth are explored in detail. For additional discussion of ZigBee see
Refs. [,].
23.3.6.1 Wireless Ethernet (CSMA/CA)
Wireless Ethernet, based on the IEEE . standard, can replace wired Ethernet in a transparent
way as it implements the two lowest layers of the ISO-OSI model [,]. Besides the physical layer,
the biggest difference between . and . is in the medium access control. Unlike wired Ether-
net nodes, wireless stations cannot “hear” a collision. A CA mechanism is used but cannot entirely
