Horner APG XL4 OCS HE-ETN300 - Manual (Page 13)

SUP0740-07 CH.2
11/30/2009 Page 13 of 98 # 958
Ethernet Switches normally don’t support Multicast IP Addressing, while Ethernet Hubs do
support Multicast IP Addressing. Some Ethernet Routers, known as Multicast Routers, do support
Multicast IP Addressing, by using Internet Group Management Protocol (IGMP).
Note: For those customers wanting to use Multicast Routers to connect EGD devices, the
Ethernet Module automatically handles IGMP communication with Multicast Routers.
For more information regarding EGD protocol, refer to Chapter 6 of this manual.
2.3.3 Internet Connectivity
Since the Ethernet Module uses a standard TCP/IP protocol stack (powered by NetX and
ThreadX), it can communicate beyond the local network, and on the Internet, for all protocols
except EGD. To do so, the Ethernet Module must be configured with the IP Address of a Network
Gateway server, which allows communication outside the local network. See Default Gateway
configuration under step 5 of Section 3.1 (page
18 ) in this manual for details.
Note: As network complexity increases, due to Ethernet Hubs, Routers, Switches, Gateways,
and the Internet, the worst-case network delay increases. In many cases, the client
software must be configured to account for this time lag. For example, Cscape’s Timeout
can be adjusted as shown under step 2 of Section 4.2 (page
24 ) in this manual.
2.3.4 IMPORTANT: Wireless Network Considerations
When using wireless equipment with industrial networks, make sure the system is designed and
installed by personnel that have been trained to use wireless networks in industrial environments.
Site surveys, selection of equipment and installation can be critical in network performance.
In general the 802.11b- based equipment is not a good choice in industrial environments. The
frequencies and modulation techniques used in the “b” standard are very susceptible to multi-
path interference in industrial environments (large metal objects, dense walls and floors, etc.)
The 802.11a and 802.11g are less susceptible to this interference.
Using UDP based protocols such as Ethernet Global Data (EGD) must be carefully considered
when using wireless networks. Wireless networks are more likely to lose or damage
communication packets. Many UDP based protocols, including EGD, do not detect and retransmit
lost or damaged packets and depend on periodic data transmissions to compensate for this lost
data. If your system requires a UDP protocol with a wireless network, make sure it is designed
such that random periods without refreshed data do not adversely affect the operation of your
system.
Depending on the architecture of the wireless network and the protocols used, wireless networks
often produce collisions and extra data packets that are not experienced when using a traditional
wire and switch-based network. The extra collisions and traffic coupled with the typically lower
bandwidth and higher latency of wireless networks can cause degradation in
performance.