Combining Multiple LonWorks Networks Using UnicastReplicated vs

							Combining Multiple LonWorks Networks
Using Unicast/Replicated
vs. Multicast IP Addressing
  NCB Technical Note                                             TN 020


The NCB-Etherlon Network Combiner Module provides for the connection of multiple LONWORKS
networks by way of Ethernet TCP/IP backbone networks, as shown in the following example drawing:

                 BUILDING 1                                             BUILDING 2

         LONWORKS           LONWORKS                              LONWORKS          LONWORKS
           NODE               NODE                                  NODE              NODE


                         NCB-ETHERLON                             NCB-ETHERLON


         LONWORKS           LONWORKS                              LONWORKS          LONWORKS
           NODE               NODE                                  NODE              NODE




                                               ETHERNET
                                               NETWORK



                 BUILDING 3                                             BUILDING 4

         LONWORKS           LONWORKS                              LONWORKS          LONWORKS
           NODE               NODE                                  NODE              NODE


                         NCB-ETHERLON                             NCB-ETHERLON


         LONWORKS           LONWORKS                              LONWORKS          LONWORKS
           NODE               NODE                                  NODE              NODE



                                                                                         CA-80372-100




In this example, a packet sent by a LONWORKS node in Building 1 destined to a LONWORKS node in
Building 4 is first received by the NCB-Etherlon module in Building 1. It is then forwarded to the NCB-
Etherlon modules in Buildings 2, 3, and 4 by way of the Ethernet Network. Finally, the packet is
forwarded to the local networks in Buildings 2, 3, and 4 to be received by the intended destination node in
Building 4.
The NCB-Etherlon modules support three different IP Addressing Modes for use in forwarding packets
between themselves on the Ethernet network. Two of these IP Addressing Modes (Unicast/Replicated and
Multicast) apply where there are more than two LONWORKS networks to be combined. This information is
intended to help choose the proper mode for a given situation.


Unicast/Replicated IP Addressing Mode
Using Unicast/Replicated IP Addressing Mode in the example system shown above, a single LONTALK
packet entering an NCB-Etherlon module will be forwarded onto the Ethernet network as three separate
Unicast IP messages, one IP message destined to each of the other three NCB-Etherlon modules.


                                                                                               April 28, 2000

CTI Products, Inc.                                         1211 W. Sharon Road, Cincinnati, OH 45240
Phone: +1.513.595.5900                                     Email: info@ctiproducts.com
Fax:   +1.513.595.5983                                     Web:    www.ctiproducts.com
  Technical Note                                                                          TN 020
Multicast IP Addressing Mode
Using Multicast Addressing Mode in the example system shown above, a single LONTALK packet entering
an NCB-Etherlon module will be forwarded onto the Ethernet network as a single multicast IP packet to be
simultaneously received by all of the other three NCB-Etherlon modules.


Making the Choice
On the negative side, Unicast/Replicated IP Address Mode requires generation of multiple Ethernet packets
(one minus the number of NCB-Etherlon modules in the system) to forward one LONTALK packet.
Therefore, careful consideration must be given to how many LONWORKS networks (and the number of
nodes in each) can be combined given available Ethernet network bandwidth. On the positive side, because
Unicast/Replicated mode simply generates a series of Unicast IP packets, it is supported by all IP routers
and gateways with even the oldest of firmware.
On the positive side, Multicast IP Address Mode requires generation of only one Ethernet packet to forward
one LONTALK packet. As the amount of Ethernet traffic does not increase for every NCB-Etherlon module
attached, an unlimited number of LONWORKS networks may be combined. If none of the NCB-Etherlon
modules are separated by IP routers or gateways, Multicast mode is clearly superior. On the negative side,
if NCB-Etherlon modules are attached to Ethernet segments which are separated by IP routers or gateways,
these routers or gateways must support IP Multicasting. Historically, IP Multicasting has been part of the
Internet Protocol specifications for years, but some IP routers and gateways have only implemented these
specifications within the past several years (since about 1995). Thus, when NCB-Etherlon modules must
communicate over Ethernet via these routers or gateways, check with your network manager to be sure that
IP Multicast services are available and enabled in the IP routers or gateways before attempting to use
Multicast Addressing Mode.


Summary
Overall, Multicast IP Addressing Mode is the better choice, as much less bandwidth is used on the Ethernet
channel. If IP routers or gateways exist in the path between NCB-Etherlon modules, be sure they support
IP Multicasting services.




                                               Page 2                                       April 28, 2000