Mocomtech CRS-300 - Manual (Page 47)

3–1
Chapter 3. ETHERNET NETWORK
CONFIGURATIONS
3.1 Introduction
For operations requiring Ethernet-based terrestrial data handling, it is important to emphasize the
need for Users to avoid Ethernet looping connection problems – with or without use of the
CRS-300 1:10 Redundancy Switch.
The intent of this chapter is to outline the differing methods for Ethernet-based data handling with
the various modems featured throughout this manual. Additionally, this chapter outlines use of
the CDM-700 Satellite Modem in redundancy. The CDM-700 provides the added functionality of
multiple data type handling simultaneously with Ethernet; i.e., Ethernet & HSSI, Ethernet &
G.703, etc.
3.2 Ethernet Routers vs. Switches
Routers and switches allow connection of one or more computers or networked devices to other
computers or network devices. Each has two or more connectors, called ports, in which cables
connect to other network devices.
An Ethernet switch examines the traffic that comes across it, and learns where particular MAC
addresses are. An Ethernet switch maintains what is known as a CAM (Content Addressable
Memory) table, listing the MAC addresses for each switch port. The Ethernet switch uses the CAM
table to determine where to forward Ethernet frames. By default, Ethernet switches will update the
CAM table automatically; for example, if an Ethernet switch sees traffic from ‘Machine A’ coming
in on ‘Port 2’, it now knows that ‘Machine A’ is connected to that port, and that traffic destined for
‘Machine A’ needs to only be sent to that port and not any of the others.
An Ethernet router determines where to forward IP traffic based upon the destination IP address
and the Route table entries in the router. An Ethernet router can be programmed to understand and
route the data it is directed to handle; for example, broadband routers include the ability to "hide"
computers behind a type of firewall, which involves slightly modifying the packets of network
traffic as they traverse the device. All routers include some kind of user interface for configuring
how the router will treat traffic: larger routers include the equivalent of a full-blown programming
language to describe how they should operate, as well as the ability to communicate with other
routers to describe or determine the best way to direct network traffic from ‘Point A’ to ‘Point B’.