Star or Hub-and-Spoke networks | 3Com NCG-PLM, PLM Series guide

Network Connections and Topologies 5

5.2.2 Star or Hub-and-Spoke networks

An alternative approach is to implement a network with Star topology, also referred to as ‘hub-and- spoke’ or ‘radial’ topology, using a number of Ethernet switches. (See figure 5.2.2.) In such a network, a group of PLMs (typically those inside the same rack) are connected directly to a switch also housed in the rack. These local switches are then connected to a “central” switch.

If dual redundancy mode is used, then a completely parallel secondary network can be created. The primary network would connect the primary port of each Dante equipped device (PLM or DLP) and the secondary network would connect all the secondary ports.

The dual redundancy mode has the benefit that any single switch can fail without causing an audible interruption in the network. However, the control and monitor PC will have to be manually switched between the primary and the secondary network if a failure on one network layer should occur.

A dual redundancy configuration doubles the number of switches and cables needed.

Also note that the Dolby Lake Processor (DLP) does not support this redundancy scheme via dual rear panel Ethernet connectors, so

one DLP per network layer would be required.

5.2.3 Daisy-chained switches

In such a topology, each group of PLM Series units (typically those inside the same rack) have a switch inside the rack to which each has a direct connection. These “local” switches are connected in a daisy chain (figure 5.2.3). Systems of this type can be made quite large if the switches are using 1000BASE-T (Gigabit Ethernet), and although this is a very convenient system when it comes to wiring, a topology of this type can potentially develop SPF issues.

5.2.4 Daisy-chained switch ring

This is an enhanced variant of the above that can be created if the switches support RSTP, or Rapid Spanning Tree Protocol. (See section 7, References and Definitions, for more information.) The benefit of this configuration is that, if there is a cable failure, the network will recover; all devices on the network (PLMs, switches, routers, etc.) will still be able to communicate. If a switch fails, all devices will remain connected to the network, with the exception of those devices that are directly connected to the failed switch. If Dante is being used, there will be a brief audible interruption in the sound (5 ms – 2 s), the length of which will depend on the size of the system and the vendor of the switch.

The PLM’s own internal switches do not support RSTP. Care must be taken to not create a ring (closed loop) with the PLM’s rear panel connectors.

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Figure 5.2.2: Two level star topology

PLM Series Network Configuration Guide 9

NCG-PLM, PLM Series specifications

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