Convergence Channel: How to Avert Traffic Gridlock on the Network

This becomes more important if you try to use a 100Mbps port as a trunk connection between two switches. You can quickly overwhelm 40-60 percent of that link sending multiple cameras across it.

The consequence of trying to push too much information down a link? Collisions, packet loss and congestion. None of which are good.

The Deluge of Converging Streams

As we move into more advanced and complex network-based systems, there are of course more risks to the network.


We have discussed multicasting in this column before. Multicasting is basically a way to minimize throughput on the network by allowing the network devices themselves (switches) to replicate a single stream from a camera to multiple viewing devices, instead of making the camera spit out multiple streams from the beginning.

As we have also mentioned, multicasting requires specific capabilities of your network hardware. Multicasting is an excellent way to mitigate traffic problems on your network; yet, there are caveats to consider.

Not all devices handle multicast traffic the same way. Different manufacturers of network switches have implemented different ways of dealing with this type of traffic. And when I say deal with it, if everything is as it’s supposed to be, nothing bad will happen.

The problems come in, however, when a switch doesn’t recognize a destination of a packet or there is some corrupted data in it. Some switches, when they get a packet that is corrupted or not recognized, will simply drop it. End of story.

Some, however, will flood or send the packet to all ports on the switch, hoping that some device will recognize it and allow it to reach a final destination.

Under normal E-mail/Internet circumstances, that may not pose a big problem. With streaming video, however, it can cause big issues.

If a stream is received at a switch and it has an unknown destination address, or the multicast information is incorrect, every packet in that stream may be flooded to all of the ports on that switch. Imagine a multi-megapixel video stream is suddenly sent to all ports, including those with traffic from other incoming cameras. It would bring that switch, and possibly the rest of the network, to its knees.

Tips for Managing the Traffic

There are several things you can do to minimize the impact of traffic problems on your network.

In the planning phases, buying infrastructure hardware that is capable of handling the traffic you are going to throw at it is critical. Not all switches are created equal, and that sub-$100 switch at your local computer retailer may not be able to handle as much data as a commercially rated one. Make sure you do more than read the specifications, though. Talk to the manufacturer of the systems you are going to install and ask if they have a qualified switch list or a switch testing program. Most manufacturers want trouble-free installations so many offer these types of programs.

If you already have your switches in place and need to isolate some ports from others to contain traffic and flooding problems, the easiest way is through the use of VLANs, or virtual LANs. VLANs take switch ports, or groups of ports, and link them together as an isolated network. This prevents traffic from flowing to other ports not on the same VLAN. Most, if not all, managed switches should allow you to enable VLANs.

An important point to remember is that if you need any traffic to flow between VLANs, then the switch needs to be a Layer3 switch with IP routing capabilities, as each V
LAN acts as its own separate network. If your switch is only Layer2 and can’t do IP routing, then you need to connect a router to that switch to handle those duties.

MCSE- and CCNA-certified Steve Payne has more than 15 years of industry experience and heads Convergence Consulting, an IP and security solutions consulting firm. Be sure to also read his Integrated Thoughts blog.


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