The differences and functions of various pieces of network hardware have been discussed many times in this column and many other places, so this time I want to focus on one specific device: the network switch.
The switch has emerged over other devices on the network as the powerhouse. A switch’s main goal is to forward packets to and from directly connected nodes (PCs, other switches, NVRs, IP cameras) as fast as possible. As CPUs have become faster and switches have been able to utilize more memory, their role has increased steadily during the past few years.
Switches Starting to Act as Routers
In order to truly see where switches have come recently, we need a little review. OK class get out your Networking 101 books. Remember the OSI 7-Layer model? This was the way we separated different network functions into different layers, to make learning and troubleshooting a little easier.
Originally, switches were decidedly Layer-2 devices. They operated at the data link layer and focused primarily on MAC addresses. They knew what end-point devices were directly connected to them and that was about it.
Routers, however, operate at Layer 3, speak the language of IP addresses and talk only to other networks or routers, not individual computers. In fact, when you sign up for broadband at home, quite often the little box your provider sends you has several ports on it, usually a single WAN port and a few LAN ports. It is true that this device is a router, connecting your local home network with the larger provider network, but the box actually contains a small switch, providing the LAN ports. It does two functions in one.
Now, however, switches are being updated to function at Layer 3 as well. They are now doing the job of routers. Combine that Layer-3 intelligence with the speed of Layer-2 forwarding, and you have a pretty capable and powerful device.
This Layer-3 functionality now means that switches speak the language of IP. While the implications of this are more for the Internet as a whole, it does offer some benefits for our industry, such as multicasting.
Speed Guides Switch Selection
As our IP video systems are becoming larger and more bandwidth intensive, it is also becoming more and more important that the right switches are being used for these projects. So let’s examine what separates a super switch from a merely mediocre one.
The first big thing a switch needs to do is be fast. Speed is really the key to switches. Regardless of whatever else it can do, a switch needs to move packets from one place to another as fast as possible. When you start moving live streaming video across that switch, it becomes even more important.
Let’s look at two components that make for a fast switch, suitable for video.
Bandwidth May Not Be Enough
The important thing to remember here is that bandwidth is only one factor. It is not the end-all, be-all deciding factor of a switch. It is dangerous to think that simply because you have a 100MB or gigabit switch that it will handle all of the IP or megapixel cameras you can throw at it.
Now, if you are only doing four or eight cameras, speed probably won’t be an issue. These things we’re discussing here will come into play as you start approaching hundreds of cameras or more.
Generally, the bandwidth on an individual camera port isn’t really an issue. If I have a 10MB switch, then it may be, but if my device is rated for 100MB or more, a single camera generally isn’t going to even approach that limit.
The port on the switch where bandwidth really needs to be considered is the backbone, or trunk connections between switches. Another would be the ports that connect to recording boxes or storage devices that pull multiple streams in from multiple cameras.
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Video Surveillance · Systems Integration ·
IP Address ·
MAC Address ·
Network Switch ·
The Convergence Channel with Steve Payne ·
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