Understanding Bandwidth
Bandwidth is the amount of data transmitted across a network infrastructure per second. Data, in the case of IP video surveillance, is the transmission or streaming of either live video from cameras or storage playback. With regards to an IP video surveillance system, bandwidth is the sum of all of the data communications flows of all of the various components. Some data flows are for inter-device communications, called overhead, which do not generate enough data bandwidth to be statistically relevant. Calculating the total bandwidth required for an IP video surveillance system can be simplified by following an old IT rule of thumb: “Goes Into.”
Goes Into is basically the process of summing up all of the fixed video streams (live) and all of the potential video streams (storage playback and multiple instances of any live stream) for the entire IP video surveillance system and/or any specific network section. An example is a 32 IP camera system with all storage on a NVR on a dedicated LAN. Each camera’s live stream is 3Mbs and the stored stream is 1.5Mbs. Each camera will require at all times a minimum of 1.5Mbs for a system total minimum of 48Mbs.
Understanding Network Switches
Ethernet network switches are devices that join computers and other network based devices together within a single physical local area network (LAN). Switches are also used to link together multiple network switches. The original benefit of network switches was the ability to isolate the data communications to/from any connected device from any of the other connected devices. Network switches have become increasingly more intelligent and can now provide VLANs as well as some network traffic prioritization or queuing.
Understanding VLANs
VLANs or Virtual Local Area Networks are logical LANs, created within the network switches, too segment multiple networks across a single physical network infrastructure. The benefit of using VLANs is being able to converge the IP video surveillance network (data traffic) onto the same physical network as the corporate data, thus reducing costs and increasing the ROI of the corporate network infrastructure.
Interdependencies – How They All Relate
The interdependency between the bandwidth, network switch and VLANs at first glance appears simple. The network switch isolates the data communications (bandwidth) of connected devices from each other and the VLANs isolate the data communications (bandwidth) of different networks from each other. However; it’s not quite that simple. Even though the network switches and VLANs isolate data communications (bandwidth) and can even prioritize types of data communications, there is still one element that is grossly over looked in network designs for IP video surveillance. That element is maximum performance of the network infrastructure or roadway. The best example is a 16-lane highway (eight lanes in either direction) represents a single network switch. On this six16-lane highway (network switch) there is a maximum of eight lanes in either direction. Mixed across these sixteen lanes are the different VLANs. There is a finite amount of lanes or network switch processing power. There can be no more lanes, just the eight and eight. If all of the data communications (bandwidth) from all of the VLANs fills are 16 lanes (maximum packets per second for the network switch) the overall network will slow down. Traffic queuing (prioritization) helps, but if the highway is full then there will be a traffic jam.
How to prevent, or in reality to reduce the likelihood, of a network traffic jam impacting your IP video surveillance system is not always to have a separate dedicated video network, but to follow some simple rules of thumb. Always follow “Goes Into.” Know (calculate) the total minimum bandwidth required. Estimate (calculate) the worst case maximum total simultaneous bandwidth. Lastly, design the network or any segment to meet or nearly meet the bandwidth requirements for the worst case scenario. The upfront costs of the network will be slightly higher when designing for the worst case, but the return on the investment is reliability in a time of need. The ROI is in dollars. Dollars saved are varied. Dollars are saved by sharing the cost of the converged network infrastructure, potential loss due to litigation after a catastrophic event (because the system was available during this worst case scenario). In the end, understanding the basics of bandwidth, performance characteristics of network switches/VLANs and designing to the worst case potential is just smart practical business.
