How To Choose a Switch For Surveillance System
[Abstract]: With wide use of HD IP Camera, it is very important to choose an appropriate switch that meet the whole network structure of a monitoring system.

With wide use of HD IP Camera, it is very important to choose an appropriate switch that meet the whole network structure of a monitoring system. An appropriate switch not only can enable the function of the monitoring network system, but also effectively reduce the waste of resources.

 

Switch Important Parameter

 

Switch Capacity

Switch Capacity is the max data capacity of switch interface processor or the max data capacity between interface card and data bus. It shows the switch ability for total data exchanging, and its unit is Gbps, also called switching Switch Capacity. The Switch Capacity value of switch is higher, the process ability of data to is higher. Switch Capacity calculation method: Switch Capacity = Port numbers * Port speed * 2

Switch Capacity≤Nominal Switch Capacity, then the switch is wire-speed, also called non-blocking.

 

Forwarding Performance ( Sum of all port forwarding rate)

Forwarding Rate,also is known as port throughput. It refers the data packet forwarding ability of a port in switch, the unit is pps (packet per second). In general, the forwarding rate for a low-end router is from a few K to a few ten Kpps, while for a high-end router, the value could be reach to ten Mpps (Million Packets per Second), even hundreds Mpps.

 


 

Forwarding rate calculation method: Forwarding rate = Full configuration gigabit port numbers * 1.488Mpps + Full configuration 10/100M port numbers * 0.1488Mpps. As ONV product POE31016PF for an example, it is with 16x 10/100M Ports and 2x Gigabit Uplink Ports. Its forwarding rate is 5.3568Mpps (16*0.1488Mpps + 2*1.488Mpps).

Forwarding Rate ≤ Nominal Forwarding rate, the switch is wire-speed, or called non-blocking

 

Switch Selection Tip

 

The switch configuration of a large and medium scale network monitoring system consists of three parts: the access layer, the aggregation layer and the core layer.

 

 

Access Layer

The actual Switch Capacity of switch is 50% - 50% of the theoretical value, so the actual Switch Capacity for 100M port is around 50M to 70M.

As 4M * 12 = 48M for example, it is recommended that 100M switches connected to max 12 pcs of 720P network camera.

At the same time, considering the dynamic coding way of current network monitoring, the stream peak value of camera may be more than 4M. And considering the Switch Capacity redundancy design, the recommended access quantity of 100M switch is within 8pcs, if more than that, it is recommended to connect with gigabit port.

 

Aggregation Layer

 

The performance of switch in aggregation layer is higher than the requirement of access switch, and clients can choose the L2 switches with thousands of upload port as the aggregation switch.

The 10/100M port of aggregation switch is connected to the access switch and gigabit port is connected to core switch. The number of cameras on aggregation switch should be controlled at about 30.

720P network camera with 4M as example,there are 6 pcs of 720P network camera in each switch in access layer, and the aggregation switch is connected with 5 pcs of above access switch. The total bandwidth of the aggregation layer switch is 4M * 6 * 5 = 120M, therefore the aggregation switch should be connected with core switch through gigabit port.

 

Core Layer

 

Core switch is the important part of the digital monitoring system, it is the connect bridge of aggregation switch,monitoring platform and storage server etc. It is suggested to choose L3 full gigabit core switches. If the quantity of connected camera is more than 150 units, a L3 10G core switch is recommended.

 

Example

 

We usually use a 8-port switch if there are 5 IP cameras to be connected. To test if the 8-port switch is meet the requirement, we need to consider below three aspects

 

1. Switch Capacity = Port numbers *  Port speed * 2. Namely 8*100*2= 1.6Gbps/S

2. Forwarding Rate =  Port numbers * Port Speed / 1000 * 1.488Mpps. Namely 8*100/1000*1.488Mpps=1.2Mpps/S. If the forwarding rate is less than that, the switch type is non-line speed. It is easy to cause delay if there are large capacity data under receive and send.

3. Bandwidth of uplink port = IP Camera Stream * Numbers. Namely 4.5*5=22.5Mbps/S.It is recommended to use 1000M uplink port when bandwidth of IP camera is over 45Mbps.

 

Inclusion for choosing switch

 

1. For easy management, WEB management switch is recommended.a

2. Due to video flow is larger, line speed switch is recommended;

3, If there is emergent properties in video data, a larger cache switch is better;

4. Flow control function;

5. It is suggested to choose well-known brand aggregation switch and core switch.

 

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