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Figure 35 ▲

Operation of two camer-

as employing a Gigabit

Ethernet switch.

Data processing within

the switch is displayed

in the next two figures.

Figure 36 ►

Operation of two cam-

eras employing a

minimal inter packet

gap

(IPG).

Max. IPG:

On the Gigabit Ethernet

the max. IPG and the data

packet must not exceed 1

Gbit. Otherwise data pack-

ets can be lost.

Figure 37 ►

Operation of two camer-

as employing an optimal

inter packet gap (IPG).

5.3.1 Example 1: Multi Camera Operation – Minimal IPG

Setting the IPG to minimum means every image is transfered at maximum speed. Even

by using a frame rate of 1 fps this results in full load on the network. Such "bursts" can

lead to an overload of several network components and a loss of packets. This can occur,

especially when using several cameras.

In the case of two cameras sending images at the same time, this would theoretically oc-

cur at a transfer rate of 2 Gbits/sec. The switch has to buffer this data and transfer it at a

speed of 1 Gbit/sec afterwards. Depending on the internal buffer of the switch, this oper-

ates without any problems up to n cameras (n ≥ 1). More cameras would lead to a loss of

packets. These lost packets can however be saved by employing an appropriate resend

mechanism, but this leads to additional load on the network components�

5.3.2 Example 2: Multi Camera Operation – Optimal IPG

A better method is to increase the IPG to a size of

optimal IPG = packet size + 2 × minimal IPG

In this way both data packets can be transferred successively (zipper principle), and the

switch does not need to buffer the packets�