Your recent segment on Ethernet switches left out some important details

[G+_Chris W]

Your recent segment on Ethernet switches left out some important details. The first is overhead. For standard size frames, Ethernet is about 94% efficient, or a theoretical 118 MBps vs. the pure 1Gb = 128 MBps. Then you have to add in the overhead of the video protocol.

 

But the biggest detriment here is the number of devices on one network segment. Sure, GbE can do 118 MBps point to point, but add other devices and you get packet collisions. With that many cameras all pushing data continuously, throughput is going to suffer. It's really no surprise that he had to turn off half the cameras to get it to work.

[G+_Travis Hershberger]

The overhead is a great point. 

 

Network congestion and collisions not so much anymore.  I have yet to find a gigabit hub in the wild.  They're all switches at this point.  The move to switches instead of hubs has eliminated network collisions at this point.  I also haven't seen a switch that can't handle forwarding all ports at full speed all the time.  It is possible to find, but your generally looking at "If you have to ask you can't afford it." core equipment at that point.

 

Now if you start to throw wireless in, then anyone who thinks putting cameras on a wireless is a good idea needs a bit more education about how bad wireless really is (especially if you can run the cameras vie POE.)

[G+_Luke Militello]

Routers break up broadcast domains and switches breakup collision domains. Padre's suggestion is sound about adding the additional switch, it would segment a collision domain solely for the cameras speaking with their NAS boxes and, likewise, one for the workstations speaking with their NAS. One must also consider the switch fabric of the switch itself. More often than not, switches are always oversubscribed, even at the enterprise level unless you pay big bucks. As an example, most enterprise level 48 port gigabit switches only include 2-20 gigabit ASIC's which provide 40 gigabit of switch fabric. This is over subscribing, it means if you only use 40 of the 48 ports, those 40 ports will see 1 Gbps per port (raw). I don't think I need to tell you that manufactures push the interface standards multiplied by number of ports as max speed specifications. If you want to know what your switch is capable of, you need to focus on the switch fabric capacity. If they don't list it, call them and ask for it, if they don't tell you, get another brand. Also, as for collisions, the gigabit Ethernet standard has no back-off algorithm when a collision does occur because the time it takes to just resend the packet is faster than running a back-off first. Regardless, collisions on both FE and GE should seldom occur with full duplex. I will say in a situations like this, a separate VLAN for the cameras would also be beneficial for isolating the broadcasts and provide some layer of security if using ACL's, etc.?