October 19, 2011 | by Mark Coxon Smaller packet sizes can minimize the gaps in transmission, but result in more consistent traffic on the network. Think of it like rush hour. There are large masses of traffic spread out, (stop and go) letting you go 60 mph at times and 0 mph at others when traffic all converges. In the second scenario, there are smaller amounts of traffic all over the road that keep you moving, but at an average speed of 30 mph.

Depending on the frequency of convergence in the first scenario, the later may be faster or slower.

Protocol
Network protocol makes a difference in your video transmission as well. TCP protocol sends a return packet for every sent packet to verify the packet was received. As you can see, this increases the traffic on the network with the return packets going back. The advantage is that getting a receipt mitigates gaps in transmission, as if a packet is not received it can be resent. This is very important in video, especially if the packets are large.

UDP protocol is used a lot in IP telephony. It reduces traffic on the network by eliminating return packets. However, this means packets do not have the opportunity to be resent as there is no communication as to whether they were received or not. This is why in high traffic periods, IP phones have a tendency to cut in and out if not managed properly. The way that this type of system reduces gaps, is by reducing packet size of the data in its transmissions.

Switch Fabric
A 24-port gigabit switch doesn’t necessarily have the ability to pass 24 gigabits at once. Make sure you look at the total switch throughput or switch fabric to assure the switch can handle your demands. Switches, like Cisco Catalyst, are more costly but have 32 gigabit switch fabrics and management features.

Switch Management Features
If you have a complex network of mixed devices, or devices with differing priority of operation, a managed switch is most-likely a must. These switches allow you to create VLANs or virtual networks within the switch itself to limit access of one VLAN to another, or to set data ceilings and floor on the ports in the switch. In this case, you can predetermine what devices get more available bandwidth than others by limiting the throughput on that port of the switch itself. For example, the executive boardroom may always have a higher priority and more bandwidth than a middle management conference space.

Another great feature on some newer switches is VLAN by MAC address. If the CEO has a VTC client on his laptop, his VLAN can be given more priority or VLAN based on the MAC address of his machine. No matter where he plugs in at the facility, the port his machine is plugged into will be given that VLAN and those preferential settings. Now, the CEO can move around to different locations and have a jitter free videoconference call with his distributor in China.

Bursts vs Streaming
Placing a small PC or networked video player device at each screen, or close by, can decrease the consistence of network traffic.

The most simple example is trying to watch You Tube on a slow connection. Watching it real time as it is streaming is futile. You wait until it downloads, then you watch it and there are no issues. Once the data is in local memory, it is not dependent on the network to get it up on the screen.

This is why many signage players are not technically streaming content. The devices receive updated data from a signage server in a large chunk, taking up traffic for a fixed period of time. After the data received, that content is played from local storage to the screen, limited by bus and processor speed, not by the network or ISP. NetStreams uses this method, making their name a misnomer as the data really isn’t streaming. Each endpoint gets the data, they all wait to make sure everyone has it, and then they all start to play at the same time. This eliminates time delay in more traditional systems due to the varying distances.

If you need real time access, streaming is the best option. It can also be optimized to available bandwidth, like Netflix does, to evaluate the bandwidth and adjust the video quality to mitigate the instances of gaps in the data.

At the end of the day, to be a true resource to your clients, ask for introductions to their IT staff and start asking all the right questions to find out the info above. You will become their ally in the process, and you will have all the info to deliver an outstanding system which will ultimately produce a happy customer.