Network Success for Voice, Data & Video Multiple classes of service are what you need for voice and data to co-exist on your network connections
By: John Shepler
One of the big impediments in getting networks to work well for all types of traffic is that different types of traffic have different needs. Treat all packets the same and you’ll enjoy excellent results in some cases and unacceptable results in others. What’s the solution? You need to add a touch of class to your network.
Why Class of Service?
The idea behind class of service or CoS is that different types of traffic get different priorities on the network. For instance, do you really think that data backups are as sensitive to network characteristics such as latency and jitter as VoIP telephone conservations? Of course not. If your network has the capacity it may not matter. With infinite bandwidth all traffic will flow smoothly from source to destination. The problem is that we don’t have infinite bandwidth or infinitely large anything else.
The Problem With Telecom Connections
This really shows up in MAN and WAN connections. These telecom links are almost always more limited than your LAN resources simply because of the cost involved. How many companies can afford 10 or 100 Gbps private lines cross-country? In fact, even 1 Gbps is a stretch for many IT departments. Many companies will have to get everything done with 10 Mbps Ethernet or 100 Mbps Fast Ethernet MAN and WAN service.
Can this work? It likely can if you carefully manage your traffic and don’t have so much that you saturate the network. The trick is in establishing multiple classes of service and assigning each type of traffic to one of those classes. Do it right and everything on the network will run smoothly.
Separating Voice and Data
The simplest example is to establish two classes of service. One is for latency sensitive applications. The other is for everything else. A good example is a SIP trunk that provides you with both VoIP business phone service and Internet access. This is becoming a popular setup for smaller business locations because of the cost savings involved in having only one outside trunk line. The VoIP traffic is extremely sensitive to latency and jitter so it goes into the class that has priority. Most of what you do on the Internet isn’t that sensitive, so it goes into the non-priority class.
You need this type of division because voice traffic is typically low bandwidth per conversation and will break up if there is any network congestion. Data transfers and web page downloads aren’t so sensitive to congestion and will take all the bandwidth they can get. If there isn't enough, they may slow down a bit but you won’t lose any data.
Limitations to CoS
Class of Service keeps the big data and video downloads from pushing the more sensitive voice and two-way video conferences to the side. This can make your network perform much better overall without increasing bandwidth. Even so, there’s no free lunch. When the network gets congested enough, you are going to notice the slowdown on non-critical traffic and will have to increase bandwidth to make everything run as fast as it can.
Class of Service is one of the big differentiators between the Internet and private networks. There is no CoS on the Internet. In fact, it is a matter of pride that all packets are treated equally. This principle is called network neutrality. It makes the public Internet fair for all users, but inhibits performance on latency and bandwidth sensitive applications.
Is there a reason to create more than two classes of service? There is for more sophisticated operations. In medium and larger company operations not everything falls neatly into the two buckets of highly demanding or not so important categories. You may wish to subdivide your traffic into 4 or 6 classes.
Here's a typical setup. The class at the bottom of the heap is everything that just isn't time critical. That may include data backups, some file trasnfers, low priority inventory updates and business reports and the like.
The next class up will be for important and somewhat time sensitive needs such as email messaging, Web access, FTP transfers, and audio or video streaming. TCP/IP and buffering allow these applications to run just fine with some network congestion as long as it doesn't get excessive.
Higher up the totem pole are business priority needs such as access to cloud services. Moving to the cloud can be a big money saver unless response time degrades so much it damages the workflow and kills employee productivity.
The highest priority is for latency critical applications such as network voice and video conferencing. These apps simply cannot stand any packet delay or loss or they will self-destruct. You must have the capacity to make critical applications run smoothly 100% of the time or your network connections are not up to the job.
Do You Need Class of Service?
Are you frustrated by the problems that have arisen as you’ve expanded the expectations of whattypes of traffic your network is expected to handle, especially for MAN and WAN connections? If so, a private network with two or more classes of service may get everything running smoothly again at a reasonable cost.
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