Congestion is a growing concern in networks and a growing nightmare for network administrators. There are several means available today to control how traffic moves through a network from setting QoS (Quality of Service) bits to the newer SIP protocol functionality, VLANs, bandwidth managers, etc. The problem is that different systems and vendors may interpret the standards differently, making interoperability tricky.
With the growing need for reliability and real-time transmissions such as VoIP/IP Telephony, video transmissions and storage mirroring across the network, devices are creating a growing demand on network resources. Rather like a room full of people that all want to speak and try to do so at the same time, congestion is filling buffers causing discards and wreaking havoc.
Problems on these networks can be larger than on a data network as data retransmissions are acceptable at some level.
What can cause congestion? Applications are one culprit. An improper performing package, bad queries tying up system resources, applications that do not handle requests properly from attached clients or time-outs set incorrectly can all cause problems. Applications also have the ability to reset the QoS bit. This could lead to some surprises. If applications are an issue, a good tool would be a bandwidth manager and some RMON tools to help diagnose and correct the problem. A bandwidth manager basically acts like a traffic cop for the network, throttling back data and non-essentials and streamlining voice or more real-time applications.
The IETF is currently working to clarify the SIP (Session Initiation Protocol) specification to address interoperability and various interpretations of the spec by different vendors. This should help with application congestion within that protocol.
Another cause could be in the hardware itself. Hardware that does not understand or know how to process QoS attributes, has issues with routing, or has buffers that are insufficient for the traffic load can all be issues. Also putting all of your heaviest applications and servers on a switch with your voice ports may not be a good idea unless you are in a smaller environment. This is where IEEE steps in. IEEE is now looking into whether a congestion management tool is needed that would run above and not change the current lower layer specifications. Should this formally go to study group and task force stage? This is part of what is being addressed. This would help at the lower network layers as opposed to the ones above.
The third cause, as we move down the protocol stack, could be in the physical infrastructure. Faults at the physical level that are noise related or exhibit intermittent problems are some of the hardest to track down, but can cause the greatest hit to your bandwidth. As the IEEE does not plan to address physical layer issues, the onus is on the end-user to select reliable products for their physical layer and/or have the tools to properly diagnose and remedy them.
Congestion for both wired and wireless networks is also becoming a pain. The FCC is currently planning to give new frequencies to one cellular company to allow them to retune their spectrum so that emergency personnel can use the current spectrum. This has a few other carriers expressing some dismay, but it is necessary to relieve the congestion and saturation (as it is more commonly known in the wireless world).
If your network is designed around occasional retransmissions, well, that is pretty normal. If you are beginning to encounter frequent retransmissions and congestion within your enterprise, one thing is certain – if you don't fix it, it will only get worse!
Carrie Higbie, Global Network Applications Market Manager, The Siemon Company
Carrie has been involved in the computing and networking industries for nearly 20 years. She has worked with manufacturing firms, medical institutions, casinos, healthcare providers, cable and wireless providers and a wide variety of other industries in both networking design/implementation, project management and software development for privately held consulting firms and most recently Network and Software Solutions.
Carrie currently works with The Siemon Company where her responsibilities include providing liaison services to electronic manufacturers to assure that there is harmony between the active electronics and existing and future cabling infrastructures. She participates with the IEEE, TIA and various consortiums for standards acceptance and works to further educate the end user community on the importance of a quality infrastructure. Carrie currently holds an RCDD/LAN Specialist from BICSI, MCNE from Novell and several other certifications.
