Lessons Learned: Transitioning from TDM to IP

Cell-phone-tower-near-Lozen-Bulgaria-Aviat-Networks-network-solutions-architect-Hadi-Choueiry-recounts-3-TDM-to-IP-lessons-learned-18Oct13

Cell phone tower near Lozen, Bulgaria. Photo credit: Plamen Agov • studiolemontree.com [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons

The transition from the Time Division Multiplexing (TDM) cell phone networks of the 2G and 3G mobile era has been a long time coming. However, the mobile industry seems to be at one of its proverbial inflection points where IP (Internet Protocol) technology is ascendant and TDM has begun the long but inevitable decline into legacy status.

Aviat Networks has been there all along the way, helping operators design and deploy aggregation systems. We’ve seen and learned a lot as some of the leading mobile phone carriers have upgraded their networks. Now as LTE works its way into mainstream status, cell phone networks are transitioning to full-IP, the underlying technology of LTE.

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The Impact of Streaming Video on Wireless Network Services

Video call between Sweden and Singapore, on So...

Sustained video streaming, such as a video call over a mobile network, strains the stat mux paradigm of oversubscribing Ethernet microwave backhaul. However, proper management can ensure a consistent, high-quality user experience can be maintained. Image via Wikipedia (author: Kalleboo)

Mobile backhaul networks today support Ethernet microwave transport for 3G and 4G wireless technology services alongside legacy 2G and 3G TDM-based microwave equipment. However, as late as 2009 these wireless network services were solely TDM transport. One of the primary benefits of moving to Ethernet microwave transport has been the inherent statistical multiplexing (stat mux) gains. Stat mux relies on the fact that not everyone is “talking” at the same time and when they do, their IP radio packet sizes are variable, whereas networks based on TDM have to be provisioned statically for peak rates to individual wireless microwave sites.

With the advent of Ethernet, the typical practice is to oversubscribe all the wireless network services (based on individual peak rates) knowing that there is a statistical improbability of hitting the peak rate across all your wireless communication towers at the same exact moment.

Now enter video streaming where data is “streamed” between two wireless communication points over a sustained period (e.g., 30-second YouTube video clips, Skype HD Video Conferencing, Netflix movies). The sustained aspect of these video streams begins to strain the overall stat mux paradigm. Not only does video remain sustained but also it uses large-size IP radio packets that do not vary greatly. VoIP does the same thing, but the effect is much less significant as the overall bandwidth utilization is much lower.

Oversubscription becomes more challenging the more active video streaming is at any given moment. Imagine a scenario where the latest cat-playing-a-piano video gets posted online and everyone starts viewing it at virtually the same time. For a large swath of bandwidth, stat mux will reach zero for approximately four minutes. The upside is that you can add more bandwidth and/or offer differentiated wireless network services levels that guarantee certain bandwidth or application performance. Even so, video streaming does not totally negate the benefits of an Ethernet microwave transport, it just needs to be properly understood and managed to ensure a consistent user experience across all applications and services for your global wireless solutions.

Steve Loebrich
Director of Product and Solutions Marketing
Aviat Networks

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