Monday, February 22, 2010

Mobile Signaling Causes Congestion, Not Bandwidth

Executives highly familiar with mobile broadband network operations know that radio networks can, and do, become congested for reasons having to do with signaling, rather than bandwidth consumption. Executives at Spirent and Alcatel-Lucent Bell Labs,  for example, have pointed out that mobile phone design can itself cause problems.

As it turns out, that is true of the iPhone as well, which tries to save power by disconnecting from the network whenever possible.

Now engineers at U.K. mobile provider O2 point out that the iPhone uses more power-saving features than previous smartphone designs. That's good for users, but bad for radio networks.

Most devices that use data do so in short bursts—a couple e-mails here, a tweet there, downloading a voicemail message, etc. Normally, devices that access the data network use an idling state that maintains the open data channel between the device and the network.

However, to squeeze even more battery life from the iPhone, Apple configured the radio to simply drop the data connection as soon as any requested data is received. When the iPhone needs more data, it has to set up a new data connection, O2 engineers say.

The result is more efficient use of the battery, but it can cause problems with the signaling channels used to set up connections between a device and a cell node.  Simply put, the signaling overhead congests the network, not the bearer channels. It is signaling load, not bandwidth consumption, that causes much congestion.

It's important to note, however, that this technique is not limited to the iPhone. Android and webOS devices also use a similar technique to increase battery life. While the iPhone was the first and currently most prolific device of this type, such smartphones are quickly becoming common, and represent the majority of growth in mobile phone sales in the past year.

Networks designed to handle signaling traffic dynamically, shifting more spectrum to signaling channels when needed, can mitigate this problem. But even with more signaling capacity, network nodes may not be able to set up a data session, or may have problems getting a valid network address from an overloaded DHCP server.

In fact, the fact that Europe embraced heavy text messaging and data use far earlier than users in the United States meant that the signaling networks were configured early on for heavy signaling traffic.

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