By: Josee Loudiadis, Director of Network Intelligence, Alcatel-Lucent (@joseeloudiadis)
What do consumers know about the effects of signaling? We pay attention to our data plan costs — such as how many bytes of data we use for Skype calls, sending photos or watching YouTube videos. But signaling remains mysterious, because we don’t pay for it in any obvious way. And because it operates transparently, we are not aware of its impact.
The Alcatel-Lucent Mobile App Rankings report wants to change that, by including signaling information in the “application cost” section of this report, right along with “data volume costs.” This data can help consumers and mobile app developers gain a better understanding of these nearly invisible events that impact batteries all day long – even when not actively using the mobile phone.
Signaling depletes batteries
The bottom line is this: Mobile applications that signal more often will deplete your device batteries faster. Of course, there are other factors affecting battery life. Among the worst drains are very bright phone screens, Wi-Fi constantly searching for a signal and apps checking regularly for new software versions. But the signaling that an application generates is another significant drain, sapping your battery’s power. Our Mobile Apps Rankings study found that an average user’s mobile device signaled 250 times every day – every 6 minutes on average!
But it’s important to recognize that applications vary widely in the amount of signaling they generate. Figure 1 makes this very clear. Apps appearing near the top of the graph generate the most signaling. And it makes sense that they’re primarily social media apps, since these app users often send short text messages and receive lots of notifications telling them that someone wants to connect or someone has retweeted a message.
Figure 2 examines daily signaling events more closely to discover how many events (on average) can be attributed to a given app installed on a mobile device. Yahoo! Messenger, for example, generates 76% of an average user’s daily signaling events. (That’s 190 out of 250 events every day.)
To help reduce battery drain, these kinds of high-signaling applications would obviously benefit from signaling optimization. But to understand what steps can be taken, we first need to take some of the mystery out of signaling.
What is signaling?
Signals are the messages sent between your device and the network to set up whatever is needed for data to start flowing. The signaling activity falls within four main categories of events:
- Context setting. When you turn your mobile on or off, a whole sequence of messages is triggered. The messages help allocate an IP address to your device and establish the terms of connectivity, such as which services are available over what technology and so forth. This “context setting” needs to occur before any network resources are devoted to transporting your data traffic. Any user’s context can vary from one network to the next, but it is generally kept for a number of days, provided the user’s mobile remains powered. As a result, context setting generates little signaling.
- Radio channel allocation. Here’s where the most signaling is generated – multiple events per second or minutes. When you use your phone to receive or send data from an app, it must use signaling messages to request a radio channel. The channel is allocated to your data for the whole transmission. Then it’s released after a certain number of seconds of inactivity, if no more data needs to be sent.That means multiple short bursts of data, spread over time, trigger multiple signaling events. But a sustained data transmission, with a large data burst, will hold the channel for a long period without re-signaling.
- Paging (or downlink signaling). Apps are increasingly using notifications to keep users engaged. For example, they might send you a “new Twitter follower” message, a “new photo posted by Facebook” message, or a red bubble reporting 6 new emails. For each notification, the sending app triggers a paging mechanism in the network. The network uses signaling to find the location of your device and allocate a radio channel, so the app’s notification can be transmitted. Apps vary widely in their paging rate.
- Handover. Handover signaling occurs when you’re transmitting data while on the move (typically while in a car). Signaling is used to seamlessly transfer the connectivity between towers. That is, a channel is allocated on the new tower before the data transfer is moved over. Although this process generates a lot of signaling, it makes up a comparatively small portion of all the signaling crossing a network. That’s because most cellular communication occurs while users are stationary. Highly mobile users, however, are likely to experience faster battery drain than stationary users, as a result of this type of signaling.
Ways to reduce signaling
How can battery drain be reduced? Strategies usually revolve around the combination of two approaches: They focus on reducing the number of notifications that wake up the phone. Or they reduce the number of times a phone must grab or release a channel during active use.
Strategy 1: Reducing notifications. Notifications can’t be turned off completely, because they are a necessary part of messaging. But app developers can promote reductions by offering configuration options for different types of notifications. Then consumers can play an important role by looking for apps that provide this flexibility — and carefully choosing just how much notification they want to receive. Here are some examples of these options and how they work:
- Email apps. Mail application have the most advanced options. (Mail apps are all clumped in the same general signaling profile in Figure 1, which suggests that these apps having converged to very similar optimization options.) “Push” notifications can be turned off, which stops the app from paging your device whenever new mail arrives. Instead, you can have your mail fetched every 15, 30 or 60 minutes, or you can completely disable this feature, and your mail will be fetched when you open the mail app.
- Twitter. Settings are available to prevent mail from going out for several types of events, such as new followers, retweets, mentions in a tweet, “favorited” and so on.
- Facebook. This app also has on/off settings for push notifications for messages, friend requests, pokes, photo tags, friend confirmation, activities missed and more.
Social media apps. These apps could improve their flexibility by offering different options for how frequently notifications are sent. For example, retweet notifications could be sent immediately, while new followers could be grouped into one notification per day or week.
Strategy 2: Reducing channel allocation “grab & release” cycle. This type of optimization is in the hands of app developers. But here are a few key points that everyone should know about:
- Balancing responsiveness and battery life. Often, developers must choose which to focus on — making the app responsive or improving battery life. In this case, it’s crucial to have a good understanding of the app’s usage patterns. That is, the choice will differ, depending on whether the app has a flurry of 30 messages, followed by silence, or one message every hour. Flurries of messages can be grouped together, or the channel can be held open slightly longer in case a new message arrives.
- Optimizing app usage metrics. Some apps send information on usage from your device to their server. For example, consumer apps might report the amount of time the app was used in a day or get location information at regular intervals. Reducing how often these processes are triggered — and staggering each user’s data over multiple hours — can lighten the load on the network and on the user’s battery.
- Reducing M2M and enterprise signaling. Machine-to-machine (M2M) devices and enterprise apps introduce different design requirements. For example, some applications keep a “heartbeat” to ensure continuous reachability. Or they may send telemetry data at regular intervals. Reducing signaling means extending the time between heartbeats, when linked to the mobile network, and ensuring that telemetry is sent in fewer, larger batches.
The Alcatel-Lucent Mobile App Rankings report helps shed some light on the impacts of signaling, which are not widely understood, so far. By learning more about signaling, notification and channel allocation, consumers can gain more control over their battery consumption. And developers can design better options for reducing the load on networks and batteries. The collaboration between these three stakeholders ultimately enhances consumers’ experience with their mobile devices.
Alcatel-Lucent Analytics Beat studies examine a representative cross-section of mobile data customers using the Alcatel-Lucent Wireless Network Guardian, and they are made possible by the voluntary participation of our customers. Collectively, these customers provide mobile service to millions of subscribers worldwide.