In part, this is due to the high roundtrip latencies, but we also cant forget the overhead ( Figure 8-2 ) of dns, tcp, tls, and control-plane costs! Components of a "simple" http request In the best case, the radio is already in a high-power state, the dns is pre-resolved, and an existing tcp connection is available: the client may be able to reuse an existing connection and avoid the overhead of establishing. However, if the connection is busy, or nonexistent, then we must incur a number of additional roundtrips before any application data can be sent. To illustrate the impact of these extra network roundtrips, lets assume an optimistic 100 ms roundtrip time for 4G and a 200 ms roundtrip time for.5G networks: The rrc control-plane latency alone can add anywhere from hundreds to thousands of milliseconds of overhead. Once the radio is active, we may need to resolve the hostname to an ip address and then perform the tcp handshake—two network roundtrips. Then, if a secure tunnel is required, we may need up to two extra network roundtrips (see tls session Resumption ).
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Then, measure the impact with aro or a similar tool and adjust accordingly. Eliminate Unnecessary Application keepalives The connection state and the lifecycle of any tcp or udp connection is independent of the radio state on the device: the radio can be in a low-power state while the connections are maintained by the carrier network. Then, when a new packet arrives from use the external network, the carrier radio network will notify the device, promote its radio to a connected state, and resume the data transfer. The application does not need to keep the radio "active" to ensure that connections are not dropped. Unnecessary application keepalives can have an enormous negative impact on battery life performance and are often put in place due to simple misunderstanding of how the mobile radio works. Refer to Physical layer. Application layer Connectivity and Packet Flow paper in a mobile network. Most mobile carriers set a 530 minute nat connection timeout. Hence, you may need a periodic (5 minute) keepalive to keep an idle connection from being dropped. If you find yourself requiring more frequent keepalives, check your own server, proxy, and load balancer configuration first! Anticipate network latency overhead A single http request for a required resource may incur anywhere from hundreds to thousands of milliseconds of network latency overhead in a mobile network.
Finally, while we have so far focused on the battery, intermittent network access required for techniques such as progressive enhancement and incremental loading also carries a large latency cost due to the rrc state transitions! Recall that every state transition incurs a high control-plane latency cost in mobile networks, which may inject hundreds or thousands of for extra milliseconds of latency—an especially expensive proposition for user-initiated and interactive traffic. To illustrate the impact of periodic polling on battery life, lets do some simple math. The numbers are not exact but are within range of a typical 3G/4G mobile handset: 5 watt-hours, or 18,000 joules of battery capacity ( ) 10 joules of consumed energy to cycle radio from idle to connected and back 1 minute polling interval consumes 600. All it would take is a couple of applications with non-overlapping polling intervals to drain your battery by midday. Although, to be fair, a push application with frequent, unbuffered updates can have an even higher energy consumption profile. Battery life optimization and frequency of updates are inherently at odds. Consider the requirements of your specific application to determine the optimal strategy: bundling of updates, adaptive update intervals, pull. Push, and.
Unfortunately, today there is no cross-browser api to deliver a gcm-like experience to all clients. However, the W3c push api (see ) house should address this use case in the future. Intermittent beacon requests such as audience measurement pings and real-time analytics can easily negate all of your careful battery optimizations. These pings are mostly harmless on wired and even wifi networks but carry an outsized cost on mobile networks. Do these beacons need to happen instantaneously? There is a good chance that you can easily log and defer these requests until next time the radio is active. Piggyback your background pings, and pay close attention to the network access patterns of third-party libraries and snippets in your code.
Avoid polling and costly xhr techniques when possible. A simple aggregation strategy of bundling multiple notifications into a single push event, based on an adaptive interval, user preference, or even the battery level on the device, can make a significant improvement to the power profile of any application, especially background applications, which often. nagle and Efficient Server Push, tcp aficionados will undoubtedly recognize the request aggregation and bundling advice as Nagles algorithm, except reimplemented at the application layer! Nagles algorithm attempts to combine multiple small tcp messages into a single packet to reduce protocol overhead and the number of packets on the wire. Not surprisingly, our mobile applications can benefit a great deal from leveraging the same technique. A simple implementation of such a strategy is to aggregate messages on the server by time, count, or size, instead of triggering an individual push for each one. A more involved, but significantly more efficient, strategy is to push updates only when the radio is already active on the client—e. G., defer the messages until the client initiates a request or leverage a third-party service that is aware of the clients radio state. For example, services such as google Cloud Messaging (GCM) for Android and Chrome offer message delivery apis which can aggregate messages and deliver updates only when the device is active: the server pushes its messages to gcm, and gcm determines the optimal delivery schedule.
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Inefficiency of Periodic Transfers. In fact, extending this same logic yields the following rules: Polling is exceptionally expensive on mobile networks; minimize. Where possible, push delivery and notifications should be used. Outbound and inbound requests should be coalesced and aggregated. Noncritical requests should be deferred until the radio is active. In general, push delivery is more efficient than polling. However, a high-frequency push stream can be just as, if not more, expensive.
Whenever there is a need for real-time updates, you should consider the following questions: What is the best training interval of updates and does it match user expectations? Instead of a fixed update interval, can an adaptive strategy be used? Can the inbound or outbound requests be aggregated into fewer network calls? Can the inbound or outbound requests be deferred until later? For push delivery, native applications have access to platform-specific push delivery services, which should be used when possible. For web applications, server-sent events (SSEs) and WebSocket delivery can be used to minimize latency and protocol overhead.
To capture a trace, load the collector, hit Record, interact with your application, and then copy the trace to your system. Once a trace is available, you can open it with the analyzer to get insights into radio states, energy consumption, and traffic patterns of your application. One of the great features about the analyzer is that it will also provide recommendations for common performance pitfalls, such as missing compression, redundant data transfers, and more. Two important things to note: the battery consumption and radio states are generated via a specified model of the device and the type of radio network. In other words, the generated numbers are not exact measurements from the device in use but estimates based on specified parameters in the model.
On the upside, this allows you to import different device and network models and compare their energy use—e. Finally, the collector is Android only, but the aro analyzer can also accept any regular packet trace (pcap) file produced by tcpdump or a compatible tool; ios users will have to use the tcpdump method. To get started with aro, head. Eliminate periodic and Inefficient Data Transfers. The fact that the mobile radio incurs a fixed power cost to cycle into the full power state, regardless of the amount of data to be transferred, tells us that there is no such thing as a "small request" as far as the battery. Intermittent network access is a performance anti-pattern on mobile networks; see.
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However, because keeping the radio house active is so expensive in terms of battery life, our applications should maximize the amount of transferred data while the radio is on and then seek to minimize the number of additional data transfers. Even though wifi uses a radio interface to transfer data, it is important to realize that the underlying mechanics of wifi, and consequently the latency, throughput, and power profiles of wifi, when compared with 2G, 3g, and 4G mobile networks are fundamentally different; see our. Consequently, the networking behavior can and often should be different when on wifi. measuring Energy Use with at t application Resource Optimizer. Despite the high emphasis on optimizing energy use, most platforms currently lack the necessary tools to help developers measure and optimize their applications. Thankfully, there are third-party tools that can help, such as the free application Resource Optimizer (ARO) toolkit developed by. At fruit t application Resource Optimizer. Aro consists of two components: a collector and an analyzer. The collector is an Android application that runs in the background (on a real phone, or within an emulator) and captures the transferred data packets, radio activity, and other interactions with the phone.
were put in place, ask a simple question: how does it impact or improve the battery life? In fact, this is a great question to ask for any and every feature in your application also. Networking performance on mobile networks is inherently linked to battery performance. In fact, the physical layers of the radio interface are specifically built to optimize the battery life against the following constraints: Radio use at full power can drain a full battery in a matter of hours. Radio power requirements are going up with every wireless generation. Radio is often second in power consumption only to the screen. Radio use has a nonlinear energy profile with respect to data transferred. With that in mind, mobile applications should aim to minimize their use of the radio interface. To be clear, that is not to say that you should avoid using the radio entirely; after all we are building connected applications that rely on access to the network!
To add insult to injury, poor networking decisions will also have an plan outsized negative impact on the battery life of the device. There is no universal solution for these three constraints. There are best practices for the presentation layer, the networking, and the battery life performance, but frequently they are at odds; it is up to you and your application to find the balance in your requirements. One thing is for sure: simply disregarding any one of them wont get you far. With that in mind, we wont elaborate too much on the presentation layer, as that varies with every platform and type of application—plus, there are plenty of existing books dedicated to this subject. But, regardless of the make or the operating system, the radio and battery constraints imposed by mobile networks are universal, and that is what we will focus on in this chapter. Throughout this chapter and especially in the following pages, the term "mobile application" is used in its broadest definition: all of our discussions on the performance of mobile networks are equally applicable to native applications, regardless of the platform, and applications running in your browser.
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Introduction, first off, minimizing latency through keepalive connections, geo-positioning your for servers and data closer to the client, optimizing your tls deployments, and all the other protocol optimizations we have covered are only more important on mobile applications, where both latency and throughput are always. Similarly, all the web application performance best practices are equally applicable. Feel free to flip ahead. Primer on Web Performance ; well wait. However, mobile networks also pose some new and unique requirements for our performance strategy. Designing applications for the mobile web requires careful planning and consideration of the presentation of the content within the constraints of the form factor of the device, the unique performance properties of the radio interface, and the impact on the battery life. The three are inextricably linked. Perhaps because it is the easiest to control, the presentation layer, with topics such as responsive design, tends to receive the most attention. However, where most applications fall short, it is often due to the incorrect design assumptions about networking performance: the application protocols are the same, but the differences in the physical delivery layers impose a number of constraints that, if unaccounted for, will lead to slow.