Behavior Analysis of Smartphone. version 1.1

Transcription

1 Behavior Analysis of Smartphone version 1.1

2 Behavior Analysis of Smartphone 1 Background Always-on-line application Always-on-line PDP context Fast Dormancy Summary...9

3 Background ears ago, when smartphones were introduced to the market, they were promoted as devices to help the busy, on-the-go, business professional. It was a tool primarily made available to access one s , calendar and contacts when away from the office or travelling. Today, that is far from the case they are integrated into the daily lives of all types of people. According to the statistics of Gartner, Smartphone sales to end users totaled 61.6 million units in the second quarter of 2010, a 50.5 percent increase from the same period in But unfortunately, with the widespread introduction of smartphones, mobile network operators are confronted with new challenges: congested network resources, worsening network KPIs and increasing complaints from end users. Smartphone has changed the mobile network greatly the same way it did to the world. How does Smartphone behave? How does it affect the mobile network? The answer falls back on the basic three characteristics of smartphones: Always-on-line applications Always-on-line PDP context Fast dormancy Open operating system, which distinguishes the smartphones from feature phones, enables the mobile phone software developer to design various programs similar to the ones running on desktops. Business, games, news, instant messaging, entertainments and even the latest social networking service, almost every application has its mobile-oriented version on Smartphone. Experience expectation from end users for real-time service demands the applications to be always-on-line, so does the lower layer bearer, the PDP context. Compared with the steady power supply of desktops, however, Smartphone is equipped with small, limited battery, which will impact the application and OS behavior. 1

4 Always-on-line application Portable and smart as it is, smartphones allow people to access the Internet anytime anywhere for any kind of service. Users expect to get up-to-date information from the network timely with the help of smartphones. For real-time web services, a logical always-on-line connection between the client and the server is required. Frequent or periodical heartbeat packets, the most possible mobile signaling triggers, work as the keep-alive packets to maintain the C/S connection, but they are more than keep-alive packets. Three interaction technologies are mainly used for smartphone applications with different heartbeat characteristics: Pull/Polling Pull or polling technology is a style of network communication where the initial request for data originates from the client, and then is immediately responded to by the server. Every polling procedure corresponds to a heartbeat. For pull technology, Iu signaling may be triggered by uplink polling request. Long-polling Long polling is a variation of the traditional polling technique and allows emulation of an information push from a server to a client. With long polling, the client makes a request for information to the server, which is kept open until the server has new data available or after a suitable timeout. Iu signaling may be triggered by uplink polling requests and the downlink responses. Push With push technology, the server pushes the new content or notification directly to the client, whenever new information is available or certain event happens. Periodic keep-alive packets are sent by the client just to inform the server of its activity. Iu signaling may be triggered by uplink periodical keep-alive packets, downlink notifications and uplink data synchronization requests. 2

5 For iphones, the most popular applications are based on pull technology, except the APNS. App on iphone Pull(Polling) Long-polling Push Twitter ebuddy Facebook APNS 50s/205s 5 or 6s 5 to 60s 10~15min While for HTC android smarthones, the IM and social networking client applications are basically implemented on polling technology. App on HTC Android Twitter Facebook MSN Google Talk Pull (Polling) Long-polling Push 5min 30m/1H/2H/4H/ Never 40 to 60min 30min As for smartphones of symbian system, the proprietary Nokia messaging application is based on long-polling with adjustable heartbeat interval. App on Nokia symbian Pull (Polling) Long-polling Push Nimbuzz Nokia Messaging 2min 39s 5m to 30m As can be seen, for most applications on mobile devices, polling technology is used widely, and the same application can be implemented with different technology on different platforms and represent different heartbeat characteristics, such as the Facebook application. Besides, self-adaptive heartbeat is usually adopted by applications to adjust with the network constraint from session TTL of firewall or other NAT devices. 3

6 Always-on-line PDP context Always-on-line application requires a permanent IP connection, thus gives rise to the Always-on-line PDP context. Type/OS GPRS Attach Power On Source: HUAWEI Smart Lab Triggered by application PDP Context Activation Power On iphone 3.0 iphone 4.0 Nexus One(Android) HTC HD2(WM) Triggered by application As can be seen, smartphones on android OS generally attach to GPRS network and activate a PDP context at once with the mobile phone power on. A mobile network dominated with android smartphones may expect high GPRS penetration rate and PDP activation rate. In contrast, iphone 3.0 only get attached with power-on, the PDP context is activated by applications launch. In case that push notification function is enabled, the PDP context can be activated by default when the push task is started to run background. As for smartphones based on window mobile OS, the access to GPRS network is completely triggered by applications, for instance, when the user opens a web browser or sends an MMS. PDP context deactivation may happen when the upper layer application quit, or most typically, when the mobile phone is powered off. It can also occur due to user inactivity when no data is transmitted on the PDP for a certain period of time, or due to screen auto lock for battery saving of smartphones. 4

7 PDP Deactivation by MS Type/OS Application quit Screen Lock Power off iphone 3.0 iphone 4.0 Nexus One(Android) HTC HD2(WM) Source: HUAWEI Smart Lab PDP Deactivation by Core Network Type/OS Deactivation Accept Deactivation Ignore Re-Activate PDP After Deactivation iphone 3.0 iphone 4.0 Nexus One(Android) HTC HD2(WM) Source: HUAWEI Smart Lab If the PDP deactivation is initiated by core network in case of network failure or other cases, the smartphones respond diversely. HTC HD2 accepts the deactivation request normally while iphone 3.0 and Nexus one on android OS re-activate PDP context instantly after the deactivation, which may be attributed to some inherent always-on-line applications such as Push Notification on iphone. Always-on-line PDP feature changes the traffic model of mobile phones greatly. Longer PDP context duration means less PDP activation attempt in the busy hour but possible more Iu signaling procedures such as paging, service request and Iu release. At the same time, always-on-line PDP context consumes the static resources of network equipment, which is ultimately limited by the physical memory size of the equipment. Besides, as an IP address may be occupied for a long period of time, more IP addresses are needed for the concurrent PDP contexts. 5

8 Furthermore, always-on-line PDP context also leaves the Smartphone a permanent IP reachable endpoint in the IP network and subject to malicious programs, such as virus attacks. Compared with the wired Internet, the attacks destined to mobile Internet devices not only threaten the smartphones but also endanger the mobile network. For example, an intensive IP address scan/sweep attack on MS can evoke a paging storm, and consequently, a connection setup storm, which would overload the mobile network equipment such as the RNCs and the SGSNs. Attacker MS IP POOL RAN SGSN Mobile Network GGSN 6

9 Fast Dormancy Most Smartphones adopt fast dormancy, a feature formally defined in 3GPP R8, to enhance UE battery performance. Release-8 fast dormancy feature extends SCRI message with a cause IE indicating to the network that the UE no longer requires currently assigned radio resources due to PS session end. On receiving SCRI with this cause, the RNC may initiate a state transition to an efficient battery consumption RRC state such as IDLE, CELL_PCH, URA_ PCH or CELL_FACH state. But for most smartphones, the pre-r8 fast dormancy implementation is a little different from the standard Release-8 version. Smartphones send SCRI messages without cause IEs, which is originally defined for UEs in abnormal cases to indicate to the UTRAN that one of its signalling connections has been released. In such cases, the RNC may release the RRC connection as well as Iu connection, change the UE to IDLE mode. Thus any subsequent packet data transfer requires the connection to be set up again at first. According to the SCRI test result, smartphones such as iphone, HTC G6 and Black berry send SCRI shortly after the data transmission to save battery, in less than 3 to 10s. It is obvious that for a mobile network dominated by these kinds of smartphones, to transfer to IDLE state for fast dormancy would give rise to frequent mobile signaling interaction. Source: HUAWEI Smart Lab Smartphone Type UE Software UE Sending SCRI or Not Samsung360 NO NO Time for UE to Send SCRI After Data Transmission SonyEricsson X10 R2BA013 ES around 5 to 10s Black berry Storm ES around 3 to 10s Black berry Bold ES around 3s iphone Pre-comercial iphone ES around 10s iphone ES around 10s Nokia5800 NO NO HTC g6 2.1 ES around 5s 7

10 In order to avoid frequent connection setup and tear down, most RNC vendors prefer to change the UE into PCH state rather than IDLE state on receiving SCRI message. At the cost of a slight more battery consumption, transmission to PCH state can keep Iu connection and RAB unreleased. But problems still remain. Being a proprietary feature, pre-r8 fast dormancy implementation may vary with Smartphone models, hardware, operating system and software version. Some smartphones change to IDLE state directly after sending SCRI regardless of the indications from RNCs. Some smartphones may send SCRI again even in PCH state. Some may fail to transfer from PCH back to FACH or other state for data transmission with the result of returning to IDLE state again. Due to mobile phone compatibility problems, pre-r8 fast dormancy feature remains an uncontrollable feature for legacy network to some extent. For UEs that never send SCRIs such as Nokia5800 and Samsung360, the state transfer is controlled by RAN. RNCs can choose to change the UEs to IDLE or PCH state when certain implementation dependent timers expire. 8

11 Summary Smartphones impact the mobile network greatly due to its three characteristics. Always-on PDP context calls for more resources such as SAU, PDP storage, IP address for concurrent PDP contexts. Fast dormancy for longer battery life tends to release connection immediately after each data transmission. Heartbeats of always-on-line applications together with other service packets result in frequent data transmission on smartphones. As a result, repeated connection setup and release accompanied by vast mobile signaling would overload the mobile network. Signaling congestion can be solved partially by solution of Cell/URA PCH. But due to the uncertainty of smartphone implementation for pre-r8 fast dormancy feature, frequent connection setup and release is inevitable in certain scenarios. Hence, capacity expansion would be an effective and simple solution which meets the requirement for static resources consumption and signaling processing capability as well. What s more, smartphone service results in frequent paging, which brings extra high paging s load to PS CN and BSS. Huawei provides Smart Paging solution to reduce the paging messages between the SGSN and PCU/RNC. Huawei also provides Smart Direct Tunnel solution to reduce the signaling impact to the GGSN. SGSN identify the specific smartphone and disable Direct Tunnel for the specific smartphone. These solutions can be candidates for the deployments to optimize the smartphone s impacts. 9

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