Behavior Analysis of Smartphone

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Behavior Analysis of Smartphone

1 Background ...................................................................................................................1

2 Always-on-line application .............................................................................................2

3 Always-on-line PDP context ...........................................................................................4

4 Fast Dormancy ................................................................................................................7

5 Summary .....................................................................................................................9

1

Background

Years 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 email, 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 2009.

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.

2

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.

3

For iPhones, the most popular applications are based on pull technology,

except the APNS.

While for HTC android smarthones, the IM and social networking client

applications are basically implemented on polling technology.

App on iPhone Pull(Polling) Long-polling Push

Twitter 50s/205s

eBuddy 5 or 6s

Facebook 5 to 60s

APNS 10~15min

App on HTC Android

Pull (Polling) Long-polling Push

Twitter 5min

Facebook30m/1H/2H/4H/Never

MSN 40 to 60min

Google Talk 30min

As for smartphones of symbian system, the proprietary Nokia messaging

application is based on long-polling with adjustable heartbeat interval.

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.

App on Nokia symbian

Pull (Polling) Long-polling Push

Nimbuzz 2min 39s

Nokia Messaging

5m to 30m

4

Always-on-line PDP context

Always-on-line application requires a permanent IP connection, thus gives rise

to the Always-on-line PDP context.

Source: HUAWEI Smart Lab

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.

GPRS Attach PDP Context Activation

Type/OS Power OnTriggered by application

Power OnTriggered by application

iPhone 3.0 Y Y

iPhone 4.0 Y Y

Nexus One(Android)

Y Y

HTC HD2(WM) Y Y

5

Source: HUAWEI Smart Lab

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.

PDP Deactivation by MS

Type/OS Application quit Screen Lock Power off

iPhone 3.0 Y Y

iPhone 4.0 Y Y Y

Nexus One(Android)

Y

HTC HD2(WM) Y

PDP Deactivation by Core Network

Type/OSDeactivation Accept

Deactivation Ignore

Re-Activate PDP After Deactivation

iPhone 3.0 Y

iPhone 4.0 Y

Nexus One(Android)

Y

HTC HD2(WM) Y

6

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.

RAN

Attacker

MS IP POOL

SGSN GGSN

Mobile Network

7

Smartphone Type

UE Software UE Sending SCRI or Not

Time for UE to Send SCRI After Data Transmission

Samsung360 NO NO

SonyEricsson X10 R2BA013 YES around 5 to 10s

Black berry Storm YES around 3 to 10s

Black berry Bold YES around 3s

iphone Pre-comercial iPhone

YES around 10s

iphone 3.1.2 YES around 10s

Nokia5800 NO NO

HTC g6 2.1 YES around 5s

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

8

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.

9

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.

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