Signaling Measurements on the Packet Domain

of 3G-UMTS Core Network

G. Stephanopoulos (National Technical University of Athens, Greece)

G. Tselikis (4Plus S.A. Athens, Greece)

R. Ratz (SIEMENS ICMN Munich, Germany)

N. Stephanopoulos (4Plus S.A. Athens, Greece)

N. Papadoukakis (4Plus S.A. Athens, Greece)

Key Targets

• Presentation and Analysis of Iu-PS Signaling protocol Stack

• Analysis of most vital 3G - GMM procedures and their functional and logical explanation based on signaling interactions, between Mobile Stations and Core Network, for the integration of Mobility Management mechanisms on mobile network basis

• Simulators Usage necessity for the conformance and performance analysis of basic switching nodes

• Testing topology and testing definitions

• Real Traffic scenarios and completion times on full signaling exchange basis

• Experimental results and analysis

• The mobility support “penalty”

Real PS Network

Simulated Network

Non Access Stratum Layer (NAS)Functional models for the:• Mobility Management (MM) • Call Control (CC) (CS connections)

• Session Management (SM) (GPRS services)

• Radio Resource Management (RRM) (CS and GPRS services) MM FUNCTIONSUsed to: Establish, Maintain, Release connections between MS and CN (over which User information is exchanged)MM ENTITIESSupport the mobility of user terminal:• informing the network of its present location• providing user identity confidentiality CC FUNCTIONS Used to: Establish, Maintain, Release CS connections. SM FUNCTIONS Used to: Establish, Modify, Release Packet Data Protocols (PDP) contexts towards the PS domain.

Non Access Stratum Layer (NAS)• NAS messages exchanged between the CN and the User Equipment (UE) are transported transparently by the RNC in the payload of RANAP messages. • NAS signaling messages are consisted of a certain number of protocol specific Information Elements (IEs), defining and conveying all procedural necessary information, for the functional accomplishment of UE-CN negotiation

• The service that Access Stratum provides to the Non-Access Stratum (NAS) for data transfer between UE and CN is referred to as Radio Access Bearer (RAB) • RANAP layer handles all RAB related procedures and conveys NAS messages transparently between the CN and UE without interpreting them

Radio Access Network Application Part Layer (RANAP)

• SCCP connection oriented services are used for the transfer of the upper layer signaling messages between the CN and the RNC (SCCP connection is established each time the UE needs to communicate with the CN and no SCCP connection exists between them)• Upper layer signaling messages are transferred transparently through the established SCCP connection.• SCCP uses the routing services of the MTP3b and the SAAL transport mechanisms that enable the reliable transfer of the signaling messages with protection from loss, missinsertion, corruption and disordering.

Signaling Connection Control Part (SCCP)Message Transfer Part (MTP-3b)Signaling ATM Adaptation Layer (SAAL)

The Attach Procedure• GMM procedure that is always initiated by the UE • used either to perform a normal GPRS attach for GPRS services only or to perform a combined GPRS attach for GPRS and non-GPRS services, provided that the CN operates in the proper mode.

The Routing Area Procedure• GMM procedure that is always initiated by the UE and it is usedeither to periodically notify the availability of the UE to the CN or whenever a routing area border is crossed.

The Detach Procedure• GMM procedure that may be triggered by either the UE or the CN• It is invoked by the UE, when it is switched off or the USIM card is removed or its service capabilities are disabled. • It is invoked by the CN, when either the asked services are no longer allowed or a re-attach is required.

Testing Topology

Real Traffic Scenarios - ExperimentsThe experiments simulate the most common subscriber’s behavior that is, switch on the UE, attach to the CN, remain within the same Routing Area (RA) for nearly 10 hours and then detach. According to statistical reports and RAU periodic timer values defined by operators each subscriber performs approximately 2.2 RAU requests per hour.Therefore, the most common user behavior is modeled as execution of the Attach procedure, then perform (22) RAU procedures, either Periodic RAU or intra-RAU when the UE moves from one radio cell to another within the same RA and conclude with the Detach procedure.

In hour level, the total number of signalling requests transmitted by each subscriber is 0.1 Attach_Req + 2.2 RAU_Req + 0.1 Detach_Req = 2.4 Reqs/hour.

The BHCA (Busy Hour Call Attempt) term refers to the transmitted signaling requests per hour and it is the product of the number of users (Nu) multiplied by the 2.4 Reqs/hour. All users follow the same traffic model that is

(0.1)Attach – (2.2)RAU – (0.1)Detach per hour. The duration of each scenario was more than 1 hour, that is 70 mins.

Scenario BHCA Requests/Sec Nu (Number of Users)

1 200,000 55 80,0002 400,000 111 170,0003 600,000 166 250,0004 800,000 222 340,0005 1,000,000 277 420,0006 1,200,000 333 500,000

Table 1: Scenario Parameters

0

200000

400000

600000

800000

1000000

1200000

0 200000 400000 600000 800000 1000000 1200000

user BHCA

RA

U /

h

0

100000

200000

300000

400000

500000

600000

700000

MS

eq

uiv

alen

ts

RAU / h User equivalent

0

200000

400000

600000

800000

1000000

1200000

0 10 20 30 40 50 60 70

time (min)

BH

CA

(req

s/se

c)

scenario 1

scenario 2

scenario 3

scenario 4

scenario 5

scenario 6

BHCA on Scenario Basis

150

170

190

210

230

250

270

0 10 20 30 40 50 60 70

time (min)

Att

ach

mea

n t

ime

(m

sec)

scenario 1

scenario 2

scenario 3

scenario 4

scenario 5

scenario 6

Attach Mean Time on Scenario Basis

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

time (min)

Det

ach

mea

n t

ime

(mse

c)

scenario 1

scenario 2

scenario 3

scenario 4

scenario 5

scenario 6

Detach Mean Time on Scenario Basis

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

time (min)

RA

U m

ean

tim

e (

mse

c) scenario 1

scenario 2

scenario 3

scenario 4

scenario 5

scenario 6

RAU Mean Time on Scenario Basis

1 23 4 5 6 7

8

0

50

100

150

200

250

GM

M p

roc

mea

n t

ime

(mse

c)

time (min)

DETACH mean-time

RAU mean-time

Attach mean-time

GMM proc completion time factors

66%

22%

12%

Attach completion time

RAU completion time

Detach completion time

GMM proc Mean Time

GMM proc Completion Times

Scenario BHCA Mean Processor Usage1 200,000 8.4 (%)2 400,000 10.6 (%)3 600,000 13.3 (%)4 800,000 16.3 (%)5 1,000,000 19.1 (%)6 1,200,000 22 (%)

Table 2. SGSN Processor Utilization

Conclusions

• Attach procedure is the most consuming procedure (due to the absense of the authentication procedure within the RAU)

• Signaling traffic that does not bring any profit to the service provider, consumes significant network and processing resources

• HLR – SGSN dialogs are heavy consuming procedures.