Chapter 3 - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/6109/11/11_chapter 3.pdf · Call-related functions are to establish a voice call to a ported ... The Number Range Holder

Chapter 3 Universal SMS Routing

Ph.D Thesis of Asoke K Talukder 59

Chapter 3

Universal SMS Routing 3.1 Introduction

In the previous chapter we have presented a ubiquitous routing algorithm by help of proposed

USRS-technology for SMS-data where the MSISDN number is not portable. However, in this

chapter we extend the idea of providing SMS-data ubiquitously, irrespective of service provider

in case of number portability. It is a practical problem because the regulatory bodies of different

countries have started promoting number portability, as it will help the end users (as explained in

detail in this section).

For many individuals or self-employed professionals mobile phone is their identity and

also the business storefront. Figure 3.1 shows a picture from Johannesburg, South Africa [Africa]

where people publish their phone numbers as storefront. In many parts of India, auto-rickshaw

drivers publish mobile phone numbers so that they can be contacted like a radio taxi. Vegetable

vendors, plumbers, carpenters, electricians, tour operators, insurance agents, doctors, and many

such people use mobile phone as their business identity. With the convergence of IT (Information

Technology) and CT (Communications technology) phone numbers are likely to become the

identity of a business.

Subscribers are reluctant to change the existing network service provider and go to a

competitive service provider, because doing so would require them to surrender their existing

connection. This in turn means that they have to change their long held phone number. Changing

phone number means loosing touch with all customers. Therefore, it is desirable that a subscriber

should be able to change the network service provider but keep the old phone number. The

technology of number portability helps solving this complex challenge.

In telecom networks traditionally numbers are divided into two categories, viz.,

geographic numbers and non-geographic numbers. Geographic numbers are allocated in blocks

(10,000) by the regulatory authorities to network operators and specific to geographical location.

Looking at the geographic number it is possible to guess where the telephone is located. For

example +91 80 25227752 is a BSNL (Bharat Sanchar Nigam Limited) number in Bangalore city

within India, serviced by Indiranagar telephone exchange. In case of geographic numbers, the

association between the dialled number and the subscriber’s telephone connection is fixed. Till



the time the subscriber subscribe to the service of the network, the telephone number belongs to

the subscriber.

A non-geographic number on the other hand does not have any fixed association with any

telephone exchange. Non-geographic numbers are associated with a country (examples are 1-800-

1234567 in the US or 1-600-123456 in India). Non-geographic numbers are virtual numbers.

When someone dials a non-geographic number, the call is connected to the subscriber's telephone

connection by resolving the routing details at the time of call. The virtual to physical mapping is

achieved by a process called Global Title Translation (GTT) through lookup in a database called

SMS/800 (Service Management System/800) [SMS800A, SMS800B].

Figure 3.1: Telecommunications storefront on the outskirts of Johannesburg [Africa]

In advanced economies, regulators decided that a local geographic numbers should be

portable. This is known as Local Number Portability (LNP) [LNP2004]. In LNP, following types

of portability are allowed:

• Service provider portability – this allows a subscriber to select a new service provider

while keeping their existing telephone number.

• Service portability – this allows subscribers to change the type of service they have

while keeping their telephone number. For example, if the subscriber changes from

POTS (Plain Old Telephone Service) to ISDN (Integrated Service Digital Network)

he or she has to obtain a new telephone number, because the switching equipment



used to provide the ISDN service supports a different block of numbers. With LNP

the subscriber does not have to give up the telephone number when changing the type

of service. If the numbering scheme is same for fixed and mobile, a subscriber can

change from fixed to mobile and assign the same number to the mobile phone.

• Location portability – this will allow a subscriber to move from city to city or even

state to state while maintaining the same telephone number.

In recent years, to encourage competition, many countries have passed laws to ensure that

PLMN centric mobile numbers are portable across network service providers. This is called

wireless local number portability (WLNP) in the US. In the domain of GSM/GPRS, and ETSI,

this facility is called Mobile Number Portability (MNP). In MNP, the philosophy is that the

telephone number is the identity (property) of the consumer. Therefore, telephone subscriber is

allowed to keep the telephone number and move from one network operator to another within a

geographic area. Research suggests that MNP has direct impact on the economy [NPUK1997]

[NPUS].

Through number portability acts, (for example in US [NPACTUS], or in Europe through

NPACTEU]) many countries in the world directed the network operators to develop system so

that consumers can port their numbers as they change network service providers. Other countries

in North America, South America, European Union, Asia, Australia have already gone for

Number portability. Rest of the world will soon follow suite [INTUG].

At a high level, the porting process begins when a subscriber desires to change service

provider. Steps followed to port a number are as following:

1. The subscriber visits the New Service Provider (NSP) to sign up for service.

2. During this sign up process, the NSP’s representative will ask the subscriber if they

want a new number or if they want to keep their existing phone number.

3. In case the subscriber decides to keep the existing number, the NSP will start the

process of MNP.

4. Databases and registers within OSP (Old Service Provider) and NSP will be updated.

The number portability database will be updated.

5. Subscriber will be disconnected from OSP.

6. Billing responsibilities shift from OSP to the NSP.

7. Subscriber will be activated in NSP.

8. The NSP will become the home network. The old home network will become the

OSP



In different literature, OSP is also referred as Donor Network, or Relinquishing Network,

or Number Range Holder Network (NRHN). The NSP, where the number has been ported is also

called Home Public Land Mobile Network (HPLMN) or Recipient Network or Subscription

Network. Figure 3.2 (a) depicts the porting process for the first time where the subscriber ported

the number from network “A” to network “B”. In Figure 3.2 (b), the porting is from second

operator to the third operators. Time taken to do the porting of the MNP (or WLNP) varies from

country to country. MNP takes 2.5 hours in the US to a maximum of 28 days in the UK.

Figure 3.2: Networks in the MNP scenario

In the absence of MNP, customers have to give up their mobile number and must adopt a

new number when they switch operators. As a result, customers face switching costs associated

with informing people about changing their number, printing new business cards, changing all

everything that carries the old phone numbers, missing valuable calls from people that do not

have the new number, etc. In the absence of MNP, consumers usually distinguish between

different mobile networks through the number prefix. However, with MNP this is not possible; as

a result, if calling prices differ between different networks, consumers may be unaware of exact

charges for placing calls to mobile networks. As a result, while fostering competition for mobile

customers, MNP may also induce operators to increase termination charges for calls to mobile

networks. Buehler et al [Buehler2003] examined MNP based on call-forwarding, termination fee

regulation, and alternative means of carrier identification charges. Some other works have been

A Donor/Relinquishing

Network (OSP)

B Recipient Network

(NSP)

(a) First Porting from A to B

A Donor Network

B Relinquishing

Network (OSP)

C Recipient

Network (NSP)

(b) Subsequent or 2nd Porting



done on MNP related to routing and signalling cost in wired, wireless, and converged network.

Lin [Lin2003] analyzed mobile number portability routing mechanisms and their implementation

costs using Signalling Relay Function (SRF)-based solution and the Intelligent Network (IN)-

based solution. Lin et al [Lin1999] presented a cache approach to speed up address transfer,

which can effectively reduce the network overhead incurred by AIN query for number portability.

Kim et al [Kim1998] proposed the integrated number portability protocols for wire and wireless

network using Intelligent Network. For this, they integrated the LNP DB of wire network and

HLR/VLR of wireless network. Chao et al [Chao2003] proposed an algorithm called IPv6-GSM

where a subscriber using ported GSM phone can communicate with VoIP terminals efficiently.

Dalgic et al [Dalgic1999] demonstrated how personal information can be coupled with an IP

telephony service to provide user-customized call handling by the network.

Along with research community, ETSI and GSM standards committees came up with few

recommendations and specifications on MNP. GSM specifications as defined by GSM 03.66

[GSM-03.66] define the routing procedures of voice calls and SMS point-to-point for portable

numbers. As SMS-data is outside of GSM scope, this specification does not include any

procedure to route SMS-data. Also, to stop revenue leakage, during the porting process, the OSP

disconnects all services. This includes access to OSP’s SC through the SMS-IWMSC. Therefore,

following porting, all SMS-data services that the subscriber was using in the OSP will cease to

operate. To the best of our knowledge there is no literature or standard that addressed the

ubiquitous routing of SMS-data to old services following porting of the number.

In this chapter we present our contribution through the novel technology of auto

portability of SMS-data services. This technology will allow routing of SMS-data to the old

application via the old SC without going through the SMS-IWMSC. We call this technology as

Universal SMS Routing Service (USRS) through USRS-tunnelling [AKTSP2005],

[AKTNP2005]. It presents the experimental and simulation results for SMS-data portability over

MNP in this chapter. The results show that USRS-tunnelling algorithm is scalable and

comparable with USRS in performance.

3.2 Porting of Call Related Functions

In the context of MNP it is necessary to make a distinction between call-related functions and non

call-related functions. Call-related functions are to establish a voice call to a ported terminal and

are managed through ISUP (ISDN User Part) messages. In this section we present technologies

for voice call routing to a ported number. Following are some of the procedures suggested by

ETSI [ETSI-101-118] for routing of voice call related functions in MNP.



1. Onward Routing: With the Onward Routing principle, the call to a potentially

ported MSISDN is routed to the Number Range Holder network. Number range

holder network is the network that was issued a range of numbers for the first time by

the regulatory authority – for example, a mobile number 9844723451 is a number

from a number range of 9844000000 to 9844999999 issued to Spice network in

Karnataka. The Number Range Holder network has access to the NPDB (Number

Portability Database) to retrieve the routing information, corresponding to the called

MSISDN. If the MSISDN is ported, an IAM (Initial Address Message) will be sent to

the home PLMN. If the MSISDN is not ported, the call will be treated internally

within the network.

2. Call Dropback: With the Call Dropback mechanism, the call to a potentially ported

MSISDN is first routed to the Number Range Holder network, without performing a

NPDB query. If the MSISDN is ported out from the Number Range Holder network,

a REL (Release) message (release cause #23), or FAC (Facility) message, with

special indication that the MSISDN has been ported, will be sent back to the

preceding network. Rerouting information is enclosed in this release message

(retrieved after NPDB query). Based on the retrieved re-routing information, the

previous network will route the call to the HPLMN. If the HPLMN is the same as the

Transit network, the call is treated internally within the Transit network.

3. Query on Release: With the Query on Release mechanism, the call to a potentially

ported MSISDN is first routed to the Number Range Holder network, without

performing a database query. If the MSISDN is ported out from the Number Range

Holder network, a REL message with release cause #14 will be sent back to the

previous network. On receipt of this special release, the previous network will

perform a database query into NPDB. Based on the retrieved routing information, the

call will be routed to the HPLMN. If the HPLMN is the same as the transit network,

the call is treated internally within the transit network.

4. All Call Query: In this scenario, the Transit network has access to the NPDB to

retrieve the routing information, corresponding to the potentially ported MSISDN. If

the MSISDN is ported, the call will be routed to the HPLMN. If the MSISDN is not

ported, the call will be routed towards the Number Range Holder network



3.3 Porting of SMS Point-to-Point

In GSM, non call-related features are these function that do not use the ISUP messages.

Supplementary services, SMS (Short Message Service), voicemail or MMS (Multimedia Service)

falls in non call-related category. Degree of complexity varies for call-related and non-call related

functions. Portability issues for SMS need to be handled for SMS Point-to-Point and SMS-data.

In this section we present procedures recommended by ETSI [GSM-03.66] to handle SMS point-

to-point routing for number portability.

During the porting process, though the MSISDN number will be carried by the subscriber

to the new network, the SIM card will change. The new service provider will issue a new SIM

card and a new IMSI (International Mobile Subscriber Identification) to the ported subscriber. As

the home network changes, the home SC will also change. The new SC will already be

configured in the new SIM as supplied by the new service provider.

3.3.1 Routing of SMS Point-to-Point

SMS is a non-call related signalling function using MAP (Mobile Application Part) messages.

Therefore, SMS routing [GSM-03.66] needs to be handled differently compared to call related

functions. SMS routing for ported numbers will be handled based on the status of the porting.

These could be:

1. Party A not-ported – Party B not-ported

2. Party A ported – Party B not-ported

3. Party A not-ported – Party B ported

4. Party A ported – Party B ported

For case 1, it is the standard classical procedure before the porting as defined by GSM 03.40

[GSM-03.40] standard. This has been described in Section 1.3. However, when a network

implements the number portability, many of the network elements in the core network will be

changed. Some new network elements will be added. Therefore, the classical routing mechanism

will also undergo changes. Following sections describe some of these procedures as

recommended in GSM 03.66 [GSM-03.66].

3.3.2 Routing of SMS – Direct Routing Using MNP-SRF

In this section we explain the delivery of SMS point-to-point from a ported/non-ported number to

a non-ported number through direct routing as recommended in MNP standard 03.66. In this

architecture it is assumed that the subscription network has installed MNP-SRF (Signalling Relay



Function for support of MNP) that can be used as higher level relay. Figure 3.3 shows the MNP-

SRF operation for delivering an SMS message from Party-A to Party-B where Party-A could be

either a ported number or a non-ported number. Party-B is a non-ported number.

Figure 3.3: SRF operation for delivering an SMS message from a ported/non-

ported number to a non-ported number

1. The SCA forwards the SM to the SMS-GMSCA via a proprietary interface. The procedure

for this will be {Forward_SM {MSISDN}} (transaction 1).

2. The SMS-GMSCA generates a routing enquiry for SM delivery. The MAP message

SRI_for_SM (Send Routing Information for Short Message) message generated by SMS-

GMSCA is routed to the network’s MNP-SRF with Translation Type value set to 0 The

CdPA (Called Party Address) for this part of the procedure will be the address of the

target element, which is the MSISDN. The CgPA (Calling Party Address) for this part of

the procedure will be the SMS-GMSCA address. The procedure for this will be

{Forward_SM (MSISDN address) with CdPA = MSISDN, TT = 0 and CgPA =

SMS-GMSCA address} (transaction 2).

3. When MNP-SRFB receives the message, it terminates the TCAP (Transaction

Capabilities Application Part) dialogue and an MNP-SRF operation is triggered. The

MNP-SRF functionality analyses the MSISDN in the TCAP portion of the message and

identifies the MSISDN as being non-ported using information which may be retrieved

from an NP database. The MNP-SRF function then initiates a new dialogue and routes

SCA SMS-GMSCA

MNP-SRFB

HLRB

VMSCB MSB

Subscription Network Serving Network

1

2 5

3 4

7 6

Forward_SM (MSISDN)

Forward_SM (MSISDN) CdPA = MSISDN, TT = 0

CgPA = SMS-GMSCA address

Forward_SM (MSISDN) CdPA = HLRB address

CgPA = MNP-SRFB address

SRI_for_SM ack (VMSCB address) CdPA = MNP-SRFB address CgPA = HLRB address

SRI_for_SM ack (VMSCB address) CdPA = SMS-GMSCA address CgPA = MNP-SRFB address

Forward_SM (VMSCB)



the message to HLRB. The procedure for this dialogue will be {Forward_SM {MSISDN}

with CdPA = HLRB address and CgPA = MNP-SRFB address} (transaction 3).

4. HLRB responds to the routing enquiry by sending back a SRI_for_SM ACK with the

address of the VMSC. The procedure for this dialogue will be {SRI_for_SM ACK

(VMSCB address) with CdPA = MNP-SRFB address and CgPA = HLRB

address} (transaction 4).

5. MNP-SRFB responds to the routing enquiry by sending back a SRI_for_SM ACK with

the address of the VMSC to the SMS-GMSCA. The procedure for this dialogue is

{SRI_for_SM ACK (VMSCB address) with CdPA = SMS-GMSCA address and

CgPA = MNP-SRFB address} (transaction 5).

6. The SMS-GMSC can now deliver the message to the VMSCB using a Forward_SM

message. The procedure for this will be {Forward_SM (VMSCB)} (transaction 6).

7. VMSCB further delivers the message to MSB (transaction 7).

Figure 3.4: SRF operation for delivering an SMS message to a ported number,

where Network-A does not support direct-routing

SCA SMS-GMSCA

MNP-SRFB

HLRB

VMSCB MSB

Interrogating Network

Serving Network

1 7 6 Forward_SM

(MSISDN)

SRI_for_SM (MSISDN) CdPA = MSISDN, TT=0 CgPA = SMS-GMSCA address

Forward_SM (VMSCB)

MNP-SRFB

2

3

4

5

Number Range Holder Network

Subscription Network

SRI_for_SM (MSISDN) CdPA = HLRB address CgPA = SMS-GMSCA address

SRI_for_SM (MSISDN) CdPA = RN (+MSISDN)

CgPA = SMS-GMSCA

SRI_for_SM ACK (VMSCB address) CdPA = SMS-GMSCA address

CgPA = HLRB address



3.3.3 Routing of SMS – Indirect Routing


a ported/non-ported number through indirect routing as recommended in MNP standard 03.66

[GSM-03.66]. Figure 3.4 shows the MNP-SRF operation for delivering an SMS message to a

ported number where the interrogating network does not support direct routing.

1. The SCA forwards a SM to the SMS-GMSCA via a proprietary interface using the

procedure {Forward_SM (MSISDN)} (transaction 1).

2. The SMS-GMSCA generates a routing enquiry for SM delivery. As the interrogating

network does not support direct routing, the MAP message SRI_for_SM is routed to the

number range holder network’s MNP-SRF using the dialogue {SRI_for_SM (MSISDN)

with CdPA = MSISDN, TT=0 and CgPA = SMS-GMSCA address} (transaction 2).

3. When MNP-SRFB’ (Mobile Network Portability – Signalling Relay Function – Party B

network) receives the message, MNP-SRF operation is triggered. The MNP-SRF

functionality analyses the MSISDN in the CdPA (Called Party Address) and identifies the

MSISDN as being ported using information which may be retrieved from an NP

database. As the message is non-call related, the MNP-SRF function then populates the

CdPA with either a routing number or a concatenation of a routing number and MSISDN.

After modifying the CdPA, the message is routed to MNP-SRFB in the subscription

network. The procedure for this will be {SRI_for_SM (MSISDN) with CdPA = RN

(+MSISDN), TT=0 and CgPA = SMS-GMSCA address} (transaction 3).

4. When MNP-SRFB receives the message, MNP-SRF operation is triggered. The MNP-

SRF functionality analyses the MSISDN in the CdPA and identifies the MSISDN as

being ported into the network using information which may be retrieved from an NP

database. The MNP-SRF function then populates the CdPA with an HLRB address. After

modifying the CdPA, the message is routed to HLRB. The procedure for this dialogue

will be {SRI_for_SM (MSISDN) with CdPA = HLRB address and CgPA = SMS-

GMSCA address} (transaction 4).


address of the VMSC. Procedure for this dialogue will be {SRI_for_SM ACK (VMSCB

address) with CdPA = SMS-GMSCA address and CgPA = HLRB address}

(transaction 5).


message using dialogue {Forward_SM (VMSCB)} (transaction 6).




3.3.4 Routing of SMS – Direct Routing


a ported/non-ported number through direct routing as recommended in MNP standard 03.66

[GSM-03.66]. Figure 3.5 shows the MNP-SRF operation for such delivery where the

interrogating network supports direct routing. The message flows for this scenario are based on

the use of an SCCP-relay function in the MNP-SRFs. Like in the previous cases, the SMS will be

delivered from the MSA to the SCA without and problem.

Figure 3.5: SRF operation for delivering an SMS message to a ported number,

where Network-A supports direct-routing

1. The SCA forwards the SM to the SMS-GMSCA via a proprietary interface using dialogue

{Forward_SM (MSISDN)} (transaction 1).

2. The SMS-GMSCA generates a routing enquiry for SM delivery. The MAP SRI_for_SM

message is routed to the network’s MNP-SRF using dialogue {SRI_for_SM (MSISDN)

with CdPA = RN (+MSISDN), TT=0 and CgPA = SMS-GMSCA address}

(transaction 2).

3. When MNP-SRFA receives the message, MNP-SRF operation is triggered. The MNP-


SCA SMS-GMSCA

MNP-SRFB

HLRB

VMSCB MSB

Interrogating Network Serving Network

1 7 6 Forward_SM

(MSISDN)

SRI_for_SM (MSISDN) CdPA = MSISDN, TT=0

CgPA = SMS-GMSACA address

Forward_SM (VMSCB)

MNP-SRFB 3

4


SRI_for_SM (MSISDN) CdPA = HLRB address CgPA = SMS-GMSCA address

2

5


CgPA = HLRB address

SRI_for_SM (MSISDN address) CdPA = RN (+MSISDN), TT = 0 CgPA = SMS-GMSCA address



being ported using information which may be retrieved from an NP database. As the

message is non-call related, the MNP-SRF function then populates the CdPA with either

a routing number or a concatenation of a routing number and MSISDN. After modifying

the CdPA, the message is routed to MNP-SRFB in the subscription network. The

procedure for this dialogue will be {SRI_for_SM (MSISDN address) with CdPA =

RN (+MSISDN), TT = 0 and CgPA = SMS-GMSCA address} (transaction 3).

4. When MNP-SRFB receives the message, MNP-SRF operation is triggered. The MNP-


being ported into the network using information which may be retrieved from an NP

database. The MNP-SRF function then populates the CdPA with an HLRB address. After

modifying the CdPA, the message is routed to HLRB. The dialogue for this part of the

transaction will be {SRI_for_SM (MSISDN) with CdPA = HLRB address and CgPA

= SMS-GMSCA address} (transaction 4).


address of the VMSC. This dialogue will be {SRI_for_SM ACK (VMSCB address)

with CdPA = SMS-GMSCA address and CgPA = HLRB address} (transaction 5).


message using dialogue {Forward_SM (VMSCB)} (transaction 6).


3.4 Porting of SMS-data

In Section 2.4 we have described that in GSM – for call-related functions MSRN is used to locate

the receiving roaming MS; whereas, for SMS, VMSC address is used to locate the receiving

roaming MS. In Section 2.4 we presented how we mask the VMSC address to route SMS-data to

an application.

In Section 3.3.2 through 3.3.4, we have seen that in case of number portability, the main

challenge for routing of SMS point-to-point message is to determine the VMSC address of the

Party-B’s current visiting network. Depending upon various conditions and network

configurations, the correct procedure is adopted by the interrogating or subscription network.

Here in this section we will examine how is it possible to mask the VMSC address to route SMS-

data to an application in a number portability scenario. We can redraw the architecture diagram of

Ubiquitous SMS routing depicted in Figure 2.1 in Chapter 2 as Universal SMS routing in Figure

3.6 in line with number portability.



We have mentioned that the NSP will provide the subscriber a new SIM card. Along with

the new SIM card the subscriber will be assigned with a new IMSI number. To stop revenue

leakage, the OSP enforces a mechanism, which stops access to the SC within the OSP network

through SMS-IWMSC. Therefore, as the home SC changes, SMS-data services in the OSP will

no longer be available to the ported number in the NSP.

Figure 3.6: SMS-data routing in a number portability environment

The new SIM card provided by the NSP will have the new home SC address, which will

allow SMS routing for SM MO through the new home SC (SC of the NSP). In the context of

MNP and Universal SMS routing we defined following networks:

1. Donor Network: This is the network where the subscriber originally signed up for

mobile service. This was the subscription network before porting of the mobile

number (MSISDN) to a new network.

2. Recipient Network: This is the new subscription network for the subscriber. This is

the new Home network after porting of the MSISDN.

3. Service Network: This is the network which is servicing the data service. The

application is connected to the SMSC of this network through an SME. This is

similar to Data Network as described in Section 2.4. However, the data network is

private to a PLMN and accessible only through an SME.

SCA SMS-GMSCA

HLRB

VMSCB (USRS)

Subscription Network Host Network

1 4 Forward_SM

(MSISDN) Forward_SM (VMSCB)

Foster Network

2

SRI_for_SM (MSISDN address) CdPA = SMS-GMSCA address CgPA = HLRB address

3 SRI_for_SM ACK (VMSCB address)

CdPA = SMS-GMSCA address CgPA = HLRB address

Content URI



4. Foster Network: As described in Section 2.4.

5. Host Network: As described in Section 2.4.

6. Serving Network: As described in Section 2.4.

3.5 Universal SMS Routing Service for SMS-data

The origin server for the SMS-data service can be either within the operator network or outside of

the network operator. In Section 1.6.2, we have described three different deployment types of

contents. These are OCC (Operator Centric Content), CCC (Consumer Centric Content), and

GCC (Geography Centric Content). CCC will generally be outside of the operator’s network. It is

also likely that these contents will be on the Internet accessible through http. Therefore, CCC

contents can accessed and made ubiquitous through USRS procedures as described in Chapter 2.

OCC are primarily infotainment contents proprietary to a PLMN. GCC on the other hand may be

exclusive to operators and unlikely to be available over http. These contents are available over

CG-SME interface only as depicted in Figure 1.5. However, these contents are of general interest

and need to be available over number portability. Examples will be location aware applications,

workplace IM. Using universal SMS routing we ensure that these contents will be available even

after porting of the MSISDN. In this case, the SMS-data will be tunnelled to the origin server

through the old service provider’s SC. In following sections we discuss this procedure.

3.5.1 SMS-data Routing in MNP

In section 3.4 we mentioned how the Ubiquitous SMS routing technology as presented in Chapter

2 and depicted in Figure 2.1 transforms into Figure 3.6. Also, it is evident that the technology

presented in Figure 3.6 is a different representation of SMS routing in Figures 3.3, Figure 3.4, and

Figure 3.5 and specified in GSM 03.66. Using masked numbers routing for SDSI, we have

already been able to resolve the VMSCB address. Universal SMS routing technology performs

like the direct routing as discussed in 3.3.4. This is also evident from this discussion that USRS is

NP neutral. To put USRS in use, we do not need to make any changes in the origin server. Also,

we do not need and change in the interfaces to these applications or services.

Using USRS technology, the SMS-data is routed from the MSA to the USRS (VMSCB).

As USRS technology is NP neutral, all services that use USRS technology for SMS routing are

auto-ported in number portability scenario. In Section 2.5 we have presented the USRS

architecture including functions for service (application) interface. This is achieved through

Kannel SMS gateway. We have also discussed in Section 2.3 how to configure Kannel to access

an application over http. The same interface of HTTP proxy will allow an SMS-data service over



http to work transparently in number portability scenario. Therefore, using USRS technology all

services over http are automatically ported to the new service provider.

The SMS-data portability procedures as depicted in Figure 2.6 for CCC contents will

work in the following fashion:

1. The SCA forwards the SM to the SMS-GMSCA via a proprietary interface using dialogue

{Forward_SM (MSISDN)}.

2. The SMS-GMSCA generates a routing enquiry for SM delivery. The SM needs to be

delivered to the virtual number from a number range in the Foster network. The MAP

SRI_for_SM message is routed to the Foster network’s HLR using dialogue

{SRI_for_SM (MSISDN) with CdPA = MSISDN address and CgPA = SMS-GMSCA

address}.

3. The HLRB already has been updated by the location update transaction by the USRS that

the VMSC address for this MSISDN is visiting in Host network. Therefore, as a response

to the routing enquiry, the HLRB sends back a SRI_for_SM ACK with the address of the

VMSCB, which happens to be the USRS server. This dialogue will be {SRI_for_SM

ACK (VMSCB address) with CdPA = SMS-GMSCA address and CgPA = HLRB

address}.


message using dialogue {Forward_SM (VMSCB)}. In reality VMSCB is the USRS server.

Therefore, the SMS arrives at the USRS.

5. USRS further delivers the message to the service URI. This part will be different for

different types of URI. This is described in the following sections.

3.6 Proposed SMS-data Tunnelling in MNP

We mentioned that OCC and GCC type contents are private to PLMNs and are not available

through any public network. Therefore universal SMS routing procedure will not be able to

access these contents. In this section we will discuss how to access PLMN proprietary data

services from the origin server through Tunnelling. Tunnelling architecture in an MNP scenario is

depicted in Figure 3.7. This type of architecture is appropriate for applications which are

connected through SME only. An example of such porting scenario is described in section 3.8. In

this scheme the SMS-data is routed to the SC without accessing the SMS-IWMSC. The

subscriber was accessing the content trough the OSP SC using the SMS-IWMSC of the OSP.

However, after porting the SMS-data is tunnelled to the OSP SC through USRS.



Figure 3.7: SMS-data routing for GT based URI

3.6.1 Proposed Steps of Tunnelling Algorithm for SMS-data

Service

In this section we explain how SMS-data tunnelling works. We explain this for a PLMN centric

content like IM (Instant Messaging) that is available through SME. IM has long been a popular

application in Internet [Lawton2003]. IM has become a way of communication in business,

corporate world, community informatics, and military [Cherry2002]. It is estimated that IM will

be used more than email by end of 2006 [Lawton2003]. Most of the IM applications are available

Serving Network

Foster Network

HLR

Host Network

MAP Location Update with VMSC as

USRS

Service Network

SC SME

IM Application Server

Recipient Network

SC

Serving Network

Routing Information SMS Forward

SMS Forward

SMS Forward

SMPP

USRDB

Subscriber from Service Network using IM through Short Code (before porting)

Subscriber from a Recipient Network using IM through Global Title (after porting)

SMS Response

(Donor Network)

1

2

3

4

5 6

7

8

9 10

Route for Operator Centric IM (6946) Request – 9, 4, 5 Response – 6, 7, 10

Route for Operator Independent IM (919886946462) Request – 1, 2, 3, 4, 5 (using Donor SMSC) Request – 1, 2, 11, 12 (without using Donor SMSC) Response – 6, 7, 8

SME

USRS

11

12



over Internet and SMS. The accessibility of these IM over Internet is universal. However, for

SMS these IM services are operator centric.

Figure 3.8: SMS-data Tunnelling

Let us assume that the IM service is available only through the old service provider’s

network. This IM service is currently accessed through an SDSI 6949 (MYIM). For this service

to be NP neutral, another global service number +919886946462 (+91988MYIMINC) is

identified as its global SDSI. Once ported, the subscriber will access the IM service with

+919886946462 instead of 6946. The sequence of service access will be as following:

1. A record is created in the HLR database of the foster network with this virtual MSISDN

(+919886946462), IMSI and other necessary details.

2. Mobile User (let us assume a subscriber from Bangalore with number +919845062550

ported from donor network “A” to recipient network “B” roaming in a serving network in

Germany) sends a message to the IM application at (+919886946462). Before porting,

the SC address of the subscription network was +919845087001 (Airtel in Bangalore).

Following porting the SC address of the subscription network is +919886005444 (Hutch

in Bangalore).

3. The serving network (in Germany), submits the SMS to the home SC of the sender (“B”)

through SMS-IWMSC.

Forward_SM (MSISDN )

SMS-GMSCA

HLRB

1 4

Forward_SM (MSISDNA)

Forward_SM (VMSC )

2 SRI_for_SM (MSISDN address) CdPA = SMS-GMSCA address CgPA = HLRB address

3


CgPA = HLRB address

IM/SMS-data

SMSC

SMSC MS

5

6

7

SME 0

Location Update


Serving Network

Host Network

Service Network

Foster Network

VMSCB (USRS)



4. The Home SC (+919886005444) will have to deliver the message to the IM application at

(+919886946462). The Home SC does a SendRoutingInfoForSM query, which comes to

foster network’s HLR.

5. The HLR entry in the foster network indicates that the IMSI with MSISDN number

(+919886946462) is currently roaming in a foreign network. The foster network HLR

sends the VMSC address (number of USRS Server in “Host Network”) and IMSI as a

response to home SMSC (“B”).

6. The Home SMSC sends the “ForwardShortMessage” message to the given VMSC

address. Because the VMSC points to USRS server, the SMS is delivered to the USRS

server in the host network. The VMSC address is +919837099975 in Escotel host

network.

7. The “ForwardShortMessage”, which came from the recipient network SMSC as a SM

MT (Short Message Mobile Terminated) message to the USRS, is converted into an SM

MO (Short Message Mobile Originated) by the USRS. This SM MO

“ForwardShortMessage” message is created with most of the fields copied from the SM

MT message. The SM MO message is submitted to the SC in the service network. While

submitting the SMS to the SMSC in the service network, the target address (B-Party

address) is changed from 919886946462 to the short number 6946 of the IM service.

8. The SMSC in the service network (which is also the donor network) forwards this SMS

to the SME.

9. The SME forwards the SMS sent by the ported subscriber to the IM service.

10. The response from IM application will be sent to the user using the SMSC in the service

network.

Though the IM service is connected to an origin server, which is internal to the old service

provider’s network and not accessible through an http URL, the SMS has been delivered to the

IM service connected to an SME. This routing is done independent of the home SMSC of the

ported MSISDN without using the TP-Reply-Path. With carrier grade SMS-data technology this

type of routing is not possible.

In the number portability scenario, though the OSP has disconnected the connection

between the subscriber and the SC, the IM service still uses the OSP SC for IM routing.

Commercial issues related to revenue for such routing will be handled by the IM service provider.



Figure 3.9: USRS topology for Global title as Service URI

3.7 Simulation Modelling of Universal SMS Routing

Figure 3.9 presents the network topology for services that are accessed through USRS-tunnelling.

In this case the destination origin server is connected only to an SME private to a PLMN.

Therefore, the SMS-data needs to be tunnelled to an SC of a foreign PLMN whose URI is the

Global Title of the SC.

For example, MSX was a subscriber of PLMN “A”, but ported the number to PLMN “X”.

This subscriber needs to access a service connected to the SCA through SCX. As a part of the

porting process, to stop revenue leakage, the connection between MSX and SCA is discontinued.

Therefore, for security reason the SMS cannot be submitted by any MSC through the SMS-

IWMSCA. In USRS-tunnelling, the subscriber MSX’s SMS request is submitted to the home SC

(SCX). This SMS is then tunnelled into the SC of the old service provider (SCA). Thus, the old

service provider’s SC (SCA) will be used for message switching to the origin server.

As discussed in this chapter, we have done further architectural changes to USRS to

support MNP (Section 2.5.1). In this model, an SM MO is delivered by the SCX to the USRS. The

USRS will not process the SMS; instead it will tunnel the SMS to a different SCA. The target SCA

will then forward the SMS to a SME connected to the content server. Like in the model of OTA-

GSMM, and USRS with HTTP URI (Section 2.6.3 and Section 2.6.4 respectively), the scope of

the simulation is only the part from SC to USRS to the target SC. Because MS to wireless tower

USRS

SCA

SMS Read

SCB

HLR

SME

FIFO Queue

SMS Write

Content over Internet/ Intranet

Scope of OMNeT++ Simulation



transmission and wireless tower to SC through MSC is independent of MNP, these portions of the

network have not been included within the simulation. The USRS for GT URI has only two

functions. These are “Read SMS” and “SMS Write”.

The USRS will read the SMS using the “Read SMS” module. It will change the header

information and send the SMS to a different SC. Like previous cases, we made following

assumptions for the traffic simulation.

1. Every SMS user request is 10 octets long

2. The response of this request is 70 octets long

3. The transmission speed for SMS is 64000 bits/second

4. An SMS header of 24 octets are added to both request and response messages.

5. The arrival rate of traffic was assumed to be Poisson distribution.

3.7.1 Results and Discussions of USRS-tunnelling Algorithm

The result of the simulation is presented in Figure 3.10. In this diagram X-axis is the arrival rate

of SMS-data per second; whereas, Y-axis is the average delay in seconds. The average delay is

about 0.51 seconds for a traffic rate of 80/second. When the traffic rate crosses 100, the queue

starts building up.

Figure 3.10: Plot of USRS-Tunnelling



Figure 3.11: Average delay versus average SMS traffic arrived at both the USRS architectures

Figure 3.12: Average delay versus average SMS traffic for OTA-GSMM and USRS systems



Figure 3.11 depicts the traffic delay for both USRS and USRS-tunnelling. In USRS, the

SMS-data is taken from the SC in the ported network to the service; whereas, in USRS-

tunnelling, the SMS-data is taken from the SC in the ported network but delivered to the SC in

the donor network; the donor SC in turn forwards the SMS-data to the service. We can see from

this simulation result that USRS-tunnelling is marginally better in performance compared to

USRS. This is understandable; because, the responsibility of the USRS-tunnelling ends with

tunnelling the SMS to the donor network SC. In this diagram X-axis is the arrival rate of SMS-

data per second; whereas, Y-axis is the average delay in seconds.

In Section 1.4.2, we presented the SMS modem technology (OTA-GSMM) that uses the

over the air SMS point-to-point technology to transfer SMS-data to an application. In Figure 3.12

we have compared the simulation results for OTA-GSMM and USRS-tunnelling. In this diagram

X-axis is the arrival rate of SMS-data per second; whereas, Y-axis is the average delay in

seconds. However, as the arrival rates are at different scales, logarithm scale is used to fit both

OTA-GSMM and USRS-tunnelling. This result is also summarized in Table 3.1.

3.8 Results from Real-World Implementation of USRS

Mobile Number Portability is not yet available in India. However, the technology presented here

was tested in India through ported numbers from London and Stockholm. SMS service enquiries

to USRS services were issued from London and Stockholm. It was found that for these ported

numbers were able to route the SMS-data to the USRS, which then tunnelled this SMS to an

operator centric service. It was able to route the request to a service not connected to the home

SC. The USRS system was also tested with these ported numbers while individuals with these

numbers and phones roaming in India. In Chapter 2 we have presented the results from

OMNeT++ simulation. In simulation we found that both HTTP and GT can take a load of about

100 messages/second. We have also discussed that our loop-back test confirms these simulation

results. These tests confirm that we can easily support a throughput of 252,000 BHSM. We know

that as SMS PP service is portable in NP environment, OTA-GSMM technology is portable.

However, as OTA-GSMM technology does not scale, in NP scenario, for carrier grade SMS-data

USRS is the solution.



Table 3.1: Summary of results

Serial

Number

Types of

Architecture

Data

rate

Average

number of

SMS-data

served per

minute

(Simulation)

Average delay

in seconds

(simulation)

Actual result in

real-world live

implementation

Remarks

1 Over-The-

Air GSM

Modem

315

bits/sec

8

messages/minute

(OMNeT++)

10.614 (arrival

rate = 0.12/secs)

7

messages/minute

(Using Nokia

Data suite 3.0

and Nokia 5110)

Ubiquitous,

not

Scalable

2 Carrier

Grade SME

(CG-SME)

64000

bits/sec

12000

messages/minute

(Fakesmsc [33])

No queue

observed at 200

messages/second

Constrained by

the SC

performance

(1200 to 9000

messages/minute)

Not

ubiquitous,

Scalable

3 USRS

Architecture

64000

bits/sec

4800

messages/minute

(OMNeT++)

2.930 (arrival

rate = 80/secs);

5.402 (arrival

rate = 100/secs)

6000

messages/minute

Ubiquitous,

Scalable

4 USRS-

Tunnelling

64000

bits/sec

6000

messages/minute

(OMNeT++)

1.527 (arrival

rate = 80/secs);

2.931 (arrival

rate = 100/secs)

6000

messages/minute

Ubiquitous,

Scalable

Table 3.1, presents results obtained through simulation and real-world implementation for each

architecture’s capacity to serve number of SMS-data and also the average delay built up by the

system. For completeness, this table also include some of the results presented in table 2.5.

As of date, the only technique possible to route an SMS to an application outside of the

home network is through OTA-GSMM. We have also seen that OTA-GSMM uses the slow over

the air radio interface. In USRS, we used the HLR masking to route the SMS to the origin server

over the SS#7 network directly. This gave us enormous performance gain on ubiquitous SMS



routing. Moreover, as USRS used SS#7 network over the wire, transmission has better reliability

as the message is not being transmitted over the wireless interface.

The results obtained through simulation and real-world realization suggest that we

could have about 8 messages/minute through OTA-GSMM. Also, through USRS-

tunnelling we could get busy hour short message of 360,000. This is the same range of

performance with respect to high performance carrier grade SCs (~ 100 messages per

seconds). This is a major achievement for USRS. Hence, from the comparison given in

Table 2, we observe that USRS architectures provide carrier-grade scalable topology with

ubiquitous routing.

3.9 Summary

In this chapter we looked at number portability in general and mobile number portability in

particular. In mobile number portability, the subscriber changes the network operator (PLMN) but

does not surrender the telephone number. In this case the originating or intermediate

(interrogating) telecommunications network may not know that the subscription network for this

mobile phone has changed. Therefore, to locate the MS, a different HLR needs to be interacted.

There are many technical and operational challenges associated with number portability.

We looked at issues related to number portability for voice calls and SMS (non-voice calls). We

also looked at some of the recommendations GSM specifies for routing of voice call and SMS to

the old number in a new network. However, GSM does not recommend any standard for SMS-

data in number portability scenario; therefore, SMS-data services are not portable in number

portability scenario. As part of our contribution, we presented how the USRS procedure presented

in Chapter 2 will work for consumer centric contents for ported numbers.

OCC and GCC type contents are available only to the PLMN subscriber through SME,

where the origin server is physically connected to the SME. These contents are not available for

ported numbers. We therefore presented our contribution of SMS-data tunnelling through USRS-

tunnelling where the SMS will be routed to the old SC without using the old SMS-IWMSC. This

offers auto-porting of SMS-data service for OCC and GCC. This means that using USRS-

tunnelling, we can ensure ubiquitous/universal SMS routing. USRS for SMS-data tunnelling can

support more that 360,000 messages/hour.

After supporting ubiquitous and universal routing of SMS-data irrespective of service

provider, it is important to maintain statefulness of some of the upcoming applications added to

system. Next chapter addresses regarding maintenance of stateful SMS-data communication.

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