Location Update Mechanism In Ip Multimedia Subsystem Computer Science Essay

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To provide high speed data traffic and maintain promised QoS in wireless systems IMS was introduced in 3rd generation networks. IMS uses SIP style session creation and maintaining means. As IMS deals with high rate data transfer so this module can be used for purposes other than catering QoS. Here we propose a technique in which IMS has been used for location update of any mobile node , it not only gives exact location of any randomly moving node but it also helps in emergency state where location determination of any node can be a setback. As a result real time position of any user equipment is obtained which can be further used by network operator or can be provided to use on his/her request in rescue cases.

Keywords- IMS, Location, Moving, Emergency


As cellular networks are being getting more advanced like 3G, 3.5G and upcoming 4G, user's requirements regarding bandwidth, mobility and QoS provisioning are being increased. To cater for users QoS needs, a new module has been added in cellular systems i.e. IP Multimedia Subsystem (IMS). Managing QoS in networks is not new idea at all; in wired networks QoS has been maintained using Session Initiation Protocol (SIP) and the reason that this mechanism is being implemented in wireless networks is that so much of bandwidth was not available in cellular networks for user. But with the deployment of 3G and other new standards, higher data bandwidth is available .Now not only multimedia traffic is being routed using data standards but traditional voice traffic is also routed using Internet Protocol (IPS). [1] Discusses IMS in context of user requirements, enterprise requirements, operator requirements and regulatory requirements. It further highlights the overall scenario of IMS functioning and its importance. Vertical and horizontal integration of services is also discussed here. [2] IMS also adds up towards proper billing and incorporation of services. It develops a java based client for IMS which is further deployed in mobiles devices. Overall system is tested in test bed and they claim that their proposed IMS java based client performs better in user adaptation and messaging communication. [3] Presents UMTS packet switch realm as IMS packet based admission network. As Diffserv is already implemented in wired networks, it uses Diffserv based QoS provisioning in IMS, it mentions what are the key parameters for this i.e. QoS mapping, router configuration and right of entry control etc. In [4] importance of IMS is argued in providing all IP solution to all users belonging to either fixed network or mobile network. They confer the importance of different parts of IMS module like HSS, SLA in adaptation of mobility and other services. The key idea of this paper is to use pertinence of information for QoS provisioning and to permit a subscriber to be registered with more than one operator at any time.[5] establishes a test bed for network operators ,service providers to test their application development ,testing QoS mechanism using IMS and other experiments regarding IMS to remove fear of network operator related to IMS implementation ,its problems and troubleshooting since due to this fear its taking long in practical deployment of IMS in some areas. So it depicts the objectives of settlement of establishing their IMS test bed to shatter panic of IMS implementation. [6] Tries to remove extra delays which may cause due to re registration in IMS system since in early IMS system it was not added in it that automatic registration will be done while user faces macro mobility and gets new IP address so there re registration process had to be initiated for continuation of services. It represents a solution that by sharing information and participating call spots this delay can be reduced as IMS have the status and session information. [7] Describes the role of IMS as core module for offering multimedia services in wired and wireless networks. So any network having implemented IMS can provide QoS either in wired or in wireless scenario. It focuses it discussion to IMS components and explains their functionalities while provisioning QoS different scenarios. As IMS and other modules are being evolved with the passage of time so there is need to fully grasp their functionalities to conduct extensive research.


IMS has been put into operation since release of 3GPP (UMTS) but work on it is continue on different aspects. As IMS now is integral part of cellular / wireless networks, it can also be used for location management of user's mobile device since it has separate module for its billing and traffic management. [8] Describes terminal based method for location update. Global positioning system is used in hand held device and its information is then used for finding location and may be used for any purpose like notification handling, access control and privacy management. Position of any mobile device obtained form long; lat of GPS can even be transmitted to any server for initiation of any specific service or to any client as well. [9] Highlights the research going on investigation of IMS having SIP and non SIP based architecture. They performed different experiments on SIP and non SIP based IMS and verified results that how much performance is degraded. Further more they applied these mobility management techniques on Wi Fi and PPP networks. All this had been done on their own developed test bed and they offer their services to all those who want to use these infrastructure using IPv6 on IMS. [10] Starts its discussion by mentioning that existing mobile IP protocols are not suitable for maintaining sessions and location updation can not be done efficiently using these protocols. Conversely IMS is used to plan user's QoS demands according to promised levels. So they integrate mSCTP into IMS system to provide services of session continuity and up to some extent location update. mSCTP helps in maintaining QoS to a standard level while user is moving in different heterogeneous networks. Finally they prove that this approach is much faster than conventional approach. [11] Develops their own IMS environment using Fraunhofer OpenIMS. Here existence information of different users is shared using session initiation protocol. In their test bed they also study interconnection of 3rd layer to distribute location information obtained using SIP to any other demanding applications. It can be deployed in specific IMS client as well. In [12] an extension of IMS is presented which mainly deals with improved location emergency services. They claim that their proposed model deal with context aware emergency scenarios quite well and addresses location related problems efficiently. Finally they present a scenario where this model has been applied. [13] Describes issues while transferring from traditional cellular networks like GSM to new cellular networks like IMS (UMTS) in context of location management. They discuss that if a user is moved from GSM network to IMS enabled network then how location information will be handled and what new entities have to be added to GSM and IMS network to cater for this problems. It further discusses services degradation that may occur during this handover procedure


Numerous Internet applications require the creation and management of a session, where a session is considered being an exchange of information among a relationship of participants. The applications are complex, because the participants may 1) convey between endpoints, 2) be addressable by a multitude of names and 3) communicate, possibly simultaneously, with different media. Many protocols can transmit different forms of real-time multimedia session data. SIP operates harmoniously with these protocols by enabling Internet endpoints (user agents) to locate each other and decide on the traits of a session that they want to share. In order to discover viable session participants and other functions, SIP enables the creation of an infrastructure of network hosts (proxy servers) to which user agents can submit registrations, invitations to sessions and other requests. SIP is a quick, generic-purpose tool for establishing, modifying and ending sessions, which function independently of the underlying transport protocols and independent of the session type being created. [3]

SIP is an application-layer management protocol that can generate, modify and terminate multimedia sessions. SIP can invite participants to sessions that already exist. Media can be removed from, or added to, a prevailing session. SIP supports the mapping of names and redirection services transparently. These services support personal mobility, hence the users can

uphold a single externally visible identifier regardless of their actual location in the network. [3]

The details of the session (e.g. the type of media) are not depicted using SIP. The body of a SIP message includes a description of the session, which is encoded in some other protocol format. One of such formats is SDP. This SDP message is conveyed by the SIP message in a manner which is analogous to a document attachment being conveyed by an email message. [3]

A proxy server receives SIP requests and forwards them in behalf of the requestor. After the call set up has been performed and the two-phase exchange has provided the basic negotiation capabilities of the media session (see figure 2), the media session has begun and the two parties transmit media packets utilizing the format to which they previously agreed to. Generally, the end-to-end media packets take a different route from the SIP signaling messages. Disconnection also is routed directly between the endpoints, thus bypassing the proxies. [3]

There are cases where it may be useful for proxies in the SIP signaling path to perceive all the messaging between the endpoints for the duration of the session. For example, if a proxy server would desire to remain in the SIP messaging path beyond the initial INVITE message, it would add to the INVITE a required routing header file, which is known as the Record- Route. The Record-Route contains a Universal Resource Identifier (URI) resolving to the hostname or IP address of the proxy. Briefly, the Record-Route header field is added by proxies in a request to force the future requests of the dialog to be routed through the proxy. [3]

A proxy is discriminated to be loose routing if it is according to the procedures of its specification for handling the Route header field. These procedures distinguish the destination of the request from the set of proxies that need to be visited along the path. A proxy that is complies with these mechanisms is known as a loose router. [3] The 3GPP IP Multimedia Call Control Protocol based on SIP and SDP states that each IP Multimedia (IM) Core Network (CN) subsystem functional entity shall apply the loose routing policy denoted in RFC 3261 [3], when a SIP request is processed. [12]

A user agent delineates an end system. It includes a UAC, which creates requests, and a UAS, which responds to the requests. A UAC is able to generate a request based on some external stimulus and handling a response. A UAS is able to receive a request and generate a response based on user input, external stimulus, the result of a program execution or some

other mechanism. When a UAC transmits a request, the request conveys through a number of proxy servers, which forward the request to the UAS. When the UAS generates a response, the response is forwarded to the UAC. [3]



The P-CSCF is the first point of contact within the IM CN subsystem. The P-CSCF acts like a proxy, i.e. it accepts requests and services them internally or forwards them on. The P-CSCF shall not change the Request URI in the SIP INVITE message. The PCSCF may act like a User Agent (UA), i.e. in the case of abnormal situations it may terminate and independently create SIP transactions. [2]

The S-CSCF does the session control services for the User Equipment (UE). It upholds a session state as required by the network operator for support of the services. Within an operator's network, different SCSCFs may have different kinds of functionalities. A few functionalities performed by the S-CSCF are the ensuing:

_registration, S-CSCF may act as a Registrar,

_session-related and session-unrelated flows, SCSCF may act as a Proxy Server or as a User Agent,

_ endpoint destination, S-CSCF forwards a SIP request or response to a P-CSCF for a mobile terminated procedure to a home user within the home network, or for a user roaming inside a visited network where the home network operator has chosen not to have an Interrogating-CSCF (I-CSCF) in the path [2].

An Application Server (AS) provisions value added IP multimedia services. It is located either in the user's home network or in a third party location. The third party can be a network or simply a stand-alone AS. [2]

Figure 1. The endpoints of the IMS and their

most relevant connections. [2]


Since IMS has been deployed successfully in cellular networks, extensive research is continue on different parts of IMS to increase its usability and to increase predictability of existing cellular networks. One of the important facts of IMS is that it can be used as location update mechanism. We propose a model where IMS is used as location update system. IMS uses traditional Session Initiation Protocol for its signaling purposes (SIP) to maintain promised QoS in cellular networks. We devise modification in SIP packet for inserting location information of any mobile device that may go any where, so its location information will be transmitted in SIP packet which may help operator and device itself in many cases, especially in emergency, location of victimized node can be found quickly .Structure of traditional SIP packet is shown in figure 2, we can observe that in conventional SIP packet there is no field for preserving position data ,it is just used for communication of signaling sequence

Figure 2

We modified the SIP packet as shown in figure 3 Opnet 11.5 was used for SIP packet modification

Figure 3

In this modified packet we added two new fields i.e. X Location and Y Location respectively. To check the effects of these new added fields on overall traffic of IMS system we developed the IMS model as shown in figure 4

Figure 4


We conducted following traffic analysis with both type of SIP packets i.e. original and modified


In figure 5 FTP traffic results have been shown which uses original SIP packet

Figure 5


In figure 6 IP traffic results have been shown which uses original SIP packet

Figure 6


In figure 7 Voice traffic results have been shown which uses original SIP packet

Figure 7


Ethernet delay while using standard SIP packet is shown in figure 8

Figure 8



FTP Traffic Analysis while using modified SIP packet is shown in figure 9

Figure 9


In figure 10 IP traffic results have been shown which uses modified SIP packet

Figure 10


In figure 11 Voice traffic results have been shown which uses modified SIP packet

Figure 11


Ethernet delay while using modified SIP packet is shown in figure 12

Figure 12


From this research activity, we wrap up that IMS can be used for getting location updates for any mobile / fixed device. And this can be easily done by modifying SIP packet and adding X, Y location of related device that location can be obtained from GPS or any other source and then get integrated in SIP packet.

Experimental data shows that modification in SIP packet doesn't have major effect on different types of traffic and doesn't introduce major delays in traffic.


We performed experiments on hybrid model of wireless LAN and fixed network in this activity, same work can be done for LTE and HSPA