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Seminar Contents

p

Introductionp Mobile IP & SIP

p IP in 3G networks

p Mobile IP in 3G networks

p IP Multimedia Services and SIP in 3G networks

p SIP interworking with Mobile IPV4

p SIP interworking with Mobile IPV6

p Security Considerationsp Conclusion

p

p


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INTRODUCTION

3G cellular networks have been designed to provide a

variety of IP data services.

Mobile IP is becoming a key technology for managingmobility wireless networks.

The SIP is the key to realizing and provisioning services

in IP-based cellular networks.

3G network have introduced support of IP mobility throughMobile IP(MIP).

3G partnership project 2(3GPP2) deploy MIP to supportterminal mobility between points of attachment to thenetwork.

i.


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3GPP has defined and standardized a network

infrastructure called the IP Multimedia Subsystem(IMS)based on SIP

The substantial differences between 3GPP & 3GPP2 ishow SIP services can be provided through the IMS


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Mobile IP

MIP for a mobile node(MN) to move across different

connection points while maintaining connectivity with othernodes on the Internet.

Two versions of MIP have been defined depending on theIP version used in the network:

MIPV4 for IPV4 networks and MIPV6 for IPV6 MN maintains a fixed IP address called the Home address

(HoA)

As the MN roams into a visited network it also obtains a

care-of Address(CoA) valid on the new link(MIPV6) MIPV6 also supports direct peer-to-peer communication

called route optimization


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Session Initiation Protocol

SIP is currently the most popular protocol for

establishing peer-to-peer IP communication . SIP specifications define an architecture of user agents

and servers that support communications between SIP peers.

In SIP each user is uniquely identified by SIP universal

resource indicator(URI). SIP begins with a user sending an INVITE message to a

accepts the request and the initiator is notified, the actualdata flow begins.

An INVITE message typically carries a description of thesession parameters.


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IP in 3G Networks

The large address space available,IPv6 allows for the concept ofalways on "networks by enabling devices to have IPaddresses assigned permanently

This particularly applies to services such as VoIP and streaming

that are especially of interest to 3G networks. IPv6 addresses are globally routable, with IPv6 the end-to-end

communication model of the Internet is applicable to 3Gnetworks.

The option of adopting IPV6,especiallly for new services ,ensures that these networks will not have to worry about the

transition between IPV4 and IPV6.


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MOBILE IP IN 3G NETWORKS

3g networks have introduced support of IP mobility throughMIP.

MIP is used in cdma2000 and General Packet RadioServices(GPRS)/Universal Mobile Telecommunication

System(UMTS).

i. Mobile IP in CDMA2000

ii. Mobile IP in GPRS/UMTS


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MOBILE IP IN CDMA2000

Code-division multiple access (CDMA) networks , in particularcdma2000 networks specified by 3GPP2, deploy MIPv4 tosupport terminal mobility between points of attachment to thenetwork.

The PDSN is the actual point of attachment of the MN to the IPnetwork and acts as an FA to support IP mobility in order to

allow the MS to move from one PDSN to another.

In such a scenario, the MIPv4 HA is the anchor point for the MStraffic, especially if reverse tunneling from the FA is utilized.


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MOBILE IP IN GPRS/UMTS

GPRS and UMTS networks specified in 3GPP do not

explicitly support MIP. IP mobility, in particular MIPV6, can be used to support

terminal mobility for multi-access networks, networks that supportboth cellular access through GPRS/UMTS and, say ,wirelessLAN(WLAN) access.

MIPv6 is in fact transparent to the mechanisms GPRS/UMTSdefine to provide IP connectivity to an MN. When MIPv6 is usedin GPRS , the MN gets local IP connectivity at the GGSN.

When MIPV6 is used in GPRS, the MN gets local IP connectivityat the GGSN.

The address obtained by the GGSN is used as COA.

The MN then sends a MIPV6 binding update(BU) messages to theHA and any CN enable route optimization


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IP MULTIMEDIA SERVICES AND SIP IN3G NETWORKS

SIP is the protocol of choice for the support of IP multimediaservices in the IMS [6] of the 3GPP UMTS.

The main elements are the P-CSCF,S-CSCF and I-CSCF.

The P-CSCF acts as a SIP proxy between the MN and the I-CSCF/S-CSCF.

The S-CSCF implements the actual SIP registrar functionalityand session control, including service triggering.

After gaining IP connectivity through the packet network, theMN registers with the S-CSCF.

The registration request is forwarded via the P-CSCF. S-CSCFauthenticates the MN and retrieves the user profile.

After successful authentication, the MN is registered and readyto set up or receive SIP calls.


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IMS in 3GPP2

3GPP has completed specifying the architecture and interfacesfor IMS Release5 and 3GPP2 is currently in the process of

adopting the same IMS architecture. IMS has designed considering the GPRS/UMTS core packet

network needs careful consideration.


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SIP INTERWORKING WITH MOBILEIPV4

When connecting to an IPv4 network with or without MIPv4,the MN obtains an IPv4 address that may be public or

private.

NAT needs to modify the external IP header to convertbetween IPv4 and IPv6 headers and addresses.

The IMS specifies the use of a security association betweenthe MN and the P-CSCF in order to protect the integrity ofSIP messages.

To support IPv4/IPv6 conversion the ALG needs to beimplemented as part of the IMS, and needs the ability toinstruct the NAT on how addresses should be mapped.


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If MIPv4 is used, further issues arise. The location of P-CSCF

and S-CSCF with respect to the FA and HA has implicationson the way SIP and MIPv4 interact.

When the P-CSCF is located in the visited network, with MIPv4in 3GPP2 packets destined to the MN are routed through the

HA and tunneled to the MN, whereas packets from the MNmay be sent directly to the destination or tunneled throughthe HA.


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SIP INTERWORKING WITH MOBILEIPV6

The adoption of SIP services with MIP introducesa set of issues.

i.Addressing considerationii.Architectural consideration


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Addressing consideration

Both SIP and MIP support mobility of the MN. When MIP is used, the MN has two addresses: the HoA and

CoA. MIP supports node mobility by allowing applications tobe unaware of a change in node address. Therefore, the

addresses used by the MN for SIP communications is theHOA.

This requires the MN to use the same address for the sourceaddress and the address provided at the SIP level.

This requires the MN to use the same address for the source

address and the address provided at the SIP level.


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The security requirements for MN addressing and allows directoptimized routing of both SIP signaling and SIP sessionmedia, this corresponds to using SIP mobility. In fact, the

MN needs to reregister the new CoA with the SIP proxyevery time it changes its point of attachment to the network.In particular, if the MN is involved in an active SIP sessionwith other nodes, it needs to re-invite the nodes providing thenew CoA.

The MN provides both the CoA and HoA in SIP signaling. Thisrequires changes to current SIP standards, and defies thereason MIP was introduced: to make applications unaware ofthe node mobility.

The MN provides the HoA at SIP registration and for sessionestablishment, and uses the HoA as source address. In thisway, MIP mobility is used, and the MN does not need toreregister or re-invite other nodes when it changes CoA.When the MN is involved in an active SIP session, the MN

updates the other nodes with the new CoA through MIPsignaling.


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Architectural consideration

From an architectural point of view, with MIPv6 the location ofP-CSCF and S-CSCF with respect to the HA needs to beconsidered for SIP and MIP interactions.

In a second case for MIPv6, the P-CSCF is located in thevisited network, while the HA is located in the home network.

In such scenario, MIPv6 can be supported transparent to SIP. The SIP signaling between the MN and the P-CSCF is routed

directly without requiring tunneling through the HA.


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SIP REGISTRATION AND SESSION SETUP

SIP session setup for the IMS in 3G networks in the presence ofMIPv6. Several options are possible for the MN to send BUmessages to the CN. In the basic scenario (option 1), the MNreceives packets from the CN tunneled though the HA, and

initiates the route optimization procedure. This can have implications on quality of service (QoS), since QoS is

initially established only for the route from the MN to the HA andto the CN, whereas QoS for the optimized route is not established.

Packets from the CN can still be received through the HA

before the BU procedure is completed. An additionaloptimization is to send the BU message while the SIP sessionis still being set up to ensure that the CN is willing and ableto accept the SIP session.


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SECURITY CONSIDERATION

Security mechanisms have been defined for MIPv6 inparticular to allow authentication of the MN with the HA tosend BU messages. In addition, MIPv6 has defined thereturn routability (RR) test as a mandatory mechanism to be

implemented by MIPv6 nodes to support route optimization. when an MN initiates the procedure, the CN challenges the

MN to prove that it owns the HoA and is currently located atthe CoA.

The RR test needs to be re-executed at a certain frequency

in order to ensure that no session hijacking takes place andthe CoA registered for the MN is still valid, since the MNcan change CoA rather often.


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How SIP is used with MIPv6, and conclude that the MNneeds to see the P-CSCF as a CN and perform BU

procedures. According to MIPv6 specifications, this implies

that the RR test is executed between the MN and the P-CSCF at regular intervals.

In order to avoid the overhead introduced by the RR test,this article proposes to reuse the security associations set upat SIP registration between the MN and the PCSCF. The

security association is currently used to integrity protect theSIP signaling, but it can be used also to authenticate theMIPv6 BU messages between the MN and the P-CSCF.


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CONCLUSION

Standardization of IMS support of SIP services in 3GPP2 forcdma2000 is proceeding. The implications of supporting bothIPv6 and IPv4 for SIP services. MIP and SIP are two key

protocols for 3G cellular networks. Interworking between SIPSolutions have been described for use of MN addresses and amobility procedure when SIP is used


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