Techmahindra 80216e 3gpp_systems_networkhandover

© Tech Mahindra Limited 2010

802.16e & 3GPP Systems Network Handover

Interworking

Venkat Annadata Tech Mahindra (R&D) Services Ltd.

Abstract: Next Generation Mobile Networks are paving its waytowards the ubiquitous wireless access abilities whichprovide the automatic handovers for any movingdevices in the heterogeneous networks combiningdifferent access technologies. In this technical paper, intend to present a possibleMobile WIMAX‐3GPP/2 Network Interworkingarchitecture based on the 3GPP/2 standards andpropose the seamless inter‐system handover schemewhich enables the service continuity with lowhandover latency and packet loss.

This technical approach of enabling handover featureis purely based on the IEEE 802.16e Mobile WiMAX &3GPP/2 Standards.

APRIL ‐2010

1 © Tech Mahindra Limited 2010

Introduction Today Mobile WiMAX (IEEE 802.16e) is one of the wireless broadband standards capable of providing the Quadruple play Technologies ‐ Data, Voice, Video & Mobility using a single network. The introduction of the 802.16e WiMAX flavor is creating new markets for mobile broadband services. Abilities of the 802.16e standard to provide seamless mobility to end users in their homes, offices, and during transit, are spurring the demand for innovative mobile services. Users can now take advantage of complex IP‐based data‐intensive applications while traveling at vehicular speeds. This is made possible by IP‐specific optimizations of 802.16 and its built‐in support for high‐speed handoffs. Mobile customers shall now be able to download full‐length DVD‐quality movies quickly or host multi‐party video‐conferencing sessions from their WiMAX–enabled handheld devices. Regardless of the deployment of this IP‐based version of WiMAX, it is clear that 802.16e is providing a strong mobility platform to help accelerate convergence. In the current paper Handover Interworking scenarios for Mobile WiMAX and 3GPP/2 are presented with Network Interworking Architecture along with the call flows from WiMAX to 3GPP and vice –versa. Roadmap for evolution of WiMAX‐IMS (3GPP2) interworking architecture is also presented as per the NWG WiMAX stage 2 specifications.

Handover Solution Architecture

Architecture Description At the onset, let us understand the differences between 3GPP‐WLAN interworking and 3GPP‐WIMAX interworking. The WLAN in hot‐spot areas forms the micro‐cells within the 3GPP macro‐cells. The mobility between 3GPP and WLAN can be referred to fully overlapping handover. Accordingly, the required time for switching from 3GPP to WLAN connection can be tolerantly long. Moreover, when the mobile is connected to WLAN, it can maintain simultaneously the Packet Data Protocol (PDP) context of 3GPP so that it can reconnect immediately to 3GPP without need of PDP context re‐activation. On the contrary, from the below figure 1, the mobility between 3GPP and WIMAX is referred to partially overlapping handover since the WIMAX coverage is in order of 3GPP coverage area. Consequently, the handover should be done quickly to maintain the connection particularly when the speed of the mobile terminal is high. In order to enable the mobility between two access networks 3GPP and WIMAX, we propose a solution under some following conditions: minimum change of the existing network infrastructure of these two technologies and feasible solution for short term. By using IP as the common interconnection protocol, the mobile can connect to multiple networks seamlessly ignoring the heterogeneity of access technologies. This is achieved by using Mobile IP mechanism that hides the heterogeneities of lower‐layer technologies. The proposed architecture for 3GPP‐WIMAX interworking, depicted above is based on interworking architecture models of 3GPP standards.

Figure: 1


The mobile subscriber (MS) is a mobile node that can communicate with both 3GPP network and WIMAX network. However, note that it can connect to only one access network at a time. Therefore, the handover between 3GPP‐WIMAX must be the hard handover. The WIMAX Access Network (AN) provides the WIMAX access services for the MS. The mobility inside WIMAX network is managed by the WIMAX Home Agent (HA) located between the ASN gateway and the WAG. The WIMAX HA is not necessarily included in 3GPP core network to keep its independence from 3GPP system. The Foreign Agents (FA) located in ASN Gateway is considered as the local FAs in the interworking architecture. The WIMAX AN is connected to the 3GPP network via WAG and to the 3GPP AAA server for the WIMAX authentication process. The WAG is a gateway through which the data from/to WIMAX AN is routed to provide MS with 3GPP services. The functions of WAG include enforcing routing of packets through PDG, performing accounting Information and filtering out packets. The main functions of PDG are to route the packets received from/sent to the PDN to/from the MS and to perform the FA functions. The mobility within the 3GPP network is managed by its own mobility mechanism and the FA functions implemented in the GGSN. In order to enable the vertical handover between these two technologies, the HA is placed in the PDN and manages FAs of both WIMAX and 3GPP networks. IP Address Management In WIMAX network, each time the mobile changes its ASN gateway; it will obtain a new local IP address through the DHCP server. The ASN GW can learn this new local IP address and also ask to the DHCP server the WIMAX HA’s address since it plays the role of the DHCP relay agent in the DHCP discovery process. The ASN GW then informs the serving BS the MS’s new local IP address and sends the Mobile IP (MIP) registration to the WIMAX HA. A generic IP‐in‐IP tunnel such as Generic Routing Encapsulation (GRE) may be used to transport the IP packets between the WIMAX HA and the FA. Each time

the mobile switches the connection to the 3GPP network, it will initiate the PDP context activation procedure. No IP address is allocated to the MS at the PDP context activation. The remote address provided by HA or an external entity in PDN will be kept unchanged and will be informed to the GGSN via PDP context activation. The remote IP address is a global home address that is used to address to the external network and the correspondent node. It may be a static address or a dynamic address acquired from the HA or another external entity when the mobile first time connects to the network, discovers and registers with the HA. The PDG/GGSN is then responsible for relaying MS’s remote allocated IP address to the MS. Handover Procedure To reduce the interruption time during the handover, we have specified a forward handover procedure. That is to say, before leaving the serving network, the mobile prepares a new attachment in the target network. In order to reduce the packet loss during handover, the old FA notifies the HA the MS’s movement so that the HA can buffer the packets and forward them to the MS as soon as the HA receives the MIP update from the MS.

Handover Call Flows Scenario 1: Handover from WIMAX Access Network to 3GPP Network From the Figure:2 below, before the handover is initiated, the mobile is connected to the 3GPP services through WIMAX access network. When the MS enters to an overlapped zone, the MS can measure signal quality from the 3GPP neighboring cells. If the triggering conditions for vertical handovers are satisfied, the handover decision is then taken. The target 3GPP‐UTRAN will be notified the imminent handover from the WIMAX network via the HO request message routed through the core network. The MS will perform the GPRS attach procedure with the 3GPP‐UTRAN. Mobility management contexts are established at the MS and SGSN. The MIP registration between the HA and new GGSN/FA


can be updated after the PDP context is activated between GGSN and MS. The details of handover procedure from a WIMAX cell to a 3GPP cell is depicted in below call flow: 1. The WIMAX BS sends periodically the topology advertisement message to inform the MS of neighboring WIMAX BSs and NodeBs. Alternatively, the MS can scan different channels to discover the neighboring topology. However, it is not a good solution and it will be our future work. Throughout our study here, we assume that there exists a total cooperation between the 3GPP and WIMAX networks operators. Thus, the 3GPP NodeB can transmit to the MS the WIMAX neighboring cell information and vice versa. 2. Based on the topology advertisement, the MS performs synchronization and measurement procedure. The event‐triggered inter‐system measurement may be based on the degradation of current signal quality or on the necessity of switching between access technologies to support higher QoS requirements or low cost. Since the WIMAX operates in TDD mode, during the downlink frame duration, only some OFDM symbols are addressed to the mobile. Accordingly, the remaining time can be used to measure neighboring cell signals. Note that, to facilitate the measurement on 3GPP cell, the information such as scrambling code, carrier

frequency, should be included in advertisement messages. 3. After the measurement step, the mobile shall send the measurement report to the WIMAX BS. The report must contain the signal quality level of each candidate 3GPP cell. 4. The WIMAX BS initiates the handover procedure by notifying the potential target 3GPP via handover (HO) request message. The PDG will perform a DNS request to know the addresses of GGSNs which serve the current MS’s Access Point Name (APN). The PDG then selects one GGSN in the result list of GGSNs from the DNS request phase and sends the HO request to this selected one. If the PDG does not receive any response from the GGSN for a certain time, it will select another GGSN in the found list and resend the HO request message. 5. The GGSN then sends the HO request message to the SGSNs who serve the indicated nodeBs. In order to be able to retrieve the address of SGSN that serves a specific nodeB, we assume that the DNS server or the Home Location Register (HLR) stores this routing information. 6. The target RAN establishes bearer resources, including radio resources, for the MS. This step aims to check if the candidate 3GPP NodeBs can accept the MS handover with the required QoS.

Figure: 2


7. The NodeB which supports the MS handover will send a HO support message to the ASN GW which contains the handover decision function. 8. Upon receiving HO support messages, the ASN GW selects the best target 3GPP cell and then returns the HO command to the MS. This message must include the recommended target NodeB and all the required information for setting up a new connection. The above exchange may require a large amount of information and add more latency to handover, it is therefore Preferable to use a pre‐configuration mechanism. It means that only a reference number corresponding to a predefined set of 3GPP‐3GPP‐3GPP‐UTRAN parameters is inserted in the handover command. The MS should download the predefined radio configurations before. During this temporary connection, the MS can reconfigure the connection into a suitable one. 9. Right after that the ASN GW sends the handover confirmation which includes the target NodeB identifier to the PDG/FA. The allocated resources in the WIMAX network will be then released. 10. Upon reception the handover confirmation message, PDG/FA will send a MIP update message to HA to notify the MS’s movement. The HA then stops sending the packets to the MS via this PDG/FA and buffers the inbound packets until it receives the MIP update from the target 3GPP network.

11. The MS performs the GPRS attachment procedure to 3GPP‐3GPP‐3GPP‐UTRAN network. The GPRS attachment procedure consists of accessing to SGSN, authenticating with the AAA server and updating the location. 12. After performing successfully the GPRS attachment, the MS starts the PDP context activation through which the MS informs its remote IP address (its global home address) to the GGSN. 13. After the connection is established between a new GGSN/FA and MS, the GGSN/FA will perform the MIP registration with the HA including the MS’s remote IP address and its care of address (address of GGSN/FA). The data will then be transmitted to MS via the new NodeB and the handover procedure is completed. Scenario 2: Handover from 3GPP to WIMAX Access Network Before the handover is initiated, the MS is in the 3GPP network. When the MS moves to an overlapped zone, it can measure the signal quality from the neighboring WIMAX BSs. When the network decides to handover to WIMAX, the MS will set up the connection with WIMAX AN, perform the authentication and MIP registration update, etc. The handover scheme from a 3GPP cell to a WIMAX cell is depicted in below figure 3:

Figure: 3


1. The 3GPP‐3GPP‐UTRAN is responsible for detecting the handover need and initiating the inter‐system measurement process by sending the measurement control message to the MS. This message contains the neighboring WIMAX cell information, the compressed mode pattern, etc. 2. While the MS has an on‐going communication in FDD mode, in order to perform the measurement on the neighboring WIMAX cells, it must enter in the compressed mode. Note that the measurement on WIMAX cell is performed on the preamble of each WIMAX frame. 3. After the measurement period, the MS sends the measurement report to the network. The report must contain the parameters indicating the signal quality level of the neighboring WIMAX BSs. 4. The RNC initiates the handover procedure by notifying the potential target WIMAX BSs where the mobile may handover. The HO request message including the MS’s APN, the candidate BS identifiers, the required QoS of MS’s current applications, etc. will be sent to the GGSN. The GGSN performs the DNS request to learn the addresses of the PDGs which serve the MS’s current APN. The GGSN selects one PDG in the result list and sends it the HO request message. If the GGSN does not receive any response from the PDG after a certain time, it will send the HO request to another PDG in the list. The HO request message will then be transmitted to the potential WIMAX BSs based on the routing information at the PDG. This step aims to check if the target WIMAX BS can accept the MS handover with the required QoS. 5. The WIMAX BSs which support the MS handover will return a HO support to the RNC. 6. The RNC will select the best target WIMAX BS among the supporting BSs and then sends the HO command to the MS. This message includes all the required information for setting up the connection to the selected target WIMAX BS. 7. Right after that the RNC sends the HO confirmation. The mobile is then disconnected

from the 3GPP network and starts the connection setup to the target WIMAX BS. 8. Upon receiving the handover confirmation, GGSN/FA sends a MIP update message to the HA to notify the MS’s movement. The HA then stops sending the packets to the MS via this GGSN/FA and buffers the inbound packets until it receives the MIP update from the target WIMAX network. 9. Based on the information included in the HO request message, the WIMAX BS can provide a non‐contention based initial‐ranging opportunity to the MS by placing a Fast Ranging Information Element in the UL MAP. This information will facilitate the RAN connection setup of the MS. If not, the MS must perform the normal ranging procedure which takes more time. 10. The MS initiates the connection setup by exchanging Ranging Request (RNGREQ)/ Ranging Response (RNG‐RSP) with the target WIMAX BS. 11. In the WIMAX AN, the MS will perform DHCP request to obtain new local IP address. In this scenario, we describe an address allocation procedure based on IPv4 mechanism. If IPv6 is used, the local address can be allocated by Stateless Address Autoconfiguration mechanism without the presence of the DHCP server. Through this procedure, the ASN GW will also learn the WIMAX HA address which serves for MIP registration in the following step. 12. The MS will perform the MIP registration to associate the MS’s local address with its care of address. 13. The MS performs DNS resolution for PDG address. MS uses APN to indicate the network service it wants to access. The DNS request will be relayed to ASN GW which in turn relays the request to the DNS server. The MS will select one suitable PDG among the list of PDGs given in DNS response. Note that the selected PDG here may be different from the PDG selected by GGSN during HO request/support step.


14. The MS then establishes an end‐to‐end tunnel with the selected PDG using IKEv2 protocol. Through this process, the MS will inform the PDG about its local and remote IP address. Each time the mobile changes its ANS network, it obtains a new local IP address and therefore a new tunnel should be correctly configured. Regarding inter‐WIMAX mobility, the time required for setting up a new IPSec tunnel when changing of ASN may be too long that the seamless mobility cannot be achieved. To speed up this kind of IPSec tunnel relocation, we can use the MOBIKE mechanism proposed by the IETF MOBIKE WG. 15. The PDG performs the MIP registration with the HA as soon as it will be notified the MS’s remote IP address. The data packets will be transmitted to MS via the WIMAX AN. The handover procedure is completed. Proposed WiMAX –IMS interworking Network Reference Model NOTE: Figure:4 below architecture diagram is evolving. It may contain old representations that will be resolved at a later stage of investigation. Also, this assumes that the CSN functionality is provided by the 3G Network. This includes IP address space allocation.

Solution benefits

This network architecture approach offers the following benefits:

• Offers interworking handover functionality between Mobile WiMAX & 3GPP Networks.

• Seamlessly integrates wireless technology specific functionality with IP networking equipment

• Allows for the use of a common IP network for multiple wireless access technologies

• Enables cost‐effective implementation for deployments ranging from small to large scale

• Enables the use of mobile devices and optimizes handovers

• Scalable to 3GPP2 IMS Networks for feature rich multimedia applications & quadruple play technologies.

• Enables new types of transport networks such as metro Ethernet, and wireless point‐to‐point for backhaul

• Enables distribution of “application level” functionality such as content delivery networks

Figure: 4


Conclusion & Future Work In this paper, we have introduced a practical 3GPP‐WIMAX interworking architecture based on 3GPP standards and proposed a handover procedure which promises a low packet loss and low interruption time during the switching of the communication. The mobility between two access networks is achieved by the MIP mechanism at the network layer. The packet loss during handover is reduced since the old FA notifies the HA the MS’s movement and consequently the HA buffers the data packets destined to the MS. The proposed interworking architecture does not require lot of changes on existing network infrastructures which is a big advantage. The proposed handover scheme needs the exchange of messages between the PGD and the GGSN which serve the same APN with the help of the DNS server. In case the MS connects to multiple APNs, the handover preparation phase may be more complex, which will be our future work with some performance evaluation of our proposed mechanisms in a large scale network. Moreover, we aim to consider the tightly‐coupled interworking architecture approach for 3GPP‐WIMAX and 3GPP‐WLAN interworking which allows a seamless handover with less handover latency and less packet loss. The future interworking architecture should be based on the architecture evolution proposed by 3GPP standards. We therefore plan to consider the roaming architecture as well as the mobility scheme in the context of multiple operator environments.

References 1. An Architecture for UMTS‐WIMAX Interworking ‐ Quoc‐Thinh Nguyen‐Vuong, Lionel Fiat and Nazim Agoulmine 2. IEEE P802.16e/D11, ”Part 16: Air Interface for fixed and mobile broadband wirelessaccess system”, Sept. 2005. 3. Salkintzis,A.K.; Fors, C.; Pazhyannur, R.; ”WLAN‐GPRS integration for nextgeneration mobile data networks”, IEEE Wireless Communication, Vol.9, pp. 112‐124, Oct. 2002. 4. Shiao‐Li Tsao; Chia‐Ching Lin; ”Design and evaluation of 3GPP‐WLAN interworking strategies”, Proceedings. VTC 2002‐Fall, IEEE 56th Volume 2, pp.777 ‐781, Sept. 2002 5. Hyun‐Ho Choi; Song, O.; Dong‐Ho Cho; ”A seamless handoff scheme for 3GPPWLAN interworking”, Globecom, 2004, pp.1559 ‐ 1564, Vol.3. Dec. 2004 6. V. Varma, S. Ramesh, K.D. Wong, M. Barton, G. Hayward and J. Friedhoffer. ”Mobility Management in Integrated 3GPP/WLAN Networks”, IEEE ICC, Anchorage, Alaska, USA, May 2003. 7. Muhammad Jaseemuddin. ”An Architecture for Integrating 3GPP and 802.11 WLAN Networks”, 8th IEEE ISCC,p.716, 2003. 8. N. Vulic, S.H. Groot, I. Niemegeers, ”A comparison of Interworking Architectures for WLAN Integration at 3GPP Radio Access Level”,ConWIN05, July 2005. 9. G. Cunningham, P. Perry and L. Murphy, ”Soft, Vertical Handover of Streamed Multimedia in a 4G network”,5th International Conference on 3G mobile communications Technologies, London, UK, Oct. 2004.

Glossary AAA Authentication, Authorization & Accounting E2E End to End IMS IP Multimedia Subsystem IP Internet Protocol MGC Media Gateway Controller MGW Media Gateway P‐CSCF Proxy‐Call Session Control FunctionPDF Policy Decision Function POC Proof Of Concept QoS Quality of Service RADIUS Remote Access for Dial‐In User ServicesSBC Session Border Controller TM Tech Mahindra VoIP Voice over IP VSA Vendor Specific Attributes WISP Wireless Internet Service Provide

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