Internet Engineering Task Force                                  Qi Shen
Internet Draft                                                       CWC
draft-shen-ipv6-flow-trans-00.txt                           Winston Seah
Date: February 2001                                                  CWC
Expires: July 2001                                            Anthony Lo

       Flow Transparent Mobility and QoS Support for IPv6-based
                      Wireless Real-time Services


   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
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1 Abstract

   This draft proposes a Mobile IPv6 and RSVP interworking scheme. In
   this scheme, the underlying mobility support mechanism is required to
   provide a unique flow identity regardless of node mobility, making
   node mobility transparent to flow QoS handling mechanisms. Thus QoS
   signaling delay as well as data packet delays and losses during
   handoff can be reduced. We also discuss solutions to achieve this
   scheme which utilizes the new IPv6 flow label. Finally, issues
   related to security and scalability will also be considered.

2 Introduction

   Interworking of Mobile IP [1,2] and RSVP [3] may provide simultaneous
   mobility and QoS support for wireless mobile Internet real-time
   services. The crucial aspect for such a scheme is the resultant
   handoff QoS performance. Specifically, the handoff QoS signaling

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   delays are required to be small enough to minimize the handoff data
   packet delays and losses, thus also minimize possible service
   degradation during handoff. In this draft we propose a Flow
   Transparent Mobile IP and RSVP integration scheme to achieve this
   goal. By taking advantage of the new IPv6 flow label, we can greatly
   facilitate the implementation of this scheme. Thus the scheme fits
   more naturally for the integration of Mobile IPv6 and RSVP with flow
   label support, although the Flow Transparency concept applies also to

   The organization of this draft is as follows, we begin with the Flow
   Transparency concept, followed by the handoff operation of the flow
   transparent scheme as well as its main features; then we provide
   solutions to accomplish the scheme; finally we discuss security and
   scalability aspects of this scheme.

3 Flow Transparency Concept

   According to IPv6 specification [4], a flow is a sequence of packets
   sent from a particular source to particular destination for which the
   source desires special handling by the intervening routers. This
   special handling can be non-best effort QoS treatment set up through
   RSVP. In a fixed network, the flow source and flow destination are
   fixed after the RSVP resource reservation is established for that
   flow. In a mobile environment running Mobile IPv6, however, the flow
   source or flow destination may change in the middle of an application
   session.  This is because existing work on Mobile IPv6 and RSVP
   integration [5,6] usually identifies the flow source or flow
   destination with the Mobile Node (MN) 's care-of address. According
   to Mobile IPv6's built-in route optimization, the Correspondent Nodes
   (CNs) usually send packets directly to MN's care-of address when MN
   acts as receiver; Mobile IPv6 also substitutes the MN's home address
   in the source address field of outgoing packets with MN's care-of
   address when MN acts as sender.

   The result of this is that at the network layer, the flow identity
   changes each time the MN performs a handoff and obtains a new care-of
   address. Thus a single application session corresponds to multiple
   network layer flows, each requires a new RSVP renegotiation. This
   could cause situations where the new reservation is denied because
   the old reservation is still active and blocks resources. More
   importantly, change of network layer flow identity means all
   intermediate routers along the path have to re-build related flow
   information. So all handoff RSVP renegotiations have to be performed
   end-to-end, no matter how significant the handoff affects the flow
   path. This introduces long handoff QoS signaling delay and increases
   the delays and losses of data packets, which could lead to notable
   handoff service degradation.

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   To address these issues, we introduced a Flow Transparency concept
   [7]i.e., the underlying mobility support scheme is required to keep
   node mobility completely transparent to network layer flow handling
   mechanism.  Essentially, flow transparency calls for a unique flow
   identity irrespective of the change of MN's address thus enables the
   network layer flow handling mechanism to function normally regardless
   of node mobility. A flow transparent approach naturally avoids the
   above two problems.

   First, since the network layer flow identity remains the same after a
   handoff, old reservation can be reused by the same flow whenever
   possible. This prevents deny of reservation for that flow caused by
   resources blocked by old reservation. Second, with a constant flow
   identity after handoff, the routers residing in the common portion of
   the new and old flow path could be exempted from performing handoff
   QoS update; only those routers that are in the newly added portion of
   the flow path may be needed for the update process. This avoids the
   end-to-end renegotiation.

   It is worth noting that with node mobility, the number and identity
   of routers involved in the same flow are dynamic and usually
   unpredictable. It is the routers common to both new and old path of
   the flow that constitute the scope of flow transparency. This implies
   that automatic flow handling adaptation for those routers in the
   newly added path is required in order to exploit the flow
   transparency concept.

4 Handoff Operation of Flow Transparent Mobile IPv6 and RSVP Integration

   In this section we describe the handoff operation of the flow
   transparent Mobile IPv6 (with route optimization) and RSVP
   interworking and summaries its major features. We assume a constant
   flow source and flow destination are kept for a specific application
   session, so that the network layer flow identity is constant for the
   router flow handling mechanism (e.g., the packet classifier)
   regardless of node mobility. Detailed solutions will be presented in
   the later sections.  In order to achieve an efficient integration, we
   also exploit existing RSVP features in our scheme, namely, Merge and
   Local Repair. Figure 1 shows the architecture where both scenarios,
   MN as sender and MN as receiver, will be considered.

4.1 Scenario 1: Mobile Node as Sender

   After a handoff, the MN sends a Binding Update to CN according to
   Mobile IPv6, and it immediately triggers a Path message to CN - with
   the same source flow identity as the one before handoff. According to
   RSVP, this Path message can be merged at a router where there is

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                                   | Router  |
                                   |   at    |------ CN
                                   |subnet C |
                                    |     <-- Common flow path
                               |Nearest |
                               | Common |
                               | Router |
                Obsoleted         |  |         Newly added
                flow path -->  ...|  |...  <-- flow path
                              /          |
                             /           |
                       ---------      ---------
                      | Router  |    | Router  |
                      |   at    |    |   at    |
                      |subnet A |    |subnet B |
                       ---------      ---------
                           |              |
                           |              |
                           |    Handoff   |
                           MN ----------> MN

         Figure 1: Flow Transparent Mobile IPv6 and RSVP Integration

   already a path state for that flow which is created during previous
   RSVP message exchanges. In this case, the router where merge occurs
   is also the nearest router common to both the old and new path (
   Nearest Common Router ) for the flow from MN to CN.  It sees the same
   Path message arriving with a previous hop address that differs from
   the one stored in the original path state. This will cause RSVP to
   trigger a Local Repair for sender route change, which is actually due
   to sender mobility. So it will immediately send a Resv message
   associated with that flow to reserve resources along the newly added
   path to the MN. Thus resources for the flow will be reserved in the
   newly added flow path, while in the common flow path the previously

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   reserved resources will be reused.

4.2 Scenario 2: Mobile Node as Receiver

   The situation becomes more complicated when the MN is acting as a
   receiver. After a handoff, the receiver sends a Binding Update to the
   CN, at the same time, it should inform the Nearest Common Router of
   its mobility information to trigger a handoff Path message from the
   Nearest Common Router. This avoids waiting for a handoff Path message
   from the CN, which usually has to be issued after the CN gets the
   Binding Update.

   As an extension to RSVP, the mobility information, containing the
   flow destination and the MN's current location, will either be
   carried alone in a new RSVP message if MN acts solely as a receiver,
   or be piggybacked in the Path message sent by MN itself for sender
   mobility if the MN acts as both sender and receiver. This message
   will have CN as destination address and will be examined by each
   intermediate routers.  Upon receiving this message, the router
   decides whether it is the Nearest Common Router by looking up its
   existing RSVP states. If it decides itself as the Nearest Common
   Router, a Local Repair for receiver route change will be triggered,
   that is, the router sends a handoff Path message for the flow
   indicated by the flow destination, to the MN's new location. Then the
   original RSVP message will be discarded. After receiving this handoff
   Path message, the MN replies with a Resv message to reserve resources
   along the newly added flow path. Again because of RSVP merge
   functionality, this Resv message will not be forwarded farther than
   the Nearest Common Router since there is already a reservation for
   this flow made from that router onwards during the previous RSVP
   message exchanges.

4.3 Seamless Handoff QoS Provision

   Seamless handoff QoS provision is always desired in a mobile QoS
   scheme. Normally this requires to explicitly reserve resources in
   advance at the cells that the MN is about to visit [8,9,10,11]. The
   challenge for these schemes is, how to predict the MN's movement
   behavior so that pre-reservation may be done only in necessary cells.
   If prediction is not available, resource pre-reservation may have to
   be performed in all neighboring cells, which wastes resources.
   Although this waste may be alleviated through definition of new RSVP
   reservation models (like active reservations and passive
   reservations), the expense would be extra protocol complexity.

   The flow transparent RSVP and Mobile IPv6 interworking provides a
   relatively simple alternative of making seamless handoff QoS
   provision possible.  In the handoff mobility and QoS signaling as

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   mentioned above, it is likely that the RSVP message will traverse
   shorter than the Binding Update , because the handoff RSVP message
   ends at a Nearest Common Router while the Binding Update has to reach
   the CN all the time. Thus the RSVP renegotiation holds a possibility
   of being finished before the CN is updated with MN's new care-of
   address, especially when there are congested links within the path
   between the Nearest Common Router and CN. This implies that before CN
   starts sending packets to MN's new location, resources could have
   already been set up along that path. As a consequence, all packets
   subsequently destined for MN's new location from the CN will be
   offered QoS as desired and no any extra handoff delay may incur due
   to handoff. In other words, the QoS provision to the flow is seamless
   during the handoff, which might give great improvements to handoff
   service quality of mobile real-time services.

5 Proposed Solutions

   A flow transparent mobility support is fundamental in the above
   scheme. With Mobile IPv6 and RSVP, the natural solution to provide
   flow transparency, i.e., a unique flow identity regardless of node
   mobility, is to use MN's home address instead of its care-of address
   to identify a flow. By using MN's home address as flow identifier, we
   separate routing and QoS function in a router. The former is based on
   care-of address, reflecting the node mobility; the latter based on
   home address, without the impact of node mobility.

5.1 Requirements for Mobile IPv6

   A potential problem of using MN's home address as flow identifier
   with current Mobile IPv6 specification [2] is packet classification.

   When MN acts as sender, for packets sent by a MN, Mobile IPv6 will
   move the MN's home address in IPv6 packet header to a Home Address
   option carried in an IPv6 Destination Options Header. Since this
   header will not be examined until reaching the packet destination,
   intervening routers will not be able to correctly classify packets
   belong to the flow. Therefore, when flow transparency is required, we
   suggest that Mobile IPv6 SHOULD ignore this special processing for
   MN's home address and leave it in the IP source address field to
   enable router QoS processing. Note that this only requires
   modifications at end nodes.

   When MN acts as receiver, for packets sent to a MN, Mobile IPv6 also
   hides the MN's home address from all intermediate routers. In this
   case, however, no modification is required for Mobile IPv6 to support
   Flow Transparency due to IPv6 flow label support. In IPv6, a flow can
   be uniquely identified by the flow source and flow label, therefore
   allows the router to perform packet classification without examining

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   the flow destination. This is why the flow transparent scheme fits
   naturally in IPv6.

5.2 Requirements for RSVP

   On the RSVP side, it is more natural and convenient to use MN's home
   address instead of its care-of address, specifically,

   When MN acts as sender, the MN's home address is used as flow source
   and put in the SENDER_TEMPLATE field of RSVP Path messages, and
   subsequent Resv messages sent by the receiver will also use MN's home
   address in the FILTER_SPEC field;

   When MN acts as receiver, the MN's home address is used as flow
   destination and put in the SESSION object of RSVP messages.

   As described in the operation of the flow transparent scheme, when MN
   acts as sender, no additional RSVP signaling is needed; when MN acts
   as a receiver, however, extension to RSVP is required. MN should
   notify the Nearest Common Router of its flow identity and new
   location to enable the issuing of handoff Path message. This
   information can be encoded in a new RSVP MOBILITY object and then
   either be piggybacked in a Path message or sent alone in a newly
   defined RSVP PathReq message.

   The PathReq message has a common header followed by the objects like
   any other RSVP messages defined in Section 3.1 of RFC2005, except
   that Meg Type is given 18. Figure 2 shows the MOBILITY object.

   The length field indicates total object length in bytes. The Class
   Num for the MOBILITY object is 28. The C-Type is 2 since it is
   intended for IPv6. Following this common object header are two 128-
   bit fields, each containing an IPv6 address.

   The first address is MN's home address which serves as the flow
   destination and indicates the whole RSVP session. According to RSVP
   specification, when doing adaptation to receiver route change, which
   is actually receiver mobility in our case, a Local Repair should be
   triggered for all flows with a particular destination, regardless of
   other parameters such as flow label.  So only the MN's home address
   is required for the Nearest Common Router to decide which Path
   message to send out.  The second address in the mobility object is
   MN's current care-of address denoting the updated location of the MN.
   This address will be put in the destination address field of the
   subsequent handoff Path message sent by Nearest Common Router to
   ensure correct routing of the message to the MN. These two addresses
   are the minimum information required for the flow transparent scheme

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                   0             1              2             3
         |       Length (bytes)      |  Class-Num  |   C-Type    |
         |                                                       |
         +                                                       +
         |                                                       |
         +                   Flow Destination                    +
         |                                                       |
         +                                                       +
         |                                                       |
         |                                                       |
         +                                                       +
         |                                                       |
         +                   Current Location                    +
         |                                                       |
         +                                                       +
         |                                                       |

                         Figure 2: MOBILITY Object

   to work when MN is a receiver.

6 Security Considerations

   The solution for MN as sender could cause a problem with Ingress
   Filtering [12], which is a security measure used to defeat denial of
   Service attacks that employ IP source address spoofing. Packets
   directly using MN's home address as source address will likely to be
   dropped by the Ingress Filtering routers if they are sent from a
   foreign network. We suggest two alternative approaches to this
   problem below.

6.1 Approach I

   In this approach, when a packet is sent by MN, we still have MN's
   home address as packet source address, but we substitute current
   Mobile IPv6 special processing about MN's home address with a new
   processing about its care-of address. We define a new Care-of Address
   Option similar to the current Home Address Option in Mobile IPv6 as
   shown in figure 3.

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       0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                     |  Option Type  | Option Length |
     |                                                               |
     +                                                               +
     |                                                               |
     +                        Care-of Address                        +
     |                                                               |
     +                                                               +
     |                                                               |

                     Figure 3: Care-of Address Option

   This Care-of Address Option will then be carried as an IPv6
   Destination Options Header in each outgoing packets sent by MN
   (similar to current Mobile IPv6 specification). The remaining part is
   for Ingress Filtering mechanism to attend to this change. So the
   Ingress Filtering routers will be required to not only examine the IP
   address in the source address field, but also look for the Care-of
   Address Option before making a decision. If the care-of address
   matches the incoming interface of the packet, it SHOULD also forward
   the packet as appropriate.

   Note that in this case although the care-of address option is carried
   as a Destination Options Header, it is actually examined by an
   intermediate router - the router which performs Ingress Filtering. If
   this is seen as a confliction with the Destination Options Header
   definition, which says it carries optional information that needs to
   be examined only by a packet's destination node(s), then a new IPv6
   extension header, called Intermediate Router Options Header, may be
   defined similarly. It will have the same format as the Destination
   Options Header except for the Header Type value, and it will carry
   optional information that needs to be examined by intermediate
   routers like in this case.

6.2 Approach II

   If the current Ingress Filtering is to remain unchanged, MN will have
   to use its care-of address as source address, then modifications to

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   all intermediate routers will be required. Two alternatives are

   First: At the end nodes, the current MN Home Address Option is still
   carried in Destination Options Header, but a new Flow Transparency
   Route Alert Option carried in a Hop-by-hop Options Header may be
   inserted into the outgoing packets sent by MN to notify each
   intermediate routers the need for flow transparent handling.

   Second: At the end nodes, Mobile IPv6 may simply move the Home
   Address Option into a Hop-by-hop Options Header when flow
   transparency is required, so that all intermediate routers will have
   access to the MN's home address.

   Both of the above alternatives also require modifying intermediate
   routers to look for MN's home address at appropriate place to perform
   packet classification correctly.

6.3 Evaluation of the Two Approaches

   In the above two approaches to the Ingress Filtering problem, the
   first one might be better in terms of implementation, because it
   requires changes only in end nodes and specific routers deploying
   Ingress Filtering mechanism. In contrast, the second approach
   requires changes to all nodes and routers.

7 Scalability Considerations

   There has been wide concern over the scalability of end-to-end RSVP
   and Integrated Service (Intserv) architecture, which has led to the
   development of relatively simple and coarse methods of providing
   differentiated classes of service for Internet traffic, such as
   Differentiated Service (Diffserv). However, Intserv, RSVP and
   Diffserv may still be viewed as complementary technologies in the
   pursuit of end-to-end QoS and a framework combining Intserv/RSVP and
   Diffserv offers great benefits [13,14]. A possible architecture of
   this kind could be Diffserv deployed in the backbone or core networks
   and Intserv/RSVP in access or edge networks.  If this is the case,
   the flow transparent scheme may be viewed as a "Micro Mobile QoS"
   scheme which improves handoff QoS performance within a domain
   consists of wireless and fixed access networks, because this scheme
   can also accommodate Flow Transparency incapable clouds. Routers that
   do not understand the newly defined MOBILITY object can simply ignore
   and forward it until a capable router is reached and decides itself
   as the Nearest Common Router. To one extreme, if all routers along
   the path are flow transparency capable, each handoff will involve
   minimum routers possible. To the other extreme, if none of the
   routers in the path understand flow transparency, it goes back to the

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   normal end-to-end scheme. If some of the routers are flow
   transparency enabled, the effect will be something in between,
   depending on the specific router deployment.

8 Concluding Remarks and Future Work

   This draft proposes a Flow Transparent Mobile IPv6 and RSVP
   interworking scheme. The scheme requires the node mobility to be kept
   transparent from QoS flow handling mechanism, thus makes it possible
   to relieve the RSVP renegotiation from being performed end-to-end
   each time when the MN changes its care-of address. This could
   minimize delays and losses of the handoff QoS signaling and data
   packets. Depending on the network scenario, seamless handoff QoS
   provision might be achieved, which would further improve handoff
   performance of mobile real-time services. The scheme also illustrates
   a possible way of using the IPv6 flow label to facilitate the
   development of new protocols or mechanisms.

   The future network architecture is likely to be the Internet
   connecting with heterogeneous wireless access networks, such as
   UMTS/GPRS, Wireless LAN, Bluetooth and etc. Different access
   technologies may overlap since they possess different
   characteristics. Flow Transparency might particularly makes sense in
   the case where the MN performs a handoff at the same location, simply
   switching between subnets of different access technologies.

   It is possible that in the wireless Internet framework, the QoS
   mechanism in the access part would involve Packet Data Protocol (PDP)
   and/or RSVP, and that of the core network would include Diffserv
   and/or MPLS. Further work is required to formulate details about how
   the flow transparent scheme operates in such a framework, change of
   QoS requirements during handoff should also be considered.
   Multicasting support may be taken into account too. Furthermore, Flow
   Transparency itself might be extended from single-flow to multiple-
   flow transparency to accommodate mobility support with coarser QoS
   technologies like Diffserv.

9 Acknowledgments

   This work received Research Grant from National University of
   Singapore (NUS). We would also like to thank the following people for
   commenting, discussing or answering questions regarding early
   versions of this draft: Prof. C-C Ko, Dr. Y.M. Jiang, Dr. C.C. Foo,
   Ms. X. Shangguan and Ms. Y. Ge of NUS, Prof. C-K Toh of Georgia
   Institute of Technology, Dr. I. Curcio of Nokia, and Mr. J. Shankar
   of CWC.

10 Bibliography

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   [1] C. Perkins, "IP Mobility Support," RFC 2002 , October 1996.

   [2] D. Johnson and C. Perkins, "Mobility Support in IPv6," IETF
   Internet Draft , November 2000.  work in progress.

   [3] R. Braden, L. Zhang, S. Berson, S. Herzog, and S. Jamin,
   "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
   Specification," RFC 2205 , September 1997.

   [4] S. Deering and R. Hinden, "Internet Protocol, Version 6 (IPv6)
   Specification," RFC 2460 , December 1998.

   [5] G. Fankhauser, S. Hadjiefthymiades, N. Nikaein, and L. Stacey,
   "RSVP Support for Mobile IP Version 6 in Wireless Enviroments," Tech.
   Rep.  TIK-Report Nr. 58, Computer Engineering and Networks
   Laboratory, Swiss Federal Institute of Technology (ETH) Zurich, 1998.

   [6] G. Chiruvolu, A. Agrawal, and M. Vandenhoute, "Mobility and QoS
   Support for IPv6-based Real-time Wireless Internet Traffic," 1999
   IEEE International Conference on Communications , vol. 1, pp. 334--8,

   [7] Q. Shen, A. Lo, W. Seah, and C.C. Ko, "On Providing Flow
   Transparent Mobility Support for IPv6-based Wireless Real-time
   Services," Proceedings of the Seventh International Workshop on
   Mobile Multimedia Communications (MoMuC2000) , pp. 2B--4--1 -- 2B--4-
   --6, October 2000.

   [8] A.K. Talukdar, B.R. Badrinath, and A. Acharya, "MRSVP: A
   Reservation Protocol for an Integrated Services Packet Network with
   Mobile Hosts," Tech. Rep. DCS-TR-337, Department of Computer Science,
   Rutgers University, U.S.A., 1997.

   [9] W. Chen and L. Huang, "RSVP Mobility Support: A Signaling
   Protocol for Integrated Services Internet with Mobile Hosts,"
   Proceedings of IEEE INFOCOM 2000: Conference on Computer
   Communications , vol. 3, pp. 1283--92, 2000.

   [10] D.O. Awduche and E. Agu, "Mobile Extensions to RSVP,"
   Proceedings of Sixth International Conference on Computer
   Communications and Networks , pp. 132--6, 1997.

   [11] I. Mahadevan and K.M. Sivalingam, "An Experimental Architecture
   for Providing QoS Guarantees in Mobile Networks Using RSVP,"
   Proceedings of Ninth International Symposium on Personal, Indoor, and
   Mobile Radio Communications (PIMRC'98) , vol. 1, pp. 50--4, 1998.

   [12] P. Ferguson and D. Senie, "Ingress Filtering: Defeating Denial

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   of Service Attacks Which Employ IP Source Address Spoofing," RFC 2827
   , May 2000.

   [13] Y. Bernet, P. Ford, R. Yavatkar, F. Baker, and et al., "A
   Framework for Integrated Services Operation over Diffserv Networks,"
   RFC 2998 , November 2000.

   [14] Y. Bernet, "The Complementary Roles of RSVP and Differentiated
   Services in the Full-Service QoS Network," IEEE Communications , vol.
   38, no. 2, pp. 154--162, 2000.

11 Authors' addresses

   Qi Shen
   Centre for Wireless Communications
   National University of Singapore
   20 Science Park Road
   #02-34/37, TeleTech Park
   Singapore Science Park II
   Singapore, Singapore 117674
   Phone: +65 870-9358

   Winston Seah
   Centre for Wireless Communications
   National University of Singapore
   20 Science Park Road
   #02-34/37, TeleTech Park
   Singapore Science Park II
   Singapore, Singapore 117674
   Phone: +65 870-9163

   Anthony Lo
   Ericsson EuroLab Netherlands
   Business & Science Park
   Institutenweg 25
   P O Box 645, 7500 AP Enschede
   The Netherlands
   Phone: +31 53-450-5480

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