Can Mobile Ip Be Used As a Link Between Imt 2000 Technologies and Operators

CAN MOBILE IP BE USED AS A LINK BETWEEN IMT 2000 TECHNOLOGIES AND OPERATORS?

M. Kraner, C.N. Yap, S. Cvetkovic, Erika Sanchez

Department of Electronic and Electrical Engineering, University of Sheffield, UK

ABSTRACT conference with data and video support of different streaming sources etc. IMT 2000 technologies provide IP based services to cellular telephones. Network operators are consequently This can gradually lead to a situation in which offering data services comparable to Internet Service network operators become wireless Internet Service Providers. A rising issue is to provide interoperability Providers. On the other side it is imaginable that between the technologies and between the different Internet Service Providers will offer Cellular contracts providers. A possible candidate suggested by 3GPP and with different network operators. It might even be 3 GPP2 is Mobile IP. possible that “micro cellular” network operators will offer services around their premises to everybody The major decision point whether or not Mobile IP passing their cell that is linked to the Internet. is suitable is the performance of handoffs between Consequently solutions are required which allow hand- different networks. The paper therefore studies the offs between different wireless ISPs with the capability performance delay for TCP, UDP and suggests an to be scaled down to the size of one wireless cell with a enhanced Mobile Internet Protocol since MIP proved to range of less than 100m (see Figure 1) be unsuitable. IIP is using strong cell switching and avoids tunnelling. It therefore performs superior to Figure 1: Hand-off between 2 network operators Mobile IP. While Mobile IP performs handoffs with an end-to-end delay for TCP within seconds and UDP Internetworking traffic in average in about 500ms IIP allows handoff to Home Agent End Host be performed below 100 ms.

Finally a solution is suggested to avoid handoffs. Radio Network PDSN 1 PDSN 2 Radio Network The solution would allow Mobile IP to be deployed even for interactive real time applications such as IP based telephony. However the solution is in work in progress state. Mobile Station Mobile Station Ideally the hand-off event should not cause service interruption and should support different technologies INTRODUCTION and protocols. In the context of the Internet Protocol (IP) hand-off means transgression between two different The first IMT 2000 standards are emerging and the sub-networks with the consequence that hosts are not first UMTS licenses are auctioned in the UK. In about anymore visible in the new sub-network unless the host two years the mobile user will face a variety of will be reconfigured or the new sub-network or the host providers offering services based on analogue wireless supports a IP enhancement providing mobility support, systems, GSM (900 and 1800) and UMTS. The such as Mobile IP. But also hand-off between sub- providers are facing increasing competition and networks results in different transmission paths with consequently will steadily offer more services such as different transmission characteristics. The different data services beyond a diversity of plain telephony and delay or caused data-loss might be interpreted in upper messaging services. layer protocols in different ways and might lead to transmission throughput degradation. Protocols like Schulzrinne et al. [0] shows a scenario on how TCP would assume congestion and throttle down the future telephony integrates with data services using the traffic. Internet. Telephony on packet-based networks may offer services such as dialling to different telephones of The capability to perform hand-offs without service one user in a multicast way. The user just picks the interruption is the decision point, which can prevent the communication device, which is most convenient and usage of Mobile IP as link technology between IMT commences as a member of a multipoint telephone 2000 technologies and network operators. The paper reviews hand-off results of Mobile IP and IIP and the influence on TCP and UDP protocols. Furthermore it reports on work in progress, which aims at seamless and interruption free hand-offs. Foreign Agent Foreign Agent Subnet C Subnet B MOBILE IP

Mobile Node Mobile Node In 1996 Mobile IP was proposed [0] as an Correspondent Node enhancement of IP to provide support for mobility in contrary to portability. Portability requirements are Mobile Node provided with DHCP [0], which allows setting of new Home Agent parameters within a network segment during the booting Subnet A process of a host. Mobility tries to avoid the reconfiguration of a host while moving between different networks. Mobile IP requires new network elements and specifies a protocol for the interaction of Figure 2: Test-bed for TCP performance of a MIP the new components and the host. Very briefly the new handoff components and notions are Mobile Node, Measurements of TCP performance on an early Correspondent Node, Home Agent, Foreign Agent. As implementation of Mobile IP demonstrate the depicted in Figure 1 the Mobile Station (Mobile Node) degradation of performance of TCP during a hand-off. moves between two operators with different IP Figure n presents the results for the case of eager cell networks. Any end host (Correspondent Node) switching with a service interruption of about 7.7s of communicating with the mobile node still addresses the which 5 s are due to TCP congestion control packets with the mobile node’s address. Since the mechanism. UDP would therefore see an interruption mobile node has changed the network the data packets interval of about 2.7s [0]. Eager cell switching can’t reach the destination and thus the home agent represents the motion detection technology, which pretends to be the Mobile Node, intercepts the traffic allows the quickest hand-off and therefore represents and tunnels it to the foreign agent, which “de- the best case aside from using strong cell switching capsulates” the packet and relays it to the Mobile Node. methods, which MIP currently does not support. The Periodic advertisements between the Mobile Node and analysis presented in [0] and depicted in Figure n show Home and Foreign Agents and the usage of the Address that theoretically the handoff can be finished in 500ms, Resolution Protocol (ARP) facilitate the hand-off which is a forth of the measured value stated before. process. There are different methods, which allow detecting the movement of the Mobile Node from one lost advertisments network to another one. Eager cell switching assumes a A x movement as soon as the mobile node receives y z advertisements of a different network. Lazy cell 0 Time switching waits until three advertisements have timed B x out and changes to the new network’s advertisement thereafter. Prefix cell switching differs in that it uses the Figure 3: Event diagram for eager cell switching network prefix of the IP address to determine the location of the Mobile Node. Another different The delay is the mean elapsed time in which the technology is called strong cell switching and is based advertisement of the new sub network B can be on beacons provided from Data Link Layer protocols expected. Therefore x/2 represents the expected mean indicating the movement to the Transport Layer delay for movement detection with x denoting the Protocol Mobile IP. advertisement period of 1s and y representing the offset value at which the movement takes place. TCP PERFORMANCE OF MOBILE IP DUE TO HAND-OFFS However the delay of 500 ms as best case is not acceptable for real-time applications such as telephony, The measurements are based on an experimental set- which expect end-to-end delays below 300ms. up using standard PC in which the mobile node is Additionally eager cell switching can lead to equipped with two network interface cards. The handoff oscillations when the mobile node frequently moves is performed with switching the data transmission from between the same cells with the effect of small TCP one network card to the other, which is connected to a transmission windows and poor performance. different sub-network (see Figure 2) [0]. Consequently MIP is not suitable to be used for 3rd Generation cellular systems unless it is optimised for these systems. Reg (CoLA) MOBILE IP USING STRONG CELL SWITCHING MOVEMENT Ack DETECTION Periodicly this is redone Query Add (CN) Ack (CoLA) One optimisation is to study the influence of the Data without tunneling movement detection method and to identify the possible mobile node moved Data loss gain if strong cell switching were used. An experiment Binding update Reg ( New CoLA) therefore has been set up to explore the influence of the Ack different type of movement detection method. In Periodicly this is redone addition the experiment should provide UDP Correspondent Base hOme Mobile Node in Mobile Node in measurements on Mobile IP since UDP is important for Node ReGister Subnet A Subnet B IP telephony. Figure 4 shows the measured result.

Mobile Internet Protocol 42 Figure 5: IIP timeline

36 Major differences to Mobile IP are the lack of data r e

m encapsulation for tunnelling and the avoidance of u N

e 24 c triangular routing. Consequently the ratio between n e u

q 18 header and transported data is better than with MIP and e S

e data transmission through firewalls is not prevented as it k

c 12 a

P would be with the source routing characteristics of 6 Mobile IP. The imposed delay for ingress routing using 0 the foreign agent to pass firewalls can be saved. The 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 Time (seconds) performance of IIP in respect of handoffs is mainly tH t t R P dependent on the DHCP service of the network tF Figure 4: IIP handoff using eager cell switching segments into which the Mobile Node migrates and from which it obtains its new IP address. The movement detection method eager cell switching required tH-tR=720ms, which is about 220ms The handoff delay was measured on an experiment slower as the theoretical mean value. The time required consisting of 3 Intel Pentium based PCs with Windows for registration request tR and registration reply tP until 2000 operation system installed. The measurement was the handoff was finished tF took 150ms. Consequently taken on a separate PC with a public domain version of Mobile IP could improve the handoff performance TCP Dump. The computers were equipped with 64 drastically to 150ms if strong cell switching movement Mbytes of RAM. The set-up deliberately was based on detection were used. almost minimum requirements in order to get conservative results, i.e. computers with higher IIP – ITINERANT INTERNET PROTOCOL specifications and carefully selected software components could improve the speed of the handoff. The handoff event was initiated alike the experiment for IIP is an enhanced version of Mobile IP optimised MIP as described above. The mobile node switched for Wireless Networks using Home Location Registries from one network interface to a second one configured (HLR) and Strong Cell Switching movement detection with other network parameters [0]. The test data method. The design is based on the suggestion of Jain consists of a UDP stream with a rate of 25ms and a [0]. The protocol uses as entities Mobile Nodes, Home packet size of 200 octets. Location Registries and Correspondent Nodes. It assumes that all Nodes are mobility enabled, i.e. all Figure 6 depicts a typical measurement for UDP nodes have an IIP compliant mobility protocol stack. based traffic using IIP. The functionality described in brief: A Correspondent Node first queries the Home Location Registry and Itinerant Internet Protocol obtains the IP address of the Mobile Node at its current 48 location. Further traffic is directly addressed to the 42 r

Mobile Node. The Mobile Node informs the b m u communication partner and the Home Location register N 30

e c n whenever it moves between networks. Movement is e 24 u q e

detected via a beacon provided by the data link layer of S 18 t e k the used transport technology. Figure 5 depicts the c a 12 protocol timeline [0]. P 6

0 0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 Time (Seconds) Figure 6: IIP handoff using UDP The handoff is completed within 69ms and is Agent 1 (PFA1) would for a short period of time, i.e. therefore suitable for IP telephony. Analysis of this time while the mobile node is within the interception area of period revealed that the DHCP process takes about 9ms, both Base Stations, multicast the data traffic to both the binding update about 20ms and the update of the Foreign Agents 11 and 12. Due to eager cell switching routing table about 40ms. Therefore the remaining movement detection and lazy cell switching based budget for end-to-end delay suitable for IP telephony connection abundance the mobile node would switch to would be about 231ms. the new cell once it receives advertisements but still have bindings to both networks in place. In the current SEAMLESS HANDOFFS base station the mobile node would receive agent advertisements of FA12 and FA3 and would establish a binding with both. Moving to the Base Station of Although the optimisations of Mobile IP allows the Foreign Agent 4 would represent a handoff between usage for real-time applications the remaining time with networks, which requires the Top Proxy Foreign Agent service interruption can still cause problems with (TPFA) common to both Foreign Agents 3 and 4 to protocols such as TCP. The service interruption of multicast the traffic. The movement between Base several seconds can be of an order in which the mobile Stations attached directly to TPFA or a Foreign Agent host is able to pass several cells. In this case even and both representing a network directly linked to the session interruptions are imaginable. Consequently Internet until now would still represent a service either TCP needs to be adjusted to the requirements of interruption unless the Mobile Node would not be able wireless systems or handoffs need to be avoided. to store the whole hierarchical order of Proxy Agents in lists and it would not be able to accept multiple One solution to enable seamless handoffs suggests a bindings. However another mechanism would still be structural improvement, which allows movement required. The Home Agent would need to be informed predictions based on multicast of data traffic to all and needed to store the information about the Mobile possible cells the Mobile Node might move to [0]. Node being in the interception area of two different networks. Consequently the Home Agent needs to FAST HANDOFF METHOD FOR REAL-TIME TRAFFIC OVER tunnel the data traffic to both entities, i.e. TPFAs or SCALABLE MOBILE IP NETWORKS FA6.

The proposed Fast Handoff Method suggests a Further study is required to explore the performance hierarchical order of Proxy Foreign Agents (PFA) and of notification while the Mobile Node is in the multicasting of traffic when mobile nodes move interception area of Base Stations of several TPFAs. between cells. Mobile nodes hold multiple bindings to Another area subject to further investigation is the Foreign Agents (FA) and receive traffic from both Base roaming stability and oscillation likelihood if multiple Stations (BS) for a short time[0]. Figure 7 presents a Foreign Agents share one Base Station. Oscillations are possible structure. possible since the Mobile Node accepts bindings from any Foreign Agent representing a different network. The Mobile Node is required to eager switch between networks and to lazy release the binding to the network, TPFA which it is leaving. In case of a shared Base Station it TPFA consequently would assume continuous movement between two networks. Also open for research is the PFA1 FA6 solution for Mobile IP systems without Foreign Agent and for IIP. FA11 FA12 FA3 FA4 FA5

CONCLUSIONS BS BS BS BS BS BS BS BS Handoffs between different networks have been identified as a knock out factor in order to investigate the feasibility of the usage of Mobile IP for IMT 2000 Figure 7: Fast Handoff Hierarchy based technologies. Plain Mobile IP has been studied and the measured handoff delays showed that it is not The movement of a mobile node between wireless suitable for real time applications such as IP based cells of base stations are handled by link layer telephony services. The results obtained for eager cell technologies, which is transparent to the IP layer. switching movement detection method was about Handoffs between cells only occur when sub-networks 720ms. Even the theoretical mean value of 500 ms are passed. If the Mobile Node passed the Base Station would not be acceptable according to the widely of Foreign Agent 11 (FA11) to Foreign Agent 12 accepted threshold of 300ms. In case of TCP based (FA12) and both represented a different network a applications the short interruption could build up to a handoff would occur. In this case the Proxy Foreign service interruption of several seconds due to the inbuilt congestion and flow control mechanisms. Additionally AUTHORS the transmission throughput would decrease remarkably. Consequently Mobile IP would not even be satisfactory to users for elastic applications in respect of Quality of Prof. Srba Cvetkovic was born Service requirements. in Yugoslavia. He is currently the professor and head of The main part of the delay is caused by the Mobile Communications Research Group at the movement detection, which could be improved using Departments of Electrical strong cell switching based on Link Layer beacons. Engineering / Computer Science, University of Sheffield. For this purpose Mobile IP was enhanced to IIP He gained his BSc (1983, City University, London) and PhD protocol, which proved to be suitable for real time (1987, University College London) degrees in Electronic interactive data services since the delay below 100 ms Engineering. He held academic posts at Surrey (1987) and were measured. However it still suffers from service Brunel (1992) Universities, before joining the University of interruptions, which TCP would interpret as congestion. Sheffield in 1995. His research interests are mobile communications. He is an Honorary Member of Eta-Kappa- In order to prevent handoffs a Fast Handoff Method Nu Association in the USA and a Member of the Institution of was introduced which has been published as an Internet Electrical Engineers in the UK. He can be contacted at: [email protected] (100 words) draft and therefore represents work in progress. The Fast Handoff Method assumes hierarchically structured Matthias Kraner born in Germany Foreign Agents and traffic multicasting while the gained his Dipl.- Ing. Mobile Node is in an interception are of base stations of University in Electrical Engineering different networks. Several issues are open for future and Information Technology. research. Among these are roaming stability for Mobile (Technical University of Munich, Nodes in shared Base Stations and performance of the Germany, 1992), and an MSc. In notification of the Home Agent if the handoff would Data Communications (Brunel University, London, UK in take place between two Top Level Proxy Foreign 1995). After running a consultancy firm and a company for soft and hardware solution for 5 years Mr. Kraner joined the Agents (TPFA). Department of Computer Science at the University of Sheffield in 1998. His research interests are network REFERENCES: architectures, QoS for mobile communication systems, virtual environments for healthcare and education. Mr Kraner is [0] H. Schulzrinne, J. Rosenberg, "The IETF Internet Member of the Chamber of Engineers in Baden- Württemberg, Telephony Architecture and Protocols", May/June 1999, IEEE Germany. He can be contacted at Network, pp 18 - 23 [email protected] (98 words) [0] C. Perkins, “IP Mobility Support (MIP)”, Request For Comment 2002, Oct 1996, http://www.ietf.org Erika Sánchez was born in Mexico. [0] R. Droms, “Dynamic Host Configuration Protocol”, In 1996 she obtained a First Degree Request for Comments 2131, March 1997, http://www.ietf.org in Computer Systems Engineering [0] N. A. Fikouras, K. El Malki, S.R. Cvetkovic, C. (ITESM CEM, Mexico), later she Smythe, “Performance of TCP and UDP during Mobile IP gained a Masters Degree in Handoffs in Single-Agent Subnetworks”, Proceedings IEEE Computer Science in 1998 (ITESM WCNC ’99 (Wireless Communication Networks Conference, CEM, Mexico). While studying she held a position as an New Orleans), September 1999. academic in the ITESM CEM. In 1999 she began her PhD [0] N. A. Fikouras, K. El Malki, S.R. Cvetkovic, M. studies in the Mobile Communications Research Group at the Kraner, “Performance Analysis of Mobile IP handoffs”, Department of Computer Science in the University of Proceedings IEEE APMC ’99 (Asia Pacific Microwave Sheffield. Her research interests are network security and Conference, Singapore), December 1999. programming languages. She can be contacted at [0] Jain, Ravi, Enhancing Survivability of Mobile Internet [email protected] Access Using Mobile IP with Location Register, IEEE Transaction on Networking, Mar 1999 Chern Nam Yap was born in [0] S.R. Cvetkovic, C. N. Yap, N. A. Fikouras and M. Singapore. In 1994 he obtained a Kraner, “Novel and Enhanced Mobile Internet Protocol for Degree in Mechatronics and a BSc in Third Generation Cellular Environments Compared to MIP Computing and Information Systems. and MIP-LR”, 28.3.2000, IEE International Conference in 3G From 1997 and 1998 he was working Mobile Communication Technologies 2000. with EDNOVATION on VRML on [0] Chern Nam Yap, “Itinerant Internet Protocol”, Master Education. In 1999 he finished his MSc(Res) working on MIP in Research Dissertation 1999, University of Sheffield, and IIP and is reading for his PhD since then. Currently he is Department of Computer Science, Regent Court, 211 researching into mobility performance issues of concurrent Portobello Street, Sheffield S1 4DP, UK mobile systems. He can be contacted at [email protected] [0] K. El Malki, N. A. Fikouras, S. Cvetkovic, “Fast Handoff Methods for Real-Time Traffic over Scalable Mobile IP Networks”, June 1999, Internet Draft – work in progress, http://www.ietf.org