The objective of this paper is to study the performance of handoff procedures for an integrated wireless LAN/WAN in- frastructure, both qualitatively and ...
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➡ HIERARCHICAL HANDOFF SCHEMES OVER WIRELESS LAN/WAN NETWORKS FOR MULTIMEDIA APPLICATIONS Syed Irtiza Ali, Hayder Radha Department of Electrical & Computer Engineering Michigan State University East Lansing, MI 48824 {alisyed4, radha}@egr.msu.edu ABSTRACT
The objective of this paper is to study the performance of handoff procedures for an integrated wireless LAN/WAN infrastructure, both qualitatively and quantitatively. We make use of a proposed hierarchical mobility management scheme to evaluate the performance of a handoff procedure with a hierarchy level of one. Also, we propose a design and perform the analysis for a two-level hierarchy architecture that is applicable for integrated 802.11-based WLAN/WAN scenarios. The focus of our analysis is on performance measures that are suitable for real-time multimedia applications. In particular, we observe and analyze the improvement in handoff latencies and packet loss ratios that are obtained by employing hierarchical mobility schemes for UDP based traffic sessions under different network scenarios. We also study the scalability of the proposed schemes by evaluating the impact of the number of mobile nodes on the above performance measures.
1. INTRODUCTION The technological advancements in the wireless LAN sector and the immense usage of the Internet during the last decade braces for the demand for “all time and anywhere” mobile connectivity. This translates into a need for network domain connectivity of mobile terminals (e.g. laptops, Mobile phones, Palm pilots etc), while moving from one access point to another. A sizeable amount of research has concentrated on identifying and incorporating a feasible mobility-framework. This has resulted into development of different mobility management schemes. Mobile IP [1], an example of such a scheme, introduced the mobility feature in Internet Protocol ver. 4 (IPv4). (It is worth remembering that IPv4 was originally developed for wired infrastructures.) The reliability of the process of “Hand-Off Registration,” plays an important role in maintaining a quality connection with the network terminals. In such a process, the Mobile Node (MN) on powering up, registers itself with a designated (or available) base station, known as a Home Agent (HA), and consequently, the HA assigns an IP address to the MN. On
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entering a new domain, in order to stay connected with the network, the MN tries to establish a connection with a new base station, known as Foreign Agent (FA). It also requests the new FA to provide a new IP Address termed as Care of Address (CoA). At this juncture, the MN needs to update the HA, with network information of the new access point (AP). The reliability of the Handoff procedure is critical for TCP based services, whereas low Handoff Latency (HoL) and reduced Packet loss ratio (PLR) are important parameters for UDP based multimedia services. The growing number of mobile users and evolution of network architectures from the Micro-cell to Pico-cell have necessitated further research of mobility at the two distinct levels. These levels are Global (Inter) Domain) Mobility Level (GML) and Local (Intra Domain) Mobility level. The local mobility level (LML) can be considered as the movement of mobile user at corporate environments like offices, markets and airports. On the other hand, the mobility of mobile user from one local mobility level scenario to another is termed as GML. The problem of mobility management has been addressed numerous times in the literature. The efforts like Cellular IP [2], Hawaii [3], a Hierarchical Mobile IP[4], and EMA1[5] dealt effectively with the aforementioned issues at local mobility level. Tele MIP [6] approached the Mobility issue in IP base wireless networks at GML. Most of these schemes consider Mobile IP as a strong contender for Global Mobility Management. On the contrary, the recent developments highlight the need to re-investigate the performance aspects in the integrated Wireless LAN/WAN scenarios. Implementations that are based on integrating cost-effective IEEE WLAN standard 802.11b solutions at the LML and the utilization of existing WAN infrastructure at GML have been recommended ([10],[11]). This paper presents and analyzes a hierarchical handoff scheme to manage mobility in the aforementioned WLAN/WAN scenario. The Handoff Latency (HoL) and Packet-Loss-Ratio (PLR) in the context of scalability (in terms of the number of mobile nodes that are supported) are the target performance measures. The rest of the paper is organized as follows: Section 2 discusses some general topologies and handoff procedures. Section 3 takes a look at the experimental setup for 1
Edge Mobility Architecture was proposed to deal with scalability.
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➡ evaluating the proposed hierarchical scheme. The corresponding simulation results are discussed in Section 4. This section also compares the performance of the proposed hand off scheme with Standard Mobile IP. Finally, in section 5 we summarize the key conclusions of this paper and discuss some future directions for the presented work.
are intended to evaluate the influence of increased number of nodes and changing levels of hierarchy on the performance measures mentioned earlier.
C la s s ic a l w ir e d N e tw o rk CAP
2. METHODOLOGY
In te rn e t
In general, the handoff registration process in any IP-based network is carried out either by any of the mobile network entities (HA, FA, routers e.t.c.) or by the MN itself. Lower handoff latencies are observed when the handoff decisions are initiated by the MN {[12], [2]}. The next sub-section discusses the system topologies that are associated with the proposed handoff schemes. This is followed by the description of the proposed hierarchical mobility management and related registration procedure.
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In te r D o m a in B ackbone W AN
W LAN 8 0 2 .1 1
W LAN 8 0 2 .1 1 DAP
DAP
CAP AP4 AP5
AP1 M N1
AP6
AP3
AP2
Figure 2 Two-level Hierarchy
2.1. Hierarchical Topologies Figure 1 depicts a high-level scenario for an integrated Wireless LAN/WAN architecture at hierarchy of level one. The various IEEE 802.11 based AP’s are connected to a common Domain Access Point (DAP) in a hierarchical manner. A similar scheme has been proposed in [4].
C la s s ic a l w ir e d N e tw o rk
W LAN 8 0 2 .1 1
GAP
W LAN 8 0 2 .1 1
In te rn e t GAP
DAP
DAP AP1 MN1
AP3
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AP4 I n te r D o m a in B ackbone W AN
AP6 AP5
Figure 1 One-level Hierarchy
The DAP is subsequently connected to Gateway Access point (GAP), which provides an access to Internet services for all the nodes in the corresponding network domain. Two or more GAP’s are connected through Inter-Domain Backbone (i.e WAN infrastructure). Movement of a MN from one GAP domain to another is considered as ”Global Mobility”. On the contrary, movement of a MN within a domain which is administered by the same DAP is termed as the “Local Mobility”. In this paper, we consider higher order of hierarchy. The Figure 2 illustrates the scenario with hierarchy at level two. In this case, Corresponding Access point (CAP) is used to connect two or more DAP. CAP is then connected to a GAP, with the same functionality as previously mentioned. The adoption of a hierarchical scheme is beneficial once we increase the number of nodes in the certain domain. However, this increases the complexity associated with the mobility management protocol. The simulations performed in the later section
The next subsection illustrates the algorithm used to manage the mobility of the MN from one domain to other.
2.2. Handoff Protocol During mobility, the MN comes across the region where it ends up receiving the advertisement signals from different 802.11 Access Points (AP). The MN decides if there is a need to initiate the handoff by comparing the strength (C/I ratio)2 of the received signals. This comparison is done on the basis of a pre specified table3. This kind of scheme is generally, adaptive to varying link conditions. The following exchange of messages takes place once MN decides to carry out the handoff. Figure 3 illustrates the listed procedure. 1. The MN requests the new AP to provide a new IP address. 2. The new AP replies back with the required information. 3. MN attempts to update the (original) designated AP4 with obtained information through Binding Update (BU) message. In addition, MN requests the previous AP to discontinue sending the IP traffic with a defined time Stamp. 4. a. In standard MIP, the HA replies back with an acknowledgement to BU. Once the MN receives this reply, it requests the previous AP to release the buffered traffic. This concludes the Handoff process. b. However, employing the procedure proposed in [4], the MN now sends a BU message to the newly connected AP through DAP. 5. DAP matches the information with listed routing table. This results in two possibilities, whether designated AP belongs to same domain or to a foreign domain.
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Signal Carrier to Interference Ratio The table is based on Bit Error Rate (BER) scheme employing BPSK or QPSK modulation schemes. 4 Considered as HA in Standard Mobile IP. 3
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➡ a. In case 1 where the MN belongs to the same domain, DAP will reply back with BU acknowledgement instead of the designated AP. This saves the messaging and the processing time that would be required otherwise. b. In case 2, where the designated AP belongs to the foreign domain, DAP will utilize the defined routing protocol to look for the designated AP. Having done this, the procedure stated in 4.a will be followed to conclude the handoff. Two-Level Hierarchy One-Level Hierarchy 1
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bile nodes are distributed randomly in the network domain.
4. PERFORMANCE ANALYSIS To perform our analyses, a MN is subjected to two types of movement. At first the MN moves from AP1 to AP3, this is considered as LML. In the second type, the MN is moving from AP1 to AP4, to be considered as GML. The following analyses are performed to compare the effect of the hierarchical schemes with the mechanism defined for standard Mobile IP.
4.1. Scalability and Handoff Latency 6
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Hand-Off Latency (HOL) is defined as: HOL = RLD (ms) + ROMT (ms) 1000 900 800 700 600 500 400 300 200 100 0
Figure 3 Handoff Procedure
The above procedure is appropriate for a hierarchy at level one. The following steps are required for hierarchy of twolevels. Now, two or more DAP’s are connected to the Corresponding Access Point (CAP) as shown in Figure 2. 7. On receiving the BU from a MN, DAP forwards the received message to CAP. CAP then again matches the routing table entries with the two possibilities, either the designated AP of the MN is in the same domain or not. 8. a. In case 1 it belongs to the same domain, CAP replies to the MN with the acknowledgement to BU. This completes the Handoff registration process by saving messaging and processing time. b. In case 2, the well-defined routing protocol is utilized to forward the message to the designated AP. It is then followed by the procedure stated in 4.a to conclude the handoff procedure.
… (4-I).
One-Level Hieararchy Two Level Hierarchy STD-MIP
Handoff Latency (ms)
6.
Performance Degradation
10 20 30 40 50 60 70 80 90 100110120130 Number of Mobile Nodes
Figure 4 Movement of MN1 from AP1 to AP3 Hand Off latency (ms)
1200 1100 1000 900 800 700 600 500 400 300 200 100 0
3. EXPERIMENTAL SETUP
One-Level Hierarchy Two Level Hierarchy Standard MIP
*Performance Degradation
*PD
10 20 30 40 50 60 70 80 90 100110120130 Number of Mobile Nodes
The scenarios depicted in Figure 1 and Figure 2 is evaluated using simulator “GloMoSim”. Initially it was developed to analyze the Mobile Adhoc Networks. However, the availability of the extension Mobile IP [9] and flexibility to modify the original source code makes it possible to simulate the integrated wireless/wired topologies described above. In the experiments performed, the MN is subjected to communicate with the other terminals in the network domain. This is achieved by replicating UDP (Constant bit rate (CBR) for the ongoing discussion scenario) based multimedia services5 at different simulation times, between the subjected MN and other terminals in the network. The link delay of 4ms is kept throughout network. The data rate of the wireless channel is set at 2Mbps while the data rate for wired links are set at 1.544Mbps. The IP packet size is set to 512. Moreover, to simulate a practical scenario, all Mobile Nodes (MN’s) in the domain are subjected to a random walk motion. Also, the Mo5
Like Constant bit rate (CBR) and Varying bit rate services.
Figure 5 Movement of MN1 from AP1 to AP4
Where RLD is Radio link delay and ROMT is round messaging time that includes processing & messaging time from start of hand-off procedure until packets are released from previous AP. The above figure shows the effect of increasing number of mobile nodes on the handoff latency (ms). In general, it can be observed that as the number of mobile nodes increases, there is an increase in HoL for both the hierarchical and standard Mobile IP schemes. However, and over a large range, the HoL of the proposed scheme is better than the standard MIP. We can observe an improvement of about 20-25%. A rather dramatic increase in performance degradation is observable at a very high number of mobile nodes. Nevertheless, the change in slope for the proposed schema is much less than level of increase in degradation for the standard MIP. Although both, the one-level and two-level hierarchy based solutions are showing a very close HoL performance numbers, we will see below that at higher level of hierarchy, it is possi-
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➠ ble to manage more number of mobile nodes while maintaining smaller packet loss rations. Thus, making the proposed solution more scalable.
4.2. Packet Loss Ratio and Mobility Speed.
Packet Loss Ratio
Packet Loss Ratio (PLR) is the number of packets that fails to reach at the destination point. It is defined as: PLR = (PT - PR)/PT x 100 … (4-II) Where PT represents the number of transmitted packets while PR represents the received packets. For this scenario, the domain under consideration is densely populated with MN’s. The speed of the subjected MN1 is being varied from 1m/s to 10m/s at regular interval during the movement of MN1 at two different levels. 7 6 5 4 3 2 1 0
6. REFERENCES [1] C. Perkins, “IP Mobility Support for IPv4,” IETF RFC 3344, August 2002.
[2] A. T Campbell, J. Gomez, S. Kim, A. G. Valko, C-Y. WAN,
STD-MIP One-level Hierarchy Two-level Hierarchy
and Z. Turanyi, “Design, implementation, and evaluation of Cellular IP,” IEEE Personal Communication. Mag., vol. 7, no. 4, August 2000.
[3] R. Ramjee. T.L. Porta, S. Thuel, K. Varadhan, and S.Y. Wang, “HAWAII: A domain-based approach for supporting mobility in wide-area wireless networks, “ in IEEE intl. Conf. on Network Protocols (ICNP’99), Toronto, Canada, Nov. 1999. 1
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4 5 6 7 8 Mobility Speed (m/s)
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[4] Eva. Gustafsson, Anika. Jonsson, Charles. E. Perkins,
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“MIPv4 Regional Registration”, IETF Internet draft, work in progress, October 2002.
Figure 6 Movement of MN1 from AP1 to AP3
[5] A. O’Neill and S. Corson, “An approach to Fixed/Mobile
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nodes, modifications in the standard MIP procedure could facilitate an improvement in connectivity for multimedia services. As part of our future work, we intend to develop a model that should be helpful in analyzing the performance of the hierarchical based wireless networks at higher levels. An intelligent mobility agent can be helpful in the prediction of the MN in advance. This possibility shall also be explored. This could considerably reduce the time that is required to complete the handoff registration process.
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Converged Routing,” Technical Report TR-2000-5, University of Maryland, Institute for System Research, March 2000.
STD-MIP One level Hierarchy Two level Hierarchy
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[6] A. Misra, S. Das, A. Dutta et al, “TeleMIP: An intra-domain
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mobility architecture for next generation wireless networks,” in IPCN 2000, Paris, France, May 2000
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[7] A. T. Campbell and J. Gomez, “IP Micro-Mobility Protocols,” ACM SIGMOBILE, Mobile Comp. and Commun. Rev., vol. 4, no. 4, Oct. 2001, pp. 45-54.
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3
4 5 6 7 8 Mobility Speed (m/s)
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[8] Tan, CL, S Pink and KM Lye, “A fast Handoff Scheme for
Figure 7 Movement of MN1 from AP1 to AP4
The above results depict the fact that PLR increases with increase in the mobility speed. However, using hierarchal approach shows an improvement in the PLR factor. Consequently, the proposed hierarchical framework makes possible to achieve rapid handoff while reducing the PLR experienced by the MN.
5. CONCLUSIONS AND FUTURE DIRECTIONS
Wireless Networks,” 2nd ACM International Workshop on Wireless Mobile Multimedia, 20 Aug 1999, Washington, USA.
[9] http://pcl.cs.ucla.edu/projects/glomosim/models.html. [10] S. Helal, C. Lee, Y. Zhang, G. G. Richard III, “An Architecture for Wireless LAN/WAN Integration,” Proceedings of the IEEE Wireless Communications and Networking Conference, (WCNC 2000).
[11] ACM SIGCOMM Computer Communication (CCR), “Spe-
In this paper, the performance of hierarchical handoff schemes in an integrated Wireless LAN/WAN topology has been evaluated. We observed that scalability issues could be dealt effectively by making use of a hierarchical approach in such integrated WLAN/WAN environments that are based on 802.11 solutions. It was also observed that at a higher level of hierarchy, the number of mobile nodes at the LML could be increased and are limited only by the existing physical layer standards. It was also shown that for faster moving mobile
cial Issue on Wireless Extensions to the Internet,” Guest Editors, Andrew T. Campbell and Mischa Schwartz, October 2001.
[12] M. Kounavis, A. T. Campbell, G. Hito and G. Bianchi "Design, Implementation and Evaluation of Programmable Handoff in Mobile Networks," ACM Journal on Mobile Networks and Applications (MONET), Special Issue on Mobile Multimedia Communications, Vol. 6, No. 5, pp. 443-461, September 2001.
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