Handover Latency Analysis of Mobility Management Protocols in all-IP Networks

Deepak Kumar Panwar

RD001/NGN CSU, TechMahindra Ltd Pune (MH), India

deepakdeeppanwar@gmail.com

Shyam Lal Dept. of E & C Engg.,

Moradabad Institute of Technology Moradabad(UP)-India

shyam_rao24@rediffmail.com

Ila Chaudhary Dept. of E & C Engg.,

Nemi Chand College of Engg, Panipat(HR)-India

er.ilachaudhary@gmail.com

Abstract- The future generation wireless systems target to provide users with high-speed Internet access and multimedia services besides voice. Mobile IP was developed to provide the freedom of mobility to the users with continuous network access. MIPv6 is the grown up version of Mobile IP and eliminates the problem associated with address space of IPv4 and gives extra bit of inherent security (IPSec). To minimize the high location update traffic induced by the frequent location changes, HMIPv6 was introduced with a new agent node called MAP (Mobility Anchor Point). HMIPv6 classifies mobility into global and local mobility and hence reduces the registration traffic flow into the network. This paper presents simulation based performance evaluation and comparison of mobility management protocols in all-IP Networks. The metric which we have used to compare the performance of mobility management protocol is handover latency. Handover latency is an important factor while transferring the call to new access area. We have analyzed the handover latency of MIPv6 and HMIPv6 protocols as a function of MAP domain size. The numerical results are obtained by simulating pico-cellular environments and graphically shown here. We have shown that HMIPv6 does not always outperforms MIPv6 in terms of handover latency and needs optimization techniques for Movement Detection and DAD procedure to shorten this delay. Keywords- Mobility management, MIPv6, HMIPv6, Handover latency.

I. INTRODUCTION In recent years, wireless communication technology has undergone a tremendous change. Since the advent of the Third Generation Partnership Project (3GPP) proposal for a 3GPP-WLAN internetworking architecture, the 4G mobile system appeared on the horizon. Since 3G networks basically evolved from a circuit-switched cellular network, they have their own gateways to interpret Internet Protocol (IP) from the backbone network. They also have their own protocols and interfaces for the communication within themselves. To overcome these problems, it is expected that next generation networks will have a packet-switched simple structure based on all-IP where Internet Protocol (IP) packets traverse an access network and a backbone network without any protocol conversion [1, 2, 3]. Mobile IP (or MIPv4) was developed to provide the freedom of mobility to a user while seamlessly accessing the network resources. IETF further enhanced this protocol to MIPv6 to overcome the exhaustive communication process and integrate the pros of IPv6, e.g., huge address space (theoretically, thousands of IP addresses per square meter on earth) and enhanced routing and security features[4]. Each Mobile Node (MN) is assigned a home address on its home network. This address remains the same irrespective of the actual location of the MN. When an MN leaves its home network and enters a foreign network, it sends its location information to its Home Agent (a router on the home network). This agent keeps the track of the MN’s current location through temporary address in foreign network, known as Care

of Address (CoA). This new IP address can be statefull or stateless IPv6 address. MIPv6 enable node can auto-configure the node address and sends it back to the Home Agent (HA), eliminating the need of Foreign Agent (FA) in the new network and consequently reduces the overhead on network router node[5,6]. But MIPv6 is designed for the global or macro-mobility scenarios and not suitable for the environment where MNs change their location very frequently and induce a significant volume of traffic of binding update packets destined to HA/CN causing the latency in delivery resulting in traffic loss. To reduce the frequent location changes, it is devised to have a cluster of cells differentiating local and global mobility [7, 8]. The movement within the cluster is considered as local and binding update for this movement is sent to a controlling node within the local domain instead of HA. This new protocol is christened as Hierarchical MIPv6 by IETF and the new controlling node introduced in local domain with enhanced responsibility of Access Router (AR) is known as Mobility Anchor Point (MAP). The binding update packets reach at HA only when MN moves from one cluster or MAP domain to another. In spite these evolutions in mobility management protocols, provisioning the seamless handover is still a challenging work and attracts the researchers. There is a lot of research being carried out to reduce the signaling traffic flow in IPv6 wireless networks. It has been shown qualitatively and analytically that HMIPv6 beats MIPv6 in terms of signaling performance. This is because of the discrimination in local and global mobility by MAP. However, the handover latency of mobility management protocols is somehow not taken into consideration. In this work, we have analyzed the latency of HMIPv6 against MIPv6 in a pico-cellular environment with and without optimization of various factors contributing in latency. It has been observed in simulation results that HMIPv6, being a traffic efficient protocol, needs the optimization techniques of movement detection and address configuration to shorten the average latency and increase the benefits over MIPv6. In section II we have discussed system architecture and mathematical model to analyze the latency performance and simulation results are obtained in section III followed by the result & discussion and conclusion in section IV.

II. SYSTEM ARCHITECTURE AND MOBILITY MODELING

To analyze the performance of MIPv6 and HMIPv6 protocols, we have assumed ARs in the pico-cellular internet environment with hexagonal cells as shown in figure 1. Number of tier represents the MAP domain size R, and it is assumed that MAP domain is always an integer number and each MAP domain consists of the same number of rings. Each

2009 International Conference on Advances in Computing, Control, and Telecommunication Technologies

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DOI 10.1109/ACT.2009.102

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ring )0( ≥nn is composed of n6 cells. User mobility profile is modeled by random walk mobility model. The nodes in analysis are arranged as per figure 2. When MN moves to a new subnet (cell) while preserving the communication with a Correspondent Node(CN), MIPv6 and HMIPv6 usually assume that the L3 (network layer) handover procedure is initiated only after the L2 (link-layer) handover procedure comes to an end. Thus, handover latency can be defined as the time elapsed after the L2 handover comes to an end until MN receives the first packet of ongoing session through the new AR of the new network. Handoff latencies affect the service quality of real-time applications of mobile users. With Mobile IP (MIP), the handoff latency highly depends on the distance, i.e. delay, between Home Agent (HA) and Foreign Agent (FA). Hierarchical MIP (HMIP) minimizes handoff latencies but depends on additional network elements introduced on the path between HA and FA. Three main procedures run to perform the L3 handover- (a) Movement Detection (MD), (b) Duplicate Address Detection (DAD) and (c) Registration procedure. Therefore, the overall latency in handover depends on the delay incurred in these three procedures and the transmission delay through wired/wireless media, i.e., average latency in L3 handover can be expressed as, RDADMD TTTT ++= (1) Where XT is average latency in process X. To further analyze the latency, let us define the following parameters,

MAPARd − Average number of hops between AR & MAP

HAMAPd − Average number of hops between MAP & HA

CNMAPd − Average number of hops between MAP & CN

CNHAd − Average number of hops between HA & CN

αt Latency of an IP Packet delivery between MN & AR (over wire and wireless medium)

1

2

3

2

2

3

3

3

3

0

1

2

3

1

1

2

3

2

2

2

3

3

3

3

3

1

1

2

3

2

2

2

3

3

3

3

3

1st Ring

2nd Ring

3rd Ring

Figure 1. Hexagonal cell structure with MAP domain size R=3.

5200

Figure 2. Node arrangement in analysis

βt Latency of IP packet’s one hope delivery only through wired medium

HAMNt − Latency of a packet delivery between MN & HA

CNMNt − Latency of a packet delivery between MN & CN CNHAMNt −− Latency of a packet delivery between MN & CN

via HA MAPMNt − Latency of a packet delivery between MN & MAP

Form the network architecture of figure 2, we can deduce the different transmission delays of network segments as: ( ) βα tddtt HAMAPMAPARHAMN ⋅++= −−− (2) ( ) βα tddtt CNMAPMAPARCNMN ⋅++= −−− (3)

( ) βα tdddtt CNHAHAMAPMAPARCNHAMN ⋅+++= −−−−− (4)

βα tdtt MAPARMAPMN ⋅+= −− (5) In the following sub-sections, we have discussed the three procedures and their effect on latency. A. Movement Detection (MD) This is the beginning procedure of L3 handover procedure and aims at determining the movement of MN to a new subnet.[9, 10]. In IPv6-based networks, MD usually relies on the reception of the Router_Advertisement (RA) message from a new AR. An RA message includes the AR’s network prefix information and matching this with previous one it comes to know about the existence of a new network. An AR sends (pseudo) periodic unsolicited RA message to all nodes. Whenever such an RA is sent from an AR, a timer is reset to a uniformly-distributed random value between the router’s configured Min_Rtr_Adv_Interval minRAIT and Max_Rtr_Adv_Interval maxRAIT . When the timer is expired, new unsolicited RA is again sent. Movement is confirmed by receipt of a new RA from a new AR. If UST represents the time between L2 handover completion and reception of a new unsolicited RA at MN, we can get average UST as:

( ) αtTTTTTT

TERAIRAI

RAIRAIRAIRAIUS +

++⋅+

=minmax

min2

minmaxmax2

3][ (6)

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Another method of MD is also defined in MIPv6 specifications with a 32-bit Advertisement_Interval option in RA [11,12], which contains the max time, in milliseconds, between two successive unsolicited RA messages sent by the AR on its interface link. An MN continually monitors the periodic RAs and interprets the absence of RA as a movement hint. The configured value is equal to the router’s configured value, i.e., Max_Rtr_Adv_Intrval RAIST . Here, just one missing RA is considered as the movement hint, although the MN may implement its own policy regarding the number of missing RAs and movement detection. On such a movement hint MN can multicast a Router_Solicitation (RS) message to all the routers. A new AR receives such RS responds by sending its RA message to all-nodes multicast address. And finally, movement is confirmed by receiving the solicited RA from the new AR. If ST denotes the time interval between link-layer re-establishment and the receipt of new solicited RA, the expectation of ST can be given by equation (7) as:

αtTTE RAIS

S 22

][ += (7)

Now the average latency in movement detection can be estimated as:

( ) ( ) ][Pr][Pr USSMD TEUSSTEUSST ⋅≥+⋅<= (8) Where, S and US denote the Solicited and UnSolicited RA events, respectively. Some MNs can accelerate MD procedure by using the link-layer trigger [13, 14]. That is, the changes on the underlying link-layer status can be relayed to the IP layer in the form of link-layer event notification, such as link-up event. On receiving such a link-up notification, the network-layer of MN can optimize the MD procedure by sending an RS message to get a solicited RA. A new AR, receiving such RS, responses it by sending RA message to the MN. Movement is finally confirmed by the reception of such solicited RA from the new AR. So, if MD procedure is executed with the link-layer notification, the optimized MD latency will be

αtTMD 2= (9) B. Address Configureuration (AC) It is specified in MIPv6 specifications; a mobile node (MN) should generate a new care-of address (CoA) by using IPv6 stateless (or stateful) address auto-configuration whenever it moves to a new link [15]. To verify the uniqueness of this CoA, it should run duplicate address detection (DAD) algorithm before assigning the address to its interface. The algorithm determines if the address chosen by an MN is already in use. MN must perform DAD every time it handovers between IPv6 networks and cannot begin communication until DAD completes. After a successful DAD, it registers the new CoA to its home agent (HA) and correspondent nodes (CNs) using binding update (BU) messages. The current and simplest form of DAD was laid out as part of RFC 2462. When an MN wishes to create a new address on an interface, it combines the network prefix with a suffix generated from its interface identifier to generate the tentative

address. Then MN sends a neighbor solicitation (NS) message from the unspecified address to the tentative address. If the address is already in use by another node, that node will reply with a neighbor advertisement (NA) message defending the address. Once a node has sent the NS, it waits for Retrans_Timer RT milliseconds to see if a defending NA is forthcoming, and this solicit-and-wait process is repeated Dup_Addr_Detect_Transmits times, DTimes . With the assumption that there is no collision in the subnet, DAD latency can be modeled as given in equation (10):

DTimesRTTDAD ⋅= (10) The default value of Retrans_Timer is 1000 ms, and by default the process is done only once, resulting in a delay of 1000 ms, during this time, the node cannot communicate with a node. So, obviously, RFC 2462 DAD is a time consuming process, particularly when MN in need of seamless handover runs it. The DAD optimization is required to avoid such a large delay in handover process. The Optimistic DAD (oDAD) procedure is based on the assumption that DAD is far more likely to be successful than failure. oDAD modifies IPv6 neighbor discovery protocol. Similarly, advanced DAD (aDAD) is also a solution for optimization. In aDAD, each AR reserves a bunch of unique CoAs in advance and allocates one of them into a newly connected MN. Both schemes, oDAD and aDAD, do not cause any latency. So, if these DAD optimization schemes are applied to MIPv6 and HMIPv6, DAD latency will be reduced almost to 0=DADT . C. Registration Procedure (RP) The time required to complete the registration process depends on how fast the binding caches of CN are updated. Also for authentication purpose Return Routability procedure [12] is run which leads to additional delay. Assuming CNHAHAMAPCNMAP ddd −−− +< MIPv6 registration latency can be expressed as:

{ }

βα tddddttt

tttT

CNHACNMAPHAMAPMAPAR

CNMNCNHAMN

CNMNCNMNCNHAMNMIPR

⋅++++=+=

+=

−−−−

−−−

−−−−−

)2(2422

22,2max (11)

In HMIPv6, the local and global registrations are performed depending upon the movement of MN. The latency in local and global registrations can be expressed by equation (12) and (13), respectively.

βα tdtttT MAPARMAPMNlocalHMIPR ⋅⋅+== −−− 222 (12) { }

( )DTimesRT

tddddt

tttTtT

CNHACNMAPHAMAPMAPMN

CNMNCNMNCNHAMNDADMAPMNglobalHMIPR

⋅+

++++=

+++=

−−−−

−−−−−−

βα 22266

22,2max2 (13)

Using DAD optimization, such as oDAD or aDAD, equation (13) can again be written as:

( ) βα tddddtT CNHACNMAPHAMAPMAPMNglobalHMIPR −−−−− ++++= 22266 (14)

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From equation (11) and (12), the average latency in HMIPv6 registration can be given as:

HMIPlocalR

HMIPglobalRHMIPR

TRR

TRRT

−

−−

⋅+→−+

⋅+→=

})1Pr{1(

}1Pr{ (15)

Where, }1Pr{ +→ RR , is the probability of domain crossing and can be obtained by random-walk mobility model.

III. SIMULATION AND NUMERICAL RESULTS To study the handover latency in MIPv6 and HMIPv6, we have considered a MAP domain as shown in figure 1. A pico-cellular environment is considered with an average hexagonal cell radius of 20m. The parameters taken for the analysis are listed in Table 1. The handover latency results are obtained for the cell residence probability of 0.5. The tools used for simulation are MATLAB® 7.0.4 and MATHEMATICA® 5.1.

Table I. Parameters used in numerical analysis

Parameter Value

R 1 – 4

cL 120m

sλ 10 session/sec

CNN 5

cT 0.1- 10 sec

CNHAd − , CNMAPd − , HAMAPd − , MAPARd − 6,4 6,2

αt 3 ms

βt 2 ms

minRAIT 1.0 sec.

maxRAIT 3.0 sec

RAIST 3.0 sec

RT 1.0 or 0.0 sec

Figure 3. Handover Latency Analysis, No optimization, q=0.5

Figure 4. Handover Latency Analysis, Movement Detection Optimization

Figure 5. Handover Latency Analysis, DAD optimization

Figure 6. Handover Latency Analysis, MD and DAD optimization

Figure 3 demonstrates the average IP layer handover latency as a function of MAP domain size for both mobility management schemes without any optimization of delay parameters. It is observed from here that the handover latency is sensitive to MAP domain size in HMIPv6 networks. This is because of less probability of registration updates sent to HA/CN. More are the subnets in the MAP domain lower is the latency. On the other hand MIPv6 exhibits fixed latency regardless of MAP domain size. So MIPv6 outperforms HMIPv6 in terms of average handover latency without any optimization. The reason examined behind this is that the DAD procedure runs for RCoA (though it is not frequent) as well as LCoA. Moreover, HMIPv6 would meet MIPv6 latency for a very large MAP size. Figure 4 illustrates the effect of Movement Detection optimization on handover latency. It is observed that the

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handover latency improves with MD optimization but still HMIPv6 is behind the MIPv6. MD optimization reduces the handover latency by 1.29 secs here, which shows more than 50% reduction. Figure 5 demonstrates that MIPv6 always outperforms HMIPv6 unless DAD optimization is supported. It can be justified by noting that HMIPv6 requires large and frequent DAD procedure not for only RCoA but also for LCoA when an MN moves to a new domain. Though HMIPv6 shows better comparative numerical results, However, only DAD optimization is not sufficient to improve the overall average latency of HMIPv6 and MIPv6 and dominance of movement detection procedure can still be seen. Figure 6 depicts the delay performance of mobility management schemes after MD and DAD optimization. The average latency reduces to 52ms for MIPv6 and less then 40ms for HMIPv6. With full optimization, L3 latency exhibits up to 80% reduction in delay w.r.t. non-optimized scheme.

IV. CONCLUSION

In this paper, we have evaluated and compared the handover latency performance of IPv6 Mobility Management Protocols in all-IP networks based on the recent RFCs and research works. It has been observed that handover latency is a function of MAP domain size. Movement detection and duplicate address detection procedures have a significant affect on the average handover latency. HMIPv6 shows higher delay in handing over the session unless DAD optimization (aDAD or oDAD) is supported in the network. We also found that DAD latency is a major but not the only contributing factor for causing delay in the transfer of call to the new access router. Movement detection also plays an important role and can trigger handover process at an appropriate instant. Simulation results demonstrated that HMIPv6 would be appropriate for real-time applications only if it can possess the lower handover latency which is possible when MD and DAD optimization is done.

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