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A cross-layer mobility handover scheme for IPv6-based vehicular networks
Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524
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A cross-layer mobility handover scheme for IPv6-based vehicular networks Wang Xiaonan ∗ , Le Deguang, Yao Yufeng Changshu Institute of Technology, Jiangsu, Changshu 215500, China
a r t i c l e
i n f o
Article history: Received 17 December 2013 Accepted 7 July 2015 Keywords: Vehicular network IPv6 Road domain Road segment Cluster
a b s t r a c t This paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. In this scheme, the architecture for vehicular networks is proposed and it is made up of three hierarchies including road domains, road segments and clusters. A vehicular network is made up of multiple road domains, a road domain consists of multiple road segments, and a road segment includes multiple clusters. Based on this architecture, the cluster generation algorithm based on the link duration time is proposed, and the cross-layer mobility handover algorithm is presented. In the handover algorithm, the handover in the network layer (L3) is launched before the one in the link layer (L2). Through the L3 handover process the information on the L2 handover can be acquired in order to achieve the fast L2 handover. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address, so the L3 handover delay and packet loss are reduced. The performance of the proposed scheme is evaluated, and the data results show that this scheme shortens the handover delay and lowers the packet loss rate. © 2015 Elsevier GmbH. All rights reserved.
1. Introduction With the technology development of vehicular networks and the emergence of new applications, it is necessary to connect vehicular networks to the Internet in order to meet users’ demands for new applications [1,2]. These applications require vehicular networks to support seamless wireless Internet services in vehicles with high speed [3]. In wireless networks, the total handover is made up of the L2 handover and L3 handover. In the L2 handover, the channel scanning is time-consuming, and it is a main factor influencing the handover delay [4]. In the L3 handover, the care-of address configuration occupies a large proportion of the L3 handover delay. The L3 handover standards such as mobile Internet protocol version 6 (MIPv6) [5] are typically applied in the wired networks. When these protocols are applied in wireless networks, they cannot work efficiently due to high packet loss and long delay [6]. Moreover, these L3 handover protocols are totally separated from the L2 handover ones, and they do not help improve the L2 handover performance. In order to shorten the total handover delay and lower the packet loss, this paper proposes a cross-layer mobility handover scheme for vehicular networks. The main goal of this scheme is to
∗ Corresponding author. Tel.: +86 15851550692. E-mail address: [email protected] (X. Wang). http://dx.doi.org/10.1016/j.aeue.2015.07.003 1434-8411/© 2015 Elsevier GmbH. All rights reserved.
combine the L3 handover with the L2 handover to improve the total handover performance. This paper has the following contributions:
1) The architecture for vehicular networks is proposed, and it is made up of three hierarchies including road domains, road segments and clusters. A vehicular network is made up of multiple road domains, a road domain consists of multiple road segments, and a road segment is composed of multiple clusters. 2) Based on this architecture, the cluster generation algorithm based on the link duration time is proposed. 3) Based on this architecture, the cross-layer mobility handover algorithm is presented. In this algorithm, the L3 handover is launched before the L2 one. Through the L3 handover process, a vehicle can acquire the channel information in order to achieve the fast L2 handover without scanning all channels. Moreover, in the L3 handover process, a vehicle does not need to be configured with a care-of address. As a result, the total handover delay is reduced and the packet loss rate is lowered.
The remainder of this paper is organized as follows. In Section 2, the related work on the handover schemes is discussed. The proposed handover scheme is presented in Section 3, and the performance is evaluated in Sections 4 and 5. This paper concludes with a summary in Section 6.
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2. Related work In wireless networks, two kinds of handovers are included, namely the L2 handover and L3 handover. 2.1. L2 handover In the L2 handover, the channel scanning is time-consuming, and it is a main factor influencing the handover delay [4]. Therefore, the L2 handover schemes focus on reducing the scanning delay. Chiu et al. [7] propose a fast handover scheme where the information on the physical layer is shared with the link layer in order to reduce the handover delay. This scheme operates based on mobile multi-hop relay technique that allows inter-vehicle communications to access the Internet via a relay vehicle. In Ref. [8], the channels usually used by access points are selected in order to avoid the full scanning process and reduce the scanning delay. In Refs. [9,10], a mobile node first performs the full pre-scanning process in order to get the information on all neighbor access points. Based on the information, the mobile node selects the best access point to perform the L2 handover. The data results show that the L2 handover delay is reduced to some extent. 2.2. L3 handover The L3 handover standards such as MIPv6 [5] are typically applied in wired networks. When these protocols are applied in wireless networks, they cannot work efficiently due to high packet loss and long delay [6]. Islam and Huh [11] propose the sensor PMIPv6 (SPMIPv6). SPMIPv6 presents the network architecture and message formats for the mobility handover process, and it also evaluates the mobility handover cost. The results show that SPMIPv6 reduces the mobility handover cost significantly. In Ref. [12], the mobility handover process is achieved in the link layer, so the mobility handover delay and cost are reduced. Bag et al. [13] propose a scheme which reduces both the mobility handover cost and tunnel establishment cost. This scheme depends on dispatch types to determine source or destination of a packet. As a result, intermediate nodes forwarding a packet have to identify all dispatch types in order to determine the next hop, so the delay is increased and the network scalability is also limited. Moreover, a header structure is added between the adaptation layer and the network layer, so the transmission delay is increased. Denko and Wei [14] propose a mobility management scheme for integrating MANETs into the Internet using multiple mobile gateway (MGs) and foreign agents (FAs). This scheme extends the ad hoc on demand distance vector (AODV) and MIP to achieve the integration. The simulation results show that the use of both multiple MGs and the hybrid gate discovery mechanism enhances the network performance. Fan et al. [15] provide the localized mobility management scheme in mesh networks which uses the multi-path routing to achieve the mobility handover. However, this scheme requires some special signaling costs to deal with mobile terminals, so the delay is prolonged to some extent. Lee et al. [16] use an intermediate-mobile access gateway (iMAG) to perform the mobility handover for vehicular networks. iMAG must be geographically located between the home domain and foreign domain, so this scheme cannot support the global mobility management. In addition, iMAG must store the information on all road-side units, and maintaining the information consumes a lot of network resources. In Ref. [17], clusters are employed to improve the mobility handover performance. In this scheme, cluster heads are in charge of IP mobility for other vehicles. Wang and Qian [18] propose a mobility handover scheme for IPv6-based vehicular networks, and this
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scheme improves the handover performance to some extent. However, this scheme does not use the information in the link layer to shorten the handover delay. Kim et al. [19] propose an enhanced PFMIPv6 (ePFMIPv6) for vehicular networks. In ePFMIPv6, the serving MAG pre-establishes a tunnel with multiple candidate MAGs. When the serving MAG performs the mobility handover, it can forward the packets to the next MAG. ePFMIPv6 shortens the mobility handover delay and lowers the packet loss, but it increases the mobility handover cost. In the above L3 handover schemes, a mobile node needs to be configured with a care-of address. These schemes do not address how to reduce the care-of address configuration delay although the care-of address configuration delay occupies a large proportion of the L3 handover delay.
2.3. Our solution From the above discussion, it can be seen that the following factors influence the handover performance: 1) The L3 handover is totally separated from the L2 handover, and it does not help improve the L2 handover performance. 2) The channel scanning is time-consuming and occupies a large proportion of the L2 handover. 3) The care-of address configuration is time-consuming and occupies a large proportion of the L3 handover. In order to shorten the handover delay and lower the packet loss, this paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. The main goal of this scheme is to combine the L3 handover with the L2 handover to improve the total handover performance. This scheme proposes the following strategies to improve the handover performance: 1) The L3 handover provides the channel information in order to help achieve the fast L2 handover without scanning all channels. 2) In the L2 handover, a vehicle does not need to scan all channels, so the L2 handover delay is reduced. 3) In the L3 handover, a vehicle does not need to be configured with a care-of address, so the L3 handover delay is reduced.
3. Cross-layer mobility handover 3.1. Architecture A vehicular network is made up of access routers (ARs), base stations and vehicles. An AR is connected to the IPv6 Internet, and a base station is connected to an AR. The area covered by all base stations connected to one AR is called a road domain (RD), and the area covered by a base station is called a road segment (RS). Vehicles are divided into three categories: a cluster head (CH) with routing and forwarding function, a cluster member (CM) without routing or forwarding function, and an isolated vehicle (IV). A CH communicates directly with a base station, and a CM achieves the communication with the Internet through its CH. An IV is a node which does not join a cluster. In this way, the architecture is made up of three hierarchies: an RD which is identified by an AR, an RS which is identified by a base station, and a cluster which is identified by a CH. An RD is made up of multiple RS, and an RS consists of a number of clusters. A CH is usually acted by large automobiles, such as buses. A vehicle is uniquely identified by its home address during the mobility process, as shown in Fig. 1.
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assumed that the coordinate of the vehicle Vi /Vj is (xi , yi )/(xj , yj ), the speed of Vi /Vj is vi /vj , the moving angle of Vi /Vj is i / j (0 ≤ i , j < 2), and the communication range of a vehicle is r. Then, the link duration time Tij between Vi and Vj can be estimated according to Eq. (1) [22].
Tij =
2
(a2 + c 2 )r 2 − (ad − bc) − (ab + cd) a2 + c 2
(1)
where a = vi cos i − vj cos j b = xi − xj c = vi sin i − vj sin j d = yi − yj
Fig. 1. Architecture.
3.4. Mobility handover for CH
Table 1 IPv6 address structure. (128-i-j) bits
i bits
j bits
RD ID
RS ID
Vehicle ID
3.2. Address structure Based on the proposed architecture, the hierarchical IPv6 address structure for vehicular networks is proposed, as shown in Table 1. In Table 1, an address consists of three parts. The first part is RD ID which is the global routing prefix and uniquely identifies an RD. In an RD, the RD IDs of the base stations and the RD IDs of the addresses acquired from this RD are the same, and the value is equal to the one of the AR in the same RD. The second part is RS ID which uniquely identifies an RS. The RS IDs of the IPv6 addresses acquired from one RS are the same, and the value is equal to the one of the base station in the same RS. The third part is vehicle ID which uniquely identifies a vehicle. The address of an AR or a base station is preconfigured, the RD ID and vehicle ID of an AR’s address are zero, and the vehicle ID of a base station is zero. The values of i and j are determined by the size of a vehicular network and the density of vehicles. Taking generality into account, this scheme sets i to 16 and j to 32, as shown in Fig. 1. The IPv6 address configuration for vehicular networks is achieved through our previous work [20]. After a CH acquires an address in an RS, the AR in the same RD records the associate relationship between the CH and the base station in the same RS. 3.3. Establishment of clusters In this scheme, a CH is acted by a large automobile. After a large bus starts, it marks itself as a CH and periodically broadcasts a dedicated short range communication (DSRC) message-BasicSafetyMessage [21] whose payload includes the node type, the speed, the mobile angle, the geographic coordinate, the working channel and the address of the base station in the RS where it is located. If a vehicle is not a large automobile, then it marks itself as an IV and scans all channels to receive the DSRC messages from neighbor CHs. Then, the IV selects the CH with the longest link duration time, joins the cluster identified by the CH, marks itself as a CM and begins to periodically broadcast BasicSafetyMessage whose payload includes the node type, the speed, the mobile angle, and the geographic coordinate. A vehicle can acquire its geographic coordinate through some systems, for example, the global positioning system (GPS). It is
In this scheme, a base station stores the geographical coordinates and working channels of its neighbor base stations, and a CH periodically broadcasts a DSRC message whose payload includes the mobile angle, speed and geographic coordinate. The work in Ref. [23] has shown that a node can determine the neighbor node with the best communication performance via listening to a DSRC message from its neighbors. This scheme adopts the method in Ref. [23] to determine the next RS where a CH is entering. It is assumed that the CH C1 is located in the RS S1 which is identified by the base station B1. Then, B1 can acquire C1’s mobile angle, speed and geographic coordinate through receiving a DSRC message from C1. If B1 detects that C1 is leaving its communication range, then it calculates the link duration time between C1 and its neighbor base stations according to formula (1) and selects as C1’s next base station the base station B2 with the largest link duration time. That is, the RS identified by B2 is C1’s next RS. 3.4.1. CH inter-RS handover If B1 and B2 belong to one RD where the AR is R1, then B1 launches the following operations: 1) B1 sends R1 a Handover message whose payload is the addresses of C1 and B2. 2) After R1 receives the Handover message, it updates C1’s associate base station with B2 and returns a Handover-Ack message to B1. 3) After B1 receives the Handover-Ack message, it sends C1 a Handover message whose payload is B2’s working channel. 4) After C1 receives the Handover message, it uses B2’s working channel to directly switch to B2 and begins to receive the data messages from B2, as shown in Fig. 2(a) and (b). In Fig. 2(a) and (b), at the time T1, C1 is leaving B1’s communication range and entering the next RS identified by B2, R1 stores the associate relationship between C1 and B1, and B1 launches the CH inter-RS handover by sending a Handover message. At the time T2, C1 switches to B2 and R1 stores the associate relationship between C1 and B2. At this stage, the CH inter-RS handover process ends. 3.4.2. CH inter-RD handover If B1 belongs to the RD where the AR is R1 and B2 belongs to the RD where the AR is R2, then B1 launches the following operations: 1) B1 sends R2 a Handover message whose payload is the addresses of C1 and B2. 2) After R2 receives the Handover message, it can determine that B1 belongs to the different RD by checking B1’s address.
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it stores these data messages. After C1 switches to B2, B2 forwards these data messages to C1.
3.5. Mobility handover for CM It is assumed that the CH C1 of the CM M1 is located in the RS S1 which is identified by the base station B1, S1 belongs to the RD where the AR is R1, and the IPv6 node N1 is located in the subnet where the AR is R2. Then, the communication process between M1 and N1 is as follows: 1) M1 sends C1 a data message whose destination address is N1. C1 forwards this data message to B1. B1 records the associate relationship between M1 and C1, and then forwards the data message to R1. 2) After R1 receives the data message, it records the associate relationship between M1 and C1, and then builds a tunnel reaching R2. Through this tunnel, the data message reaches R2 which forwards the data message to N1. 3) The data message returned by N1 first reaches R2 which routes the message to R1 through the tunnel. Based on the associate relationship between M1 and C1 and the one between C1 and B1, R1 forwards the data message to B1. Similarly, according to the relationship between M1 and C1, B1 forwards the data message to C1 which then forwards the data message to M1, as shown in Fig. 4.
Fig. 2. CH inter-RS handover.
Therefore, R2 records the associate relationship between C1 and B2, and sends a Handover message to the AR HR of the RD where C1 acquires the home address. The payload of the Handover message is C1’s address. 3) After HR receives the Handover message, it updates C1’s associate AR with R2 and returns a Handover-Ack message to R2. 4) After R2 receives the Handover-Ack message, it sends B1 a Handover-Ack message. After B1 receives the Handover-Ack message, it sends C1 a Handover message whose payload is B2’s working channel. 5) After C1 receives the Handover message, it uses B2’s working channel to directly switch to B2 and begins to receive the data messages from B2, as shown in Fig. 3(a) and (b). In Fig. 3(a) and (b), at the time T1, C1 is leaving B1’s communication range and entering the next RS identified by B2, HR stores the associate relationship between C1 and R1, R1 stores the associate relationship between C1 and B1, and B1 launches the CH interRD handover by sending a Handover message. At the time T2, C1 switches to B2, HR stores the associate relationship between C1 and R2, and R2 stores the associate relationship between C1 and B2. At this stage, the CH inter-RD handover process ends. In the CH inter-RS/inter-RD handover process, the L3 handover is performed before the L2 one. If B2 receives the data messages destined for C1 but it does not receive a DSRC message from C1, then
In Fig. 4, after the life time of the associate relationship between M1 and C1 expires, it is deleted from B1 and R1. In this scheme, a CH or CM periodically broadcasts a DSRC message whose payload includes the mobile angle, speed and geographic coordinate. This scheme adopts the method in Ref. [23] to determine the next cluster where a CM is entering. It is assumed that the CH C1 of the CM M1 is located in the RS S1 which is identified by the base station B1, and S1 belongs to the RD where the AR is R1. Through listening to a DSRC message from M1, C1 can acquire M1’s mobile angle, speed and geographic coordinate. If C1 detects that M1 is leaving its communication range, then it calculates the link duration time between M1 and its neighbor CHs according to Eq. (1) and selects as M1’s next CH the CH C2 with the largest link duration time. That is, the cluster identified by C2 is M1’s next cluster. This scheme employs a DSRC message to determine the next cluster head. Since a CM periodically broadcasts a DSRC message, it does not need to support the additional operations to determine the next cluster head. Moreover, it is the CH that determines the next CH for its CM, so the CM does not need to report its neighbors to its CH. In this scheme, only if a CM is communicating with an IPv6 node during its mobility process, the handover process for a CM is performed. The handover process for a CM is discussed according to the following three situations.
3.5.1. CM intra-RS handover If C1 and C2 belong to one RS and M1 is communicating with an IPv6 node, then C1 launches the following operations: 1) C1 sends B1 a Handover message whose payload is the addresses of M1 and C2. 2) After B1 receives the Handover message, it updates M1’s CH with C2 and then returns a Handover-Ack message to C1. 3) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel.
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Fig. 3. CH inter-RD handover.
Fig. 4. Communication process.
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Fig. 5. CM inter-RS handover.
4) After M1 receives the Handover message, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2. 3.5.2. CM inter-RS handover If C1 and C2 belong to different RS in the same RD, C2 is located in the RS which is identified by the base station B2, and M1 is communicating with an IPv6 node, then C1 launches the following operations:
R1 and B2 store the associate relationship between M1 and C2. At this stage, the CM inter-RS handover process ends. 3.5.3. CM inter-RD handover If C1 and C2 belong to different RD, C2 is located in the RS which is identified by the base station B2, C2 is located in the RD where the AR is R2, and M1 is communicating with an IPv6 node in the subnet where the AR is R3, then C1 launches the following operations:
1) C1 sends B2 a Handover message whose payload is the addresses of M1 and C2. 2) After B2 receives the Handover message, it stores the associate relationship between M1 and C2 and sends a Handover message to R1. 3) After R1 receives the Handover message, it updates M1’s CH with C2, and returns a Handover-Ack message to B2. After B2 receives the Handover-Ack message, it sends C1 a Handover-Ack message. 4) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel. 5) After M1 receives the Handover message, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2, as shown in Fig. 5(a) and (b).
1) C1 sends B2 a Handover message whose payload is the addresses of M1, C2 and R3. 2) After B2 receives the Handover message, it stores the relationship between M1 and C2, and forwards the Handover message to R2. R2 stores the relationship between M1 and C2, and forwards the Handover message to R3. 3) After R3 receives the Handover message, it establishes the tunnel reaching R2 and returns a Handover-Ack message to R2. After R2 receives the Handover-Ack message, it sends a Handover-Ack message to B2 which then sends a Handover-Ack message to C1. 4) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel. 5) After M1 receives the Handover messages, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2, as shown in Fig. 6(a) and (b).
In Fig. 5(a) and (b), at the time T1, M1 is leaving C1’s communication range and entering the next cluster identified by C2, R1 and B1 store the associate relationship between M1 and C1, and C1 launches the CM inter-RS handover by sending a Handover message. At the time T2, M1 switches to C2 and marks C2 as its CH, and
In Fig. 6(a) and (b), at the time T1, M1 is leaving C1’s communication range and entering the next cluster identified by C2, R1 and B1 store the associate relationship between M1 and C1, and C1 launches the CM inter-RD handover by sending a Handover message. At the time T2, M1 switches to C2 and marks C2 as its CH, and
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Fig. 6. CM inter-RD handover.
R2 and B2 store the associate relationship between M1 and C2. At this stage, the CM inter-RD handover process ends. In the CM intra-RS/inter-RS/inter-RD handover process, the L3 handover is launched before the L2 one. If C2 receives the data messages destined for M1 but it does not receive a DSRC message from M1, then it stores these data messages. After M1 switches to C2, C2 forwards these data messages to M1.
4. Analysis 4.1. Handover delay 4.1.1. CH handover delay Based on Fig. 2(b), the CH inter-RS mobility handover delay TCH-RS is made up of the L3 handover delay TL3-CH-RS and the L2 handover delay TL2 , as shown in Eq. (2) where tHandover /tHandover-Ack is the delay of transmitting a Handover/Handover-Ack message between two neighbor nodes, DAR-BS is the distance between an AR and a base station in the same RD, and DBS-CH is the distance between a base station and a CH in the same RS. TCH-RS = TL3-CH-RS + TL2 where TL3-CH-RS = tHandover · DAR-BS + tHandover-Ack · DAR-BS
distance between the AR of the RD where a vehicle is located and the AR where the vehicle acquires an address. TCH-RD = TL3-CH-RD + TL2 where TL3-CH-RD = (tHandover + tHandover-Ack ) · DAR-BS
(3)
+ (tHandover + tHandover-Ack ) · DAR-HR + tHandover · DBS-CH 4.1.2. CM handover delay The CM intra-RS mobility handover delay TCM-CH includes the L3 handover delay TL3-CM-CH and the L2 handover delay TL2 , as shown in Eq. (4) where DCH-CM is the distance between a cluster member and a cluster head in the same cluster. TCM-CH = TL3-CM-CH + TL2 where TL3-CM-CH = (tHandover + tHandover-Ack ) · DBS-CH
(4)
+ tHandover · DCH-CM Based on Fig. 5(b), the CM inter-RS mobility handover delay TCM-RS consists of the L3 handover delay TL3-CM-RS and the L2 handover delay TL2 , as shown in Eq. (5). TCM-RS = TL3-CM-RS + TL2
(2)
+ tHandover · DBS-CH Based on Fig. 3(b), the CH inter-RD mobility handover delay TCH-RD is made up of the L3 handover delay TL3-CH-RD and the L2 handover delay TL2 , as shown in Eq. (3) where DAR-HR is the
where TL3-CM-RS = (tHandover + tHandover-Ack ) · DAR-BS
(5)
+ (tHandover + tHandover-Ack ) · DBS-CH + tHandover · DCH-CM Based on Fig. 6(b), the CM inter-RD mobility handover delay TCM-RD is made up of the L3 handover delay TL3-CM-RD and the L2 handover delay TL2 , as shown Eq. (6) where DAR-DR is the distance
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between the AR of the RD where a vehicle is located and the AR of the subnet where a destination IPv6 node is located. TCM-RD = TL3-CM-RD + TL2 where TL3-CM-RD = (tHandover + tHandover-Ack ) · DAR-BS
(6)
+ (tHandover + tHandover-Ack ) · DBS-CH + (tHandover + tHandover-Ack ) · DAR-DR + tHandover · DCH-CM 4.2. Packet loss The real-world traffic traces and synthetic mobility models demonstrate that it is a reasonable assumption that the vehicle arrival follows Poisson distribution [24,25]. In this scheme, the vehicle arrival follows Poisson distribution. It is assumed that the position of a base station is 0, the transmission range of a base station is R, is the vehicle density measured in vehicles per meter (vpm), and the transmission range of a CH or CM is r which is less than R. For a vehicle located at x in [0,R], p1 (x) is the probability of a CH being directly connected to a base station, and p2 (x) is the probability of a CM being connected to a base station through a CH which is directed connected to a base station. Then, p1 (x) and p2 (x) are shown in Eqs. (7) and (8) [26] where gBS (x) is the probability that a CH and a base station separated by a distance x are directly connected, and gCH (x) is the probability that a CM and a CH separated by a distance x are directly connected. p1 (x) = gBS (x) p2 (x) = 1 − e
−
2r 0
(7) gCH (x−y)p1 (y)dy
(8)
4.2.1. CH packet loss During the CH inter-RS and inter-RD mobility handover processes, the L3 handover is performed before the L2 one, so during the L3 handover a CH can still receive the data messages from the original serving base station. As a result, the inter-RS packet loss rate PCH-RS and inter-RD packet loss rate PCH-RD are shown in Eqs. (9) and (10) where v is the average speed. PCH-RS =
PCH-RD =
tHandover-Ack · DAR-BS + tHandover · DBS-CH + TL2 · p1 (x) R/v
(9)
tHandover-Ack · (DAR-BS + DAR-HR ) + tHandover · DBS-CH + TL2 R/v ·p1 (x)
(10)
4.2.2. CM packet loss During the CM intra-RS, inter-RS and inter-RD mobility handover processes, the L3 handover is performed before the L2 one, so during the L3 handover a CM can receive the data messages from the original CH. As a result, the intra-RS packet loss rate PCM-CH , the inter-RS packet loss rate PCM-RS and the inter-RD packet loss rate PCM-RD are shown in Eqs. (11)–(13). PCM-CH =
tHandover-Ack · DBS-CH + tHandover · DCH-CM + TL2 · p2 (x) r/v (11)
PCM-RS =
tHandover-Ack · (DAR-BS + DBS-CH ) + tHandover · DCH-CM + TL2 r/v ·p2 (x)
(12)
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Table 2 Simulation parameters. Parameters
Values
v
10–30 m/s 25 ms 1–2 km 200–300 m 5 ms 1 4 10 0.95 500 s
TL2 R r tHandover /tHandover-Ack DAR-BS /DBS-CH /DCH-CM DAR-HR /DAR-DR Rounds Confidence level Simulation time
PCM-RD =
tHandover-Ack · (DAR-DR + DAR-BS + DBS-CH ) + tHandover · DCH-CM + TL2 r/v
·p2 (x)
(13)
Based on Eqs. (14) and (15) [26], PCH-RS , PCH-RD , PCM-CH , PCM-RS and PCM-RD can be evaluated.
gBS (x) =
0; otherwise
gCH (x) =
1; x ≤ R
1; x ≤ r 0; otherwise
(14)
(15)
5. Simulation NS-2 is used to evaluate the performance of the proposed scheme. In this scheme, the link protocol adopts the IEEE 802.11p standard which is defined by Ref. [27], so the simulation parameters are set based on Ref. [27], as shown in Table 2. In the simulation, after a node starts it periodically broadcasts a BasicSafetyMessage at a rate of every 100 ms. The average speed of a vehicle ranges from 10 m/s to 30 m/s, and the L2 handover delay is set to 25 ms. The average data of 10 simulation rounds are used to evaluate the handover delay and packet loss rate, and the simulation time for one round is 500 s. The traffic model follows Poisson distribution. In Poisson process, the number of events in a given interval follows Poisson distribution [28,29]. In the traffic model, Poisson process is used to describe the arrivals of vehicles in a given interval. That is, in a given period the number of vehicles arriving follows Poisson distribution. 5.1. The effect of speed 5.1.1. The effect of speed on CH When R is 1 km, the CH handover delay and packet loss rate based on speed are shown in Figs. 7 and 8. With the increase in speed, the frequency of a CH performing the inter-RS/inter-RD mobility handover increases and the link stability weakens, so both the network traffic and the packet loss rate grow, as shown in Fig. 8. Since the retransmission of the lost packets causes the extra delay, there is a slight increment in the delay, as shown in Fig. 7. From Figs. 7 and 8, it can be seen that both the inter-RS handover delay and packet loss rate are lower than the inter-RD ones. 5.1.2. The effect of speed on CM When r is 250 m, the CM handover delay and packet loss rate based on speed are shown in Figs. 9 and 10.
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5.2. The effect of communication range 5.2.1. The effect of communication range on CH When the average speed is 20 m/s, the CH handover delay and packet loss rate based on R are shown in Figs. 11 and 12. When R increases, the frequency of a CH performing the inter-RS/inter-RD handover reduces. Therefore, the network traffic caused by the CH handover decreases and the network performance enhances. As a result, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced. Hence, the packet loss rate and the handover delay are reduced, as shown in Figs. 11 and 12. 5.2.2. The effect of communication range on CM When the speed is 20 m/s, the CM handover delay and packet loss rate based on r are shown in Figs. 13 and 14. With the increased in r, the frequency of a CM performing the intra-RS/inter-RS/inter-RD handover decreases, so the network traffic caused by the CM handover reduces and the network performance enhances. Also, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced, so the handover delay is decreased, as shown in Figs. 13 and 14.
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From Fig. 7 to Fig. 14, it can be seen that the delay and packet loss rate in the simulation do not totally match the ones in the analysis, and the main reasons are analyzed as follows:
1) The analysis only focuses on the delay caused by the handover process itself. That is, the handover delay in the analysis is the interval from the time when the handover process is launched to the time when the handover process is complete, and it does not include the extra delay caused by the retransmission of the lost packets. In the simulation, the handover delay is made up of the delay caused by the handover process itself and the extra delay caused by the retransmission of the lost packets. Therefore, compared with the handover delay in the analysis, the handover delay in the simulation has a slight increment which tends to be equal to the extra delay caused by the retransmission of the lost packets. 2) The analysis only focuses on the packet loss caused by the handover process itself, so the packet loss does not include the extra packet loss caused by the link instability. In the simulation, the packet loss is made up of the packet loss caused by the handover process itself and the extra packet loss caused by the link instability. Therefore, compared with the packet loss rate in the analysis, the packet loss rate in the simulation has a slight increment which tends to be equal to the extra packet loss rate caused by the link instability.
In order to evaluate the performance of this scheme, we compare our scheme with the standard [1] and the new handover scheme – ePFMIPv6 [19]. When R is 1 km and r is 250 m, the handover delay and packet loss rate comparison based on speed are shown in Figs. 15 and 16. With the increase in speed, the link stability weakens and the frequency of a vehicle performing the mobility handover increases. Therefore, the network traffic caused by the handover grows and the network performance degrades. As a result, the handover delays and the packet loss rates in these three solutions all grow, as shown in Figs. 15 and 16. In this scheme, the number of CMs is much more than the number of CHs, so the overall performance tends to present the performance of the CM handover. When the speed increases, the frequency of a CM performing the Inter-RD handover grows. Because the packet loss rate and the delay in the inter-RD handover are more than the ones in both the intra-RS handover and inter-RS handover, the packet loss rate and the delay grow with the increase in speed. Since the number of CMs is much more than the number of CHs, the overall performance tends to present the performance of the CM handover. Therefore, the handover delay and packet loss rate based on r are evaluated. When the speed is 10 m/s and R is 1 km, the handover delay and packet loss rate based on r are shown in Figs. 17 and 18. With the increase in r, the frequency of a vehicle performing the handover decreases, so the network traffic caused by the handover reduces and the network performance enhances. As a result, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced, so the handover delay is also decreased, as shown in Figs. 17 and 18.
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This work is supported by Jiangsu Nature Science Foundation (BK20141230) and National Natural Science Foundation of China (61202440).
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From Fig. 15 to Fig. 18, it can be seen that the proposed scheme has better performance than the standard and ePFMIPv6. In the standard and ePMIPv6, a vehicle needs to be configured with a new care-of address, so the frequent change of a vehicle’s address increases the packet loss rate. In addition, a vehicle needs to scan all channels to achieve the L2 handover, so the total handover delay and packet loss rate grow. In the proposed scheme, the L3 handover is performed before the L2 one. Through the L3 handover process, a vehicle can achieve the L2 handover without scanning all channels, so the L2 handover delay is shortened and the packet loss rate is lowered. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address, so the handover delay in L3 is reduced and the packet loss is decreased. 6. Conclusion This paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. In this scheme, the L3 handover is performed before the L2 one, and through the L3 handover process a vehicle can achieve the fast L2 handover. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address. The performance of the proposed scheme is evaluated and the data results show that this scheme improves the handover performance.
[1] IEEE 1609 WG.1609. 3-2010 IEEE Standard for Wireless Access in Vehicular Environments (WAVE) – Networking Services. IEEE Std 1609. 3-2010 (Revision of IEEE Std 1609.3-2007), 2010. [2] Gerla M, Kleinrock L. Vehicular networks and the future of the mobile internet. Comput Netw 2011;55(2):457–69. [3] Park JT, Chun SM. Fast mobility management for delay-sensitive applications in vehicular networks. Commun Lett IEEE 2011;15(1):31–3. [4] Mishra A, Shin M, Arbaugh W. An empirical analysis of the IEEE 802.11 MAC layer handoff process. ACM SIGCOMM Comput Commun Rev 2003;33(2):93–102. [5] Perkins C, Johnson D, Arkko J. Mobility Support in IPv6. RFC 6275; 2011. [6] Kun Zhu, Dusit Niyato, Ping Wang, Ekram Hossain, Dong In Kim. Mobility and handoff management in vehicular networks: a survey. Wirel Commun Mob Comput 2011;11(4):459–76. [7] Chiu K, Hwang R, Chen Y. Cross-layer design vehicle-assisted handover scheme in VANETs. Wirel Commun Mob Comput 2011;11(7):916–28. [8] Shin S, Forte AG, Rawat AS, et al. Reducing MAC layer handoff latency in IEEE 802.11 wireless LANs. In: Proceedings of the second international workshop on Mobility management & wireless access protocols. ACM; 2004. p. 19–26. [9] Ramani I, Savage S. SyncScan: practical fast handoff for 802.11 infrastructure networks. In: INFOCOM 2005. 24th Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings IEEE, vol. 1. IEEE; 2005. p. 675–84. [10] Wu H, Tan K, Zhang Y, et al. Proactive scan: Fast handoff with smart triggers for 802.11 wireless LAN. In: INFOCOM 2007. 26th IEEE international conference on computer communications, IEEE. IEEE; 2007. p. 749–57. [11] Islam MM, Huh EN. Sensor proxy mobile IPv6 (SPMIPv6) – a novel scheme for mobility supported IP-WSNs. Sensors 2011;11(2):1865–87. [12] Wang X, Zhong S, Zhou R. A mobility support scheme for 6LoWPAN. Comput Commun 2012;35(3):392–404. [13] Bag G, Raza MT, Kim KH, et al. LoWMob: intra-PAN mobility support schemes for 6LoWPAN. Sensors 2009;9(7):5844–77. [14] Denko MK, Wei C. A multi-gateway-based architecture for integrating ad hoc networks with the internet using multiple foreign agents. Int J Ad Hoc Ubiquitous Comput 2008;3(2):99–110. [15] Fan Y, Zhang J, Shen X. Mobility-aware multi-path forwarding scheme for wireless mesh networks. In: Wireless communications and networking conference, 2008. WCNC 2008. IEEE. IEEE; 2008. p. 2337–42. [16] Lee KW, Seo WK, Cho YZ, et al. Inter-domain handover scheme using an intermediate mobile access gateway for seamless service in vehicular networks. Int J Commun Syst 2010;23(9–10):1127–44. [17] Boukerche A, Zhang Z, Fei X. Reducing handoff latency for NEMO-based vehicular ad hoc networks. In: Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE. IEEE; 2011. p. 1–5. [18] Wang X, Qian H. A mobility handover scheme for IPv6-based vehicular ad hoc networks. Wirel Pers Commun 2013;70(4):1841–57. [19] Kim MS, Lee SK, Golmie N. Enhanced fast handover for proxy mobile IPv6 in vehicular networks. Wirel Netw 2012;18(4):401–11. [20] Wang X, Zhong S. Research on IPv6 address configuration for a VANET. J Parallel Distrib Comput 2013;73(6):757–66. [21] Dedicated Short Range Communications (DSRC) Message Set Dictionary. SAE J2735; 2009. [22] Benslimane A, Barghi S, Assi C. An efficient routing protocol for connecting vehicular networks to the Internet. Pervasive Mob Comput 2011;7(1):98–113. [23] Xiaonan Wang, Huanyan Qian. Constructing a VANET based on cluster chains. Int J Commun Syst 2012, http://dx.doi.org/10.1002/dac.2484. [24] Tan WL, Lau WC, Yue OC, et al. Analytical models and performance evaluation of drive-thru internet systems. IEEE J Sel Areas Commun 2011;29(1):207–22. [25] Tonguz OK, Viriyasitavat W, Bai F. Modeling urban traffic: a cellular automata approach. IEEE Commun Mag 2009;47(5):142–50. [26] Ng SC, Zhang W, Zhang Y, et al. Analysis of access and connectivity probabilities in vehicular relay networks. IEEE J Sel Areas Commun 2011;29(1):140–50. [27] 802.11p-2010 – IEEE Standard for Information technology – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 6: Wireless Access in Vehicular Environments; 2010. [28] Cannizzaro F, Greco G, Rizzo S, et al. Results of the measurements carried out in order to verify the validity of the Poisson-exponential distribution in radioactive decay events. Int J Appl Radiat Isot 1978;29(11):649–51. [29] Frank A. Haight handbook of the Poisson distribution. New York: John Wiley & Sons; 1967.
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REGULAR PAPER
A cross-layer mobility handover scheme for IPv6-based vehicular networks Wang Xiaonan ∗ , Le Deguang, Yao Yufeng Changshu Institute of Technology, Jiangsu, Changshu 215500, China
a r t i c l e
i n f o
Article history: Received 17 December 2013 Accepted 7 July 2015 Keywords: Vehicular network IPv6 Road domain Road segment Cluster
a b s t r a c t This paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. In this scheme, the architecture for vehicular networks is proposed and it is made up of three hierarchies including road domains, road segments and clusters. A vehicular network is made up of multiple road domains, a road domain consists of multiple road segments, and a road segment includes multiple clusters. Based on this architecture, the cluster generation algorithm based on the link duration time is proposed, and the cross-layer mobility handover algorithm is presented. In the handover algorithm, the handover in the network layer (L3) is launched before the one in the link layer (L2). Through the L3 handover process the information on the L2 handover can be acquired in order to achieve the fast L2 handover. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address, so the L3 handover delay and packet loss are reduced. The performance of the proposed scheme is evaluated, and the data results show that this scheme shortens the handover delay and lowers the packet loss rate. © 2015 Elsevier GmbH. All rights reserved.
1. Introduction With the technology development of vehicular networks and the emergence of new applications, it is necessary to connect vehicular networks to the Internet in order to meet users’ demands for new applications [1,2]. These applications require vehicular networks to support seamless wireless Internet services in vehicles with high speed [3]. In wireless networks, the total handover is made up of the L2 handover and L3 handover. In the L2 handover, the channel scanning is time-consuming, and it is a main factor influencing the handover delay [4]. In the L3 handover, the care-of address configuration occupies a large proportion of the L3 handover delay. The L3 handover standards such as mobile Internet protocol version 6 (MIPv6) [5] are typically applied in the wired networks. When these protocols are applied in wireless networks, they cannot work efficiently due to high packet loss and long delay [6]. Moreover, these L3 handover protocols are totally separated from the L2 handover ones, and they do not help improve the L2 handover performance. In order to shorten the total handover delay and lower the packet loss, this paper proposes a cross-layer mobility handover scheme for vehicular networks. The main goal of this scheme is to
∗ Corresponding author. Tel.: +86 15851550692. E-mail address: [email protected] (X. Wang). http://dx.doi.org/10.1016/j.aeue.2015.07.003 1434-8411/© 2015 Elsevier GmbH. All rights reserved.
combine the L3 handover with the L2 handover to improve the total handover performance. This paper has the following contributions:
1) The architecture for vehicular networks is proposed, and it is made up of three hierarchies including road domains, road segments and clusters. A vehicular network is made up of multiple road domains, a road domain consists of multiple road segments, and a road segment is composed of multiple clusters. 2) Based on this architecture, the cluster generation algorithm based on the link duration time is proposed. 3) Based on this architecture, the cross-layer mobility handover algorithm is presented. In this algorithm, the L3 handover is launched before the L2 one. Through the L3 handover process, a vehicle can acquire the channel information in order to achieve the fast L2 handover without scanning all channels. Moreover, in the L3 handover process, a vehicle does not need to be configured with a care-of address. As a result, the total handover delay is reduced and the packet loss rate is lowered.
The remainder of this paper is organized as follows. In Section 2, the related work on the handover schemes is discussed. The proposed handover scheme is presented in Section 3, and the performance is evaluated in Sections 4 and 5. This paper concludes with a summary in Section 6.
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2. Related work In wireless networks, two kinds of handovers are included, namely the L2 handover and L3 handover. 2.1. L2 handover In the L2 handover, the channel scanning is time-consuming, and it is a main factor influencing the handover delay [4]. Therefore, the L2 handover schemes focus on reducing the scanning delay. Chiu et al. [7] propose a fast handover scheme where the information on the physical layer is shared with the link layer in order to reduce the handover delay. This scheme operates based on mobile multi-hop relay technique that allows inter-vehicle communications to access the Internet via a relay vehicle. In Ref. [8], the channels usually used by access points are selected in order to avoid the full scanning process and reduce the scanning delay. In Refs. [9,10], a mobile node first performs the full pre-scanning process in order to get the information on all neighbor access points. Based on the information, the mobile node selects the best access point to perform the L2 handover. The data results show that the L2 handover delay is reduced to some extent. 2.2. L3 handover The L3 handover standards such as MIPv6 [5] are typically applied in wired networks. When these protocols are applied in wireless networks, they cannot work efficiently due to high packet loss and long delay [6]. Islam and Huh [11] propose the sensor PMIPv6 (SPMIPv6). SPMIPv6 presents the network architecture and message formats for the mobility handover process, and it also evaluates the mobility handover cost. The results show that SPMIPv6 reduces the mobility handover cost significantly. In Ref. [12], the mobility handover process is achieved in the link layer, so the mobility handover delay and cost are reduced. Bag et al. [13] propose a scheme which reduces both the mobility handover cost and tunnel establishment cost. This scheme depends on dispatch types to determine source or destination of a packet. As a result, intermediate nodes forwarding a packet have to identify all dispatch types in order to determine the next hop, so the delay is increased and the network scalability is also limited. Moreover, a header structure is added between the adaptation layer and the network layer, so the transmission delay is increased. Denko and Wei [14] propose a mobility management scheme for integrating MANETs into the Internet using multiple mobile gateway (MGs) and foreign agents (FAs). This scheme extends the ad hoc on demand distance vector (AODV) and MIP to achieve the integration. The simulation results show that the use of both multiple MGs and the hybrid gate discovery mechanism enhances the network performance. Fan et al. [15] provide the localized mobility management scheme in mesh networks which uses the multi-path routing to achieve the mobility handover. However, this scheme requires some special signaling costs to deal with mobile terminals, so the delay is prolonged to some extent. Lee et al. [16] use an intermediate-mobile access gateway (iMAG) to perform the mobility handover for vehicular networks. iMAG must be geographically located between the home domain and foreign domain, so this scheme cannot support the global mobility management. In addition, iMAG must store the information on all road-side units, and maintaining the information consumes a lot of network resources. In Ref. [17], clusters are employed to improve the mobility handover performance. In this scheme, cluster heads are in charge of IP mobility for other vehicles. Wang and Qian [18] propose a mobility handover scheme for IPv6-based vehicular networks, and this
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scheme improves the handover performance to some extent. However, this scheme does not use the information in the link layer to shorten the handover delay. Kim et al. [19] propose an enhanced PFMIPv6 (ePFMIPv6) for vehicular networks. In ePFMIPv6, the serving MAG pre-establishes a tunnel with multiple candidate MAGs. When the serving MAG performs the mobility handover, it can forward the packets to the next MAG. ePFMIPv6 shortens the mobility handover delay and lowers the packet loss, but it increases the mobility handover cost. In the above L3 handover schemes, a mobile node needs to be configured with a care-of address. These schemes do not address how to reduce the care-of address configuration delay although the care-of address configuration delay occupies a large proportion of the L3 handover delay.
2.3. Our solution From the above discussion, it can be seen that the following factors influence the handover performance: 1) The L3 handover is totally separated from the L2 handover, and it does not help improve the L2 handover performance. 2) The channel scanning is time-consuming and occupies a large proportion of the L2 handover. 3) The care-of address configuration is time-consuming and occupies a large proportion of the L3 handover. In order to shorten the handover delay and lower the packet loss, this paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. The main goal of this scheme is to combine the L3 handover with the L2 handover to improve the total handover performance. This scheme proposes the following strategies to improve the handover performance: 1) The L3 handover provides the channel information in order to help achieve the fast L2 handover without scanning all channels. 2) In the L2 handover, a vehicle does not need to scan all channels, so the L2 handover delay is reduced. 3) In the L3 handover, a vehicle does not need to be configured with a care-of address, so the L3 handover delay is reduced.
3. Cross-layer mobility handover 3.1. Architecture A vehicular network is made up of access routers (ARs), base stations and vehicles. An AR is connected to the IPv6 Internet, and a base station is connected to an AR. The area covered by all base stations connected to one AR is called a road domain (RD), and the area covered by a base station is called a road segment (RS). Vehicles are divided into three categories: a cluster head (CH) with routing and forwarding function, a cluster member (CM) without routing or forwarding function, and an isolated vehicle (IV). A CH communicates directly with a base station, and a CM achieves the communication with the Internet through its CH. An IV is a node which does not join a cluster. In this way, the architecture is made up of three hierarchies: an RD which is identified by an AR, an RS which is identified by a base station, and a cluster which is identified by a CH. An RD is made up of multiple RS, and an RS consists of a number of clusters. A CH is usually acted by large automobiles, such as buses. A vehicle is uniquely identified by its home address during the mobility process, as shown in Fig. 1.
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assumed that the coordinate of the vehicle Vi /Vj is (xi , yi )/(xj , yj ), the speed of Vi /Vj is vi /vj , the moving angle of Vi /Vj is i / j (0 ≤ i , j < 2), and the communication range of a vehicle is r. Then, the link duration time Tij between Vi and Vj can be estimated according to Eq. (1) [22].
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Fig. 1. Architecture.
3.4. Mobility handover for CH
Table 1 IPv6 address structure. (128-i-j) bits
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3.2. Address structure Based on the proposed architecture, the hierarchical IPv6 address structure for vehicular networks is proposed, as shown in Table 1. In Table 1, an address consists of three parts. The first part is RD ID which is the global routing prefix and uniquely identifies an RD. In an RD, the RD IDs of the base stations and the RD IDs of the addresses acquired from this RD are the same, and the value is equal to the one of the AR in the same RD. The second part is RS ID which uniquely identifies an RS. The RS IDs of the IPv6 addresses acquired from one RS are the same, and the value is equal to the one of the base station in the same RS. The third part is vehicle ID which uniquely identifies a vehicle. The address of an AR or a base station is preconfigured, the RD ID and vehicle ID of an AR’s address are zero, and the vehicle ID of a base station is zero. The values of i and j are determined by the size of a vehicular network and the density of vehicles. Taking generality into account, this scheme sets i to 16 and j to 32, as shown in Fig. 1. The IPv6 address configuration for vehicular networks is achieved through our previous work [20]. After a CH acquires an address in an RS, the AR in the same RD records the associate relationship between the CH and the base station in the same RS. 3.3. Establishment of clusters In this scheme, a CH is acted by a large automobile. After a large bus starts, it marks itself as a CH and periodically broadcasts a dedicated short range communication (DSRC) message-BasicSafetyMessage [21] whose payload includes the node type, the speed, the mobile angle, the geographic coordinate, the working channel and the address of the base station in the RS where it is located. If a vehicle is not a large automobile, then it marks itself as an IV and scans all channels to receive the DSRC messages from neighbor CHs. Then, the IV selects the CH with the longest link duration time, joins the cluster identified by the CH, marks itself as a CM and begins to periodically broadcast BasicSafetyMessage whose payload includes the node type, the speed, the mobile angle, and the geographic coordinate. A vehicle can acquire its geographic coordinate through some systems, for example, the global positioning system (GPS). It is
In this scheme, a base station stores the geographical coordinates and working channels of its neighbor base stations, and a CH periodically broadcasts a DSRC message whose payload includes the mobile angle, speed and geographic coordinate. The work in Ref. [23] has shown that a node can determine the neighbor node with the best communication performance via listening to a DSRC message from its neighbors. This scheme adopts the method in Ref. [23] to determine the next RS where a CH is entering. It is assumed that the CH C1 is located in the RS S1 which is identified by the base station B1. Then, B1 can acquire C1’s mobile angle, speed and geographic coordinate through receiving a DSRC message from C1. If B1 detects that C1 is leaving its communication range, then it calculates the link duration time between C1 and its neighbor base stations according to formula (1) and selects as C1’s next base station the base station B2 with the largest link duration time. That is, the RS identified by B2 is C1’s next RS. 3.4.1. CH inter-RS handover If B1 and B2 belong to one RD where the AR is R1, then B1 launches the following operations: 1) B1 sends R1 a Handover message whose payload is the addresses of C1 and B2. 2) After R1 receives the Handover message, it updates C1’s associate base station with B2 and returns a Handover-Ack message to B1. 3) After B1 receives the Handover-Ack message, it sends C1 a Handover message whose payload is B2’s working channel. 4) After C1 receives the Handover message, it uses B2’s working channel to directly switch to B2 and begins to receive the data messages from B2, as shown in Fig. 2(a) and (b). In Fig. 2(a) and (b), at the time T1, C1 is leaving B1’s communication range and entering the next RS identified by B2, R1 stores the associate relationship between C1 and B1, and B1 launches the CH inter-RS handover by sending a Handover message. At the time T2, C1 switches to B2 and R1 stores the associate relationship between C1 and B2. At this stage, the CH inter-RS handover process ends. 3.4.2. CH inter-RD handover If B1 belongs to the RD where the AR is R1 and B2 belongs to the RD where the AR is R2, then B1 launches the following operations: 1) B1 sends R2 a Handover message whose payload is the addresses of C1 and B2. 2) After R2 receives the Handover message, it can determine that B1 belongs to the different RD by checking B1’s address.
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it stores these data messages. After C1 switches to B2, B2 forwards these data messages to C1.
3.5. Mobility handover for CM It is assumed that the CH C1 of the CM M1 is located in the RS S1 which is identified by the base station B1, S1 belongs to the RD where the AR is R1, and the IPv6 node N1 is located in the subnet where the AR is R2. Then, the communication process between M1 and N1 is as follows: 1) M1 sends C1 a data message whose destination address is N1. C1 forwards this data message to B1. B1 records the associate relationship between M1 and C1, and then forwards the data message to R1. 2) After R1 receives the data message, it records the associate relationship between M1 and C1, and then builds a tunnel reaching R2. Through this tunnel, the data message reaches R2 which forwards the data message to N1. 3) The data message returned by N1 first reaches R2 which routes the message to R1 through the tunnel. Based on the associate relationship between M1 and C1 and the one between C1 and B1, R1 forwards the data message to B1. Similarly, according to the relationship between M1 and C1, B1 forwards the data message to C1 which then forwards the data message to M1, as shown in Fig. 4.
Fig. 2. CH inter-RS handover.
Therefore, R2 records the associate relationship between C1 and B2, and sends a Handover message to the AR HR of the RD where C1 acquires the home address. The payload of the Handover message is C1’s address. 3) After HR receives the Handover message, it updates C1’s associate AR with R2 and returns a Handover-Ack message to R2. 4) After R2 receives the Handover-Ack message, it sends B1 a Handover-Ack message. After B1 receives the Handover-Ack message, it sends C1 a Handover message whose payload is B2’s working channel. 5) After C1 receives the Handover message, it uses B2’s working channel to directly switch to B2 and begins to receive the data messages from B2, as shown in Fig. 3(a) and (b). In Fig. 3(a) and (b), at the time T1, C1 is leaving B1’s communication range and entering the next RS identified by B2, HR stores the associate relationship between C1 and R1, R1 stores the associate relationship between C1 and B1, and B1 launches the CH interRD handover by sending a Handover message. At the time T2, C1 switches to B2, HR stores the associate relationship between C1 and R2, and R2 stores the associate relationship between C1 and B2. At this stage, the CH inter-RD handover process ends. In the CH inter-RS/inter-RD handover process, the L3 handover is performed before the L2 one. If B2 receives the data messages destined for C1 but it does not receive a DSRC message from C1, then
In Fig. 4, after the life time of the associate relationship between M1 and C1 expires, it is deleted from B1 and R1. In this scheme, a CH or CM periodically broadcasts a DSRC message whose payload includes the mobile angle, speed and geographic coordinate. This scheme adopts the method in Ref. [23] to determine the next cluster where a CM is entering. It is assumed that the CH C1 of the CM M1 is located in the RS S1 which is identified by the base station B1, and S1 belongs to the RD where the AR is R1. Through listening to a DSRC message from M1, C1 can acquire M1’s mobile angle, speed and geographic coordinate. If C1 detects that M1 is leaving its communication range, then it calculates the link duration time between M1 and its neighbor CHs according to Eq. (1) and selects as M1’s next CH the CH C2 with the largest link duration time. That is, the cluster identified by C2 is M1’s next cluster. This scheme employs a DSRC message to determine the next cluster head. Since a CM periodically broadcasts a DSRC message, it does not need to support the additional operations to determine the next cluster head. Moreover, it is the CH that determines the next CH for its CM, so the CM does not need to report its neighbors to its CH. In this scheme, only if a CM is communicating with an IPv6 node during its mobility process, the handover process for a CM is performed. The handover process for a CM is discussed according to the following three situations.
3.5.1. CM intra-RS handover If C1 and C2 belong to one RS and M1 is communicating with an IPv6 node, then C1 launches the following operations: 1) C1 sends B1 a Handover message whose payload is the addresses of M1 and C2. 2) After B1 receives the Handover message, it updates M1’s CH with C2 and then returns a Handover-Ack message to C1. 3) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel.
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Fig. 3. CH inter-RD handover.
Fig. 4. Communication process.
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Fig. 5. CM inter-RS handover.
4) After M1 receives the Handover message, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2. 3.5.2. CM inter-RS handover If C1 and C2 belong to different RS in the same RD, C2 is located in the RS which is identified by the base station B2, and M1 is communicating with an IPv6 node, then C1 launches the following operations:
R1 and B2 store the associate relationship between M1 and C2. At this stage, the CM inter-RS handover process ends. 3.5.3. CM inter-RD handover If C1 and C2 belong to different RD, C2 is located in the RS which is identified by the base station B2, C2 is located in the RD where the AR is R2, and M1 is communicating with an IPv6 node in the subnet where the AR is R3, then C1 launches the following operations:
1) C1 sends B2 a Handover message whose payload is the addresses of M1 and C2. 2) After B2 receives the Handover message, it stores the associate relationship between M1 and C2 and sends a Handover message to R1. 3) After R1 receives the Handover message, it updates M1’s CH with C2, and returns a Handover-Ack message to B2. After B2 receives the Handover-Ack message, it sends C1 a Handover-Ack message. 4) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel. 5) After M1 receives the Handover message, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2, as shown in Fig. 5(a) and (b).
1) C1 sends B2 a Handover message whose payload is the addresses of M1, C2 and R3. 2) After B2 receives the Handover message, it stores the relationship between M1 and C2, and forwards the Handover message to R2. R2 stores the relationship between M1 and C2, and forwards the Handover message to R3. 3) After R3 receives the Handover message, it establishes the tunnel reaching R2 and returns a Handover-Ack message to R2. After R2 receives the Handover-Ack message, it sends a Handover-Ack message to B2 which then sends a Handover-Ack message to C1. 4) After C1 receives the Handover-Ack message, it sends M1 a Handover message whose payload is C2’s working channel. 5) After M1 receives the Handover messages, it uses C2’s working channel to directly switch to C2 and starts receiving the data messages from C2, as shown in Fig. 6(a) and (b).
In Fig. 5(a) and (b), at the time T1, M1 is leaving C1’s communication range and entering the next cluster identified by C2, R1 and B1 store the associate relationship between M1 and C1, and C1 launches the CM inter-RS handover by sending a Handover message. At the time T2, M1 switches to C2 and marks C2 as its CH, and
In Fig. 6(a) and (b), at the time T1, M1 is leaving C1’s communication range and entering the next cluster identified by C2, R1 and B1 store the associate relationship between M1 and C1, and C1 launches the CM inter-RD handover by sending a Handover message. At the time T2, M1 switches to C2 and marks C2 as its CH, and
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Fig. 6. CM inter-RD handover.
R2 and B2 store the associate relationship between M1 and C2. At this stage, the CM inter-RD handover process ends. In the CM intra-RS/inter-RS/inter-RD handover process, the L3 handover is launched before the L2 one. If C2 receives the data messages destined for M1 but it does not receive a DSRC message from M1, then it stores these data messages. After M1 switches to C2, C2 forwards these data messages to M1.
4. Analysis 4.1. Handover delay 4.1.1. CH handover delay Based on Fig. 2(b), the CH inter-RS mobility handover delay TCH-RS is made up of the L3 handover delay TL3-CH-RS and the L2 handover delay TL2 , as shown in Eq. (2) where tHandover /tHandover-Ack is the delay of transmitting a Handover/Handover-Ack message between two neighbor nodes, DAR-BS is the distance between an AR and a base station in the same RD, and DBS-CH is the distance between a base station and a CH in the same RS. TCH-RS = TL3-CH-RS + TL2 where TL3-CH-RS = tHandover · DAR-BS + tHandover-Ack · DAR-BS
distance between the AR of the RD where a vehicle is located and the AR where the vehicle acquires an address. TCH-RD = TL3-CH-RD + TL2 where TL3-CH-RD = (tHandover + tHandover-Ack ) · DAR-BS
(3)
+ (tHandover + tHandover-Ack ) · DAR-HR + tHandover · DBS-CH 4.1.2. CM handover delay The CM intra-RS mobility handover delay TCM-CH includes the L3 handover delay TL3-CM-CH and the L2 handover delay TL2 , as shown in Eq. (4) where DCH-CM is the distance between a cluster member and a cluster head in the same cluster. TCM-CH = TL3-CM-CH + TL2 where TL3-CM-CH = (tHandover + tHandover-Ack ) · DBS-CH
(4)
+ tHandover · DCH-CM Based on Fig. 5(b), the CM inter-RS mobility handover delay TCM-RS consists of the L3 handover delay TL3-CM-RS and the L2 handover delay TL2 , as shown in Eq. (5). TCM-RS = TL3-CM-RS + TL2
(2)
+ tHandover · DBS-CH Based on Fig. 3(b), the CH inter-RD mobility handover delay TCH-RD is made up of the L3 handover delay TL3-CH-RD and the L2 handover delay TL2 , as shown in Eq. (3) where DAR-HR is the
where TL3-CM-RS = (tHandover + tHandover-Ack ) · DAR-BS
(5)
+ (tHandover + tHandover-Ack ) · DBS-CH + tHandover · DCH-CM Based on Fig. 6(b), the CM inter-RD mobility handover delay TCM-RD is made up of the L3 handover delay TL3-CM-RD and the L2 handover delay TL2 , as shown Eq. (6) where DAR-DR is the distance
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between the AR of the RD where a vehicle is located and the AR of the subnet where a destination IPv6 node is located. TCM-RD = TL3-CM-RD + TL2 where TL3-CM-RD = (tHandover + tHandover-Ack ) · DAR-BS
(6)
+ (tHandover + tHandover-Ack ) · DBS-CH + (tHandover + tHandover-Ack ) · DAR-DR + tHandover · DCH-CM 4.2. Packet loss The real-world traffic traces and synthetic mobility models demonstrate that it is a reasonable assumption that the vehicle arrival follows Poisson distribution [24,25]. In this scheme, the vehicle arrival follows Poisson distribution. It is assumed that the position of a base station is 0, the transmission range of a base station is R, is the vehicle density measured in vehicles per meter (vpm), and the transmission range of a CH or CM is r which is less than R. For a vehicle located at x in [0,R], p1 (x) is the probability of a CH being directly connected to a base station, and p2 (x) is the probability of a CM being connected to a base station through a CH which is directed connected to a base station. Then, p1 (x) and p2 (x) are shown in Eqs. (7) and (8) [26] where gBS (x) is the probability that a CH and a base station separated by a distance x are directly connected, and gCH (x) is the probability that a CM and a CH separated by a distance x are directly connected. p1 (x) = gBS (x) p2 (x) = 1 − e
−
2r 0
(7) gCH (x−y)p1 (y)dy
(8)
4.2.1. CH packet loss During the CH inter-RS and inter-RD mobility handover processes, the L3 handover is performed before the L2 one, so during the L3 handover a CH can still receive the data messages from the original serving base station. As a result, the inter-RS packet loss rate PCH-RS and inter-RD packet loss rate PCH-RD are shown in Eqs. (9) and (10) where v is the average speed. PCH-RS =
PCH-RD =
tHandover-Ack · DAR-BS + tHandover · DBS-CH + TL2 · p1 (x) R/v
(9)
tHandover-Ack · (DAR-BS + DAR-HR ) + tHandover · DBS-CH + TL2 R/v ·p1 (x)
(10)
4.2.2. CM packet loss During the CM intra-RS, inter-RS and inter-RD mobility handover processes, the L3 handover is performed before the L2 one, so during the L3 handover a CM can receive the data messages from the original CH. As a result, the intra-RS packet loss rate PCM-CH , the inter-RS packet loss rate PCM-RS and the inter-RD packet loss rate PCM-RD are shown in Eqs. (11)–(13). PCM-CH =
tHandover-Ack · DBS-CH + tHandover · DCH-CM + TL2 · p2 (x) r/v (11)
PCM-RS =
tHandover-Ack · (DAR-BS + DBS-CH ) + tHandover · DCH-CM + TL2 r/v ·p2 (x)
(12)
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Table 2 Simulation parameters. Parameters
Values
v
10–30 m/s 25 ms 1–2 km 200–300 m 5 ms 1 4 10 0.95 500 s
TL2 R r tHandover /tHandover-Ack DAR-BS /DBS-CH /DCH-CM DAR-HR /DAR-DR Rounds Confidence level Simulation time
PCM-RD =
tHandover-Ack · (DAR-DR + DAR-BS + DBS-CH ) + tHandover · DCH-CM + TL2 r/v
·p2 (x)
(13)
Based on Eqs. (14) and (15) [26], PCH-RS , PCH-RD , PCM-CH , PCM-RS and PCM-RD can be evaluated.
gBS (x) =
0; otherwise
gCH (x) =
1; x ≤ R
1; x ≤ r 0; otherwise
(14)
(15)
5. Simulation NS-2 is used to evaluate the performance of the proposed scheme. In this scheme, the link protocol adopts the IEEE 802.11p standard which is defined by Ref. [27], so the simulation parameters are set based on Ref. [27], as shown in Table 2. In the simulation, after a node starts it periodically broadcasts a BasicSafetyMessage at a rate of every 100 ms. The average speed of a vehicle ranges from 10 m/s to 30 m/s, and the L2 handover delay is set to 25 ms. The average data of 10 simulation rounds are used to evaluate the handover delay and packet loss rate, and the simulation time for one round is 500 s. The traffic model follows Poisson distribution. In Poisson process, the number of events in a given interval follows Poisson distribution [28,29]. In the traffic model, Poisson process is used to describe the arrivals of vehicles in a given interval. That is, in a given period the number of vehicles arriving follows Poisson distribution. 5.1. The effect of speed 5.1.1. The effect of speed on CH When R is 1 km, the CH handover delay and packet loss rate based on speed are shown in Figs. 7 and 8. With the increase in speed, the frequency of a CH performing the inter-RS/inter-RD mobility handover increases and the link stability weakens, so both the network traffic and the packet loss rate grow, as shown in Fig. 8. Since the retransmission of the lost packets causes the extra delay, there is a slight increment in the delay, as shown in Fig. 7. From Figs. 7 and 8, it can be seen that both the inter-RS handover delay and packet loss rate are lower than the inter-RD ones. 5.1.2. The effect of speed on CM When r is 250 m, the CM handover delay and packet loss rate based on speed are shown in Figs. 9 and 10.
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Inter-RS-Ana Inter-RD-Ana
Inter-RS-Ana Inter-RD-Ana
Inter-RS-Sim Inter-RD-Sim
120
100
100
80 Delay(ms)
Delay(ms)
80 60 40 20
60 40 20
0 10
15
20
25
30
0
Speed(m/s)
1000
1200
1400
Inter-RS-Ana Inter-RD-Ana
1600
1800
2000
R
Fig. 7. CH handover delay based on speed.
Fig. 11. CH handover delay based on R.
Inter-RS-Sim Inter-RD-Sim
Inter-RS-Ana Inter-RD-Ana
5 4
Inter-RS-Sim Inter-RD-Sim
2
3
Loss rate(‰)
Loss rate(‰)
Inter-RS-Sim Inter-RD-Sim
2 1 0 10
15
20
25
1.5 1 0.5
30
0
Speed(m/s)
1000
Fig. 8. CH packet loss rate based on speed.
1200
1400
1600
1800
2000
R
Intra-RS-Ana Inter-RS-Ana Inter-RD-Ana
Intra-RS-Sim Inter-RS-Sim Inter-RD-Sim
100
With the increase in speed, the frequency of a CM performing the intra-RS/inter-RS/inter-RD mobility handover increases and the link stability weakens, so both the network traffic and the packet loss rate grow, as shown in Fig. 10. Since the retransmission of the lost packets causes the extra delay, there is a slight increment in the delay, as shown in Fig. 9. From Figs. 9 and 10, it can be seen that the intra-RS handover delay and packet loss rate are minimum, and the inter-RD handover delay and packet loss rate are maximum.
Delay(ms)
80 60 40 20 0 10
15
20
25
30
Speed(m/s) Fig. 9. CM handover delay based on speed.
Intra-RS-Ana Inter-RS-Ana Inter-RD-Ana
Intra-RS-Sim Inter-RS-Sim Inter-RD-Sim
10 8 Loss rate(‰)
Fig. 12. CH loss rate based on R.
6 4 2 0 10
15
20
25
Speed(m/s) Fig. 10. CM packet loss rate based on speed.
30
5.2. The effect of communication range 5.2.1. The effect of communication range on CH When the average speed is 20 m/s, the CH handover delay and packet loss rate based on R are shown in Figs. 11 and 12. When R increases, the frequency of a CH performing the inter-RS/inter-RD handover reduces. Therefore, the network traffic caused by the CH handover decreases and the network performance enhances. As a result, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced. Hence, the packet loss rate and the handover delay are reduced, as shown in Figs. 11 and 12. 5.2.2. The effect of communication range on CM When the speed is 20 m/s, the CM handover delay and packet loss rate based on r are shown in Figs. 13 and 14. With the increased in r, the frequency of a CM performing the intra-RS/inter-RS/inter-RD handover decreases, so the network traffic caused by the CM handover reduces and the network performance enhances. Also, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced, so the handover delay is decreased, as shown in Figs. 13 and 14.
X. Wang et al. / Int. J. Electron. Commun. (AEÜ) 69 (2015) 1514–1524
Intra-RS-Ana Inter-RS-Ana Inter-RD-Ana
120
Intra-RS-Sim Inter-RS-Sim Inter-RD-Sim
Proposed
Standard
ePFM IPv6
90 80 Delay(ms)
100 Delay(ms)
1523
80 60
70 60
40
50
20
20
0 200
225
250
275
22
24
26
28
30
Speed(m/s)
300
Fig. 15. Delay comparison based on speed.
r Fig. 13. CM handover delay based on r.
Proposed
Standard
ePFM IPv6
Intra-RS-Ana Inter-RS-Ana Inter-RD-Ana
Intra-RS-Sim Inter-RS-Sim Inter-RD-Sim
10
Loss rate(‰)
8 6 4
Loss rate(%)
8 6 4 2 0 20
2
22
24
26
28
30
Speed(m/s) 0 200
225
250
275
300
r
Fig. 16. Loss rate comparison based on speed.
5.3. Comparison
Fig. 14. CM loss rate based on r.
From Fig. 7 to Fig. 14, it can be seen that the delay and packet loss rate in the simulation do not totally match the ones in the analysis, and the main reasons are analyzed as follows:
1) The analysis only focuses on the delay caused by the handover process itself. That is, the handover delay in the analysis is the interval from the time when the handover process is launched to the time when the handover process is complete, and it does not include the extra delay caused by the retransmission of the lost packets. In the simulation, the handover delay is made up of the delay caused by the handover process itself and the extra delay caused by the retransmission of the lost packets. Therefore, compared with the handover delay in the analysis, the handover delay in the simulation has a slight increment which tends to be equal to the extra delay caused by the retransmission of the lost packets. 2) The analysis only focuses on the packet loss caused by the handover process itself, so the packet loss does not include the extra packet loss caused by the link instability. In the simulation, the packet loss is made up of the packet loss caused by the handover process itself and the extra packet loss caused by the link instability. Therefore, compared with the packet loss rate in the analysis, the packet loss rate in the simulation has a slight increment which tends to be equal to the extra packet loss rate caused by the link instability.
In order to evaluate the performance of this scheme, we compare our scheme with the standard [1] and the new handover scheme – ePFMIPv6 [19]. When R is 1 km and r is 250 m, the handover delay and packet loss rate comparison based on speed are shown in Figs. 15 and 16. With the increase in speed, the link stability weakens and the frequency of a vehicle performing the mobility handover increases. Therefore, the network traffic caused by the handover grows and the network performance degrades. As a result, the handover delays and the packet loss rates in these three solutions all grow, as shown in Figs. 15 and 16. In this scheme, the number of CMs is much more than the number of CHs, so the overall performance tends to present the performance of the CM handover. When the speed increases, the frequency of a CM performing the Inter-RD handover grows. Because the packet loss rate and the delay in the inter-RD handover are more than the ones in both the intra-RS handover and inter-RS handover, the packet loss rate and the delay grow with the increase in speed. Since the number of CMs is much more than the number of CHs, the overall performance tends to present the performance of the CM handover. Therefore, the handover delay and packet loss rate based on r are evaluated. When the speed is 10 m/s and R is 1 km, the handover delay and packet loss rate based on r are shown in Figs. 17 and 18. With the increase in r, the frequency of a vehicle performing the handover decreases, so the network traffic caused by the handover reduces and the network performance enhances. As a result, the packet loss rate and the additional delay caused by the retransmission of the lost packets are reduced, so the handover delay is also decreased, as shown in Figs. 17 and 18.
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Proposed
Standard
ePFM IPv6
100
This work is supported by Jiangsu Nature Science Foundation (BK20141230) and National Natural Science Foundation of China (61202440).
Delay(ms)
90 80
References
70 60 50 200
225
250
275
300
r Fig. 17. Delay comparison based on communication range.
Proposed
Standard
ePFM IPv6
4 3 Loss rate(%)
Acknowledgements
2 1 0 200
225
250
275
300
r Fig. 18. Loss rate comparison based on communication range.
From Fig. 15 to Fig. 18, it can be seen that the proposed scheme has better performance than the standard and ePFMIPv6. In the standard and ePMIPv6, a vehicle needs to be configured with a new care-of address, so the frequent change of a vehicle’s address increases the packet loss rate. In addition, a vehicle needs to scan all channels to achieve the L2 handover, so the total handover delay and packet loss rate grow. In the proposed scheme, the L3 handover is performed before the L2 one. Through the L3 handover process, a vehicle can achieve the L2 handover without scanning all channels, so the L2 handover delay is shortened and the packet loss rate is lowered. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address, so the handover delay in L3 is reduced and the packet loss is decreased. 6. Conclusion This paper proposes a cross-layer mobility handover scheme for IPv6-based vehicular networks. In this scheme, the L3 handover is performed before the L2 one, and through the L3 handover process a vehicle can achieve the fast L2 handover. Moreover, during the L3 handover process, a vehicle does not need to be configured with a care-of address. The performance of the proposed scheme is evaluated and the data results show that this scheme improves the handover performance.
[1] IEEE 1609 WG.1609. 3-2010 IEEE Standard for Wireless Access in Vehicular Environments (WAVE) – Networking Services. IEEE Std 1609. 3-2010 (Revision of IEEE Std 1609.3-2007), 2010. [2] Gerla M, Kleinrock L. Vehicular networks and the future of the mobile internet. Comput Netw 2011;55(2):457–69. [3] Park JT, Chun SM. Fast mobility management for delay-sensitive applications in vehicular networks. Commun Lett IEEE 2011;15(1):31–3. [4] Mishra A, Shin M, Arbaugh W. An empirical analysis of the IEEE 802.11 MAC layer handoff process. ACM SIGCOMM Comput Commun Rev 2003;33(2):93–102. [5] Perkins C, Johnson D, Arkko J. Mobility Support in IPv6. RFC 6275; 2011. [6] Kun Zhu, Dusit Niyato, Ping Wang, Ekram Hossain, Dong In Kim. Mobility and handoff management in vehicular networks: a survey. Wirel Commun Mob Comput 2011;11(4):459–76. [7] Chiu K, Hwang R, Chen Y. Cross-layer design vehicle-assisted handover scheme in VANETs. Wirel Commun Mob Comput 2011;11(7):916–28. [8] Shin S, Forte AG, Rawat AS, et al. Reducing MAC layer handoff latency in IEEE 802.11 wireless LANs. In: Proceedings of the second international workshop on Mobility management & wireless access protocols. ACM; 2004. p. 19–26. [9] Ramani I, Savage S. SyncScan: practical fast handoff for 802.11 infrastructure networks. In: INFOCOM 2005. 24th Annual Joint Conference of the IEEE Computer and Communications Societies. Proceedings IEEE, vol. 1. IEEE; 2005. p. 675–84. [10] Wu H, Tan K, Zhang Y, et al. Proactive scan: Fast handoff with smart triggers for 802.11 wireless LAN. In: INFOCOM 2007. 26th IEEE international conference on computer communications, IEEE. IEEE; 2007. p. 749–57. [11] Islam MM, Huh EN. Sensor proxy mobile IPv6 (SPMIPv6) – a novel scheme for mobility supported IP-WSNs. Sensors 2011;11(2):1865–87. [12] Wang X, Zhong S, Zhou R. A mobility support scheme for 6LoWPAN. Comput Commun 2012;35(3):392–404. [13] Bag G, Raza MT, Kim KH, et al. LoWMob: intra-PAN mobility support schemes for 6LoWPAN. Sensors 2009;9(7):5844–77. [14] Denko MK, Wei C. A multi-gateway-based architecture for integrating ad hoc networks with the internet using multiple foreign agents. Int J Ad Hoc Ubiquitous Comput 2008;3(2):99–110. [15] Fan Y, Zhang J, Shen X. Mobility-aware multi-path forwarding scheme for wireless mesh networks. In: Wireless communications and networking conference, 2008. WCNC 2008. IEEE. IEEE; 2008. p. 2337–42. [16] Lee KW, Seo WK, Cho YZ, et al. Inter-domain handover scheme using an intermediate mobile access gateway for seamless service in vehicular networks. Int J Commun Syst 2010;23(9–10):1127–44. [17] Boukerche A, Zhang Z, Fei X. Reducing handoff latency for NEMO-based vehicular ad hoc networks. In: Global Telecommunications Conference (GLOBECOM 2011), 2011 IEEE. IEEE; 2011. p. 1–5. [18] Wang X, Qian H. A mobility handover scheme for IPv6-based vehicular ad hoc networks. Wirel Pers Commun 2013;70(4):1841–57. [19] Kim MS, Lee SK, Golmie N. Enhanced fast handover for proxy mobile IPv6 in vehicular networks. Wirel Netw 2012;18(4):401–11. [20] Wang X, Zhong S. Research on IPv6 address configuration for a VANET. J Parallel Distrib Comput 2013;73(6):757–66. [21] Dedicated Short Range Communications (DSRC) Message Set Dictionary. SAE J2735; 2009. [22] Benslimane A, Barghi S, Assi C. An efficient routing protocol for connecting vehicular networks to the Internet. Pervasive Mob Comput 2011;7(1):98–113. [23] Xiaonan Wang, Huanyan Qian. Constructing a VANET based on cluster chains. Int J Commun Syst 2012, http://dx.doi.org/10.1002/dac.2484. [24] Tan WL, Lau WC, Yue OC, et al. Analytical models and performance evaluation of drive-thru internet systems. IEEE J Sel Areas Commun 2011;29(1):207–22. [25] Tonguz OK, Viriyasitavat W, Bai F. Modeling urban traffic: a cellular automata approach. IEEE Commun Mag 2009;47(5):142–50. [26] Ng SC, Zhang W, Zhang Y, et al. Analysis of access and connectivity probabilities in vehicular relay networks. IEEE J Sel Areas Commun 2011;29(1):140–50. [27] 802.11p-2010 – IEEE Standard for Information technology – Local and metropolitan area networks – Specific requirements – Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications Amendment 6: Wireless Access in Vehicular Environments; 2010. [28] Cannizzaro F, Greco G, Rizzo S, et al. Results of the measurements carried out in order to verify the validity of the Poisson-exponential distribution in radioactive decay events. Int J Appl Radiat Isot 1978;29(11):649–51. [29] Frank A. Haight handbook of the Poisson distribution. New York: John Wiley & Sons; 1967.