An ID / Locator Separation Based Group Mobility Management in Wireless Body Area Network

Mobility management in wireless sensor network is the most important factor to be considered for applications such as healthcare system. Recently, Identifier (ID)/Locator (LOC) separation based mobility management scheme has been proposed for wireless sensor network. However, it does not performwell in group-basedmobility management in wireless body area network, and thus it tends to induce large registration, packet delivery, and handover delays. To overcome these limitations, we propose a group-based mobility management scheme based on ID/LOC separation concept for ID-based communications with location-based routing to reduce the number of control messages. In the proposed scheme, each sensor device has a globally unique device identifier (GDID) which contains the information of its home network domain. For handover support, each access gatewaymaintains its home GDID register (HGR) and visiting GDID register (VGR) which are used to keep the GDID-locator (LOC) mappings for primary mobile devices in the distributed manner. Besides, in the proposed scheme, only the coordinator will send Router Solicitation and Router Advertisement messages to reduce the control messages further. By numerical analysis, we show that the proposed scheme can significantly reduce the registration, packet delivery, and handover delays, compared to the existing schemes.


Introduction
Wireless body area networks (WBANs) are emerging as an important part of the daily life for ambient assistive living.A WBAN typically consists of lightweight, low power sensors that operate in the proximity of the human body.These sensors can be attached to human body or clothes [1][2][3] and can be used to measure the parameters associated with human body, typically observing physiological signals emanating from different body organs, body motions, and the surrounding environment.The measured values can be gathered and transmitted to the main server by using the IPv6 over low power wireless personal area network (6LoWPAN) [4,5], in which it is possible to connect wireless sensor nodes to IPv6 networks.In mobile environments, it is required to provide these sensor nodes with mobility management, such as handover control.
Many IPv6-based mobility management protocols have attracted much interest in 6LoWPAN networks.We can classify the protocols into the host-based schemes and the network-based schemes.For example, Mobile IPv6 (MIPv6) is a host-based protocol [6] and Proxy Mobile IPv6 (PMIPv6) is a network-based protocol [7].In hostbased mobility schemes, the sensor exchanges Binding Update (BU) and Binding Acknowledgment (BA) messages with its Home Agent (HA), when it moves from one mobility domain to another.On the other hand, in network-based mobility schemes, when a sensor changes the domain, the protocols do not require any mobility-related signaling.Instead, a mobile access gateway (MAG) is responsible for detecting movement and exchanging signaling messages on behalf of the sensors.It is noted that PMIPv6 can be considered as the most suitable mobility scheme in 6LoWPAN-WBAN.However, the conventional PMIPv6 [7] scheme has a drawback that a lot of Proxy Binding Update (PBU) and Proxy Binding Ack (PBA) messages should be exchanged between LMA and MAGs for all body sensors.To enhance this conventional PMIP scheme, the PMIP-Group [8] was proposed, in which a single De-Registration (DeReg) message is exchanged between MAG and LMA by aggregating the associated messages from all sensors.The PMIP-Coordinator scheme [9] was proposed for further enhancement of group-based mobility support in 6LoWPAN-based WBAN network.In this scheme, the Coordinator will communicate with MAG on behalf of the body sensor.The PMIP-Coordinator still has large registration and handover delay.
The Identifier (ID)/Locator (LOC) based mobility management scheme has been proposed for 6LoWPAN wireless sensor network [10].In this scheme each primary mobile device (PMD) or 6LoWPAN sensor has a 128-bit global unique device identifier (GDID), which is used for end-toend communication, and a link-layer address can be used as the access identifier (AID).Each local network domain will have a local home mobility agent and a local visited mobility agent, which are configured based on the logical overlay network that supports the distributed mapping management.However, this scheme does not perform well in group-based wireless body area network, because each sensor sends Router Solicitation (RS) and Router Advertisement (RA) messages to PMD.In addition, for location update and discovery, the additional control messages are exchanged between access gateway and distributed local mapping agents.This tends to induce large registration and handover delays.For this reason, how to decrease the times of exchanging the control messages in case that a number of sensors are attached on one PMD is an important issue.
To overcome these limitations, we propose a groupbased mobility management scheme based on the ID/LOC separation concept.In the proposed scheme, each sensor and each primary mobile device has a globally unique device identifier (GDID) which contains the information of home network domain.For handover support, each access gateway maintains "home GDID register" and "visiting GDID register" that are used to keep the GDID-global locator (GLOC) mappings for primary mobile devices in the distributed manner.The proposed scheme also reduces the number of control messages, including RS/RA.This is because only the Coordinator will exchange RS/RA messages with PMD, instead of each sensor.
The rest of this paper is organized as follows.In Section 2, we review the existing ID/LOC schemes for 6LoWPAN-WBAN networks.In Section 3, we describe the proposed ID/LOC scheme in detail.The performances of the existing and proposed schemes are analyzed in Section 4 in terms of the registration delay, packet delivery delay, and the handover delay.We provide the numerical results and discuss them in Section 5. Finally, we conclude this research in Section 6.

Related Works
In conventional PMIPv6 scheme [7], a lot of Proxy Binding Update (PBU) and Proxy Binding Ack (PBA) messages are exchanged between LMA and MAGs for all body sensors.To enhance this conventional PMIP scheme, the PMIP-Group [8] was proposed, in which a single De-Registration (DeReg) message is exchanged between MAG and LMA for all body sensors.
The PMIP-Coordinator scheme [9] was proposed for further enhancement of PMIP-Group scheme.In this scheme, the Coordinator will communicate with MAG on behalf of the body sensor.
As shown in Figure 1, when the Coordinator is detached from previous MAG (p-MAG), a single DeReg message is exchanged between p-MAG and LMA by aggregating the associated messages from all sensors.
When the Coordinator is attached to n-MAG, then it sends a single Router Solicitation (RS) message, which contains the associated group information, MN-IDs, and link-layer address, to n-MAG by way of PMD at a time.Upon reception of RS messages from body sensors, n-MAG will send the Authentication-Authorization-Accounting (AAA) query messages for authentication for all body sensors.After authentication, AAA server responds with AAA reply messages, containing the LMA address, to n-MAG.Then, n-MAG will send aggregated Proxy Binding Update (PBU) message to LMA for all body sensors.Now, LMA will perform the AAA query operation with AAA server by exchanging AAA query and reply messages for each sensor.After that, LMA sends aggregated Proxy Binding ACK (PBA) message to n-MAG in response to the respective aggregated PBU message.Then, n-MAG responds with a Router Advertisement (RA) message to the Coordinator in response to the RS message.
If PMD wants to communicate with the corresponding PMD (C-PMD), then PMD will send a data packet to LMA directly and LMA will forward the data packet to corresponding MAG (c-MAG) and further to C-PMD.
The ID/LOC-based mobility management scheme has been proposed for 6LoWPAN wireless sensor network [10].In this paper, we will consider it for 6LoWPAN-based wireless body area network.In the ID/LOC scheme, each primary mobile device (PMD), such as smartphone or tablet PC and 6LoWPAN sensor, has a 128-bit globally unique device identifier (GDID), which is used for end-to-end communication, and a link-layer addresses can be used as the access identifier (AID).Each local network domain will have the home and visited distributed local mobility management agents, which are based on the logical overlay network that supports the distributed mapping management.The device ID can be generated through cryptographical generated address (CGA).
As shown in Figure 2, when the body sensors are attached to PMD, then all body sensors generate their IDs and send Router Solicitation (RS) messages to PMD.Upon reception of RS messages from body sensors, PMD will send the Location Update Request to access gateway (AGW).Then, the AGW will update its GDID-global locator (GLOC) mapping table and also GDID-access identifier (AID) mapping table.After that, the AGW responds with Location Update Response message to PMD.After location update, the AGW also performs the Location Update Request and Response messages with distributed local mapping agent (DLMA) for adding GDID-GLOC mapping for global communication.
When PMD moves from the previous access gateway (p-AGW) to a new access gateway (n-AGW), the PMD will send Attachment Trigger to n-AGW.After Attachment Trigger, n-AGW sends Device Context Request message to p-AGW.Then, p-AGW will send the Location Update Request message to home DLMA (H-DLMA).The H-DLMA updates the information and responds with Location Update Response message to p-AGW.After receiving the Location Update Response, the p-AGW will send Device Context Reply message to n-AGW.
As shown in Figure 3, PMD wants to communicate with a particular PMD that is residing in the corresponding gateway (c-AGW).The PMD will send a Device ID Request message to AGW.After receiving the Device ID Request from PMD, the AGW will look up its mapping table, whether the request ID exists or not.If there is no information, then AGW sends a Location Discovery Request message to corresponding DLMA (C-DLMA).The C-DLMA will look up its mapping table and reply with a Location Discovery Response message to AGW.Upon the receipt of the Location Discovery Response message from the CDLMA, the AGW will add the information in its mapping table.Then, the AGW sends Route Setup Request message to c-AGW.After that, the c-AGW performs the GDID Discovery Query and Reply messages with corresponding PMD (C-PMD).After that, the c-AGW responds with Route Setup Complete message to AGW.After that, the AGW responds with Device ID Response message to PMD.Now, the data packets will be forwarded to C-PMD via AGW and c-AGW.

Proposed Scheme
In this section, we describe the proposed ID/LOC-based 6LoWPAN-WBAN mobility management scheme.To this end, first we need to specify the network model.a group of 6LoWPAN sensors that are attached to human body, and one of them acts as Coordinator and only the Coordinator can exchange the control signaling messages with the primary mobile device (PMD).In the proposed scheme, each sensor or PMD has a 128-bit globally unique device identifier (GDID) [10].The link-layer addresses can be used as the access identifier (AID).The GDID contains the information about its home network domain.As for locators, the location of PMDs is identified by local locators (LLOC) and global locators (GLOC).The local locators are the AIDs of PMDs, and it is used within the home domain.The GLOC represents the IP address of access gateways (AGW), and it is used for interdomain communication.Each AGW keeps home GDID register (HGR) and visiting GDID register (VGR).HGR keeps track of the GDID-LOC mapping information for PMDs and VGR maintain the list of GDID-LLOC mapping information for the visited PMDs.
In the proposed scheme, only one time Router Solicitation (RS) and Router Advertisement (RA) messages are sent by Coordinator and thus reduce lots of control messages.
Initially, the PMD communicates with correspondent PMD (C-PMD) in the previous AGW (p-AGW) domain.Now, the PMD moves to a new AGW (n-AGW) by handover.In addition, we assume that each PMD moves around only within its home domain.

Comparison of Existing and Proposed
Schemes.Before describing the proposed scheme in detail, we compare the considered mobility management schemes in the architectural perspective in Table 1.
In the viewpoint of the mobility management, PMIP-Coordinator is the centralized architectures, in which all the control and data traffic are processed by a centralized agent such as LMA.Data packets are delivered to the centralized agents first and forwarded to the corresponding host.In PMIP-Coordinator, the identifier corresponds to HoA and the locator does CoA.In PMIP-Coordinator, the Coordinator will exchange RS/RA messages only one time with mobile access gateway (MAG) on behalf of the body sensors.
In ID-LOC-based scheme, the GDID is used as identifier, and AID and GLOC are used for locators.The DLMA and AGW are used to manage the mobility of PMDs.In ID-LOCbased scheme, the body sensors exchange RS/RA messages with PMD.
On the other hand, in the proposed schemes, the GDID is used as identifier and LLOC and GLOC are used for locators.The AGW manages the mobility for PMDs.In the proposed scheme, the Coordinator exchanges RS/RA messages with PMD only one time on behalf of body sensors.The proposed scheme is described in the subsequent sections.

Initial Registration.
The initial registration procedure of the proposed scheme is shown in Figure 5.
In the figure, when the Coordinator is attached to PMD, the Coordinator sends a Router Solicitation (RS) message containing the information on the group, MN-IDs (GDID), and Link-Layer Addresses (AIDs) to PMD (Step 1).Upon reception of the RS message from the Coordinator, the PMD responds with RA message to Coordinator (Step 2).Then, PMD sends Location Update Request message to AGW.On the reception of this message, the AGW will update its home GDID register (HGR) which maintains GDID-LOC mapping  Table 3: Visiting GDID register (VGR).

Number ID LLOC (in the visited domain)
Home domain

Performance Analysis
In this section, we analyze the performances of candiate mobility management schemes: PMIP-Coordinator, ID-LOC-based scheme, and proposed scheme.As performance metrics, we consider the delays associated with registration, packet delivery, and handover delay, since such delays are very impormant in mobility management.

Analysis Model.
We define several notations for analysis and summarize them in the Notations section.We illustrate the considered network model in Figure 8.
In Figure 8, we denote by  − () the transmission delay of a message with size  from node  to node  via a wireless link.It can be expressed as  − () = ((1 − )/(1 + )) ⋅ ((/  ) +   ).In the meantime, we denote by  − (,  − ) the transmission delay of a message with size  from node  to node  via a wired link, where  − represents the number of wired hops between node  to node .Note that it is expressed as  − (,  − ) =  − ⋅ ((/  ) +   +   ).

Analysis of Registration Delay (RD)
4.2.1.PMIP-Coordinator.As shown in Figure 1, when Coordinator is attached to MAG, then it sends RS message to MAG by way PMD.After that, the MAG performs Authentication-Authorization-Accounting (AAA) query and reply operation with AAA server for authentication for all body sensors.Then, the MAG performs the AAA query operation with AAA server, and then MAG performs aggregated PBU operation with LMA.Then, LMA performs the AAA query and reply operations with AAA server for each body sensor.
After authentication, LMA respond with aggregated PBA to MAG.Now, the MAG responds with aggregated RA message to Coordinator.Accordingly, we get the RD of PMIP-Coordinator as follows: (1)

ID-LOC-Based Scheme.
As shown in Figure 2, when body sensors are attached to PMD, then it performs RS and RA messages to PMD by way of Coordinator.After that, the PMD performs Location Update Request and Response operation with AGW.Then, the AGW also performs the Location Update Request and Response operation with H-DLMA.Accordingly, we get the RD of ID-LOC-based scheme as follows: 4.2.3.Proposed Scheme.As shown in Figure 5, when Coordinator is attached to PMD, then it performs aggregated RS and RA messages to PMD.After that, the PMD performs Location Update Request and Response operation with AGW.Accordingly, we get the RD of proposed scheme as follows:

Numerical Results and Discussion
Based on the analytical equations given in Section 4, we compare the performances of the considered mobility management schemes.In the numerical results, the default value of each parameter has been configured as follows, referring to [11]; that is,  where   denotes the number of sensors in the network.Among the various parameters, we note that   ,   ,   , and  GW-LMA/DLMA can depend on the network conditions.Thus, we evaluate the performances of the considered schemes by varying the values of these parameters.

Registration Delay.
We show the impact of the delay of wireless links (  ) on the registration delay in Figure 9.We can see that the registration delay increases linearly as   becomes larger in every considered scheme.In particular, the PMIP-Coordinator mobility scheme is more sensitive to the delay of wireless links than the ID-LOC mobility scheme, since they exchange the signaling messages for the registration over wireless links and also perform AAA query operation with AAA server for each body sensor.The PMIP-Coordinator also performs PBU/PBA operation with LMA for binding.While ID-LOC mobility scheme performs better than PMIP-Coordinator, this is because there is no AAA query operation with AAA server, since it performs RS/RA messages with PMD for each body sensors over wireless link.We observe that the proposed scheme performs best among the candidate schemes.This is because the Coordinator performs RS/RA messages with PMD and also there is no binding operation with DLMA, since the binding operation performs with AGW.node.For the two schemes, PMIP-Coordinator and ID-LOCbased scheme, the registration delay increases linearly as   increase because the two schemes exchange the signaling messages with AAA, LMA, and DLMA over the wired network.In contrast, proposed scheme is not affected by the average queuing delay at all since it exchanges the signaling messages for the registration over wireless links only.We can see that the proposed scheme performs well compared to the existing schemes.We next illustrate the registration delay for different number of sensors in the network (  ) in Figure 11.We observe that the PMIP-Coordinator gives worse performances than the ID-LOC-based scheme.This is because of the signaling messages for authentication with AAA server by GW and

3. 1 .
Network Model.The proposed ID/LOC-based 6LoW-PAN wireless body area network mobility management scheme is shown in Figure 4.In the model, we consider

Figure 8 :
Figure 8: Network model for performance analysis.

Table 1 :
Comparison of mobility management architectures.

Table 2 :
Home GDID register (HGR).Location Update Request message to c-AGW for route optimization.On the reception of the Location Update Request message, c-AGW will update its mapping table and send a Location Update Response to n-AGW.n-AGW and c-AGW will now use the optimized route (Steps 4 and 5).
will look up its HGR mapping table and reply with Location Discovery Response message to AGW (Steps 2 and 3).Upon the receipt of the Location Discovery Response message from the c-AGW, the AGW will add the information in its mapping table.After that, the AGW responds with Device ID Response message to PMD (Step 4).Now, the data packets will be forwarded to C-PMD via AGW and c-AGW.3.5.Handover Operation.When PMD moves from the previous access gateway (p-AGW) to a new access gateway (n-AGW) in the same home network domain, the PMD will send Based Scheme.When PMD wants to communicate with particular C-PMD, PMD will send Device ID Request message to AGW.If there is no information, then AGW performs Location Discovery Request and Response message with C-DLMA.Then, AGW sends Route Setup Request message to c-AGW.After that, the c-AGW performs the GDID Discovery Query and Reply messages with corresponding PMD (C-PMD).After that, the c-AGW responds with Route Setup Complete message to AGW.After that, the AGW responds with Device ID Response message to PMD.Now, the data packets will be forwarded to C-PMD via AGW and c-AGW:PDD ID-LOC = 4 PMD-GW (  ) + 2 GW-LMA/DLMA (  ) + 2 GW-GW (  ) + 2 PMD-GW (  )+  GW-GW (  ) .When PMD wants to communicate with particular C-PMD, PMD will send Device ID Request message to AGW.If there is no information, then AGW performs Location Discovery Request and Response message with c-AGW.After that, the AGW responds with Device ID Response message to PMD.Now, the data packets will be forward to C-PMD via AGW and c-AGW: PDD Proposed Scheme = 2 PMD-GW (  ) + 2 GW-GW (  ) + 2 PMD-GW (  ) +  GW-GW (  ) .As shown in Figure2, when PMD is attached with n-AGW, then PMD will send Attachment Trigger to n-AGW.After that, the n-AGW performs Device Context Request and Reply messages with p-AGW.Then, p-AGW performs Location Update Request and Response messages with H-DLMA.Accordingly, we get the HD of ID-LOC-based scheme as follows:HD ID-LOC =  PMD-GW (  ) + 2 GW-GW (  ) + 2 GW-LMA/DLMA (  ) +  GW-GW (  ) .As shown in Figure7, when PMD is attached with n-AGW, then PMD will send Attachment Trigger to n-AGW.After that, the n-AGW performs Location Update Request and Response messages with p-AGW.Accordingly, we get the HD of proposed scheme as follows: = 2 PMD-GW (  ) + 2 GW-LMA/DLMA (  ) .= 2 C-PMD (  ) + 2 PMD-GW (  ) + 4 GW-LMA/DLMA (  ) +   × {2 GW-AAA (  ) + 2 LMA-AAA (  )} +  GW-LMA/DLMA (  ) .