Distributed mobility management in named data networking

WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Wirel. Commun. Mob. Comput. (2015) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/wcm.2652

RESEARCH ARTICLE

Distributed mobility management in named data networking Zhiwei Yan1 , Sherali Zeadally2* , Siran Zhang3 , Ruowei Guo3 and Yong-Jin Park4 1

China Internet Network Information Center, Beijing 100190, China College of Communication and Information, University of Kentucky, Lexington,KY 40506, U.S.A. 3 Global Information and Telecommunication Studies, Waseda University, Tokyo 169-8555, Japan 4 Department of Communications and Computer Engineering, School of Fundamental Science, Waseda University, Tokyo 169-8555, Japan 2

ABSTRACT The information-centric networking concept was proposed to fulfill the scalability and efficiency requirements of the content-centric Internet in the future. Among the multiple information-centric networking proposals, Named Data Networking (NDN) is one of the most important representatives. NDN uses a hierarchical name to identify the data after which the on-path cache can be deployed to improve the efficiency of data retrieval. However, with the development of mobile Internet, how to extend NDN in the mobile environment to enable efficient and scalable mobility management remains a challenge. We propose a distributed mobility management scheme for both the mobile receiver and the mobile publisher in NDN. Our proposed approach is based on the basic NDN naming and routing principles to select the branching node of the previous and new access locations of the mobile terminal after which the on-path routing states are dynamically adjusted accordingly. Then we propose a novel analytical model to analyze the performance of the proposed scheme. The results demonstrate that the proposed scheme inherits the scalability and efficiency of NDN in the mobile Internet. Copyright © 2015 John Wiley & Sons, Ltd. KEYWORDS NDN; mobility management; cost; latency *Correspondence Sherali Zeadally, College of Communication and Information, University of Kentucky, Lexington, KY 40506, U.S.A. E-mail: [email protected]

1. INTRODUCTION To make the current Internet more suitable for contentcentric applications in the near future, the concept of information-centric networking [1] was proposed, and the Named Data Networking (NDN) [2] is one of the most important components among the information-centric networking proposals. In NDN, content such as a picture is divided into a set of individually named smaller content objects. Content object names are hierarchical and human-readable as the domain names in the current Internet, which can be arbitrarily long, for example, /cnnic/lab/z.jpg/1. As shown in Figure 1, communications are all receiverinitiated in NDN. In other words, a receiver retrieves an individual content object by sending out an Interest packet that specifies the name of the desired content object. When an NDN router receives the Interest packet and has a copy of the content object in its local Cache/Content Store (CS), Copyright © 2015 John Wiley & Sons, Ltd.

it immediately sends back the copy without further propagating that Interest packet. If the NDN router has no copy, it looks up the next-hop neighbor(s) in the Forwarding Information Base (FIB) to forward the Interest packet by performing a longest-prefix match of the name against its forwarding table. Whenever the Interest packet is relayed, the NDN router maintains the information of the Interest packet in its Pending Interest Table (PIT) so that the related response can be routed to the receiver along the reverse path. Each table entry in the FIB maps a name prefix, for example, /cnnic, to a set of next-hop neighbors. The Interest packet is forwarded until it eventually arrives at a node that stores the requested content or is able to produce the content. When the Interest packet arrives, the node sends back the content object along the reverse path. NDN routers forward a content object and also store that content object in their local caches in order to directly response requests later. Forwarding tables are populated by prefix announcements. If a node has content associated

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Distributed mobility management in named data networking

2. RELATED WORK Siris et al. [4] summarized several NDN applications for the mobile environment and stated that the efficient mobility management schemes for both receiver and publisher are very important for the large-scale deployment of NDN in the future [4]. 2.1. Receiver mobility Figure 1. Named Data-networking communication model. CS, Cache/Content Store; PIT, Pending Interest Table; FIB, forwarding information base.

with a certain name prefix, it announces this prefix information to others in the network. It is worth noting that the announcement approach is similar to that used by the Border Gateway Protocol (BGP). It is assumed that names in the NDN are provider-assigned names. In other words, the top-level components of a name represent a content provider so that the provider-assigned names enable aggregation of prefixes while increasing scalability with small forwarding tables. Although the NDN approach can inherently support mobility because of its connectionless nature (the mobile receiver only needs to re-issue the Interest packets from the new location), how to minimize the handover latency as much as possible remains a challenge [3]. For the publisher mobility, how to re-establish ongoing communications when the publisher moves and reduce the signaling cost are significant challenges. In this paper, we propose a distributed fast handover scheme for the mobile receiver and the mobile publisher in the NDN. A new signaling message is introduced to adjust the routing states on the content transmission paths so that the handover cost can be reduced significantly. Besides, the handover procedure proposed in this paper needs no central-point entity and inherits the distributed feature of the basic NDN to guarantee its scalability in the mobile Internet. This solution is mainly suitable for point-to-point applications, in which only two mobile terminals are involved. The main contributions of this work are summarized as follows: * Our proposed handover scheme supports both publisher mobility and receiver mobility. * Our scheme minimizes handover latency for the mobile receiver. * Our scheme minimizes routing update costs for the mobile publisher. In the remainder of this paper, we use data, content, and object interchangeably, and the remainder of this paper is organized as follows. First, we present and analyze recent related works on NDN mobility management solutions. Second, we describe our proposed mobility management scheme for NDN followed by a performance evaluation of the scheme. Finally, we make some concluding remarks.

As stated earlier, the content routing has no relationship with its location in NDN. The mobile receiver can re-issue the Interest packets at the new location to support its mobility. However, how to use this loose routing scheme and on-path caching for efficient mobility management remains an area of open research [5]. D. Kim differentiated realtime services and nonreal-time services in NDN. Then a rendezvous point is deployed for the necessary location management for the mobile receiver [6]. This approach is not scalable, and this architecture is not compatible with the decentralized architecture of NDN. J. Lee and some other researchers proposed the proxy-based mobility management schemes for a mobile receiver in NDN [7–9], mainly, to reduce the packet loss during the handover. The main operations of this scheme include the following: * As soon as the receiver detects its movement, it immediately sends a “Hold request" message to its proxy. * Upon receipt of the “Hold request" message, the proxy stops delivering Data packets and stores the Data packets in its local repository for subsequent retransmissions. * When the mobile receiver acquires the new location information, it notifies the location information to its proxy node with “handover notification" message. Then the proxy node transmits the stored data packets to the new location of the mobile receiver. 2.2. Publisher mobility In practice, the content publisher may also be a mobile device [10]. S. Mullender analyzed the issues of publisher mobility in NDN: it not only causes high signaling cost to be incurred because of the routing state aggregation but also makes content validation difficult [11]. J. Lee analyzed the problems of publisher mobility in NDN and proposed the tunnel-based solution [12]. This scheme guarantees the transparency of publisher mobility for the NDN routers and avoids the flooding-based FIB updates. The basic operations of this scheme are as follows: * After the mobile publisher finishes the handover, it sends a Prefix Update message indicating its new location to its home domain Content Router (CR). * Upon receipt of the Prefix Update message, the home domain CR sends back a prefix acknowledgement Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

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message indicating the prefix update has been successful. Meanwhile, the mobile publisher’s new location is recorded by the home domain CR. * After the attachment to the new location, Interest packets to the mobile publisher are normally forwarded to the home domain CR according to the NDN routing. Upon receipt of these Interest packets, the home domain CR encapsulates them and then forwards the encapsulated Interest packets to the foreign domain CR and finally to the mobile publisher. Similarly, the Data packets are retrieved along the reverse path. Besides, D. Han [13] proposed the scheme of publisher mobility in NDN, and this scheme maintains two kinds of FIB in the routers: stable FIB and dynamic FIB. The stable FIB is used for the static publisher, and the dynamic FIB is only used for location management of the mobile publisher. F. Hermans [14] also proposed a similar solution to support the publisher mobility. These solutions have proposed mainly fast handover and redirection ideas in the NDN network but did not really consider the characteristics of NDN. Besides, other issues such as sub-optimized data transmission paths and high protocol costs are incurred. Moreover, previously proposed solutions have addressed NDN mobility that focus on either receiver mobility or publisher mobility but not both, and then these solutions are hard to deploy due to this complexity.

3. PROPOSED SOLUTION 3.1. New signaling message To trigger the handover in advance and synchronize the routing states on the NDN routers, we propose a new signaling message. In order to inherit the hierarchical naming structure and basic signaling format in NDN, we adopt the same format as that of the Interest packet. The new signaling message named as “Control” for the receiver mobility scenario contains the name “/AR/handoverreceiver/content” to trigger the handover. The first part contains the handover target Access Router (AR) information, and the second part indicates the receiver handover procedure. The last part is the content that will be synchronized among the routers. In addition, a one-bit flag is used in this packet to identify whether the branching node (this is the first node that is in the two packet transmission paths before and after the handover) between the current path and the new path that is selected. Similarly, in order to trigger the publisher’s mobility in advance and adjust the forwarding states accordingly, a Control packet is also used, and the name it contains for publisher mobility is “/AR/handover-publisher/content”. The basic principle of the proposed handover scheme and the function of the Control packet are shown in Figure 2. When the handover is triggered in advance, the old AR sends a Control packet toward the new AR along Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm


Figure 2. Proposed mobility management model.

Figure 3. The receiver handover procedure.

the reverse direction of the current Interest packet transmission path (in the mobile publisher case) or the current Data packet transmission path (in the mobile receiver case). Then, the on-path router (such as N1 and N2) checks whether it is the branching node of the current Interest/Data packets transmission path and along the path from the old AR to the new AR. If so, the branching node will transmit the subsequent Interest/Data packets along the new path. 3.2. Receiver mobility The Control packet is sent along the reverse direction of the Data packet transmission path. The routers encountered along the path from the receiver to the publisher compare the FIB entries corresponding to the related publisher and the new AR. If they are different, it means that the encountered router is the branching node of the current AR and the target AR. The branching node then adds the network interface (denoted by “Face”) corresponding to the target AR to the related PIT entries, and it sends the following Data packets along the new direction. In addition, the one-bit flag is set to “1" to indicate that the branching node has been selected. When the following routers receive the Control packet, they only create the PIT entries identified in the Control packet and send the Data packet hop-by-hop until the target AR is reached. Figure 3 shows the detailed procedure. As illustrated earlier, the proposed scheme introduces two kinds of operations for the NDN router as follows. Before the branching node is selected, the routers optionally delete the related PIT entries related to that mobile receiver (depending on the application type);

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after the branching node is selected, the routers create the PIT entries and add the Face in the direction of the new AR. For the branching node, it also needs to redirect the cached data to the new AR and reset the one-bit flag. Two special cases are as follows: the branching node is the current AR, and the branching node is the publisher. In the first case, the handover will be executed with the lowest latency because the redirection can be finished immediately, and in the second case, the un-used PIT states can all be deleted; the following Data packets can be redirected toward the new direction. To illustrate the proposed scheme more explicitly, we present an example of the handover procedure for the receiver later. In this example, the mobile receiver moves from AR1 to AR2 as shown in Figure 4. The mobility management procedure is as follows: (1) When the mobile receiver moves into the overlapped area between AR1 and AR2, it will anticipate the possible handover. (2) In order to trigger the mobility management procedure, the mobile receiver has to send a Control packet (containing the target AR information) to the current AR to trigger the handover as in the fast handover scheme in an IPv6 environment [15]. (3) When the AR1 receives this Control packet, it checks its PIT table to find any pending Interest packets corresponding to this mobile receiver, and then it sends out the Control packet with the AR2 identification and the names of the pending content. Besides, AR1 will delete the corresponding PIT entries because the mobile receiver will detach soon. Along the reverse path of the related FIB, this Control packet is transmitted hop-by-hop. For the intermediate routers, the FIB entries corresponding to publisher and AR2 are compared in order to check whether it is the branching node. If yes, the router needs to delete the related PIT entries as AR1 did because this path will not be used any more. (4) If not, it means that the router is the branching node. Then the branching node will change the Face in the PIT from AR1 to AR2 in order to redirect the related

Figure 4. Example of the receiver handover procedure. PIT, Pending Interest Table.

traffic to the correct location. The one-bit flag is also changed to “1” to indicate that the branching node has been selected. (5) The following routers on the path from branching node to AR2 establish the PIT entries to prepare for the oncoming traffic. In this way, when the mobile receiver attaches to the AR2, it can receive the data as soon as possible, and then the handover latency can be reduced significantly. 3.3. Publisher mobility In the publisher mobility case, the Control packet is sent along the reverse direction of the related Interest packet transmission path. In this case, the routers encountered have to compare the FIB entry Face corresponding to the new AR and PIT entry Face corresponding to this content. If they are different, it means that the bypassed router is the branching node of the current AR and the target AR. In this case, the branching node adds the Face corresponding to the target AR to its established FIB entry and sends the Interest packet toward the new direction. Afterwards, the one-bit flag is set to “1” to indicate that the branching node has been selected. The following routers only need to create the FIB entries accordingly and send the Control packet hop-by-hop until the target AR is reached. Figure 5 shows the detailed procedure. As illustrated earlier, the proposed scheme also requires two types of operations for the NDN router as follows. Before the branching node is selected, the routers have to delete the FIB entries not related to the content of that publisher; after the branching node is selected, the routers create the FIB entries and add the Face to point to the new AR and create the PIT entries based on the information identified in the Control packet. For the branching node, it also needs to redirect the Interest packet to the new AR and resets the one-bit flag. There are also two special cases: the branching node is the current AR, and the branching node is the receiver. In the first case, the handover will be executed with the lowest cost. In the second case, the un-used FIB states can all be deleted, and the following data can be requested from the new location to avoid NDN data re-routing costs. In order to illustrate the earlier scheme more explicitly, we give an example of the publisher’s handover procedure.

Figure 5. Publisher handover procedure. Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

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Figure 6. An example of the publisher handover procedure. PIT, Pending Interest Table; FIB, forwarding information base.


In the case of publisher mobility, only the active session handover is supported by this scheme (for example, live video or audio streams). We consider this kind of mobility with our scheme from two perspectives as follows. The first one is that the immutable content is always stored in the fixed server, the data can also be cached on the NDN routers, and then their handovers are infrequent and should be supported by the content management function or just the routing update; the second one is that the point-to-point communication (for audio and video) is very popular in the current Internet and the handover has to be efficient and distributed enough to guarantee good user experience and network scalability. 3.4. Handover failure and recovery

In this example, the mobile publisher moves from AR1 to AR2 as shown in Figure 6. The mobility management procedure is described as follows: (1) When the mobile publisher moves into the overlapped area between AR1 and AR2, it will anticipate the possible handover. (2) In order to trigger the mobility management procedure, the mobile publisher has to send a Control packet to the current AR to trigger the handover as in the fast handover scheme in an IPv6 environment [15]. (3) When the AR1 receives this Control packet, it checks its FIB table to find the content corresponding to this mobile publisher, and then it sends out the Control packet containing with the AR2 identification and the names of the announced content. In addition, AR1 deletes the corresponding FIB entry because the mobile publisher will detach soon. Along the reverse path of the related PIT, this Control packet is transmitted hop-by-hop. For the intermediate routers, the FIB entry corresponding to AR2 and the PIT entry corresponding to the content are compared in order to check whether it is the branching node of AR1 and AR2. If yes, the router needs to delete the related FIB entries as AR1 did because this path will not be used any more. (4) If not, it means that the router is the branching node between AR1 and AR2. Then the branching node will change the face in FIB from AR1 to the AR2 in order to redirect the related Interest packets to the correct location. The one-bit flag is also changed to “1” to indicate that the branching node has been selected. (5) The following routers on the path from branching node to AR2 establish the PIT entries and FIB entries to prepare for the oncoming traffic and Interest packets. In this way, when the mobile publisher attaches to AR2, it can receive the pending Interests as soon as possible and sends out the data to the requested receiver immediately. Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

To enable the handover in advance and improve the mobile user experience in NDN, the proposed scheme uses the fast handover scheme, and the target access router information is provided by the terminal based on its measurement and anticipation. In this way, the actual access router may be different from the anticipated one. In the usual case, the anticipated handover can be separated into two phases: the detachment from the current access router and the attachment to the new access router. In general, the first phase is likely to happen, but for the second phase, it is difficult to accurately anticipate the new location. This means we should effectively handle the state recovery for the routers handling the Control packet. In order to recover from a failed handover prediction, a timer should be used in the Control packet in reality. Then all the bypassed routers adjust the PIT or FIB states together with this timer. If this timer expires but the routers still do not receive the normal Data or Interest packets (that means the adjusted PIT/FIB is not be used as anticipated), the routers have to delete the related state and wait for the basic operation of NDN mobile receiver and publisher. In particular, the mobile receiver will re-issue the pending Interest packets to establish the PIT on the routers, and the mobile publisher will announce the prefix to construct the FIB on the routers (these operations in successful cases are replaced by handling of new incoming Data or Interest packets). A case using this temporary state management is when the receiver and the publisher move at the same time (for example, in the case of a vehicular information network [16]). The communication failure may happen because the receiver or the publisher may not reach the other part because of some incorrect state, and this case is illustrated in Figure 7. When the receiver moves, the PIT will be adjusted to the new access router based on related branching node. However, subsequent Interest packets will be transmitted to the “previous” location of the publisher, which is also moving at the same time. On the publisher side, the FIB is adjusted because its related branching node and the data is routed to the “previous” location the receiver has left. To solve this problem, the temporary state management scheme mentioned earlier can be used as the following two cases:

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Figure 7. Simultaneous handover case.

(1) The branching node of the receiver is first selected: If the publisher mobility-related Control packet is received by the branching node of the receiver, the prefix information matching triggers the branching node to send a new Control packet to the receiver side. In this Control packet, the Timer field is set to zero to make the routers bypassed delete the FIB states immediately. Then the receiver will re-issue the Interest packets, and the routers will fetch the Data packets according to the normal routing information. Because the publisher-related Control packet contains the location of the publisher, the Interest packets can be routed along a specified path even while the publisher is moving. (2) The branching node of the publisher is first selected: If the receiver mobility-related Control packet is received by the branching node of publisher, the prefix information matching triggers the branching node to send a new Control packet to the publisher side. In this Control packet, the Timer field is set to zero to make the routers bypassed delete their PIT states immediately. Then the publisher announces its new location to the receiver according to the location information contained in the Control packet similar to the active publishing scheme proposed in [17]. However, the publisher may also need to announce its new location to the whole network to make the routers update their FIB states and attract the related Interest packets from other receivers to its new location [18].

4. PERFORMANCE ANALYSIS As mentioned earlier, the main goals of our proposed mobility scheme are twofold as follows: to reduce the handover latency for the mobile receiver and to reduce the routing update cost for the mobile publisher. We focus on the receiver’s mobility performance in terms of the handover latency and the publisher’s mobility performance in terms of signaling cost. Although there are some proposals that support receiver mobility and publisher mobility, different assumptions and network architectures are adopted. Besides, as we mentioned earlier, some of them support receiver mobility only, and others support publisher mobility only. Others proposed an overlay architecture, and they do not follow the basic principle of pure NDN, which is

Figure 8. Network model.

distributed and decentralized. In this work, we compare the performance of our proposed scheme with previously proposed solutions (supporting receiver mobility and publisher mobility separately) to investigate the efficacy of our proposed approach. For the quantitative analysis, the adopted network model is shown in Figure 8, and the parameters used to model the network are summarized as follows. R is used to estimate the area of the NDN network. It can also be treated as the average path length between the AR of the receiver and the AR of the publisher. N is the total number of NDN routers in the network. d and c denote the one-hop transmission latency and per-router-processing cost for the basic NDN-signaling message, respectively. We assume that (1) the routers are distributed uniformly; (2) the receiver and the publisher handovers are considered separately; (3) AR has a single wired-hop link, and the possibility that the AR is the branching node is zero; and (4) the cost and the delay introduced by state maintenance and local checks are not considered. 4.1. Handover latency for mobile receiver The handover latency is the interval between the moment when the last Data packet was received from the old AR and the moment when the first Data packet was received from the new AR. If the anticipated target AR is the attached target AR, the mobile receiver can receive the Data packet as soon as possible after the link-layer (L2) handover, and it is the best case. In this case, the handover latency is the sum of the L2 handover latency .dL2 / and the one-hop wireless link delay .dw /. Otherwise, the mobile receiver attaches to another AR but not the anticipated one. In this case, the handover causes pending Interest packets to be re-issued by the receiver after its new attachment, which conforms to the basic NDN procedure. However, if the mobile receiver accesses the new AR and the Data packet has not yet arrived, the mobile receiver treats it as a new subscription. This means that the handover in our proposed scheme should be triggered in advance of the actual L2 access. During the time interval from the triggering of Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

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the handover to the actual L2 attachment, the current AR has to probe the branching node, which redirects the Data packets to the new location, and in this case, the handover latency is as follows:

DD

1 2 1 .1 C 1/ d C 1 .2 C 2/ d R R R 2 3 1 1 .3 C 3/ d C 1 R R R YR1 R k .R C R/ d 1 C C kD1 R R (1)

The previous equation shows that when the first-hop router is not the branching node, the Control packet is sent to the next upstream router. Similarly, the final state is when the publisher receives the Control packet. The handover latency consists of the Control packet transmission latency and the Data packet redirection latency. Dpro D pŒ.dL2 C X/ > D .dL2 C dw / C pŒ.dL2 C X/ < D .D C dL2 C 2dw X/ (2) where X denotes the time interval from the moment when the handover is triggered to the moment when the L2 handover is completed. Then, the handover preparation delay is as follows: Dppro D X D D dL2

(3)

Figure 9 shows that the L2 handover happens after handover triggering by X and X is the handover preparation or prediction time. The handover will be seamless if it is triggered in advance of the L2 handover by X. Lee et al. [7] proposed an approach to support NDN receiver mobility using proxy, which is the entity on the communication path between publisher and receiver. With the same assumption and logic, the latency to exchange the Hold request message and Handover notification message is as follows:

Figure 9. Mobile receiver handover timeline. Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

D1 D

1 .R C R/ d R 1 2 C 1 ..R 1/ C .R 1// d R R 2 3 1 1 ..R2/ C .R2// d C 1 R R R YR1 R k .1 C 1/ d 1 C C kD1 R R (4)

Then the handover latency of the proxy-based scheme is as follows: Dproxy D dL2 C

D1 C 2dw 2

(5)

For the basic NDN, the handover of the mobile receiver is naturally supported by re-issuing Interest packets at the new location, and the handover latency depends on the PIT hit probability along the path from the receiver to the publisher. We assume that the re-issued Interest packets can be satisfied by the branching node, and in this case, the handover latency is Dbasic D dL2 C D. 4.2. Signaling cost for mobile publisher In the basic NDN, the mobile publisher has to announce its new location after the handover if it wants to provide the content continuously. This announcement can use a routing technique such as flooding and is different from our proposed hop-by-hop-routing update. With our proposed approach, we also have to consider the number of routers involved in the publisher handover until the FIB is updated (at least until reaching the branching node). According to our model, the number of nodes within the i-hop range is as follows: 2 i hopArea i .i d/2 N.i/ D N D N D N 2 TotalArea R .R d/ (6) Then the signaling cost (defined as the total number of signaling packets that should be handled during the publisher handover) for the basic NDN is as follows: 1 2 1 N.2/ c Cbasic D N.1/ c C 1 R R R 2 3 1 1 N.3/ c C 1 R R R YR1 R k N.R/ c C C 1 kD1 R R (7) Our scheme for the publisher mobility case is supported by the hop-by-hop-routing adjustment along the path from the publisher to the branching node and the path from the branching node to the receiver. The signaling cost is as follows:

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Cpro D

1 .c 1 C c 2/ R 1 2 C 1 .c 2 C c 3/ R R 2 3 1 1 .c 3 C c 4/ C 1 R R R YR1 k R Œc R C c 1 C C kD1 R R

Table I. Related parameters. Parameter

N R dL2 dw Á d

Value 200 6 hops 200 ms 10 ms 2 100 ms

.R C 1/ (8) where is the ratio of the Control packet’s size in our proposed scheme to the announcement packet’s size in the basic NDN (the Control packet in our proposed approach contains more information and incurs more operations). Then the signaling cost ratio between our proposed scheme C pro and the basic NDN is Cratio D C pro . basic Lee et al. [12] dealt with publisher mobility by using a tunnel mechanism. Its key point is to redirect the incoming Interest packets using tunnel between the publisher’s CR in the home domain and the CR in the foreign domain. In this case, the signaling messages establish a tunnel between the publisher’s home domain CR and the foreign domain CR. We also assume that the ratio between the average signaling message size in this scheme and the announcement packet size in the basic NDN is . Thus, the signaling cost of this solution is as follows: Ctunnel D

1 .2c 1 C 2c 2/ R 1 2 C 1 .2c 2 C 2c 3/ R R 2 3 1 1 .2c 3 C 2c 4/ C 1 R R R YR1 R k Œ2c R 1 C C kD1 R R C 2c .R C 1/ (9)

Then the signaling cost ratio between this scheme and tunnel D Ctunnel . the basic NDN is Cratio C basic

5. NUMERICAL RESULTS In this section, we compare the performance of our proposed scheme with the proxy-based scheme [7] in the mobile receiver case. We also compare the performance of our proposed scheme and the tunnel-based scheme [12] with the mobile receiver case. For the former one, the key metric is the handover latency, while for the later one, the key metric is the signaling cost. We set the default values of the related parameters as shown in Table I [12,19,20]. 5.1. Handover latency of mobile receiver Figure 10 shows the variation of handover latency of the mobile receiver for our proposed scheme, proxy-based

Figure 10. Handover latency of mobile receiver with different preparation time. NDN, Named Data Networking.

scheme, and the basic NDN with prediction time changes. For the basic NDN, the handover latency does not depend on the time when the handover is triggered. As a result, the mobile receiver only re-sends the pending Interest packets after the L2 attachment is finished. Although the proxy-based scheme efficiently avoids the Data packet loss during the receiver mobility, the Data packets are cached in the proxy, which has several hops to reach the new location of the mobile receiver, and in this way, its handover latency is similar with that in the basic NDN. However, we adopt fast handover process for the mobility management in NDN. The current AR probes the branching node in advance, and then the branching node redirects the cached and subsequent Data packets along the new path accordingly. In this way, the handover latency can be significantly reduced. In addition, the handover latencies for various distances between the publisher and the mobile receiver (e.g., the values of R) are shown in Figure 11. It shows that the handover performance of the proposed scheme depends on the handover triggering moment. In particular, when the handover is triggered with enough preparation time, the handover is very fast, and the mobile receiver can get the Data packets as soon as possible after its L2 attachment (when the distance between the receiver and the publisher is lower than 6 hops). Otherwise, the basic NDN operation will be followed, and the handover latency increases. For the proxy-based scheme, the mobile receiver always sends the Handover notification message after the L2 attachment, Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

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Figure 11. Variation of handover latency of mobile receiver for different distances between the mobile receiver and the mobile publisher. NDN, Named Data Networking.


Figure 13. Variation of signaling cost ratio for the mobile publisher with number of network nodes (N ). NDN, Named Data Networking.

different handover preparation time should be set based on different network topologies. 5.2. Signaling cost ratio of mobile publisher

Figure 12. Variation of handover preparation time with distance between publisher and receiver.

and then the handover latency increases with the prolonged path between the publisher and the receiver (e.g., the value of R). However, we assume that the proxy is deployed near the receiver because it is used by the mobile receiver, while the branching node location depends on the network topology. In this way, the handover latency of the proxy-based scheme is lower than our proposed scheme when the handover is not triggered with enough preparation time, and the distance between the receiver and the publisher is larger than 8 hops. That is because the proxy is reached sooner than the branching node under our reasonable assumption. As long as the handover is triggered earlier than the required preparation time, the handover of our proposed scheme will be seamless. As a result, the mobile receiver can get the content as soon as the L2 handover is finished. Figure 12 shows the variation of the handover preparation time under different network topologies (for various distances between the publisher and mobile receiver’s AR). In other words, if we want the handover to be seamless, Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm

Figure 13 shows that the variation of the signaling cost ratio with our proposed scheme depends on the network topology and the network size (total number of routers/nodes in the network). When the network size increases, the mobile publisher has to send the Control packet further for the routing update, and as a result, the signaling cost ratio increases in our proposed scheme. However, the signaling cost ratio with the basic NDN decreases with increase in network size because fewer nodes will be involved in the routing update. However, our proposed scheme performs better for high density networks where the targeted update will be more efficient. In contrast, the reduced signaling cost ratio with our proposed scheme increases when the size of the network increases. This is because more nodes will need to be reached for the mobile publisher in the basic NDN in this scenario. In contrast, our proposed scheme can significantly reduce the number of nodes for unnecessary updates. We highlight two points in Figure 13. In those cases, the signaling cost ratio of our scheme and the tunnel-based scheme are equal to that in the basic NDN (the scenario for our proposed scheme is N D 100, R D 6; while the scenario for the tunnel-based scheme is N D 300, R D 10). When the distance increases for the same network size, our scheme and the tunnel-based scheme perform worse than the basic NDN. This result demonstrates that our scheme and the tunnel-based scheme are efficient when the network topology is small and has a large number of network nodes while the flooding-based routing update approach used by the basic NDN is suitable when the network has few nodes that are sparsely distributed.


The tunnel-based scheme adopts the idea of Mobile IPv6 [21]: a tunnel is established between the home domain and foreign domain and used to transmit the Interest packets and Data packets. In this way, the mobility of publisher is transparent to the receiver and NDN routers. This scheme also avoids the flooding-based announcement of mobile publisher’s new location information as our proposed scheme, but its procedure is complex because of the adoption of Mobile IPv6 principle. And then the signaling cost is higher than our proposed scheme.

6. CONCLUSION In this paper, we propose a novel mobility management scheme to support fast handover for both the mobile receiver and publisher in NDN. In order to guarantee the scalability of NDN and inherit its basic naming and addressing scheme, this proposal uses the hierarchical names to identify the target AR. Then the network-based branching node selection is adopted for the distributed mobility management [22]. In this way, the mobile receiver can obtain the data as soon as possible after the handover, and the established states can be used during the handover. Similarly, the publisher mobility is also based on the branching node selection and hop-by-hop state update. We showed that the signaling cost caused by the flooding approach can be reduced significantly using our proposed scheme.

ACKNOWLEDGEMENTS We thank the anonymous reviewers for their valuable comments that help us to improve the quality and presentation of this paper. This paper was supported by the National Natural Science Foundation of China under Grant No. 61303242. The work of Yong-Jin Park was supported by the FP7/NICT EU-JAPAN GreenICN project.

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AUTHORS’ BIOGRAPHIES Zhiwei Yan received his PhD degree from the National Engineering Laboratory for the Next Generation Internet Interconnection Devices at Beijing Jiaotong University. He joined the China Internet Network Information Center in 2011 and is currently an Associate Professor of the Chinese Academy of Sciences. Since April 2013, he has been an Invited Researcher at Waseda University, Japan. His research interests include mobility management, network security, and next-generation Internet. Sherali Zeadally is an Associate Professor at the University of Kentucky. He received his bachelor degree from the University of Cambridge, England, and his doctoral degree in Computer Science from the University of Buckingham, England. He is a Fellow of the British Computer Society and a Fellow of the Institution of Engineering Technology, England.

Wirel. Commun. Mob. Comput. (2015) © 2015 John Wiley & Sons, Ltd. DOI: 10.1002/wcm


Siran Zhang received his BE degree from the University of Electronic Science and Technology of China in 2013 and ME degree from Waseda University in 2015. Her research interests include information-centric networking and network mobility management. Ruowei Guo received his BE degree from Shizuoka Sangyo University in 2012 and ME degree from Waseda University in 2014. His research interests include information-centric networking and network mobility management.

Yong-Jin Park spent more than 30 years in research and education at Hanyang University, Seoul, and he became the professor emeritus in 2010. He joined Waseda University, Tokyo, in 2010 and is currently a professor in the Department of Computer Science and Engineering. He was the President of Korea Institute of Information Scientists and Engineers in 2003, the Director of Secretariat of Asia Pacific Advanced Network during 1999–2003, and President of Open Systems Interconnection Association during 1991–1992. He visited the Department of Computer Science, University of Illinois, Urbana-Champaign, as a Visiting Associate Professor from 1983 to 1984. He also visited by Computing Laboratory, University of Kent, Canterbury, England, from 1990 to 1991 as a Research Fellow. He was IEEE Region 10 Director and a member of IEEE Board of Directors during 2009-2010. Currently, he is a member of IEEE MGA Nominations & Appointments Committee, IEEE Region 10 Advisory Committee, and IEEE Japan Council Executive Committee. He is an IEICE Fellow.