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Future Network & MobileSummit 2010 Conference ProceedingsPaul Cunningham and Miriam Cunningham (Eds)

IIMC International Information Management Corporation, 2010ISBN: 978-1-905824-18-2

Functional Enhancements of CooperativeSession Control for Minimum Core

Architecture

Takayuki WARABINO, Youji KISHI and Hidetoshi YOKOTA

KDDI R&D Laboratories,2-1-15 Ohara, Fujimino City, Saitama Prefecture 356-8502, JAPAN

E-mail: {warabino, kishi, yokota}@kddilabs.jp

Abstract: This paper proposes functional enhancements of cooperative sessioncontrol for Minimum Core architecture. In past work, the authors invented acooperative session control in which the call setup time is guaranteed through

cooperating core and overlay networks while minimizing processing and traffic loadon the core network. In the session control, each peer selects the core or overlaynetwork for session establishment based on the measured latency on the overlaynetwork. Proprietary technology (the so-called Blacklist method) was applied forlatency decision on the overlay network. However, the performance of the nativeBlacklist method degrades during peer join and leave events. Accordingly, this paperproposes two approaches: Voluntary Latency Acquisition (VLA) and BlacklistSharing (BS) as enhancements of the Blacklist method. These approaches allow theefficient detection of new blacklist entries that emerge due to peer join and leave

events. This paper also reports simulation results that reveal the basic properties ofthe invented session control in a large-scale network and its performance during peerjoin and leave events.

Keywords: New Generation Network, Minimum Core, Overlay Network, P2PSIP,DHT, Chord.

1. Introduction

ICT (Information and Communication Technology) is adopting the role of a new

infrastructure for production activities since it overcomes constraints of time and location

by exchanging a huge amount of information at once [1]. In particular, mobile

communication systems have experienced remarkable growth and they have become

prevalent as social infrastructure. Since their development will be further accelerated thanksto innovative wireless technologies, the performance of mobile systems will be comparable

to that of fixed-line communications. On the other hand, another trend will see user devices

continue to evolve. In addition to existing personal computers and cellular phones, new

types of devices such as home appliances and car navigation and sensor devices are

connecting to the network. In such a ubiquitous environment, the number of network

devices will overwhelm that of current mobile subscribers.

Based on the above prospects, the authors considered that the New Generation Network

(NWGN) over the next few decades should:

x Converge fixed and mobile networks while supporting mobility as one of its

fundamental functionalities

x provide high-speed access (i.e., over 100Mbps - 1Gbps) even when user devices are

connected through wireless links

x have the capability for a tremendous volume of network devices

Copyright 2010 The authors www.FutureNetworkSummit.eu/2010 Page 1 of 9

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The authors invented Minimum Core as a key concept toward NWGN [2]. In the

concept, network functionalities in a core network are minimized by shifting them to access

networks. This avoids traffic concentration on the core network by localizing the signaling

and data traffic within the access networks. This approach ensures the high scalability that

is vital for future network architecture. In addition, a session control method was invented

as one of the key technologies for Minimum Core [2]. In this method, call setup time is

guaranteed through cooperating core and overlay networks, while minimizing processing

and traffic load on the core network. In this method, proprietary technology (the so-called

Blacklist method) was applied for latency decision on the overlay network. However, the

performance of the native Blacklist method degrades during peer join and leave events.

AS

AAAAS

Registrar/MM

User device

Access/

Transport

Network

Overlay

Network

(Virtual)

Minimum

Core

SBS: Small Base Station,MM: Mobility Management,AS: Application Server

Network functionalities are minimized

by shifting them to access network

Signaling Data

Network functions are distributed into

a vast number of SBSs

SBSs

User device

Fig 1. Minimum Core architecture

In order to handle these situations, this paper proposes two approaches: Voluntary

Latency Acquisition (VLA) and Blacklist Sharing (BS) as enhancements of the Blacklistmethod. These approaches allow the efficient creation of new blacklist entries that emerge

due to peer join and leave events. This paper also reports simulation results that reveal the

basic properties of the invented session control in a large-scale network and its performance

during peer join and leave events.

2. Architecture and Techniques for Minimum Core concept

2.1 Minimum Core Architecture

To embody NWGN (NeW Generation Network), the authors invented Minimum Core

architecture (Fig. 1). In this architecture, network functionalities in the core network (e.g.,

mobility management, session control and application servers, etc.) are minimized by

shifting them to the access networks. In current network architectures such as NGN, the

system is composed of service and transport stratums and transport stratum is divided into

core and access networks. In this architecture, all service nodes are allocated in/over the

core network and all signaling and data traffic is necessarily routed via the core network

even for communications between user devices. In contrast, the Minimum Core

architecture avoids traffic concentration on the core network by localizing signaling and

data traffic within access networks. This approach ensures high scalability as future

network architecture.In our current design, the network functions are allocated in small base stations (SBSs)

such as Wireless LAN and Femtocell access points. They have scalability advantages since


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a vast number of SBSs will be deployed in future networks. Our immediate goal involves

efficiently providing various types of services in the Minimum Core architecture without

degrading current usability such as mobility performance, service quality and security.

60

57

42

3

7

19

24

293733

60

57

42

3

7

19

24

293733

(a) Latency measurement (b) Latency acquisition

Ping/Pong

1. Request

2. Response

ID=33, R(29,33)

ID=33, R(29,33)ID=29, R(24,29)

(c) Blacklist registration

If R(3,19) + R(19,24) > th.,ID space from Peer 24 to Peer

33 is registered

Registered

ID space

R(x,y): RTT from Peer x to Peer y

60

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3

7

19

24

293733

ID=33, R(29,33)ID=29, R(24,29)ID=24, R(19,24)

7, R(3,7)19, R(3,19)

37, R(3,7)

Fig. 2. Blacklist registration

2.2 Cooperative Session Control

The authors invented a session control method for Minimum Core [2]. The method

integrates the core network with an overlay network composed of SBSs. The overlay

network is a virtual network on top of IP networks. While session control on the overlay

network have been developed so far (e.g., dSIP [3], P2PP [4] and P2PSIP [5]), these

technologies are utilized by some systems such as Skype [6].

It is assumed that P2PSIP, which is currently standardized in IETF, is utilized for

session control on an overlay network. In the P2PSIP, the functionalities of existing SIP

servers are distributed into user devices and which compose the overlay network,

whereupon a serverless systems is realized. For the overlay construction and management,

P2PSIP utilizes prominent DHT (Distributed Hash Table) technologies such as Chord [7],Bamboo [8] and Tapestry [9]. DHT is an abstract hash table service realized by storing the

hash table contents across a set of peers. Out standing features includes absence of

centralized server, system scalability and autonomous network management etc. However,

current P2PSIP technologies are based on a best-effort principle and lack mechanisms to

guarantee the quality of call setup time (CST). In contrast, our invented method guarantees

CST through cooperating core and overlay networks, while minimizing processing and

traffic load on the core.

In cooperative session control, each peer selects the core or overlay network as the

system to be used for session establishment based on the measured latency on the overlay

network. For system selection, the authors have invented the Blacklist method. In this

method, each peer measures latency on the overlay network by utilizing maintenance traffic,etc. and registers an ID space, for which the latency exceeds the desired threshold, in a

blacklist. When initiating a session, each peer checks whether the destination ID is included

in the blacklist or not. If the destination ID is not included in the blacklist, the overlay

network is used. Otherwise, the core network is used.

2.2.1 Basic Operations of Blacklist Creation

In the following, the blacklist creation procedures are explained when Chord [7] is used as a

DHT algorithm (Fig. 2). In the Chord, each peer maintains a neighbor table (a so-called

finger table) for efficient overlay routing.


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(a) Latency measurementEach peer periodically measures the RTT (Round Trip Time) to other peers registered in its

own finger table (Fig. 2 (a)). In the measurement, a keep-alive message to the fingers,

which represents one type of maintenance traffic in the Chord, can be utilized.

(b) Latency acquisition

Each peer acquires the measured RTTs on a message path by utilizing the maintenance andother messages on the overlay network. In the actual procedures, when a peer relays a

response message, the measured RTT to the previous relayed peer is attached to the

message as well as the ID of the previous peer. In Fig. 2 (b), Peer 29 adds RTT to Peer 33,

while Peer 24 adds RTT to Peer 29. Consequently, the peers receiving and relaying

response messages can acquire latency on the relayed path on a hop-by-hop basis.

(c) Blacklist registrationAfter (b), a peer conducts blacklist registration based on the acquired RTTs. A feature of

blacklist registration is that it allows for the peers to register a range of ID space to which

latency exceeds a preconditioned threshold. In the detailed method, the peer totals up the

RTTs from the closer peers. During the addition, when the sum of the RTTs exceeds the

threshold, the peer registers the ID space from a corresponding peer to a responding peer.

For example, in Fig. 2 (c), since the sum of R(3,19) and R(19,24) exceeds the desired

threshold, the ID space from Peers 24 to 33 is registered in the blacklist.

The blacklist has three fields: From, To and Expiration time. In the above case, the IDs

of Peer 24 and 33 are set at the From and To fields, respectively. The expiration time is set

based on the registered time and used for blacklist maintenance.

(d) Blacklist maintenanceIf the expiration time of a blacklist entry expires without any updates, a peer sends a

dedicated message destined to an ID that is included in a To field. The peer then updates

information on the entry when receiving a response message.

3. Functional Enhancements for Handling Peer Join and Leave

In Minimum Core, the overlay network consists of SBSs such as wireless LAN and

Femtocell access points. The peer join and leave rates are low compared with ordinary P2P

applications since SBSs are usually powered on and stably connected to the access

networks. However, once a join and leave event occurs, they require the blacklists to be

updated on the overlay network. This section analyses the situations and proposes some

extensions of the Blacklist method.

3.1 System Analysis of Impact of Peer Join and Leave

When a peer joins or leaves, routing tables in other peers are automatically updatedaccording to the maintenance mechanisms of DHT. Since these updates change the routing

paths of overlay messages, the blacklists in the overlay network must be updated. There are

two cases regarding blacklist updates: (a) the creation of a new blacklist entry and (b) an ID

space change/deletion of an existing entry. Fig. 3 shows simple examples of both cases. In

both cases, when Peer B leaves the network, Peer F is added in the routing table of Peer A

instead of Peer B. In the case of (a), since the routing update causes an increase in latency

to Peer E, the ID space that should be registered in the blacklist of Peer A newly emerges.

In the case of (b), Peer A already has an entry from Peer C to Peer E. Since the routing

update decreases the latency to Peer E, the ID space of the entry should be decreased. In

addition, the expansion of the ID space of an existing entry and the deletion of the entry are

included in case (b).Meanwhile, case (b) can be handled by the blacklist maintenance shown in Section

2.2.1 (d) since the latest status of existing entries is checked by sending dedicated messages


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after expiration. However, case (a) cant be fully supported by current mechanisms. In the

basic operations shown in Section 2.2.1, new blacklist entries are not created until

maintenance or other messages are sent through the corresponding ID space. Then, when

the peer join and leave rates increase, performance degrades. In addition, blacklist

maintenance cant handle case (a) since it has no mechanisms to detect new blacklist entries.

Accordingly, this paper proposes the following two approaches to realize efficient detection

of new blacklist entries.

(2)

(3)

(4)

A B C D EF

100ms 100ms 100ms 100ms

Peer

RTT

A C D EF

100ms 100ms

250ms

No Blacklist

A B C D EF

250ms 250ms 100ms 100ms

Peer

RTT

A blacklist entry has to

be created (from C to E)

A C D EF

100ms 100ms

200ms

Blacklist entry (from C to E)

ID space has to be

updated (from D to E).

Case (a)

Case (b)

Threshold of blacklist

registration: 500 msWhen Peer B departs, Peer F is

added in routing table of Peer A

Fig. 3. Simple examples of impact of peer join and leave events

3.2 Proposed Enhancements of Blacklist Method

3.2.1 Voluntary Latency Acquisition (VLA)

In this method, each peer selects an ID on the overlay network and sends a dedicated

message destined to the selected IDs (destination ID). When the peer receives a response

message, the blacklist registration procedures are conducted as shown in Section 2.2.1 (c).This method allows the detection of new blacklist entries that emerge due to peer join and

leave events.

For efficient blacklist creation, it is desirable to select the destination ID so that it can

take long time for the message to reach the destination. As one can imagine, latency

increases according to the number of message hops. Then, an estimation technique of the

number of message hops is invented and utilized for the ID section. Fig. 4 shows the

pseudo-code of the estimation method.

(1) Each peer first selects a target ID in a random manner.

(2) The peer derives the distance from its own ID to the target ID and the average ID space

that one peer is responsible for. The average ID space can be calculated by dividing the

ID space covered by successors registered in a successor list by the number of

successors.

(3) The peer estimates the number of message hops to the target ID by simulating the

original Chord shortcut routing. In each shortcut in the overlay network, the distance to

the target ID shortens by 2i (i is an integer decreasing from 1591 to 0). The shortcut

continues until the distance becomes smaller than the average ID space.

(4) If the estimated number of message hops is larger than the threshold, the peer sends a

dedicated message to the selected target ID. Otherwise, the procedures are repeatedly

conducted from (1) to (4).

In summary, the method realizes efficient detection of new blacklist entries by utilizing

the invented estimation technique of the number of message hops.

1It is derived based on the length of the ID in the Chord (160 bits).


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targetID = randID(); // generate a random target ID

distance = targetID - ownID; // calculate ID distance from own ID to target ID.

interval= cal_interval();

// calculate average ID interval which one peer is responsible for.

eHop = 1; // initialize an expected hop count.

for (i=159; i > 0; i--) {

if(distance < interval) break;

// if the distance is smaller than interval, finish increment of eHop

if(distance >= pow(2,i) ) {

eHop ++; // increment eHop for shortcut on Chord network.

distance - = pow(2,i);}

}

if(eHop > threshold) request_sendto(targetID);

// if the eHops is larger than threshold, send an overlay message to target ID.

Otherwise, go back to first line of pseudo-code.

(1)

(2)

(3)

(4)

Fig. 4. Pseudo-code of estimation of message hops for Voluntary Latency Acquisition (VLA)

3.2.2 Blacklist Sharing (BS)

In addition, blacklist sharing (BS) enables efficient blacklist creation by sharing blacklist

information between peers. The procedures of blacklist sharing are as follows (Fig. 5):

(1) Each peer periodically sends blacklist sharing requests toward its own fingers, which

carry the IDs of both the destination finger (Peer 19) and its next finger (Peer 37).

(2) A peer receiving the request searches the entries existing between the two IDs attached

in the request within its own blacklist. The peer sends a response message to the

originator (Peer 3) with the corresponding entries.

(3) When the originator receives the blacklist sharing response, it compares receivedentries with entries registered in its own blacklist and checks whether the response

includes new blacklist entries.

(4) If the new entries exist, the originator sends dedicated request messages destined to IDs,

which are set at the To field of the entries, in order to reflect the most recent status of

the overlay network. Corresponding response messages are returned to the originator.

(5) Finally, when the originator receives a response message, it conducts the blacklist

registration procedures as shown in Section 2.2.1 (c).

(6) Each peer repeatedly conducts the above procedures (i.e., from (1) to (5)) to all fingers.

This method has two effects for efficient blacklist creation. When a peer detects a new

blacklist entry, the method allows the peer to quickly share the information with otherpeers. In addition, the method is effective when a new peer joins the network. Since the

new peer has no blacklist, the method helps the peer create a network-wide blacklist

immediately after joining.

4. Simulation Evaluations

4.1 Evaluation Setup

The authors have developed a simulator based on Oversim [10] (an open-source overlay

simulator) and have conducted evaluations to validate the proposed cooperative session

control and additional functionalities of the Blacklist method. The evaluation parametersare shown in Table 1. In these evaluations, the authors evaluated the basic properties when

changing the number of peers up to 16,000 and the impact of peer join and leave events.


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As a network model, a traditional transit-stub model [11] was used since its architecture

resembled the assumed future network (Fig. 6). Transit and stub domains correspond to

core and access networks, respectively. In the model, all peers were allocated in stub

domains and the packet transmission delay was configured based on previous studies

[7][12]. The target CST was set to 3 [s] according to Japanese regulations [13]. Moreover,

each measurement was conducted by starting the actual measurement after a 2-hour test run.

During the test run, each peer conducted voluntary latency acquisition and intentionally

sent overlay messages to destination IDs in order to create as many blacklist entries as

possible.

3 19 37

Peer 3(black)

Peer 19 (gray)

(1) Blacklist sharing request

(Peer19, Peer37)

(2) Blacklist sharing response

(a,b,c,d)

(4) Dedicated request/response

messages (to b and c)

(5) Blacklist registration

(b, c)

(3) Detection of new entries

(b, c)

Existing blacklist

entriesa b c d e

Fig. 5. Procedures of Blacklist sharing

Table 1. Evaluation parameters

Number of peers up to 16,000

Evaluation period 2 [hour]

Target CST(Blacklist registrationthreshold)

3 [sec](1.5 [sec])

Session initiation model Poisson distribution

DHT algorithm Chord

Stabilize interval 15 [sec]

Fix finger interval 120 [sec]

Network model

Transit-Stub model

T-T link: 100 [ms]

T-S link: 10 [ms]S-S link: 1[ms]

Stub domain

(Access transport)

Stub domain

Transit domain

(Core transport)

Core

Small BSs

(Peer)

Transit-Transit link

Transit-Stub link

Stub-stub link

Fig. 6. Network model for evaluations

4.2 Evaluation Results

(a) Basic properties of proposed session control in a large-scale networkFirst, the authors have evaluated CST in terms of both the proposed session control and a

conventional P2PSIP in order to validate the former. In the P2PSIP method, the session

being established is always conducted on the overlay network.

Distributions of CST are shown in Figs. 7 when changing the number of peers. These

figures indicate a similar tendency, while the CST in P2PSIP slightly increases according to

the number of peers. Table 2 summarizes these results. For example, when the number of

peers is 16,000, the percentage of CST exceeding the desired time reaches 12.97 [%] in

P2PSIP. In contrast, the proposed methods suppress that to be less than 0.4 [%], whichrepresents approximately one-thirtieth of that of P2PSIP. These results also show that the

proposed methods satisfy the Japanese regulations [13], which stipulate that the probability


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0

5

10

15

20

25

30

0.0 0.6 1.2 1.8 2.4 3.0 3.6

Call Setup Time [sec]

Percentage[%]

Proposal

P2PSIP

(a) 8,000 peers

0

5

10

15

20

25

30

0.0 0.6 1.2 1.8 2.4 3.0 3.6

Call Setup Time [sec]

Percentage[%]

Proposal

P2PSIP

(b) 16,000 peers

Fig. 7. Distribution of the call setup time (CST)

Table 2. Evaluation results of CST Table 3System utilization

Probability of CST

exceeding 3 seconds

Average CST [sec]

# of peers P2PSIP Proposal P2PSIP Proposal

4,000 2.63 0.14 2.05 1.86

8,000 6.69 0.23 2.22 1.86

16,000 12.97 0 9.3 2.36 1.82

Via overlay Via core

4,000 89.06 [%] 10.94 [%]

8,000 79.61 [%] 20.39 [%]

16,000 70.32 [%] 29.68 [%]

of CST exceeding 3 [s] should be less than 1 [%]. In addition, Table 3 shows the percentage

of selected systems for the proposed methods. As shown in Table 3, the proposed methods

can reduce the processing burden of the core by up to roughly 70 [%]. When the core

network is dimensioned based on system occupation which is defined as the average arrival

rate divided by the average service rate in queuing theory. Given the constant system

occupation, the service rate is proportional to the arrival rate. This implies server facilities

dimensioned in the core network are proportional to the load imposed on the core network.

Based on the above notion, the evaluation result shows that proposed approach can reduce

server facilities in the core network by 70 [%] compared to existing centralized approach.(b) Performance characteristics when peers join and leave

Next, the impact of peer join and leave events on the proposed session control was

investigated. As explained in Section 3, the authors proposed two approaches (i.e.,

voluntary latency acquisition (VLA) and blacklist sharing (BS)) to handle peer join and

leave events.

Fig. 8 shows the evaluation results of CST, which is less than 3 [s]. In the evaluations,

one peer joins and another leaves at constant intervals. The model maintains a constant

number of joining peers. The number of peers is 10,000. The intervals of voluntary latency

acquisition and blacklist sharing are 10 [s] and 15 [s], respectively. As shown in Fig. 8,

each method improves the performance compared with the native Blacklist method (w/o

extensions in Fig. 8). In particular, utilizing the two proposed methods achieves aprobability of 99 [%] when the join/leave interval exceeds 1 [s]. The interval corresponds to

each peer remaining within the network for 2.8 [hours]. In contrast, the proposal without

extensions achieves a probability of 99 [%] when the join/leave interval exceeds 20 [s].

Throughout the evaluations, it was confirmed that the two proposed approaches can

improve the performance of the Blacklist method when the peers constantly join and leave.

5. Conclusions

This paper proposes two approaches as enhancements of our proprietary Blacklist method:

Voluntary Latency Acquisition (VLA) and Blacklist Sharing (BS). While the native

procedures of the Blacklist method cant handle peer join and leave events, these methodsallow the detection of new blacklist entries that emerge due to peer join and leave events.


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This paper also reports simulation results in a large-scale network. These results reveal

the basic properties of the proposed session control and performance during peer join and

leave events. For example, when the number of peers is 16,000, the probability is reducedfrom 12.97 [%] in conventional P2PSIP to 0.4 [%]. In addition, the proposed methods

mitigated the processing burden of the core by roughly 70 [%] in comparison with the

current centralized architecture. It was also confirmed that the two proposed approaches

could handle low peer join/leave rates.

96

97

98

99

100

1 10

Join/Leave interval [sec]

Probability[%]

100

Proposal (w/o extensions)Proposal with VLA

Proposal with BS

Proposal with VLA and BS

Fig. 8. Probability of CST less than 3 [sec] when changing join/leave interval (10,000 peers)

The authors will conduct detailed evaluations on a large-scale network. In addition,

there are plans to implement the proposed mechanisms into actual SBSs and conduct

system evaluations with a core system prototype.

Acknowledgments

This work is supported by the National Institute of Information and Communications

Technology (NICT) of Japan.

References

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[2] T. Warabino, et al., Session Control Cooperating Core and Overlay Networks for Minimum Core Architecture IEEE Global

Communications Conference (GLOBECOM 2009), Dec. 2009.

[3] D. Bryan et al., dSIP: A P2P Approach to SIP Registration and Resource Location, draft-bryan-p2psip-dsip-00, Feb. 2007.[4] S. Baset et.al., Peer-to-Peer Protocol (P2PP), draft-baset-p2psip-p2pcommon-01, Feb. 2007.

[5] IETF P2PSIP WG. Available: http://www.ietf.org/html.charters/p2psip-charter.html[6] Skype. Available: http://www.skype.com

[7] I. Stoica, et al., Chord: A Scalable Peer-to-peer Lookup Service for Internet Applications, Proc. ACM SIGCOMM'01, Sept. 2001.

[8] S. Rhea et al., Handling Churn in a DHT, Proceedings of the USENIX Annual Technical Conference, Jun. 2004.

[9] B. Y. Zhao et al., Tapestry: A Resilient Global-Scale Overlay for Service Deployment, IEEE Journal on Selected Areas in

Communications, 2004.[10] The OverSim P2P simulator. Available: http:// www.oversim.org/

[11] Zegura, et al., A quantitative comparison of graph-based models for Internet topology, IEEE/ACM Transactions on Networking,Dec. 1997.

[12] S. Ratnasamy, et al., A Scalable Content-Addressable Network, Proc. ACM SIGCOMM'01, Sept. 2001.

[13] Ministry of Internal Affairs and Communications (in Japanese). Available:http://law.egov.go.jp/htmldata/S60/S60F04001000030.html


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