an adaptive path routing scheme for satellite ip networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMSInt. J. Commun. Syst. 2003; 16:5–21 (DOI: 10.1002/dac.577)

An adaptive path routing scheme for satellite IP networks

Jing Chenn,y and Abbas Jamalipourz

School of Electrical and Information Engineering, The University of Sydney, Sydney NSW 2006, Australia

SUMMARY

Mobile satellites can be considered as the promising solution to the global IP network. In order to providequality of service (QoS) in future networks, mobile satellite can be integrated with the asynchronoustransfer mode (ATM) to switch IP datagrams in the space. For such a network, new and sophisticatedrouting and handoff algorithms are essential. In this paper, a new scheme called adaptive path routingscheme (APRS) is proposed. It is shown that the APRS can provide superior performance for routing andhandoff in mobile satellite networks compared with conventional schemes. Copyright # 2003 John Wiley& Sons, Ltd.

KEY WORDS: mobile Internet; WATM; LEO/MEO SATATM networks; routing; handoff; QoS

1. INTRODUCTION

The low/medium earth orbit (LEO/MEO) satellite networks take more and more importantroles in the wireless communications world because of several outstanding features, such asglobal coverage, low propagation delay and high capacity [1, 2]. Asynchronous transfer mode(ATM) has already demonstrated its capability in providing network quality of service (QoS)guarantee along with its reliable high-bandwidth capability [3, 4]. In order to take theadvantages of the LEO/MEO satellite network and the ATM, it is proposed to integrate thesetwo to form a new network, namely LEO/MEO SATATM network, for the futurecommunication systems [1, 2, 5]. Within this network, inter satellite links (ISL) may be appliedas the space links to provide global accessibility and to enable the LEO/MEO SATATMnetworks to be used as the backbone for the next generation global wireless networks [1, 3, 4].

Internet protocol (IP) has already been widely and rapidly developed for both private andpublic networks. But due to the lack of capability of providing QoS guarantee, IP has beenprevented from being further utilized in many applications that require strict QoS requirements.Such an issue motivates the research of combining ATM and mobile IP (MIP) networks togenerate a new kind of network, the ‘MIP over ATM’ network [6–8]. The LEO/MEO SATATMnetwork is a very promising solution to global MIP services because of its capability of global

Received 31 March 2002Revised 30 June 2002

Accepted 31 August 2002Copyright # 2003 John Wiley & Sons, Ltd.

yE-mail: [email protected]

nCorrespondence to: Jing Chen, School of Electrical and Information Engineering, The University of Sydney, SydneyNSW 2006, Australia.

zE-mail: [email protected]

coverage and QoS guarantees [2, 5–8]. This leads to the proposal of IP-over-LEO/MEO-SATATM network by overlaying MIP on the LEO/MEO SATATM networks. However, thisraises many open issues, and one of the most critical ones is how to support IP mobility over aWATM environment, i.e. to support the mobility of wireless ATM while the Internet service isbeing provided. In order to make comprising between the connection-oriented ATM end-to-endswitching mode and the connectionless IP hop-by-hop routing mode without any conflict, ATMaddress resolution protocol (ATMARP) defines the mirror relationship between the IP addressesbelonging to different IP sub-networks and the destinations’ ATM addresses or the ATMaddresses of routers closer to the destinations [6, 8, 9]. With the ATMARP, an end-to-endconnection based on the IP addresses can be set up to avoid the use of a hop-by-hop routingmethod.

At present, the best-effort scheme, which is based on the Bellman–Ford algorithm [10] and fora hop-by-hop routing, is widely used as routing method in IP networks. However, two of itsdisadvantages are that it does not provide QoS guarantees and it dose not take some importantsystem factors, such as channel traffic and delay jitter, etc. into consideration while building arouting path. As a consequence, it will cause some undesirable issues, such as traffic congestionbecause of too much concentration on some popular ISLs and delay jitter due to sharp variationin the paths’ length. On the other hand, the modified dijkstra shortest path (MDSP) routingscheme is also a desirable routing method for an LEO/MEO SATATM network [1]. But for theMDSP scheme, although it takes the actual distance between the satellite nodes into account, itdoes not consider the predictable and natural feature of an LEO/MEO satellite network, so itdoes not provide any advantages in reducing the handoff frequency. So, none of these twoschemes seems to be suitable for an IP-over-LEO/MEO-SATATM network that requires QoSguarantee such as delay jitter, call drop probability, etc. which are very significant for an MIPapplication. Therefore, it is necessary to describe a new routing scheme that can be applied in anIP-over-LEO/MEO-SATATM environment.

In this paper, we present a routing scheme called adaptive path routing scheme (APRS) forthe IP-over-LEO/MEO-SATATM network. The proposed APRS scheme aims to improve thesystem QoS performance from handoff and new call admission rates, end-to-end delay, anddelay jitter point of views. These three factors significantly affect the performance of an MIPnetwork and therefore they are used to measure the efficiency in an MIP application. The mainideas of the APRS scheme are, firstly to use the periodical and predictable movement knowledgeof the LEO satellites to reduce the handoff frequency. Secondly, to consider the ISL trafficsituation to alleviate the traffic congestion on some particular ISLs, which improves theadmission rate for both handoff calls and new calls. And thirdly, to apply the parameter ‘sliding-

width’ to reduce the delay variance during handoffs to reduce the system delay jitter.In the following sections, we will discuss the proposed adaptive path routing scheme for the

IP-over-LEO/MEO-SATATM. Then, based on simulation results, we will demonstrate theperformance of this scheme and analyse the feasibility of the proposal.

2. DESCRIPTION OF THE ADAPTIVE PATH ROUTING SCHEME (APRS)

The speed of LEO/MEO satellites results in frequent handoffs, which in turns causes a negativeeffect on the network QoS performance. In an MIP network, normally sorts of QoS categoriessuch as end-to-end delay, delay jitter, and the continuation of communication are important in

Copyright # 2003 John Wiley & Sons, Ltd. Int. J. Commun. Syst. 2003; 16:5–21

J. CHEN AND A. JAMALIPOUR6

evaluating the network efficiency [1–3] although it also depends on the requirements fromdifferent applicants. One of the significant differences between a mobile satellite network and aterrestrial cellular network is that the former one is a periodical and predicable network. Thismeans that because of the satellites’ periodical movement along the corresponding earth orbits,the position of the satellites in the space can be accurately predicted and pre-calculated [1–3].This information is very important because in a mobile satellite network, the movement of thesatellites can be considered as the main cause of handoffs. The system can use this knowledge topreserve some available paths in the database prior to a handoff. This allows the system toretrieve paths from the database straight away instead of re-building them, which can reduce thedelay caused by path re-building and the handoff blocking termination due to the pathunavailability.

To overcome those drawbacks introduced by the best-effort scheme and MDSP scheme in anIP-over-LEO/MEO-SATATM network while providing relatively fast routing solutions at thesame time, we propose a routing and handoff scheme, named APRS, to improve the networkQoS performance. The proposed APRS will consists of three sub-component schemes, namelythe moving estimation-based Dijkstra shortest path (MEBDSP) routing scheme, traffic detectingscheme (TDS), and sliding-width-based path selection scheme (SWBPSS), respectively. TheAPRS is proposed and evaluated for an SATATM network using inter-satellite links.

In order to better describe and evaluate the proposed scheme, prior to introducing thescheme, we will give the suggested network protocol model of the IP-Over-LEO/MEO-SATATM network and the ISL channel model on which the APRS is based. Then, the threesub-component schemes of the APRS will be described. Finally, the procedure of the APRS willbe provided.

2.1. Protocol model of IP-over-LEO/MEO-SATATM networks

In an ATM-based satellite (SATATM) network, all satellites in the network use multispotbeams with complex onboard processing and switching (OBP/OBS) capabilities [2–4]. This canalleviate the network dependency on the ground services such as the gateway stations and thenetwork control centre (NCC), and it can also provide a quick deployment of ATM connectivityusing the exiting satellites. Therefore, providing the high-speed network access by user terminalsand high-speed interconnection between remote ATM networks is possible under this networkprotocol [1, 2, 8].

Besides, in an SATATM system that employs inter-satellite links (ISLs), such as an LEO/MEO SATATM network, each satellite will act as an ATM node and the whole network canprovide both network access and network interconnectivity. Under this type of network, theinterfaces between the satellites and the ground terminals are network-to-network (NNI) type[2]. Here, series of consecutive ISLs will form a single virtual channel connection (VCC) betweena pair of ATM satellite nodes, and finally couples of VCCs will form a virtual path connection(VPC) between the two nodes. By this, we can build a complete high-speed ATM network in thespace by considering on every LEO/MEO satellite as an ATM node, which can bring thenetwork the capability of utilizing advantages of ATM routing schemes and accessing any fixedterrestrial ATM network [2].

However, a major drawback of this architecture is that the direct ATM connections betweenhosts not belonging to the same IP subnet are not allowed. A solution to this is to use the next

hop resolution protocol (NHRP), which is based on the ATMARP proposal and is defined within


ADAPTIVE PATH ROUTING SCHEME 7

the ATM Forum multi-protocol over ATM (MPOA) model [8, 10]. The basic idea of the NHRPis to allow the IP nodes to use the shortcut routing, i.e. direct switched virtual connections(SVCs), instead of the IP hop-by-hop routing. NHRP is an extension of the ATMARP. TheNHRP server (NHS) is featured with all NHRP functions and has the knowledge of all the IP-ATM address mappings. An NHRP client (NHC) is always located at the interface pointbetween a WATM and a mobile IP network. This means that an IP terminal can use itscorresponding NHC to send an NHRP request to the system NHS to ask for the ATM addressof the closest next-hop edge node towards the IP destination [8]. Figure 1 shows an illustrationof this architecture. The main advantages of this scheme are that, firstly, it avoids the trianglerouting issue of an MIP network. Secondly, it does not need too much modification on theexisting ATM and MIP networks and thus it avoids new service’s re-investment. But, this needsstrong support from the NHS and the NHC.

2.2. Model for ISL channels in IP-over-LEO/MEO-SATATM networks

In this paper, we assume that new calls can be generated with equal probabilities from allsatellites in the network. We also assume that both the interarrival time and the duration of acall obey a Poisson distribution. The suitability of this assumption has already been verified invoice-based communication networks but not in packet-based mobile networks. However,because currently there is no better alternative, we still use it as our model [4]. Thus, the holdingtime of an ISL channel can also be considered to obey a Poisson distribution and the ISL can betreated as a M/M/C/C model, as illustrated in Figure 2. Therefore, the whole system can betreated as an M=M=C=C model. In an M=M=C=C; the two M ’s represent that the interarrivaltime of new calls and the call duration both obey the Markovian policy; the first C represents themaximum number of calls that can be handled concurrently in the system; the second Crepresents that the system not being able to queue any new incoming calls once the systemcapacity is fully occupied.

Figure 1. The NHRP for IP-over-WATM model.



Within such a system, the failure in accepting a new call request, especially a handoff callrequest, may occur because of either two reasons. One is that currently there are already Ccustomers in the system and the system can no longer accept any additional new calls. Here, weuse PC to denote the probability of there being C customers in the system, and we have

PC ¼ðl=mÞC=C!

PCi¼0 ðl=mÞ

i=i!ð1Þ

where l is arrival rate of new calls and m is the average duration time of the call [11]. Theother reason is that although there are less than C customers in the system, a call requestis still rejected because the involved ISL resources are insufficient to support thebandwidth requirement (i.e. a QoS) of the requested call. For a handoff call request, theprobability of this is denoted as Ph: Thus, the handoff blocking probability, PHBP; can becalculated by

PHBP ¼ 1� ð1� PCÞð1� PhÞ ð2Þ

where PC is a fixed system parameter. Therefore, in order to reduce the probability PHBP; theonly way is to reduce the probability Ph:

In order to simplify the problem, in this paper, we only consider two types of handoffs, link

handoff and connection handoff [1, 2]. Link handoff is caused by releasing of some ISLs when thesatellites are approaching some particular situations; e.g. either of the earth poles. Connection

handoff is caused by the relative movement between end users and their corresponding satellites.Here, all the parameters PC ; Ph; and PHBP are assumed to remain unchanged during the periodsthat the corresponding satellites remain in their current footprints.

2.3. Moving estimation-based Dijkstra shortest path (MEBDSP) routing scheme

This scheme is based on the Dijkstra shortest path algorithm. but it also considers thepredictable movement knowledge of an LEO/MEO mobile satellite network in determining the

Figure 2. The model of ISL channel (M=M=C=C).



routing path. Therefore, it can reduce the handoff frequency and thus provide the network withbetter QoS [2].

Unlike the terrestrial cellular mobile systems, a LEO/MEO satellite network can useinformation about the periodical movement of the satellites in the networks to obtain theknowledge of satellites’ location at a particular time, and to predict satellites’ location in thefuture. Therefore, we can have an accurate knowledge of the network topology at any time. Thisknowledge can further be used in selecting a path to avoid any unnecessary link handoff andconnection handoff. When constructing a path between any two earth terminals (through thosemobile satellites and ISLs), we shall avoid using the satellites that are approaching one of thetwo earth poles, but choose the satellite nodes that will keep the current ISLs in the next timeslot as much as possible. Moreover, in this scheme, not only the number of the satellite nodeswithin a path, but also the actual distance between any pair of satellite nodes are taken intoaccount in determining the path. In order to apply this algorithm in an LEO/MEO SATATMnetwork, we define the following parameters:

* DISL: The distance between any pair of adjacent satellites located in the same orbital plane.We further assume that the value of DISL remains unchanged in the system (as it is in a realcase).

* disi: The distance of each ISL connection in the path, i ¼ 1; 2; . . . ;N � 1; where N is thetotal number of the satellite nodes in a given path. This distance may be variable as thedistance between satellites on different orbital planes changes during the movement of thesatellites.

* Tdel: The average satellite switching delay factor (per satellite node). The value of thisparameter is shown as a relative value to the total delay of a path.

* LWi = disi=DISL ði ¼ 1; 2; 3; . . . ;N � 1): The link weight of a single ISL connection in apath.

* TLW ¼ ðN � 1Þ*Tdel þXN�1

k¼1

LWk ð3Þ

* HO trigger: The triggering value of handoff event. It has a value between 0 and 1. It can bedefined as the ratio of the least TLW value of all the candidate paths and the TLW value ofthe current path. The larger HO trigger value we select, the more handoffs it mighthappens.

The following scenario can describe the scheme:

* For a decided pair of satellite nodes, list all possible shortest paths [2].* Calculate TLW values for the all listed shortest path.* Select those paths of which TLW values meet system QoS requirement.* Based on the predefined HO trigger value, and the moving estimation knowledge

of LEO/MEO satellite networks, a path which that can minimise the number ofboth the link handoffs and the connection handoffs, and also at the same timesatisfy the HO trigger requirement is chosen. It is then denoted as the MEBDSP-basedpath.



So, when applying the MEB-MDSP scheme, because proper paths are selected to prevent thehappening of link handoff events, the total number of handoffs during the communication canbe decreased, which alleviates the network performance degradation due to frequent handoffevents.

2.4. Traffic detecting scheme (TDS)

Channel traffic management can improve the network QoS performance by efficiently utilizingthe ISL channel resources [4]. As mentioned earlier, in an SATATM network, a series ofconsecutive ISLs build a VCC between any pair of satellite nodes and finally forms a VCP. Forany pair of end terminals, normally there is more than one path that can satisfy the system QoSrequirement. In order to alleviate the traffic congestion situation in the system, we shall avoidusing a path that is either via the hot spot nodes or containing some ISLs that have already beenin a high traffic situation [12].

For a pair of satellites A and B; let us denote the number of the paths between satellite B ofwhich TLW value meet system QoS requirements as NA�B: Then, we define:

* Cði;jÞ; the number of occupied channels in the ith ISL step of jth path ð14j4NA�BÞ;* ACj; the average number of occupied channels of the jth path, and we have

ACj ¼Xn

i¼1

Cði;jÞ=n ð8ISL 2 jth pathÞ ð4Þ

where n is the total number of ISL steps in the jth path.* MCj; the minimum number of occupied channels among all the ISL steps of the jth path,

we have

MCj ¼ MINðACjÞ for all ISLs 2 jth path ð5Þ

* TWj; the traffic weight of the path j; and we have

TWj ¼ Q*ACj þ ð1� QÞ*MCj ð6Þ

where Q is the traffic coefficient parameter, which depends on the system QoS requirementand is valued between 0 and 1.

* MTW, the minimum traffic weight among all possible paths, i.e.

MTW ¼ MINðTWjÞ ðfor 14j4NA�BÞ ð7Þ

The purpose of the traffic detecting scheme is to choose a path with the minimum trafficweight value, i.e. MTW, from all candidate paths, so as to alleviate the accumulated traffic onISL resources by more uniformly traffic distribution in the system.

As an example, Figure 3 shows two potential shortest paths for routing between nodes A andB; represented by P1; P2 and are shown with solid and broken lines, respectively. The numberattached to each ISL represents the number of occupied channels in each ISL. If we define



Q ¼ 0:5; for path P1; we have

ACP1 ¼ ð3þ 5þ 4þ 6Þ=4 ¼ 4:5

MCP1 ¼ 3

TWP1 ¼ 3:75

And for path P2; we have

ACP2 ¼ ð3þ 2þ 3þ 2Þ=4 ¼ 2:5

MCP2 ¼ 2

TWP2 ¼ 2:25

If there are only two paths, i.e. P1 and P2; available between satellite A and B; since

MTW ¼ MINðTWP1;TWP2Þ ¼ 2:25

Then, path P2 is therefore selected.

2.5. Sliding-width-based path selecting scheme (SWBPSS)

For reducing the delay jitter caused by the handoffs, normally there are two solutions. One is toreduce the number of handoffs during the period of communication, and the other one is tokeep a relatively consistent path length. However, in an LEO/MEO SATATM network, the fastmovement of satellites causes not only frequent handoffs, but also the changes in relativepositions between any two satellites nodes that do not belong to the same satellite orbit. Thelatter may result in huge delay jitter. The aim of this scheme is to minimize the delay jittercaused by the handoffs while at the same time keeping delay itself as low as possible. It isexpected to choose a new path that is not much different in its path length from the previous oneduring handoffs, although sometimes the path selected under such criteria is not the best onefrom the path-length point of view. In this scheme, the parameter sliding-width is used to select apath with more gradual and graceful change in its path length. Figure 4 shows an example toexplain this. During the time slot t1; the two end satellites A and B use the path P1 with pathlength 15 as its routing path. When the time slot 2 comes, a handoff event happens and it isasked to change the path as the consequence. Assuming that at this time there are threecandidates that can provide the routing path, which are path P2�1 with the path length 13, path

Figure 3. An example of the traffic detecting path selecting scheme.



P2�2 with the path length 14 and path P2�3 with the path length 8. Here we define the sliding-width ¼ 3 as the maximum difference between the path length before and after the handoff.Although at this stage the path P2�3 is the best one from the shortest path length point of view,but in the mean time it also causes a dramatic change in the path length and will therefore resultin large delay variance. The path P2�1 is not as good as path P2�3 from the shortest path point ofview, but it can more gracefully decrease the path length and better reduce delay variance,therefore the path P2�1 is selected.

2.6. Procedure of the adaptive path routing scheme (APRS)

The proposed APRS is a combined routing scheme based on the MEBDSP scheme, the TDS,and the SWBPSS. The main idea of the APRS is to improve the network performance byreducing the frequency of handoff, alleviating the traffic congestion on some particular ISLchannels, and reducing the fluctuation in the end-to-end delay.

The main procedure of the APRS is as following:

I. At the time slot i; path initialization:1. while a new call is accepted and a path needs to be built for the new call, use scheme

MEBDSP scheme to list all path candidates,2. for each path’s candidate selected in step 1, use TDS to calculate the traffic weight of

the path, and further find the path with the MTW value.3. use the path located by step 2 as the final path for the new call,

II. At the time slot i; path preservation for the coming time slot iþ 1 according to theforeseen knowledge of satellites’ location:1. based on the predicable network topology for system time slot iþ 1; use MEBDSP

scheme to list all potential paths in time slot iþ 1;2. sort out those paths that satisfy the requirement of SWBPSS,4. execute TDS to get the path with the MTW value,

Figure 4. An example of the sliding-width based path selecting scheme (SWBPSS).



3. if the path for the time slot iþ 1 is neither available nor optimal, (here ‘‘optimal’’means that the path shall satisfy some particular requirements), preserving actionfails and a path rebuilding process will be handled in time slot iþ 1;

III. At the time slot iþ 1; assuming that there is no connection handoff [1] event, useMEBDSP scheme to see if a handoff is necessary.* If no, just elongate the original path by adding one more ISL from the old terminal

node to the new terminal node.* If yes, then1. use MEBDSP scheme to list all path candidates,2. use SWBPSS to list those paths that satisfy the requirement of SWBPSS,3. for each path’s candidate selected in step 2, use TDS to calculate the traffic weight of

the path, and further find the path with the MTW value,4. use the path located by step 3 as the final path for the new call,5. execute step II to preserve a potential path for the time slot iþ 2;

IV. At the time slot iþ 1; if it encounters a connection handoff event, which means a handoffwill happen unavoidably, then,1. use MEBMDSP scheme to list all path candidates,2. sort out those paths that satisfy the requirements of SWBPSS,3. for each path’s candidate selected in step 2, use TDS to calculate the traffic weight of

the path, and further find the path with MTW value,4. use the path located by step 3 as the final path for the new call,5. execute step II to preserve a potential path for the time slot iþ 2;

V. At any time slot when a path rebuilding is necessary,1. if there is no path available under MEBDSP scheme, it means that a handoff

drop (or handoff call termination) will happen and it will trigger a call dropevent,

2. If there is no path under SWBPSS available and the path preservation process failedin the previous time slot, it means that currently there is no path available to provideQoS guarantee from delay jitter point of view. However, because the call drop isnormally be put in one of the highest priorities, the path is still available but schemeSWBPSS is ignored here.

The procedure of the APRS is also shown in Figure 5. In this scheme, in order to simplify thesituation and describe our scheme better, we assume that a handoff happens only at the startmoment of a system time slot, and the traffic situation in any ISL remains unchanged duringthat time slot.

3. NUMERICAL RESULTS AND DISCUSSIONS

In order to evaluate the proposed scheme, a simulation programme has been developed. In thesimulation, an LEO/MEO satellite network model with eight orbit planes and 12 satellites perorbit is built. In this model, we set the system parameters as following:

* Tdel ¼ 0:1:



Figure 5. Procedure of the adaptive path routing scheme (APRS).



* Define a two-dimension array SatISL½i�½j� ¼

fO;E;W;E;W;E;W;O;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;W;E;W;E;W;E;W;

O;E;W;E;W;E;W;O;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;F;F;F;F;F;F;W;

E;W;E;W;E;W;E;Wg;

SatISL½i�½j� represents the connection status of the satellite node Lði; jÞ; where symbol ‘O’means that no west-way and west-way ISL existed at that node, ‘E’ no west-way ISLexisted at that node, ‘W’ no east-way ISL existed at that node, and ‘F’ there are four ISLsexisting at that node [1, 2].Based on the system parameters defined earlier, the following numeric parameters areapplied in the MEBDSP scheme:

* HO trigger=0.8,* number of channels in an ISL is 50,* each call uses one channels as its bandwidth,* whole constellation period is divided into 12 time slots, which corresponds to the 12

satellites per orbit. A handoff is assumed to happen only at the moment while changing thetime slot because in this paper only the link handoff and connection handoff are considered,

* sliding-width = 2;* the whole system obeys the M=M=C=C policy, the mean duration time of a call is assumed

to be 10 min; and the new call arrival rate (calls per minute) is between (10, 300),* new calls can be generated from each satellites with the same probabilities,* delay jitter is measured as the variance of the path length divided by the average path

length,* bandwidth capacities of the uplink/downlink are far larger than those of ISLs, which is to

avoid the happening of traffic bottleneck at uplink/downlink places.

The ARPS has been compared with the MDSP and best-effort schemes. Figure 6 shows acomparison of the average path length among the MDSP, best-effort, and APRS schemes atdifferent traffic situations. From the figure, we can find that when the traffic density is light, thebest-effort scheme has the best performance from the viewpoint of the average path length butits performance degrades sharply when the traffic increases. This can be easily understoodbecause the best-effort always focus on the fastest source-to-destination delivery, even in a very



heavy traffic situation and it tries to find any available path to build the connection. However,MDSP and APRS schemes illustrate very similar performance and are less affected by thesystem traffic. The reason is that they have a stricter requirement on the path length, especiallyin heavy traffic situations, if compared with the best-effort. They also need to sacrifice PHBP inorder to guarantee the end-to-end delay.

Figure 7 shows a comparison among the three schemes for the delay jitter. We can find thatthe performance of the APRS is superior among the three. This is because that in the APRSscheme, it uses a gateway step, i.e. sliding-width, in preventing the scheme from selecting a pathwhose length greatly differs from the old one. Employing the MEBDSP scheme reduces thefrequency of the handoffs. This enables the APRS to change the path length more gracefully andsmoothly compared with the other two and therefore the end-to-end delay jitter is reduced. Ofcourse, the path that is selected according to the APRS may not be always the optimal one,which can be seen in Figure 8, but it can decrease the path length gap between the twoconsecutive time slots so as to minimize the delay jitter caused by the handoffs. This feature isextremely important in an IP case, which is more sensitive to delay jitter than to delay itself.

Figure 6. Comparison of average path length among best-effort, MDSP and APRS schemes.

Figure 7. Comparison of delay jitter caused by handoff events amongbest-effort, MDSP, and APRS schemes.



In Figure 8, we can find another advantage of the APRS. In MDSP scheme, with the increaseof network traffic, the path with the least end-to-end transmission delay is not always available,which results in a large PHBP in heavy traffic situations. While both the APRS and best-effort

schemes have more attractive results because they are more flexible in selecting the paths, thefigures of forced communication terminations are lower. With the increased system traffic, theAPRS shows its superiority over the best-effort scheme with its ability to reduce the frequency ofhandoffs, and to alleviate traffic situation on ISL channels by employing the TDS so thatresource utilization is improved. The path preserving procedure of the APRS can give a handoffcall more opportunities in obtaining the ISL channel resources so that the handoff droppingsituation is alleviated to some degree.

The two factors that need to be further discussed here are the parameters’ setting of theHO trigger and the sliding-width. Because the HO trigger is used to control the trigger of ahandoff, it mostly impacts the system handoff frequency and the average end-to-end delay.Figure 9 shows the simulation results on system handoff frequency defined as the averagenumber of handoffs per constellation period, and Figure 10 shows the simulation results of theend-to-end delay. From these results we can see that the larger the HO trigger value is, thehigher the handoff frequency will be, but the lower the end-to-end delay is. Also, with

Figure 8. Comparison of PHBP values among best-effort, MDSP, and APRS schemes.

Figure 9. Handoff frequency in APRS based on different HO trigger values.



decreasing the HO trigger, it gradually losses control on the system end-to-end delay, which isless desirable from the QoS point of view.

On the other hand, the sliding-width will impact the delay jitter and the delay itself (but moreon delay jitter), as illustrated in Figures 11 and 12, respectively. From these two figures it can be

Figure 10. Average path lengths in APRS based on different HO trigger values.

Figure 11. Delay jitter performance in APRS based on different sliding-width values.

Figure 12. Delay performance in APRS based on different sliding-width values.



found that by increasing the sliding-width, it gradually losses control on system delay jitter but atthe same time it impacts less on the system end-to-end delay. Apparently, these two areconflicting within the APRS and a tradeoff needs to be made, which depends on the particularsystem QoS requirements.

In the simulation, the time spent on VCC searching and VPC building during the handoffs isnot taken into account, although this could also negatively impact system end-to-end delayperformance. In fact, due to the path preserving process in the APRS, the time spent on the pathrebuilding is less compared with the best-effort and MDSP schemes, which gives APRS furtherpossibility in getting lower end-to-end delay.

4. CONCLUSION AND THE FUTURE WORKS

MIP over LEO/MEO SATATM network has been recently proposed to provide broadbandservices for the next generation communication network because of its outstanding combinedcharacteristics from the LEO/MEO satellite network, ATM, and MIP network. QoS is veryimportant in evaluating the success and efficiency of a network performance. In this paper,based on the currently proposed IP-over-LEO/MEO-SATATM network model [5–8], weproposed an APRS. From the simulation results, we can see that the APRS improves thenetwork QoS performance such as end-to-end delay, delay jitter, and handoff/call admissionrates compared to some other conventional schemes. Therefore, the proposed scheme could be apromising routing and handoff algorithm in the future mobile satellite networks that employISLs.

REFERENCES

1. Werner M. ATM-based routing in LEO/MEO satellite networks with intersatellite links. IEEE Journal on SelectedAreas in Communications 1997; 15 (1):69–82.

2. Chen J, Jamalipour A. An improved handoff scheme for ATM-based LEO satellite systems. Proceedings of the 18thAIAA International Communication Satellite Systems Conference and Exhibition, Oakland, CA, 10–14 April 2000.

3. Macro Ajmone Marsan, Carla Farbiana Chia. Local and global handovers for mobility management in wirelessATM networks. IEEE Personal Communications 1997; 4 (5):16–24.

4. Chen J, Jamalipour A. Adaptive channel management for routing and handoff in broadband WATM mobilesatellite networks. IEEE International Conference on Communications (ICC2001), Helsinki, Finland, 11–14 June2001.

5. Yegenoglu F, Alexander R. An IP transport and routing architecture for next-generation satellite networks. IEEENetwork 2000; 14 (5):32–38.

6. Umehira M, Nakura M. Wireless and IP integrated system architectures for broadband mobile multimedia services.IEEE Wireless Communications and Networking Conference, WCNC 1999; 2:593–597.

7. Kim W-T, Park Y-J. Scalable QoS-based IP multicast over label-switching wireless ATM networks. IEEE Network2000; 14 (5):26–31.

8. Mum Y, Kim Y. IP mobility support over wireless ATM. IEEE International Conference on Communications(ICC1999) 1999; 1:319–323.

9. Guarene E, Fasano P. IP and ATM integration perspectives. IEEE Communications Magazine 1998; 36 (1):74–80.10. Ihara T. Mobile IP route optimization method for a carrier-scale IP network. Sixth IEEE International Conference

on Engineering of Complex Computer System (ICECCS2000) 2000; 120–121.11. Gross D. Fundamentals of Queuing Theory (A Wiley Publication in Applied Statistics). Wiley: New York, 1974.12. Farserotu J, Prasad R. Broadband wide-area networking via IP/ATM over SATCOM. IEEE Journal on Selected

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AUTHORS’ BIOGRAPHIES

Jing Chen received his BEng degree from the Beijing University of Post andTelecommunication in 1990, and the MS degree from the Shanghai JiaoTongUniversity in 1993. Following this, he joined the Department of Telecommunicationat the Fujian Electronic Power Bureau. He has been working towards PhD degree atthe School of Electrical and Information Engineering at the University of Sydney,Australia since 1998. Now he is also an R&D engineer with the Motorola AustraliaResearch & Software Centre. His main research interests are wireless networking,ATM/IP, 3G and beyond systems, and satellite communication.

Abbas Jamalipour has been with the School of Electrical and InformationEngineering at the University of Sydney, Australia, since 1998, where he isresponsible for teaching and research in wireless data communication networks andsatellite systems. He holds a PhD in Electrical Engineering from Nagoya University,Japan. He is the author for the first technical book on networking aspects of wirelessIP, The Wireless Mobile Internet } Architectures, Protocols and Services, John Wiley& Sons 2003. In addition, he has authored another book on satellite communicationnetworks with Artech House in 1998 and coauthored two other technical books onwireless telecommunications. He has authored over 80 papers in major journals andinternational conferences, and given short courses and tutorials in majorinternational conferences. He has served on several major conferences technical

program committees, and organized and chaired many technical sessions and panels at internationalconferences including a symposium in IEEE Globecom2001. He is the Vice Chair to the Satellite and SpaceCommunications Committee and the Asia Pacific Board, Co-ordinating Committee Chapter, IEEEComSoc. He has organized several special issues on the topic of 3G and beyond systems as well asbroadband wireless networks in IEEE magazines and journals. He is a technical editor to the IEEEWireless Communications Magazine and a Senior Member of the IEEE.



an adaptive path routing scheme for satellite ip networks

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