Enhanced Signaling Scheme with Admission Control in the Hybrid Optical Wireless (HOW) Networks

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1 Enhanced Sgnalng Scheme wth Admsson Control n the Hybrd Optcal Wreless (HOW) Networks Yng Yan, Hao Yu, Henrk Wessng, and Lars Dttmann Department of Photoncs Techncal Unversty of Denmark Lyngby, Denmark {yya, haoyu, hewe, ladt}@fotonk.dtu.dk Abstract The hybrd optcal wreless (HOW) network has been vewed as a promsng soluton to meet the ncreasng user bandwdth and moblty demands. Due to the basc dfferences n the optcal and wreless technologes, a challengng problem les n the Meda Access Control (MAC) protocol desgn so that t can support strngent Qualty of Servce (QoS) requrements. In ths paper, we descrbe and evaluate a resource management framework desgned for the HOW networks. There are two parts n the resource management framework The frst part s the Enhanced MPCP (E-MPCP) scheme amng at mprovng sgnalng ablty between the optcal and wreless networks. The second part s an Integrated Optcal Wreless Admsson Control (IOW-AC) scheme amng at provdng the ntegrated bandwdth allocaton n the HOW networks. Our results show that the performances of the system n terms of throughput, delay and packet droppng probablty depend on several factors. These factors nclude the frame duraton, the traffc load and the total number of shared users. The results also hghlght that our proposed system acheves sgnfcant mprovements over the tradtonal approach n terms of user QoS guarantee and network resource utlzaton. Keywords- call admsson control, MPCP, resource allocaton, the hybrd optcal wreless network I. INTRODUCTION Recent years have wtnessed the explosve growth of the multmeda applcatons, whch are characterzed wth hgh speed and strngent QoS requrements. An ntegraton of optcal and wreless technologes has been vewed as a vable soluton to delvery the quadruple play servces (data, voce, vdeo and moblty). In the HOW networks, complementary characterstcs of the optcal network and wreless network are combned. In optcal access network, such as Ethernet Passve Optcal Network (EPON), has been deployed to satsfy bandwdth demands for broadband servces, but t has a fxed archtecture and lmted coverage. Among varous avalable wreless technologes, the recent Worldwde Interoperablty for Mcrowave Access (WMAX) technology has promsed ubqutous and hgh data rate connectons for both fxed and moble communcaton. A hybrd EPON and WMAX network s an example of the HOW network, whch s a convergence of an EPON deployed as a backhaul and multple WMAX networks connected as the front-end networks. Snce the optcaland wreless-access technologes are orgnally desgned to address dfferent ssues and deployed n dfferent scenaros, any smple combnaton of them cannot derve optmal network performances. One major challenge n the HOW network s how to desgn a heterogeneous resource management framework, whch can be exploted to maxmze the overall resource utlzaton and optmze QoS performances n both the optcal doman and the wreless doman smultaneously. There are several aspects needed to be addressed n advance to acheve an effcent resource management. The man techncal ssues are as follows: (1) routng algorthm, (2) packet classfcaton and schedulng and (3) resource management. Frst, the ntegrated routng algorthm has been proposed n [1,2] to select the optmum routes for transmssons n both optcal and wreless doman. A rsk- and delay- aware routng algorthm s proposed for the front-end wreless network n [3, 4]. Second, schedulng algorthm s also mproved to consder the network condton jontly n the optcal and wreless doman [5]. In [6], we proposed a scheduler, whch prortzes connectons n the optcal doman, whle takng wreless channel qualty nto account. At last, for the resource management, as proposed n [7], a central controller s desgned n the optcal doman to have a vew of the hybrd network. The connecton requests submtted n the wreless doman are delvered to the optcal doman. As desgned for the HOW network, a utlty-based bandwdth allocaton scheme s proposed n [8]. Capacty analyss and wavelength multplexng are exploted n [9] for flexble bandwdth allocaton. Although the dea of an ntegrated resource management s proposed, how to realze such scheme has /09/$

2 not been addressed. In ths paper, we presents our study and desgn of a resource management framework for the HOW networks. Our proposed scheme can jontly and optmally admt the request connectons and allocate the network resources for both the optcal network and the wreless network wth an overall consderaton. Under an ntegrated resource management framework, the potental network congeston s able to be avoded, the resource utlzaton can be maxmzed and the prescrbed QoS requrements are able to be successfully satsfed. The rest of ths paper s organzed as follows. Secton II ntroduces our proposed resource management framework. Secton III presents the smulaton results and analyss. Fnally, concluson s gven n Secton IV. II. ENHANCED SIGNALLING SCHEME WITH AC A. Hybrd EPON and WMAX Network Archtecture The hybrd EPON and WMAX network archtecture s llustrated n Fgure 1. In EPON, a centralzed Optcal Lne Termnal (OLT) communcates wth multple connected Optcal Network Users (ONUs) va a passve optcal spltter. In the Pont-to-Multpont (PMP) WMAX network, a Base Staton (BS) manages channel allocaton to Subscrber Statons (SSs) as a central controller [14]. In hybrd network archtecture, the ONU functons and BS functons are ntegrated nto a sngle devce, namely an Access Gateway (AG), whch handles connectons wthn the wreless network, and connectons cross both EPON and WMAX network. The upstream traffc s frst aggregated at an AG and then forwarded to the OLT. For the downstream traffc, packets are frst transmtted to the AG and then forwarded to each SS n the allocated channel slots. Tradtonally network control mechansms are desgned separately and exclusvely for ether optcal Fgure 1. Integrated optcal wreless network model networks or wreless networks. The characterstcs and challenges of the HOW network are gnored. To acheve desred network performances, the exstng control planes n EPON and WMAX should be ntegrated and mproved wth advanced admnstraton functons. Fgure 2. shows an overvew of operatons mplemented n the OLT and the AG for schedulng, resource allocaton and admsson control. In ths paper, we propose a modfed resource negotaton scheme at the optcal uplnk bandwdth allocator block n the OLT and a delay-aware admsson control at the CAC block n the AG. B. Basc MPCP Operatons A typcal EPON system s a tree-based archtecture, whch conssts of one Optcal Lne Termnal (OLT) functonalzed as a central control staton, one 1:N (for example, N=16 or 32) passve optcal spltter and multple Optcal Network Users (ONUs). The framework of the EPON MAC layer, known as the MultPont Control Protocol (MPCP), s defned n IEEE 802.3ah Ethernet n the Frst Mle (EFM) Task Force [10]. MPCP s a sgnalng access protocol, whch uses two 64-byte MAC control messages to regster the connected ONUs and allocaton upstream bandwdth among ONUs (va GATE and REPORT messages). Snce the upstream transmssons from multple ONUs to the OLT share a common optcal lnk, an mportant ssue n EPON s to effcently allocate resources to mult-users, whch s not specfed n the standard. Two control messages, REPORT and GATE, are defned n the MultPont Control Protocol (MPCP) as sgnalng between the OLT and AGs n the hybrd network. The REPORT message s n the downstream drected to the OLT and the GATE message s n the upstream ntated from the OLT. The OLT regsters attached AGs wthn the dscovery perod, whch s repeated perodcally so that newly connected AGs can seamlessly be added wthout nterruptng the current network operaton. After dscoverng and regsterng the connected AGs, the OLT sets up an entry table, whch contans the AG node dentfcaton (NID) and the round trp tme (T rtt ). Snce multple AGs share a common optcal lnk n the upstream drecton, the OLT requres assgnng the bandwdth n a manner of farness and wthout conflct. The upstream transmsson perod s dvded nto multple tme slots and each ONU can only transmt durng ts own slot tme. In the normal processng state, the OLT polls regstered AGs and assgns tme slots ether statcally based on the TDMA scheme or dynamcally based on the desgned resource requrement negotaton [11-13]. In ths paper, we use the TDMA n the EPON doman. In TDMA scheme, one AG s granted a fxed tme slot length and s polled n order. In ths paper, a cycle (T cycle ) refers to a perod n whch all

3 Fgure 2. Functonal overvew of an ntegrated control framework AGs are served and a subframe refers to a perod, whch s assgned to an AG for the uplnk transmsson. C. Enhanced MPCP Scheme In the ntegrated archtecture, an AG performs resource management operatons for both optcal and wreless networks. In order to calculate the packet transmsson delay n the optcal doman, the AG needs to know the estmated watng tme for ts next poll. Ths extra nformaton can be derved from the OLT usng a modfed GATE message. Orgnally defned n MPCP, the GATE message conssts of a 1-byte granted start tme (t start ) and a 2-byte granted bandwdth (BW). We add a 3- byte feld, the next cycle tme (T next ), whch s the nterval between two adjacent pollng operatons to an AG. After the OLT computes the start tme and subframe length for each AG, the OLT can obtan the total transmsson length (T cycle ) for all k AGs. We use t to ndcate the tme and T to ndcate the duraton BW T cycle = ( + Tg ) (1) R k 1 = 0 where R o s the transmsson rate of the optcal uplnk and T g s the guard tme between two successve upstream transmssons. After a perod of T cycle, an AG s polled agan. The nterval between two adjacent pollng operatons, the next cycle tme, can be calculated and added nto the orgnal GATE message as a new feld. The GATE control message can be embedded wthn an Ethernet frame. The recever recognzes the GATE control message and then extracts the followng 6-byte grant nformaton. The o enhanced MPCP scheme under the TDMA s shown n Fgure 3. The pollng sequence of AGs s scheduled n the OLT. The value of granted bandwdth s fxed and same to all k AGs. In other words, each AG has to wat T cycle as the pollng wat tme. The value of t start and T cycle are updated and changed once there are new AGs regstered and scheduled. The expected next cycle tme for the th AG s calculated n Eq. (2). The entry table s updated after the perodc dscovery process. The value of t next for each AG s computed at the begnnng of each cycle. t next TDMA = t = t start start + T + k cycle BW R ( + T g o ) (2) D. Integrated Optcal Wreless Admsson Control A key characterstc of our proposed resource management s to provde overall consderatons of both optcal and wreless network condtons. Although EPON and WMAX use dfferent channel access mechansms, they both need admsson control to determne how much traffc can be handled n the optcal and the wreless domans separately, so that the prescrbed QoS for each traffc stream can be mantaned. Implementng two ndvdual admsson control schemes for each network s not effectve and effcent. An Integrated Optcal Wreless Admsson Control (IOW-AC) scheme s proposed to cope wth ths problem, whch provdes delay bounds to multdoman connectons. We frst present a model to evaluate the delays experenced by SSs and then descrbe the proposed IOW-AC scheme.

4 When traffc arrves at the AG from the SSs, AG s able to estmate the watng tme for the traffc to be served. The overall estmated delay (d est ) ncludes the watng tme untl AG s polled by the OLT (d pollng ), the watng tme for the pror data n the same queue beng served (d queueng ) and the wreless transmsson (d tx-wreless ) and propagaton delay (d prop-wreless, ). d est = d + d + d d (3) pollng queung tx wreless + prop wreless Where d pollng s calculated based on the next cycle tme (t next ) and the packet arrval tme (t). The t next s computed as we explaned earler. d queueng s determned by the current subqueue sze and the assgned bandwdth wthn a subframe. If the subframe has enough empty space, the new comng packet can be served rght after the queued packets n the followng subframe. Snce the queung delay s not our focus, we assume the avalable buffer sze n AG s enough. d tx-wreless s calculated based on the packet sze and the wreless lnk rate. d pollng s determned by the nformaton (e.g. the startng transmsson tme t 0, the granted slot tme t granted and the next transmsson tme t next ) provded n the GATE message. In the case t [t 0, t 0+T granted), the request arrves at the tme when the AG s beng polled. the request of j th SS, SS j, arrves when the AG s beng polled. A request can be accepted and served wthn the current subframe only f the correspondng packets can be receved before the current subframe s fnshed. Thus, d pollng = 0.Otherwse, d pollng = t next -t. If the request of SS arrves at the AG, whch s watng to be polled,.e., t [ t 0 +T granted, t 0 +T next-tx), the packet has to wat untl the remanng part of an uplnk transmsson from other AGs to the OLT s completed. The earlest tme for the request to get served s the next pollng tme. Thus, d pollng = t next -t It s noted that an ncrease on the subframe sze T granted can result n a larger number of accepted requests, but t also ncreases the pollng delay. In order to support and protect the QoS of real-tme traffc streams, n addton to bandwdth allocaton, an AC scheme s requred to decde whether to admt a realtme traffc stream based on both admsson polces and QoS requrements suppled by the applcaton at the end users. Assumng for real-tme servces, QoS metrcs are predefned and varous thresholds are specfed. The realtme traffc flows are characterzed by the demand QoS parameters, for example, the delay bound (d mn ). The AG can perform rate-based AC that s based on the delay requrement of the new arrvng flow and the estmated delay. The IOW-AC provdes guaranteed QoS and ncreases the network throughput by acceptng requests wthout volatng the delay constrants. The proposed IOW-AC scheme can be accomplshed as follows. As llustrated n Fgure 4., when there s a new request receved at AG. The transmsson and propagaton delay are frst calculated accordng to the wreless network Fgure 3. Enhanced MPCP wth TDMA scheme Fgure 4. Operatons of the proposed uplnk IOW-AC scheme.

5 condtons and traffc profle. Secondly, the queung delay s evaluated based on the current buffer occupancy. Then, usng the pollng status nformaton, the expected pollng delay s computed as explaned n Eq. (1) and Eq. (2). Fnally, when the IOW-AC approach determnes the overall delay, d est, for a multdoman connecton request, t compares the delay wth the delay bound, d mn. If the requred delay bound s satsfed, the request s accepted (d est < d mn ). Otherwse, the request s rejected. III. PERFORMANCE EVALUATION Extensve smulatons have been conducted usng OPNET modeler [15] to evaluate the performance of the proposed enhanced MPCP and IOW-AC scheme for the HOW network. Smulaton results are shown to compare the proposed framework wth the tradtonal separated resource management schemes. Smulatons are carred out for dfferent network szes and traffc loads. The total number of AGs K s 32 and the EPON lnk rate s assumed as 1 Gb/s. The guard tme between two adjacent transmssons on the optcal uplnk fber s 5 s. We assume that the AG supports a 70 Mb/s WMAX uplnk data rate. Based on the IEEE standard, both rtps and BE traffc are consdered. For users of rtps traffc, e.g. vdeo streamng servce, the traffc profle has a varable packet sze, unformly dstrbuted between 1200 and 1500 bytes. The delay bound for the real tme traffc s set as 75ms. Fgure 5a. shows the rato of admtted requests n the total receved requests for both real-tme traffc and BE traffc, usng the two dfferent AC schemes. The ncomng requests can be admtted only when ther QoS requrements are met. Ths fgure shows that the IOW- AC admtted larger amount of conformng traffc than the Normal-AC for both the real-tme and BE traffc. The dfferences become more sgnfcant when the traffc arrval rate ncreases. The channel utlzaton becomes better n the IOW-AC because there s wastage n the Normal-AC scheme taken by the nonconformng traffc. In Fgure 5b we compare the smulaton results for the droppng probablty for the real-tme traffc and BE traffc when there s lmted buffer sze at an AG node. IOW-AC scheme acheves lower droppng probablty for both real tme traffc and best effort (BE) traffc. Ths s because that IOW-AC only accepts conformng traffc and saves more bandwdth for the conformng real tme traffc wthout any drop even under hgh real-tme traffc rate. We observe the smlar result, whch s that IOW- AC yelds better bandwdth utlzaton. In Fgure 5c we plot the percentage of accepted requests for dfferent length of subframe perod rangng from 1 ms to 5 ms. As we mentoned before, when the subframe perod (T granted ) ncreases, there are more requests can be served n the uplnk optcal lnk. However, the total cycle tme (T cycle ) becomes larger and the pollng delay ncreases smultaneously. In ths fgure, the IOW-AC scheme blocks nonconformng traffc especally when the subframe perod s large. Under the Normal-AC scheme, the accepted real-tme traffc s most of nonconformng traffc. In Fgure 6a we examne the pollng delay (d pollng ) experenced at the AG node n the IOW-AC scheme. The buffer sze s specfed as unlmted. Therefore, the T queung of voce and vdeo traffc wll not be a domnatng Fgure 5. (a) Admtted request Vs. traffc arrval rate. (b) Packet droppng probablty Vs. traffc rate. (c) Admtted request Vs. subframe length Fgure 6. (a) Pollng delay Vs. subframe length. (b) Admtted RT request Vs. number of AGs. (c) Admtted BE request Vs. number of AGs

6 factor n the AC. On the contrary, the nfluence of T pollng on AC s hghlghted, whch s mportant to observe n smulatons. The value of the pollng delay s zero f the request packet s receved durng the subframe perod. Otherwse, the pollng delay s the nterval between the current tme and the next poll tme. In ths fgure, the pollng delay s a tme average value. As the subframe perod ncreases, the pollng delay becomes larger because t takes longer tme for the OLT to serve all AGs. Therefore, the pollng delay s also dependng on the number of connected AGs. The more the number of AG, the longer the pollng delay. In Fgure 6b and Fgure 6c we compare admtted realtme traffc and the BE traffc under dfferent number of AGs and dfferent length of subframes, n the IOW-AC scheme. The number of blocked requests s ncreased usng the IOW-AC scheme when the number of AGs and the perod of subframe become larger. We have observed that the beneft of our proposed ntegrated resource management framework s hghly depends on the network sze and traffc profle. IV. CONCLUSION In ths paper we present an ntegrated resource management framework for the hybrd optcal wreless networks amng for maxmum user QoS and maxmum network throughput. Smulatons conducted usng the OPNET modeler show that the proposed system acheves sgnfcant mprovements over the tradtonal admsson control approach n terms of user QoS guarantee and network resource utlzaton. These gans are acheved wthout complex modfcaton on the exsted network protocols. Another nterestng observaton s that f the number of AGs and the assgned subframe perod for each AG are ncreased, the proposed admsson control scheme acheves more sgnfcant mprovements. Snce the network throughput s relevant to the AG parameters, an operator can estmate the performance based on ths smulaton results. The beneft of our proposed ntegrated resource management framework hghly depends on the network sze and traffc profle. The analyss could be a good assstance or gudance n future research n many felds of hybrd optcal wreless network archtecture, ncludng resource management, optmzng QoS and demandng servce provsonng. REFERENCES [1] W.-T. Shaw, D. Guterrez, K. S. Km, N. Cheng, S.-H. Wong, S.-H. Yen, and L. G. Kazovsky, GROW-Net A hybrd optcal wreless access network, n Proc. 9th Jont Conf. Informaton Scences. (Invted Paper), Oct [2] W.-T. Shaw, S.-H. Wong, N. Cheng, K. Balasubramanan, X. Zhu, M. Maer and L. G. Kazovsky, Hybrd archtecture and ntegrated routng n a scalable optcal wreless access network, Journal of Lghtwave Technology, Vol. 25, No. 11, Nov [3] S. Sarkar, S. Dxt and B. Mukherjee, Hybrd wreless-optcal broadband-access network (WOBAN): a revew of relevant challenges, Journal of Lghtwave Technology (nvted paper), Vol. 25, No.11, Nov [4] S. Sarkar, H. Yen, S. Dxt and B. Mukherjee, DARA: delayaware routng algorthm n a hybrd wreless-optcal broadband access network (WOBAN), n Proc. IEEE Internatonal Conference on Communcatons, Jun [5] G. Shen, R. S. Tucker and C. Chae, Fxed moble convergence archtectures for broadband access: ntegraton of EPON and WMAX, IEEE Communcatons Magazne, pp , Aug [6] Y. Yan, H. Yu and L. Dttmann. "Wreless channel condton aware schedulng algorthm for hybrd optcal/wreless networks", n Proc. 3rd Internatonal Conference on Access Networks, Oct [7] Y. Luo, S. Yn, T. Wang, Y. Suemura, S. Nakamura and M. Cvjectc, QoS-aware schedulng over hybrd optcal wreless networks, n Proc. Optcal Fber Communcaton Conference and Natonal Fber Optc Engneers Conf., 2006, pp 1-7. [8] P. Ln, C. Qao, T. Wang and J. Hu. Optmal utlty-based bandwdth allocaton over ntegrated optcal and WMAX networks, n Proc. Optcal Fber Communcaton Conference and Natonal Fber Optc Engneers Conf., 2006, pp 3. [9] H. Km and A. Wolsz. "A rado over fber based wreless access network archtecture for rural areas", n Proc. 14 th IST Moble and Wreless Communcatons Summt, Jun [10] Ethernet n the Frst Mle Allance (EFMA), Ethernet Passve Optcal Network (EPON) tutoral, Revson 4, (2004). [11] Kramer Glen, Mukherjee Bswanath, and Pesavento Gerry. IPACT: a dynamc protocol for an Ethernet PON (EPON), IEEE Communcaton Magazne 40(2), (2002). [12] C. Ass et al., Dynamc bandwdth allocaton for qualty-ofservce over Ethernet PON, IEEE JSAC, vol. 12, no. 9, pp (2003). [13] M. Ma, Y. Zhu, and T. H. Cheng, A systematc scheme for multple access n ethernet passve optcal access networks, J. Lghtwave Tech., vol. 23, no. 11, pp (2005). [14] Jeffrey G. Andrews, Arunabha Ghosh and Ras Muhamed, [Fundamentals of WMAX], Prentce Hall (2007). [15] OPNET Modeler 14.0, ACKNOWLEDGMENT Ths work was supported n part by the European Commttee through project ALPHA (Archtectures for flexble Photonc Home and Access networks).