Mobility Support for a QoS Aggregation Protocol

Transcription

1 Mobility Support for QoS Aggregtion Protocol A. Kloxylos^, D. Vli*, S. Psklis+, G. Pngiotou^, I. Goninkis^, E. Zervs # ^ Deprtment of Telecommunictions Science n Technology, University of Peloponnese, Greece * OTE Reserch, ellenic Telecommunictions Orgniztion - OTE S.A,, Greece + Deprtment of Informtics n Telecommunictions, University of Athens, Greece #Deprtment of Electronics, TEI Athens, Greece Abstrct - The en-to-en QoS support for multimei pplictions is n importnt issue. owever, existing proposls either en up in corse-grine QoS support or they re simply not sclble. To ress this issue, ynmic ggregtion of iniviul reserve sessions into common clsses is recommene. In en-to-en communictions it is importnt to crefully select the strting n ening point for n ggregtion. The gol is to minimize stte informtion n processing lo in the routers. Moreover, the cpbility of the users to switch their ctive connections/sessions from one point to nother, n even from one opertor to nother, plces extr requirements in the mngement of the ggregte informtion. Our work iscusses the performnce of existing protocols n buils upon BGRP, sclble protocol tht is esigne to efficiently ggregte resources. We propose the ition of mobility extensions to BGRP n ssess their performnce through some simple metrics. I. INTRODUCTION QoS support is well-stuie issue n severl proposls n stnrs hve been issue uring the pst yers. A number of protocols re propose to hnle QoS in locl networks or even en-to-en ([], []). The IETF Next Steps in Signling working group ([3]) is currently working to stnrize IP signling protocols with QoS signling s the first use cse. In [4], protocol for the routing n trnsport of per-flow signling messges is presente, while in [5] the NSIS Signling yer Protocol (NSP) for signling QoS reservtions in the Internet is escribe. These protocols o not follow the corsegrine QoS support of Diffserv [7], but provie similr functionlity to RSVP [6]. Obviously, specil cre hs been tken to support itionl fetures such s sener bse reservtion s well s receiver bse reservtions. From these efforts it is cler tht in orer to ynmiclly control en-to-en QoS schemes, signling hs to trvel from one en to the other ech time new session is to be estblishe. owever, this my rise scling issues, especilly for the core network routers. To meliorte this buren, ggregtion of signling informtion is require. The scheme tht one shoul use to minimize the processing lo n the signling informtion store in the routers remins s n open issue. Another chllenge is to stuy how these ggregtion schemes will perform with mobile terminls. Future scenrios expect users to be ble to verticlly hnoff their connections from one rio ccess technology to nother or even ynmiclly select to switch from one Opertor, or Internet Service Provier, to nother (e.g., hnover from/to WAN to/from WiMAX, UMTS etc). In these cses it is possible tht the new en-to-en pth, lthough shring lrge segment with the ol one, will not inclue the previous ggregtion point. Thus, resources nee to be re-estblishe in n en-to-en fshion, espite the fct tht portion of the previously estblishe pth coul be re-use. To tckle this issue our proposl buils on BGRP [8], n existing inter-omin protocol for ggregting resources. With minor moifictions we hve esigne n extene version of it, clle Mobile BGRP (MBGRP) tht efficiently hnles the movement of terminls. This pper is orgnize s follows. In Section II, we iscuss existing protocols esigne to ggregte reservtions. In Section III, we exmine more closely ggregtion schemes sclbility issues n iscuss the reson why we nee mobility support for these protocols. In Section IV, we present the etils of MBGRP n perform simple quntittive evlution of the new protocol. We conclue the pper in Section V. II. REATED WORK There re severl lterntives for ggregting informtion. The first one is escribe in [9] n suggests the use of single RSVP reservtion to ggregte other RSVP reservtions cross trnsit routing region. With this technique, n ggregtion region is efine s contiguous set of systems tht cn perform ggregtions long ny possible route throughout this region. Obviously, this solution mnges to reuce the number of sttes n signling exchnge insie these res. owever, it oes not specify selection mechnism for the pproprite plcement of ggregtors n e-ggregtors in the en-to-en pth. It merely specifies s pproprite selections the ingress n the egress routers of the ggregtion region. Thus, we believe tht if use in ento-en schemes this solution will result in significnt number of ggregtes for the noes locte insie the core network. Another proposl is escribe in [0]. The DARIS (Dynmic Aggregtion of Reservtions for Internet Services) rchitecture ssumes the existence of centrl resource mngement entity (similr to the bnwith broker pproch) insie ech DiffServ omin tht hs complete knowlege n control of the resources insie the omin. It lso vils the inter-omin BGP routing tble. DARIS enbles the cretion of n ggregte between two rbitrry omins s soon s threshol of ctive common reservtions between the two omins is exceee. In this cse, ll intermeite ege routers cn substitute the respective per-flow sttes with single ggregte stte. The DARIS ggregtion pproch reuces store sttes n signling messges when compre to per-flow protocol tht oes not perform ggregtion. owever, the penlty to py is the nee for this centrl entity n the mechnisms to keep it upte with routing

2 n QoS informtion. Also, the support of neste ggregtes s to the complexity of the protocol. A QoS signling protocol specificlly esigne for inter-omin usge between heterogeneous omins (AS - Autonomous Systems) is the Borer Gtewy Reservtion Protocol (BGRP) [8]. BGRP opertes in en-to-en moe only between omin borer routers. It ims minly t ggregting reservtions between ministrtion omins improving thus, sclbility. BGRP uses the sink-tree ggregtion pproch n performs reservtion ggregtion by builing sink tree for ech estintion omin. Reservtions from ifferent source omins tht re trgete towrs the sme estintion omin re ggregte long the pth forming sink-tree. The root of this tree is the estintion s omin ege router. BGRP s bsic functionlity inclues messge sent by the source omin towrs the receiver to etermine resource vilbility n to recor the reservtion pth. The estintion omin ege router termintes the n sens bck messge long the reverse pth. This messge performs the ctul inter-omin reservtion n triggers the intr-omin QoS mechnisms in trnsit omins. The messges follow the sme pth with messge since recor route informtion is gthere uring the probing phse. The estintion omin ege router is the e-ggregtion point for the reservtion ggregte, while the source omin ege routers re the ggregtion points. By performing sink tree bse ggregtion of reservtions towrs ech estintion omin, BGRP results in storing perestintion omin QoS sttes in borer routers. This is significnt contribution to sclbility when compre to the per-flow RSVP. Anlysis results presente in [8] show tht BGRP mintins fewer reservtion sttes thn RSVP n tht the BGRP messge rte is significnt lower thn the respective RSVP messge rte, resulting in lower messge processing, storge buren n link bnwith. The Shre-segment bse Inter-omin Control Aggregtion Protocol (SICAP) ([]) is nother pproch for supporting ggregte inter-omin reservtions between Autonomous Systems (ASs). SICAP combines the shre-segment ggregtion n the tree-bse ggregtion pproches to crete tree-bse reservtion ggregtes tht o not necessrily exten up to the estintion omins. Aprt from the estintion omin e-ggregtor point, Intermeite De-ggregtion octions re iscovere n crete long the pth, so tht reservtion requests tht shre common pth segment but o not en-up to the sme estintion omin re ggregte up to one of their common routers long the pth. SICAP, similrly to BGRP, performs receiverbse reservtions n uses two-phse setup mechnism for their estblishment. Simultion results support tht SICAP mintins fewer ggregte sttes thn BGRP. owever, SICAP is more complex protocol thn BGRP since n lgorithm to elect the most suitble intermeite e-ggregtion points is neee. Moreover, the choice of using these points my en up in situtions where core routers will hve to e-ggregte n ggregte from scrtch significnt number of ctive sessions. III. SCAABIITY ISSUES To provie clerer picture bout the stte informtion neee when ggregting resources, we provie short nlysis for [8] n [9]. Aggregte RSVP is currently supporte on the ongoing work of NSIS. BGRP is, in our opinion, not only sclble but lso the simplest from the existing lterntives. Thus, it is more likely to be consiere for option in the future. BGRP cn be more sclble thn ggregte RSVP n moreover it cn be esily extene to work in mobile environments. S S S3 S4 S5 S6 S7 S8 T T T3 T4 300 T5 300 T T7 T8 Figure : BGRP n RSVP ggregtion As n exmple consier fig. where simplifie topology in the form of binry tree structure is rwn. Every circle represents n AS. From every source AS (S- S8) N uniirectionl sessions re ctive n re eqully istribute in every one of the trget AS (D-D8). As n exmple N equls in fig. Insie every circle in the trnsit networks we hve lso mrke the number of connections they serve. Without ggregtion we cn observe the sclbility issue insie the core network. Suppose tht we use ggregte RSVP n efine n ggregtion region, with T, T, T3, T4 s the ggregtors n T, T3, T4, T5 s the e-ggregtors. Then the lrge number of sttes tht h to be store in T7,T8,T9 is minimize. Ech of these noes will now only to hve 6 reservtion sttes, while T5, T6, T0, T only 8. owever, T-T4 n T-T5 will still hve lrge number of sttes to support. In orer to fin the number of signling sttes tht we cn summrize in the whole network if [9] is use, we efine s the tree length. n re the ggregtor s n the e-ggregtor s level in the hierrchy. Ech lef of the tree is consiere to be in level. V i () is the number of connections pssing through noe (i.e., AS) in level i n is given by V i () = c* i-. c is the number of connections in ech lef of the network (e.g., in the exmple of Figure ). i () is the number of noes in the binry tree t level n is given by i () = -i. In the exmple given, (=5)=6, hlf of which ply the role of source omins n the others ct s estintion omins. T9 RSVP Aggregtion Region 300 T0 300 T T T3 T4 T5 D D D3 D4 D5 D6 D7 D8 BGRP Sink Tree Aggregte to D

3 In generl cse the totl gin from the number of sttes tht cn be eliminte ue to ggregtion is given from (): + 0,5* V + + 0,5* V * 0,5* * ( ) 0,5* * ( ) () The first two terms clculte the number of sttes in the levels between the ggregtor n the e-ggregtor tht will be replce by ggregte sttes. The lst two terms represent the number of the new ggregte sttes tht will be instlle in ll noes from the ggregtor to the eggregtor. Note tht the incentive for one to ct s n ggregtor/e-ggregtor is smll since this noe will hve ll sttes of the ctive connections n in ition the new ggregte sttes, i.e., it will suffer n ggregtion penlty. Eqution () hols lso if the ggregtors n e-ggregtors re plce in ifferent tree levels. Stuying () we see tht in orer to mximize the gin (i.e., minimize the totl number of sttes in the network) we nee to buil the longest possible ggregtes. owever, in this cse the core network noes will hve more ggregtes sttes, the number of which is equl to the number of noes in the ggregtors level multiplie by the number of noes in the e-ggregtors level (e.g., 6 sttes for T8 in the exmple of Figure ). In the cse of BGRP the corresponing eqution for the sme topology is given by (): 0,5* V + 0,5* V * + i ( ) 0,5* ( )* i 0,5 * ( )* i () From () we cn see tht the first two terms re equl to the ones of eqution () when = n =. owever, the number of the ggregte sttes is t most equl to the number of estintion omins (8 sttes in the exmple of fig ). Obviously this fct plces n upper boun to the lst two terms of (). Using BGRP, one cn expect tht the source ASs will choose to ct s ggregtors if they wnt their users session to enjoy n en-to en QoS. In this cse, the ggregtion penlty is unconitionlly impose to ll the ege omin borer routers. From the bove elements it is cler tht in n en-to-en communiction BGRP behves more efficiently thn Aggregte RSVP. owever, wht both protocols (i.e., [8] n [9]) o not offer is the support for the cses where terminl moves from one re to nother such tht the new brnch of the en-to-en pth bypsses the ggregtor. For exmple, in cse terminl locte in AS S performs hnover (e.g., from UMTS opertor to wireless ISP) to the S3 system then neither BGRP nor ggregte RSVP will hve ny mens to etect tht. Thus, en-to-en signling will be issue to reserve resources tht re lrey reserve. In this cse, the moving terminl will fce unnecessry ely n the opertors will en up with n mount of oublereserve resources ue to moving terminls. MT S3 NSP_QUERY (Flow Is, RR) NSP_RESERVE NSP_RESPONSE T (RR, RESERVE Info) T5 (RR, RESERVEInfo) T (RR,RESERVEInfo) Figure : MBGRP opertion in source movement IV. MBGRP DESCRIPTION S (RR, RESERVEInfo) MBGRP is n extension of BGRP tht tkes into consiertion the terminls mobility. It is esigne to cooperte with the protocols esigne in NSIS. For this, we ssume tht MBGRP uses GIST [4] to trnsfer its messges. We lso ssume tht the borer routers in the stub omins (i.e., S i, D i, where i =..8 in fig ) support both NSP [5] n MBGRP. As with BGRP, MBGRP nees to be plce only in the borer routers of the ASs. In ition to BGRP, MBGRP requires tht the recor route informtion be communicte to the en terminls, through, for exmple, NSP. This informtion is neee in cse of hnover, n is use by the mobile terminl to notify MBGRP routers tht resources hve lrey been reserve for certin pth. The informtion is lso use by the MBGRP routers to check if they re crossover routers or not. Another extension to BGRP is the ition of two messges, clle R_ n NOTIFY. These messges re neee when terminls locte t the root of the MBGRP sink tree chnge their loction. When new session nees to reserve resources (receiver initite moe), then n NSP QUERY messge is issue. This messge reches the borer router of the AS (e.g., S). This router will issue MBGRP messge tht inclues the QUERY s messge informtion. The messge will eventully rech the borer router of the estintion AS (e.g., D). The e-ggregtion point will issue NSP QUERY messge towrs the estintion host. The estintion host will issue NSP RESERVE messge tht will eventully rech the source host. This informtion will be trnsferre with messges through the MBGRP enble routers. Finlly, NSP messges will be trnsferre by GIST, trnsprently through the MBGRP routers, to the estintion host. This wy, resources re reserve in n en-to-en fshion but lso, the inter-omin signling sttes n resources re utomticlly ggregte s escribe in [8]. n messges contin the recor route of the pth. This informtion is use in orer to fin the crossover MBGRP noe when terminl chnges ASs. For exmple, suppose tht terminl moves from S to S3. In the BGRP cse, en-to-en n messges nee to be exchnge. Wht tkes plce in the cse of MBGRP is shown in fig.

4 MT D3 T3 T0 T D NSP_RESERVE R_ (RR,RESERVEInfo) R_ (RR, ReserveInfo) (RR, ReserveInfo) (RR, ReserveInfo) In the secon cse, terminl locte in the root of sink tree chnges its loction n the relte cost is given by: Cost= 3* Distnce(crossover, new loction) + Distnce (crossover, ol loction) + Distnce (Crossover, src loction) =5, source move =5 trget move =0 source move =0 trget move Upte messges to ll Routers inclue in RR BGRP-MBGRP NSP_RESPONSE NOTIFY Figure 3: MBGRP opertion in estintion movement Firstly, NSP QUERY messge will be issue (receiver bse reservtion). The messge contins the recor route of the ctive sessions. The first MBGRP router sens messge tht will rech the crossover MBGRP router. This router will recognize tht it is crossover router (its ress is in the recor route list) n will initite two new messges: to relese resources in the ol brnch, n to the new loction of the terminl. A slightly ifferent proceure tkes plce when the moving terminl is t the root of sink tree. Consier the cse where the terminl chnges its loction from D to D3. Since it is receiver-initite reservtion, NSP RESERVE will be issue for its ctive sessions. The first MBGRP router nees to initite the reservtion n ggregtion of resources on the new brnch. Thus, it sens reverse (R_) messge tht eventully reches the crossover MBGRP router. This will ter the resources in the ol pth n will initite / exchnge for the new pth. Upon successful completion of this proceure it will notify the borer MBGRP router of the new AS to sen NSP RESPONSE bck to the terminl. The crossover router hs to upte in the upstrem irection (i.e., towrs the source omins) the informtion store in the MBGRP routers bout the reltion of reserve bnwith n the roots of the sink trees. The number of signling exchnges n processing for BGRP in cse terminl moves from one plce to nother is lwys: Cost = 3 * Distnce (src loction, st loction) This is becuse en-to-en / n messges hve to be issue. For the cost in MBGRP we istinguish two cses. In the first cse, terminl is moving from one source AS to nother: Cost = *Distnce (crossover, new loction) + Distnce(crossover, ol loction) The first term is relte to the exchnge of / messges n the secon one to the isptch of messges Distnce between Crossover n new/ol plce Figure 4: BGRP Vs MBGRP This cost is higher, since prt from the, n messges, R_s nee to be issue n UPDATE messges must trvel ll the wy bck to the communicting terminls in source ASs. In fig 4 we present, for illustrtive resons, some simple exmples of the cost ifference between BGRP n MBGRP, for binry tree topology where the tree length =5 for the first exmple n =0 for the secon. In these exmples, we hve ssume tht the moving terminl hs ctive sessions n it cn move only from one lef to nother. As we cn observe, MBGRP nees to exchnge fr less messges even in the cses where terminl moves from the first lef of the tree to the lst (e.g., from S to S8), or when terminl locte t the root of the sink tree chnges its loction. V. CONCUSIONS In this pper we hve presente rguments on necessity n merits of ggregtion signling, n exmine more eeply the sclbility issues of two ggregtion protocols. After selecting BGRP, bse on its performnce n its potentil to operte in mobile environments, we presente n extene version tht cn work more efficiently when terminl s movement obsoletes the ol ggregtors loction. By mens of simple nlysis we hve shown tht MBGRP results in fewer messges, minimiztion of the lo in core routers s well s the time neee to reestblish the en-to-en QoS supporting pth.

5 REFERENCES [] J. Mnner, X. Fu, Anlysis of Existing Qulity of Service Signlling Protocols, RFC 4094, My 005. [] D. Vli, S. Psklis, A. Kloxylos,. Merkos, A survey of Internet QoS Signlling, IEEE Communictions Surveys n Tutorils, Fourth Qurter 004, Vol6, No 4. [3] IETF Working group, Next Steps in Signlling, [4]. Schulzrinne, R. ncock, GIST: Generl Internet Signling Trnsport, Internet Drft rft-ietf-nsis-ntlp-08.txt [5] J. Mnner, et l., NSP for Qulity-of-Service signlling, Internet Drft, rft-ietf-nsis-qos-nslp-09.txt. [6] Bren, R., Zhng,., Berson, S., erzog, S. n S. Jmin, Resource Reservtion Protocol (RSVP) Version Functionl Specifiction, RFC 05, September 997. [7] S. Blke et l., An Architecture for Differentite Services, IETF RFC 475, December 998. [8] P. Pn, E. hne n. Schulzrinne, BGRP: A Tree-Bse Aggregtion Protocol for inter-domin Reservtions, Journl of Communictions n Networks, Vol.., No., June 000. [9] F. Bker, C. Iturrle, F. e Fucher, B. Dvie, Aggregtion of RSVP for IPv4 n IPv6 Reservtions, IETF RFC 375, September 00. [0] R. Bless, Dynmic Aggregtion of Reservtions for Internet Services, ICTSM 0, Oct. 00. [] R. Sofi, R. Guerin, n P. Veig, SICAP, Shre-segment Interomin Control Aggregtion Protocol, Technicl Report, ESE, University of Pennsylvni, October 00