802.16 MAC Layer Scheduling and its Effect on TCPerfor!anceProfessor Thong NguyenUniversity of Technology Sydney (UTS)AUSTRALIA1. 802.16 MAC Layer Ser"ice #ata $nit %S#$&' Data units exchanged et!een ad"acent #rotocol layersProtocol #ata $nit %P#$&' Data units exchanged et!een #eer entities$ e$g$ %A&PDU is the data unit exchanged et!een the %A& layers of a 'S and its SSs$(igure 1.1' (i%A) Protocol ArchitectureSender )ecei"erSDU&S SAP SDUPDU PDU%A& &o**on Part Sulayer P+, SAP P+, LA,-RPDU PDUAirlin.Service/S#ecific &onvergence Sulayers%A& SAP Privacy SulayerMACP*+Pac.et Pac.et1.1Ser"ice,Secific%Protocol& Con"ergenceSu-layers%CS&%ATMCS. Pac/etCS&The (i%A) %A& #rotocol su##orts a variety of ac.haul re0uire*ents includingoth cell/ased AT% and #ac.et/ased IP #rotocols (including 123$45-thernet)$ The%A& &onvergence Sulayers *a# the trans#ort/layer/s#ecific traffic to a %A& that isflexile enough to efficiently carry any traffic ty#e$Inthefollo!ing6 !edescrie onlythePac.et &S$ This sulayer #erfor*s thefollo!ing functions relying on the service of the %A& &PS7/ &lassification of the higher/layer PDU(fro*'S host) into a##ro#riate(i%A) connection6/ Su##ression of #ayload header infor*ation (o#tional)6/ Delivery of the resulting &S PDU to the %A& SAP associated !ith the serviceflo! for trans#ort to peer %A& SAP at the other end (e$g$ SS end)6 / Recei#t of &S PDU fro* the peer %A& SAP (only)6/ Reuilding of any su##ressed #ayload header infor*ation (o#tional)An IP Pac.et PDU arrives at the (i%A)8s %A& layer is called a %A& SDU$Classification &lassificationis a #rocess y!hicha %A&SDUis *a##ed ontoa #articularconnection for trans*ission et!een %A& peers$ The *a##ing #rocess associates a%A& SDU to a connection (!ith a &ID) and to the service flo! characteristics (i$e$ alist of 9oS #ara*eters) of that connection !hich #rovide the 9oS for the #ac.et$A classifierisaset of*atchingcriteriaa##liedtoeach#ac.et entering(i%A)net!or.$ It consists of so*e #rotocol/s#ecific #ac.et *atching criteria (e$g$destination IP address)6 a #riority6 and a reference to a &ID$If *atched6 the #ac.et isthendeliveredtotheSAPfor deliverytotheconnectionidentifiedythe&ID$I*#le*entation of each s#ecific classification ca#aility (e$g$ IPv:/asedclassification) is o#tional$Several classifiers *ay refer to the sa*e service flo!$Inthiscasetheclassifier #riorityisusedtoorder thea##licationof classifierstoa#ac.et$Do!nlin. classifiers are a##lied y the 'S to #ac.ets it is trans*itting6 andu#lin. classifiers are a##lied at the SS$ Priority ofservice flo!&lassification Para*eters(encoded using ty#e5length5value for*atting sche*e)&ID andS;ID123$4 123$3TL>4TL>:3 and :bytes(igure 1.2' Classifier for!atThe 3/yte &ID *a#s each :/yte S;ID to a connection$The TL> sche*e adds a tagto each trans*itted value !hich contains the ty#e and length of the encoded#ara*eter$The relevant #ara*eters for &S &lassifiers are7TL>< (-thernet)7 destination and source addresses6 -therty#e5SAPTL>3 (123$LAN IDTL>4(IP)7 ToS Range5%as.6 Protocol6 Source address5*as.6 Destinationaddress5*as.TL>: (T&P5UDP)7 T&P5UDP source #ort start6 T&P5UDP source #ort end6 T&P5UDPdestination #ort start6 T&P5UDP destination #ort end$(igure 1.0a' Classification and C1# !aing %2S to SS&(igure 1.0-' Classification and C1# !aing %SS to 2S&Packet Header Suppression %P*S&Since(i%A)isaconnection/orientedservice6 *ost ofroutinginfor*ationina#ac.et eco*es redundant (i$e$ re#etitive) once the connection is set u#6 therefore thePac.et &onvergence Sulayer also#rovides apacket header suppression(P+S)*echanis* in order to avoid the trans*ission of redundant infor*ation in the headersof the%A&SDUs$ Thesu##ressedinfor*ationisthenrestoredat thereceiver$I*#le*entation of theP+Sca#ailityiso#tional$If P+S is enaled atthe%A&connection6 each %A& SDU is #refixed !ith a P+SI !hich references the Payload+eader Su##ression;ield(P+S;)$ Theclassifier uni0uely*a#s a#ac.et toitsassociated P+S rule$Therefore !hen a classifier is deleted6 any associated P+S ruleshall also e deleted$ The receiver uses the &ID and the P+SI to restore the P+S;$The %A& SDU (i$e$ the Pac.et PDU) can e #rocessed as is (i$e$ !ith header) if the1/it P+SI index ?26 or it can e o#tionally added a P+SI @ 2 (i$e$ !ithout header)$ P+S has a Payload +eader Su##ression >alid (P+S>) o#tion for use to verify or notverifythe#ayloadheader eforesu##ressingit$ P+SalsohasaPayload+eaderSu##ression %as. (P+S%) o#tion to allo! select ytes not to e su##ressed$ TheP+S% facilitates su##ression of header fields that re*ain static !ithin a higher/layersession(e$g$ IP addresses)6 !hileenalingtrans*issionoffieldsthatchangefro*#ac.et to#ac.et (e$g$ IP Total Length)$The 'S shall assign all &ID values and all P+SI values$-ither sending or receivingentity shall s#ecify the P+S; and the Payload +eader Su##ression SiAe (P+SS)$This#rovision allo!s for #reconfigured headers or for higher level #rotocols outside thesco#e of (i%A) standards to estalish cache entries$ SS to BS oerationA #ac.et is su*itted to the #ac.et &S$The SS a##lies its list of &lassifiers rules$A*ach of the rule shall result in an U#lin. Service ;lo!6 &ID6 and a P+S Rule$ TheP+S Rule #rovides P+S;6 P+SI6 P+S%6 P+SS6 and P+S>$ If P+S> is set or not#resent6the SS shall co*#are the ytesinthe#ac.et header!ith theytes in theP+S; that are to e su##ressed as indicated y the P+S%$The SS shall then #refixthe PDU !ith a P+SI to turn it into a %A& SDU to e #resented to the %A& SAP fortrans#ort on the U#lin.$At the 'S6 !hen the %A& PDU is received and the 'S %A& layer shall deter*inethe associated &ID y exa*ining the generic %A& +eader$The 'S %A& layer sendsthe PDUA& SAP associated !ith that &ID$ The 'S (receiver) #ac.et &S uses the&ID and the PS+Itoloo.u# P+S;6P+S%6 andP+SS$ The'Sreasse*les the#ac.et$If P+S> !as not enaled6 then there is no guarantee that the restored P+S;ytes *atch the original header ytes$ A si*ilar o#eration can e descried for 'S to SS do!nlin. o#eration$oIP !ith silence$Sincethe siAe of arriving #ac.ets is not fixed in rtPS6 'S has to #oll the connection of thisclass #eriodically (unicast #olling) to as. ho! *uch and!idth is needed$Traffic 9oS s#ecification #ara*eters are7 *ini*u* reserved traffic rate6 *axi*u*sustained traffic rate6 and *axi*u* delay5latency$$on real"ti#e Polling Serice(nrtPS) 6 for traffic !ithout any s#ecific delayre0uire*ent6 e$g$ ;TP traffic6 has higher #riority than the lo!est #riority '- class$Itis the sa*e as '- class exce#t it *ay have additional and!idth allocated throughnon #eriodic #olling$nrtPS therefore6 is not li.ely to e NstarvedO$Traffic s#ecification #ara*eters are7 *ini*u*reserved traffic rate6 *axi*u*sustained traffic rate6 and traffic #riority$Best %ffort('-)classisusedtosu##ort traffic!ithno9oSsuchas+TTP andT-LN-Ttraffic$ This class is allo!edtouse onlycontention/asedand!idthre0uest$There is a fixed nu*er of *ini slots in the UL sufra*e that all SSs have toshare to #lace their re0uests (;igure :$3)$An increase in the nu*er of slots can onlye *ade at a decrease in the and!idth availale for the trans*ission of the actualdata$ There is #ossiilitythat '-traffic is starvedythe lac.of and!idth$&ollisions of re0uests cancorru#t so*e slots andcontentionac./off cancauseserious delay to so*e SSs$Traffic s#ecification #ara*eters are7 *axi*u*sustained traffic rate6 and traffic#riority$Ta-le 3.1' Characteristics of Ser"ice (lo5of Classes of $Lser"ice andcorresonding ;oS ro"ided -y Mo-ile oice !ith activitydetection (>oIP) %in reserved rate %ax sustained rate %ax latency tolerance Pitter tolerance Traffic #rioritynrtPSNon/real/ti*e PollingService(contention re0uestsallo!ed6 #olled lessfre0uently);or nrtS;s !ith etter thanest/effort service6 e$g$and!idth/intensive filetransfer %in reserved rate %ax sustained rate Traffic #riority2E'est/-ffort Service(contention re0uestsallo!ed6 9oS notguaranteed);or '- traffic6 e$g$ generictraffic6 data transfer6 !ero!sing6 etc$ %ax sustained rate Traffic #riority3.3 Poular Algorith!s for 802.16 MAC Layer Schedulers)ound )o-in %))& 829As the na*e descries6 the RR algorith* allocates the resource to the SSs in a cyclicorder in a fair and deter*inistic ti*e *anner$Therefore it ignores the current channelconditions$ Theasenceof theschedulingada#tationtotheshort/ter*channelvariations goes against the ada#tive *odulation and coding nature of (i%A)resulting in lo! net!or. through#ut$Its advantage is its si*#licity$(air ;ueuing %(;& 819'and!idth and uffer s#ace are the t!o ovious sharing resources$;air allocation ofuffer s#aceissi*#leydro##ing#ac.ets inthelong0ueueif necessary$ ;airallocation of and!idth is not si*#le$ ;I;G or ;&;S 0ueuing disci#line is not fairecause it delegates all congestion control to the traffic sources and therefore favoursNaggressiveOsourceshavinglong#ac.etsandcontinuoussuchas;TP$PureRRsche*e also favours long #ac.ets and continuous traffic such as ;TP !hich is al!ays#resent at the0ueueandnever*issestheo##ortunity$ Pac.etsfro*inter*ittenttraffic such as e*ail is 0uite often asent at the 0ueue6 thus *issing the RR #olling$Su##ose the 'S allocates a total a*ount of resource Qtotal toSSs each re0uesting aa*ount Ri$ Under a certain allocation sche*e each SS is allocated an a*ount Qi6 sothat==

ii total< $ Su##osethereisafairsharea*ount Qfairthat all SSsshouldreceive$ The *ax/*in fairness criterion states that an allocation is fair if7 (i)no user receives *ore than its re0uest6 i$e$ ) 6 *in(i fair i =6(ii) nootherallocationsche*esatisfyingcondition(i)hasahigher*ini*u*allocation6 and(iii)&ondition (3) re*ains recursively true as !e re*ove the *ini*al userand reduce the total resource accordingly ) (*in total totalIn K