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QoS Architecture for NGNJuyoung Park a n d S h i n Gak K a n g

Protocol EngineeringCenter , ETRIjypark@epi.re.kr; gkang@etr i . re .kr

Abstract - NG N (Next Generation Network) architecture isassumed as a next generation network where wired and wirelessservices are converged and quality of service is guaranteed.Though there have been several works on QoS provisioningmechanisms to improvequality of service in the current Internet,such as RSVP, DiffServ, because of the complexcity andscalabilty issues hese mechanisms have notbeen deployed yet. Inthis paper, we propose a QoS mechanism to enhance end-to-endQoS though it is very simple but reasonable. The proposedmechanism uses controlling signal to reserve network resourcesfrom sending network to receiving network similarly to RSVP,then send data with QoS enabled flag similarly to DiffServ. Inthis paper we illustrate the proposed resource reservationmechanism withnetwork topology and signaling.Keywords -NGN, scalable InternetQoS Architecture

1. IntroductionRecently the demand on multimedia services especially suchas VoIP, IPTV, Tele-conference has been greatly raised, Butthese kinds of services cannot be completely supp orted by thecurrent Internet environment without any con sideration on theInternet quality of service (Quality of Service: QoS) such astransmission delay and delay jitter etc.Of course there have been a lo t of researches about InternetQoS for past several years. Among them, IntServ[Z],Diffierv[3], RSVP[4] are the representative researches toguarantee Internet QoS. However these mechanisms are notfully used in actual Internet environment because of severalcrucial problems, such as scalability and the way ofreservation.In this paper, we propose a very light Inte met infrastructure bysimplifying the intemal resource reservation scheme and italso can provide end-to-end Qo S between a source to adestination. The proposed method uses an out-of-bandsignaling for resources reservation and handles simple queuemechanism for data delivery. The most remarkable features ofthe proposed mechanism are that each router can minimize thestate information used for resource reservation so thatscalability can be provided. Secondly, it is a sender-based softstate resources reservation so that data delivery path is

identical to reserved path without any additional informationmanagement required. Finally it provides a fully end-to-endresource reservation mechanism.In the section 2, some related studies of this proposed structureare presented as a background of this proposal a nd pointed outwhat is the problem in current Internet QoS. In the section 3,the outline of proposed structure is described. In the Section 4an d 5 we present QoS signaling and the details about a QoSdata delivery scheme. The final section concludes theproposed scheme and shows some further study left.

2. Related StudyIntServ is one of a most representative standard model of anInternet QoS infrastructure for the current Internetenvironment w here only best-effort service can be provided.Especially resource reservation signaling, admission controland a packet schedu ling mech anism is defined here. As one ofsignaling mechanisms for resource reservation, RSVP hasbeen proposed.The most featured characteristic of RSVP is that it canguarantee per flow end-to-end QoS through receiver-basedsoft-state approach. In th e RSVP, a sender advem'ses thecharacteristics of data flow to send by way of the periodicPATH message, and the receiver reserves the resources usingRESV message according to the flow specification advertisedby PATH message. With this RESV message, RSVP routerscan renew resources reservation state. To release th e reservedresources from soutce to destination, a receiver can sendTEAR message to the source, or do nothing. If a periodicRESV message does not appear within a specific timeoutperiod, an RSV P router can release the reserved resources forthe receiver. Also multiple hosts can share network resourceswith others to have more efficient network resourceutilization.Traditionally, an L3 router simply switches ingress packets toits egress interfaces by lookup routing table. But in the RSVP,each router should mange the per-flow state informationcontaining IP addresses and port numbers from source todestination. This causes RSVP router to be overburden, toprovide scalability.To solve this problem, a DiffServ mechanism is proposed. Inthis mechanism, every packet holds PHB(Per Hop

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Behavior)[6] information according to the CoS(C1ass ofService) previously defined, and a DiffServ router onlyforwards packets according to PHB set. Marking PHB bits canbe done by source or edge router of a DS network. If DiffServpacket passes between two DS network, a PHB bit can beadjusted by the policies of the two. As th e largest merit of aDiffServ mechanism, it can solve the scalability problemshown in IntServ by diminishing the size of information arouter should manage.However a DiffServ cannot provide end-to-end QoS servicesto users,but only differentiated CoS(C1ass of Service ) serviceswhere network resource competition happens. Bu t underheavily competed situation, a packet having better PH B alsocan be suffered Iikewise the packet having worse PHB.

3. An Overview of Proposed QoS StructureIn this section, an overview of proposed QoS structure ispresented. Basically, a proposed structureconsists of 4 parts,source/destination hosts, QoS handlers, ingresskgress edgerouters and a series of core routers as shown in Figure 1.

Figure 1 Proposed lotemet pO S StructureThere twomajor parts of the proposed structure are show n infigure2, which are signaling and data delivery modules.

Figure 2.Signsling & Da t a Transmission ModuleIn this scenario, a data must be classified into tw o classes, i.e. aQoS-enabled and Qo S-disabled class, and the classified packetis transmitted from source to destination by data deliverymodule.Role of an edge router takes charge of transmitting packetsfrom a sending host to a core router by resources reservationacceptance control. Resource reservation procedure is done byan out-of-band signaling and data forwarding from end host isdelivered according to the QoS bit setting in the packet headertelling QoS-enabled or not. In the case of QoS-disabledpacket, an edge router transmits the packets with best effort.

On the contrary, for the QoS-enabled packets, additionaltraffic monitoring is done by an edge router. If an end hostconforms to the bandwidth wh ich he mad e a reservation for, apacket is delivered to a core router. If not, the correspondingpackets are set up as QoS-disabled.A queue mechanism of this proposal is different from that ofRSVP or Diff-Sew. Router resources are divided into amultiple class in case of RSVP or DiffServ[l], there are onlytwo classes which are In-service and an Out-Service class inthis proposal.An In-service bandwidth is used for a delivery ofQoS-enabled pack ets, the. another is used for the delivery o fnot that kind of packets. Resource request for the InlServicebandwidth can be done by OOB signaling but not for theOut-Service. If the In-service bandwidth is not fully reserved,the left portion can be used for the delivery of Out-Servicepackets for better utilization.Figure 3shows the elements which an edge router is composedof. An edge router is managing QoS reservation state abouteach flow, and monitors whether the incoming flow from asending host violates the contract. If a violated QoS-enabledpacket is found, it converts the QoS-enabled bit intoQoS-disabled.

Figure 3. Insides of Qo S HandlerIt is composed of a series of core router from an edge router toa receiving side edge router, Resources reservation signalingof this part consists of a hop-by-hop way. The details ofa QoSsignaling between end hosts are presented in the followingparagraph. And the reserved path between end nodes isidentical to a path obtained by a routing table.

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-5 Sipallins. , _... ....,.I I I '

Figure 4. Insides of Proposed RouterIf an error arises during the resources reservation, an errormessage is delivered with reverse-course, and the resourcesreservation is canceIed. Only after a successful resourcesreservation QoS-enabled packets are transmitted according tothe queue from source to destination made by the reservation.Each router manages only two queues like figure 4. AnIS(In-Service) queue is a queue for QoS service to b e provided,an d an OS(0ut-Service) queue is a queue to transmit an besteffort service packet. As a result a router can manage only alittle state according to managing only two queues per eachinterface.

4. SignalingAmong othm router resources generally a bandwidth is thelargest consideration object. In a mechanism proposed to anobject mak ing a reservation for is the sender that delivers QoSdata, and an object carrylng out resources reservation isachieved in routers between a sender and receivers. Resou rcesreservation signaling consists of a hop-by-hop way from asender to a receiver like looking in figure 5 .

I

Figure 5. ResourceReservation Signaling

As mentioned above with figure 1, there are two kinds ofrouters between a sender and receivers, The router whichbordered on an end host is called an edge router. This routerdoes an admission control for the resource reservation andmonito ring on the ingress packets from its network.

The series of routers between edge routers are defined as corerouters, A core router does not perform admission control , apolicy control no r packet monitoring. A core router makes aresource reservation according to resource availability andforwards the incoming QoS data properly.The most important information that core routers must manag eare how much the resources are used and ho w much theresources are available. Figure 6shows the modified routingtable holding the necessary information.The sending host which reserves ' resources needs to sendresources reservation request message periodically. An edgerouter requests to a core router according to this message onlyafter the admission control is accepted.Similar to RSVP, a soft-state manageme nt is needed. R esourcereservation can be renewed by periodic resources requestmessage. And if there is no a explicit cancellation request, areserved resources information can be flushed a s the routingtable is renewed. However, this state management i sperformed only in an edge router, but not in a core router.

NetMaskGateway Current routinginfomation

Newly addedroutinginfomationFigure6. Modified RoutingTable

5 . Data DeliveryA sender can send QoS data to the receiver only after it made areservation successfully through a OOB signaling. A QoSpacket is marked as a QoS-enabled and delivered to thereceiver following the pre-reserved QoS channel.After successful reservation, a sending host must monitor thequantity of sending QoS packets. Because it can collect all th einfomation about traffics it generates, not*onlyper-flow butalsoper-host, and resources it has reserved for an interface. Asending host must performs traffic monitonng not t o violatethe reservation conformation.As well as sending host, a QoS handler mon itors the traffic tomake a decision whether the packet conforms the contract ornot. If a packets violates the contract for the reservation, anedge changes the corresponding QoS-enabled packet intoQoS-disabled packet, then treats as QoS- disabled.Traffic passing an In-Sewice(IS) queue ensures guaranteedservice, and the traffic passing an Out-Service(0S) queueprovides only best-effort service, therefore passing OS queue

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packets can be sluffered from loss or delay when a router these packets is granted by a Qo S handler to degrade intobecame congested. non-QoS data.If we consider the traffic generated from he source is divided As a result, the core router is always ensured data toin to two streams, one for guaranteed service which is correspond to resources reserved for. Only structure about aconforming to the contract and the other is it s best-effort QoS guarantee mechanism was proposed at present,services and can be presented as in equation (1). simulation performance validation and a prototype

implementation will be continued.

This stream is appeared in the ingresspoint ofQoS Handler asstream from node i to node j , while bi jpresents that the besteffort stream from node i to nodej.presented in equation (2). Th e rIrpresents that the reserved Dl

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[61This stream is appeared in the egress point of QoS Handler aspresented in equation (3). Th e r'iipresents that the reservedstream from node i to node j , while b' , presents that the besteffort stream from node i to nodej.

REFERENCESGeoff Huston, internet Performance Survival Guide, Wiley ComputerPublishing,2000R. Braden et al., "lntegrated Services in th e Internet Architecture: anOvewiew",RFCl633, June 1994.S. Blake@ al., "A n Architecture for Differentiated Services".RFC2475,Dec. 1998R.Braden, et al., "Resource ReSerVation Protocol (RSVP)-V enionlFunctional Specification," RFC2205, Sep.1997Nichots, K. et al., "Definition of fhe D iffer-entiated Services FieId (DSField) in the IPv4 and IPv6 Headers",RF C 2474, Dec. 1998K. ichols, et al., "ATwo-bit DifferentiatedServices Architecture for theInternet", draft-nicholsdiff-svc-a~h-D0.txt,ov. 9

The dv presents the amount of packet drop caused by esourceinsufficiency and is equalt to the difference between the inp utand output amount of stream.

T h e main role of the proposed architecture is to make thepacket drop rate to zero by conforming to the contract.

6 . ConcIusion and Further StudyInternet quality of service offer plan is the very importantmatter to be considered so that a multimedia service can beprovided in Internet. Showing that the global Internet QoSmechanism has not been proposed yet, although Internet QoSrelated study had been camed out for past several years,Intemet QoS is not an easy work.Therefore we propose a noble lntemet QoS guarantee schemethat can be easily applied to the current Internet from themerits and demerits of the past study results. Le, by using a setof procedure, a sending host can reserve a guaranteed QoSpath identical to router path. An one bit QoS data is passed bythe reserved path.

' A sending host must coordinate traffic in order to conform toreservation resources, if a contract was broken , a penalty about

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