Special Feature: NGN FocusBandwidth Management andControl Technology in the NGNMasahiro Miyasaka, Noritaka Horikome,and Koji KishidaAbstractThis article describes bandwidth management and control technology in the Next Generation Network(NGN). This is one of the key technologies that enable the NGN to provide a wide variety of high-qual-ity services including Internet service provider access, retransmission of digital terrestrial broadcasts,telephony, and video on demand. With this technology, a resource and admission control function on acall control server manages the bandwidth resources within the network and guarantees communicationquality by reserving the requested bandwidths for the session described in session initiation protocolmessages.1. IntroductioninFig. 1. The transport network of the NGN consistsof an access network and a core network. The formerMost networks based on Internet protocol (IP) suchconsists of optical fibers and transmission equipmentas the Internet are best-effort networks, which meansthat distributes those fibers to user networks, and thethat when they become congested, packets may belatter consists of high-capacity routers. The core net-dropped or grea tly delayed and c ommunicationswork connects to other networks via edge routers.quality will be deteriorated. On the other hand, theThere are two types of edge routers: a subscriber ser-Next Generation Network (NGN), which providesvice edge (SSE) that connects to the access networkvarious network services, is designed to provide sta-and intermediate border gateway equipment (IBE)ble communication quality, for w hich bandwidththat connects to the networks of other carriers. A userma nagement and control technology [] plays annetwork made up of home terminals and routers con-important role. It guarantees communications qualitynects to the SSE via the access network.by allocating network bandwidth resources to pro-There are also two types of session control servers:vide adequate communication quality for each ser-a subscriber session control (SSC) server that admitsvice, taking into account the application quality, IPsubscriber sessions and an intermediate session con-traffic characteristics, and network composition.trol (ISC) server that performs relay processing. TheSSC and ISC servers c ontrol the SSE a nd IBE,2. Network functionsrespectively, through H.248/Megaco protocol [3]. Asession control server has a call session control func-To guarantee communications quality for a varietytion (CSCF) for SIP signaling and a resource andof network services such as digital terrestrial broad-admission control subsystem (RACS) for controllingcasts, telephony, a nd video on demand, the NGNthe SSE and IBE edge routers. The SSC server alsoimplements a bandwidth control mechanism in coop-has a network attachment subsystem that manageseration with the session initiation protocol (SIP) [2].the IP address space and authenticates terminals byThe session control functions in the NGN are shownmeans of the dynamic host configuration protocol. Inthe NGN, these functions interact for each sessionrequest and perform appropriate processing to secure NTT Network Service Systems Laboratoriesbandwidth.Musashino-shi, 80-8585 JapanNTT Technical Review Special Feature: NGN FocusSSC server ISC serverCSCF CSCFSIPNASSRACS RACSDHCPMegaco MegacoNNISSE NGN core network IBEUNIUserNGN accessnetworknetworkDHCP: dynamic host configuration protocolNASS: network attachment subsystemNNI: network-to-network interfaceUNI: user-to-network interfaceFig. 1. Session control functions in the NGN.3. Transport quality classesmunications, CSCF establishes a SIP session. CSCFinteracts with RACS to perform bandwidth reserva-The NGN provides four transport quality classestion and control of the SSE and IBE for packet mark-[4], [5] ranging from the top-priority class to the best-ing.effort class. Specifically, it uses the best-effort classThe mechanism of bandwidth management in thefor conventional ISP (Internet service provider) con-SSC server is shown inFig. 2. At session establish-nections and the top-priority class for voice and videoment, upon receiving a SIP INVITE message, CSCFcommunications, which require realtime characteris-informs RACS of the requested bandwidth and thetics and stable quality. The NGN makes use of SIPtransport quality class from the media description insession control, when reserving network bandwidththe session description protocol. RACS performsfor each service request, and guarantees these quali-bandwidth admission processing to determine wheth-ties, which are classified by performance objectiveser the bandwidth request from CSCF can actually befor packet delay and packet discard rate. In othersecured on the access network. The judgment is basedwords, the ability to select one of these four transporton the design data of virtual paths as an abstractquality classes for each NGN service makes it possi-model of the configuration of the physical transportble to integrate diverse services on the network whilenetworks.guaranteeing the communications quality required byMedia communic ations are starte d by creatingeach application.media streams on SSE or IBE. A session w hoserequest has been admitted sets the media stream on4. Bandwidth management mechanismthe SSE first as a reserved state. If network addressport translation is performed, the converted address isBandwidth management in the NGN is performedreceived from the SSE at this time. When the 200 OKby means of priority forwarding on the transport net-response is received, the IP address and the port forwork and bandwidth admission control by the sessionthe media stream are all configured and the commit-control server in ac cordanc e w ith e ach sessionted bandwidth value is set on the SSE. Then, the ses-request.sion requesting the media stream changes to the com-Priority forwarding of data packets on the transportmitted state. These session establishment and statenetwork is performed according to the Differentiatedmanagement procedures enable stable media com-Services (Diffserv) model standardized by the Inter-munication to be started.net Engineering Task Force (IETF). This involvesThrough these mechanisms, the NGN is set up somarking each IP packet with its transport qualitythat incoming traffic exceeding the requested band-class at the SSE and IBE and executing priority for-width is discarded at the SSE. Next, the NGN pre-warding among the various transport quality classesvents IP addresses within the network from beingat transport equipment in the core network by refer-conveyed to the outside network.ring to the packet marks. In addition, when bandwidthis reserved for each service request as in voice com-Vol. 7 No. 7 July 20092 Special FeatureSSC serverINVITE: m=audio, b=100 kbit/sCSCFVirtual-path composition200 OK: m=audio,Ad d re ss , po rt ,Ad d re ss , po rt ,OK/no goodNode#3 Node#2 Node#1b=100 kbit/sb = 10 0 kb i t/ s ,b = 10 0 kb i t/ s ,NAPT addresst o p- pr io ri t yt o p- pr io ri t yVirtual path #2 Virtual path #1cl a sscl a ssAt INVITE: reservedAt INVITE: reservedRACSTo pTo pAt 200 OK: committedAt 200 OK: committed1 0 0 k b it / s1 0 0 k b it / sband width addition/Bandwidth addition/Hi ghHi ghsubtractionsubtraction1 0 0 k bi t / s1 0 0 k bi t / sA d dr es s, p or t ,A d dr es s, p or t ,NAPT addressb = 1 0 0 k bi t / s,b = 1 0 0 k bi t / s,Me d iumMe d iumMax. bandwidth Max.t o p -p rio r it yt o p -p rio r it yc la ssc la ssBe st -e f fo rtBe st -e f fo rtbandwidthUNIUserNGN access networkNGN core networkSSEnetwork100 kbit/sMedia communicationsTopTo pHig hH ighSet when 200PriorityOK responseforwardingPriorityMe d iu mM ed iu mis receivedforwardingBe st -e f fo rtBe s t- e ffo r tNAPT: network address port translationFig. 2. Bandwidth management in the NGN.5. Role of session control serverfunctions including a regulatory function for trafficcongestion, an automatic system backup function, anAs described above, the session control se rverautomatic restoration function, and a function for giv-rese rves bandwidths on the basis of SIP sessioning preference to emergency calls and priority calls.requests. To deal with many multimedia services in aThese functions help to achieve safe and secure com-flexible manner, the server may manage bandwidth inmunications. Commercial N GN servic es in Japanthe form of a quality-of-service (QoS) profile. Thiswere launched in March 2008. Looking forward, wefunction can also be used to allocate bandwidth in aplan to focus on further developing the session con-fixed manner such as for multicast services like digi-trol server, an indispensable function of NGN ser-tal terrestrial broadcasting, instead of using SIP ses-vices.sion control. Thus, bandwidth can be secured by set-ting up a QoS profile when a service contract is made.ReferencesIn addition, releasing details about the session controlservers interface in the form of user-to-network[] ETSI/TISPAN ES 282 003.interface (UNI) specific ations should le ad to the[2] H. Kasahara, J. Nishikido, K. Oda, K. Onishi, and Y. Kajiyama, Net-work Core Technologies for a Next Generation Network, NTT Tech-development of many sophisticated services.nical Review, Vol. 5, No. 6, June 2007.In this article, we introduced the session controlhttps://www.ntt-review.jp/archive/ntttechnical.php?contents=ntr2007server with a focus on bandwidth management and06sf2.html[3] ITU-T Recommendation H.248..control technology as a feature of the NGN. We point[4] ITU-T Recommendation Y.540.out here that the session control server also has other[5] ITU-T Recommendation Y.54.3NTT Technical Review Special FeatureMasahiro MiyasakaKoji KishidaResearch Engi neer, NTT Network ServiceSenior Research Engineer, Supervisor, NTTSystems Laboratories.Network Service Systems Laboratories.He received the B.E. and M.E. degrees fromHe received the B.E. and M.E. degrees fromOsaka University in 996 and 998, respectively.Tokyo University of Science in 987 and 989,He joined NTT Network Service Systems Labo-respectively. He joined NTT Communicati onratories in 998 and engaged in research on traf-Switching Laboratories in 989 and has beenfic management and control and methodologiesresearching design methods for the Object Ori-for IP networks. He is now engaged in R&D ofented Switching System. His current R&D inter-admission control for multimedia communica-ests are in the development of realtime andtions. He is a member of the Institute of Electron-high-availability server systems. He is a memberics, Information and Communication Engineersof IEICE.(IEICE) of Japan.Noritaka HorikomeResearch Engi neer, NTT Network ServiceSystems Laboratories.He received the B.S. and M.E. degrees from theUniversity of Tsukuba, Ibaraki, in 2003 and2005, respectivel y. He joined NTT Net workService Systems Laboratories in 2005. His cur-rent R&D area is session control technologies forthe NGN. He is a member of IEICE.Vol. 7 No. 7 July 200944