IEEE 802.16 m evaluation methodology document

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Published Date:25-10-2017
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IEEE 802.16m Reference Model and Protocol Structure INTRODUCTION The IEEE 802.16-2009 standard defines a generic reference model where major functional blocks (i.e.,physicallayer,securitysub-layer,MACcommonpartsub-layer,andservicespecificconvergence sub-layer)andtheirinterfaces,thepremisesofIEEE802.16entity,andageneralnetworkcontroland management system are specified. The IEEE 802.16m has modified this reference model by further classifyingtheMACcommonpartsub-layerfunctionsintotwofunctionalgroups,resultinginamore structured approach to characterizing the data link layer functions and their interoperation. Theearlierrevisionsand/oramendmentsoftheIEEE802.16standarddidnotexplicitlydefineany detailed protocol structure; rather, the functional elements in the specification were implicitly clas- sified as convergence sub-layer, MAC common part sub-layer, security sub-layer, and physical layer. While each of these layers and/or sub-layers comprises constituent functions and protocols, no perspective was provided on how various components were interconnected and interoperated from a system standpoint. In fact, the IEEE 802.16 standards have never been developed with a system engineering approach; rather, they specify components and building blocks that can be integrated (obviously various combinations are potentially possible) to build a working and performing system. An example is the mobile WiMAX system profiles 1, where a specific set of IEEE 802.16-2009 features were selected to form a mobile broadband wireless access system. In an attempt to improve theclarityofthepreviousIEEE802.16standardsandtotakeasystematicapproachindevelopmentof the advanced air interface, IEEE 802.16m has defined a protocol structure and the functional components are classified into different layers and sub-layers, as well as differentiated based on data- plane or control-plane categories. The protocols and functional elements defined by the IEEE 802.16 standard correspond to the physicalanddatalinklayersoftheOpenSystemInterconnection(OSI)seven-layernetworkreference model as shown in Figure 3-1. In the context of protocol structure, we will frequently use the terms “service” and “protocol.” It must be noted that services and protocols are distinct concepts. A service is a set of primitives or operationsthatalayerprovidestothelayer(s)withwhichitisinterfaced2.Theservicedefineswhat operations a layer performs without specifying how the operations are implemented. It is further relatedtothe interface between twoadjacentlayers. Aprotocol,incontrast,is aset ofrulespresiding over the format and interpretation of the information/messages that are exchanged by peer entities within a layer. The entities use protocols to implement their service definitions. Thus, a protocol is related to the implementation of a service. 61 OSI Seven-Layer Network Model Application Layer Presentation Layer Session Layer Scope of IEEE 802.16 Standards Protocols Transport Layer Service Specific Convergence Network Layer Sublayer Data-Link Layer Medium Access Control Common Part Sublayer Physical Layer Security Sublayer Physical Layer FIGURE 3-1 The mapping of IEEE 802.16 protocol layers to an OSI seven-layer network model Layer N+1 Layer N+1 SDU PDU Layer N Layer N Layer N Services or Functions Protocol Services or Functions PDU SDU Layer N-1 Layer N-1 Source Destination FIGURE 3-2 An illustration of service, protocol, PDU, and SDU concepts 2 AsshowninFigure3-2,aProtocolDataUnit(PDU)isapacketexchangebetweenpeerentitiesof thesameprotocol layerlocatedat the sourceanddestination. On the downward direction,the PDU is the data unit generated for the next lower layer. On the upward direction, it is the data unit received fromthepreviouslowerlayer.AServiceDataUnit(SDU),ontheotherhand,isadataunitexchanged between two adjacent protocol layers. On the downward direction, the SDU is the data unit received fromtheprevioushigherlayer.Ontheupwarddirection,itisthedataunitsenttothenexthigherlayer.Network Control and Management System M-SAPC-SAP 3.1 The IEEE 802.16m reference model 63 This chapter provides a top-down systematic description of IEEE 802.16m reference model and protocol structure, starting at the most general level and working toward details or specifics of the protocol layers, their functional constituents and interconnections. An overview of 3GPP LTE protocol structure is further provided to enable readers to contrast the corresponding protocols and functionalities. It must be noted that while the IEEE 802.16 standard does define a generic network reference model (or a network abstraction model), the mobile WiMAX systems use the specific network reference model and system architecture that were described in Chapter 2 to achieve interoperability. Therefore, the network reference model and associated components and interfaces described in Section 3.1 are only informative, and they should not be interpreted as normative for implementation and deployment of the IEEE 802.16m systems. 3.1 THE IEEE 802.16M REFERENCE MODEL Figure 3-3 illustrates the IEEE 802.16 reference model 3. The data link layer of IEEE 802.16 standard comprises three sub-layers. The service-specific convergence sub-layer (CS) provides any IEEE 802.16 Entity CS SAP Service Specific Convergence Sublayer (CS) CS Management/Configuration MAC SAP MAC Common Part Sublayer (MAC CPS) MAC Management/Configuration Security Sublayer Management Information Base (MIB) PHY SAP Physical Layer (PHY) PHY Management/Configuration Data/Control Plane Management Plane FIGURE 3-3 The IEEE 802.16 reference model 364 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure transformationormappingofnetwork-layerdatapacketsintoMACSDUs.Onthetransmitterside,the CS receives the data packets through the CS Service Access Point (SAP) and delivers MAC SDUs to the MAC Common Part Sub-layer (MAC CPS) through the MAC SAP. This includes classifying network-layer SDUs and associating them with the proper MAC Service Flow Identifiers (SFID) and Connection Identifiers (CID). The convergence sub-layer also includes payload header suppression function to compress the higher-layer protocol headers. Multiple CS specifications are provided for i interfacing with various network-layer protocols such as Asynchronous Transfer Mode (ATM) and packet-switched protocols such as IP or Ethernet. The internal format of the CS payload is unique to theCS,andtheMACCPSisnotrequiredtounderstandtheformatoforparseanyinformationfromthe CS payload. The MAC CPS provides the core MAC functionality of system access, bandwidth allocation, connection establishment, and connection maintenance. It can receive data from the various conver- gence sub-layers, through the MAC SAP classified into particular MAC connections. An example of MACCPSservice definitionisgiveninreference3.TheQualityofService(QoS)isfurtherapplied to the transmission and scheduling of data over the physical layer. The MAC also contains a separate security sub-layer providing authentication, secure key exchange, andencryption.Theuserdata,physical layercontrol,andstatisticsaretransferred between the MAC CPS and the Physical Layer (PHY) via the PHY SAP which is implementation-specific. The IEEE 802.16physical layer protocols include multiple specifications, defined through several amendments and revisions, each appropriate for a particular frequency range and application. The IEEE 802.16 compliant devices include mobile stations or base stations. Given that the IEEE 802.16 devices may be part of a larger network, and therefore would require interfacing with entities for management and control purposes, a Network Control and Management System (NCMS) abstraction has been introduced in the IEEE 802.16 standard as a “black box” containing these entities 3. The NCMS abstraction allows the physical and MAC layers specified in the IEEE 802.16 standard to be independentofthenetworkarchitecture,thetransportnetwork,andtheprotocolsusedinthebackhaul, and therefore would allow greater flexibility. The NCMS entity logically exists at both BS and MS sides of the radio interface. Any necessary inter-BS coordination is coordinated through the NCMS entityattheBS.AnIEEE802.16entityisdefinedasalogicalentityinanMSorBSthatcomprisesthe physical and MAC layers on the data, control, and management planes. The IEEE 802.16f amendment (currently part of IEEE 802.16-2009 standard 3) provided enhancementstoIEEE802.16-2004standard,definingamanagementinformationbase(MIB),forthe physical and medium access control layers and the associated management procedures. The management information base originates from the Open Systems Interconnection Network Manage- ment Model and is a type of hierarchical database used to manage the devices in a communication network5,6.Itcomprisesacollectionofobjectsinavirtualdatabaseusedtomanageentitiessuchas routers and switches in a network. i Asynchronous Transfer Mode (ATM) is a packet switching protocol that encodes data into small fixed-sized cells and provides data link layer services that run over OSI layer 1, differing from other technologies based on packet-switched networkssuchasIPorEthernet,inwhichvariable-sizedpacketsareused.ATMexploitspropertiesofbothcircuit-switched andsmallpacket-switchednetworks,makingitsuitableforwideareadatanetworking,aswellasreal-timemediatransport. ATM uses a connection-oriented model and establishes a virtual circuit between two end-points before the actual data exchange begins 4.Management Plane Data/Control Plane 3.1 The IEEE 802.16m reference model 65 ii TheIEEE802.16standarddescribestheuseofaSimpleNetworkManagementProtocol(SNMP), i.e., an IETF protocol suite, as the network management reference model. The standard consists of aNetworkManagementSystem(NMS),managednodes,andaserviceflowdatabase.TheBSandMS managednodescollectandstorethemanagedobjectsintheformofWirelessMANInterfaceMIBand Device MIB that aremadeavailabletonetworkmanagement systemviamanagement protocols, such as SNMP. A Network Control System contains the service flow and the associated Quality of Service informationthathavetobeprovidedtoBSwhenanMSentersintothenetwork.TheControlSAP(C- SAP)andManagementSAP(M-SAP)interfacethecontrolandmanagement planefunctionswiththe upperlayers.TheNCMSentitypresentswithineachMS.TheNCMSisalayer-independententitythat may be viewed as a management entity or control entity. Generic system management entities can perform functions through NCMS and standard management protocols can be implemented in the NCMS. If the secondary management connection does not exist, the SNMP messages, or other management protocol messages, may go through another interface in the customer premise or on a transport connection over the air interface. Figure 3-4 describes a simplified network reference Network Control and Management Network Control and Management System (NCMS) System (NCMS) IEEE 802.16 C-SAP M-SAP C-SAP M-SAP Air-Interface IEEE 802.16 Entity IEEE 802.16 Entity Data/Control Planes Mobile Station (MS) Base Station (BS) FIGURE 3-4 The IEEE 802.16 generic network reference model 3 ii An SNMP-managed network consists of three key components: (1) a managed device; (2) an agent; and (3) a network managementsystem.AmanageddeviceisanetworknodethatcontainsanSNMPagentandresidesinamanagednetwork. Managed devices collect and store management information and make this information available to NMSs using SNMP. Managed devices, sometimes called network elements, can be any type of device including, but not limited to, routers, access servers, switches, etc. An agent is a network-management software module that resides in a managed device. An agent has local knowledge of management information and translates that information into a form compatiblewith SNMP. A network management system executes applications that monitor and control managed devices. The NMSs provide the processing and memory resources required for network management. One or more NMSs may exist on any managed network 7,8.NCMS-N Network Interfaces Control and Management Interface NCMS-E M-SAPC-SAP 66 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure model.MultiplemobilestationsmaybeattachedtoaBS.TheMScommunicatestotheBSovertheair interface using a primary management connection, basic connection or a secondary management connection 3. The latter connection types have been replaced with new connection types in IEEE 802.16m standard 12. 3.1.1 The MS and BS Interface iii The MAC management PDUs that are exchanged over the primary management connection can trigger, or are triggered by, primitives that are exchanged over either the C-SAP or the M-SAP, depending on the particular management or control operation. The messages that are exchanged over the secondary management connection can trigger or are triggered by primitives that are exchanged overtheM-SAP.ThisinterfaceisasetofSAPbetweenanIEEE802.16entityandNCMSasshownin Figure 3-5. It consists of two parts: the M-SAP is used for delay-tolerant management-plane primi- tives; and the C-SAP is used for delay-sensitive control-plane primitives that support handovers, Scope of IEEE 802.16 Standard CS SAP Service Specific Convergence Sublayer (CS) CS Management/Configuration MAC SAP MAC Common Part Sublayer (MAC CPS) MAC Management/Configuration Security Sublayer Management Information Base (MIB) PHY SAP Physical Layer (PHY) PHY Management/Configuration Control Plane/Data Plane Management Plane Other Network Embodyment of IEEE 802.16 Entity Entities FIGURE 3-5 Partitioning of the IEEE 802.16 network control and management system 3 iii A management connection is used for transporting MAC management messages or standards-based messages. The primary management connection is established during network entry and is used to transport delay-tolerant MAC management messages. The secondary management connection may be established during MS registration that is used to transport standards-based messages; e.g., SNMP, DHCP messages.3.1 The IEEE 802.16m reference model 67 security context management, radio resource management, and low power operations such as idle mode and paging functions. 3.1.2 Network Control and Management System TheNetworkControlandManagementSystemisnotpartoftheIEEE802.16standards,andistreated asa“blackbox.”Itmaybedistributedwithcomponentsresidingondifferentnodesinanetwork.Part of the NCMS may be physically collocated with the IEEE 802.16 entity referred to as NCMS-E. The remaining part of the NCMS may be physically distributed across one or more network entities. This part of the NCMS is referred to as NCMS-N. Figure 3-5 shows the partitioning of the NCMS into NCMS-E and NCMS-N. The NCMS-E may have its own software platform and network protocol implementation,allowingittocommunicatewithexternalentitiesintheNCMS-N.TheNCMS-Emay provide an SNMPAgent compliant to IETF RFC3418 13 and the SNMP/TCP/IP protocol stack, to allow for interactions with an SNMP manager. The NCMS-E may provide an Object Request Broker andimplementaprotocolstacktointeractwithcomponentsonothernetworkentitieswithinNCMS-N iv based on the CORBA architecture. The messages available to a manager in the NCMS-N are v specified using Interface Description Language (IDL). These messages encapsulate the interactions vi with the MIB. The IEEE 802.16 entity can be managed through Web Services. 11 Thedecomposition ofNetworkControl and Management Systemis depictedin Figure 3-6. These entities may be centrally located or distributed across the network. The exact functionality of these entities and their services is outside the scope of the IEEE 802.16 standard, but is shown here for illustration purposes and to allow description of the management and control procedures. The NCMS service manifestations on the MS and BS may have different configurations and functions. TheIEEE802.16mreferencemodelisverysimilartothatoftheIEEE802.16-2009standard,with the exception of soft classification of MAC common part sub-layer into radio resource control and management and medium access control functions. As shown in Figure 3-7, this functional parti- tioningislogical, i.e.,noSAP isrequiredbetween thetwoclassesoffunctions andnoadditional sub- headersareappendedtotheSDUs.Furthermore,thefunctionalelementsonthedataandcontrolpaths areexplicitlyclassifiedintodata-andcontrol-planefunctions.Whilesimilarfunctionalitiesexistinthe IEEE 802.16-2009 standard, the functions and protocols are not explicitly categorized in the legacy standard except explicit separation of PHY, MAC CPS, and CS functions in the specification 3. The categorization of the functions based on functional characteristics and relative position in the data/signaling processing path would ease analogy, and contrast with other radio access technologies iv The Common Object Requesting Broker Architecture (CORBA) is a standard defined by the Object Management Group that enables software components written in multiple computer languages and running on multiple computers to work together 9. v An Interface Description Language (IDL) is a specification language used to describe a software component’s interface. IDLs describe an interface in a language-independent way, enabling communication between software components that do not share a language; e.g., between components written in Cþþ and Java 10. vi AWeb Service is a software system designed to support interoperable machine-to-machine interaction over a network. It has an interface described in a machine-processable format. Other systems interact with the web service in a manner prescribed by its description using SOAP-messages (Simple Object Access Protocol is a lightweight protocol intended for exchanging structured information in a decentralized, distributed environment) typically conveyed using HTTP with an XML serialization in conjunction with other web-related standards.Network Control and Management System M-SAPC-SAP 68 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure Network Control and Management System Mobility Management AAA Services Security Services Services Radio Resource Service Flow Paging and Idle Mode Management Services Management Services Services Multicast Broadcast Location Based Services Media Independent Services Management Management Handover Functions Subscriber Station Network Management Management Services (Only MS Side) FIGURE 3-6 Decomposition of the network control and management system 3 IEEE 802.16 Entity CS SAP Radio Resource Service Specific Control and Convergence Management Sublayer Functional Group (CS) MAC SAP CS Management/Configuration Medium Access Control Functional MAC CPS Group MAC Management/Configuration Security Sublayer Management Information Base (MIB) PHY SAP Physical Layer (PHY) PHY Management/Configuration Control Plane Data Plane Management Plane FIGURE 3-7 The IEEE 802.16m reference model 123.1 The IEEE 802.16m reference model 69 suchas3GPPLTE/LTE-Advancedthathavebeendesignedbasedonsimilarstructuredprotocoldesign methodology. Furthermore, the structured functional/protocol design in IEEE 802.16m would elimi- nate the inherent complexity and ambiguity of studying, understanding, and implementing the legacy standard. Itmustbenotedthattherearenew,modifiedorextendedfunctionsandprotocolsthatareclassified undergenericclassesofPHY,MACCPS,andCSinIEEE802.16m,wheretherearenocounterpartsin the legacy standard. Therefore, similarity of the reference models should not be interpreted as func- tional compatibility at the service access points. The backward compatibility of the IEEE 802.16m with the legacy standard ensures that non-compatible functions/protocols are not utilized in the time intervals where legacy base stations and mobile stations are supported in the network. 3.1.3 Data-Plane TheMACandPHYfunctionsoftheIEEE802.16mcanbeclassifiedintothreecategoriesnamelydata- plane, control-plane, and management-plane. The data-plane (alternatively known as user-plane) comprises functions in the user data processing path, such as service flow classification and header compression,aswellasMACandPHYdatapacketprocessingandencryptionfunctions.Asshownin Figure3-8,theIEEE802.16mdata-planeentitycomprisestheservicespecificConvergenceSub-layer, IEEE 802.16m Data-Plane Entity CS SAP Service Specific Convergence Sublayer (CS) MAC SAP Medium Access Control Functional Group (Data Plane Functions) Security Sublayer (Data Plane Security) PHY SAP Physical Layer (PHY) FIGURE 3-8 The IEEE 802.16m data-plane entity 1270 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure MACfunctionalgroup,security,andphysicallayerprotocolscorrespondingtodata-planeuserpacket processing.TheMACandPHYSAPs,whileconceptuallythesameasthosespecifiedbyIEEE802.16- 2009 standard, have different manifestation due to the new and/or modified MAC and PHY features introduced in the IEEE 802.16m standard. There is no significant change in CS SAP relative to that specified in the IEEE 802.16-2009 standard 3. The CS provides a mapping of external network data formats (e.g., IP layer packets, ATM cells) received through CS SAP into MAC SDUs that are delivered to the MAC CPS via MAC SAP. This includesclassifyingexternalnetworkSDUsandassociatingthemwithaproperServiceFlowIdentifier andConnectionIdentifier.AServiceFlow(SF)isaMACtransportservicethatprovidesunidirectional transport of packets inthe downlink oruplink 14. It is identified by a 32-bit SFID. A service flow is characterizedbyasetofQoSparameters,i.e.,aparametersetassociatedwithaserviceflowidentifier containing traffic parameters which define scheduling behavior of uplink or downlink service flows associated with transport connections. An admitted and active service flow is uniquely mapped to aCID.NotethattheIEEE802.16standardsupportstwophaseactivationmodel.i.e.,theresourcesfor a service are first admitted or reserved and once the BS and MS negotiations are completed, the resources are activated 3. TheGenericPacketCS(GPCS)isanetworklayerprotocol-agnosticpacketconvergencesub-layer thatsupportsmultiplenetworkprotocolsoverIEEE802.16airinterface.TheGPCSprovidesageneric packet convergence sub-layer. This layer uses the MAC SAP and exposes a SAP to GPCS applica- tions.TheGPCSdoesnotredefineorreplaceotherconvergencesub-layers.Instead,itprovidesaSAP that is not protocol specific. With GPCS, packet parsing occurs above GPCS. The results of packet parsing are classification parameters provided to the GPCS SAP for parameterized classification; however, upper layer packet parsing is left to the GPCS application. With GPCS, the upper layer protocol that is immediately above the IEEE 802.16 GPCS is identified by a parameter known as GPCSprotocoltype.TheGPCSprotocoltypeis includedinservice flowmanagementprimitivesand connectionestablishmentmessages.TheGPCSdefinesasetofSAPparametersastheresultofupper layer packet parsing. These are passed from upper layer to the GPCS in addition to the data packet. The SAP parameters include SFID, the MS MAC Address, data, and length. The GPCS allows multiplexing of multiple layer protocol types (e.g., IPv4, IPv6, and Ethernet) over the same IEEE 802.16 MAC connection. It is outside the scope of the GPCS protocol to specify how the upper layer multiplexes and de-multiplexes multiple protocol data packets over an IEEE 802.16 connection or service flow 3. In multimedia streaming applications, the overhead of Internet Protocol (IP) 15, User Datagram Protocol(UDP)16,andReal-timeTransportProtocol(RTP)17,18payloadheadersare40bytesfor IPv4(or60bytesforIPv619).Forvoice-over-IP,thiscorrespondstoapproximately60%ofthetotal amountofencodedvoicedata(e.g.,theRTPpayloadof3GPPAdaptiveMulti-Rate12.2kbpsfull-rate codecconsistsof33bytes20).Suchlargeoverheadsmaybetolerableinwiredlinkswherecapacity is often not an issue, but are excessive for wireless systems where bandwidth is scarce. The IEEE 802.16 standard defines a native header compression algorithm that is part of the convergence sub- layer. The Payload Header Suppression (PHS) defined in the IEEE 802.16 standard compresses the repetitiveorredundantpartsofthepayloadheaderreceivedfromnetworklayer.ThePHSoperationis based on the PHS rules, which provide all the parameters corresponding to header suppression of the SDU. Other standard header compression algorithms, such as Robust Header Compression (RoHC) defined by IETF 21, are also supported.3.1 The IEEE 802.16m reference model 71 TheRoHCschememaybeusedasanalternativetoPHStocompresstheRTP/UDP/IPheaderofan IP packet. When RoHC is enabled for a service flow, the service flow constitutes what in IETF RFC 3095 is referred to as a RoHC channel 21,3. Two service flows cannot share an RoHC channel, and two RoHC channels cannot share the same service flow. On a service flow for which RoHC has been enabled, all of the IP packet passes through the RoHC compressor on the transmitter side and the decompressoronthereceiverside.ThesupportofRoHCisnegotiatedbetweentheBSandMSduring capability negotiation 3. The data-plane part of MAC CPS includes functions such as Automatic Repeat reQuest (ARQ), Packet Fragmentation/Packing, MAC PDU formation and encryption. The scheduler on the BS side allocates radio resources and multiplexes the users, and selects the appropriate MIMO mode, modulation and coding scheme based on the measurement reports that are received from the mobile stations.TheARQisanerrorcontrolmechanismatdatalinklayerwherethereceivermayrequestthe transmitter to resend a block of data that was erroneously detected or not received. An ARQ block is a distinct unit of data that is carried on an ARQ-enabled connection. Such a data unit is assigned a sequence number and is managed as a distinct entity by the ARQ state machines. The ARQ block size is a parameter that is negotiated during connection establishment. The ARQ mechanism may be disabled for some delay sensitive applications such as VoIP. Fragmentation is a process in which a MAC SDU is divided into one or more MAC SDU fragments. Packing is a process where multiple MAC SDUs are packed into a single MAC PDU payload. Both processes may be initiated by either a BS for a downlink connection or an MS for an uplink connection. Several MAC PDUs may be concatenated into a single transmission in the downlink or uplink. The MAC PDUs containing user data are processed by the physical layer for over-the-air trans- mission.Itmustbenotedthatthephysicallayerprocessingoftheusertrafficcanbedifferentinterms of the permissible MIMO modes or modulation and coding schemes that are used. 3.1.4 Control-Plane A set of Layer 2 control functions are needed to support various radio resource configuration, coordination,signaling,andmanagement.Thissetoffunctionsiscollectivelyreferredtoascontrol- plane functions. The IEEE 802.16m control-plane entity comprises Radio Resource Control and Management (RRCM), MAC functional group, and physical layer protocols corresponding to control path. The RRCM functional class includes all control and management functions such as network entry/re-entry management, paging and idle mode management, multicast and broadcast service, etc. This group of functions is also known as Radio Resource Control (RRC) in other air interface standards such as 3GPP LTE. The MAC functional group consists of functions that perform physical layer control and signaling, scheduling services, QoS, etc. This functional group corresponds to Radio Link Control (RLC) and MAC layers in other air interface standards such as 3GPP LTE. Figure 3-9 illustrates the IEEE 802.16m control-plane entity. As shown in this figure, the RRCM performscontrolandmanagementoflower-layerfunctions.Thecontrolinformationiscommunicated with the mobile station via MAC management messages. The underlying functional elements of the RRCM sub-layer will be described in Section 3.2. The security sub-layer in Figure 3-9 is shown with dotted line, since the IEEE 802.16m selectively encrypts and protects unicast MAC management messages. If the selective72 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure IEEE 802.16m Control-Plane Entity Radio Resource Control and Management Functional Group (RRCM) Medium Access Control Functional Group (Control Plane Functions) Security Sublayer (Control Plane Security) PHY SAP Physical Layer (PHY) FIGURE 3-9 The IEEE 802.16m control-plane entity 12 confidentiality protection is utilized, the negotiated keying materials and cipher suites are used to encrypt the management messages. There are three levels of selective confidentiality protection appliedtoMACmanagementmessages in the IEEE 802.16m: (1) no protection where the MS and BShavenosharedsecuritycontextorprotectionisnotrequired,thenthemanagementmessagesare neither encrypted nor authenticated. Management messages before the authorization phase also fall vii into this category; (2) cipher-based message authentication code (CMAC) integrity protection protects the integrity of the entire MAC management message; and (3) advanced encryption stan- viii dard-based (AES-CCM) authentication/encryption protects the integrity of payload and MAC header 3. vii A cipher-basedMAC (CMAC)is ablock cipher-basedmessage/code authentication algorithm. It maybeused to provide assurance ofthe authenticity and integrityof user payloads. AES-CMACprovidesstronger assurance of data integritythan a checksum or an error-detecting code. The verification of a checksum or an error-detecting code detects only accidental modifications of the data, while CMAC is designed to detect intentional, unauthorized modifications of the data, as well as accidental modifications. viii The counter with CBC-MAC (CCM), as defined in IETF RFC 3610, is a generic authenticated encryption block cipher mode. CCM is only defined for use with 128-bit block ciphers, such as AES. It is an authenticated encryption algorithm designed to provide both authentication and privacy.Network Control and Management System M-SAPC-SAP 3.1 The IEEE 802.16m reference model 73 3.1.5 Management-Plane Amanagement-planeisalsodefinedforexternalmanagementandsystemconfiguration.Therefore,all managementandprotocolconfigurationentities,aswellasmanagementinformationbase,fallintothe management-planecategory.DefinitionofmanagementinformationbasesareoutofscopeoftheIEEE 802.16mstandard.AsshowninFigure3-10,themanagemententityandthemanagementinformation bases contained in the management-plane, configure and manage the functional entities in the data- and control-plane protocol layers. The IEEE 802.16 specification includes control and management SAPs as part of the management-plane that exposecontrol-plane and management-plane functions to upper layers. Management-plane primitives and the C-SAP are used for more time sensitive control- plane primitives that support handovers, security context management, radio resource management, and low power system operations. In addition, under the IEEE 802.16 standard, a user can be associated with a number of service flows, each characterized with different QoS parameters. This information is provisioned in a subscriber management system (e.g., AAA database) or a policy server. There are two service models:(1) static service model,where thesubscriberstation isnot allowedtochangetheparameters ofprovisionedserviceflowsorcreatenewserviceflowsdynamically;and(2)dynamicservicemodel, where an MS or BS may create, modify or delete service flows dynamically. In the latter case, IEEE 802.16 Management Plane Entity CS Management/Configuration MAC Management/Configuration Security Management/Configuration Management Information Base (MIB) PHY Management/Configuration FIGURE 3-10 The IEEE 802.16 management-plane entity 374 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure adynamicserviceflowrequestisevaluatedagainsttheprovisionedinformationtodecidewhetherthe request could be authorized. More precisely, the following steps are provisioned in the IEEE 802.16 specification for dynamic service flow creation 22: 1. PermittedserviceflowsandassociatedQoSparametersareprovisionedforeachsubscriberviathe management plane (management entity). 2. A service flow request initiated bytheMS or BSis evaluatedagainstthe provisionedinformation, and the service flow is created if permissible. 3. Aserviceflowthuscreatedtransitionstoanadmitted,andfinallytoanactive,stateduetoBSaction (this is possible under both static and dynamic service models). Transition to the admitted state involves the invocation of admission control in the BS and (soft) resource reservation, and transition to the active state involves actual resource assignment for the service flow. The service flow can directly transit from provisioned state to active state without going through admitted state. 4. Aserviceflowcanalsotransitioninthereversefromanactivetoanadmittedtoaprovisionedstate. 5. A dynamically created service flow may also be modified or deleted. As mentioned earlier, management information bases are collections of various network objects that are operated with the use of a Simple Network Management Protocol or SNMP 8,13. The exact structure of the objects included in the management information base will depend on the configu- ration of the particular SNMP. However, additional extensions can allow for the addition of new objects outside the initial structure. Both the initial management information base and its extensions can be related to specific functions within a network. Some MIBs may be related to the definition of the domain name system, while other extensions may be associated with network objects like the fiber distributed data interface. While the initial management information base is usually defined as part of the SNMP, the extensions are generally set up as part of the basic management information base. The Subscriber Station Management Primitives are a set of primitives to manage the status of mobile station. A management entity in the NCMS can change the status of mobile terminal. Those primitivesarealsousedtonotifytheNCMSofinformationoreventswhicharerelatedtothestatusof the mobile terminal. The NCMS is a layer-independent entity that may be viewed as a management entity or control entity. 3.1.6 Service Access Point A Service Access Point is defined as a reference point in a protocol stack where the services of a layer are available to its immediately neighboring layer. In other words, a SAP is a mapping between services of two neighboring layers. There are a number of SAPs in the IEEE 802.16 reference model (see Figure 3-7) that interface the adjacent protocol layers including PHY, MAC, and CS SAPs. The Management SAP may include primitives related to System configuration, Monitoring statistics, Notifications/Triggers, and Multi-mode interface management. The NCMS interacts with the MIB through the M-SAP. The Control SAP may include, but is not limited to, primitivesrelatedtohandovers(e.g.,notificationofhandoverrequestfromMS),idlemodemobility management (e.g., mobile station entering idle mode), subscriber and session management (e.g., mobile station requesting session set-up), radio resource management, AAA server signaling3.1 The IEEE 802.16m reference model 75 ix x (e.g., Extensible Authentication Protocol payloads), Media Independent Handover (MIH) services,andlocationdetectionandreportingcapability.Unlike3GPPLTE,theIEEE802.16mdoes not explicitly define logical, transport, and physical channels (although the functionalities exist in the air interface protocols). In that case, the mapping between logical to transport and transport to physical channels would determine the SAPs between the corresponding layers. 3.1.7 Media-Independent Handover Reference Model for IEEE 802.16 The IEEE 802.21-2008 standard provides link-layer intelligence and other related network informa- tiontoupperlayerstooptimizehandoversbetweenheterogeneousnetworks23.Thisincludesmedia types specified by 3GPP, 3GPP2, and both wired and wireless media in the IEEE 802 family of standards. In the IEEE 802.21-2008 standard, media refers to the method or mode of accessing a telecommunication system (e.g., cable, radio, satellite), as opposed to sensory aspects of commu- nication (e.g., audio, video). The standard addresses the support of handovers for both mobile and stationary users. For mobile users, handovers can occur when wireless link conditions change due to the users’ movement. For the stationary user, handovers become imminent when the surrounding networkenvironmentchanges,makingonenetworkmoreattractivethananother.Asanexample,when making anetwork transition duringaphone call, thehandover proceduresshould beexecuted insuch a way that any perceptible interruption to the conversation will be minimized. The standard supports cooperativeuseofinformationavailableatthemobilenodeandwithinthenetworkinfrastructure.The mobilenodeiswell-positionedtodetectavailablenetworks.Thenetworkinfrastructureiswell-suited to store overall network information, such as neighborhood cell lists, location of mobile nodes, and higher layer service availability. Both the mobile node and the network make decisions about connectivity. In general, both the mobile node and the network points of attachment (such as base stationsandaccesspoints)canbemulti-modal(i.e.,capableofsupportingmultipleradiostandardsand simultaneously supporting connections on more than one radio interface). Figure3-11showstheMediaIndependentHandoverFunction(MIHF),i.e.,afunctionthatrealizes MIH services, for IEEE 802.16 based systems. The M-SAP and C-SAP are common between the MIHF and Network Control and Management System. The M-SAP specifies the interface between the MIHF and the management plane and allows MIHF payload to be encapsulated in management messages (such as MOB_MIH-MSG defined in the IEEE 802.16-2009 standard 3). The primitives specified by M-SAP are used by a mobile node to transfer packets to a base station, both before and after it has completed the network entry procedures. The C-SAP specifies the interface between the MIHFandcontrol-plane.M-SAPandC-SAPalsotransportMIHmessagestopeerMIHFentities.The CS-SAP is used to transfer packets from higher layer protocol entities after appropriate connections havebeenestablishedwiththenetwork.TheMIH-SAPspecifiestheinterfaceoftheMIHFwithother higherlayerentitiessuchastransportlayer,handoverpolicyengine,andLayer3mobilityprotocols.In this model, C-SAP and M-SAP provide link services defined by MIH-LINK-SAP; C-SAP provides servicesbeforenetworkentry;whileCS-SAPprovidesservicesoverthedata-planeafternetworkentry. ix Extensible Authentication Protocol (EAP), as defined by IETF RFC 3748 and updated by IETF RFC 5247, is a universal authentication framework commonly used in wireless networks and point-to-point connections 24. x Media Independent Handover (MIH) is a standard developed by the IEEE 802.21 to enable handover and interoperability between heterogeneous network types including both 802 and non-802 networks 23.MIH-SAP M-SAPC-SAP 76 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure Layer 3 Mobility Protocols CS SAP Service Specific Convergence Sublayer (CS) CS Management/Configuration MAC SAP Media MAC Common Part Sublayer Independent (MAC CPS) Handover Function (MIHF) MAC Management/Configuration MIH event Security Sublayer service Management Information Base MIH command (MIB) service PHY SAP MIH information service Physical Layer (PHY) PHY Management/Configuration Data/Control Plane Management Plane FIGURE 3-11 MIH reference model for the IEEE 802.16 standard 23 3.2 THE IEEE 802.16M PROTOCOL STRUCTURE In this section, we further examine the functional elements of each protocol layer and their interac- tions. The 802.16m MAC common part sub-layer functions are classified into radio resource control and management functional group and medium access control functional group. The control-plane functions and data-plane functions are also separately classified. This would allow more organized, efficient, and structured method for specifying the MAC services in the IEEE 802.16m standard specification. As shown in Figure 3-12, the radio resource control and management functional group comprises several functional blocks including:  Radioresourcemanagementblockadjustsradionetworkparametersrelatedtothetrafficload,and also includes the functions of load control (load balancing), admission control, and interference control;Layer 3 Layer 2 Layer 1 3.2 The IEEE 802.16m protocol structure 77 Network Layer Management SAP and Control SAP CS-SAP System Location Relay Radio Resource configuration Convergence Sublayer Functions Management management management Mobility Idle Mode MBS Multi-Carrier Management Management Classification Service flow and Security Network-entry Connection Self Organization Header Management management Management suppression Radio Resource Control and Management (RRCM) MAC SAP Fragmentation/Packing Medium Access Control (MAC) ARQ Multi Radio Sleep Mode Scheduling and QoS Coexistence Management Resource Multiplexing MAC PDU formation PHYControl Control Link Adaptation Encryption Data Forwarding Interference Signaling Ranging (CQI, HARQ, power Management control) Control-Plane Data-Plane PHY Protocol (FEC Coding, Signal Mapping, Modulation, MIMO processing, etc.) Physical Layer FIGURE 3-12 The IEEE 802.16m general protocol stack 12  MobilitymanagementblockscansneighborBSsanddecideswhetherMSshouldperformhandover operation;  Network-entry management block controls initialization and access procedures and generates management messages during initialization and access procedures;  Location management block supports location based service (LBS), generates messages including the LBS information, and manages location update operation during idle mode;  Idlemodemanagementblockcontrolsidlemodeoperation,andgeneratesthepagingadvertisement message based on paging message from paging controller in the core network;  Securitymanagementblockperformskeymanagementforsecurecommunication.Usingmanaged key, traffic encryption/decryption and authentication are performed;  Systemconfigurationmanagementblockmanagessystemconfigurationparameters,andgenerates broadcast control messages such as superframe headers;78 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure  Multicast and broadcast service (MBS) block controls and generates management messages and data associated with MBS;  Service flow and connection management block allocates Station Identifier (STID) and Flow Identifiers (FIDs) during access/handover service flow creation procedures. The medium access control functional group, on the control plane, includes functional blocks which are related to physical layer and link controls such as:  PHY control block performs PHY signaling such as ranging, channel quality measurement/ feedback (CQI), and HARQ ACK or NACK signaling;  Control signaling block generates resource allocation messages such as advanced medium access protocol, as well as specific control signaling messages;  Sleepmodemanagementblockhandlessleepmodeoperationandgeneratesmanagementmessages related to sleep operation, and may communicate with the scheduler block in order to operate properly according to sleep period;  Quality-of-service block performs rate control based on QoS input parameters from connection management function for each connection;  Schedulingandresourcemultiplexingblockschedulesandmultiplexespacketsbasedonproperties of connections. The MAC functional group on the data-plane includes functional blocks such as:  Fragmentation/packing block performs fragmentation or packing of MAC Service Data Units (MSDU) based on input from the scheduling and resource multiplexing block;  Automatic Repeat Request block performs MAC ARQ function. For ARQ-enabled connections, a logical ARQ block is generated from fragmented or packed MSDUs of the same flow and sequentially numbered;  MAC protocol data unit formation block constructs MAC PDU (MPDU) such that BS/MS can transmit user traffic or management messages into PHY channels. The IEEE 802.16m protocol structure is similar to that of the IEEE 802.16, with some additional functional blocks in the control-plane for new features including the following:  Relay functions enable relay functionalities and packet routing in relay networks.  Self organization and self-optimization functions enable home BS or femto-cells and plug- xi and-play form of operation for indoor BS (i.e., femto-cell ).  Multi-carrier functions enable control and operation of a number of adjacent or non-adjacent RF carriers (i.e., virtual wideband operation) where the RF carriers can be assigned to unicast and/ or multicast and broadcast services. A single MAC instantiation will be used to control several physical layers. The mobile terminal is not required to support multi-carrier operation. However, if it does support multi-carrier operation, it may receive control and signaling, broadcast, and synchronization channels through a primary carrier and traffic assignments (or services) via the secondary carriers. xi Femto-cells are low-power wireless access points that operate in licensed spectrum to connect standard mobile devices to a mobile operator’s network using residential DSL or cable broadband connections 25,26.3.2 The IEEE 802.16m protocol structure 79 IEEE 802.16m BS Air Interface Multi-Radio Device IEEE Radio i Radio i Radio j Radio j 802.16m Access Point Device Device Access Point MS inter-radio interface FIGURE 3-13 A generic multi-radio coexistence model 12  Multi-radio coexistence functions in IEEE 802.16m enable the MS to generate MAC management messages in order to report information on its collocated radio activities, and enable the BS to generate MAC management messages to respond with the appropriate actions to support multi-radio coexistence operation. Furthermore, the multi-radio coexistence functional block at the BS communicates with the scheduler functional block to assist proper scheduling of the MS according to the reported collocated coexistence activities. The multi- radio coexistence function is independent of the sleep mode operation to enable optimal power efficiency with a high level of coexistence support. However, when sleep mode provides sufficient collocated coexistence support, the multi-radio coexistence function may not be used (see Figure 3-13).  Interference management functions are used to manage the inter-cell/sector interference effects. The procedures include MAC layer functions (e.g., interference measurement/assessment reports sent via MAC signaling and interference mitigation by scheduling and flexible frequency reuse), and PHY functions (e.g., transmit power control, interference randomization, interference cancellation, interference measurement, transmit beamforming/precoding). The inter-BS coordination functions coordinate the operation of multiple base stations by exchanging information, about interference statistics between the base stations via core-network signaling. 3.2.1 Data-Plane and Control-Plane Functions in Base Stations and Mobile Stations Figure 3-14 shows the user data processing path at the BS and MS. As shown in the figure, the user data traverses the path from network layer to physical layer and vice versa. In the transmitter side, a network layer packet is processed by the convergence sub-layer, the ARQ function (if enabled), the fragmentation/packing function, and the MAC PDU formation function, to form the MAC PDU to be sent to the physical layer for processing. In the receiver side, a physical layer SDU is processed by MAC PDU formation function, the fragmentation/packing function,80 CHAPTER 3 IEEE 802.16m Reference Model and Protocol Structure Network Layer Management SAP and Control SAP Radio Resource Control and Management (RRCM) CS SAP System Convergence Sublayer Relay Radio Resource Location Configuration Management Functions Management Management Service Flow Classification Idle Mode Mobility E-MBS Multi-Carrier Management Management Header Service flow and Suppression Network-entry Security Connection Self Organization Management Management Management MAC SAP Scheduling and Resource Multiplexing Fragmentation/Packing ARQ Multi Radio Sleep Mode QoS Coexistence Management PHYControl MAC PDU Formation Control Link Adaptation Data Forwarding Interference Signaling Ranging (CQI, HARQ, power Management control) Encryption HARQ/CQI Ranging Medium Access Control (MAC) Feedback PHY SAP PHY Protocol (FEC Coding, Signal Mapping, Modulation, MIMO processing, etc.) Physical Layer Control-Plane Data-Plane Control Primitives between MAC CPS Functions Control Messages/Signaling (Control Plane) Data Path (Data Plane) FIGURE 3-14 Signal flow graph in data- and control-planes 12 the ARQ function (if enabled), and the convergence sub-layer function, to form the network layer packets. The control primitives between the MAC CPS functions and between the MAC CPS and PHY that are related to the processing of user traffic data are also shown in Figure 3-14. The control-plane signaling and processing flow graph at the BS and the MS are shown in Figure 3-14. In the transmitter side, the flow of control primitives from control-plane functions to data-plane functions and processing of control-plane signals by data-plane functions in order to L1 L2 L3

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