IEEE /WIMAX- Overview. E.Borcoci

Transcription

1 IEEE /WIMAX- Overview E.Borcoci Contents 1 IEEE Wireless MAN overview Introduction IEEE 802 standards IEEE Summary WiMAX summary WiMAX Forum Other related Standards ETSI Broadband Radio Access Networks (BRAN) HIPERACCESS ETSI Broadband Radio Access Networks (BRAN) HIPERMAN Basic IEEE Scope Protocol Stack IEEE MAC (I) IEEE (10 66 GHz) PHY Characteristics IEEE a (2-11GHz) PHY Characteristics PHY Details GHz Downlink (DL) subframe Uplink Subframe (10 66 GHz) MAC Details Service Specific Convergence Sublayer (SSCS) Common Part Sublayer SS operation Network Entry Service flows and QoS support Service Flows Scheduling Request/Grant Scheme GPSS vs. GPC Architectural Issues Reference Architectures WiMAX Forum Reference Architectures References IEEE WIRELESS MAN OVERVIEW Acknowledgement : This text does not contain original ideas. It is fully based on materials given in the references. Editing and material organization only, belong to the author. The text is for academic tutorial purposes individual usage only. WirelessMAN.org IEEE /WiMAX Overview- oct E.Borcoci. Page 1 of 30

2 1.1 Introduction IEEE 802 standards Figure 1-1 IEEE 802 LAN/MAN Standards IEEE Summary Standard for Wireless Broadband Access (WBA) o set up like cellular systems o using base stations (BS) that service a radius of several miles/kilometers o BS do not necessarily have to reside on a tower o BS antenna will be located on a rooftop of a tall building or other elevated structure such as a grain silo or water tower o Subscriber Stations (SS) connect radially to BSes o CPE unit is similar to a satellite TV setup, is all it takes to connect the base station to a customer. Goals: Provide high-speed Internet access to home and business subscribers, without wires. Base stations (BS) can handle thousands of subscriber stations (SS) Access control prevents collisions. Supports: Legacy voice systems, VoIP, TCP/IP, Appl. with different QoS requirements. solves The Last Mile (or the First Mile ) problem o Fast local connection to network o Data, voice, video, multimedia flows o Business, Residential access o Attractive for operators standards:.1 (10-66 GHz licensed spectrum, line-of-sight (LOS), up to 134Mbit/s, fixed pointto-multipoint (PMP)), 2001, Officially called the WirelessMAN ).2 (minimizing interference between coexisting WMANs.) IEEE /WiMAX Overview- oct E.Borcoci. Page 2 of 30

3 a (2-11 Ghz ( licensed/unlicensed), Mesh, non-line-of-sigth (NLOS), <70MBps, distances up to 31 miles to be used by low latency applications such as voice and video), 2003 b (5-6 Ghz) c (detailed system profiles) d (2004) basic current fixed mode- standard e (Mobile Wireless MAN), 2005 a: (compared with :11-66GHz) reach many more customers less expensively, but with lower data rates. Such services are oriented towards individual homes or small to medium-sized enterprises. WiMax (Worldwide Interoperability for Microwave Access) is a wireless broadband technology: point to point (PP) and point to multi-point (PMP) broadband wireless access. WiMax is basically a new shorthand term for IEEE Standard, which was designed to support the European standards and interoperability Note: not all equipments are certified WiMAX Forum! The IEEE initial wireless standard: max 30 miles, max 75 Mbps The /WiMax initial standard has been extended : This extension : NLOS in bands like 2-11 GHz. - licensed /unlicensed - increase max distance from 31 to 50 miles and supports PMP (point to multipoint) and mesh technologies. Basic std. d - June 2004; three working groups were formed to evaluate and rate the standards. Fixed wireless is the base concept for the metropolitan area networking (MAN), given in the standard. In fixed wireless, a backbone of base stations is connected to a public network. Basic Components: Base stations (BS) use MAC to allocate uplink (UL) and downlink DL bandwidth to subscribers as per their individual needs - real time (rt) and non-real-time (nrt) classes of services) many fixed Subscriber Stations (e.g. WiFi hot spots or fire walled enterprise networks) o SS single user o SS multiple users has behind- LANs, WLANs, etc. o mobility is added in SS might also be mounted : on roof-tops of the users; indoor units The MAC layer is a common I/F that makes the networks interoperable Typical infrastructure: hotspots, hosted by MANs - They serve as wireless local area networks (LANs) APs and would serve the end users directly too. Definitions: IEEE /WiMAX Overview- oct E.Borcoci. Page 3 of 30

4 BS Base Station ;SS Subscriber Station ; Downlink (DL) BS to SS ; Uplink (UL) SS to BS SS SS BS Core SS BS RP SS Figure 1-2 IEEE Point to multipoint topology RP - Repeater SS1 BS SS1 SS SS SS SS SS SS Figure 1-3 IEEE a Mesh Network Topology WiMAX summary WiMAX = Worldwide Interoperability of Microwave Access WiMAX is: Acronym for Worldwide Interoperability for Microwave Access. Based on Wireless MAN technology. IEEE WMAN standard WiMAX : operate similar to WiFi; but at higher speeds; over greater distances; and for a greater number of users. A wireless technology optimized for the delivery of IP centric services over a wide area. IEEE /WiMAX Overview- oct E.Borcoci. Page 4 of 30

5 A scaleable wireless platform for constructing alternative and complementary broadband networks. A certification that denotes interoperability of equipment built to the IEEE or compatible standard. The IEEE Working Group develops standards that address two types of usage models: o A fixed usage model (IEEE -2004). o A portable usage model (IEEE e). WiMax is seen as a standardized wireless version of Ethernet intended primarily as an alternative to wire technologies (Cable Modems, xdsl and T1/E1 links ) to provide WBA to customer premises. WiMAX has the ability to provide service even in areas that are difficult for wired infrastructure to reach and the ability to overcome the physical limitations of traditional wired infrastructure. WiMAX compliant systems will provide fixed wireless alternative to conventional DSL and Cable Internet. WiMax changes the last mile problem for broadband in the same way as WiFi has changed the last one hundred feet of networking. WiMAX system parts ( same as in ): Base Station (BS) : - indoor/outdoor electronics and a WiMAX tower. Subscriber Station - SS and antenna could be a stand-alone box or a PCMCIA card that sits in laptop or computer- radial access to BS Several BSes can be inter-connected by use of high-speed backhaul microwave links. This would allow for SS roaming between BSes Important Wireless MAN IEEE (WiMAX) Specifications o o o o o Range theoretically- 30-mile (50-km) radius from base station. Typically, a base station can cover up to 10 km radius Speed - Up to 70 megabits per second Non-Line-of-sight (LoS/NLoS) between user and base station Frequency bands - 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed bands) Defines both the MAC and PHY layers and allows multiple PHY-layer specifications WiMAX Forum WiMAX Forum industry trade organization - leading communications component producers and equipment vendor companies (founded April 2001): in anticipation of the publication of the original GHz IEEE specifications. WiMAX is to as the Wi-Fi Alliance is to purpose - to actively promote and certify compatibility and interoperability of broadband wireless access equipment that conforms to the IEEE and ETSI HIPERMAN standards lead to a wider penetration of BB access in areas that for time, cost and reachability reasons cannot be served with alternative solutions. contributes to the IEEE project by providing further extensions to the standard, e.g. of IEEE e. IEEE /WiMAX Overview- oct E.Borcoci. Page 5 of 30

6 1.1.5 Other related Standards ETSI Broadband Radio Access Networks (BRAN) HIPERACCESS ETSI Broadband Radio Access Networks (BRAN) HIPERMAN Basic IEEE Scope Specifies the air interface including the MAC and PHY layers of fixed PMP broadband wireless access systems providing multiple services. The MAC supports multiple PHY specifications optimized for the frequency bands of the application. The initial standard includes a particular PHY layer spec. broadly applicable to systems operating between GHz Protocol Stack Figure 1-4 Basic IEEE protocol stack IEEE MAC (I) Designed for PMP broadband wireless access applications - very high bit rates, UL and DL Access and bandwidth allocation algorithms must accommodate hundreds of terminals per channel; terminals that may be shared by multiple end users MAC Characteristics IEEE /WiMAX Overview- oct E.Borcoci. Page 6 of 30

7 Connection orienteded: Connection ID (CID), Service Flows(FS) Uplink and down link radio channels o FDD mode o TDD mode BS arbitration and access control for many SSes Channel access: UL-MAP: Data structure defining uplink channel access Defines uplink data burst profiles DL-MAP: Data structure - defines downlink data burst profiles UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD). Services offered to higher layers Legacy time-division multiplex (TDM) voice and data, Internet Protocol (IP) connectivity Support any application flow: data, VoIP,VoD, video streaming, etc. MAC features: accommodate : continuous and bursty traffic, QoS classes assured provides a wide range of service types analogous to (ATM) service categories as well as newer categories such as guaranteed frame rate (GFR). support a variety of backhaul requirements, including ATM and packet-based protocols Convergence sublayers - map the transport-layer-specific traffic to a MAC in a flexible way to efficiently carry any traffic type MAC Features for increasing efficiency: payload header suppression, packing, and fragmentation Transport efficiency assured at the MAC/PHY IF: e.g. modulation and coding schemes are specified in a burst profile that may be adjusted adaptively for each burst to each SS MAC can make use of bandwidth-efficient burst profiles under favorable link conditions but shift (if necessary) to a more reliable one, although it may be less efficient Resources - request-grant mechanisms : scalable, efficient, and self-correcting - is efficient when presented with multiple connections per terminal, multiple QoS levels per terminal large number of statistically multiplexed users wide variety of request mechanisms: balancing the stability of contentionless access with the efficiency of contention- oriented access. While extensive bandwidth allocation and QoS mechanisms are provided, the details of scheduling and reservation management are left unstandardized and provide an important mechanism for vendors to differentiate their equipment. MAC privacy sublayer : authentication of network access and connection establishment to avoid theft of service, provides key exchange and encryption for data privacy. a MAC enhancements: automatic repeat request (ARQ) support for PMP but also mesh network architectures. IEEE /WiMAX Overview- oct E.Borcoci. Page 7 of 30

8 IEEE (10 66 GHz) PHY Characteristics Line of Sight (in band GHz) o Negligible multi-path Large channels Broadband Channels o Wide channels (20, 25, or 28 MHz) o High capacity DL and Uplink Multiple Access o TDM/TDMA o High rate burst modems o Adaptive Burst Profiles on UL and DL Multiple duplex schemes o Time-Division Duplex (TDD) o Frequency-Division Duplex (FDD) [including Burst FDD] o Support for Half-Duplex Terminals PHY details PMP, LOS, single-carrier (SC) modulation selected The air interface is designated WirelessMAN-SC. PMP the BS transmits in TDM mode to SSs UL Access is TDMA Operating modes: TDD - timedivision duplexing UL and DL share a frequency channel but do not transmit simultaneously FDD - frequency-division duplexing (FDD) UL and DL operate on separate channels, sometimes simultaneously Support for half-duplex FDD SSs is possible (less expensive) SS does not send and receive simultaneously Both TDD and FDD alternatives support adaptive burst profiles in which modulation and coding options may be dynamically assigned on a burst-by-burst basis. The burst design allows both TDD and FDD to be handled in a similar fashion. Adaptive Data Burst Profiles Transmission parameters (e.g. modulation and FEC settings) can be modified on a frame-byframe basis for each SS. Profiles are identified by Interval Usage Code (DIUC and UIUC) IEEE a (2-11GHz) PHY Characteristics Non-line-of-sight (NLOS) operation. -residential applications are expected, lower rooftops may multipath propagation may be expected The three 2 11 GHz air I/F specifications in a are: WirelessMAN-SC2: This uses a single-carrier modulation format. WirelessMAN-OFDM: orthogonal FDM with a 256- point transform Access is by TDMA. This air I/F is mandatory for license-exempt bands. WirelessMAN-OFDMA: a 2048-point transform. Multiple access is provided by addressing a subset of the multiple carriers to individual receivers. IEEE /WiMAX Overview- oct E.Borcoci. Page 8 of 30

9 Propagation requirements advanced antenna systems are supported. 1.2 PHY Details GHz SC modulation with adaptive burst profiling in which transmission parameters, including the modulation and coding schemes may be adjusted individually to each SS on a frame-by-frame basis. Both TDD and burst FDD variants are defined Channel bandwidths: 20 or 25 MHz (typical U.S. allocation) or 28 MHz (typical European ) Nyquist square-root raised-cosine pulse shaping with a rolloff factor of Randomization is performed - for spectral shaping - ensure bit transitions for clock recovery. Protection: FEC: Reed-Solomon GF(256), with variable block size and error correction capabilities This is paired with an inner block convolutional code to robustly transmit critical data, (e.g. frame control and initial accesses) The FEC options are paired with QPSK: 16-QAM, and 64-QAM to form burst profiles of varying robustness and efficiency. If the last FEC block is not filled, that block may be shortened Shortening in both UL and DL is controlled by the BS and is implicitly communicated in the uplink map (ULMAP) and DL map (DL-MAP). Frames duration: 0.5, 1, or 2 ms. The frame : divided in PHY slots (PS) for the purpose of bandwidth allocation and identification of PHY transitions. One PHY slot is defined to be 4 QAM symbols. TDD -PHY: UL subframe follows the DL subframe on the same carrier frequency. FDD -PHY: UL and DL subframes are coincident in time but are carried on separate frequencies. IEEE /WiMAX Overview- oct E.Borcoci. Page 9 of 30

10 Downlink (DL) subframe Table 2 Bit Rates for different channel bandwidth Figure 1-5 TDD Frame (10-66 GHz)- IEEE Std PS = Physical Slots Number of physical slots = n =Frame duration/(t symbol *4) BS Tx/Rx and Rx/Tx gaps The Tx/Rx Transition Gap (TTG) is a gap between the downlink burst and the subsequent uplink burst. This gap allows time for the BS to switch from transmit to receive mode and SSs to switch from receive to transmit mode. The Rx/Tx Transition Gap is a gap between the uplink burst and the subsequent downlink burst. This gap allows time for the BS to switch from receive to transmit mode and SSs to switch from transmit to receive mode. IEEE /WiMAX Overview- oct E.Borcoci. Page 10 of 30

11 DIUC - Downlink Interval Usage Code Figure 1-6 TDD Downlink subframe IEEE Std TDD DL Subframe structure: Frame Start Preamble: synchronization and equalization. Frame control section: DL and UL maps stating the no. of the PSs at which bursts begin. TDM portion : - data, organized into bursts with different burst profiles and different level of transmission robustness. - The bursts are transmitted in order of decreasing robustness e.g: with the use of a single FEC type with fixed parameters, data begins with QPSK modulation, followed by 16-QAM, followed by 64-QAM. - Each SS receives and decodes the control information of the downlink and looks for MAC headers indicating data for that SS in the remainder of the DL subframe. FDD Downlink subframe TDM portion : data transmitted to one or more of the following: full-duplex SSs half-duplex SSs scheduled to transmit later in the frame than they receive half-duplex SSs not scheduled to transmit in this frame. TDMA portion - used to transmit data to any half-duplex SSs scheduled to transmit earlier in the frame than they receive. - This allows an individual SS to decode a specific portion of the downlink without the need to decode the entire downlink subframe - each burst begins with the DL TDMA Burst Preamble for phase resynchronization. - Bursts in the TDMA portion need not be ordered by burst profile robustness - The FDD frame control section includes a map of both the TDM and TDMA bursts. IEEE /WiMAX Overview- oct E.Borcoci. Page 11 of 30

12 Figure 1-7 The DL subframe structure. Dynamics of bandwidth demand mixture and duration of burst profiles presence or absence of a TDMA portion both vary dynamically from frame to frame The TDD downlink subframe, which inherently contains data transmitted to SSs that transmit later in the frame than they receive, is identical in structure to the FDD downlink subframe for a frame in which no halfduplex SSs are scheduled to transmit before they receive. Recipient SS is implicitly indicated in the MAC headers (not in the DL-MAP) SSs listen to all portions of the DL subframe they are capable of receiving For FD-SSs, this means receiving all burst profiles of equal or greater robustness than they have negotiated with the BS. Figure 1-8 Burst FDD Framing Extracted from IEEE Std PHY Downlink modulation IEEE /WiMAX Overview- oct E.Borcoci. Page 12 of 30

13 multilevel modulation scheme. The constellation can be selected per SS based on the quality of the RF channel. If link conditions permit, then a more complex modulation scheme (max. airlink throughput while still allowing reliable data transfer). If the airlink degrades over time, (e.g. environmental factors), one can revert to the less complex constellations to allow more reliable data transfer. BS shall support QPSK and 16-QAM modulation and, optionally, 64-QAM. This would create the possibility of a cross layer optimization PHY-MAC if the scheduling algoritrhm takes into account the variation of the channel capacity in time. Note that this cross layer- optimisatio will not destroy the architectural stack because it is internal to BS in the control plane Uplink Subframe (10 66 GHz) The SSs transmit in their assigned allocation using the burst profile specified by the Uplink Interval Usage Code (UIUC) in the UL-MAP entry granting them bandwidth. The UL subframe may also contain contention-based allocations for initial system access and broadcast or multicast bandwidth requests. Figure 1-9 The uplink subframe structure Three classes of bursts may be transmitted by the SS during the UL subframe: Uplink Periods Initial Maintenance opportunities Ranging To determine network delay and to request power or profile changes. Collisions may occur in this interval Request opportunities SSs request bandwith in response to polling from BS. Collisions may occur in this interval as well. Data grants period (Unlike the DL, the UL-MAP grants bandwidth to specific SSs) SSs transmit data bursts in the intervals granted by the BS. Transition gaps between data intervals for synchronization purposes. Any of these burst classes may be present in any given frame IEEE /WiMAX Overview- oct E.Borcoci. Page 13 of 30

14 - in any order and any quantity (limited by the number of available PSs) within the frame - at the discretion of the BS uplink scheduler as indicated by the UL_MAP The bandwidth allocated for Initial Maintenance and Request contention opportunies may be grouped together and is always used with the uplink burst profiles specified by (UIUC=2) (UIUC=1) The remaining transmission slots are grouped by SS During its scheduled bandwidth, an SS transmits with the burst profile specified by the BS. The access opportunities for initial system access are sized to allow extra guard time for SSs that have not resolved the transmit time advance necessary to offset the round-trip delay to the BS. Transmission Convergence (TC) sublayer between the PHY and MAC - transforms variable length MAC PDUs into the fixed length FEC blocks (plus possibly a shortened block at the end) of each burst - TC layer has a PDU sized to fit in the FEC block currently being filled. It starts with a pointer indicating where the next MAC PDU header starts within the FEC block. Figure 1-10 TC PDU format. Notes: The TC PDU format allows resynchronization to the next MAC PDU in the event that the previous FEC block had irrecoverable errors. Without the TC layer, a receiving SS or BS would potentially lose the entire remainder of a burst when an irrecoverable bit error occurred. IEEE -versus IEEE a IEEE /WiMAX Overview- oct E.Borcoci. Page 14 of 30

15 Table 1 versus a 1.3 MAC Details Operation mode: MAC connections CO style Service Specific Convergence Sublayer (SSCS) ATM CS is defined for ATM services Packet CS is defined for mapping packet services such as IPv4, IPv6, Ethernet, and virtual local area network (VLAN) SSCS primary task classify service data units (SDUs) to the proper MAC connection preserve or enable QoS and enable bandwidth allocation The mapping takes various forms depending on the type of service In addition SSCS may have: more sophisticated functions such as - payload header suppression and reconstruction to enhance airlink efficiency Common Part Sublayer On the DL, data to SSs are multiplexed TDM The uplink is shared between SSs in TDMA fashion. MAC is connection-oriented CO all services, including inherently connectionless services, are mapped to a connection. This provides a mechanism for requesting bandwidth, associating QoS and traffic parameters, transporting and routing data to the appropriate convergence sublayer, and all other actions associated with the contractual terms of the service. IEEE /WiMAX Overview- oct E.Borcoci. Page 15 of 30

16 Connections : 16-bit connection identifiers (CIDs) may require continuously granted bandwidth bandwidth on demand. SS : has a std. 48-bit MAC address, this serves mainly as an equipment id., since the primary addresses used during operation are the CIDs. Management connections Upon entering the network, the SS is assigned three management connections in each direction reflecting the three different QoS requirements used by different management levels. 1. Basic connection: transfer of short, time-critical MAC and radio link control (RLC) messages 2. Primary mng. conn : transfer longer, more delay-tolerant messages (e.g. used for authentication and connection setup. 3. Secondary mng. conn : transfer of std-based mng. messages such as Dynamic Host Configuration Protocol (DHCP) Trivial File Transfer Protocol (TFTP) Simple Network Management Protocol (SNMP) Data connections SSs are allocated transport connections for the contracted services. Transport connections are unidirectional to facilitate different UL and DL QoS and traffic parameters; they are typically assigned to services in pairs. The MAC reserves additional connections for other purposes - contention-based initial access - broadcast transmissions in the downlink as well as for signaling broadcast contention-based polling of SS bandwidth needs. Additional connections are reserved for multicast, rather than broadcast, contention-based polling. SSs may be instructed to join multicast polling groups associated with these multicast polling connections. MAC PDU Formats fixed-length MAC header a variable-length payload optional (CRC). IEEE /WiMAX Overview- oct E.Borcoci. Page 16 of 30

17 Figure 1-11 Format of the generic header for MAC PDU. Two header formats, distinguished by the HT field, are: generic header (Figure 1-12) bandwidth request header. Bandwidth request MAC PDUs have no payload Other MAC PDUs either contains MAC management messages or convergence sublayer data. Three types of MAC sub-header may be present. - grant mng. subheader is used by an SS to convey bandwidth mng. needs to its BS - fragmentation subheader contains information that indicates the presence and orientation in the payload of any fragments of SDUs - packing subheader indicate the packing of multiple SDUs into a single PDU The grant mng. and fragmentation sub-headers may be inserted in MAC PDUs immediately following the generic header if so indicated by the Type field. The packing sub-header may be inserted before each MAC SDU if so indicated by the Type field. 1.4 SS operation Network Entry First action: an SS needs to successfully complete the network entry process with the desired BS. The network entry process is divided into main phases: 1. DL channel synchronization 2. initial ranging 3. capabilities negotiation 4. authentication message exchange 5. registration 6. IP connectivity stages. The network entry FSM moves to reset if it fails to succeed from a state. Upon completion of the network entry process, the SS creates one or more service flows to send data to the BS. IEEE /WiMAX Overview- oct E.Borcoci. Page 17 of 30

18 Downlink Channel Synchronization o SS scans for a channel in the defined frequency list o Normally an SS is configured to use a specific BS with a given set of operational parameters, when operating in a licensed band o If the SS finds a DL channel and is able to synchronize at the PHY level (it detects the periodic frame preamble), then the MAC layer looks for DCD and UCD to get information on modulation and other DL and UL parameters. Scan DL channel synchronised Not synchronised Get parameters Contention allocation for initial ranging W ait for ULM AP to get contention slot Initial ranging ok Exchange capabilities fail ok Authentication fail ok Registration fail ok IP connectivity ok Create connections Periodic ranging fail fail Figure 1-12 Network entry process Initial Ranging o When an SS has synchronized with the DL channel and received the DL and UL MAP for a frame it begins the initial ranging process by sending a ranging request MAC message on the initial ranging interval using the minimum transmission power If it does not receive a response, the SS sends the ranging request again in a subsequent frame, using higher transmission power Eventually the SS receives a ranging response The response either indicates power and timing corrections that the SS must make or indicates success. If the response indicates corrections, the SS makes these corrections and sends another ranging request If the response indicates success, the SS is ready to send data on the UL. Capabilities Negotiation o SS sends a capability request message to the BS describing its capabilities in terms of the supported modulation levels, coding schemes and rates, and duplexing methods o BS accepts or denies the SS, based on its capabilities. Authentication IEEE /WiMAX Overview- oct E.Borcoci. Page 18 of 30

19 o o o o After capability negotiation, the BS authenticates the SS and provides key material to enable the ciphering of data The SS sends the X.509 certificate of the SS manufacturer and a description of the supported cryptographic algorithms to its BS The BS validates the identity of the SS, determines the cipher algorithm and protocol that should be used, and sends an authentication response to the SS The response contains the key material to be used by the SS. The SS is required to periodically perform the authentication and key exchange procedures to refresh its key material. Registration o After successful completion of authentication the SS registers with the network o The SS sends a registration request message to the BS o BS sends a registration response to the SS o The registration exchange includes IP version support, SS managed or non-managed support, ARQ parameters support, classification option support, CRC support, and flow control. IP Connectivity o The SS then starts DHCP (IETF RFC 2131) to get the IP address and other parameters to establish IP connectivity o The BS and SS maintain the current date and time using the time of the day protocol (IETF RFC868) o The SS then downloads operational parameters using TFTP (IETF RFC 1350). Transport Connection Creation After completion of registration and the transfer of operational parameters, transport connections are created For pre-provisioned service flows, the connection creation process is initiated by the BS The BS sends a dynamic service flow addition request message to the SS and the SS sends a response to confirm the creation of the connection. Connection creation for non-preprovisioned service flows is initiated by the SS by sending a dynamic service flow addition request message to the BS The BS responds with a confirmation. 1.5 Service flows and QoS support Service Flows The MAC provides QoS differentiation for different types of applications that might operate over networks. The standard defines the following types of uplink scheduling services: Unsolicited Grant Services (UGS): UGS supports Constant Bit Rate (CBR) services, such as T1/E1 emulation, and Voice Over IP (VoIP) without silence suppression. Real-Time Polling Services (rtps): rtps supports real-time services that generate variable size data packets on a periodic basis, such as MPEG video or VoIP with silence suppression. Non-Real-Time Polling Services (nrtps): nrtps supports non-real-time services that require variable size data grant burst types on a regular basis. Best Effort (BE) Services: BE services are typically provided by the Internet today for Web surfing. 4 basic types of Scheduling Service: IEEE /WiMAX Overview- oct E.Borcoci. Page 19 of 30

20 Unsolicited Grant Service (UGS) o Real-time, periodic fixed size packets (e.g. T1 or VoIP) o Restrictions on bw requests (Poll-Me bit) o Slip Indicator (SI) Real-Time Polling Service (rtps) o Real-time, periodic variable sizes packets (e.g MPEG) o BS issues periodic unicast polls. o Cannot use contention requests, but piggybacking is ok. Non-Real-Time Polling Service (nrtps) o Variable sized packets with loose delay requirements (e.g. FTP) o BS issues unicast polls regularly (not necessarily periodic). o Can also use contention requests and piggybacking. Best Effort Service o Never polled individually o Can use contention requests and piggybacking Recent Extension of Classesd of Services WiMAX standard plans five types of different Class of Services (CoS). Unsolicited Grant Service (UGS) real-time services like T1 and E1 lines, and for VOIP services with fixed packet sizes. Real Time and Variable Rate (rtps) - is used for real-time services such as streaming video - offers a variable bit rate, but with a guaranteed minimum rate and guaranteed delay. - popular for fixed wireless operators (or WISPs) to guarantee E1/T1-type data rates with wireline-equivalent SLAs, but to allow customers to burst higher if and when there is extra capacity on the network.. Enhanced Real-Time Variable Rate (ertps) - is specified in e - and will be used for VOIP services with variable packet sizes as opposed to fixed packet sizes typically, whith silence suppression is used. This will include applications such as Skype. Non-Real-Time Variable Rate (nrtps) Best-Effort (BE) - is for services where a guaranteed bit rate is required - no delay guaranteed (file transfer, http,..) - the old standby for and browsing, etc., - similar to a DSL line at home today. IEEE /WiMAX Overview- oct E.Borcoci. Page 20 of 30

21 CoS Name Description UGS Unsolicited Grant Service Used for VoIP with fixed packet size CoS rtps Real-time Polling Service Real-time, variable bitrate, guaranteed minimum bandwidth, guaranteed delay ertps Enhanced real-time Polling Service Used for VoIP with variable packet size, silence suppression nrtps Non real-time Polling Service Used for FTP, guaranteed bit rate, not guaranteed delay BE Best Effort Used for web access The WiMAX Forum Applications Working Group (AWG) - five initial application classes. Initial WiMax Forum Certified systems are capable of supporting these five classes simultaneously. Figure 1-13 WiMAX application classes Metric missing : mobility, specifically the handover between sectors and cells. This is likely to be added in the forthcoming wave of mobile WiMax profiles due to start later in The application classes map to the five QoS classes specified in the standards, as shown in the next table. Class Unsolicited Grant Service Real-Time Polling Service Description VOIP, E1; fixed-size packets on periodic basis Minimun rate Maximum rate x x x Latency Jitter Priority Streaming audio/video x x x x IEEE /WiMAX Overview- oct E.Borcoci. Page 21 of 30

22 Enhanced Real- Time Polling Service Non-Real-Time Polling Service Best-Effort VOIP with activity detection x x x x x FTP x x x Data transfer, Web browsing, etc. x = QOS specified. Source: Light Reading, 2006 x x Each SS to BS connection is assigned a service class as part of the creation of the connection. When packets are classified in the CS, the connection into which they are placed is chosen based on the type of QoS guarantees that are required by the application. Figure1-14 depicts the QoS mechanism in supporting multimedia services, including TDM voice, VoIP, video streaming, TFTP, HTTP, and . Figure 1-14 MAC layers and interactions IEEE /WiMAX Overview- oct E.Borcoci. Page 22 of 30

23 There are two types of polling mechanisms: Unicast: When an SS is polled individually, it is allocated bandwidth to send bandwidth request messages. Contention-based: Contention-based bandwidth request is used when insufficient bandwidth is available to individually poll many inactive SS s. The allocation is multicast or broadcast to a group of SS s that have to contend for the opportunity to send bandwidth requests. Mapping from MAC SDU fields (e.g destination IP address or TOS field) to CID and SFID Scheduling Downlink scheduling module Simple, all queues in BS Uplink scheduling module Queues are distributed among SSs. Queue states and QoS requirements are obtained through BW requests. Algorithms are not defined in standard GPSS Grant Per Subscriber Station Uplink Transmissions Invited transmissions Transmissions in contention slots Bandwidth requests Contention resolved using truncated exponential backoff Transmissions in initial ranging slots Ranging Requests (RNG-REQ) Contention resolved using truncated exponential backoff Bursts defined by UIUCs Transmissions allocated by the UL-MAP message All transmissions have synchronization preamble Ideally, all data from a single SS is concatenated into a single PHY burst Uplink Channel Descriptor Defines uplink burst profiles IEEE /WiMAX Overview- oct E.Borcoci. Page 23 of 30

24 Sent regularly All Uplink Burst profiles are acquired Burst profiles can be changed on the fly Establishes association between UIUC and actual PHY parameters Uplink MAP Message - defines usage of the uplink Contains the "grants" Grants are addressed to the SS Time given in mini-slots unit of uplink bandwidth allocation 2 m physical slots in GHz PHY, physical slot is 4 symbols PHY, Time expressed as arrival time at BS Uplink Services - UGS No explicit bandwidth requests issued by SS Prohibited from using any contention requests No unicast request opportunity provided May include a Grant Management (GM) sub-header containing Slip indicator: indicates that there is an backlog in the buffer due to clock skew or loss of maps Poll-me bit: indicates that the terminal needs to be polled (allows for not polling terminals with UGS- only services). Uplink Services - rtps Intended for rt-vbr-like service flows such as - MPEG video Prohibited from using any contention requests Terminals polled frequently enough to meet the delay requirements of the SFs BW request messages (a special MAC PDU header) May use Grant Management sub-header new request can be piggybacked with each transmitted PDU Uplink Service - nrtps Intended for non-real-time service flows with better than best effort service e.g. bandwidth-intensive file transfer Works like rt-polling except that polls are issued less frequently Allowed to use contention requests May use Grant Management sub-header new request can be piggybacked with each transmitted PDU Uplink Service - BE Generic data e.g. HTTP, SMTP, etc. No QoS guarantees Allowed to use contention requests May use Grant Management sub-header new request can be piggybacked with each transmitted PDU Request/Grant Scheme Self Correcting No acknowledgement All errors are handled in the same way, i.e., periodical aggregate requests Connection Bandwidth Requests are always per Connection Grants are either per Connection (GPC) or per Subscriber Station (GPSS) IEEE /WiMAX Overview- oct E.Borcoci. Page 24 of 30

25 Grants (given as durations) are carried in the UL-MAP messages SS needs to convert the time to amount of data using information about the UIUC GPSS vs. GPC Bandwidth Grant per Subscriber Station (GPSS) - BS grants bandwidth to the SS - SS may re-distribute bandwidth among its connections, maintaining QoS and SLAs - Suitable for many connections per terminal; off-loading base station s work - Allows more sophisticated reaction to QoS needs - Low overhead but requires intelligent subscriber station - Mandatory for P GHz PHY Bandwidth Grant per Connection (GPC) BS grants bandwidth to a connection Mostly suitable for few users per SS Higher overhead, but allows simpler SS 1.6 Architectural Issues Reference Architectures The Figure 1, [ ], describes a network reference model along with the interfaces that are within the scope of specification g. Multiple SS or MS maybe attached to a BS. The SS communicate to the BS over the U interface using a Primary Management Connection or a Secondary Management Connection. MS typically only utilize the Primary Management Connection over the U interface for management and related control functions. Figure 1-15 (IEEE g-05/008r2, December 2005) IEEE /WiMAX Overview- oct E.Borcoci. Page 25 of 30

26 Figure 1-16 (IEEE g-05/008r2, December 2005) Figure 1-17 Relation IEEE vs. WiMAX NWG, [] IEEE-2004 & e : define only data and control plane f & g (NETMAN): Management plane functions IEEE /WiMAX Overview- oct E.Borcoci. Page 26 of 30

27 IEEE P does not deal with functions usually provided by the RAN WiMAX NWG objective: standardization of the missing parts of a portable/mobile WiMAX access network Purpose of Management Plane: provide conformant equipment with procedures and services to enable interoperable and efficient management of network resources, mobility, and spectrum, and to standardize management plane behavior in fixed and mobile devices. Figure 1-18 (IEEE g-05/008r2, December 2005) The Figure 3 show the different functional entities that make up the Network Control and Management System. These entities may be centrally located or distributed across the network. The exact functionality of these entities and their services is outside the scope but shown here for illustration purposes and to allow the description of the management and control procedures WiMAX Forum Reference Architectures WiMAX Forum Network Reference Model The WiMAX Forum Network Reference Model (NRM) is a logical representation of the network architecture. The NRM identifies functional entities and normative reference points (RP) over which interoperability is achieved between functional entities. Figures 4, 5, 6 show the NRM, consisting of the following logical entities: MS, ASN, and CSN. The figure depicts the RPs. Each entity, MS, ASN and CSN represent a grouping of functional entities. Each of these functions may be realized in a single physical device or may be distributed over multiple physical devices. The grouping and distribution of functions into physical devices within a functional entity (such as ASN) is a manufacturer implementation choice. The NRM objective is to allow multiple implementation options for a given functional entity, and yet achieve interoperability (among different realizations of entities) based on the definition of communication protocols and data plane treatment between functional entities, to achieve an overall E2E function (e.g. security or mobility management) IEEE /WiMAX Overview- oct E.Borcoci. Page 27 of 30

28 The functional entities on either side of RP represent a collection of control and bearer (data) plane end-points. Interoperability will be verified based only on protocols exposed across an RP, which would depend on the E2E function or capability realized (based on the usage scenarios supported by the overall network). Notations BS Base Station MS Mobile Station GW - Gateway ASN Access Service Network CSN Connectivity Service Network NAP Network Access Provider ( may own and administer one or more ASNs) NSP Network Service Provider H-NSP Home Network Service Provider V-NSP Visited Network Service Provider The NAP and NSP are the business entities which own and administer the ASN and CSN respectively. Private IP Service tunelling Roaming FA AAA HA, AAA,.. Wireless Traffic Control Missing in fixed scenarios Here an IP backbone may exist Figure 1-19 WiMAX architecture Network Reference Model including mobility [] IEEE /WiMAX Overview- oct E.Borcoci. Page 28 of 30

29 1.7 References [1] Carl Eklund, Roger B. Marks, Kenneth L. Stanwood and Stanley Wang, Ensemble Communications Inc. IEEE Standard : A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access, IEEE Communications Magazine, June 2002, pp [2] Roger B. Marks, Carl Eklund, Ken Stanwood, Stanley Wang, The WirelessMAN MAC: It s Done, but What Is It?, IEEE -01/58r1, [3] IEEE Std Standard, The Institute of Electrical and Electronics Engineers, Inc. 3 Park Avenue, New York, NY , USA, 8 April 2002 [4] A.Ganz, Z.Ganz, and K. Wongthavarawat, Multimedia Wireless Networks, Prentice Hall, List of Acronyms 3GPP: The 3rd Generation Partnership Project. ADSL: Asynchronous DSL AP: Access Point ARQ: Automatic Repeat Request AS : Autonomous System ApS: Application Server ATM: Asynchronous Transfer Mode BRAS: Broadband Remote Access Server BS: Base Station BWA: Broadband Wireless Access. CDMA: Code Division Multiple Access CES: Circuit Emulation Service (in ATM) Consumers: Private users, subscribers CPE: Customer Premises Equipment DCD Downlink Channel Descriptor DHCP: Dynamic HostConfiguration Protocol DSL: Digital Subscriber Line DSLAM: DSL Access Multiplexer ETSI: European Telecommunications Standards Institute EUL:Enhanced Up Link, same as HSUPA FDD: Frequency Division Duplex GPRS: General Packet Radio Service GSM: Global System for Mobile communication HSPA: High Speed Packet Access, refers to both downlink (HSDPA) and uplink (EUL/HSUPA) HSDPA: High Speed Downlink Packet Access HSUPA: High Speed Uplink Packet Access, same as EUL IEEE: Institution for Electrical and Electronics Engineers. Standardization body. IMT-2000: International Mobile Telecommunications-2000 (IMT-2000) IMS: IP Multimedia Subsystem IP: Internet Protocol ITU: International Telecommunication Union. LOS: Line-Of-Sight MAC: Medium Access Control MAN: Metropolitan Area Network MTBF: Mean Time Between Failure NAT: Network Address Translation IEEE /WiMAX Overview- oct E.Borcoci. Page 29 of 30

30 NLOS: Non-Line-Of-Sight OFDM: Orthogonal Frequency Division Multiplexing OFDM: Orthogonal Frequency Division Multiple Access PDA: Personal Digital Assistant PHY: Physical Layer PSTN: Public Switched Telephone Network QoS: Quality of Service RF: Radio Frequency SGSN: Serving GPRS Support Node SIP: Session Initiation Protocol SME: Small and Medium size Enterprises SoHo: Small Office Home Office SS: Subscriber Station STC: Space-Time Codes TCO: Total Cost of Ownership TDD: Time Division Duplex TDM: TimeT TDivisionT TMultiplexing TDMA:Time-Division Multiple Access UCD Upnlink Channel Descriptor VDSL: Very high bitrate DSL VoIP: Voice over Internet Protocol WCDMA: Wideband Code Division Multiple Access WiFi: Wireless Fidelity, or Wireless Local Area Network, WLAN WiMAX: World-wide interoperability for Microwave Access WISP: Wireless Internet Service Provider IEEE /WiMAX Overview- oct E.Borcoci. Page 30 of 30