1 IEEE Wireless MAN (Wireless Metropolitan Network) A Technical Overview of the WirelessMAN TM Air Interface for Broadband Wireless Access, Carl Eklund, Roger B. Marks, Kenneth L. Stanwood and Stanley Wang June 2002 Presented by Phuong Nguyen For 681 Advanced Computer Network Fall 2007

2 Topics Introduction Physical Layer MAC Layer (Medium Access Control) References

3 Introduction Goal: Provide high-speed Internet access to home and business subscribers, without wires. Base stations (BS) can handle thousands of subscriber stations (SS) BS can control all data traffic goes between BS and SS through the allocation of bandwidth on the radio channel is a Bandwidth on Demand system Access control prevents collisions. Supports Legacy voice systems Voice over IP TCP/IP Applications with different QoS requirements. Main advantage : fast deployment, dynamic sharing of radio resources and low cost

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5 Architecture Uplink: direction from SS to BS Downlink: direction from BS to SS Source: D. Miorandi Create Net

6 IEEE Extension standard was approved in (10-66 GHz, line-of-sight, up to 134Mbit/s) (minimizing interference between coexisting WMANs.) a Support lower frequency 2 to 11Ghz both licensed and license-exempt So reach more customers with less expensive Lower data rates Support Mesh-Network b Increase spectrum to 5 and 6GHz Provide QoS (for real-time voice and video service) c Represents a 10 to 66GHz system profile d Improvement and fixes for a e Addresses on Mobile Enable high-speed signal handoffs necessary for communications with users moving at vehicular speeds Focus on

7 SAP: Service Access Point PDU: Protocol Data Unit Accept, perform classification, process higher PDUs Deliver CS PDU to MAC SAP Receive CS PDUs from the peer entity System access, bandwidth allocation connection establishment, connection maintenance Authentication, security key exchange, encryption IEEE Std protocol layering, showing SAPs Multiple specifications each appropriate to frequency range (ex: GHz up to 134Mbit/s) and application

8 Physical layer 10-66GHz line of sight propagation. US use 20-25MHz, EU use 28MHz Point – to – multipoint BS transmit a TDM (Time Division Multiplexing) signal with individual SSs allocated time slots serially Access the uplink by time division multiple access (TDMA) Burst single-carrier modulation Allows use of directional antennas Allows use of two different duplexing schemes: Frequency Division Duplexing (FDD) Time Division Duplexing (TDD) Support for both full and half duplex stations

9 Time Division Duplexing (TDD) Uplink and downlink share a channel but do not transmit simultaneously Source: D. Miorandi Create Net

10 Frequency Division Duplexing (FDD) Uplink and downlink operate on separate channels sometime simultaneously Support full duplex SSs which can transmit and receive simultaneously Half duplex which do not Adaptive Data Burst Profiles Transmission parameters (e.g. modulation and FEC settings) can be modified on a frame-by-frame basis for each SS. Profiles are identified by Interval Usage Code (DIUC and UIUC) Using both TDM (Time Division Multiplexing) and TDMA (Time Division Multiple Access)

11 Media Acces Control (MAC) Supports many different physical layer specifications, both licensed and unlicensed. Connection orienteded Connection ID (CID) Channel access: UL-MAP Defines uplink channel access Defines uplink data burst profiles DL-MAP Defines downlink data burst profiles UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).

12 FDD Downlink subframe Source: D. Miorandi Create Net

13 Uplink subframe Source: D. Miorandi Create Net Grant bandwidth to specific SSs SSs transmit in assigned allocation using burst profiles UIUC in UL-MAP

14 MAC sublayers Service Specific Convergence Sublayer ATM CS defined for ATM service Packet CS defined for IPv4, IPv6, Ethernet Classify service data unit SDUs to proper MAC connection, preserve or enable QoS and enable bandwidth allocation

15 Common Part Sublayer Point to multi point Request bandwidth, associate QoS, transport and routing data SS has universal 48bit MAC address. BS has 48-bit Base Station ID (not MAC address) Connections identified by 16-bit CID. used to distinguish between multiple uplink channels associated with the same downlink channel many higher-layer sessions may share same CID (with same service parameters) Used in MAC PDU

16 Common Part Sublayer SS enter network is assigned 3 management connections Basic connection: transfer short critical MAC messages Primary connection: transfer longer more delay torelent messages (authentication, connection setup) Secondary connection: transfer of standard base management messages such as DHCP, TFTP, SNMP In addition, transport connection for contracted services Other additional connections: Contention based initial access Broadcast transmissions for Downlink, polling of SSs if needed Additional connections for multicast

17 MAC PDU format MAC PDU Formats -The MAC PDU (protocol data unit) is the data unit exchanged between the MAC layers of the BS and its SSs. -Consists of a fixed-length MAC header, a variable-length payload, and an optional cyclic redundancy check (CRC). MAC Header Formats Two MAC header formats: The first is the generic MAC header that begins each MAC PDU containing either MAC management messages or CS data. The second is the bandwidth request header used to request additional bandwidth.

18 MAC PDU header

19 Transmission of MAC PDUs Transmission Convergence sublayer is between MAC and PHY Transformation of variable length MAC PDUs into fixed length FEC block MAC MessageSDU 1 SDU2 PDU1PDU2PDU3PDU4PDU5 MAC PDUs PFEC1FEC2FEC3 Burst Preamble FEC blocks

20 MAC Management Messages (rules) Handle initial ranging, negotiation, SS authentication and registration, and describing downlink and uplink link describing: BS transmits channel uplink and downlink descriptor messages (UCD and DCD) at periodic intervals UCD and DCD contain burst profile: info on modulation, error- correction, preamble length, etc. uplink and downlink map messages (UL-MAP, DL-MAP) define burst start times and allocate access to corresponding link channel ranging: subscriber stations transmit ranging requests at initialization and then periodically determines power and burst profile changes (starts with lowest power level and then moves up) Create - net

21 MAC Management Messages Uplink schedule service Unsolicited Grant Service (UGS) Real-Time Polling Service (rtPS) Non-Real-Time Polling Service (nrtPS) Best Effort Service Bandwidth request and grants SS authentication and registration

22 Bandwidth request and allocation SSs may request bw in 3 ways: Use the contention request opportunities interval upon being polled by the BS (multicast or broadcast poll). Send a standalone MAC message called BW request in an allready granted slot. Piggyback a BW request message on a data packet. BS grants/allocates bandwidth in one of two modes: Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC) Decision based on requested bw and QoS requirements vs available resources. Grants are realized through the UL-MAP. Source: D. Miorandi Create Net

23 Approaches to Bandwidth Grant Two basic approaches on the way to grant BW Bandwidth Grant per Subscriber Station (GPSS) Base station grants bandwidth to the subscriber station Subscriber station may re-distribute bandwidth among its connections, maintaining QoS and service-level connections agreements Suitable for many connections per terminal; off-loading base stations work Allows more sophisticated reaction to QoS needs Low overhead but requires intelligent subscriber station Bandwidth Grant per Connection (GPC) Base station grants bandwidth to a connection Mostly suitable for few users per subscriber station Higher overhead, but allows simpler subscriber

24 Bandwidth allocate by Unicast Polling 1. BS allocates space for the SS in the uplink subframe. 2. SS uses the allocated space to send a bw request. 3. BS allocates the requested space for the SS (if available). 4. SS uses allocated space to send data. Poll(UL-MAP) Request Alloc(UL-MAP) Data BSSS Source: D. Miorandi Create Net

25 Initial Ranging Upon learning what parameters to use for its Initial ranging, SS scanning for UL_MAP messages present in every frame SS will send the burst using minimum power setting and try again if it does not get response BS command timing advance and power adjustment to SS based on SS request. Also provide SS with basic and primary management CIDs SS receive response: 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.

26 Negotiation Capabilities and Authentication Negotiation Capabilities After successful completion of initial ranging, the 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. The BS accepts or denies the SS, based on its capabilities. Authentication After negotiation, the BS authenticates the SS and provides key material to enable the ciphering of data. The SS sends the X.509 digital certificate and certificate of 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 Reply contain Authorization Key encrypted with SSs public key.

27 Registration and IP connectivity Registration SS will register the network after successful completion of authentication It sends a registration request message to the BS, and the BS sends a registration response to the SS. The registration exchange includes IP version support SS managed or non-managed support ARQ parameters support Classification option support CRC support Flow Control IP connectivity After registration SS attains an IP address via DHCP and establishes time of day via Internet Time Protocol

28 References IEEE Standard : A technique overview of the WirelessMAN TM Air Interface for Broachband Wireless Access, Carl Eklund, Roger B. Marks, Kenneth L. Stanwood and Stanley Wang, June IEEE std standard 2004 part 16 (895 pages )

29 Questions ?