WiMAX protocol stack
This article describes wimax protocol stack with functions of each in the system, which include wimax physical layer,WiMAX MAC layer and upper layers. The same protcol stack is depicted below in figure with sub layers.
WiMAX physical layer are of five types viz. SC,SCa,HUMAN,OFDM and OFDMA as decribed in IEEE 802.16-2004/802.16e standards. Any one out of these will be used in the system. For example fixed wimax uses OFDM type of physical layer and mobile wimax uses OFDMA type. For more on OFDM and OFDMA refer following links.
Physical layer takes MAC PDU consisting of MAC GMH, MAC payload and CRC and perform following functions.
2. Forward error correction
5. Cyclic prefix insertion
6. Pass the IQ data to RF module for radio frequency modulation and transmission into the air, hence often this layer is referred as transmission layer. There are 2.5 GHz/3.5 GHz and 5.8 GHz frequency bands supported in wimax.
MAC layer consists of three sub layers viz. MAC privacy sub layer, MAC common part sub layer and MAC convergence sub layer as mentioned in the figure.
MAC privacy sub layer:
It does Authentication,encryption and key management functions.
MAC common part sub layer:
It does ranging,scheduling,connection setup,bandwidth allocation,hybrid ARQ and QoS functions. Various QoS schemes and applications of each supported in wimax are as follows. It is Connection oriented protocol, which assigns connection ID (A 16-bit value that identifies a connection to equivalent peers in the MAC) to each service flow on both uplink and downlink pair between BS and SS. Each service flow (uniquely identified by a SFID, 32-bit value) has it own QoS parameter setting (latency, jitter & throughput).
UGS-Unsolicited Grant Service,here periodically SS will get service from network. It is used for VOIP without silence suppression.
rtPS-Real-time Packet Services,here BS asks SSs to send bandwidth request periodically(no contention involved here). It is used for streaming audio/video.
ertPS-Extended real time Packet Services, here piggybacking is taken care. It is used for VOIP with silence supression or activity detection.
nrtPS-Non-real time Packet Services, here whenever BS finds some interval it will ask SSs to send bandwidth request message(contention based). It is used for FTP
BE-Best Effort, SS can request for bandwidth anytime, SS will get it or not that depends on the wimax system. It is used for data transfer and web browsing
For more on MAC frames used for establishing connection between Base Station(BS) and Subscriber Station(SS) or Mobile Station(MS) are mentioned in our article on wimax MAC frame. Refer following link.
MAC convergence sub layer:
Functions performed by MAC convergence specific sublayer are mentioned below.
-Make upper layer frames compatible to be used by wimax MAC/PHY layers.
-Map upper layer addresses into wimax protocol addresses.
-Translate upper layer QoS fields into wimax MAC format and more
-Classify external network data and associate them to proper MAC service flow identifier (SFID) and connection id (CID)
- Handle TCP/IP based traffic
Above MAC there are IP,TCP,UDP and Applications layers, One can refer RFCs from IETF(http://www.ietf.org/rfc.html ) and wimax forum(http://www.wimaxforum.org/ ) published documents to gain more knowledge on the same.
Links to WiMAX MAC Layer resources
REG REQ and REG RSP
SBC REQ and SBC RSP
DSA REQ and DSA RSP
DLMAP and ULMAP
WiMAX Ranging Procedure
WiMAX Bandwidth Request procedure
WiMAX Network Entry Procedure
WiMAX CID vs SFID
WiMAX FCH header format
WiMAX TLV Format basics
WiMAX Network Interface types
WiMAX QoS Classes