The IEEE 802.16m Reference Model

Figure below illustrates the IEEE 802.16 reference model. The data link layer of IEEE 802.16 standard comprises three sub-layers. The service-specific convergence sub-layer (CS) provides any transformation or mapping of network-layer data packets into MAC SDUs. On the transmitter side, 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 interfacing with various network-layer protocols such as Asynchronous Transfer Mode (ATM)i and packet-switched protocols such as IP or Ethernet. The internal format of the CS payload is unique to the CS, and the MAC CPS is not required to understand the format of or parse any information from the CS payload.  

The IEEE 802.16 reference model

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 convergence sub-layers, through the MAC SAP classified into particular MAC connections. An example of MAC CPS service definition is given in reference. The Quality of Service (QoS) is further applied 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, and encryption. The user data, physical layer control, and statistics are transferred between the MAC CPS and the Physical Layer (PHY) via the PHY SAP which is implementation-specific. The IEEE 802.16 physical 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. The NCMS abstraction allows the physical and MAC layers specified in the IEEE 802.16 standard to be independent of the network architecture, the transport network, and the protocols used in the backhaul, 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 entity at the BS. An IEEE 802.16 entity is defined as a logical entity in an MS or BS that comprises the physical and MAC layers on the data, control, and management planes.

The IEEE 802.16f amendment (currently part of IEEE 802.16-2009 standard) provided enhancements to IEEE 802.16-2004 standard, defining a management information base (MIB), for the physical and medium access control layers and the associated management procedures. The management information base originates from the Open Systems Interconnection Network Management Model and is a type of hierarchical database used to manage the devices in a communication network. It comprises a collection of objects in a virtual database used to manage entities such as routers and switches in a network.

The IEEE 802.16 standard describes the use of a Simple Network Management Protocol (SNMP),ii i.e., an IETF protocol suite, as the network management reference model. The standard consists of a Network Management System (NMS), managed nodes, and a service flow database. The BS and MS managed nodes collect and store the managed objects in the form of WirelessMAN Interface MIB and Device MIB that are made available to network management system via management protocols, such as SNMP. A Network Control System contains the service flow and the associated Quality of Service information that have to be provided to BS when an MS enters into the network. The Control SAP (C-SAP) and Management SAP (M-SAP) interface the control and management plane functions with the upper layers. The NCMS entity presents within each MS. The NCMS is a layer-independent entity that 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 model. Multiple mobile stations may be attached to a BS. The MS communicates to the BS over the air interface using a primary management connection, basic connection or a secondary management connection. The latter connection types have been replaced with new connection types in IEEE 802.16m standard