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
