7.4 CS and QoS

7.4 CS and QoS

During the creation of a service flow, the CS specification that the connection being set up will use is defined. Possible choices of CS specification are No CS, Packet IPv4, Packet IPv6, Packet 802.3/Ethernet, Packet 802.1Q VLAN, Packet IPv4 over 802.3/Ethernet, Packet IPv6 over 802.3/ Ethernet, Packet IPv4 over 802.1Q VLAN, Packet IPv6 over 802.1Q VLAN and ATM.

The first feature of the QoS management is to define transmission ordering and scheduling on the air interface. For this reason, packets crossing the MAC interface are associated with a service flow identified by the CID.

The QoS parameters are associated with uplink/downlink scheduling for a service flow. An exhaustive list of QoS parameters of a service flow can be found in Reference [1], Section 11.13. The main QoS parameters are shortly described in the following:

  • Scheduling service type, also called the QoS class. The value of this parameter specifies the scheduling service that is enabled for the associated service flow. The four defined scheduling service types in the 802.16 standard are (see Section 11.4 for scheduling service types) BE (default), nrPS, rtPS and UGS. A fifth scheduling service type was added with 16e: ertPS.

  • Traffic priority. The value of this parameter specifies the priority assigned to a service flow. Given two service flows identical in all QoS parameters besides priority, the higher priority service flow should be given lower delay and higher buffering preference.

  • Maximum sustained traffic rate. This parameter defines the peak information rate of the service. The rate is expressed in bits per second.

  • Maximum traffic burst. This parameter defines the maximum burst size that is accommodated for the service.

  • Minimum reserved traffic rate. This parameter specifies the minimum rate reserved for this service flow. The rate is expressed in bits per second and specifies the minimum amount of data to be transported on behalf of the service flow when averaged over time.

  • Vendor-specific QoS parameters. This allows vendors to encode vendor-specific QoS parameters. The Vendor ID must be embedded inside vendor-specific QoS parameters.

  • Tolerated jitter. This parameter defines the maximum delay variation (jitter) for the connection.

  • Maximum latency. The value of this parameter specifies the maximum latency between the reception of a packet by the BS or SS on its network interface and the forwarding of the packet to its RF interface.

  • Fixed-length versus variable-length SDU indicator. The value of this parameter specifies whether the SDUs on the service flow are of a fixed length or variable length. This parameter is used only if packing is on for the service flow.

  • SDU size. The value of this parameter specifies the length of the SDU for a fixed-length SDU service flow.

  • Request/transmission policy. The value of this parameter provides the capability to specify certain attributes for the associated service flow. These attributes include options for PDU formation and, for uplink service flows, restrictions on the types of bandwidth request opptions that may be used.