Medium Access Control (MAC) and Physical Layer (PHY) - CISE

4-June-07 P1901_PRO_016_r0
8.5 Traffic Shaping
QoS apply traffic shaping in two different ways. Each one is applied based on the service class of traffic:
• Limit bandwidth: Is applied for best-effort and ABR service classes. Is based on the credit assignation for
this service classes. This credit is assigned per-user and is renewed periodically. If the credit is not used
during the period time, it’s lost and can not be used in the next period.
• Guaranteed bandwidth: Is applied for VBR and CBR service classes. Traffic must be allowed prior to
transmit and a reservation is made for this type of traffic using the CAC protocol. Channel time is assigned
based on the resources reservation to meet bandwidth and latency requirements. Due to the explicit
reservation of resources, nodes shall have mechanisms to allocate buffer space to support the incoming
traffic.
8.5.1 QOS Requirements
To provide QoS requirements is needed support from MAC layer in order to identify the network usage by each
node and the traffic service classes in the network. This support must be provided as MAC primitives and will be:
• Transmitted priorities by a CPE. Must be a set of bits and each bit must be mapped to a priority
• Transmitted priorities by BPL subcell/cell masters.
• Single transmission Channel time: Must be the transmission time used for individual transmissions for each
node in the BPL cell.
• Transmitted data: Data transmitted since last time the token was received, so that bandwidth limitation
algorithm can be reconfigured dynamically.
• Unused channel time: The percentage of network resources assigned to this node available in the network.
Other QoS facilities should be implemented in order to guarantee QoS requirements:
• BPL node shall be able to define service classes with or without MAC Level acknowledgment capabilities.
• BPL node shall be able to assign resources in a per-user and per-service basis to guarantee constant,
variable or peak rate traffic requirements.
• BPL node shall be able to transmit to a subset of possible receivers nodes in order to guarantee unique
channel usage per-user.
• BPL node shall configure MTU per-user in order to guarantee minimum transmission time per-user.
• BPL node should be able to avoid transmission of lower priorities to guarantee preferential treatment of
higher priorities in a per-flow basis.
Submission page 185 UPA-OPERA