Nokia's TPSDA approach provides a model based on call admission for video and VoIP, with the need to guarantee delay/jitter/loss characteristics when the service connection is accepted. The architecture also meets the different QoS needs of HSI, namely per-subscriber bandwidth controls, including shaping and policing functions that have little or no value for video and VoIP services. In conjunction with the architecture's support for content differentiation, this enables differentiated service pricing within HSI.
The distribution of QoS policy and enforcement across BSA and BSR allows the service provider to implement meaningful per-subscriber service level controls. Sophisticated and granular QoS in the BSA allows the service provider to deliver truly differentiated IP services based on the subscriber as well as on the content.
In the BSR to BSA downstream direction (Figure: Downstream QoS enablement), IP services rely on IP layer classification of traffic from the network to queue traffic appropriately toward the BSA. Under extreme loading (only expected to occur under network fault conditions), lower priority data services or HSI traffic are compromised to protect video and voice traffic. Classification of HSI traffic based on source network address or IEEE 802.1p marking allows the QoS information to be propagated to upstream or downstream nodes by network elements. See Table: Downstream QoS enablement for the descriptions.
The BSR performs service distribution routing based on guarantees required to deliver the service and associated content instead of individual subscribers. The BSR only needs to classify content based on the required forwarding class for a specific BSA to ensure that each service's traffic receives the appropriate treatment toward the BSA.
| Key | Description |
|---|---|
A |
Per-subscriber queuing and PIR/CIR policing/shaping for HSI. HSI service classified on source IP range. Per-service prioritization for VoIP and video. VoIP is prioritized over video. Destination IP or DSCP classification. 802.1 marking for prioritization in the access and home. |
B |
VoIP and video queued and prioritized on per-VLAN QoS policy basis. HSI content differentiation based on DSCP. Each queue may have individual CIR/PIR and shaping. Optical overall subscriber rate limiting on VLAN (H-QoS). |
C |
For HSI, content differentiation queuing for gold, silver, or bronze based on DSCP classification. Optional overall subscriber rate limiting on VLAN. |
D |
Preferred content marked (DSCP) of trusted ingress points of IP network. |
In the upstream direction (BSA to BSR, as shown in Figure: Upstream QoS enablement), traffic levels are substantially lower. Class-based queuing is used on the BSA network interface to ensure that video control traffic is propagated with a minimal and consistent delay, and that preferred data or HSI services receive better treatment for upstream/peering service traffic than the best effort Internet class of service.
Upstream QoS enablement keys are described in Table: Upstream QoS enablement.
| Key | Description |
|---|---|
A |
HSI: Per-subscriber queuing with PIR or CIR policy or shaping. |
B |
VoIP and Video: Shared queuing for prioritization of real-time traffic over HSI. Upstream video is negligible. |
C |
Per-subscriber QoS/Content classification for content differentiation. |
D |
Video and VoIP: Policy defines priority aggregate CIR and PIR. HSI: QoS policy defines priority and aggregate CIR and PIR. Content differentiation based on ingress classification. DSCP is marked. |
The BSA is capable of scheduling and queuing functions on a per-service, per-subscriber basis, in addition to performing wire-speed packet classification and filtering based on both Layer 2 and Layer 3 fields.
Each subscriber interface provides at least three dedicated queues. TPSDA makes it possible to configure these queues such that the forwarding classes defined for all services can all be mapped to one service VLAN upstream. In the BSA, assuming hundreds of subscribers per gigabit Ethernet interface, this translates to a thousand or more queues per port.
In addition to per-service rate limiting for HSI services, each subscriber's service traffic can be rate limited as an aggregate using a bundled service policy. This allows different subscribers to receive different service levels independently and simultaneously.
Distributed multicasting today's predominant video service is broadcast TV, and remains significant. As video services are introduced, it is sensible to optimize investments by matching resources to the service model relevant at the time. Consequently, the objective of the service infrastructure should be to incorporate sufficient flexibility to optimize for broadcast TV in the short term, yet scale to support a full unicast (VoD) model as video service offerings evolve.
Optimizing for broadcast TV means implementing multicast packet replication throughout the network. Multicast improves the efficiency of the network by reducing the bandwidth and fiber needed to deliver broadcast channels to the subscriber. A multicasting node can receive a single copy of a broadcast channel and replicate it to any downstream nodes that require it, substantially reducing the required network resources. This efficiency becomes increasingly important closer to the subscriber. Multicast should be performed at each or either of the access, aggregation, and video edge nodes.
Multicasting as close as possible to the subscriber has other benefits because it enables a large number of users to view the content concurrently. The challenges of video services are often encountered in the boundary cases, such as live sports events and breaking news, for which virtually all the subscribers may be watching just a few channels. These exceptional cases generally involve live content, which is true broadcast content. Multicasting throughout the network makes it possible to deliver content under these circumstances while simplifying the engineering of the network.
Efficient multicasting requires the distribution of functions throughout the access and the aggregation network to avoid overloading the network capacity with unnecessary traffic. TPSDA realizes efficient multicasting by implementing IGMP snooping in the access nodes, IGMP snooping in the BSA and multicast routing in the BSR (Figure: Distributed multicasting in Triple Play).
