In order to provide what network engineers call Quality of Service (QoS), the flow of data in the form of packets must be predetermined and resources must be somehow assured for that predetermined flow. Simple routing does not provide a predetermined path for the traffic, and priorities that are described by Class of Service (CoS) coding simply increase the odds of successful transit for one packet over another. There is still no guarantee of service quality. The guarantee of service quality is what distinguishes QoS from CoS. CoS is an element of overall QoS.
By using the traffic management features of the 7705 SAR, network engineers can achieve a QoS for their customers. Multiprotocol Label Switching (MPLS) provides a predetermined path, while policing, shaping, scheduling, and marking features ensure that traffic flows in a predetermined and predictable manner.
There is a need to distinguish between high-priority (that is, mission-critical traffic like signaling) and best-effort traffic priority levels when managing traffic flow. Within these priority levels, it is important to have a second level of prioritization, that is, between a certain volume of traffic that is contracted/needed to be transported, and the amount of traffic that is transported if the system resources allow. Throughout this guide, contracted traffic is referred to as in-profile traffic. Traffic that exceeds the user-configured traffic limits is either serviced using a lower priority or discarded in an appropriate manner to ensure that an overall quality of service is achieved.
The 7705 SAR must be properly configured to provide QoS. To ensure end-to-end QoS, each and every intermediate node together with the egress node must be coherently configured. Proper QoS configuration requires careful end-to-end planning, allocation of appropriate resources and coherent configuration among all the nodes along the path of a given service. Once properly configured, each service provided by the 7705 SAR will be contained within QoS boundaries associated with that service and the general QoS parameters assigned to network links.
The 7705 SAR is designed with QoS mechanisms at both egress and ingress to support different customers and different services per physical interface or card, concurrently and harmoniously (refer to Egress and Ingress Traffic Direction for a definition of egress and ingress traffic). The 7705 SAR has extensive and flexible capabilities to classify, police, shape and mark traffic to make this happen.
The characteristics and nature of traffic flows in the ingress and egress directions are usually totally different. As an example, traffic is usually shaped at egress for pacing purposes and jitter tolerance imposed by the network transport rules, whereas at ingress, traffic is usually policed to ensure it fits into the traffic volumes defined in the Service Level Agreement. Thus, segregation between ingress and egress offers not only the seamless flexibility to address different requirements but as well allows fine-tuning of appropriate parameters in each direction.
The 7705 SAR supports multiple forwarding classes (FCs) and associated class-based queuing. Ingress traffic can be classified to multiple FCs, and the FCs can be flexibly associated with queues. This provides the ability to control the priority and drop priority of a packet while allowing the fine-tuning of bandwidth allocation to individual flows.
Each forwarding class is important only in relation to the other forwarding classes. A forwarding class allows network elements to weigh the relative importance of one packet over another. With such flexible queuing, packets belonging to a specific flow within a service can be preferentially forwarded based on the CoS of a queue. The forwarding decision is based on the forwarding class of the packet, as assigned by the ingress QoS policy defined for the service access point (SAP).
7705 SAR routers use QoS policies to control how QoS is handled at distinct points in the service delivery model within the device. QoS policies act like a template. Once a policy is created, it can be applied to many other similar services and ports. As an example, if there is a group of Node Bs connected to a 7705 SAR node, one QoS policy can be applied to all services of the same type, such as High-Speed Downlink Packet Access (HSDPA) offload services.
There are different types of QoS policies that cater to the different QoS needs at each point in the service delivery model. QoS policies are defined in a global context in the 7705 SAR and only take effect when the policy is applied to a relevant entity.
QoS policies are uniquely identified with a policy ID number or a policy ID name. Policy ID 1 and policy ID ‟default” are reserved for the default policy, which is used if no policy is explicitly applied.
The different QoS policies within the 7705 SAR can be divided into two main types.
QoS policies are used for classification, queue attributes, and marking.
Slope policies define default buffer allocations and Random Early Discard (RED) and Weighted Random Early Discard (WRED) slope definitions.
The sections that follow provide an overview of the QoS traffic management performed on the 7705 SAR.