QoS policies

The high-priority forwarding classes are Network-Control (nc), Expedited (ef), High-1 (h1), and High-2 (h2). High-priority forwarding classes are always serviced at congestion points over other forwarding classes; this behavior is determined by the router queue scheduling algorithm. See Virtual hierarchical scheduling for more information.

With a strict PHB at each network hop, service latency is mainly affected by the amount of high-priority traffic at each hop. These classes are intended to be used for network control traffic or for delay- or jitter-sensitive services.

If the service core network is oversubscribed, a mechanism to engineer a path through the core network and to reserve bandwidth must be used to apply strict control over the delay and bandwidth requirements of high-priority traffic. In the router, RSVP-TE can be used to create a path defined by an MPLS LSP through the core. Premium services are then mapped to the LSP, with care to not oversubscribe the reserved bandwidth.

If the core network has sufficient bandwidth, it is possible to effectively support the delay and jitter characteristics of high-priority traffic without using traffic engineered paths, as long as the core treats high-priority traffic with the correct PHB.

The assured forwarding classes are Assured (af) and Low 1 (l1). Assured forwarding classes provide services with a committed rate and a peak rate, much like Frame Relay. Packets transmitted through the queue at or below the committed transmission rate are marked in-profile. If the core service network has sufficient bandwidth along the path for the assured traffic, all aggregate in-profile service packets reach the service destination.

Packets transmitted from the service queue that are above the committed rate are marked out-of-profile. When an assured out-of-profile service packet is received at a congestion point in the network, it is discarded before in-profile assured service packets.

Multiple assured classes are supported with relative weighting between them. In DiffServ, the code points for the various Assured classes are AF4, AF3, AF2, and AF1. Typically, AF4 has the highest weight of the four and AF1 the lowest. The Assured and Low-1 classes are differentiated based on the default DSCP mappings. All DSCP and EXP mappings can be modified by the user.

The best-effort classes are Low 2 (l2) and Best-Effort (be). The best-effort forwarding classes have no delivery guarantees. All packets within this class are treated by default as out-of-profile assured service packets.

The queue ID is used to uniquely identify the queue. The queue ID is only unique within the context of the QoS policy within which the queue is defined.

Unicast queues are used for all services and routing when the traffic is forwarded to a single destination.

Multipoint ingress queues are used by VPLS services for multicast, broadcast, and unknown traffic and by IES and VPRN services for multicast traffic when IGMP, MLD, or PIM is enabled on the service interface.

The type of a queue dictates how it is scheduled relative to other queues at the hardware level. Being able to define the scheduling properties of a queue is important because a single queue allows support for multiple forwarding classes.

The queue type defines the relative priority of the queue and can be configured to expedited (higher priority) or best-effort (lower) priority. However, the instantaneous scheduling priority of a queue changes dynamically depending on its current scheduling rate compared to its operational Committed Information Rate (CIR) and Fair Information Rate (FIR) (see Queue scheduling). Parental virtual schedulers can be defined for the queue using scheduler policies which enforce how the queue interacts for bandwidth with other queues associated with the same scheduler hierarchy (see Scheduler policies).

The queue type of SAP ingress and egress queues, network queue policy queues, and ingress queue group template queues are defined at queue creation time. The queue type of egress queue group template queues and shared-queue policy queues can be modified after the queue has been created.

The default behavior for SAP ingress and egress queues, network queue policy queues, and shared queue policy queues is to automatically choose the expedited or best effort nature of the queue based on the forwarding classes mapped to it. This is achieved by configuring the queue type to auto-expedited. As long as all forwarding classes mapped to the queue are expedited (nc, ef, h1, or h2), the queue is treated as an expedited queue by the hardware schedulers. When any best effort forwarding classes are mapped to the queue (be, af, l1, or l2), the queue is treated as best effort by the hardware schedulers.

The default queue type for ingress queue group template and egress queue group template queues is best-effort.

Packets are scheduled from queues by hardware schedulers based on the type of the queue (see Queue type) and the current scheduling rate of the queue compared to its operational CIR and FIR. This applies to unicast queues at both ingress and egress, and multipoint queues at ingress, but not to HSQ IOM queues.

The queue type should be chosen based on the kind of traffic in the forwarding classes mapped to the queue.

The hardware scheduler services queues to forward packets from them in a strict priority order, as follows:

• Ingress queues, in priority order:

  1. Expedited queues where the queue’s current scheduling rate is below its operational FIR

  2. Best effort queues where the queue’s current scheduling rate is below its operational FIR

  3. Expedited queues where the queue’s current scheduling rate is below its operational CIR

  4. Best effort queues where the queue’s current scheduling rate is below its operational CIR

  5. Expedited queues where the queue’s current scheduling rate is above both its operational FIR and CIR

  6. Best effort queues where the queue’s current scheduling rate is above both its operational FIR and CIR

• Egress queues, in priority order:

  1. Expedited queues where the queue’s current scheduling rate is below its operational FIR

  2. Best effort queues where the queue’s current scheduling rate is below its operational FIR

  3. Expedited queues where the queue’s current scheduling rate is below its operational CIR

  4. Best effort queues where the queue’s current scheduling rate is below its operational CIR

  5. Expedited queues where the queue’s current scheduling rate is above both its operational FIR and CIR

  6. Best effort queues where the queue’s current scheduling rate is above both its operational FIR and CIR

The Peak Information Rate (PIR) defines the maximum rate at which packets are allowed to exit the queue. The PIR does not specify the maximum rate at which packets may enter the queue; this is governed by the queue's ability to absorb bursts and is defined by its maximum burst size (MBS).

The actual transmission rate of a service queue depends on more than just its PIR. Each queue is competing for transmission bandwidth with other queues. Each queue's PIR, CIR, FIR, and the queue type (see Queue type) all combine to affect a queue's ability to transmit packets, as described in Queue scheduling.

The PIR is provisioned on ingress and egress queues within service ingress and egress QoS policies, network queue policies, ingress and egress queue group templates, and shared queue policies.

When defining the PIR for a queue, the value specified is the administrative PIR for the queue. The router has a number of native rates in hardware that it uses to determine the operational PIR for the queue. The user has some control over how the administrative PIR is converted to an operational PIR should the hardware not support the exact PIR value specified. The interpretation of the administrative PIR is discussed in Adaptation rule.

The Committed Information Rate (CIR) for a queue performs two distinct functions:

• profile marking by service ingress queues

  Service ingress queues (configured in SAP ingress QoS policies or ingress queue group templates) mark packets in-profile or out-of-profile based on the CIR. For each packet in a service ingress queue, the CIR is compared to the current transmission rate of the queue. If the current rate is at or below the CIR threshold, the transmitted packet is internally marked in-profile. If the current rate is above the threshold, the transmitted packet is internally marked out-of-profile. This operation can be overridden by configuring cir-non-profiling under the queue. This allows the queue scheduling priority to continue to be based on the below CIR or above CIR of the queue, but packets are not re-profiled depending on the state of the queue when they are scheduled (below CIR or above CIR). Instead, their profile state remains as out-of-profile, unless they are explicitly classified as in-profile or out-of-profile in which case they remain in-profile or out-of-profile.

• scheduler queue priority

  The scheduler serving a group of service ingress or egress queues prioritizes individual queues based on their current FIR, CIR, and PIR states. See Queue scheduling for more information about queue scheduling.

All router queues support the concept of in-profile, out-of-profile, together with inplus-profile and exceed-profile at egress only. The network QoS policy applied at network egress determines how or if the profile state is marked in packets transmitted into the service core network. If the profile state is marked in the service core packets, the packets are dropped preferentially at congestion points in the core as follows:

• exceed-profile

• out-of-profile

• in-profile

• inplus-profile

When defining the CIR for a queue, the value specified is the administrative CIR for the queue. The router has a number of native rates in hardware that it uses to determine the operational CIR for the queue. The user has some control over how the administrative CIR is converted to an operational CIR if the hardware does not support the exact CIR specified. See Adaptation rule for more information about the interpretation of the administrative CIR.

Although the router is flexible in how the CIR can be configured, there are conventional ranges for the CIR based on the forwarding class of a queue. A service queue associated with the high-priority class normally has the CIR threshold equal to the PIR rate, although the router allows the CIR to be provisioned to any rate below the PIR if this behavior is required. If the service queue is associated with a best-effort class, the CIR threshold is normally set to zero; however, this is flexible.

The CIR for a service queue is provisioned in ingress and egress service queues within service ingress QoS policies and service egress QoS policies respectively. CIRs for network queues are defined within network queue policies. CIRs for queue group instance queues are defined within ingress and egress queue group templates.

The adaptation rule provides the QoS provisioning system with the ability to adapt specific FIR-, CIR-, and PIR-defined administrative rates to the underlying capabilities of the hardware that the queue is created on to derive the operational rates. The administrative FIR, CIR, and PIR rates are translated to operational rates enforced by the hardware queue. The adaptation rule provides a constraint used when the exact rate is not available because of hardware implementation trade-offs.

For the FIR, CIR, and PIR parameters individually, the system attempts to find the best operational rate depending on the defined constraint. The supported constraints are:

minimum

finds the hardware supported rate that is equal to or higher than the specified rate

maximum

finds the hardware supported rate that is equal to or lesser than the specified rate

closest

finds the hardware supported rate that is closest to the specified rate

Depending on the hardware on which the queue is provisioned, the operational FIR, CIR, and PIR settings used by the queue depends on the method that the hardware uses to implement and represent the mechanisms that enforce the FIR, CIR, and PIR rates.

As the hardware has a very granular set of rates, Nokia’s recommended method to determine which hardware rate is used for a queue is to configure the queue rates with the associated adaptation rule and use the show pools output command to display the rate achieved.

To illustrate how the adaptation rule constraints (minimum, maximum, and closest) are evaluated in determining the operational CIR or PIR rates, assume there is a queue where the administrative CIR and PIR rates are 401 Mb/s and 403 Mb/s, respectively.

The following output shows the operating CIR and PIR rates achieved for the different adaptation rule settings:

*A:PE# # queue using default adaptation-rule=closest
*A:PE# show qos sap-egress 10 detail | match expression "Queue-Id|CIR Rule"
Queue-Id             : 1                Queue-Type           : auto-expedite
PIR Rule             : closest          CIR Rule             : closest
*A:PE#
*A:PE# show pools 1/1/1 access-egress service 1 | match expression "PIR|CIR"
Admin PIR        : 403000               Oper PIR         : 403200
Admin CIR        : 401000               Oper CIR         : 401600
*A:PE#
*A:PE# configure qos sap-egress 10 queue 1 adaptation-rule pir max cir max
*A:PE#
*A:PE# show qos sap-egress 10 detail | match expression "Queue-Id|CIR Rule"
Queue-Id             : 1                Queue-Type           : auto-expedite
PIR Rule             : max              CIR Rule             : max
*A:PE#
*A:PE# show pools 1/1/1 access-egress service 1 | match expression "PIR|CIR"
Admin PIR        : 403000               Oper PIR         : 401600
Admin CIR        : 401000               Oper CIR         : 400000
*A:PE#
*A:PE# configure qos sap-egress 10 queue 1 adaptation-rule pir min cir min
*A:PE#
*A:PE# show qos sap-egress 10 detail | match expression "Queue-Id|CIR Rule"
Queue-Id             : 1                Queue-Type           : auto-expedite
PIR Rule             : min              CIR Rule             : min
*A:PE#
*A:PE# show pools 1/1/1 access-egress service 1 | match expression "PIR|CIR"
Admin PIR        : 403000               Oper PIR         : 403200
Admin CIR        : 401000               Oper CIR         : 401600
*A:PE#

The Committed Burst Size (CBS) parameter specifies the size of buffer that can be drawn from the reserved buffer portion of the queue buffer pool. When the reserved buffers for a specific queue have been used, the queue competes with other queues for additional buffer resources up to the MBS.

The CBS is provisioned on ingress and egress service queues within service ingress QoS policies and service egress QoS policies, respectively. The CBS for a queue is specified in kbytes.

The CBS for a network queue is defined within network queue policies based on the forwarding class. The CBS for the queue for the forwarding class is defined as a percentage of buffer space for the pool.

The Maximum Burst Size (MBS) parameter specifies the maximum queue depth to which a queue can grow. This parameter ensures that a customer that is massively or continuously over-subscribing the PIR of a queue does not consume all the available buffer resources. For high-priority forwarding class service queues, the MBS can be relatively smaller than the other forwarding class queues because the high-priority service packets are scheduled with priority over other service forwarding classes.

The MBS is provisioned on ingress and egress service queues within service ingress QoS policies and service egress QoS policies, respectively. The MBS for a service queue is specified in bytes or kbytes.

The MBSs for network queues are defined within network queue policies based on the forwarding class. The MBSs for the queues for the forwarding class are defined as a percentage of buffer space for the pool.

The MBS determines the maximum queue depth after which no additional packets are accepted into the queue. Additional queue drop tails are available for the different packet profiles to allow preferential access to the queue's buffers which allows higher priority packets to be accepted into a queue when there is congestion for lower priority packets.

At ingress there is a low drop tail in addition to the MBS. High enqueuing priority packets (for ingress SAP priority mode queues) and in-profile packets (for ingress SAP profile mode queues, network, and shared queues) are allowed to fill up the queue up to the MBS, however, low enqueuing priority packets (for ingress SAP priority mode queues) and out-of-profile packets (for ingress SAP profile mode queues, network, and shared queues) can only fill the queue up to the queue's low drop tail setting.

At egress there are four drop tails in addition to the MBS, one for each profile state:

• an exceed drop tail for exceed-profile packets

• a low drop tail for out-of-profile packets

• a high drop tail for in-profile packets

• a highplus drop tail for highplus-profile packets

Each profile type can only fill the queue up to its corresponding drop tail. Ingress and egress queue drop tails shows the ingress and egress queue drop tails.

At both ingress and egress, the drop tails are configured as a percentage reduction from the MBS (specifying 10% places the drop tail at 90% of the MBS) and consequently all are limited by the queue's MBS.

The default percentage for the low drop tail for ingress SAP, queue group, and shared queues is a reduction from the MBS of 10% (low)

The default percentages for the drop tails for egress SAP, queue group, and network queues is a percentage reduction from the MBS of:

• exceed = 20%

• low = 10%

• high = 0%

• highplus = 0%

The exceed, high, and highplus drop tails are not configurable for network queues, however the exceed drop tail is set to a value of 10% in addition to low drop tail and capped by the MBS.

The four drop tails can be configured in any order within egress SAP and queue group queues, however it is logical to order them (from shortest to longest) as exceed, then low, then high, then highplus.

The low drop tail configuration can be overridden for ingress and egress SAP and queue group queues, and for network egress queues. It is also possible to override the low drop tail for subscriber queues within an SLA profile using the keyword high-prio-only.

When there is congestion the drop tail ordering gives preferential access to the queue's buffers. For example, if the drop tails on an egress SAP queue are configured as exceed = 20%, low = 10%, high = 5% and highplus = 0%, when the queue depth is below 80% all profile packet types are accepted into the queue. If the depth increases above 80%, then exceed profile packets are not accepted and are therefore dropped, while the out-of-profile, in-profile, and inplus profile packets are still accepted into the queue (giving them preference over the exceed profile packets). If the queue depth goes beyond 90% the out-of-profile packets are also dropped. Similarly, if the queue depth goes beyond 95% the in-profile packets are dropped. It is only when the MBS has been reached that the inplus profile packets are dropped. This example assumes that the pool in which the queue exists is not congested.

Typically, customer markings placed on packets are not treated as trusted from an in-profile or out-of-profile perspective. This allows the use of the ingress buffering to absorb bursts over PIR from a customer and only perform marking as packets are scheduled out of the queue (as opposed to using a hard-policing function that operates on the received rate from the customer). The resulting profile (in or out) based on ingress scheduling into the switch fabric is used by network egress for tunnel marking and egress congestion management.

The high/low priority feature allows a provider to offer a customer the ability to have some packets treated with a higher priority when buffered to the ingress queue. If the queue is configured with a non-zero low drop tail setting, a portion of the ingress queue’s allowed buffers are reserved for high-priority traffic. An access ingress packet must hit an ingress QoS action in order for the ingress forwarding plane to treat the packet as high priority (the default is low priority).

If the ingress queue for the packet is above the low drop tail setting, the packet is discarded unless it has been classified as high priority. The priority of the packet is not retained after the packet is placed into the ingress queue. After the packet is scheduled out of the ingress queue, the packet is considered in-profile or out-of-profile based on the dynamic rate of the queue relative to the queue’s CIR parameter.

At access ingress, the priority of a packet has no effect on which packets are scheduled first. Only the first buffering decision is affected.

At ingress and egress, the current dynamic rate of the queue relative to the queue’s CIR and FIR (where supported) does affect the scheduling priority between queues going to the same destination (either the switch fabric tap or egress port). See Queue scheduling for information about the strict operating priority for queues.

For access ingress, the CIR controls both dynamic scheduling priority and marking threshold (unless cir-non-profiling is configured). At network ingress, the queue’s CIR affects the scheduling priority but does not provide a profile marking function as the network ingress policy trusts the received marking of the packet, based on the network QoS policy.

At egress, the profile of a packet is only important for egress queue buffering decisions and egress marking decisions, not for scheduling priority. The egress queue’s CIR determines the dynamic scheduling priority but does not affect the packet’s ingress determined profile.

The router maintains counters for queues within the system for granular billing and accounting. Each queue maintains the following counters:

• counters for packets and octets accepted into the queue

• counters for packets and octets rejected at the queue

• counters for packets and octets transmitted in-profile

• counters for packets and octets transmitted out-of-profile

The normal handling of SAP ingress access packets applies an in-profile or out-of-profile state (associated with the colors green and yellow, respectively) to each packet relative to the dynamic rate of the queue while the packet is forwarded toward the egress side of the system. When the queue rate is within or equal to the configured CIR, the packet is considered in-profile. When the queue rate is above the CIR, the packet is considered out-of-profile (this applies when the packet is scheduled out of the queue, not when the packet is buffered into the queue).

Egress queues use the profile marking of packets to preferentially buffer in-profile packets during congestion events. When a packet has been marked in-profile or out-of-profile by the ingress access SLA enforcement, the packet is tagged with an in-profile or out-of-profile marking allowing congestion management in subsequent hops toward the packet’s ultimate destination. Each hop to the destination must have an ingress table that determines the in-profile or out-of-profile nature of a packet, based on its QoS markings.

Color aware profiling adds the ability to selectively treat packets received on a SAP as in-profile or out-of-profile regardless of the queue forwarding rate. This allows a customer or access device to color a packet out-of-profile with the intention of preserving in-profile bandwidth for higher priority packets. The customer or access device may also color the packet in-profile, but this is rarely done as the original packets are usually already marked with the in-profile marking.

Each ingress access forwarding class may have one or multiple subclass associations for SAP ingress classification purposes. Each subclass retains the chassis-wide behavior defined to the parent class while providing expanded ingress QoS classification actions. Subclasses are created to provide a match association that enforces actions different than the parent forwarding class. These actions include explicit ingress remarking decisions and color aware functions.

All non-profiled and profiled packets are forwarded through the same ingress access queue to prevent out-of-sequence forwarding. Profiled packets in-profile are counted against the total packets flowing through the queue that are marked in-profile. This reduces the amount of CIR available to non-profiled packets causing fewer to be marked in-profile. Profiled packets out-of-profile are not counted against the total packets flowing through the queue that are marked in-profile. This ensures that the amount of non-profiled packets marked in-profile is not affected by the profiled out-of-profile packet rate.

The QoS mechanisms within the routers are specialized for the type of traffic on the interface. For customer interfaces, there is service ingress and egress traffic, and for network core interfaces, there is network ingress and network egress traffic, as shown in Service vs network traffic types.

The router uses QoS policies applied to a SAP for a service or to a network FP/port to define the queuing, queue attributes, and QoS marking/interpretation.

The router supports four types of service and network QoS policies:

• service ingress QoS policies

• service egress QoS policies

• network QoS policies

• network queue QoS policies

Services are configured with default QoS policies. Additional policies must be explicitly created and associated. There is one default service ingress QoS policy, one default service egress QoS policy, and one default network QoS policy. Only one ingress QoS policy and one egress QoS policy can be applied to a SAP or network entity.

When a new QoS policy is created, default values are provided for most parameters with the exception of the policy ID and queue ID values, descriptions, and the default action queue assignment. Each policy has a scope, default action, description, and at least one queue. The queue is associated with a forwarding class.

Service types and applicable service QoS policies lists which service QoS policies are supported for each service type.

Network QoS policies can be applied to the following entities:

• network interfaces

• Cpipe/Epipe/Ipipe and VPLS spoke SDPs

• VPLS spoke and mesh SDPs

• IES and VPRN interface spoke SDPs

• VPRN network ingress

• VXLAN network ingress

Network queue policies can be applied to:

• ingress FPs

• egress ports

Default QoS policies map all traffic with equal priority and allow an equal chance of transmission (Best Effort (be) forwarding class) and an equal chance of being dropped during periods of congestion. QoS prioritizes traffic according to the forwarding class and uses congestion management to control access ingress, access egress, and network traffic with queuing according to priority.

Network QoS policies define egress QoS marking and ingress QoS interpretation for traffic on core network IP interfaces. The router automatically creates egress queues for each of the forwarding classes on network IP interfaces.

A network QoS policy defines both the ingress and egress handling of QoS on the IP interface. The following functions are defined:

• ingress

  • defines DSCP, Dot1p, and IP criteria mappings to forwarding classes

  • defines LSP EXP value mappings to forwarding classes

• egress

  • defines DSCP and IP precedence mappings to forwarding classes

  • defines forwarding class to DSCP value markings

  • defines forwarding class to Dot1p/DE value markings

  • defines forwarding class to LSP EXP value markings

  • enables/disables remarking of QoS

  • defines FC to policer/queue-group queue mapping

The required elements to be defined in a network QoS policy are:

• a unique network QoS policy ID

• egress forwarding class to DSCP value mappings for each forwarding class

• egress forwarding class to Dot1p value mappings for each forwarding class

• egress forwarding class to LSP EXP value mappings for each forwarding class

• enabling/disabling of egress QoS remarking

• a default ingress forwarding class and in-profile/out-of-profile state

Optional network QoS policy elements include:

• DSCP name-to-forwarding class and profile state mappings for all DSCP values received

• LSP EXP value-to-forwarding class and profile state mappings for all EXP values received

• ingress FC fp-redirect-group policer mapping

• egress FC port-redirect-group queue/policer mapping

Network policy ID 1 is reserved as the default network QoS policy. The default policy cannot be deleted or changed.

The default network QoS policy is applied to all network interfaces that do not have another network QoS policy explicitly assigned. Default network QoS policy egress marking describes the default network QoS policy egress marking.

For network ingress, Default network QoS policy DSCP to forwarding class mappings and Forwarding class and enqueuing priority classification hierarchy based on rule type list the default mapping of DSCP name and LSP EXP values to forwarding class and profile state for the default network QoS policy.

Network queue policies define the network forwarding class queue characteristics. Network queue policies are applied on egress on core network ports or channels and on ingress FPs. Network queue policies can be configured to use as many queues as needed. This means that the number of queues can vary. Not all policies use the same number of queues as the default network queue policy. The multicast queues are only used at ingress.

The queue characteristics that can be configured on a per-forwarding class basis are:

• CBS as a percentage of the buffer pool

• MBS as a percentage of the buffer pool

• low drop tail as a percentage reduction from MBS

• PIR as a percentage of the FP ingress capacity or egress port bandwidth

• CIR as a percentage of the FP ingress capacity or egress port bandwidth

• FIR as a percentage of the FP ingress capacity or egress port bandwidth

Network queue policies are identified with a unique policy name that conforms to the standard router alphanumeric naming conventions.

The system default network queue policy is named default and cannot be edited or deleted. For information about the default network queue policy, see Network queue QoS policies.

Service ingress QoS policies define ingress service forwarding class queues and map flows to those queues. When a service ingress QoS policy is created by default, it always has two queues defined that cannot be deleted: one for the default unicast traffic and one for the default multipoint traffic. These queues exist within the definition of the policy. The queues only get instantiated in hardware when the policy is applied to a SAP. In the case where the service does not have multipoint traffic, the multipoint queues are not instantiated.

In the simplest service ingress QoS policy, all traffic is treated as a single flow and mapped to a single queue, and all flooded traffic is treated with a single multipoint queue. The required elements to define a service ingress QoS policy are:

• a unique service ingress QoS policy ID

• a QoS policy scope of template or exclusive

• at least one default unicast forwarding class queue. The parameters that can be configured for a queue are discussed in Queue parameters.

• at least one multipoint forwarding class queue

Optional service ingress QoS policy elements include:

• additional unicast queues up to a total of 31

• additional multipoint queues up to 31

• QoS policy match criteria to map packets to a forwarding class

To facilitate more forwarding classes, subclasses are supported. Each forwarding class can have one or multiple subclass associations for SAP ingress classification purposes. Each subclass retains the chassis-wide behavior defined to the parent class while providing expanded ingress QoS classification actions.

There can be up to 64 classes and subclasses combined in a sap-ingress policy. With the extra 56 values, the size of the forwarding class space is more than sufficient to handle the various combinations of actions.

Forwarding class expansion is accomplished through the explicit definition of sub-forwarding classes within the SAP ingress QoS policy. The CLI mechanism that creates forwarding class associations within the SAP ingress policy is also used to create subclasses. A portion of the subclass definition directly ties the subclass to a parent, chassis-wide forwarding class. The subclass is only used as a SAP ingress QoS classification tool; the subclass association is lost when ingress QoS processing is finished.

When configured with this option, the forwarding class and drop priority of incoming traffic are determined by the mapping result of the EXP bits in the top label. Forwarding class and enqueuing priority classification hierarchy based on rule type lists the classification hierarchy based on rule type.

Service egress queues are implemented at the transition from the service core network to the service access network. The advantages of per-service queuing before transmission into the access network are:

• per-service egress subrate capabilities especially for multipoint services

• more granular, fairer scheduling per-service into the access network

• per-service statistics for forwarded and discarded service packets

The subrate capabilities and per-service scheduling control are required to make multiple services per physical port possible. Without egress shaping, it is impossible to support more than one service per port. There is no way to prevent service traffic from bursting to the available port bandwidth and starving other services.

For accounting purposes, per-service statistics can be logged. When statistics from service ingress queues are compared with service egress queues, the ability to conform to per-service QoS requirements within the service core can be measured. The service core statistics are a major asset to core provisioning tools.

Service egress QoS policies define egress queues and map forwarding class flows to queues. In the simplest service egress QoS policy, all forwarding classes are treated like a single flow and mapped to a single queue. To define a basic egress QoS policy, the following are required:

• a unique service egress QoS policy ID

• a QoS policy scope of template or exclusive

• at least one defined default queue

Optional service egress QoS policy elements include:

• additional queues up to a total of eight separate queues (unicast)

• dot1p/DE, DSCP, and IP precedence remarking based on forwarding class

Each queue in a policy is associated with one of the forwarding classes. Each queue can have its individual queue parameters allowing individual rate shaping of the forwarding classes mapped to the queue.

More complex service queuing models are supported in the router where each forwarding class is associated with a dedicated queue.

The forwarding class determination per service egress packet is determined either at ingress or egress. If the packet ingressed the service on the same router, the service ingress classification rules determine the forwarding class of the packet. If the packet is received on a network interface, the forwarding class is marked in the tunnel transport encapsulation. In each case, the packet can be reclassified into a different forwarding class at service egress.

Service egress QoS policy ID 1 is reserved as the default service egress policy. The default policy cannot be deleted or changed. The default access egress policy is applied to all SAPs that do not have another service egress policy explicitly assigned. Default service egress policy ID 1 definition lists the characteristics of the default policy.

A scheduler policy defines the hierarchy and all operating parameters for the member schedulers. A scheduler policy must be defined in the QoS context before a group of virtual schedulers can be used. Although configured in a scheduler policy, the individual schedulers are created when the policy is applied to an object, such as a SAP or interface.

Scheduler objects define bandwidth controls that limit each child (other schedulers and policers or queues) associated with the scheduler. The scheduler object can also define a child association with a parent scheduler of its own.

A scheduler is used to define a bandwidth aggregation point within the hierarchy of virtual schedulers. The scheduler’s rate defines the maximum bandwidth that the scheduler can consume. It is assumed that each scheduler created has policers, queues, or other schedulers defined as child associations. The scheduler can also be a child which takes bandwidth from a scheduler in a higher tier.

A parent parameter can be defined to specify a scheduler further up in the scheduler policy hierarchy. Only schedulers in Tiers 2 and 3 can have parental association. When multiple schedulers, policers, and queues share a child status with the scheduler on the parent, the weight or strict parameters define how this scheduler contends with the other children for the parent’s bandwidth. The parent scheduler can be removed or changed at any time and is immediately reflected on the schedulers created by association of this scheduler policy.

When a parent scheduler is defined without specifying level, weight, or CIR parameters, the default bandwidth access method is weight with a value of 1.

If any orphaned policers or queues (where the specified scheduler name does not exist) exist on the ingress SAP and the policy application creates the required scheduler, the status on the queue becomes non-orphaned at this time.

Virtual scheduler internal bandwidth allocation shows how child queues, policers, and schedulers interact with their parent scheduler to receive bandwidth. The scheduler distributes bandwidth to the children by first using each child’s CIR according to the CIR-level parameter (CIR L8 through CIR L1 weighted loops). The weighting at each CIR-level loop is defined by the CIR weight parameter for each child. The scheduler then distributes any remaining bandwidth to the children up to each child’s rate parameter according to the Level parameter (L8 through L1 weighted loops). The weighting at each level loop is defined by the weight parameter for each child.

The following information describes QoS implementation restrictions:

• Creating additional QoS policies is optional.

• Default policies are created for service ingress, service egress, network, network queue, and slope policies. Scheduler policies must be explicitly created and applied to a port.

• Associating a service or access ports with a QoS policy other than the default policy is optional.

• A network queue, service egress, and service ingress QoS policy must consist of at least one queue. Queues define the forwarding class, CIR, and PIR associated with the queue.