Hierarchical Quality of Service (HQoS) Overview
Hierarchical Quality of Service (HQoS) is a traffic classification and prioritization framework that allows you to provide different Service Level Agreements(SLAs) on bandwidth usage. It allocates network resources to services on a prioritized basis. This is achieved by classifying, policing, shaping, scheduling and remarking the traffic based on service types. The HQoS service can be applied to Ethernet, IPv4, IPv6 or MPLS packets. The framework supports QoS at multiple levels. At only one level it allows you to allocate resources between services, but when configured at multiple levels through HQoS, it allows complex prioritization schemes.
The RtBrick Full Stack (RBFS) uses the following HQoS mechanisms:
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Classifier: Classifies each incoming packet as belonging to a specific class, based on packet contents. Supported classifiers are Behavior Aggregate (BA) and Multifield (MF). In the BA classifier, packets are classified according to the CoS field: IEEE 802.1p, IPv4/v6 ToS/TC, or MPLS EXP. In the MF classifier, packets are classified using additional fields in the IP header: source IPv4/IPv6 prefix, destination IPv4/IPv6 prefix, L4 source port, L4 destination port, and/or IP protocol.
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Policer: Policer is implemented in the ingress to drop the unwanted traffic. Policer supports the Committed Information Rate (CIR), the Committed Burst Size (CBS), the Peak Information Rate (PIR), and the Peak Burst Size (PBS). Drop behavior is to either mark traffic as green, yellow, or drop.
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Queuing: Drop unqualified packets in advance using the Weighted Random Early Detection (WRED) technology in the case of congestion to ensure bandwidth for qualified services. This is performed at the egress.
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Scheduler: Manage traffic on a device using different algorithms for queue scheduling. Such algorithms include Fair Queuing (FQ), Weighted Round Robin (WRR), and Strict Priority (SP). Queues can be connected to schedulers and schedulers can also be connected to other schedulers.
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Shaper: Shaper is implemented in the egress, traffic shaping involves buffering and delaying traffic to shape the flows. Shapers are implemented either on queues or schedulers.
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Remarking: Remarking allows you to rewrite the outgoing packet’s codepoint. Remarking can be performed in the ingress or the egress side of the hardware pipeline.
The figure below shows how QoS does ingress and egress traffic management
The sections below provide a description of various HQoS components that are configured for both ingress and egress traffic.
QoS Profiles
A profile configuration defines the QoS profile that is attached to either a Subscriber interface or an L3 interface.
Profile maps the following QoS constructs to a Subscriber or an L3 interface:
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Behavioral Aggregate (BA) Classifier
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Multifield (MF) Classifier
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Class Policer Map
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Policer
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Class Queue Map
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Scheduler Map
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Remark Map
Behavior Aggregate (BA) Classifier
Classifiers assign the class to which a packet belongs. BA classification is performed on the ingress and maps incoming packet codepoint to a predefined class. BA Classification relies upon markings (that is, codepoint) placed in the headers of incoming packets:
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IEEE 802.1p: Priority - 3 bits
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IPv4: Type of Service byte (ToS) - 8 bits.
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IPv6: Traffic Class (TC) - 8 bits.
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MPLS: Experimental bits (EXP) - 3 bits.
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Classifier configuration has the following guidelines and limitations:
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For IPv4: Only ToS-based classification is possible. Currently, DSCP-based classification is not supported.
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For IPv6: TC-based classification is possible.
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For EXP classification, RBFS uses the uniform mode to copy MSB 3-bits from 8-bits IPv4-ToS or IPv6-TC to the EXP field at the time of MPLS encapsulation at the remote box. IPv4/IPv6 Classifiers do not classify labeled traffic, hence MPLS Classifier is required for the same.
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Ingress Remarking
Ingress remarking is achieved by configuring the “remark-codepoint” field in the Classifier. Ingress remarking rewrites the IPv4-ToS or IPv6-TC field of the incoming packet at the ingress side with configured remark-codepoint. Note that the ingress remarking is not supported for the BA Classifier with match-type MPLS-EXP.
Multifield (MF) Classifier
Multifield (MF) classifiers assign the class to which a packet belongs based on multiple fields. Unlike the BA classifier, where only CoS fields are used for classification, the MF classifier additionally uses the following fields:
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class: traffic class of the packet (class-0 to class-7) set by prior BA classifier
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source prefix: source IPv4 or IPv6 prefix
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destination prefix: destination IPv4 or IPv6 prefix
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protocol: UDP or TCP
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source port: UDP or TCP source port
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destination port: UDP or TCP destination port
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qos markings: IPv4 TOS or IPv6 TC header value
The actions supported by a Multifield Classifier are:
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class: traffic class to be set (class-0 to class-7)
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Remark codepoint: remark codepoint for ingress remarking
RBFS treats all the incoming IPv4-TOS or IPv6-TC QoS field values in the incoming packet as untrusted. So a user is required to set action-remark-codepoint in the MF Classifier configuration to mark the QoS bits in the IP header of the outgoing packet. If action-remark-codepoint is not configured in the MF Classifier, the default value 0 shall be marked in the packet.
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The Multifield Classifiers can be bound globally (global.qos.global.config) or via QoS profile (global.qos.profile.config). The global Multifield Classifier applies to all traffic from any instance or interface. The Multifield Classifier assigned via the QoS profile applies only to ingress traffic received on the interface where the profile is bound to it.
The Multifield Classifier is processed after BA classification which allows it to match on selected class from BA classification or to change the assigned class by more granular match conditions. Both classification stages (BA and MF) are optional, they can be combined or used alone, controlled by configuration.
Multifield Classifiers cannot be bound to MPLS core interfaces. Therefore, the downstream traffic (from core to subscriber) should be classified via global Multifield Classifier, while upstream traffic (from subscriber to core) can be classified via Multifield Classifier from the QoS profile, which is instantiated per subscriber with an implicit match on ingress logical interface (InLIF).
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Match MPLS traffic
If MF Classifier is to be applied for MPLS traffic (that is, DOWNSTREAM traffic), match MPLS traffic has to be configured in the MF ACL. If not configured, traffic may or may not match the MF ACL entry in the h/w.
Ingress Remarking
Ingress remarking is achieved by configuring the “action remark-codepoint” in the MF Classifier. Ingress remarking rewrites the IPv4-ToS or IPv6-TC field of the incoming packet at the ingress side with configured remark-codepoint.
RADIUS Controlled Dynamic MF Classifier
As described in RBFS RADIUS Services document dynamic MF Classifier mapping is supported. The dynamic MF Classifier when configured overrides the MF Classifier mapped via QoS profile for the corresponding subscriber but not other subscribers.
For information about configuring the MF Classifier, see [mf_classifier_configuration].
Policer
Policer defines the rate at which certain applications can access the hardware resource. So as to rate-limit the traffic from an application, the policer hard-drops the unwanted packets on the ingress side.
In RBFS, policers support the “two-rate, three-color” type in a 4-level cascaded mode. This means that each policer level has two rates (CIR and PIR) and three colors (green, yellow and red) with two token buckets as shown below.
This means that traffic below CIR is marked green. Traffic above CIR but below PIR is yellow and above PIR is red. Traffic marked red will be dropped. Traffic marked yellow can be demoted by changing ToS, TC, or EXP using remark map.
In 4-level cascade mode, unused tokens can be passed from higher priority levels to lower priorities where level 1 has the highest and level 4 has the lowest priority as shown in the figure below.
Therefore a lower level configured with CIR 0 can still serve traffic if higher priority levels are not consuming all available tokens.
The available tokens per level are calculated by remaining CIR credits from upper levels and additional credits based on configured CIR per level. Per default, the resulting tokens are not limited. The optional max CIR rate attribute limits tokens from CIR and upper levels. Let us assume levels 1 and 2 are both configured with a CIR of 2Mbps. Without max CIR or max PIR (default behaviour) level 2 can reach up to 4Mbps (level 1 CIR/PIR plus level 2 CIR/PIR). This can be limited by max CIR (for example, 3Mbps). If both level 1 and level 2 have a committed information rate (CIR) of 2Mbps, then level 2 can reach a maximum of 4Mbps (which is the sum of level 1 CIR and level 2 CIR) without any consideration for the maximum CIR. However, the maximum CIR is not relevant for level 1.
Example
| CIR | RX | TX | PIR | RX | TX | |
|---|---|---|---|---|---|---|
L1 |
2M |
1M |
1M |
2.5M |
1M |
1M |
L2 |
3M |
20M |
9M |
3.5M / max CIR 8 |
20M |
8M |
L3 |
4M |
20M |
0M |
4.5M |
20M |
1M |
L4 |
1M |
20M |
0M |
1.5M |
20M |
0M |
SUM |
10M |
61M |
10M |
12M |
61M |
10M |
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Here,
Mindicates Mbps (Megabits per second)
In columns 2 through 4 of the preceding example table, L1 consumes only 1Mbps of the available 4Mbps and passes the remaining 3Mbps to L2 which adds 6m based on their own configured CIR resulting in 9m.
In columns 5 through 7 of the preceding example table, L1 consumes only 1Mbps of the available 4Mbps and passes the remaining 3m to L2 which adds 6Mbps based on their own configured CIR resulting in 9Mbps. But because of the CIR limit set to 8Mbps, only 8Mbps of 9Mbps can be used at this level. The remaining 1Mbps is now passed to L3 which does not add additional CIR-based credits. In both examples, L4 would be able to reach up to 10Mbps if upper levels are not consuming credits.
RADIUS Controlled Dynamic Policer
The RBFS RADIUS services support dynamic policer rate updates. The dynamic policer rate when configured affects only the QoS instance of the corresponding subscriber but not other subscribers.
Class-Policer-Map
Since RBFS supports up to 8 classes but only four policer levels, there is a need to map multiple classes to the same policer level. A class-policer-map defines such mappings. Using class-policer-map configuration, one can map any class to any supported policer level (that includes mapping multiple or all classes to the same level). Similar to a policer, a class-policer-map is attached to a profile.
| If class-to-level mapping is not configured, no policing will be applied to the traffic for that class. |
Queueing
Queuing helps to drop unwanted traffic in advance at the ingress side in case of congestion. This is to ensure bandwidth for qualified services.
RBFS supports the following queueing techniques:
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Tail Drop (TD): This is a conventional congestion avoidance technique. When the network is congested, drop subsequent packets from the queue.
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Weighted Random Early Detection (WRED): This technique requires configuring “Minimum Threshold”, “Maximum Threshold” and “Drop Probability”, which define the start and end range where packets may get discarded. When the average queue size is below the minimum threshold, no packets will be discarded. The drop_probability parameter can be used to specify the drop probability at the max threshold. When the average queue size is between the min and max threshold, the drop probability increases linearly from zero percent (at the min threshold) to drop_probability percent (at the max threshold). When the average queue size is greater than the maximum threshold, all packets are discarded.
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When the average queue size is less than the “Minimum Threshold”, no packets will be discarded.
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When the average queue size is greater than the “Maximum Threshold”, all packets are discarded.
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When the average queue size is between “Minimum Threshold” and “Maximum Threshold”, the drop probability increases linearly from zero percent (at the minimum threshold) to drop probability (at the max threshold).
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RADIUS Controlled Dynamic Queue
As described for RBFS RADIUS Services document dynamic Queue buffer size updates are supported. The dynamic Queue buffer values when configured affect only the QoS instance of the corresponding subscriber but not other subscribers.
Traffic Class to Queue Mapping
The traffic class to queue mapping defines the mapping of classes and queues. The Traffic Class to Queue Mapping is attached to a profile.
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Queue-Group
A Queue Group defines the Queue bundle. A Queue Group contains bundle of either 1 or 4 or 8 queues.
Scheduler
A scheduler configuration defines scheduler parameters such as type and shaping rate. The shaping rate defined for a scheduler applies to queue(s) associated with it. NOTE: For 1 Queue in Queue-Group, scheduler is not applicable.
The following scheduler types are supported:
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Fair Queueing (FQ): Uses a round-robin approach to select the next packet to service. This method ensures that all the flows are serviced equally. Configure scheduler type as fair_queueing to create FQ scheduler.
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Weighted Fair Queueing (WFQ): Uses a round-robin approach but with no guarantee of flow being serviced equally (like in FQ). The rotation of the next packet to service is based on the weight that is assigned to each flow. Configure scheduler type as weighted_fair_queueing to create WFQ scheduler.
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Supported weight: 1 to 253
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| In any WFQ scheduler, the lower the weight, the higher the bandwidth portion is awarded. |
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Strict Priority (SP): Uses priority-based approach to service the flow. SP schedulers are supported in “hybrid” mode only. Hybrid mode combines FQ-WFQ schedulers using strict priority.
| The priority order for SP is: strict_priority_0 > strict_priority_1 > strict_priority_2 > strict_priority_3 (where strict_priority_0 being highest priority and strict_priority_3 being lowest) |
The following SP scheduler types are supported:
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2 Strict Priority (2SP): Uses SP between 1-FQ and 1-WFQ. There are the following types of 2SP hybrid schedulers:
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type “2sp_wfq_independent”
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Supported weight: 1 to 63
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type “2sp_wfq_discrete”
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Supported weight: { 1, 2, 3 }
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type “wfq_independent_2sp”
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Supported weight: 1 to 63
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type “wfq_discrete_2sp”
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Supported weight: { 1, 2, 3 }
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3 Strict Priority (3SP): maps 2-FQs and 1-WFQ
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type: “3sp_wfq_discrete“
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Supported weight: { 1, 2 }
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4 Strict Priority (4SP): maps 4-FQs using SP
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type “strict_priority"
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Priority Propagation
Hierarchical QOS (HQoS) on RBFS is implemented by connecting or chaining queues to scheduler elements (Q — > SE), scheduler elements to each other (SE — > SE), and scheduler elements to ports (SE — > PORT). Each scheduler element can have different child connection points based on types described in the section Scheduler.
This means that sched_0 in the example below is not scheduling between the attached queues, but between the different child connection points SP0 to SP3. The scheduler element sched_0 cannot differentiate between Q1 and Q2 in this example because both are connected to SP2.
Without priority propagation, each scheduler element can have multiple child connection points but just one parent connection point. Therefore traffic leaving a scheduler element cannot be differentiated by the parent scheduling element. The parent scheduler element sched_1 receives the traffic from sched_0 on the selected child connection point. As already mentioned scheduling within a scheduler element happens between child connection points. Second, a scheduler element has only one parent connection point which can be connected to a child connection point of another scheduler element (output of sched_0 → input of sched_1). This results in the situation that all traffic from this SE is handled equally regardless of the queue. This may lead to dropped priority traffic like voice or control traffic in case of congestion in parent elements. For example, if sched_1 has a shaping rate lower than the one of sched_0, it will drop traffic unaware of its original priority.
This problem is addressed with priority propagation which is enabled by default.
With priority propagation, the scheduler elements operate in a dual-flow mode with high and low-priority flows. The credits generated from the physical interface will be consumed by all attached high-priority flows first and only the remaining credits will be available for low-priority flows. In this mode, an implicit FQ element is created for each scheduler element. All queues assigned to low-priority flow will be attached to this element.
An additional composite option of the scheduler element allows also the differentiation between multiple low-priority queues if required. This composite type is created implicitly and does not need to be configured.
Without priority propagation enabled, each scheduler element consumes only one scheduler resource compared to two elements if enabled. The composite type consumes three scheduler elements.
With priority propagation disabled, all traffic is considered a high-priority flow.
Now for each queue, we can select if connected to high-priority or low-priority flow where high-priority flow is selected per default if not explicitly mentioned.
Assuming the example as before but with priority propagation and Q0 assigned to low-priority flow and Q1 - Q3 assigned to high-priority flow.
The figure below shows a typical multi-level QoS configuration without priority propagation on the left and with priority propagation on the right side.
The credits generated from the physical interface will be consumed by high-priority flow first and the remaining credits will be available for low-priority flow. The high-flow traffic at any one element is scheduled based on the type and connection point. Between schedulers, it depends on how they are connected to the parent scheduling element. Per default all levels there is FQ for low and FQ for high-priority flows. The port scheduler is also FQ.
In this mode, each shaper supports two different rates for low and high-priority where the actual shaper rate is the sum of low and high-priority rates. If the low-priority rate is zero, this flow is only served if the high-priority flow is not consuming all credits. An example might be a high rate of 9Mbps and a low rate of 1Mbps which results in 10Mbps for low-priority flow if high-priority flow is not consuming any packets but at least 1Mbps is ensured.
The following example shows a typical access service provider configuration with priority propagation enabled with and without composite type.
Simple Priority Propagation Scheduling Example
Without priority propagation, the parent scheduler drops traffic equally from all classes as it is unaware of priorities:
With priority propagation, the parent scheduler serves high-priority flows first as shown in the figure below:
With priority propagation and dual-flow shaping, the parent scheduler serves high-priority flows first up to the high-flow shaping rate:
Shaper
Shaper is used to rate-limit the traffic at the egress. In RBFS, shapers can be attached to both Queue and Scheduler.
A shaper configuration defines the shaping rate in Kilo-bits-per-seconds (Kbps).
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Low-rate Shaping
The Low-rate Shaping feature performs queueing and scheduler-level traffic shaping to rates lesser than 1000 Kbps so that the higher-priority (voice) traffic to flow at optimal levels.
| Low-rate Shaping is supported only on high-priority flows, that is high-flow configuration parameter. |
RBFS Access-Leaf and Consolidated-BNG platforms have been enabled with Low-rate Shaping by default. For information about the Low-rate Shaping feature enabled platforms, see section "Feature/Resource Usage in the Platform Guide.
RADIUS Controlled Dynamic Shapers
RBFS RADIUS services support dynamic shaper updates. The dynamic shaper when configured affects only the QoS instance of the corresponding subscriber but not other subscribers.
Scheduler Mapping
Scheduler Map defines the set of relationships between parents and children in egress scheduling hierarchy. A child in a Scheduler Map configuration can be either Queue or Scheduler. A parent in a Scheduler Map configuration can be either a Port or Scheduler.
| For 1 Queue in Queue-Group, scheduler-map is not applicable. Connection Point and Weight |
Child-queue or child-scheduler in a scheduler map configuration is connected to the parent-scheduler at “connection point (CP)“. Connection point configuration also has “weight” associated with it if the parent has a WFQ scheduler corresponding to that connection point. The valid connection point value for a child to connect to parent WFQ/FQ scheduler is no_priority and to connect to parent SP/Hybrid scheduler is between strict_priority_0 to strict_priority_3 (based on a number of Strict Priority points in parent scheduler).
Connection Types
There are five connection types in a scheduler map entry:
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queue_to_port
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queue_to_scheduler
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scheduler_to_scheduler
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scheduler_map_to_scheduler_map
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scheduler_to_port
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Remarking
The packet markers set the codepoint in a packet to a particular value, adding the marked packet to a particular behavior aggregate. When the marker changes the codepoint in a packet, it "remarks" the packet. The codepoint in a packet can be IPv4-ToS, IPv6-TC, MPLS-EXP, or IEEE 802.1p field.
The following remarking options are supported in RBFS:
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IEEE 802.1p : Priority - 3 bits.
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IPv4: Type of Service byte (ToS) - 8 bits.
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IPv6: Traffic Class (TC) - 8 bits.
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MPLS-IPv4: MPLS Experimental bits (EXP) - 3 bits.
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MPLS-IPv6: MPLS Experimental bits (EXP) - 3 bits.
IPv4/v6 and IEEE 802.1p remark-map are applied on an interface - subscriber-ifl or l3ifl using Profile Name.
MPLS-IPv4/v6 remark-map is applied either globally or per instance (to support multiple VPN marking schemes) using Remark-Map Name.
In RBFS, remarking can be performed at the ingress or egress:
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Ingress remarking is achieved by configuring the remark-codepoint field in the Classifier. Ingress remarking rewrites the IPv4-ToS or IPv6-TC at the ingress side with configured remark-codepoint. The configured remark-codepoint can be modified again at the egress side using remark-map. The ingress remarking is supported for IPv4, IPv6, and IEEE 802.1p BA classifiers. Ingress remarking is supported in MF Classifier as well.
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Egress remarking is achieved by configuring the remark-map. Remark Map is the mapping of match-codepoint and color to remark-codepoint. Egress remarking helps to remark the IPv4-ToS / IPv6-TC field in the IP header, or to write the EXP field in the MPLS label(s), or to write the IEEE 802.1p field in the VLAN header.
Here Color is used to set different remark-codepoint for same match-codepoint based on color marked by the Policer (i.e. green or yellow). Color is a mandatory field in remark-map. To set the same remark-codepoint for a match-codepoint irrespective of color, we have to set color as “all”.
IPv4-ToS, IPv6-TC, or MPLS-EXP remarking:
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If the remark-codepoint is not configured in the BA Classifier or there is no hit in MF Classifier, match-codepoint in the remark-map is the ToS/TC value of the incoming IP packet.
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If the remark-codepoint is configured in the BA Classifier and there is no hit in the MF Classifier, match-codepoint is the same value as the remark-codepoint in the BA Classifier
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Irrespective of the remark-codepoint configured in the BA Classifier, if there is a hit in the MF Classifier the match-codepoint is the same value as the action remark-codepoint (0 if no action remark-codepoint configured) in the MF Classifier.
IEEE 802.1p VLAN remarking:
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L2BSA L2X VLAN Priority Remarking:
The L2BSA L2X VLAN priority remarking support for the platforms is as follows: Only A10NSP switches support VLAN operations, access-leaf is transparent.
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Downstream Traffic (Remote ISP to Subscriber):
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On A10NSP Switch:
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The class derived from the VLAN Pbit Classifier is used to remark MPLS Exp and Outer VLAN IEEE-802.1 Pbit Value, inner VLAN Pbit is transparent.
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On Q2C Access Leaf:
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The received Outer VLAN IEEE-802.1 Pbit value is retained, explicit remarking at access-leaf is not supported.
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-
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Upstream Traffic (Subscriber to Remote ISP):
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On Q2C Access Leaf:
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To remark the outgoing packet, global MPLS Exp remark map can be used.
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On A10NSP Switch:
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To remark the outgoing packet, VLAN IEEE-802.1 Pbit remark map can be used.
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For more information about L2BSA configurations, see the L2BSA User Guide.
L2VPN VLAN Manipulation QoS Remarking:
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VLAN remarking allows for various VLAN manipulations (push, swap, push-push, swap-swap, swap-push) on the outer VLAN in double-tag or single-tag scenarios.
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VLAN remarking for VLAN manipulation involving POP operations (pop, pop-pop, pop-swap) is not supported.
Header Compensation
Queue Compensation
The rate at which the packets are dequeued from a queue depends on the credit received by that queue. The source of the credit received by a queue is the egress port to which the queue is mapped. When a packet is dequeued, the credit balance is decreased by the packet size. But, the packet size that is used must be adjusted to model the packet size at the egress, rather than its actual size at the ingress queue. Thus the header compensation is used to adjust for the differences in header size between ingress queue and egress port. RBFS supports static header compensation configuration per queue (in bytes).
Port Compensation
Similar to queue header compensation where header compensation is performed at the per-queue level, RBFS supports the following header compensation at the per-port level:
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Ingress Header Compensation: In line with the header compensation option that we have per-queue, RBFS supports static header compensation configuration at the ingress to be used by the policing. Header compensation changes the effective size of the packet to compensate for changes in header size (such as the CRC removal) when considering the packet for policing. Unlike queue, RBFS ingress header compensation configuration is per ingress port (in bytes).
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Egress Header Compensation: In line with the header compensation option that we have per-queue or per-port at the ingress, RBFS supports static header compensation configuration at the egress. The egress header compensation configuration is per egress port (in bytes).
| The supported range for header compensation is -64 to +64 bytes. |
L2TP QoS
The Layer 2 Tunneling Protocol (L2TP) QoS for upstream is similar to any other locally terminated subscriber. The QoS Profile is mapped dynamically via RADIUS for the L2TP subscribers.
The L2TP QoS for Downstream requires IPv4-TOS based BA Classifier which is mapped to L2TP Tunnel. The same can be achieved by attaching l2tp-classifier-name in global QoS configuration.
forwarding-options {
class-of-service {
global {
l2tp-classifier-name l2tp-ip;
}
}
}
For Downstream queueing, there is no change. Queueing is applied using QoS Profile similar to locally terminated Subscribers.
The following features are supported for L2TP QoS.
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Upstream
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BA Classifier: IEEE 802.1p
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Policing
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Policer statistics
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Remarking
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|
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Downstream
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BA Classifier: IPv4-TOS
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Queueing/Scheduling/Shaping
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Queue statistics
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Remark-Map: IEEE 802.1p (Class to VLAN priority remarking)
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Guidelines
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To avoid control traffic policing/shaping, the assumption is that the IEEE 802.1p bits in Upstream or IPv4-TOS bits in Downstream will be different for control and data traffic, control traffic is expected to have the highest precedence.
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Upstream classification is based on IEEE 802.1p bits.
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Downstream classification is based on IPv4-TOS bits of the outer IP header.
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PBIT (IEEE-802.1p) classification and policing for the upstream traffic from IPoE subscribers is not supported.
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It is recommended to configure MFC (multi-field classifier) for the upstream classification for subscriber traffic.
Multi-level H-QoS : Level-1 to Level-5
A sample 5-level requirement looks like this.
- Level-1 (IFP)
-
Physical Interface Shaper.
- Level-2 (PON TREE)
-
Each PON tree is a TDM based shared medium with typically ~2.5 GBit/s (GPON) shared by up to 32 consumers (ONT or DPU).
- Level-3 (DPU)
-
In case of FTTB there is a single DPU with multiple consumers via G.Fast DSL connected which requires an additional hierarchy. This level is not needed for FTTH or FTTC.
- Level-4 (ANP or Session)
-
The Access Node Port (ANP) or outer VLAN level describes a single customer line. This might be an ONT in case of FTTH or DSL interface behind a DPU in case of FTTB. This level can be also represented on PPPoE sessions as long as just one session is permitted per VLAN.
- Level-5 (QUEUE)
-
The Queue level shaper is required to limit the class-of-service bandwidth like Voice or IPTV traffic limit.
The figure below shows the diagram along with QoS representing Level-1 to Level-5 Hierarchical scheduling.
Levels 4 and 5 are configured per logical interface (i.e. subscriber-ifl or l3-ifl). Separate scheduler-map representing levels 1 to 3 connectivity shall be statically configured and mapped to the corresponding physical interface (IFP).
The child scheduler in a subscriber scheduler map is connected to the parent scheduler in a physical interface scheduler map using the following way:
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Dynamically via RADIUS in case of dynamic subscribers like PPPoE sessions (Subscriber-IFL).
The figure below shows the same details as the preceding figure before with the different levels but from the DPU-PON-IFP scheduler-map point of view.
QoS Support for L2 and L3 Logical Interfaces
QoS is supported on Layer 2 and Layer 3 logical interfaces.
Support Interface-set for Grouping Logical Interfaces
An interface-set is a collection or group of logical interfaces (that is, L2 or L3) belonging to the same physical interface (IFP).
QoS Support for Interface-set Hierarchy
QoS can be configured at the interface-set hierarchy (service-group), and the IFLs belonging to this interface-set must configure the service-group scheduler to connect to the PON scheduler or directly to the IFP.
Business Service QoS
A business service can be leveraged using an interface-set. A business service comprises of a number of logical interfaces. QoS can be configured at the interface-set hierarchy (service-group) and at the logical interface level as well.
The logical-interface-scheduler is connected to an interface-set (business service group) scheduler and the interface-set-scheduler can be connected to a PON-scheduler or directly to a port-scheduler.
MPLS HQoS
The MPLS HQoS has both UNIFORM and PIPE modes. These modes provide the following functionality:
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During MPLS Encapsulation, MPLS Mode is UNIFORM. MSB 3-bits from 8-bits IPv4-ToS or IPv6-TC are copied to the EXP bits of the newly added MPLS header(s).
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During MPLS Decapsulation, MPLS Mode is PIPE. 8-bit IPv4-ToS or IPv6-TC will be retained and hence it provides ToS/TC codepoint transparency.
For the Uniform MPLS mode mapping between IPv4-ToS or IPv6-TC to MPLS-EXP see the table below:
| IPv4-TOS / IPv6-TC | EXP | DSCP |
|---|---|---|
0-31 |
0 |
0-7 |
32-63 |
1 |
8-15 |
64-95 |
2 |
16-23 |
96-127 |
3 |
24-31 |
128-159 |
4 |
32-39 |
160-191 |
5 |
40-47 |
192-223 |
6 |
48-55 |
224-255 |
7 |
56-63 |