Bandwidth Management Overview for Dynamic VLANs Based on Access-Line Identifiers
A router in a subscriber access network ensures class of service (CoS) for dynamic subscriber interfaces. An MX Series router with Modular Port Concentrator/Modular Interface Card (MPC/MIC) interfaces ensures that subscribers receive an adequate minimum bandwidth, referred to as the guaranteed rate, and maximum bandwidth, referred to as the shaping rate. For dynamic VLAN subscriber interfaces based on access-line identifiers (ALI), you can shape the bandwidth either at a per-household level for a dynamic ALI interface set, or at a per-subscriber level for a dynamic VLAN subscriber interface associated with an ALI interface set.
To help you manage bandwidth efficiently and economically for ALI-based dynamic VLAN subscriber interfaces for PPPoE subscribers, you can configure the router to use specific PPPoE vendor-specific attributes (VSAs) found in PPPoE control packets to adjust the CoS shaping-rate and overhead-accounting attributes for dynamic ALI interface sets and their associated ALI-based dynamic VLAN subscriber interfaces.
This overview covers the following topics:
CoS Shaping Rate Adjustment
The CoS shaping rate adjustment is based on the value of the Actual-Data-Rate-Downstream DSL Forum VSA [26-130] found in PPPoE Active Discovery Initiation (PADI) and PPPoE Active Discovery Request (PADR) control packets for PPPoE traffic. The Actual-Data-Rate-Downstream VSA contains the actual downstream data rate, in bits per second, of the subscriber’s synchronized DSL link.
To configure the router to use the Actual-Data-Rate-Downstream
VSA to adjust the CoS shaping-rate attribute, include the vendor-specific-tags statement with the actual-data-rate-downstream option
at the [edit dynamic-profiles profile-name class-of-service dynamic-class-of-service-options] hierarchy
level in either the dynamic profile that defines the ALI interface
set or the dynamic profile that configures the associated dynamic
PPPoE (pp0) subscriber interface.
When you enable this feature, the value of the Actual-Data-Rate-Downstream
VSA overrides the shaping-rate value configured at the [edit dynamic-profiles profile-name class-of-service
traffic-control-profiles] hierarchy level only if the Actual-Data-Rate-Downstream
VSA value is less than the shaping-rate value configured
with the CLI.
CoS Overhead Accounting Adjustment
The CoS overhead accounting adjustment is based on the value of the Access-Loop-Encapsulation DSL Forum VSA [26-144] found in PADI and PADR control packets for PPPoE traffic. The Access-Loop-Encapsulation VSA identifies the encapsulation used by the subscriber associated with the DSL access multiplexer (DSLAM) access loop from which requests are initiated.
The value of the Data Link subfield in the Access-Loop-Encapsulation VSA determines the overhead accounting mode in use on the access loop. If the Data Link subfield value is 0 (ATM Adaptation Layer 5, or AAL5), the access loop uses cell-mode encapsulation. If the Data Link subfield value is 1 (Ethernet), the access loop uses frame-mode encapsulation.
In subscriber access networks where the router passes downstream ATM traffic to Ethernet interfaces, the different Layer 2 encapsulations between the router and the PPPoE Intermediate Agent on the DSLAM make managing the bandwidth of downstream ATM traffic difficult. Using the Access-Loop-Encapsulation VSA to shape traffic based on frames or cells enables the router to adjust the overhead-accounting attribute to apply the correct downstream rate for the subscriber.
To configure the router to use the Access-Loop-Encapsulation
VSA to adjust the CoS overhead-accounting attribute, include the vendor-specific-tags statement with the access-loop-encapsulation option at the [edit dynamic-profiles profile-name class-of-service dynamic-class-of-service-options] hierarchy
level in either the dynamic profile that defines the ALI interface
set or the dynamic profile that configures the associated dynamic
PPPoE (pp0) subscriber interface.
When you enable this feature, the value of the Access-Loop-Encapsulation
VSA always overrides the overhead-accounting value configured
at the [edit dynamic-profiles profile-name class-of-service traffic-control-profiles] hierarchy level.
Dynamic Profiles and Adjustment of CoS Shaping Rate and Overhead Accounting
When you configure the router to use either or both of the Actual-Data-Rate-Downstream VSA value and Access-Loop-Encapsulation VSA value to adjust the CoS shaping rate and overhead accounting attributes, respectively, the router adjusts these attributes when the dynamic ALI interface set is created and the router receives the PADI and PADR packets from the first subscriber interface belonging to the ALI interface set.
You can configure CoS adjustment based on either or both VSAs in either or both of the following dynamic profiles:
To configure adjustment of the CoS shaping rate and overhead accounting on a per-household basis, use the dynamic profile that defines the dynamic ALI interface set.
To configure adjustment of the CoS shaping rate and overhead accounting on a per-subscriber basis, use the dynamic profile that defines the ALI-based dynamic PPPoE (
pp0) subscriber interface associated with the ALI interface set.
Table 1 summarizes how the dynamic profile in which you configure CoS adjustment for ALI-based dynamic VLANs using one or both VSAs affects the router behavior.
VSAs Specified in ALI Interface Set Dynamic Profile |
VSAs Specified in PPPoE Subscriber Interface Dynamic Profile |
Result |
|---|---|---|
Yes |
No |
Router adjusts specified CoS attributes only for dynamic ALI interface set |
No |
Yes |
Router adjusts specified CoS attributes only for ALI-based dynamic PPPoE subscriber interface |
Yes |
Yes |
Router adjusts specified CoS attributes for both dynamic ALI interface set and ALI-based dynamic PPPoE subscriber interface |
No |
No |
Router does not adjust CoS attributes for either the dynamic ALI interface set or the ALI-based dynamic PPPoE subscriber interface |
Guidelines for Configuring Adjustment of CoS Shaping Rate and Overhead Accounting
You can also configure the router to use the Actual-Data-Rate-Downstream VSA and Access-Loop-Encapsulation VSA values in PPPoE control packets to adjust the CoS shaping rate and overhead accounting attributes, respectively, for dynamic subscriber interfaces not associated with dynamic ALI interface sets.
With the exception of the constraints described in Restrictions for Configuring Adjustment of CoS Shaping Rate and Overhead Accounting for Dynamic ALI Interface Sets, most of the guidelines and restrictions that apply to this feature for use with dynamic subscriber interfaces that are not based on ALIs also apply to its use for dynamic ALI interface sets and their associated ALI-based dynamic VLAN subscriber interfaces.