OLT Migration to Using PON TLVs Instead of DSL TLVs

Before the introduction of PON-specific TLVs (see the Internet draft, Access Extensions for the Access Node Control Protocol), OLTs passed information about PON access line rates in the ANCP DSL TLVs. The DSL TLVs are overloaded with the PON data. In this situation, the access line type is classified as OTHER in the DSL-Type TLV (0x91). The raw PON line rates are conveyed in the Actual-Net-Data-Rate-Upstream TLV (0x81) and the Actual-Net-Data-Rate-Downstream TLV (0x82). For example, this is the behavior used for FTTH networks.

With the availability of the PON TLVs, OLTs provide PON access line information in one of the following ways:

• Only in DSL TLVs—OLTs that do not support the PON TLVs continue to send PON rates in DSL TLVs. This is the same situation as before the introduction of PON TLVs.

• Only in PON TLVs—OLTs that support the PON TLVs might use them exclusively to convey attributes for the subscriber access line and PON tree.

• In both DSL and PON TLVs—OLTs that support the PON TLVs might send them and also, redundantly, overload the DSL TLVs with the PON rates. This behavior enables the OLT to successfully provide rate information both to BNGs that support PON TLVs and BNGs that do not. The OLT is expected to provide both types of TLVs in both the ANCP port status messages and the PPPoE-IA tags.

The following expectations apply to OLTs that provide both DSL TLVs and PON TLVs:

• The OLT uses both types of TLVs for both ANCP port status messages and PPPoE-IA tags.

• The ANCP line attribute TLVs carry only the TLVs that match that line:

  • The DSL-Line-Attributes TLV (0x04) carries only DSL TLVs, including G.fast TLVs.

  • The PON-Access-Line-Attributes TLV (0x12) carries only PON TLVs.

  • The Access-Loop Encapsulation TLV (0x90) is independent of the transport method. The ANCP agent accepts and saves 0x90 when it is present in either the PON-Access-Line-Attributes TLV (0x12) or in PPPoE-IA tags.

• The access-line identification attributes are common to both DSL and PON access lines and convey the same information. This set of attributes consists of the following:

  • Access-Loop-Circuit-ID (0x01)

  • Access-Loop-Remote-ID (0x02)

  • Access-Aggregation-Circuit-ID-ASCII(0x03)

  • Access-Aggregation-Circuit-ID-Binary (0x04)

When the OLT sends both types of TLVs, the router accepts, saves, and process only one type or the other, according to a preference setting. The router saves or discards the corresponding line attribute that carries the TLVs for that line type. By default, the router prefers the PON TLVs over the DSL TLVs. This means that the router accepts the PON-Line-Attributes TLV (0x12) and discards the DSL-Line-Attributes-TLV (0x04).

You can change the preference with the preference (dsl | pon) option at the [edit system access-line attributes] hierarchy level. For example, when the PON TLVs are unreliable, perhaps because of an OLT issue, you might configure the router prefer the DSL TLVs for improved reliability.