IP Profile Question

Hey all

General question ...

When an IP profile change happens (up or down) ... does this cause the FTTC modem to disconnect and re-sync or does it keep the connection established and dynamically increase the sync speed?

TIA

In reply to a post by Bobby_Valentino:

Hey all

General question ...

When an IP profile change happens (up or down) ... does this cause the FTTC modem to disconnect and re-sync or does it keep the connection established and dynamically increase the sync speed?

TIA

Anyone?

The DSL sync speed is governed entirely by the line conditions and the limits which have been set by DLM.

The IP Profile is set on the upstream BRAS and the DSLAM is completely unaware of this.

The relationship is in the opposite direction: the IP profile is applied *after* the DSL link has been established. When a PPPoE session is started (or DHCP), the DSLAM adds some extra attributes saying the sync speed. The BRAS can see these attributes and select an IP profile appropriately - typically as part of an exchange with a RADIUS server.

If someone changes the settings in the RADIUS server, they won't be applied on the BRAS until the session is re-established.

If the DSLAM retrains by itself, then the BRAS won't learn about the new profile until the session is re-established (although a DSLAM retrain does typically cause a loss of connectivity to force a session to be re-established).

However, any change to the BRAS profile doesn't cause a DSL retrain - there's no mechanism for this. In any case, the DSL modems always negotiate the maximum speed available, subject to line conditions and the boundaries set by DLM, independently of whatever IP profile the BRAS decides to apply.

The reply from @candlerb is an excellent full technical description of the process of FTTC speed changes and IP profiles which you may find rather complex.

Here's a simpler answer:- when the DSLAM decides to change the sync speed a disconnect and re-sync takes place.

However there is a method called SRA (Seamless Rate Adaptation) which as you suggested can dynamically adjust the sync speed without dropping the connection. I believe it is used on G.Fast connections
Openreach did some small scale FTTC trials of this around 4 or 5 years ago but it was never implemented, not sure why.

In reply to a post by Realalemadrid:

not sure why.

I believe it was reported on thinkbroadband that with the random range of routers/devices/boxes on the end of the copper wire that are not controlled by Openreach, SRA didn't improve reliability.

Thankfully with FTTP there is an active component in the home controlled by the network operator, the ONT.

I was just thinking along the same lines as you when your post arrived. Snap. Too many unknown, possibly incompatible devices on the lines.

In reply to a post by Realalemadrid:

However there is a method called SRA (Seamless Rate Adaptation) which as you suggested can dynamically adjust the sync speed without dropping the connection. I believe it is used on G.Fast connections

Yes it use for G.fast service.

Edited by adslmax (Sat 16-Dec-23 12:48:26)

From my experience when with Plusnot I found the BT IP profile affected the Throughput not the sync speed As explained it operated at a different layer and is a BT wholesale implementation ,

which does decrease throughput by around 1-2 Mbps at the max IP profile of 77.35mbps if that has not changed when compared to an ISP that doesn't use the BT Wholesale network for Data transit , when with plus net max ds throughput was 73.20mpbs with zen on their network, it's 74.5 to 75.4 with a full 79999mbps sync and RETX low

In reply to a post by tommy45:

From my experience when with Plusnot I found the BT IP profile affected the Throughput not the sync speed

That's exactly right. IP Profile is on the BRAS, which is a router upstream from the DSLAM, and it limits the rates of IP packets.

This is so as not to swamp the DSLAM with large bursts of packets, many of which would have to be thrown away as it doesn't have a lot of buffering.