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Standard User marpoint
(newbie) Sat 27-Feb-21 09:56:56
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DSLAM and FTTP


[link to this post]
 
Do DSLAM's have a role in FTTP (ie managing the line speed) or are they just used for copper lines ?

If not, is there similar tecnology that regulates line speeds on FTTP ?
Standard User dect
(fountain of knowledge) Sat 27-Feb-21 10:05:31
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Re: DSLAM and FTTP


[re: marpoint] [link to this post]
 
In reply to a post by marpoint:
Do DSLAM's have a role in FTTP (ie managing the line speed) or are they just used for copper lines ?

If not, is there similar tecnology that regulates line speeds on FTTP ?
No DSLAMs are not used in the Openreach FTTP network, its completely passive between the exchange (where its connected to a OLT) and the customer property (where its connected to a ONT) there is a splitter between these two points but that uses mirrors I believe to split the fibre 32 ways.

Edited by dect (Sat 27-Feb-21 10:06:07)

Standard User Pheasant
(experienced) Sat 27-Feb-21 11:26:02
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Re: DSLAM and FTTP


[re: marpoint] [link to this post]
 
In reply to a post by marpoint:
If not, is there similar tecnology that regulates line speeds on FTTP ?

As noted above its the OLT (Optical Line Termination) that is configured and determines the downstream / upstream bandwidths and configures this with the ONT (Optical Network Termination) sometimes also called the ONU by some equipment vendors.

The ONT is effectively the 'optical modem' for want of better description in your home/premises.

For Openreach based FTTP the PON network is aggregated at the OLT which is located in the GEA Headend exchange - not necessarily your nearest local exchange.

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Standard User candlerb
(fountain of knowledge) Sat 27-Feb-21 12:53:06
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Re: DSLAM and FTTP


[re: marpoint] [link to this post]
 
Just to add to the above: the line bitrate (what you think of as "sync speed" in DSL) is *fixed* on FTTP. For most GPON networks, including Openreach FTTP, it's 2.4Gbps downstream, 1.2Gbps upstream.

There is no rate adaptation based on line conditions: either it works, or it doesn't. The network is designed so that the light lost over the fibre is within the "optical budget" of allowable loss.

Downstream and upstream are simultaneous, as they're on different wavelengths, but individual ONTs on the same splitter have to take it in turns to transmit upstream. This is controlled by the OLT, which allocates timeslots.

The service data rate you get is controlled by the OLT shaping traffic. Roughly speaking, delays are inserted between packets, to ensure that overalll you don't receive or send data faster than the service you paid for.
Standard User witchunt
(fountain of knowledge) Sat 27-Feb-21 13:26:03
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Re: DSLAM and FTTP


[re: dect] [link to this post]
 
Except if there is a subtended headend in the DSLAM.
Standard User Pheasant
(experienced) Sat 27-Feb-21 14:35:26
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Re: DSLAM and FTTP


[re: witchunt] [link to this post]
 
That’s indeed correct...but to provide some context to the OP, in terms of providing a simple explanation of the essential difference between FTTP and FTTC Openreach architectures - sub-tended FTTP headends are the (quite rare) exception rather than the rule smile

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Standard User dect
(fountain of knowledge) Sat 27-Feb-21 15:01:36
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Re: DSLAM and FTTP


[re: witchunt] [link to this post]
 
In reply to a post by witchunt:
Except if there is a subtended headend in the DSLAM.
When I was typing my post I was thinking to myself should I over complicate my post by making reference to a subtended headend which are probably only in a very low percentage of DSLAMs, I thought I better not but knew someone else would smile to be very honest I never in a million years expected it to be you wink
Standard User jpm
(member) Sat 27-Feb-21 15:07:05
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Re: DSLAM and FTTP


[re: candlerb] [link to this post]
 
Where are service tiers enforced? Is the ONT performing rate limiting of upstream traffic or is each ONT allowed to transmit in the allocated time slot and packets above the provisioned rate are discarded/buffered further into the network?
Standard User jimbof
(learned) Sat 27-Feb-21 15:13:01
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Re: DSLAM and FTTP


[re: candlerb] [link to this post]
 
In reply to a post by candlerb:
Downstream and upstream are simultaneous, as they're on different wavelengths, but individual ONTs on the same splitter have to take it in turns to transmit upstream. This is controlled by the OLT, which allocates timeslots.

The service data rate you get is controlled by the OLT shaping traffic. Roughly speaking, delays are inserted between packets, to ensure that overalll you don't receive or send data faster than the service you paid for.


What's to stop you giving everyone else on your splitter a "really bad day" by abusing the fibre and preventing them from being able to establish connections? How are Openreach able to deal with such situations? Thinking it could be a faulty ONT, or could be a malicious attack to take someone offline.
Standard User Pheasant
(experienced) Sat 27-Feb-21 15:38:51
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Re: DSLAM and FTTP


[re: jpm] [link to this post]
 
In reply to a post by jpm:
Where are service tiers enforced? Is the ONT performing rate limiting of upstream traffic or is each ONT allowed to transmit in the allocated time slot and packets above the provisioned rate are discarded/buffered further into the network?

See page 9 for downstream and page 21, 22 for upstream....

https://www.openreach.co.uk/cpportal/content/dam/cpp...

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