In previous articles about PSTN basics principles and Remotes & DSL and DSLAM’s, we discussed various options to overcome copper loop distance limitations by using optical fiber instead of copper extension.
Now, this comes down to 2 very important terms that you need to remember when it comes to remote switch and remote DSLAM are generic ﬁber terminals, i.e. the ﬁber ends at them and planning access networks as such.
and these are ….drum rolls….. Brownﬁelds vs Greenﬁelds!
DSL on Copper to the Premise (Brownﬁelds)
A neighborhood where copper wires were previously deployed is known as a brownﬁeld.
In brownﬁelds, a few hundred customers share a ﬁber backhaul to the network and connect to the ﬁber with DSL modems using existing copper wires for the last few hundred meters.
Eventually, most customers will use their own ﬁber terminal that is connected to WiFi and copper wires inside the house.
GPONs on Fiber to the Premise (Greenﬁelds)
In newly-constructed multi-tenant buildings and neighborhoods, ﬁber is routinely installed to the premises. This is known as greenfields.
Gigabit Passive Optical Network (GPON) technology is often used, and 32 or more customers typically time-share a ﬁber connection to the network. (note – there can be more customer per ONT or CPE in PON networks). A Central Splitting Point is used to connect one ﬁber backhaul towards the network via mirrors and lenses to 32 – 64 or more ﬁbers that lead to customer premises.
The uplink is shared in a round-robin fashion, as only a single customer can transmit at a time. Each user receives a ﬁxed amount of capacity on the uplink, whether it is being used or not.
Active Ethernet to the Premise
When Active Ethernet is deployed, the customer’s ﬁber terminates on a port on an Ethernet switch. The switch is located either at a wire center, or in the neighborhood. Customers can therefore transmit upstream any time they like and are not limited by time slots. This is known as statistical multiplexing, or bandwidth on demand.
Read more on this here.
Statistical multiplexing is more efﬁcient than channelizing and users get higher upload speeds by using the same capacity backhaul. Compared to the PON however, it needs 31 more network-side ﬁber transceivers. This makes it more expensive to install and maintain.
Active Ethernet is often used for business customers.
Why The Concept of Loop is Still Important
It should be noted that even though there are digital transmission and digital switching available for traditional telephone services in established areas today, the access circuit between the network and customers (the local loop) still uses analog technology dating back to the late 1880s.
Even with VoIP over cable modem, or Voice over IP over ﬁber, analog technology of local loops from 1880 is still used!
Telephone service from cable TV companies uses traditional analog telephony on the inside wiring. This is plugged into converters that carry it as Voice over IP over cable modems to the outside of the building.
DSL services (broadband from telephone companies) is delivered on existing local loops by modems in the remote as shown in the previous image.
We will cover 64 kb/s DSO rate for channelized digital transmission systems in a next article.
This technology is based on the frequency band supported by the traditional analog local loop. An understanding of the limitations and characteristics of local loops is therefore essential.