GB2571074A

GB2571074A - Network

Info

Publication number: GB2571074A
Application number: GB1802257.4A
Authority: GB
Inventors: Chattell Andrew
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 2018-02-12
Filing date: 2018-02-12
Publication date: 2019-08-21
Also published as: GB201802257D0

Abstract

A hybrid optical fibre-metallic access network, providing network access to a customer, comprises a multiplexer which is connected to an optical fibre cable and a first end of a metallic cable. The multiplexer may be a digital subscriber line multiplexer or a G.fast multiplexer. The access network also comprises a modem which is connected to the second end of the metallic cable and which is located away from a customer premises. The modem may be located at a distribution point. The modem is also connected to an apparatus in the customer premises by a further cable. The apparatus may transmit electrical power to the modem over the further cable. Moving the modem away from the customer premises reduces the distance between the modem and the digital subscriber line add drop multiplexer (DSLAM) which may lead to an increase in the data rate which can be obtained.

Description

NETWORK

Field of the Invention

The present invention relates to a node for use in communications networks, particularly for use in hybrid fibre-copper access networks.

Background to the Invention

Since the advent of the World Wide Web, there has been a need to provide internet access to customers at ever increasing data rates. Asymmetric Digital Subscriber Line (ADSL) technology over existing copper wires can provide data rates of up to 24 Mbit/s, but many customers will experience significantly lower data rates due to the length of the network connection. One solution is to install Fibre to the Premises (FTTP) networks, such as PONs (Passive Optical Networks), but this approach requires very significant investment.

Another approach is to install limited amounts of optical fibre and to utilise it in conjunction with the legacy copper cabling. Figure 1 shows a schematic depiction of a hybrid fibre-copper access network 100 in which a telephone exchange 110 is connected to a plurality of customer premises 500 (the customer premises may be domestic, commercial or industrial premises). One network architecture is Fibre to the Cabinet (FTTC [or FTTCabj), in which the telephone exchange 100 is connected to cabinets 120 by optical fibre cable 115. VDSL (Very-high-bit-rate Digital Subscriber Line) data signals can be transmitted over the fibre cable to equipment in the cabinet which converts the optical signal to an electrical signal which can then be transmitted over a copper cable 125 to the customer premises 500. The customer premises are connected to the cabinet via a distribution point 130, which is typically located near to the customer premises, for example at a telephone pole. The distribution point is connected to the customer premises 500 using a dropwire 135, either via a telephone pole or via an underground connection, for example within a duct.

The VDSL2 technology commonly used with FTTC networks is typically able to deliver data rates of up to 80 Mbit/s downstream and up to 20 Mbit/s upstream (or even higher) although the data rate is dependent on the length of the copper cables between the customer premises and the cabinet and commercial choices made by the network operator. The use of G.fast transmission technology, which is an advanced DSL transmission format, with such networks should provide downstream data rates of 300 Mbit/s - 1 Gbit/s, depending on the length of the copper cable connecting the cabinet to the customer premises.

Figure 2 shows a schematic depiction of a single line from the hybrid fibre-copper access network 100 described above with reference to Figure 1 in which a cabinet 120 is connected to the exchange (not shown) via optical fibre cable 115. The cabinet 120 houses a multiplexer 122 (commonly referred to as a digital subscriber line add/drop multiplexer [DSLAM]) which receives optical data signals from the optical fibre cable. The multiplexer converts these optical data signals into an electrical format, for example G.fast, which are then transmitted over a copper cable 125 to the customer premises 500. The copper cable is routed physically from the location of the cabinet to a distribution point 130, which is commonly located at, or near to the top of a telephone pole 132. The distribution point will be connected to the customer premises via a dropwire 135 and the network will terminate within the customer premises. The copper cable 125 and the dropwire 135 are connected together so that there is a continuous electrical path from the multiplexer to the customer premises.

A modem, for example a G.fast modem, can be connected to the end of the dropwire in the customer premises such that data can be communicated between the multiplexer and the modem. The modem will be connected to further customer premises apparatus 520 such that devices in the customer premises can connect to the hybrid fibre-copper access network. The customer premises apparatus 520 may comprise, for example, a router and/or a wireless access point such that other devices may connect via a Wi-Fi or wired Ethernet connection.

Summary of the Invention

According to a first aspect of the invention, there is provided a hybrid optical fibre-metallic access network comprising: a multiplexer which is connected to an optical fibre cable and a first end of a metallic cable, the multiplexer being located at a first network location; and a modem which is connected to the second end of the metallic cable, the modem being a) located at a second network location, the second location being located away from the customer premises; and b) connected to an apparatus in the customer premises by a further cable. The second location may be located at least 5 metres from the customer premises.

The invention has the effect of reducing the length of the metallic network which connects the multiplexer to the modem. This reduction in network length should lead to an increase in the data rate which can be provided over that metallic network.

The multiplexer is a digital subscriber line multiplexer and in particular a G.fast multiplexer. The modem may transmit data to and from the apparatus in the customer premises. Furthermore, the apparatus in the customer premises may transmit electrical power to the modem over the further cable. The apparatus in the customer premises may be a wireless access point and/or a router.

Brief Description of the Figures

In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a schematic depiction of a hybrid fibre-copper access network;

Figure 2 shows a schematic shows a schematic depiction of a single line from the hybrid fibre-copper access network of Figure 1;

Figure 3 shows a schematic depiction of a single line from a hybrid fibre-copper access network according to an aspect of the present invention;

Figure 4 shows a shows a graphical depiction of the relationship between bit rate and distance for VDSL and G.fast; and

Figure 5 shows a graphical depiction of the cable length between the cabinet and the customer premises.

Detailed Description of Embodiments

Figure 3 shows a schematic depiction of a single line from a hybrid fibre-copper access network 100’ according to an aspect of the present invention. Similarly to the line described above with respect to Figure 2, a cabinet 120 is connected to the exchange (not shown) via optical fibre cable 115. The cabinet 120 houses a multiplexer 122 which is connected to the optical fibre cable and a copper cable 125. The copper cable is routed physically from the cabinet to the distribution point 130, which is commonly located at, or near to the top of a telephone pole 132.

However, in the present invention the network terminates at the distribution point and the modem 510 is located at the distribution point. The modem is connected to the customer premises apparatus 520 via a further cable 505. In operation, the multiplexer receives optical data signals from the exchange via the optical fibre cable. The optical data signals will be converted into G.fast electrical signals and transmitted over the copper cable to the distribution point where they will be received by the modem. The modem will demodulate the G.fast signals and will generate a sequence of Ethernet packets. These packets can then be transmitted over the cable 505 to the customer premises apparatus 520 such that the data packets can be transmitted to the respective device.

The cable 505 preferably comprises four twisted copper pairs and meets the requirements of Category 5e twisted pair cable such that the use of Gigabit Ethernet (IEEE 802.3ab) allows a data rate of 1 Gbit/s to be supported over a length of up to 100m. The use of Power over Ethernet (PoE) means that the modem can be powered using an electrical power signal sent via the cable 505 such that there is no need to provide a dedicated electrical power supply to the distribution point.

The data rate achievable with G.fast varies strongly with the length of the metallic cable over which the G.fast signals are transmitted. Figure 4 shows a graphical depiction of the relationship between bit rate and distance for VDSL and G.fast (the graph is taken from https://networks.nokia.eom/solutions/g.fast). The horizontal line indicates the performance of VDSL with vectoring whilst the two sloping lines indicate the respective performance of two different G.fast implementations (the difference in performance is due to the different frequency bands which are used in each implementation). It can be seen from Figure 4 that for the G.fast implementation with the lower bit rate (that is, the lower sloped line in Figure 4) G.fast has a better performance than VDSL for distances of up to 350m. Referring to Figure 2, this distance is the distance between the multiplexer and the modem. It can also be seen from Figure 4 that the drop-off in bit rates is relatively steep. Referring again to the characteristic of the G.fast implementation with the lower bit rate it can be seen that for a distance of 200m the bit rate is about 450 Mbit/s whilst at a distance of 300m the bit rate is less than 250 Mbit/s.

The present invention has the effect of shortening the distance between the multiplexer and the modem. As can be seen from Figure 4, by reducing this distance it is possible to increase the data rate which can be provided to a customer. Figure 5 shows a graphical depiction of the cable length between the cabinet and the customer premises for the Applicant’s network (taken from “Assessment of the theoretical limits of copper in the last mile”, prepared for Ofcom, document reference OF013, July 2008). Figure 5 shows that nearly half of these cable lengths are less than 400m long. Thus, by reducing this median cable length by approximately 30-50m by locating the modem at the distribution point then it is possible to increase the available bit rate, potentially by up to 10%.

It should be understood that the benefit provided by the present invention will vary in accordance with the relative length of the network in question. For example, if the cable length between the cabinet and the distribution point is 50m and the cable length from the distribution point to the customer premises is 50m then the use of the present invention will reduce the length of the G.fast connection by 50% (from 100m to 50m), resulting in a significant increase in data rate. However, if the cable length between the cabinet and the distribution point is 300m and the cable length from the distribution point to the customer premises is 30m then the use of the present invention will reduce the length of the G.fast connection by 10% (from 300m to 270m), giving a smaller increase in data rate.

The modem is preferably located at least 5 metres from the customer premises. For distances below this then the advantage gained from the present invention will be minimal. The maximum distance of the modem location from the customer premises is 100m as this is the limit for the Gigabit Ethernet protocol. It is thought that there will be few customer premises where the distance to the distribution point is in excess of 100m.

Figure 3 shows the present invention being used when the distribution point is mounted at the top of a telephone pole. It will be understood that a distribution point may also be located in a footway box at the base of, or near to the base, of a telephone pole. Furthermore, Figure 3 shows that the drop wire is routed from the distribution point to the customer premises as an overhead cable. It will be understood that alternatively the drop wire may be routed from the distribution point to the customer premises through an underground duct or directly buried into the ground.

It will be understood that if the cable 505 is routed from the distribution point to the customer premises as an overhead cable then it will have additional design requirements over that of a conventional Ethernet cable. For example, the cable will need some form of strength member adding such that it can be used as a dropwire, given the mechanical loadings that will be caused by wind, ice loading etc., the sheath will need to be resistant to ultra-violet radiation and other environmental factors, the cable will require a barrier to 5 prevent water ingress, etc.

In the preceding discussion reference has been made to copper cables. Historically aluminium was sometimes used as the electrical conductor in access network cables as an alternative to copper. It will be understood that the present invention is of equal 10 applicability to cables regardless of whether the conductors are formed of copper, aluminium or other materials.

According to one aspect, the present invention provides a network architecture in which the modem in a hybrid metallic-optical fibre access network is moved from the customer premises to the distribution point. This reduces the distance between the modem and the DSLAM, leading to an increase in the data rate which can be obtained. For G.fast this can amount to a 10% increase in data rate.

Claims

1. A hybrid optical fibre-metallic access network comprising:

a multiplexer which is connected to an optical fibre cable and a first end of a metallic cable, the multiplexer being located at a first network location; and a modem which is connected to the second end of the metallic cable, the modem being

a) located at a second network location, the second location being located away from the customer premises; and

b) connected to an apparatus in the customer premises by a further cable.

2. A hybrid optical fibre-metallic access network according to Claim 1 wherein the multiplexer is a digital subscriber line multiplexer.

3. A hybrid optical fibre-metallic access network according to Claim 2 wherein the multiplexer is a G.fast multiplexer.

4. A hybrid optical fibre-metallic access network according to any preceding Claim wherein a cabinet is located at the first location.

5. A hybrid optical fibre-metallic access network according to any preceding Claim wherein a distribution point is located at the second location.

6. A hybrid optical fibre-metallic access network according to any preceding Claim wherein the second location is located at least five metres away from the customer premises

7. A hybrid optical fibre-metallic access network according to Claim 6 wherein the distribution point is located at or near to a telephone pole.

8. A hybrid optical fibre-metallic access network according to any preceding Claim wherein the modem is configured, in use, to transmit data to and from the apparatus in the customer premises.

9. A hybrid optical fibre-metallic access network according to Claim 8 wherein the apparatus in the customer premises transmits electrical power to the modem over the further cable.

5

10. A hybrid optical fibre-metallic access network according to Claim 8 or Claim 9 wherein the apparatus in the customer premises is a wireless access point and/or a router.