GB2470978A

GB2470978A - Optical fibre network in which primary nodes are connected directly to a plurality of core nodes

Info

Publication number: GB2470978A
Application number: GB1005393A
Authority: GB
Inventors: Nicholas John Medlen
Original assignee: British Telecommunications PLC
Current assignee: British Telecommunications PLC
Priority date: 2009-03-31
Filing date: 2010-03-30
Publication date: 2010-12-15
Also published as: WO2010112845A1; GB201005393D0

Abstract

The present invention relates to a communications network in which one or more primary nodes (or PCPs) 162 are connected core nodes (120a, 120b) by a fibre interconnect cable (200) which also connects a plurality of core nodes. This bypasses and obviates the local exchanges (130, Fig 9). Customer terminals 150 are connected to the primary nodes. This provides a more resilient network with only a minor increase in the amount of cable and infrastructure being required, when compared with conventional approaches to installing optical fiber into the access network. Also disclosed (e.g. in Fig. 10) is a system in which one or more core nodes comprises a handover point (such as a local exchange 130) to a further communications network.

Description

OPTICAL FIBRE NETvVORK The present invention relates to an optical fibre network, and in particular to an access network comprising optical fibre.

The structure of a conventional telecommunications network 100 is shown in Figure 1 with a core network 110 connecting a small number of core nodes 120. The core nodes are also connected to local exchanges 130 via a backhaul (or outer core) network 140. Each of the local exchanges is connected to a customer terminal located at a customer premises 150 via an access network 160. The access network 160 comprises a plurality of primary cross-connection points (PCPs) 162 which are connected to the local exchange by an exchange (or E-side) cable 161. Each of the PCPs 162 is connected to one or more distribution points 164 via a distribution (or D-side) cable 163. Each of the distribution points (DPs) is in turn connected to one or more customers, for example via a dropwire 165 which runs from the a telephone pole to the customer premises 150. A PCP can be referred to as a primary node and a DP can be referred to as a secondary node.

Optical fibre has been deployed significantly in the core and backhaul networks as it provides significantly greater bandwidth and transmission distances than the microwave and coaxial cable systems that it replaced. Although there have been trials of optical fibre in the access network since the early 1 990s (see Bickers et al, "Plans for the Bishops Storiford (UK) fibre to the home trials", ICC 90, vol.1, pp 22-26, Apr 1990) the wide scale replacement of the copper access network with a fibre access network has not become commonplace. Thus, the majority of the access network comprises copper cables.

One reason for this is that DSL (Digital Subscriber Line) technologies have been deployed widely and they have enabled the delivery of relatively high bit rate data services (for example ADSL2+ can provide up to 24 Mbit s1) for the provision of internet access, video on demand, online gaming, etc. without the need to alter the infrastructure of the access network. However, it is acknowledged that to provide significantly higher bit rate services (for example 40 -100 Mbit s1) it will be necessary to deploy fibre in the access network.

Figure 2 shows one potential solution, referred to as Fibre to the Cabinet (FTTCab), in which an optical fibre exchange cable 161 is deployed between the local exchange and the PCP 162 with the legacy copper network 163, 165 being used to carry traffic from the PCP to the customer terminals at the respective customer premises 150. VDSL (Very high speed DSL) technologies can be used to provide services with a bit-rate of approximately 40 Mbit s' Figure 3 shows a further alternative (referred to as Fibre to the Curb (FTTC)) in which an optical fibre exchange cable 161' is deployed between the local exchange and the PCP 162 and an optical fibre distribution cable 163' is deployed between the PCP arid the DP 164, with the existing copper dropwire 165 being used to carry traffic from the DP to the customer premises. Again, using a variety of VDSL it is believed that services with a bit-rate of approximately 100 Mbit s' can be supplied.

A network architecture that is of interest for delivering fibre to the premises (FTTP) is the passive optical network (PON). Referring to Figure 4, the local exchange 130 is connected to a primary optical splitter 180 which is in turn connected to a number of secondary optical splitters 185. Each of the secondary optical splitters 185 is then connected to the customer premises via a dedicated optical fibre connection: present technologies allow up to 128 customers to be connected to a single PON. One of the advantages of PONS is that the some of the network infrastructure is shared by all of the customers and thus the deployment costs are reduced compared to the cost of providing each customer with their own dedicated fibre connection to the local exchange. Some PON schemes use only a single optical splitter rather than the primary and secondary splitters shown in Figure 4. Because of the massive bandwidth available with optical fibre the limit to the bit rate that can be supplied to customers is effectively limited by ecänomic factors (for example, the cost of the transmission equipment and the degree to which access network infrastructure is shared between customers) rather than technological limits.

Extended reach PONs incorporate an optical amplifier located in the backhaul network.

This enables a network span of up to 60km between an exchange and customers based on the current ITU standards. It should be understood that the maximum span of an extended reach PON may exceed this value and that future standards may provide for such further extended reaches. It will be seen that many customers from across a geographical region can be served from a single location, which can provide economic and operational advantages. Because of this, it is common for the transmission equipment to be located in a core node. In order to improve the resilience of extended reach PONs, it is conventional for the PONs to be dual-parented such that the primary optical splitter is connected to two exchanges 130A & 130B (see ITU standard G.984.1 annex 3). One of the exchanges is operated as a live exchange and the other as a backup. In the event of a failure of the live exchange, or damage occurring to the cable connecting the live exchange to the primary splitter then the network switches over to the backup exchange such that service is not interrupted significantly. Whilst dual parenting does improve the resilience of the network there is a significant economic cost involved.

According to a first aspect of the present invention there is provided a communications network comprising a plurality of core nodes, a plurality of primary nodes, and a plurality of customer terminals, the network being configured such that each of the plurality of customer terminals are connected to one of the plurality of primary nodes and wherein the network further comprises an optical fibre interconnect cable, the optical fibre interconnect cable connecting a first one of the plurality of core nodes to a second one of the plurality of core nodes such that one or more of the plurality of primary nodes are connected to both the first one of the core of primary nodes and the second one of the plurality of core nodes. Preferably the network comprises a plurality of optical fibre interconnect cables. The first one of the plurality of core nodes and the second one of the plurality of core nodes may comprise the same core node.

The plurality of customer terminals are connected to one of the plurality of primary nodes using a fibre to the premises architecture, a fibre to the cabinet architecture or a fibre to the curb architecture. The network may comprise a passive optical network.

One or more of the core nodes may comprise a handover point to a further communications network.

The network may further comprise one or more local exchanges, wherein one or more of the primary nodes is connected to one of the local exchanges, said local exchange being connected to one of the plurality of core nodes. The or each primary node may be connected to the respective local exchange by an optical fibre connection. One or more of the local exchanges may comprise a handover point to a further communications network.

According to a second aspect of the present invention there is provided a method of upgrading a communications network, the method comprising the steps of: i) installing an optical fibre interconnect cable so as to connect a first core node to a second core node; ii) routing the optical fibre interconnect cable such that it is near to one or more primary nodes; and iii) connecting the or each primary node to the optical fibre interconnect cable such that the or each primary node is in communication with the first core node and the second core node.

Embodiments of the present invention 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 conventional telecommunications network; Figure 2 shows a schematic depiction of a Fibre to the Cabinet (FTTCab) network infrastructure; Figure 3 shows a schematic depiction of a Fibre to the Curb (FTTC) network infrastructure; Figure 4 shows a schematic depiction of a passive optical network (PON) architecture that us used to deliver fibre to the premises (FTTP); Figure 5 shows a schematic depiction of a network architecture according to the present invention; Figure 6 shows a schematic depiction of an alternative network architecture according to the present invention; Figures 7 to 9 show a schematic depiction of how a conventional communications network may undergo the transition from conventional copper access network to a fibre access network according to the present invention; and Figure 10 shows a schematic depiction of a further embodiment of the present invention Figure 5 shows a schematic depiction of a network architecture according to the present invention. An optical fibre interconnect cable is installed, connecting a first core node 120a to a second core node 120b The optical fibre interconnect cable is routed such that it connects a plurality of PCPs 162 to the first and second core nodes.

Thus, the interconnect cable provides each of the PCPs with a resilient connection to the core nodes. As the PCPs now have a fibre connection to a core node, customer premises 150 may be connected, using either FTTC or FTTP technologies. For the sake of clarity, the distribution points have not been shown in Figure 5 although it will be clear to those skilled in the art that they would be present in the network as built.

Figure 6 shows a schematic depiction of an alternative network architecture according to the present invention. In this case, some of the core nodes 120 are connected by an optical fibre interconnect cable 200 in a ring topology, with a further core node 120 being connected to the ring cable via a further optical fibre interconnect cable in a chain topology. It can also be seen that a ring can be formed that begins and ends at the same core node.

As the PCPs are directly connected to the core nodes, a network architecture according to the present invention is more resilient than conventional network architectures. For example, in a dual parented PON, the resilient connection is provided in the backhaul network, with the local exchange being connected to two different core nodes. This means that there is a single fibre connection between the local exchange and each of the PCPs connected to that local exchange. In the present invention, there is resilience down to the PCP level, with the local exchanges being bypassed as the PCPs are connected directly to the core nodes. This means that the interconnect cable 200 effectively replaces the backhaul network and the exchange side of the access network, as shown in Figure 1. Analysis of network topologies show that the provision of interconnect optical fibre cables to the PCPs will require a minor increase in the amount of cable that would be needed to be installed (and associated duct and infrastructure provision) when compared with conventional techniques for installing fibre into the access network.

Figures 7 to 9 show a schematic depiction of how a conventional communications network may undergo the transition from conventional copper access network to a fibre access network according to the present invention. Figure 7 shows the first stage of this transition in which FTTC or FTTP is deployed for a number PCPs in the network.

A conventional fibre connection is made from each PCP to a core node 120 or a local exchange as required. For the sake of clarity, the backhaul connections between each of the local nodes and the core nodes are not shown. Even though the fibre interconnect is not used to connect all of the PCPs to the core nodes, the cable routes that will be required will have been identified and sufficient fibre will have been deployed along those routed to support the rings or chains that will be needed for the fibre interconnect. Figure 8 shows the second stage of the transition process, in which the construction of the fibre interconnect is begun. The fibre cables will, in general start and terminate in exchange locations such that the chain connects the core nodes to the local exchanges. The interconnect is routed through, or near to the various PCPs that will eventually be connected to the interconnect. At this stage, the local exchanges are not bypassed but the planning of the cable routes will take into account the need to subsequently intercept the interconnect cables such that the exchanges can be bypassed. Figure 9 shows the network once the transition is completed, with the fibre interconnect 200 joining all of the PCPs to the core nodes and with the local exchanges being bypassed by the fibre interconnect.

It will be understood that a PCP may be connected to more than two local exchanges but it is unlikely that the increased resilience that would be obtained by such an arrangement would be justified by the additional costs. It is likely that a large network operator will use a mix of one or more of FTTP, FTTC or FTTCab as is required. It should be understood that a single PCP may be used to support more than one of these different network solutions depending on the type and distribution of customers, for example FTTP over PON to businesses and FTTCab for domestic customers. All of these options require that fibre be extended to the PCP and thus a network according to the present invention would be compatible with each of these network architectures.

Also, it is likely that a POP may be used as the location for a primary or a secondary optical splitter so a network according to the present invention would also be compatible with PON architectures.

Under certain regulatory regimes, some network operators are compelled to allow other communications providers (CPs) to access their network. Typically, a third party OP will construct their own core network (or possibly a core network and a backhaul network) and will pass traffic between their own network and that of the network operator in order for traffic to be transmitted to (and received from) customers. The network operator will establish a number of handover points within their own network such that other CPs can insert and extract traffic from the network operator's network.

If a third party CP is offering broadband services to their customers then the traffic will be routed via the access network and then routed to the CP's network via a handover point, either at a local exchange or at a core node.

Figure 10 shows a schematic depiction of a further embodiment of the present invention in which each of the PCPs 162 has a first fibre connection 161' to a local exchange 130 and a second connection to a core node 120, via fibre interconnect cable 200. Again, for the sake of clarity, the DPs have not been shown in Figure 10.

This hybrid approach is compatible the type of regulatory regime discussed above. If a OP is providing a standard broadband service to its customers then the data can be routed from the PCP to the local exchange via the first fibre connection 161'. If the local exchange is also a handover point then the traffic can be routed to the CP's network. Otherwise the traffic will be routed on to a core node and thence to a handover point.

If the CP also offers a more reliable broadband service that is routed via the fibre interconnect cable 200, then data will be routed from the PCP to the core node via fibre interconnect cable 200, and thence to the CPs network via a handover point. It should be noted that Figure 10 shows the PCPs being connected to a single core node via the fibre interconnect 200. It should be understood that a POP may be connected to two (or more) core nodes via the fibre interconnect.

Claims

CLAIMS1. A communications network comprising a plurality of core nodes, a plurality of primary nodes, and a plurality of customer terminals, the network being configured such that each of the plurality of customer terminals are connected to one of the plurality of primary nodes and wherein the network further comprises an optical fibre interconnect cable, the optical fibre interconnect cable connecting a first one of the plurality of core nodes to a second one of the plurality of core nodes such that one or more of the plurality of primary nodes are connected to both the first one of the core of primary nodes and the second one of the plurality of core nodes.
2. A communications network according to claim 1, wherein the network comprises a plurality of optical fibre interconnect cables.
3. A communications network according to claim 1 or claim 2, wherein the first one of the plurality of core nodes and the second one of the plurality of core nodes comprise the same core node.
4. A communications network according to any of claims I to 3, wherein the plurality of customer terminals are connected to one of the plurality of primary nodes using a fibre to the premises architecture.
5. A communications network according to any of claims 1 to 3, wherein the plurality of customer terminals are connected to one of the plurality of primary nodes using a fibre to the cabinet architecture.
6. A communications network according to any of claims I to 3, wherein the plurality of customer terminals are connected to one of the plurality of primary nodes using a fibre to the curb architecture.
7. A communications network according to any preceding claim, wherein the network comprises a passive optical network.
8. A communications network according to any preceding claim, wherein one or more of the core nodes comprise a handover point to a further communications network.
9. A communications network according to any preceding claim, the network further comprising one or more local exchanges, wherein one or more of the primary nodes is connected to one of the local exchanges, said local exchange being connected to one of the plurality of core nodes.
10. A communications network according to claim 9, wherein the or each primary node is connected to the respective local exchange by an optical fibre connection.
11. A communications network according to claim 9 or claim 10, wherein one or more of the local exchanges comprise a handover point to a further communications network.
12. A method of upgrading a communications network, the method comprising the steps of: i) installing an optical fibre interconnect cable so as to connect a first core node to a second core node; ii) routing the optical fibre interconnect cable such that it is near to one or more primary nodes; and iii) connecting the or each primary node to the optical fibre interconnect cable such that the or each primary node is in communication with the first core node and the second core node.