GB2520173A

GB2520173A - Method and scheduler for grouped transmission containers in passive optical networks

Info

Publication number: GB2520173A
Application number: GB1418192.9A
Authority: GB
Inventors: Pedro Alverez; Nicola Marchetti; Marco Ruffini; David Payne
Original assignee: College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin
Current assignee: College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin
Priority date: 2013-10-14
Filing date: 2014-10-14
Publication date: 2015-05-13
Anticipated expiration: 2034-10-14
Also published as: GB201318188D0; GB201418192D0; GB2520173B

Abstract

Dynamic Bandwidth Assignment (DBA) scheme for providing group assured bandwidth to a subset of Optical Network Units (ONU) in a Passive Optical Network (PON). Scheduling bandwidth in the PON, which comprises a plurality of ONUs configured to deliver a data service, comprising grouping connections from different ONUs as a group and assigning to a single entity the combined bandwidth from each ONU, such that the amount of bandwidth needed to perform a task at an individual ONU is shared.

Description

Method and Scheduler for Grouped Transmission Containers in Passive Optical Networks

s Field

The invention relates to a method and scheduler for use in optical networks.

Background

Optical fibre is one of the best transmissions mediums known for fixed telecommunications. Its unparalleled bandwidth and low attenuation make it the preferred medium for high throughput, long distance, fixed communications.

With this premise, fibre has been deployed in core networks for quite some time now. Deployment of fibre in the access networks however, has been delayed is due to the high investment needed to replace the legacy copper infrastructure.

Passive Optical Networks (PONs) have enabled a more economic way to bring fibre closer to the customer, and for this reason they are now being deployed in many countries. By sharing a single fibre with multiple customers and using a passive splitter to divide the signal among them, capital and operational expenditures are reduced when comparing with point to point fibre links.

Examples of optical networks include EP 1 863 204, assigned to Fujitsu, IJS7,738,490, assigned to Kim and US7,653,084, assigned to Shin.

Since a single fibre is shared among all the customers in the RON, a Medium Access Control (MAC) must be defined that allows allocating efficiently the common resources. Standards such as Gigabit-capable Passive Optical Network (G-PON) "Gigabit-Capable Passive Optical Networks (G-PON) Rec.

G.984.x, October 2008" and 10-Gigabit-capable Passive Optical Networks (XG-PON) 10-Gigabit-Capable Passive Optical Networks (XG-PON) Series of Recommendations. G.987.x, March 2010 define a Time Division Multiple Access (TDMA) MAC protocol for PONs. The standards however, do not define the scheduling algorithm for Dynamic Bandwidth Assignment (DBA), to encourage flexibility and competition, leaving it up to the manufacturers and operators to choose which algorithm to adopt.

Some schedulers were already proposed in the literature for this kind of system.

However, they were developed assuming that their customers were individual residential users and therefore, customers would only require one Optical Network Unit (ONU) to be served. However, large businesses entities such as companies, universities or mobile operators, may require more than one ONU per PON to obtain service in different locations. These entities can desire to have a single Service Level Agreement (SLA) for their group of ONUs and share the contracted capacity among the entire group of ONUs.

Currently, upstream schedulers for PONs only consider individual logical connections. Algorithms to perform DBA have been developed that consider the is QoS of the connections. Currently capacity can only be assigned to individuals, which is inefficient for users owning more than one access point in the same RON.

It is therefore an object to provide an improved method and scheduler for use in optical networks.

Summary

According to the invention there is provided, as set out in the appended claims, a method of scheduling bandwidth in a Passive Optical Network (RON) comprising a plurality of optical network units (ONU) configured to deliver a data service, said method comprising the steps of: grouping connections from different ONUs as a group and assigning to a single entity the combined bandwidth from each ONU, such that the amount of bandwidth needed to perform a task at an individual ONU is shared.

By allowing the grouping of connections from different ONUs, entities with more than one ONU in the RON can reduce the amount of assured bandwidth needed to perform with the same QoS. This can lead to new business models where both the operator providing the service and the user requesting the service will benefit.

In one embodiment there is provided a method to schedule bandwidth to a group of ONUs as opposed to a single one. By assuring bandwidth to a group, an operator can assure that whenever an ONU of a particular entity is not using its assured bandwidth, it can be assigned first to an ONU belonging to the same entity, rather than anyone else on the PON.

In one embodiment there is provided the step of performing dynamic bandwidth assignment on the group of connections.

In one embodiment there is provided the step of checking if the individual is connections of the group did not use their individual bandwidth, and if not, and the spare bandwidth is sharable, then the bandwidth available to the group is shared among the connections of that group using a dynamic bandwidth algorithm.

In one embodiment there is provided the step of allowing an entity that uses more than one ONU to schedule any unused capacity from one ONU to other ONUs within its own group, before offering them to other users as best effort service.

In another embodiment there is provided the step of system for scheduling bandwidth in a Passive Optical Network (PON) comprising a plurality of optical network units (ONU) configured to deliver a data service, said system comprising: a module or means for grouping connections from different ONUs as a group and assigning to a single entity the combined bandwidth from each ONU, such that the amount of bandwidth needed to perform a task at an individual ONU is shared.

This group scheduling has the advantage of allowing a business costumer to take advantage of inequalities in the traffic generated from its ONUs, by oversubscribing its own assured bandwidth, without fearing that the performance of its network will be affected by the other clients in the RON.

The invention provides the ability of grouping logical connections from different ONUs, thus allowing ONUs to share assure bandwidth amongst themselves.

There is also provided a computer program comprising program instructions for causing a computer program to carry out the above method which may be embodied on a record medium, carrier signal or read-only memory.

Brief Description of the Drawings

The invention will be more clearly understood from the following description of is an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:-Figure 1 illustrates a Passive Optical Network using a tree network topology; Figure 2 is a flowchart illustrating operation according to one embodiment; Figure 3 Illustration of backhauling base stations and serving fixed users using two groups; and Figure 4 illustrates a group bandwidth assignment based on the GIANT algorithm.

Detailed Description of the Drawings

A Passive Optical Networks (RON) using a tree network topology is illustrated in Figure 1. This means that data is physically broadcast to all users in the downstream direction (i.e., from the OLT to the ONUs). Upstream however synchronization is required among the ONUs to avoid data collision. The capacity scheduling mechanism that achieves this goal is carried out at the OLT and is called Dynamic Bandwidth Assignment (DBA). A new hierarchical scheme to implement DBA is provided.

This mechanism, instead of scheduling the ONUs individually, allows to schedule the ONUs in groups. This is particularly useful in those business cases where an entity might own more than one ONU (e.g., a mobile operator using RON as a backhaul, a large company, University,...).

The DBA algorithm divides the capacity per user into tour types: a tixed part, always available to the user independently of usage; on top ot this there is an assured part which is available when required, but can be used by others if underused; any bandwidth required above the assured + fix level is given as a non-assured and best etfort, i.e. only it there is unused capacity in the network.

The system and method allows an entity that uses more than one ONU to schedule any unused capacity from one ONU to other ONUs within its own group, before oftering them to other users as best etfort service. This ditfers is trom usual scheduling schemes that force the customer to divide its contracted bandwidth among all ONUs in the RON, binding capacity to individuals.

The invention will allow the costumer to use the bandwidth purchased in a more etficient manner since if capacity is not being used by one ONU, the costumer can be sure it will be assigned to another related ONU they own. A customer can obtain the same quality of service among a number of ONUs, by requesting less overall assured bandwidth compared to the case with standard DBA. This will allow the group to obtain the same service at a lower cost.

Example Embodiment

A scheduling algorithm that enables sharing resources among a group ot logical connections according to one embodiment is described. This way, a business entity can assure bandwidth to a group of ONUs and share resources among them. In one embodiment the invention can be implemented in two parts. Firstly, a concept of Group Assured Bandwidth is described. Afterwards, the actual algorithm is implemented to pertorm the scheduling.

In a G-PON or XG-PON system, logical connections can be established between the ONUs and the OLT to be able to differentiate Quality of Service (QoS) to different services. These connections can be assigned Fixed, Assured, Non-Assured or Best-Effort bandwidth depending on their QoS requirements.

When logical connections from multiples ONUs are grouped together for commercial reasons, it is possible to create a new type of bandwidth, Group Assured Bandwidth. With this type of bandwidth, resources are assured to the group of connections rather than to the individuals. Since this is assured bandwidth as opposed to fixed bandwidth, resources are only assigned to the group if someone in the group needs it. This means that bandwidth is not wasted and can still be used opportunistically by connections with non-assured bandwidth.

is Note that individual logical connections can still maintain individual assured bandwidth to guarantee some minimal service to individual connections.

The Group Assured Bandwidth shared can be obtained, but not limited, in two ways: * By sharing individual assured bandwidth unused by the connections. It is important to note, that the amount of bandwidth shared from a particular connection must be smaller or equal than the amount of individual assured bandwidth in that connection.

The unused bandwidth is assigned to connections in the group by a DBA algorithm. This type of bandwidth can be defined as Shared Group Assured Bandwidth.

* By reserving assured bandwidth for the group that is not associated with any individual connection specifically. This bandwidth is then assigned to the group's individual connections by a DBA algorithm. This type of bandwidth can be called Excess Group Assured Bandwidth.

It is then possible to describe the Group Assured Bandwidth of a group as: = (1) E Grp where dictates the total amount of group assured bandwidth in the group, indicates the amount of bandwidth that can be shared from the i-th connection belonging to the group, and indicates the amount of group assured bandwidth of the group which does not come from any particular connection.

Scheduling Algorithm To perform Dynamic Bandwidth Assignment considering groups of connections, a scheduling algorithm has to be developed in the OLT.

In order to maintain the individual assured bandwidth, in this algorithm, first the bandwidth from the individual connections is assigned using some DBA algorithm. After the individual needs are served, it is then time to serve the Group Assured Bandwidth. This is done by going through all the groups checking if the individual connections of the group did not use their individual bandwidth. If not and the spare bandwidth is sharable, then the bandwidth available to the group is shared among the connections of that group using the DBA algorithm. When all groups have been assigned their group assured bandwidth, the assured part of the DBA algorithm is finished and the allocation of Non-assured bandwidth can begin.

A simple statistical analysis using binomial distribution shows the basic advantages of the group allocation. For example, consider three base stations, all using the same RON as a backhaul. Assume a new upload video service that requires 10 Mb/s to work, and that each base station requests an assured bandwidth of 100Mb/s to the RON. Assume that each user is only active 1% of the time, and the RON is running at full capacity, then if a user wants an availability of 90% for the service can have a maximum of 700 subscribers per base station, for a total of 2,100. With the group scheduling algorithm, one can instead obtain an availability of 98% by using the same assured capacity.

Alternatively, with the same 90% availability the number of users can be s increased by 15%.

Figure 2 is a flowchart illustrating operation of the invention as described above.

Backhaulinci [TE with XG-PON In one embodiment the invention can be applied to backbaul mobile systems using XG-RON. In Figure 3, a mobile system in the RON and some fixed users is shown. Here, all the base stations from the mobile operator are joined in a group with a certain amount of Group Assured Bandwidth. This allows the is mobile operator to serve the base stations with a smaller amount of contracted bandwidth since they can make use of the statistical multiplexing properties mentioned above.

To perform the group scheduling, a GIANT algorithm can be used, as described by H. C. Leligou, "Efficient medium arbitration of FSAN-compliant GPONs," mt. J Commun. Syst., no. 19, p. 603-617, 2006, to first assign the individual assured bandwidth. After this, if there is unused individual assured bandwidth, it can be shared with the group by assigning bandwidth to the connections in the group in round-robin manner.

Using this algorithm, connections, or Transmission Containers (T-CONT5), are served periodically where the period is defined by a certain Service Interval (SI) (e.g., a particular T-CONT might be served every 2 frames). These T-CONTs can be inserted into a group of T-CONTs (gT-CONTS) or not, depending on whether or not they want to make use of group assured bandwidth.

If, when a connection is served, there is no need to use all the bytes reserved in the frame for that connection, they can be assigned to someone else in the same gT-CONT. This is illustrated in Figure 4, where it can be seen that T-CONT 1 does not use all the available bytes and shares some with T-CONT 3, a connection that also belongs to the same group of T-CONT 1, i.e. gT-CONT 1.

s Since the excess bandwidth is not associated with any particular T-CONT, it has its own service interval. This is illustrated in Figure 4 where the excess bandwidth has a SI of two frames. Here, first some bandwidth is assigned to T-CONT 4 from the Excess Group Assured Bandwidth and then, two frames later, some bandwidth is assigned to T-CONT 2 using the same type of group bandwidth.

The embodiments in the invention described with reference to the drawings comprise a computer apparatus and/or processes performed in a computer apparatus. However, the invention also extends to computer programs, is particularly computer programs stored on or in a carrier adapted to bring the invention into practice. The program may be in the form of source code, object code, or a code intermediate source and object code, such as in partially compiled form or in any other form suitable for use in the implementation of the method according to the invention. The carrier may comprise a storage medium such as ROM, e.g. CD ROM, or magnetic recording medium, e.g. a floppy disk or hard disk. The carrier may be an electrical or optical signal which may be transmitted via an electrical or an optical cable or by radio or other means.

In the specification the terms "comprise, comprises, comprised and comprising" or any variation thereof and the terms include, includes, included and including" or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

Claims

Claims 1. A method of scheduling bandwidth in a Passive Optical Network (PON) comprising a plurality of optical network units (ONU) configured to deliver a s data service, said method comprising the steps of: grouping connections from different ONUs as a group and assigning to a single entity the combined bandwidth from each ONU, such that the amount of bandwidth needed to perform a task at an individual ONU is shared.
2. The method of claim 1 comprising the step of performing dynamic bandwidth assignment on the group of connections.
3. The method of claim 1 or 2 comprising checking if the individual connections is of the group did not use their individual bandwidth, and if not, and the spare bandwidth is sharable, then the bandwidth available to the group is shared among the connections of that group using a dynamic bandwidth algorithm.
4. The method of any preceding claim comprising allowing an entity that uses more than one ONU to schedule any unused capacity from one ONU to other ONUs within its own group, before offering them to other users as best effort service.
5. A system for scheduling bandwidth in a Passive Optical Network (PON) comprising a plurality of optical network units (ONU) configured to deliver a data service, said system comprising: a module for grouping connections from different ONUs as a group and assigning to a single entity the combined bandwidth from each ONU, such that the amount of bandwidth needed to perform a task at an individual ONU is shared.
6. The system of claim 5 comprising a module for performing dynamic bandwidth assignment on the group of connections.
7. The system of claim 5 or 6 comprising a module configured for checking if the individual connections of the group did not use their individual bandwidth, and if not, and the spare bandwidth is sharable, then the bandwidth available to the group is shared among the connections of that group using a dynamic bandwidth algorithm
8. The system of any of claims 5 to 7 comprising a module configured allowing an entity that uses more than one ONU to schedule any unused capacity from one ONU to other ONUs within its own group, before offering them to other users as best effort service.
9. A computer program comprising program instructions for causing a computer when executed by a processor to perform the method of any of claims 1 to 4.is

1O.A method for scheduling bandwidth in a Passive Optical Network (PON) as substantially hereinbefore described with reference to the accompanyingdescription and/or drawings.