WO2005117300A1 - Procede et systeme de transfert de donnees - Google Patents

Procede et systeme de transfert de donnees Download PDF

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Publication number
WO2005117300A1
WO2005117300A1 PCT/SG2004/000147 SG2004000147W WO2005117300A1 WO 2005117300 A1 WO2005117300 A1 WO 2005117300A1 SG 2004000147 W SG2004000147 W SG 2004000147W WO 2005117300 A1 WO2005117300 A1 WO 2005117300A1
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Prior art keywords
data
communication path
communication
transfer
user unit
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English (en)
Inventor
Tee Hiang Cheng
Zhaohui Cai
Xu Shao
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Agency for Science Technology and Research Singapore
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Agency for Science Technology and Research Singapore
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Priority to PCT/SG2004/000147 priority Critical patent/WO2005117300A1/fr
Publication of WO2005117300A1 publication Critical patent/WO2005117300A1/fr
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/16—Time-division multiplex systems in which the time allocation to individual channels within a transmission cycle is variable, e.g. to accommodate varying complexity of signals, to vary number of channels transmitted
    • H04J3/1694—Allocation of channels in TDM/TDMA networks, e.g. distributed multiplexers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/03—Arrangements for fault recovery
    • H04B10/032—Arrangements for fault recovery using working and protection systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/14—Monitoring arrangements
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q11/0067—Provisions for optical access or distribution networks, e.g. Gigabit Ethernet Passive Optical Network (GE-PON), ATM-based Passive Optical Network (A-PON), PON-Ring
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04Q—SELECTING
    • H04Q11/00—Selecting arrangements for multiplex systems
    • H04Q11/0001—Selecting arrangements for multiplex systems using optical switching
    • H04Q11/0062—Network aspects
    • H04Q2011/0079—Operation or maintenance aspects
    • H04Q2011/0081—Fault tolerance; Redundancy; Recovery; Reconfigurability

Definitions

  • This invention relates generally to a method and a system for transfer of data in an access network. More particularly, this invention relates to a method and system for transfer of data in an optical access network including passive optical networks (PONs).
  • PONs passive optical networks
  • FIG. 1 shows a known unprotected passive optical network (PON) 2 that includes passive elements, such as fiber-optic cables 4A, 4B, passive optical splitters/couplers 6, connectors (not shown), and splices (not shown).
  • Active network elements such as an optical line termination (OLT) 8 and multiple optical network units (ONUs) 10, are located at end points of the PON 2.
  • An ONU 10 that also provides a user port or network termination function is more commonly referred to as an optical network termination (ONT) 10.
  • OLT optical line termination
  • ONT optical network termination
  • Optical signals traveling downstream across the PON 2, from the OLT 8 to the ONUs 10, are split onto multiple fiber-optic cables 4B by the optical splitters 6.
  • Optical signals traveling upstream across the PON 2, from the ONUs 10 to the OLT 8, are combined onto the single fiber-optic cable 4A by the optical couplers 6.
  • the optical couplers 6 In the PON 2, there is effectively a single communication link between each ONU 10 and the OLT 8 because of the fiber-optic cable 4A.
  • Such a point-to-multipoint configuration is typically used for residential applications.
  • each ONU 10 is connected to the OLT 8 via an additional communication link.
  • Figure 2 shows such a protected system 12 for enhancing access network survivability, wherein each ONU 10 is connected to the OLT 8 via two links 14, 16.
  • Two switching schemes known as the 1 :1 and the 1 +1 switching scheme for switching traffic between the two links 14, 16 in this protected system 12 are described in the ITU-T G.983.5 and G.983.1 standards respectively.
  • Figures 3 and 4 illustrate the 1 :1 and 1 +1 switching schemes respectively.
  • One of the two links 14, is used as a working entity or PON while the other link 16, is used as a protection entity or PON as they are known in the standards.
  • traffic is classified as either high-priority/normal traffic or low-priority/extra traffic.
  • High-priority traffic is required to be carried when one of the two PONs 14, 16 is faulty.
  • Low-priority traffic is carried only when both PONs 14, 16 are operational.
  • the high-priority traffic is carried over a working PON while the lower-priority traffic is carried over the protection PON.
  • the low- priority traffic carried over the protection PON 16 is pre-empted and the high- priority traffic is switched to be carried by the remaining protection PON 16 instead.
  • the high-priority traffic is thus said to be protected while the low- priority traffic is not.
  • a PON 14, 16 does not carry any low-priority traffic even if spare or unused bandwidth on that PON is available. Bandwidth on the PON is thus not efficiently utilized.
  • both high-priority and low-priority traffic are broadcast to selectors in the OLT 8 for them to choose the type of traffic that is to be transmitted onto the working and protection PONs 14, 16.
  • PST PON selection trace
  • a similar survivability mechanism is used for transmission in the upstream direction.
  • This ranging value may be different from the value for the primary PON 14.
  • a line card that terminates the primary PON 14 can carry out ranging over the protection PON 16, or get the information from the line card of the protection PON 16. Registration would have to be carried out for high priority/normal traffic over the protection PON 16 when it is switched over to be transferred on that PON 16.
  • the traffic is sent simultaneously on both PONs 14, 16 to be redundantly carried over the two PONs 14, 16, and there is thus less bandwidth for low-priority/extra traffic, as compared to that in the 1 :1 scheme.
  • the traffic is selected based on the signal quality and/or a PON section trace (PST) message sent by the OLT 8.
  • PST PON section trace
  • the upstream direction traffic is bridged to both working and protection PONs 14, 16 and a selection mechanism at the OLT 8 selects traffic on one of the PONs 14, 16 based on the signal quality and provisioning.
  • Switching traffic from one PON 14, 16 to the other PON 16, 14 is initiated by either the ONU 10 or the OLT 8, depending on which element 8, 10 detects a fault first.
  • the ONU 10 will detect that a fault has occurred and notify the OLT 8 of the failure in order to complete the switching event.
  • Figure 5 shows a known generic X:N protection system that supports both protected ONUs 10 and unprotected ONUs 11 as illustrated in the ITU-T G983.5 standards.
  • X number of protection PONs 16 are provided and configured for N number of working PONs 14 (with l ⁇ X ⁇ N).
  • the N working PONs 14 can support a mixture of protected and unprotected ONUs 10, 11.
  • the protected ONUs 10 can be connected to any of the X protection PONs 16.
  • the protected ONUs 10 connected to the same working PON 14 can be connected to different protection PONs 16 and protected ONUs 10 connected to different working PONs 14 can be connected to the same protection PON 16.
  • connection scheme is compatible with both the 1 :1 and 1+1 switching schemes and is independent of protocol.
  • the connection scheme provides protection against multiple failures in N working PONs 14 with less than N protection PONs 16.
  • Other protection systems having different configurations are disclosed in U.S. Patent 5,896,474, entitled Optical network having protection configuration"; U.S. Patent 5,920,410, entitled “Access network”; U.S. Patent 6,327,400, entitled “Protection scheme for single fiber bi-directional passive optical point-to- multipoint network architectures"; and U.S. Patent No. 6,351 ,582, entitled “Passive optical network arrangement”.
  • the ONU 10 before traffic of an ONU 10 can be switched over to the protection PON 16, the ONU 10 has to be initialized on the protection PON 16, i.e. the ONU 10 has to establish a connection on the protection PON 16.
  • Such an initialization includes ranging and registration of the ONU 10 with the OLT 8 of the protection PON 16.
  • Ranging is a method of measuring the logical distance between each ONU 10, 11 and the OLT 8 and of determining the transmission timing for ensuring that upstream traffic from different ONUs 10, 11 on the same PON 14, 16 do not collide.
  • the above-mentioned documents disclose protection switching but not bandwidth allocation in a PON 14, 16.
  • FIG. 6 shows an example of a Tframe 18 frame format for the ITU-T G.983 155.52/155.52 Mbit/s broadband PON (B-PON) system.
  • each Tframe 18 includes two Physical Layer Operation and Maintenance (PLOAM) cells 20, 22.
  • the first PLOAM cell 20 contains twenty-seven grant fields while the second PLOAM cell 22 contains twenty-six grant fields.
  • Both the PLOAM cells 20, 22 contain an additional 12-byte message each. This 12-byte message may contain information, such as the MESSAGE_PON_ID, MESSAGEJD, AND MESSAGE-FIELD TO MESSAGE-FIELD O.
  • the grant field specifies the GRANTJD of the ONU 10 that is granted the permission to transmit in a corresponding upstream time slot.
  • grants and bandwidth are allocated in a static manner, which is also discussed in the article by D P Shea, J E Mitchell, R P Davey, "PONdering the access network," London Communications Symposium, London, UK, 9th-10th September 2002.
  • Static bandwidth allocation refers to the allocation of a fixed amount of bandwidth to each ONU 10 in each frame.
  • the OLT 8 does not adjust the bandwidth allocation based on the real-time demand of each ONU 10. For example, some ONUs 10 may need more bandwidth at a particular time than the fixed amount while others may not need that fixed amount but the OLT 8 is not able to adjust the bandwidth allocation to give more bandwidth to those ONUs 10 in need of the additional bandwidth.
  • G.983.4 specifies two dynamic bandwidth assignment (DBA) approaches which are improvements over the static bandwidth assignment approach defined in G.983.1.
  • the first method is referred to as "idle cell adjustment”.
  • the OLT 8 monitors the bandwidth used by each of the ONUs/ONTs and when the utilization exceeds a predefined threshold, additional bandwidth will be assigned if it is available.
  • the second method is referred to as "buffer status reporting”.
  • the ONUs/ONTs 10 report the status of their buffers or queues by using minislots. These minislots are slots that are less than the size of an ATM cell of fifty-three bytes.
  • Minislots within the boundary of an ATM cell can be assigned to different ONUs/ONTs 10 for transmission of reports.
  • the OLT 8 reassigns the bandwidth according to the ONU/ONT reports.
  • the enhancement also allows DBA to accommodate several Transmission Containers (T-CONTs) in one ONU/ONT 10 and each T-CONT in an ONU/ONT 10 can operate independently of other T-CONTs.
  • T-CONTs are formats defined to separate traffic/information belonging to different streams, for example, a particular Asynchronous Transfer Mode Virtual Path or Virtual Channel. How the bandwidth is apportioned to different ONUs/ONTs 10 is not specified.
  • a method for transferring data in a communication system which comprises a first communication node and at least one user unit.
  • Each user unit is connected to the first communication node via a network of a number of communication paths such that, for each user unit, two distinct data communication connections, each on a different path, can be provided between the first communication node and the user unit.
  • the path may be a wired or a wireless path.
  • a wired path includes, but is not limited to, a path defined by copper cables and a path defined by fiber-optic cables.
  • Two communication paths are considered to be different even if they share a common section. Such a common section shared by two paths may be a section that is less prone to damage.
  • the two communication paths are totally separate from each other, i.e. they share no common section, so that a break anywhere along one of the two paths would not affect the other.
  • Such communication paths that do not share any common section are referred to herein as distinct communication paths.
  • the method includes, individually for each user unit, establishing and maintaining both data transfer connections simultaneously and assigning one of the data transfer connections as a primary connection and the other data transfer connection as a secondary connection between the first communication node and the user unit.
  • the method further includes transferring the data over a primary communication path on which the primary connection is established and switching transfer of the data instantaneously from over the primary communication path to over a secondary communication path on which the secondary connection is established, when transfer of data over the primary communication path is no longer feasible, for example when there is a break in the path or when there is a malfunction of equipment associated therewith.
  • transfer of data is referred to, hereinafter, simply as being transferred over the primary and secondary communication paths. Those skilled in the art should however appreciate that, for data transfer over each communication path to be meaningful, the data transfer should be over the logical connection established on the communication path according to a suitable communication protocol.
  • the number of distinct communication paths, i.e. paths not sharing any common section, in the network may be twice the number of user units as described above. Alternatively, the number of distinct communication paths in the network may be less than twice the number of user units such that, at least one communication section is shared by more than one communication path, and thus more than one user unit.
  • the common communication path may be used as a primary and/or secondary communication path by the user units that are assigned that path. In other words, when the user units are individually assigned their respective data transfer connections, it is possible that more than one user unit may be assigned that path for establishing only their respective primary connections thereon. It is also possible that more than one user unit may be assigned that path for establishing only their respective secondary connections thereon.
  • the above-described method may further include assigning a protected information rate (PIR) and a committed information rate (CIR) to each user unit.
  • PIR protected information rate
  • CIR committed information rate
  • the PIR and the CIR are indicative of a first maximum amount of data and a second maximum amount of data, respectively, that are transferable between that user unit and the first communication node.
  • the assignment of PIR and CIR to the user units is carried out such that, for each path of the network, the bandwidth of the communication path is able to transfer the second maximum amount of data on that path for all those user units for which the path is assigned as a primary communication path, and to transfer the first maximum amount of data on that path for all those user units for which the path is assigned either as a primary communication path or as a secondary communication path.
  • the bandwidth of a communication path is limited by the bandwidth of a critical section thereof, which might be a section shared by more than one communication path as discussed above.
  • bandwidth is allocated for the transfer of data for user units using that communication path either as a primary communication path or as a secondary communication path, subject to the PIR of those user units. In this way, the PIR of each user unit is met to ensure a protected bandwidth for each eligible user unit. [0021] After bandwidth of the communication path is allocated as described above, i.e. subjected to the CIR or PIR depending on the user units using that communication path, it is possible that there is bandwidth of the communication path remaining for further allocation.
  • the above-described method may include assigning a burst information rate (BIR), in addition to the PIR and CIR, to each user unit.
  • BIR burst information rate
  • This BIR is indicative of a third maximum amount of data that can be transferred for that user unit.
  • the remaining bandwidth can then be allocated to each user unit, subject to its BIR.
  • the remaining bandwidth may be allocated to each user unit for transfer of the additional data in proportion to the difference between the CIR and PIR, the difference between the BIR and PIR, or the difference between the BIR and CIR of the user unit.
  • Such a method has the advantage that each eligible user unit gets a share of the remaining bandwidth.
  • the bandwidth allocation may preferably take into account frame boundaries so that allocated bandwidth may fall thereat rather than therebetween so that only bandwidth corresponding to complete data frames are allocated to each user unit.
  • the remaining bandwidth may be allocated in a round- robin manner to each user unit for transfer of the additional data, subject to its CIR or BIR. Bandwidth allocated in this manner would also suffer from fragmentation unless allocation is also frame-boundary based.
  • the remaining bandwidth may be allocated according to the actual bandwidth requirement of each user unit to avoid fragmentation. In other words, the bandwidth is allocated so that all data for the user unit is transferable.
  • the above-described bandwidth allocation scheme has several advantages. Bandwidth is protected and guaranteed on a per-user unit basis. This means all the user units that are connected via the same communication path can have different levels of reliability and amount of protected and guaranteed bandwidth. Consequently, service level agreements with the user units can be more flexible. Unprotected or non-guaranteed bandwidth of individual user units could be degraded gracefully and not denied bandwidth completely when a fault occurs or when there is less unused bandwidth for non-bandwidth guaranteed user units, respectively.
  • the bandwidth allocated to such users is reduced to a level that is still sustainable but not zero.
  • the scheme allows the bandwidth reserved for protection to be used by other user units during normal operation when no fault has occurred.
  • the scheme allows unutilized bandwidth reserved for user units to meet their CIR to be re-allocated to other user units for them to burst beyond their CIRs.
  • the service level agreement is also simple, pragmatic and enforceable.
  • An example of such a communication system is an optical access network, wherein the first communication node is an optical line termination (OLT) and the user units are optical network terminations (ONTs), each being connected to the OLT via two separate communication paths, which are generally known to those skilled in the art as passive optical networks (PONs).
  • the user units may be network terminations (NTs), each being connected to the OLT via at least one optical network unit (ONU), wherein each ONU is connected to the OLT via a respective pair of PONs.
  • the NTs may be connected to an ONU via any suitable access technologies, including but not limited to, xDSL, cable modems and switched Ethernet.
  • establishing the data transfer connections includes ranging and registering each ONT and/or ONU with the OLT on the respective pair of PONs. Subsequently,. the OLT polls the ONT and/or ONU to find out if there is data thereat for upstream transfer over the PONs and allocates bandwidth of the PONs according to the above-described method.
  • Each of the primary connection and the secondary connection may be maintained by the ONT and/or ONU indicating to the OLT, via a message sent thereto, that there is no data for transfer on the respective optical links. Alternatively, the ONT and/or ONU may simply ignore the poll by not responding thereto.
  • the communication system may not be restricted to one configured in a multidrop topology as in the case of the optical access network described above.
  • the communication system may also be other types of networks, such as networks connected using copper cables, which are configured according to any suitable topologies, such as but not limited to, a bus, a star or a ring topology.
  • An application of a bus type network in which the invention can be used is one in which a host computer is connected to terminals or terminal clusters at several locations.
  • the communication system may be a wireless network wherein the above-described method can be used by a mobile station in an overlap region of two coverage areas of two respective base stations for establishing and maintaining two separate connections with the two base stations.
  • Figure 1 is a schematic drawing of a prior art unprotected PON system, to which is connected an OLT and multiple ONUs
  • Figure 2 is a schematic drawing of a prior art protected PON system wherein each ONU is connected to an OLT via two PONs
  • Figure 3 is a schematic drawing illustrating the 1 :1 switching architecture for both upstream and downstream transmission between an ONU and the OLT in Figure 2
  • Figure 4 is a schematic drawing illustrating the 1+1 switching architecture for both upstream and downstream transmission between an ONU and the OLT in Figure 2
  • Figure 5 is a schematic drawing of a X:N protection PON system on which both the 1 :1 and the 1 +1 switching architectures in Figures 3 and 4 can be implemented
  • Figure 6 is a schematic drawing of a frame format for a 155.52/155.52 Mbits/s APON
  • Figure 7 is a schematic drawing of a protected PON system according to an embodiment of the present invention
  • Figure 8 is a
  • FIG. 7 shows a protected communication system 30 having multiple PONs 14.
  • Each PON 14 is configured in a multidrop topology to form a point-to-multipoint optical access network.
  • This network includes passive optical components, such as couplers/splitters 6 with no active elements.
  • Data transmissions in the system 30 are by an optical line termination (OLT) 8 at a headend and multiple optical network units (ONUs) 10 at the other endpoints of each PON 14.
  • OLT optical line termination
  • ONUs optical network units
  • the system 30 may be used to implement a fiber-to-the-home (FTTH), fiber-to-the-building (FTTB), fiber-to-the-cabinet (FTTCab), or fiber-to-the-curb (FTTC) subscriber access network.
  • FTTH fiber-to-the-home
  • FTTB fiber-to-the-building
  • FTTCab fiber-to-the-cabinet
  • FTTC fiber-to-the-curb
  • the OLT 8 resides in a local exchange (not shown), acts as the central controller, and connects the subscriber access network to a backbone of a larger network (not shown).
  • Each ONU 10 may reside at the curb or on subscriber premises to provide a combination of data, voice, video and other services to the subscribers.
  • the ONU 10 is more commonly referred to as an optical network termination (ONT) 10.
  • ONT optical network termination
  • multiple network terminations (NTs) 32 Figure 12
  • Each ONU 10 is connected to the OLT 8 via a PON 14A-14D serving as a communication link or path therebetween. If the PON 14 A-14D is the only PON A-14D between an ONU 10 and the OLT 8, the ONU 10 is considered as unprotected. However, if the ONU 10 is connected to the OLT 8 via at least another PON 14 A-14D, the ONU 10 is considered as protected. In the protected communication system 30 in Figure 7, ONU 1, ONU 2, and ONU X are protected while ONU 3 is unprotected. Each PON 14 A-14D, for example the tagged PON 14C, i.e.
  • PON 14 under observation which is shown in thicker lines in Figure 7, may serve as a primary or working PON 14C (for ONU 1, 3 and X) and as a secondary or protection PON 14C (for ONU 2).
  • the tagged PON 14C is the primary PON for ONU X and the other PON 14D to which ONU X is connected is the secondary PON for ONU X.
  • an NT 32 connected to ONU X is connected to the OLT 8 via two separate PONs 14C, 14D.
  • Bidirectional transmission between the OLT 8 and each of the ONUs 10 can be implemented in a number of ways.
  • One way is by having two parallel PONs, one for downstream transmission from the OLT 8 to the ONUs 10 and the other for upstream transmission from the ONUs 10 to the OLT 8.
  • This configuration is known as a "simplex working" configuration according to ITU-T terminology.
  • a more economical solution, known as a "diplex working" configuration is to use different wavelengths for downstream and upstream transmissions on a single PON.
  • Another solution known as a “duplex working" configuration, provides bi-directional transmission using the same wavelength. The invention is applicable to any of the above configurations.
  • the ONUs 10 can receive all downstream transmissions by the OLT 8.
  • An ONU 10 is able, with a suitable downstream frame format, to identify the data meant for it by the position of the data in a frame or by means of the ONU identification in header information in the frame. Due to the directional property of the passive splitters 6 in the PONs 14, transmission of an ONU 10 will not typically be received by other ONUs 10 but only by the OLT 8. However, multiple ONUs 10 transmitting at the same time may prevent the OLT 8 from receiving their transmission properly. A multi-access protocol is thus used to arbitrate different ONUs' upstream transmission.
  • WDM wavelength division multiplexing
  • TDMA time-division multiple access
  • CDMA code division multiple access
  • time division multiple access is still the most efficient and cost effective multi-access solution for PON type of networks.
  • This multi-access method is specified by ITU-T for the broadband PON (B- PON) system based on Asynchronous Transfer Mode (ATM) and advocated by the IEEE 802.3ah for the Ethernet Passive Optical Network (E-PON).
  • a sequence 40 for transferring data between a protected ONU 10 for example ONU X in Figure 7 and the OLT 8 to which ONU X is dual-homed to via the primary PON 14C and the secondary PON 14D is described next with the aid of the flowchart in Figure 8.
  • the sequence 40 starts in a START step 42 and proceeds to an ESTABLISH AND MAINTAIN CONNECTIONS step 44.
  • the ONU performs separate initialization processes with respective PON line terminators (LTs) 46 of the OLT 8.
  • LTs PON line terminators
  • Each initialization process involves a registration and ranging operation known to those skilled in the art.
  • the registration and ranging operations may be, for example, similar to those used in B-PON and E-PON systems.
  • the initialization process allows ONU X to establish and maintain a first connection and a second connection on the primary PON 14C and the secondary PON 14D respectively for the transfer of data thereon between the OLT 8 and the ONU X
  • the respective PON LTs 46 in the OLT 8 assign the ONU X with respective identifiers by which ONU X uses to communicate with the OLT 8.
  • the two PONs 14 used by an ONU X are designated as the primary PON 14C and the secondary PON 14D for ONU X
  • the sequence 40 next proceeds to a TRANSFER DATA step 48, wherein data is exchanged between the OLT 8 and ONU X over the primary PON 14C.
  • Data is transferred between the OLT 8 and ONU X using any suitable protocol.
  • One such protocol involves the OLT 8 polling ONU X, and ONU X responding by indicating to the OLT 8, via a message, the amount of data of ONU X queued thereat for upstream transmission to the OLT 8.
  • Other ONUs 10 connected to OLT 8 via the primary PON 14C will similarly indicate to the OLT 8 their respective queue statuses. Based on these ONU indications or reports, the OLT 8 allocates bandwidth of the primary PON 14C to the various ONUs 10. The bandwidth allocation scheme will be described in more details shortly.
  • ONU X While exchanging data with the OLT 8 over the primary PON 14C, ONU X maintains the second connection on the secondary PON 14D by indicating to the OLT 8, when polled thereby via a message sent thereto, that no data is available for transmission over the secondary PON 14D.
  • a report and grant scheme is described in more details in U.S. Patent 6,546,014, Kramer et al., entitled “Method and System for Dynamic Bandwidth Allocation in an Optical Access Network.”
  • Other report and grant mechanisms for example those used in the broadband passive optical network (B-PON) and the Ethernet passive optical network (E-PON) may also be used.
  • the sequence 40 next proceeds to a PRIMARY PON DOWN? decision step 50, wherein the primary PON 4C is monitored to determine if it is feasible for transfer of data thereon.
  • the primary PON 14C may be detected to be unavailable, for example, by monitoring the PON 14C for the presence or loss of signal thereon. Other means of detecting a fault condition of the primary PON 14C are also possible.
  • a transmission convergence function (not shown) in the OLT 8 governing bandwidth allocation for multi-access will be notified. If it is detected in this decision step 50 that the primary PON 14C is up or operational, the sequence 40 returns to the TRANSFER DATA step 48 to continue transferring of data over the primary PON 14C.
  • Transfer of data over the primary PON 14C terminates when it is detected in the PRIMARY PON DOWN? decision step 50 that the transfer of data over the primary PON 14C is no longer feasible.
  • the sequence 40 proceeds to a SWITCH TRANSFER OF DATA step 52, wherein transfer of data is switched from over the primary PON 14C to over the secondary PON 14D. Since connections over the primary and secondary PONs 14C, 14D are set up earlier in the ESTABLISH AND MAINTAIN CONNECTIONS step 44, transfer of data over the secondary PON 14D is effected instantaneously without having to first establish a connection thereon.
  • ONU X has to merely indicate to the OLT 8 when polled that it now has data available for transmission over the secondary PON 14D. With this method, only the queue status information sent over the secondary PON needs to be changed; no registration and ranging of ONU X with the OLT 8 over the secondary PON 14 is required.
  • the sequence 40 ends in an END step 54 when no data is available for transfer between ONU X and the OLT 8. [0043] The above steps are similarly performed for ONU 1 and ONU2 to allow an NTs connected to either one of ONU 1 and ONU 2 to be each connected to the OLT 8 via two separate PONs 14A-14D. The ONUs may share one or two PONs 14A-14D.
  • ONU 1 , ONU 2, ONU 3 and ONU X share a common PON 14C.
  • This common PON 14 is assigned as a primary PON 14C for ONU 1 , ONU 3 and ONU X and as a secondary PON for ONU 2.
  • each ONU may be connected to the OLT 8 via more than two PONs 14A-14D to further increase the survivability of data transfer between the ONU 10 and the OLT 8.
  • the subscribers 60 share the primary PON 14C by multiplexing their data thereon.
  • This same PON is also used as a secondary PON 14D as described above.
  • a subscriber using the PON as a primary PON 14C and a secondary PON 14D is referred to as a primary subscriber and a secondary subscriber respectively of that PON.
  • the primary subscribers using the PON 14C as a primary PON are shown in Figure 7 as being connected to the OLT 8 by solid unbroken lines throughout.
  • All other subscribers connected to the OLT 8 via the same PON 14C but without such a connection are secondary subscribers of the PON 14. These secondary subscribers are shown in Figure 7 to be connected to the OLT 8 by a line that is at least partially broken.
  • a subscriber 60 that is dual-homed to a single ONU 10 is a primary subscriber of the primary PON 14A-14D and a secondary subscriber of the secondary PON 14A-14D of the ONU 10 to which it is connected to.
  • subscribers 60 who need additional protection could also be dual-homed or multi-homed to two or more ONUs 10. This configuration will be discussed later.
  • a subscriber 60 that is connected to two ONUs 10 (such as a primary ONU 3 and a secondary ONU 2 for subscriber 3, 1) sharing a primary PON 14C of the primary ONU 3 remains a primary subscriber of that PON 14C.
  • SLA service level agreement
  • the SLA includes a protected information rate (PIR) and a committed information rate (CIR) that are indicative of a first maximum amount of data and a second maximum amount of data, respectively, that are transferable between that subscriber 60 and the OLT 8.
  • the PIR is indicative of or specifies bandwidth that can be guaranteed or protected when all primary and secondary subscribers of a PON 14A-14D use the PON 14A-14D.
  • the CIR specifies bandwidth that is guaranteed during normal PON operation when only primary subscribers of the PON use the PON 14.
  • the difference between the CIR and the PIR of a subscriber is the amount of bandwidth of the subscriber 60 that is committed but not protected.
  • the SLA with a subscriber 60 may further include a burst information rate (BIR), which is indicative of a third maximum amount of data that can be transferred for that subscriber 60 on the PON 14A-14D.
  • BIR burst information rate
  • the BIR can be implemented easily by limiting the data transmission rate on the ONU port of the ONU 10 to which a subscriber 60 is connected.
  • BIR ⁇ CIR ⁇ PIR BIR ⁇ CIR ⁇ PIR.
  • a bandwidth allocation scheme for allocating bandwidth to a subscriber on the tagged PON 14C in Figure 7 is next described.
  • the scheme determines a first bandwidth to allocate to each active primary subscriber, subject to the committed information rate (CIR) of the subscriber 60 when there is no active secondary subscriber on the PON 14C.
  • An active subscriber is one with data at its ONU 10 for transfer over the PON 14C or to which data at the OLT 8 is to be delivered to.
  • the scheme determines a first bandwidth to allocate to each subscriber subject to a maximum of the protected information rate (PIR) of the subscriber.
  • PIR protected information rate
  • the scheme After determining the respective first bandwidths for allocation to the active subscribers, the scheme determines the remaining bandwidth available on the PON 14C. Subsequently, the scheme determines a second bandwidth from the remaining bandwidth to allocate to each active subscriber having additional data for transfer, i.e. data over and above that for which the first bandwidth is allocated. The respective first bandwidths and second bandwidths are then allocated to the active subscribers.
  • the sum of CIRs of all primary subscribers 60 of the PON 14 and the sum of the PIRs of all primary and secondary subscribers 60 of the PON 14 are assigned such that they do not each exceed the bandwidth or data rate of the PON 14C.
  • subscriber (ij) denote a subscriber 60 that is connected to Port./ of an ONU / connected to the tagged PON 14C in Figure 7.
  • the tagged PON 14C may be the sole PON 14C (in the case of an unprotected ONU, such as ONU 3), the primary PON 14 (ONU 1 , 3 and X) or the secondary PON 14 (ONU 2) for the ONU 10 to which a subscriber (/,/) is connected to.
  • the following description will be based on transmission in the upstream direction. Transmission in the downstream direction is similar but simpler, and will be briefly described later.
  • P ltj be the PIR
  • Qj be the CIR
  • B i be the BIR for the respective subscribers (i,j) in the upstream direction.
  • a primary subscriber P ⁇ R,P U a secondary subscriber PIR
  • P i a primary subscriber
  • CIR, c ⁇ . , and a secondary subscriber CIR,C. . may be defined as follows: [P t j if the taggedPONis the primaryPON for subscriber ⁇ ' , j) 0 if thetaggedPONisthesecondary,protectionPONforsubscriber(z, j)
  • D b be the one-way delay bound for delay-sensitive services.
  • each ONU needs to have a response time of, D r , that fulfills the following condition: D r ⁇ D b - D p - D 0 - D q (5) wherein D p is the one-way propagation delay from an ONU to the OLT, D o is the fixed processing delay within the ONU, and D q is the queuing delay at the ONU.
  • the upper bound of queuing delay, D q can be computed if the buffer size allocated to the subscriber is known a priori.
  • the fixed processing delay, D 0 depends on the design of the ONU and several bit-time is achievable at a data rate of 1 Gbps.
  • the ITU-T Recommendation G.114 specifies that one-way transmission time, D b , should not exceed 1.5ms for an access network, which can be taken as the default value for D b .
  • D r is 1 ms although other values are also possible.
  • Figure 9 shows a cyclic upstream transmission sequence for m ONUs, each of which transmits data during its granted transmission window within a polling cycle.
  • the cyclic sequence can simply be based on the ONU identifiers although other sequences are also possible.
  • the sequence and duration for transmission by each subscriber 60 connected to an ONU 10, within the transmission window of the ONU 10, is shown in Figure 10.
  • the subscriber identifier or other suitable means may be used to determine the transmission sequence of subscribers.
  • the queue status of individual subscribers connected to an ONU 10 will be reported by the ONU 10 to the OLT 8. The manner in which the queue status is reported will be described later.
  • the queue status and other information will be used, by the OLT 8, to determine how much bandwidth or time the OLT 8 will allocate to each subscriber 60 for transmitting its data in the ONU queue in a polling cycle n.
  • Additional notations that will be used to mathematically illustrate the bandwidth allocation scheme, are listed below: m: Total number of ONUs supported by the tagged PON (including ONUs that access the tagged PON as its secondary PON); f.
  • Information on the PIR, CIR and BIR of individual subscribers can be obtained by the OLT 8 from predetermined values stored in a central database or individually configured. That is, some operators may decide to offer different grades of services, for example, Platinium, Gold and Silver, each having a set of fixed PIR, CIR and BIR. In this case, the PIR, CIR and BIR values will be obtained from a table in the database. The operators may also choose to allow each customer, such as a major customer, to request for a desired set of PIR, CIR and BIR according its need and/or budget. In this case, the information needs to be configured for that particular customer. [0056] For an arbitrary subscriber (/ ' , j), transmission time, £7 ⁇ . , corresponding to the above-described first bandwidth when there is at least one active secondary subscriber, is set based on the PIR and the tagged PON's data rate, S, using the following equation:
  • q- is obtainable by the OLT 8 from the queue status information sent by ONU / to the OLT using a report message. It represents the bandwidth that is required by the subscriber for transmission of all of its queue data. The manner in which v" ; . and y" ⁇ is computed will be described later.
  • the allocated transmission time, u. may be set to a value just enough for the subscriber (/, J) to send complete frames whose total transmission time when added up does not exceed U ⁇ +v. + y. ).
  • z" >k be the transmission time of frame k
  • Equation (9) To allocate u" based on the exact amount of time required in accordance with Equation (9) results in additional overheads that are required to describe the length of each frame in the queue at the ONU for subscriber (i,j).
  • the overheads can be reduced by defining the length as a number of blocks, each of which is some integer multiple of bytes.
  • w" , w, and t" can be represented in terms of w". and u u using the following equations:
  • the tagged PON is the primary PON for subscriber (/ )
  • the actual value of ⁇ will be conveyed to the OLT 8 in the report message or a similar reporting mechanism.
  • the tagged PON is the secondary PON for subscriber (i,j)
  • an ONU 10 either does not send any report message to the OLT 8 or report a zero value for q" ⁇ for subscriber (ij). Note that only one report message/PLOAM cell is required in each cycle for an ONU to report the queue status of all the subscribers connected to it.
  • v" y andy" y in Equations (8) and (9) can be computed.
  • v" y is the extra time or bandwidth, over and above w". , allocated to subscriber (ij) to meet its
  • the total reserved bandwidth, , and m f, unallocated bandwidth, S - P l ⁇ could be allocated to the active primary i-l j-1 subscribers 60 on the tagged PON to transmit up to their C I .
  • Equation (16) For the case of (U t + v" y ) ⁇ q" ⁇ . , i.e. there is more queued data than is transferable based on the CIR, the following equation can be used to replace Equation (16) if the amount of time allocated is required for transmitting an integer number of complete Ethernet frames or ATM cells etc.
  • the bandwidth allocation method according to the above-described embodiment of the invention has several advantages. Bandwidth is protected and guaranteed on a per-subscriber basis. This means all the subscribers that are connected via the same ONU can have different levels of reliability and amount of guaranteed bandwidth. Consequently, service level agreements can be more flexible. Unprotected or non-guaranteed bandwidth of individual subscribers could be degraded gracefully and not denied bandwidth completely when a fault occurs or when there is less unused bandwidth for non-bandwidth guaranteed subscribers, respectively. The method allows the bandwidth reserved for protection to be used by other users during normal operation when no fault has occurred.
  • PON frame structures may also be used.
  • a number of bits say 8, could be used to report the number of subscribers supported by the ONU.
  • the use of 8 bits for such a purpose limits the number of subscribers that can be supported per ONU to 256.
  • Two bytes may be used for reporting the queue status for each subscriber. 13 of the 16 bits in these two bytes are used to indicate the number of bytes in the queue while the remaining 3 bits can be used for other purposes. This allows a maximum buffer occupancy of 8,192 bytes to be represented.
  • Guard time is primarily determined by a clock and data acquisition (CDA) function of a burst mode receiver (not shown) at the OLT.
  • CDA clock and data acquisition
  • a guard time in the order of 1 ⁇ s or 1000 bits has sufficient margin for a transceiver with a slow CDA time.
  • CDAs requiring a guard time, g, in the order of only a few bits are available.
  • the guard time, g, between two ONUs' transmissions is 1 ⁇ s.
  • the service provider assumes that all the subscribers transmit at their BIR all the time.
  • the total number of Silver service subscribers that can be supported for the following 3 cases are determined: A. When protection bandwidth is not allocated to other subscribers during normal operation, even though the protection bandwidth is unused (as practiced in the prior art); B. When the unused protection bandwidth is allocated to other subscribers during normal operation; and C. When fault has, occurred and all PIR data of Gold service subscribers has to be supported.
  • a g , a s and a b be the number of Gold, Silver and Bronze service users per ONU, respectively.
  • g , p s and p b be the PIR
  • c g , c s and c b be the PIR
  • CIR and b g , b s and b b be the BIR of the Gold, Silver and Bronze service subscribers, respectively.
  • the overhead in each cycle due to guard time, g (for example, in seconds), and the PON frame overhead is:
  • Figure 13 shows a plot of a s against a g , for the results tabulated in Table A. As can be seen from the results, higher bandwidth utilization is achievable in case B.
  • the bandwidth allocation and protection scheme described above for a PON between an ONU and its OLT can also be implemented independently for a link between an NT and its primary ONU, i.e. the NT is connected to two separate ports of the primary ONU. It is not necessary that the scheme be restricted to the type of protocol used between an NT and an ONU; any suitable protocol may be used.
  • the huge overhead of maintaining a queue for each subscriber and reporting the queue status to OLT may make the above-described bandwidth allocation scheme less attractive.
  • NTs could be dual-homed or multi-homed to two or more ONUs.
  • the subscriber For the case of a subscriber dual-home to two ONUs, say to Port j of ONU / as a primary access and Port y of ONU x as a secondary access, the subscriber is said to be subscriber (ij) with a non-zero PIR, CIR and BIR as well as subscriber (x,y) with a zero PIR, CIR and BIR during normal operation.
  • subscriber (x ⁇ y)'s PIR, CIR and BIR will assume the values of subscriber (ij) while the PIR, CIR and BIR of subscriber (ij) will be set to zero. If the two ONUs, to which the subscriber is dual-homed to, are attached to two disjoint primary and secondary PONs, the dual-homed subscriber can survive up to failures of three separate PONs.

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Abstract

Cette invention concerne un procédé de transfert de données dans un système de communication qui comprend un premier noeud de communication et au moins une unité utilisateur. Le procédé consiste, individuellement pour chaque unité utilisateur, à établir et à maintenir deux connexions de transfert de données distinctes simultanément, chacune sur une voie différente entre le premier noeud de communication et l'unité utilisateur. Une première connexion de transfert de données est attribuée en tant que connexion primaire tandis que l'autre connexion de transfert de données est attribuée en tant que connexion secondaire entre le premier noeud de communication et l'unité utilisateur. Les données sont transférées sur une voie de communication primaire sur laquelle la connexion primaire est établie et le transfert des données est basculé instantanément de la voie de communication primaire à une voie de communication secondaire sur laquelle la connexion secondaire est établie, lorsque le transfert de données sur la voie de communication primaire n'est plus possible. Cette invention concerne également un système qui met en oeuvre le procédé décrit plus haut.
PCT/SG2004/000147 2004-05-25 2004-05-25 Procede et systeme de transfert de donnees Ceased WO2005117300A1 (fr)

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CN101836379A (zh) * 2007-10-24 2010-09-15 英国电讯有限公司 光通信
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EP2795811A4 (fr) * 2011-12-22 2015-07-29 Tyco Electronics Corp Plaque de paroi de fibre optique ayant un système de redondance
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CN104092714B (zh) * 2013-09-25 2016-02-17 腾讯科技（深圳）有限公司 流媒体文件的播放方法及装置
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US10598887B2 (en) 2014-10-06 2020-03-24 Commscope Technologies Llc Facilitating installation of fiber optic networks
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CN115643504A (zh) * 2022-10-12 2023-01-24 广州芯德通信科技股份有限公司 一种双归属pon保护自动同步配置的方法
CN115643504B (zh) * 2022-10-12 2023-05-12 广州芯德通信科技股份有限公司 一种双归属pon保护自动同步配置的方法

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