A kind of EPON cascade system and optical line terminal thereof
Technical field
The present invention relates to a kind of passive optical network, relate in particular to a kind of extendible multilevel hierarchy EPON cascade system and optical line terminal thereof.
Background technology
Passive optical access network (PON) is the technical scheme that a kind of Optical Distribution Network that utilizes Passive Optical Components such as optical fiber and optical branching device to constitute carries out broadband access.It is normally by optical line terminal (OLT), and optical network unit (ONU) and Optical Distribution Network (ODN) constitute.Existing P ON technology comprises the APON/BPON based on ATM(Asynchronous Transfer Mode), based on the EPON of Ethernet and the GPON with gigabit (Gigabit) speed.
With EPON is example, EPON encapsulates data flow with 802.3 ethernet frame formats a kind of EPON.EPON uses the 8b/10b line coding of standard and has the Ethernet speed (10/100/1000/10000Mbps is a MBPS) of standard.As Fig. 1, traditional EPON system is made up of the OLT that is positioned at local side and several ONU that are positioned at user side.OLT links to each other with each ONU by ODN.At down direction, OLT sends ethernet frame, and ethernet frame arrives each ONU by passive optical splitter, and ONU receives one's own ethernet frame selectively based on the MAC Address of the ethernet frame that receives; At up direction, because each ONU shares same optical channel, PON uses the frame conflict of time division multiplexing technology (TDMA) when avoiding sending, OLT sends the corresponding time slot of data allocations for each ONU, in institute's distributed time slot, each ONU can wire rate sends the ethernet frame in its buffering area, does not also use up if the ethernet frame in its buffering area all sends the back institute distributed time slot that finish, and ONU sends 10 empty bit character so.At present to have defined that Multi-point Control Protocol (MPCP) comes be that each ONU distributes time slot to IEEE (IEEE) 802.3ah task groups.The MPCP agreement relies on two kinds of Ethernet message: door (GATE) message and report (REPORT) message.OLT sends GATE message to distribute the time slot that allows transmission for it to ONU, ONU sends REPORT message and reports its local current state (for example the current buffer length of ONU etc.) to OLT, and OLT will decide the bandwidth of distributing to each ONU according to the REPORT message that receives.Bandwidth allocation methods mainly contains two big classes: static bandwidth allocation and Dynamic Bandwidth Allocation.Wherein, the Dynamic Bandwidth Allocation scheme has greater flexibility, particularly under the burst flow situation, can more effectively improve the up link utilance.
From top description as can be known, in the traditional E PON network, OLT and ONU have strict function to divide: it is that the bandwidth of its distribution is come transmitting user data that ONU utilizes OLT, and the bandwidth demand of the ONU that bandwidth request that OLT sends according to ONU or OLT arrive according to its active monitoring, is the suitable upstream bandwidth of each ONU distribution by dynamic bandwidth allocation algorithm (DBA).Obviously in traditional E PON network, OLT does not send bandwidth request, is the primary network station structure between OLT and the ONU.
Along with the development of Internet, increasing user possesses Broadband Internet and inserts.From operator's angle, wish that single OLT can support ONU as much as possible to obtain bigger profit.Saying from technical standpoint, can support more ONU by the cascade optical branching device at present, is an EPON network that utilizes the two-stage optical branching device to form as Fig. 2, among the figure, first order optical branching device is 1: 3, and second level optical branching device is 1: 32, like this, OLT can connect 96 ONU among the figure.But support more ONU can bring other problems by the optical branching device cascade, for example: management may reach the allocated bandwidth of several thousand ONU will bring very big burden to OLT; Simultaneously, support too much ONU will make circulation (Cycle) excessive cycle of DBA algorithm.As Fig. 3 is EPON network Dynamic Bandwidth Allocation schematic diagram, detailed description can be with reference to U.S. Pat 6546014, in open day on April 8th, 2003, invention and created name is " distribution method of dynamic bandwidth in the Optical Access Network and system " (Method and system for dynamic bandwidth allocation in an opticalaccess network).Suppose that guard time is 5us (microsecond); DBA algorithm according to EPON; owing to distribute to time slot 〉=one frame time+guard time of each ONU; even the requirement of a frame time here is because ONU does not have transfer of data, also needs to send the report frame and represent that its buffering area is current and do not have data to need uplink to OLT.Suppose in the EPON network, OLT can support 4000 ONU by the cascade optical branching device, the report frame is 1000bit (bit), uplink rate is 1000,000,000bps (bps), even all ONU all do not have data to want uplink so, cycle period 〉=4000 * (5+1000 * 1000,000/1000,000,000)=4000 * 6us=24ms (millisecond), if add the data transmission period of each ONU, suppose that average each ONU can obtain the transfer of data chance of 1 1500 byte in a cycle period, cycle period will reach 24+48=72ms so, and so Chang cycle period never allows some applied business, Time Division Multiplexing business for example, TDM Over Packet/Ethernet service application etc.
Based on above analysis, be the excessive shortcoming of the cycle period that overcomes DBA algorithm in the extensive EPON, for increasing the PON system expandability and strengthening the effective bandwidth management of OLT to ONU, the present invention proposes a kind of EPON cascade system and Cascading Methods thereof simultaneously.
Summary of the invention
The present invention aims to provide a kind of large-scale group network system that can be used for EPON;
The present invention also provides a kind of passive optical network that can be used for cascade upper level optical line terminal;
The present invention is further by carrying out function expansion to the optical line terminal in the traditional passive optical-fiber network, thus can make this EPON have cascade function, to be conveniently used for setting up large-scale EPON cascade system.
The technical solution used in the present invention is as follows:
A kind of EPON cascade system, comprise first optical line terminal and the some optical network units that connect by first Optical Distribution Network, described first Optical Distribution Network further connects the plurality of cascaded EPON, and described cascade passive optical-fiber network comprises second optical line terminal and the some optical network units that are connected with second optical line terminal by second Optical Distribution Network; Second optical line terminal is connected with first optical line terminal by first Optical Distribution Network, wherein, first optical line terminal is on up direction, reception is from upstream data, the report message of second optical line terminal of each optical network unit, described cascade passive optical-fiber network, and carries out allocated bandwidth according to report message; Described first optical line terminal is on down direction, to the second optical line terminal transmitting downlink data, the authorization messages of each optical network unit, described cascade passive optical-fiber network.
In the above-mentioned EPON cascade system, second optical line terminal of cascade passive optical-fiber network receives upstream data and the report message from each optical network unit of this EPON, and carry out allocated bandwidth, and downlink data, authorization messages transmission according to report message; And receive downlink data, authorization messages, and according to this authorization messages transmit ascending data and report message from first optical line terminal.
A kind of passive optical network, comprise optical line terminal, and the some optical network units that connect by Optical Distribution Network, described optical line terminal receives upstream data and the report message from each optical network unit, and carry out allocated bandwidth according to report message, and downlink data, the authorization messages transmission, it is characterized in that described optical line terminal further comprises the cascade UFIU UMSC Fiber Interface Unit, be used to connect the upper level optical line terminal, reception is from the downlink data of upper level optical line terminal, authorization messages, and according to this authorization messages transmit ascending data and report message.
A kind of optical line terminal that is used for passive optical network, link to each other with some optical network units by Optical Distribution Network, optical line terminal communicates by LTU Line Termination Unit and described optical network unit, it is characterized in that described optical line terminal further comprises the cascade UFIU UMSC Fiber Interface Unit, be used to connect the upper level optical line terminal, reception is from downlink data, the authorization messages of upper level optical line terminal, and according to this authorization messages to upper level optical line terminal transmit ascending data and report message.
Above-mentioned optical line terminal, described cascade UFIU UMSC Fiber Interface Unit comprises the cascade transmitting element that is used for to upper level optical line terminal transmit ascending data and report message, and is used to receive the downlink data from the upper level optical line terminal, the cascade receiving element of authorization messages.
The bandwidth request report message of the optical network unit that above-mentioned optical line terminal, described cascade transmitting element are connected with this optical line terminal according to the current queue length of its data buffer zone, and generate the report message frame with this.
EPON cascade system provided by the invention and method thereof can be used for using on a large scale, neatly networking, and PON network that can a plurality of scales are less couples together forms a larger EPON.Under this cascade system, second optical line terminal in the EPON that is cascaded, on the one hand, it carries out Dynamic Bandwidth Allocation for each ONU under the passive optical network at the corresponding levels, on the other hand, as the network node of first optical line terminal in the cascade passive optical network system, it accepts first optical line terminal bandwidth of dynamic assignment for it.By this cascade mechanism, avoided going up the dynamic bandwidth allocation algorithm decreased performance that the too much ONU of management brings because of an OLT.In addition, the present invention is different from the cascade mechanism that utilizes multistage optical branching device, when adopting multistage optical branching device cascade, communication between any two ONU is because all must be through unique OLT in the PON system, delay character is directly influenced by the cycle period of the DBA algorithm of this OLT (to know from the analysis of front, under multistage optical branching device mechanism, when several thousand ONU nodes, the cycle period of DBA algorithm is bigger, for example cycle period has tens milliseconds under 4000 node situations), and in EPON cascade system of the present invention, the communication between two ONU, its delay character is greatly improved, than good under multistage optical branching device mechanism.
Description of drawings
Fig. 1, a kind of typical Ethernet passive optical network (EPON) system;
Fig. 2, the EPON network that utilizes multistage optical branching device to constitute;
Fig. 3, EPON network Dynamic Bandwidth Allocation schematic diagram;
Fig. 4, EPON cascade system of the present invention are implemented one of legend;
Fig. 5, be OLT structural representation in the cascade passive optical network system of the present invention;
Fig. 6, be OLT bandwidth request flow chart in the cascade passive optical network system of the present invention;
Embodiment
Below in conjunction with accompanying drawing, preferred implementation of the present invention is described in detail.
The present invention is different from traditional primary structure PON network that has only, and EPON cascade system of the present invention can have multilevel hierarchy, and for convenience of description, the OLT node that we claim to be in top layer is 0 grade of OLT, and 0 grade of OLT is by Optical Distribution Network (ODN0) and N
1Individual cascade passive optical-fiber network is connected with some ONU, and we claim this N
1OLT node in the individual EPON is 1 grade of OLT (intergrade OLT), and 0 grade of OLT utilizes Dynamic Bandwidth Allocation to control this N
1Uplink and downlink allocated bandwidth between individual 1 grade of OLT, some ONU to the 0 grade of OLT; Each 1 grade of OLT can be again by Optical Distribution Network and N
2Individual EPON is connected with some ONU, and we claim this N
2OLT in the individual EPON is 2 grades of OLT (intergrade OLT), and 1 grade of OLT utilizes Dynamic Bandwidth Allocation to control this N
2Uplink and downlink bandwidth between individual 2 grades of OLT to 1 grade of OLT.The rest may be inferred, and whole EPON cascade system is can cascade multistage.
In the EPON cascade system of the present invention, but the different dynamic bandwidth allocation algorithm GA of the OLT independent utility in the EPON of upper level OLT and cascade; But the bandwidth request algorithm RA that the OLT in the EPON of cascade is different with each ONU also independent utility.
In the EPON cascade system of the present invention, bandwidth request and upper level OLT that OLT in the EPON of cascade can send according to situation, its next stage ONU or the OLT of up cascade buffer queue are the information such as current bandwidth of its distribution, next stage ONU or OLT in the EPON of cascade are carried out Dynamic Bandwidth Allocation, and to upper level OLT request corresponding bandwidth.
Be without loss of generality, EPON cascade system of the present invention illustrated in Figure 4 is implemented legend and has only been provided two-stage EPON cascade system.
For 0 grade of OLT, during OLT (0) initialization, acquire the response time t of each 1 grade of OLT (i) (i=1,2,3) by ranging process
1, Res[i], OLT (0) is that each 1 grade of OLT distributes initial Grant timeslice G simultaneously
1[i] [0]; OLT (0) is in its j Grant cycle (wherein j 〉=0), according to certain scheduling rule, successively with Grant message at corresponding t constantly
1, G[i] (i=1,2,3) are distributed to each 1 grade of OLT (i) of its connection, and each 1 grade of OLT (i) is according to the Frame G of its up transmission of permission specified in the Grant message
1[i] [j] (is timeslice length in fact, can be directly corresponding with frame number, byte number or bit number) and time of beginning to send, each 1 grade of OLT (i) sends to OLT (0) with the Frame in its up buffer queue, and its Report message sends to OLT (0) at the end of last Frame of up transmission simultaneously; OLT (0) distributes each 1 grade of interior bandwidth of OLT (i) j+1 cycle, and sends to each 1 grade of OLT (i) by Grant message according to the Report message that receives.
As previously mentioned, the data flow of each 1 grade of OLT (i) transmission is at moment t
1, RWhen [i] arrived OLT (0), OLT (0) can calculate and be updated to the response time t of each 1 grade of OLT (i)
1, Res[i]=t
1, R[i]-t
1, G[i]; Here, because the in store response time t of OLT (0) to each 1 grade of OLT (i)
1, Res[i]; therefore OLT (0) can be by suitable scheduling; make being pressed for time of first bit arrival OLT (0) of OLT (2) data that send follow after last bit of OLT (1) data that send arrives the time of OLT (0), differ a boundary belt time G between the two
1, IEqually; OLT (0) is by suitable scheduling; make being pressed for time of first bit arrival OLT (0) of OLT (3) data that send follow after last bit of OLT (2) data that send arrives the time of OLT (0), differ a boundary belt time G between the two
1, IOLT (0) sends Grant message to 1 grade of OLT (1) once more by scheduling; make being pressed for time of first bit arrival OLT (0) of OLT (1) data that send follow after last bit of OLT (3) data that send arrives the time of OLT (0), differ a boundary belt time G between the two
IAt this moment OLT (0) enters its j+1 Grant cycle.
For the report mechanism of 1 grade of OLT, can pass through the bandwidth request algorithm RA
1, in its j Grant cycle (wherein j 〉=0), according to the current queue length Q of its up buffer queue
1The Report message R of [i] [j+1] and the next stage ONU transmission that is connected
2Generate a Report message, expression asks it can send R j+1 Grant cycle to OLT (0)
1The individual Frame of [i] [j+1], wherein R
1[i] [j+1]=RA
1(Q
1[i] [j+1], R
2), as previously mentioned, Report message is incidentally at the end of last Frame of the up transmission of this 1 grade of OLT (i);
For the allocated bandwidth mechanism of 0 grade of OLT, when OLT (0) receives the Report message of each 1 grade of OLT (i) transmission, by bandwidth allocation algorithm GA
1, generating corresponding Grant message, this Grant message is specified and is allowed 1 grade of OLT (i) to send G
1The individual Frame of [i] [j+1], wherein G
1[i] [j+1]=GA
1(R
1[i] [j+1]);
Fig. 5 is OLT structural representation in the cascade passive optical network system of the present invention, in a cascade passive optical network system, optical line terminal comprises Ethernet bridge 50, optical line terminal unit 51, upstream data and report message that OLT receives from this each optical network unit of passive optical network by its optical line terminal unit 51, and carry out allocated bandwidth, and output downlink data, authorization messages according to report message; Carry out cascade for ease of upper level OLT, this optical line terminal further comprises cascade UFIU UMSC Fiber Interface Unit 52, be used to connect the upper level optical line terminal, receive downlink data, authorization messages from the upper level optical line terminal, and according to this authorization messages transmit ascending data and report message.This cascade UFIU UMSC Fiber Interface Unit 52 comprises cascade receiving element 52B, downlink data, authorization messages from upper level OLT, after light/electricity conversion, decoding circuit processing, serial/parallel row conversion, export the descending cascade receiving cache queue of descending reception control unit to, after removing the PON label, removing LLID LLID, send Ethernet bridge 50 ports according to MAC Address.Equally, this connecting port unit 52 comprises cascade transmitting element 52A, its uplink control unit adds the PON label, adds LLID LLID according to MAC Address the uplink data frames from Ethernet bridge 50 ports, put into up cascade and send buffer queue, and according to upper level OLT authorization messages, Frame in its transmission buffer queue is sent to upper level OLT through parallel/serial row conversion, coding circuit processing, electricity/light after changing at the time slot position (under the clock circuit control) of authorization messages appointment; The uplink control unit also moves the bandwidth request algorithm RA, send the bandwidth request report R message of the next stage optical network unit that the current queue length Q of buffering area is connected with optical line terminal unit 51 according to up cascade, and generate the REPORT message frame with this, be attached to last Frame end and be sent to upper level OLT.
Fig. 6 is OLT bandwidth request flow chart in the cascade passive optical network system of the present invention, it comprises following concrete steps: step 60), intergrade OLT initialization, initialization procedure comprise to the upper level OLT that is connected register this intergrade OLT, ranging process that the upper level OLT that connected is initiated makes response; Step 61), intergrade OLT waits for and to receive the GATE message frame that the upper level OLT that connected sends; And step 62) in, intergrade OLT makes an explanation to the GATE message frame that receives, transmitting time and Grant time slot according to this message frame appointment are provided with timer T and send window W, the waiting timer T time is to (step 63) simultaneously; The timer T time is to showing that intergrade OLT can begin to send the traffic frame in its up transmission buffering area, step 64 now) in, this intergrade OLT notes the bandwidth request R of the next stage OLT/ONU that the current queue length Q, its that send buffering area connected; Afterwards, in step 65), intergrade OLT sends Min (Q, W-1) individual frame in the up transmission buffering area with wire rate; Step 66) intergrade OLT is by the bandwidth request algorithm RA, according to the current queue length Q of up transmission buffering area and the bandwidth request R of the next stage OLT/ONU that is connected, and generate the REPORT message frame with this, at the Min that is sent (Q, W-1) after the last frame of individual frame, this frame is sent to the upper level OLT that is connected.Afterwards, intergrade OLT enters the next GATE Messages-Waiting cycle; In the next GATE Messages-Waiting cycle, repeat above-mentioned steps 61) to step 66).
For OLT allocated bandwidth flow chart in the cascade passive optical network system of the present invention, this flow process and conventional OLT allocated bandwidth flow chart basically identical.It should be noted that, the information of the REPORT frame that the next stage ONU that conventional OLT utilization is connected is sent out to distribute the Grant timeslice for the next stage ONU that is connected, and intergrade OLT provided by the invention can utilize the information of information, himself up buffer queue of the REPORT frame that next stage OLT or ONU sent out that is connected and upper level OLT for the current Grant timeslice of its distribution etc. simultaneously, is that next stage OLT or the ONU that is connected distributes the Grant timeslice.Here be not repeated.
As a further improvement on the present invention, system can adjust according to system's needs bandwidth request algorithm RA, bandwidth allocation algorithm GA etc.
Below embodiment has been described in detail the present invention in conjunction with the accompanying drawings, and those skilled in the art can make the many variations example to the present invention according to the above description.Thereby some details among the embodiment should not constitute limitation of the invention, and the scope that the present invention will define with appended claims is as protection scope of the present invention.