1 introduction
In recent years in the global scale data current capacity’s explosion as well as the IP service’s swift development proposed many new topics for the current network construction. On the one hand the traditional telephone business and rents foundation telecommunication services and so on line service was still the present telecommunication operator business income important source, on the other hand data traffic’s high speed development force telecommunication network IP turned into is the tendency which was unable to reverse. The data, the pronunciation and the video frequency service’s fusion has become the inevitable trend which the next generation network (NGN) develops. How to let the data network load bearing TDM service as well as how to give dual attention to the existing service and the future network development has become the focal point which various telecommunications operator will pay attention. But the end-user always hoped that realizes the telephone, the video frequency and the data by as far as possible the low cost in the enterprise or the family interior and so on many kinds of service synthesis turning on. EPON as new generation’s broadband access technology to satisfy the network development and the fusion objective request, must realize many kinds of services including TDM service synthesis turning on.
how in 2EPON to realize the TDM service
The Ethernet seal way causes the EPON technology to be suitable for the load bearing IP service at the same time also to cause it faced with TDM services and so on significant difficult problem - - with difficulty load bearing pronunciation ‘OR’ circuit the way data. EPON is based on ethernet’s asynchronous transmission network, it does not have the entire net synchronization high accuracy clock, is unable to satisfy the TDM service fixed time with the synchronized request. Must solve at the same time the TDM service synchronized problem fixed time to guarantee that QoS technical difficult problems and so on TDM service not only need to make the improvement in EPON system own design, simultaneously also needs to use some specific technologies.
At present, realizes the TDM service on the EPON system to transmit the most main one method is based on the packet switching network circuit simulation technology (CESoP, CircuitEmulation over Packet Switched Net).
2.1 from circuit switching to packet switching basic philosophy
The CESoP technology is refers to the non-TDM network carries on the circuit simulation, realizes TDM service like E1/T1, E3/DS3 perhaps STM-1 and so on the packet switching network transmission. Its basic principle is builds one in the packet switching network “the channel”, through increases the masthead, seals each T1 or the E1 frame with the IP package, (PSN) passes through the packet-switched network passes to the end. After the goal end receives the data packet, produces the synchronized clock signal, simultaneously removes in the data packet the IP head, transforms the primitive TDM data stream other data, thus causes the network both sides the TDM equipment not to care that its connection network whether is the TDM network. CESoP to E1 is the transparent transmission, therefore it is good to the traditional telecommunication network compatibility, all services and so on tradition’s agreement, signaling, data, pronunciation, image, can be left intact use this new technology; Moreover is related the equipment cannot make any modification, may cause the telecommunication operator full use existing resources, traditional TDM service application in IP on-line.
2.2 circuit simulation implementation
The CESoP circuit simulation request must have alternately the connection function in the packet switching network’s both sides. In the packet switching network entrance, connects the function alternately TDM data conversion a series of groupings, but uses this in the exit a series to group produces the TDM electric circuit again. At present has the structurized simulation and non-structurized simulation these two methods realizes this kind of interactive functional module.
The structurized simulation has used in the TDM electric circuit the inherent time slot structure. First (for example in DS1 F) withdraws the frame structure from the data stream, then joins according to the order each time slot to the grouping payload, behind again with next identical time slot, so relapse. After the payload fills up completely, then adds on a grouping head, this grouping is transmitted to the packet switching network. The payload contains about eight TDM data generally (speaking of the E1 electric circuit namely has 256 eight elements). In the grouping network’s exit, the TDM data stream is had, and uses the new frame structure.
The non-structurization’s transmission mode neglects any structure which in the TDM electric circuit possibly exists, regards as the data to assign the data rate the pure potential flow. Intercepts a series of octets from the TDM potential flow according to the order to constitute the grouping payload. Therefore, constitutes each grouping payload octet quantity is stochastic. Generally the selection payload’s length causes the grouping constitution time about 1ms, regarding the T1 electric circuit, this length is 193 octets (see Figure 2). Regarding the E1 electric circuit, this length is 256 eight elements. Thus, in the TDM service’s signaling is transmitted transparently, does not need any signaling protocol conversion equipment to be possible to realize any type TDM service.
2.3CESoP standardization
The related CESoP technology’s standardized work has been launching methodically. At present has 4 Standardization organizations to be engaged in the CESoP technology the standardized work, respectively is the International Telecommunication Union (ITU, InternationalTelecommunicationsUnion); Internet project duty group (IETF, Internet Engineering Task Force); MPLS and frame relay alliance (MFA, MPLS and Frame Relay Alliance); City territory ether forum (MEF, Metro Ethernet Forum). Organizes to pay attention to oneself specialty closely respectively the domain.
ITU-T suggested that Y.1413ITU is about realizes the TDM suggestion in the MPLS network. Defined adopted the MPLS network load bearing electric circuit service the form. This suggestion mainly stipulates the TDM-MPLS network intercommunication the essential function request. This standard support structurization TDM simulation and non-structurized TDM simulation.
The IETF subordinate’s (PWE3, PseudoWireEmulation Edge-to-Edge) the work team is responsible edge to the edge false line simulation to formulate the packet-switched network (PSN) on the artificial network service mechanism. By simulation network service including the digital TDM special line, frame relay (FR), ATM cell and ATM adaptive (AAL), Ethernet and Ethernet VLAN, HDLC, PPP and so on.
MPLS and frame relay alliance (MFA) had issued recently the TDM simulation realizes agreement MFA 8.0.0, this agreement has stipulated through MPLS the network load bearing TDM circuit simulation seal form, the connection establishment and the demolition and so on; Also simplified through MPLS the load bearing TDM transmission question, allows the operator to simultaneously to provide the pronunciation, the video frequency and the data traffic sole, the fusion network shift.
MEF has authorized new telecommunication level ethernet technology standard MEFx (x=1. , 8). And, the MEF8 standard had stipulated (PDH) the circuit simulation realizes the method based on the city territory ethernet’s orbit data series. MEF 8 and will urge the city territory ethernet in view of the ethernet test step and network management’s new standard to develop into one kind of telecommunication level transmission technology together.
Along with these standard’s formulation, between the different equipment manufacturer’s interconnection intercommunication question will be solved gradually. At present the EPON manufacturer uses the TDM simulation chip mainly uses IETF PEW3 work team’s edge to edge false line simulation (PEW3) technology.
3TDMoverEPON realizes key technologies
3.1 clock recoveries and the vibration are smooth
The clock recovery and the vibration smooth are the TDM grouping circuit simulation realize the two key technologies
3.1.1 clock recoveries
In any realizes in the circuit switching technology through the grouping, one of most essential questions is the clock recovery. For example, uses between two client sides special-purpose rents the line to group in the network through the operator the simulation link to carry on the connection, then customer TDM service frequency fservice must produce precisely in the grouping network exit. The long time’s frequency will not match will cause the grouping network exit to form the Waiting line, if will produce the clock will be slower than the original clock, then the buffer is filled up, otherwise clear spatial. These two kind of situations can create the data missing and the grade of service drop. But must realize to the TDM service support, the ONU side’s clock recovery technology is the question which must first solve. Speaking of the circuit simulation technology itself, at present mainly has based on the SDH indicator adjustment way, the difference way and auto-adapted and so on 3 clock recovery way.
In IETF in formulation documents draft-ietf-pwe3-sonet-09.txt, defined has realized in the grouping network synchronization fixed time using the SDH indicator adjustment technology. Simultaneously has also defined explicit indicator adjustment relaying (EPAR:ExplicitPointerAdjustmentRelay) and the auto-adapted indicator management (APM:Adaptive Pointer Management) these two indicator mode of administration realizes the network synchronous operation: The EPAR way through the redundant transmitting end’s indicator adjustment event guaranteed that the TDM data by with the transmitting end same speed by the receiving end read, is usually applied in the transmitting end and in the receiving end existence public reference clock’s situation; When APM through maintains the TDM data receives the same speed is maintained by the receiving end read the vibration buffer the use factor at certain scope, this time usual transmitting end and receiving end not public clock reference. Because EPAR and the APM way realizes the clock recovery is based on essentially the traditional SDH technology indicator adjustment, although can guarantee system’s clock synchronization, but realizes is very complex, the cost is very high, does not suit in the EPON system scale application.
The difference way is uses the high accuracy in the transmitting end and the receiving end the clock reference source, arrives at the frequency and the main reference source difference of frequency through the comparison package carries on the compensation, realizes the TDM service synchronization. This method has the very good vibration and the drifting characteristic,
To a great extent not network time delay, network time delay change and package of loss influence, but needs to provide the public reference clock in the both sides. Should realize the way mainly to be suitable for the transmitting end and the receiving end is located at the telecommunication engine room or other existence high accuracy telecommunication clock’s situation,
The auto-adapted clock recovery way does not need the transmitting end and the receiving end has the public reference clock. The clock information which according to arrives at a package of institute in the receiving end to carry the information which may restore needs. The timing information already may be (Timestamp) the value gains through quite local and the far-end time indice, may also act according to a package of gap to arrive at the speed or the vibration buffer packing level gains. Because EPON itself mainly uses in the user access network, in addition EPON may give the specific data packet to provide the very high grade of service, therefore the auto-adapted clock recovery way will apply in the EPON system will obtain the very good clock characteristic.
3.1.2 vibrations are smooth
Because the ethernet uses shares the channel, supports the memory repeater, the data packet transmission time delay beyond control, has the very big randomness, causes Bao Yu a package of between the transmission latency to be bad, even if all groupings carry on the transmission through the network identical way, when they arrive at the network exit the interactive functional module still will have some time deviation. This random reflection in the TDM data’s sending process, the actual introduction’s instantaneous vibration can go far beyond the normal TDM line vibration allowance, we call it “the grouping vibration”. Because the TDM electric circuit has the constant invariable bit rate, therefore we may overcome the vibration through the use buffer, will arrive quickly grouping before output carries on the buffer and sorting, like this may compensate with other slow grouping between extends the time difference. But because voice communication’s timely request is quite high, buffer to loss package according to empties processing. If the buffer is too small, will present the overflow phenomenon, will cause the drop to be serious, thus cannot very good realize vibration smooth, but if the buffer will be oversized, the strobe will open the threshold value will enlarge, will cause the time delay to enlarge, but TDM services and so on pronunciation will also have the high request to the time delay, therefore buffer size design into vibration smooth key.
how do 3.2 give TDM in the multi-service grouping network the provision of service better QoS service
How in multi-service grouping network to TDM provision of service better QoS service, this is another key question which TDMoverEPON realizes. On the EPON different service is different to the QoS request. Although the TDM service takes the band width to be small, but to targets and so on time delay, vibration, drifting, error rate has the very high request; But the video frequency service must take the great band width, also has certain request to the time delay, but may tolerate the certain extent the drop; The data traffic needs to take a greater band width, and has the very strong burst characteristics, has to the data integrity and the accuracy requests high, but is also low to the time delay request. Must satisfy the different service QoS, simultaneously must give TDM the provision of service better QoS service, this requests when realizes the TDM service to consider the TDM service fully to the time delay and the vibration strict request. Solves this technical difficult problem not only to need to solve the clock recovery problem which in the circuit simulation involves, moreover must make certain function improvement on the EPON system. At present the beacon-fire correspondence proposed the solution was the TDM service has assigned higher priority logical link marking on the EPON system (LLID), thus guaranteed that the TDM data did not have the loss, and obtained the higher grade of service throughout; Furthermore uses based on each LLID dynamic bandwidth allocation algorithm, (SLA) realizes the band width effective use according to the different time’s discharge characteristic union user service level agreement through the REPORT-GATE mechanism. The experiment proved that through used these measures not only to guarantee the TDM service to target and so on time delay vibration strict requests, and has guaranteed the TDM service grade of service.
4 beacon-fire correspondences take the lead to realize EPON on system’s TDM service to realize
The beacon-fire correspondence based on the EPON FTTH entire service solution is take the EPON technology as the foundation, the use sole platform provides the data, the pronunciation, the video frequency as well as TDM special line service synthesis reliable turning on for the customer. Is worth mentioning what in here, the beacon-fire correspondence took the lead to break through IEEE to the EPON standard stipulation, unprecedentedness has realized on the EPON system the load bearing pronunciation and the electric circuit type number according to the service, was current few in number can be able to provide one of TDM service companies in the EPON system. Its independent development’s AN5000 series selects the leading PWE3 method to provide the TDM service seal, this series AN5116 bureau end equipment not only provides the large capacity TDM service connection, simultaneously the built-in 64K rank’s cross connection function, causes the TDM service the development to be more flexible, the band width use efficiency is higher.
As the FTTH research area’s outstanding person, the beacon-fire correspondence in domestic already undertook construction Wuhan long to fly at present the apartment, the Sichuan Mianyang telecommunication, the Hubei network to pass the Lake Nanhu metropolis haven plot, the Wuhan telecommunication purple song plot, Beijing to correspond extends HOUSE, the Pudong information building and so on numerous FTTH projects, and is among the best of the successful candidates in all previous technical test, gained in the rich project application experience. Take the Pudong information building as the example, this project is one of Chinese telecommunication FTTH pilot projects, simultaneously is also the national 863 project - - 3Tnet constituent, undertakes construction by the Shanghai telecommunication. In order to satisfy each kind of business user the request, the beacon-fire correspondence synthesized in this project has provided the pronunciation, the data, IPTV, TDM and so on many kinds of services. This project not only in domestic took the lead to open has cleared the service type most complete record in a project, simultaneously was also the TDMoverEPON technology in the domestic first time application.
5 concluding remark
In telecommunication market competition intense today, the operator hoped day by day could find one, in has completed in the network foundation both might provide the reliable real-time pronunciation, the video frequency and the data traffic, and may provide equates in had the network same reliability and the quality guaranteed outstanding solution. EPON takes one kind to have the competitive power broadband access technology extremely, must simultaneously provide the pronunciation, the data and the video frequency service synthesis turning on service. This is not only the communication network evolution and the need to develop, also whether is EPON soon to arrive in the FTTX construction flood tide to occupy one of superiority status determining factors.
