Patent Application
20100183301
This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Applications No. 10-2008-112945, filed on Nov. 13, 2008 and No. 10-2009-73804, filed on Aug. 11, 2009, the disclosures of which are incorporated by reference in its entirety for all purposes.
1. Field
The following description relates to an optical transport network (OTN), and more particularly, to a technology suitable for transporting client signals using the Optical Transport Hierarchy (OTH).
2. Description of the Related Art
The ITU-T G.709 standard specifies Optical channel Transport Units (OTUk) and Optical channel Data Units (ODUk) in order to stably transport high-speed optical signals requiring a large bandwidth. According to the ITU-T G 709 standard, OTU1 has a bit rate of about 2.666 Gbit/s, OTU2 has a bit rate of about 10.709 Gbit/s, OTU3 has a bit rate of about 43.018 Gbit/s and OTU4 has a bit rate of about 111.809 Gbit/s. Among Synchronous Digital Hierarchy (SDH) client signals that can be transported over an optical transport network (OTN), STM-256 has the highest bit rate of about 39.81312 Gbit/s and either of OTU3 or ODU3 can accept the bit rate.
Meanwhile, the payload area of an ODUk frame is composed of 3808 byte columns by 4 rows. Since 3808 is divisible by 32, upon dividing ODU3 in units of 32 tributary slots, each tributary slot has a capacity of about 1.254 Gbit/s. Accordingly, ODU3 can contain maximally 32 1 GbE signals by mapping a 1 GbE signal into each tributary slot and multiplexing it.
Also, when ODU4 is divided in units of 80 tributary slots, each tributary slot has a capacity of about 1.3017 Gbit/s and thus multiplexing of ODU3 into ODU4 requires only 32 tributary slots. If a data tributary unit that can be contained in 32 tributary slots is referred to as ODTU4.32, the ODTU4.32 has a capacity of about 41.654 Gbit/s and also ODU3 has a capacity of 40.654 Gbit/s. Accordingly, ODU3 can be mapped into ODTU4.32. The mapped to ODTU4.32 is mapped into ODU4 using 32 of 80 tributary slots.
However, since a payload capacity of OTU2 is about 99.952 Gbit/s and the capacity of 10 GbE is 10.3125 Gbit/s, a 10 GbE signal cannot be bit-transparently mapped into OTU2. Accordingly, in order to bit-transparently map a 10 GbE signal, an ODU2e signal having a capacity of 10.3995 Gbit/s is defined and used.
Furthermore, since the capacity of a 40 GbE signal is 41.25 Gbit/s and the payload capacity of ODU3 is about 40.15 Gbit/s, the 40 GbE signal has a bandwidth larger than ODU3 and accordingly, the 40 GbE signal cannot be bit-transparently mapped into ODU3. In other words, since the conventional optical transport signals are defined based on the SDH, there are limitations in bit-transparently mapping Ethernet signals.
The following description relates to a technology capable of adjusting the bandwidths of client signals while bit-transparently receiving and multiplexing the client signals over an optical transport network (OTN).
According to an exemplary aspect, there is provided a client signal transporting apparatus which transports a client signal using the Optical Transport Hierarchy (OTH) over an optical transport network, including: a tributary slot allocation unit to allocate a part of a payload area of an optical transport signal equally in units of a predetermined number of tributary slots and to allocate the remaining part of the payload area in units of a predetermined number of extra tributary slots or a predetermined number of fixed stuff bytes; and an optical multiplexing unit to map a client signal into the payload area using the allocated tributary slots and the allocated extra tributary slots and multiplex the mapped client signal into a higher layer optical transport signal.
According to another exemplary aspect, there is provided a tributary slot mapping apparatus which transports a client signal using the optical transport hierarchy (OTH) over an optical transport network, including: a data mapper to map data into tributary slots; a multiplex structure identifier generator to generate tributary port information for the tributary slots; an extended multiplex structure identifier generator to generate extra tributary port information for extra tributary slots; and an overhead and data selecting unit to set an overhead to transfer a payload structure identifier including the multiplex structure identifier and the extended multiplex structure identifier to an overhead area of the payload structure identifier, and to transfer the data mapped to the tributary slots to a data area.
According to another exemplary aspect, there is provided a tributary slot demapping apparatus which transports a client signal using the optical transport hierarchy (OTH) over an optical transport network, including: a frame extracting unit to receive a mapped frame and extract payload structure identifier information from the mapped frame; a payload structure identifier checker to verify whether the most significant bits of extended multiplex structure identifier information are all zero in the payload structure identifier information; and a data demapper to decode, if the most significant bits of the extended multiplex structure identifier information are all zero, multiplex structure information using tributary port information of the payload structure identifier and demap a data signal from a tributary slot area according to the decided multiplex structure information, and to decode, if all of the most significant bits of the extended multiplex structure identifier information are not zero, extended multiplex structure information using tributary port information of the multiplex structure identifier and the extended multiplex structure identifier and demap a data signal from a tributary slot area including an extra tributary slot area according to the decided, extended multiplex structure information.
According to another exemplary aspect, there is provided a client signal transporting method which transports a client signal using the optical transport hierarchy (OTH) over an optical transport network, including: allocating a part of a payload area of an optical transport signal equally in units of a predetermined number of tributary slots, and allocating the remaining part of the payload area in units of a predetermined tributary slots or in units of a predetermined number of fixed stuff bytes; and mapping a client signal into the payload area using the allocated tributary slots and the allocated extra tributary slots, and multiplexing the mapped client signal into a higher layer optical transport signal.
Therefore, the client signal transporting apparatus defines a bit rate of the optical transport hierarchy, and bit-transparently maps and multiplexes a client signal which can be received at the defined bit rate. The client signal transporting apparatus may define a range of a bit rate of an optical channel data unit 4e (ODU4e) and a bit rate which ODU3+ can have, and receive and multiplex 10 GbE, 40 GbE and 100 GbE signals within the defined bit rate range. Moreover, the client signal transporting apparatus may extend a mapping region to increase a data capacity in which tributary slots can be allocated, thereby adjusting a bandwidth.
Other objects, features and advantages will be apparent from the following description, the drawings, and the claims.
Elements, features, and structures are denoted by the same reference numerals throughout the drawings and the detailed description, and the size and proportions of some elements may be exaggerated in the drawings for clarity and convenience.
The detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses and/or systems described herein. Various changes, modifications, and equivalents of the systems, apparatuses, and/or methods described herein will likely suggest themselves to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions are omitted to increase clarity and conciseness.
Referring to
According to an exemplary embodiment, a signal having a bit rate which is higher than an optical channel data unit 3 (ODU3) is defined to bit-transparently and efficiently receive 4 10 GbE signals or a 40 GbE signal, which are client signals. The newly defined signal will be hereinafter referred to as ODU3+. In consideration of multiplexing 4 bit-transparently received ODU2e signals corresponding to 4 10 GbE signals to ODU3+, the bit rate of ODU3+ has to be at least 41.774 Gbit/s (239/236×4×10.3125 Gbit/s).
However, since increasing a bit rate of ODU3+ up to a bit rate of ODU4 without limitation is inefficient, the bit rate of ODU3+ may be fitted to be less than 41.654 Gbit/s which is the bit rate of ODTU4.32. This is because if the bit rate of ODU3+ exceeds the data capacity of ODTU4.32, the ODU3+ has to be mapped into ODTU4.33 using 33 tributary slots, instead of being mapped into ODTU4.32 using 32 tributary slots.
However, as described above, since ODU3+ has to have a bit rate of at least 41.774 Gbit/s in order to bit-transparently receive and map 4 10 GbE signals or a 40 GbE signal, in this case, an ODU3+ signal cannot be mapped into ODTU4.32 having a data capacity of 41.654 Gbit/s. That is, increasing the bit rate of ODU3+ to be a little higher than that of ODU3 simply maps the ODU3+ into ODTU4.33 further using a tributary slot of a 1.3017 Gbit/s level of OTU4.
In the case of multiplexing two ODU3 signals to OTU4, 64 tributary slots among 80 tributary slots of a 1.3017 Gbit/s level are used, and the remaining 16 tributary slots can be used to map 2 ODU2 or ODU2e signals or to map 8 ODU1 signals or 16 ODU0 signals. However, in the case of multiplexing 2 ODU3+ signals to OTU4, 66 tributary slots among 80 tributary slots of a 1.3017 Gbit/s level are used, and the remaining 14 tributary slots can map only a ODU2 or ODU2e signal or map 7 ODU1 signals or 14 ODU0 signals. That is, the multiplexing of ODU3+ to OTU4 is accompanied by inefficient mapping.
As understood from the above description, since existing optical transport network (OTN) signals are not suitable to bit-transparently map 10 GbE and 40 GbE signals which are received as to client signals, it is inevitable that a new OTU4e signal having a bit rate which is a little higher than that of an OTU4 signal needs to be defined.
According to an exemplary embodiment, a lowest bit rate of OTU4e which can be acquired through the existing inefficient mapping is defined as 112.3047 Gbit/s (255/226×40×2.48832 Gbit/s). In this case, a bit rate of ODU4e is 239/255×(a bit rate of OTU4). Also, when ODU4e is divisible in units of 80 tributary slots, each tributary slot has a capacity of about 1.307469 Gbit/s. If a data tributary unit which corresponds to 32 tributary slots of ODU4e is referred to as ODTU4e.32, ODTU4e.32 has a capacity of about 41.84 Gbit/s. Accordingly, if ODU3+ has a capacity which is greater than 41.774 Gbit/s (239/236×4×10.3125 Gbit/s) and less than 41.84 Gbit/s (3800/3808×32/80×238/226×40×2.48832 Gbit/s), then ODU3+ can be mapped into ODTU4e.32. The mapped ODTU4e.32 is multiplexed to 32 tributary slots among 80 tributary slots of ODU4e. That is, multiplexing of ODU3+ into ODU4e is performed using only 32 tributary slots.
According to another exemplary embodiment, a bit rate of OTU4e may be defined to be greater than 111.83688 Gbit/s (102/95×80/32×239/255×243/217×16×2.48832 Gbit/s) and less than 112.16234 Gbit/s (4080/1524×239/236×4×10.3125 Gbit/s). For example, a bit rate of OTU4e is defined as 111.9744 (9/8×40×2.48832) Gbit/s. Since a bit ate of 28 Gbit/s is generally considered to allow signal transport on a PCB not through a cable, a bit rate of OTU4e may be set to be within 112 (4×28) Gbit/s in consideration of 28 Gbit/s optical transport for 4 channels.
As such, a bit rate of OTU4e is defined within an allowable range of bit rates for OTU4e, then an ODU3+ signal which can be received within the bit rate range is defined, and thereafter the ODU3+ signal is multiplexed to ODU4e. For example, it is possible to bit-transparently receive and map two 40 GbE signals and two 10 GbE signals, to multiplex the signals to OTU4e/ODU4e and then to transport the multiplexed signal. Alternatively, it is possible to bit-transparently map and multiplex a 40 GbE signal and 6 10 GbE signals and transport the result as an OTU4e/ODU4e frame. Moreover, even in multiplexing arbitrary ONU signals having flexibility, as well as 40 GbE and 10 GbE signals, to ODU4, it is possible to increase a capability of receiving and mapping the ODU signals having flexibility by extending a mapping area.
For the multiplexing, the tributary slot allocation unit 10 allocates a predetermined number of tributary slots equally to a part of a payload area of an optical transport signal, and allocates extra tributary slots or fixed stuff bytes to the remaining part of the payload area.
Meanwhile, the optical transport signal may be ODUk (k=1, 2, 2e, 3, 3+, 4, 4e, flex). For example, an optical transport signal ODU3+ divides its payload area equally to 32 tributary slots, and 8 tributary slots thereof are used to bit-transparently receive, map and multiplex a 10 GbE signal. That is, through a single ODU3+ signal, 4 10 GbE signals can be bit-transparently received and mapped. In the following description, ODU4e which is an optical transport signal will be given as an example. In this case, the optical multiplexing unit 12 can map ODU3+ into OTU4e, but also can extend an arbitrary ODUk (k=1, 2, 2e, 3 flex) to ODUk+ and then map the ODUk+ into OTU4e, so as to extend a mapping area.
In order to efficiently transport client signals, a payload area of an OPH signal may be allocated tributary slots in various manners. The number of tributary slots that are allocated to a part of a payload area of an optical transport signal ODU4e by the tributary slot allocation unit 10 may be 40 or 80. However, payload bytes of an ODUk frame consist of 4 rows each having 3808 bytes and thus are not divisible by 40 or 80. In this case, allocation of tributary slots as follows can be considered.
According to an exemplary embodiment, the tributary slot allocation unit 10 may allocate a predetermined number of tributary slots to a part of a payload area of an optical transport signal, and then, allocate tributary slots, tributary slots+extra tributary slots, or tributary slots+extra tributary slots+fixed stuff bytes to the remaining part of the payload area, in a unit of a predetermined number of multiframes.
According to another exemplary embodiment, the tributary slot allocation unit 10 may allocate tributary slots to a part of a payload area of an optical transport signal, and then, allocate extra tributary slots or extra tributary slots+fixed stuff bytes to the remaining part of the payload area, in a unit of a predetermined number of rows.
Meanwhile, the optical multiplexing unit 12 receives and maps client signals using the tributary slots allocated by the tributary slot allocation unit 10 and multiplexes the client signals to the next higher layer optical transport signals. Here, the client signals may be any ones of packet signals such as Ethernet hierarchy signals, synchronous digital hierarchy signals and successive signals such as video signals.
According to an exemplary embodiment, the optical multiplexing unit 12 may set, when receiving and mapping a client signal and multiplexing it into the next higher layer optical transport signal, a bit rate of OTU4e to 111.9744 (9/8×40×2.48832) Gbit/s.
In this case, in order to multiplex ODU3+ to ODU4e at the set bit rate, the optical multiplexing unit 12 may use, when 80 tributary slots are allocated to ODU4e, 32 1.25 G tributary slots each having a capacity of about 1.307469 Gbit/s, and may use, when 40 tributary slots are allocated to ODU4e, 16 2.5 G tributary slots each having a capacity of about 2.60724 Gbit/s.
Hereinafter, a tributary slot allocation method of the tributary slot allocation unit 10 and a multiplexing method of the optical multiplexing unit 12 will be described in detail with reference to the related drawings.
OPU4e corresponds to a payload area of OTU4e/ODU4e. The payload area is to composed of 3808 byte columns by 4 rows. The 3808 byte columns are not divisible by 80. Accordingly, as illustrated in
At this time, the client signal transporting apparatus 1 divides the 48 byte columns after the 3776th byte column using 5 multiframes after dividing the 3760 byte columns in units of 80 1.25 G tributary slots. That is, since there are totally 40 (48×5) byte columns, 3 (240/80) byte columns are added for each tributary slot. That is, the structure illustrated in
Consequently, the size of an ODTU3y4e frame may depend on which tributary slots are used between the 5 multiframes. ODTU3y4e (Optical Channel Data Tributary Unit-3 into 4) means a data tributary unit which can contain ODU3+ in tributary slots to multiplex the ODU3+ to ODU4e. Also, if there is any byte column after a 1500 byte in an ODTU3y4e frame, the same number of bytes may be mapped into different locations in an ODU4e frame. Accordingly, a complicated hardware structure is needed to be able to arbitrarily allocate byte columns that exist after the 1504th byte of an ODTU3y4e frame to 48 byte columns of the end portion of an OTU4e frame. In the case of mapping ODTU3y4e into ODU4e, since 32 1.25 G tributary slots or 16 2.5 G tributary slots are used, two byte columns exist after the 1504th byte as illustrated in
Here, a tributary slot is denoted by TS and
Referring to
However, as described above, extra bytes after the 1504th byte column may vary depending on to which tributary slot of ODU4e is mapped OTU3y4e. For example, as illustrated in
Unlike the structure,
The ODTU3y4e frame structure illustrated in
As illustrated in
Referring to
In the tributary slot allocated structure of OPU4e illustrated in
However, this mapping impossibility may be resolved by utilizing the tributary slot allocated structure of OPU4e illustrated in
The client signal transporting apparatus substitutes extra tributary slots shown in
Referring to
The client signal transporting apparatus may use multiplex structure identifiers (MSIs) for use of 16 tributary slots when multiplexing an ODTU3y4e signal to an ODU4 signal. Here, since two extra tributary slots have to be distinguished from other tributary slots, the client signal transporting apparatus can correct MSI bytes. In existing MSI bytes, since only 6 bits are allocated to distinguish OPUk tributary slots, the MSI bytes could support 80 tributary slots. Accordingly, the MSI bytes according to the current embodiment may he corrected to support extensibility.
Referring to
Meanwhile, since ODU2. ODU3 and ODU3+ use 10 or less tributary slots, as illustrated in
Meanwhile, in the cases of other ODU types except for ODU3+, only MSI bytes can be used. Also, in the case where extra tributary slots have to be used in any other signal types including ODU3+, the EMSI bytes illustrated in
Referring to
Meanwhile, other signals other than ODU3+ also can use extra tributary slots in the same manner. Only in the case of ODU0 in which two signals are set in pair, as illustrated in
Referring to
Meanwhile, 4 byte columns can be all used as extra tributary slots as illustrated in
Meanwhile, a frame having the tributary slot allocated structure of OPU4e illustrated in
Referring to
When an AMP method is used to map ODU3+ into ODTU4e.32, PJ01 and PJ02 bytes may be allocated as illustrated in
Referring to
Meanwhile, since 3 byte columns are added for each row of OPU4e, as illustrated in
Referring to
Since the type of ODTU4e.32y3 is determined depending on the number of used tributary slots, separate bits for indicating an ODU type, which are illustrated in
In addition, if the client signal transporting apparatus has to use extra tributary slots, the client signal transporting apparatus may use EMSI bytes to identify a multiplex structure of extra tributary slots. At this time, the client signal transporting apparatus supports 7 bits such that bits corresponding to the same number as the number of tributary ports of MSI bytes are allocated to the extra tributary ports of EMSI bytes with respect to a tributary signal requiring extra tributary slots. Also, the remaining first bit of the EMSI bytes is used to identify whether extra tributary slots are used. That is, if the first bit of the EMSI byte is zero, then this means that no extra tributary slot is allocated, and if the first bit of the EMSI byte is 1, then this means that an extra tributary slot is used.
The elastic buffer 21 receives a data output timing signal from the timing generator 28 and transfers it to the data mapper 22 while storing a tributary signal to be mapped. The data mapper 22 receives timing information about a frame to be created and timing information of tributary slots and extra tributary slots to be mapped, from the timing generator 28, and maps data received through the elastic buffer 21 to a corresponding tributary slot.
The PT register 23 stores type information of tributary signals to be mapped, and the type information may be modified by a user. The MSI generator 24 receives a MSI timing signal of PSI multiframes from the timing generator 28 and generates tributary port information for 80 tributary ports that can be modified by a user. The EMSI generator 25 receives EMSI timing information among PSI multiframes from the timing generator 28 and generates tributary port information about 8 extra tributary slots, herein the tributary port information can be modified by a user.
The PSI overhead selector 26 receives PSI multiframe information from the timing generator 28, and selects a “0000000” value for the PT register 23, the MSI generator 24, the EMSI generator 24 and a reserve, so as to configure an overhead having a predetermined multiframe structure. The overhead and data selector 27 receives PSI overhead timing information and data timing information from the timing generator 28, and selects data and an overhead to transfer data mapped to tributary slots to a data area and transfer PIS information selected by the PSI overhead selector 26 to a PSI overhead area. An OPU4 overhead, an OTU4 overhead and an ODU4 overhead except for the PSI overhead may be added as necessary.
The timing generator 28 generates frame timing information, generates a signal regarding a timing at which the elastic buffer 21 will extract data, and then generates timing signals for tributary slots and extra tributary slots areas to be mapped and transfers the timing signals to the data mapper 22. Also, the timing generator 28 transfers timing information of each multiframe to create a PSI overhead to the MSI generator 24, the EMSI generator 25 and the PSI overhead selector 26, and provides PSI overhead timing information and data timing information to the overhead and data selector 27.
The frame detector 31 detects a start point of a received frame and informs the timing generator 36 of a frame start location. The timing generator 36 receives frame start information from the frame detector 31, generates information regarding a timing at which PSI information is to be extracted, and transfers the timing information to the PSI checker 32.
The PSI checker 32 extracts PSI information from among data received from the frame detector 31 according to the PSI timing information received from the timing generator 36. The extracted PSI information includes a payload type and MSI and EMSI information according to multiframes. Multiplex structured information of tributary slots obtained from the MSI information and multiplex structured information of extra tributary slots obtained from EMSI information are transferred to the timing generator 36.
The timing generator 36 generates timing information of tributary slots and extra tributary slots areas to be demapped according to the multiplex structured information of the tributary slots and extra tributary slots received from the frame detector 31, and transfers the timing information to the data demapper 34.
The data demapper 34 receives timing information of tributary slots and extra tributary slots of areas to be demapped, from the timing generator 36, with respect to a frame coming through the frame detector 31, and demaps a data signal. The demapped data signal is stored in the elastic buffer 35.
Referring to
Referring to
Successively, the tributary slot demapping apparatus 3 determines whether all the MSBs of 8 bytes of extended EMSI information in extracted PSI information are zero (operation 120). If all the MSB bits are zero, multiplex structure information is determined from MSI tributary port information (operation 130). Since the determined multiplex structure corresponds to a mapping method in which no extra tributary slot is used, a data signal from a tributary slot area is demapped (operation 140). Successively, the demapped data is stored in the elastic buffer (operation 150). If not all the MSBs of 8 bytes of extended EMSI information in the extracted PSI information are zero, an extended multiplex structure is decided from the MSI and EMSI tributary port information (operation 160). A data signal is demapped from a tributary slot area including an extra tributary slot area according to the decided extended multiplex structure (operation 170). Then, the demapped data is stored in the elastic buffer (operation 150).
It will be apparent to those of ordinary skill in the art that various modifications can be made to the exemplary embodiments of the invention described above. However, as long as modifications fall within the scope of the appended claims and their equivalents, they should not be misconstrued as a departure from the scope of the invention itself.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2008-0112945 | Nov 2008 | KR | national |
| 10-2009-0073804 | Aug 2009 | KR | national |
