Anoptical transport network(OTN) is a digital wrapper that encapsulates frames of data, to allow multiple data sources to be sent on the same channel. This creates an opticalvirtual private networkfor each client signal.
ITU-Tdefines an optical transport network as a set of optical network elements (ONE) connected byoptical fiberlinks, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals.[1]An ONE may re-time, re-Amplify, re-shape (3R) but it does not have to be 3R – it can be purely photonic. Unless connected by optical fibre links, it shall not be OTN. Mere functionality of switching, management, supervision shall not make it OTN, unless the signals are carried through optical fibre. Unlike SONET/SDH, OTN provides a mechanism to manage multiplexed wavelengths in aDWDMsystem.[2]
Comparing OTN and SONET/SDH
edit| OTN | SONET/SDH | |
|---|---|---|
| Scaling | 400Gbit/s (2021)[3] | 40Gbit/s |
| Error correcting | Yes,Forward Error Correction,64b/66b encoding,512B/513B encoding,1024B/1027B encoding | Yes,Forward Error Correction,BCH code |
| Timing | Does not require | Requires |
| Octet-basedblockframestructure | Fixed, 16300Byte | Variable, 2430- 622 080Byte |
| Frame rate | Variable (98.354 - 1.163 μs) | 125 μs |
Standards
edit
OTN was designed to provide higher throughput (currently 400G) than its predecessorSONET/SDH,which stops at 40 Gbit/s, per channel.
ITU-T RecommendationG.709is commonly called Optical Transport Network (OTN) (also calleddigital wrapper technologyoroptical channel wrapper). As of December 2009, OTN has standardized the following line rates.
| Signal | Marketing data Rate (Gbit/s) | True Signal rate (OTU) (Gbit/s) | Applications | Maximum number of signals per channel | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| # of ODU0, 1.2G | # of ODU1, 2.5G | # of ODU2, 10G | # of ODU2e, 10.4G | # of ODU25, 26.4G | # of ODU3, 40.3G | # of ODU50, 52.8G | # of ODU4, 104G | ||||
| OTU1 | 2.5 | 2.66 | TransportsSONETOC-48or synchronous digital hierarchy (SDH)STM-16signal | 2 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| OTU2 | 10 | 10.7 | Transports anOC-192,STM-64orwide area network(WAN) physical layer (PHY) for10 Gigabit Ethernet(10GBASE-W) | 8 | 4 | 1 | 0 | 0 | 0 | 0 | 0 |
| OTU2e[4] | 10.5 | 11.1 | Transports a 10 Gigabit Ethernetlocal area network(LAN) PHY coming from IP/Ethernet switches and routers at full line rate (10.3 Gbit/s). This is specified in G.Sup43. | 8 | 4 | 1 | 1 | 0 | 0 | 0 | 0 |
| OTU25 | 25 | 26.4 | Transports a25 Gigabit Ethernetsignal | 20 | 10 | 2 | 2 | 1 | 0 | 0 | 0 |
| OTU3 | 40 | 43 | Transports anOC-768orSTM-256signal or a40 Gigabit Ethernetsignal.[5] | 32 | 16 | 4 | 3 | 1 | 1 | 0 | 0 |
| OTU3e1/2[6] | 41 | 44.5 | develop for transport of 10G LAN PHY, and one for 10G WAN PHY, over SDH and OTN. | 32 | 16 | 4 | 3 | 1 | 1 | 0 | 0 |
| OTU50 | 50 | 52.8 | Transports a50 Gigabit Ethernetsignal | 40 | 20 | 5 | 5 | 2 | 1 | 1 | 0 |
| OTU4 | 100 | 111.8 | Transports a100 Gigabit Ethernetsignal | 80 | 40 | 10 | 10 | 2 | 2 | 2 | 1 |
| OTUCn | n x 100 | n x 105.2 | n instances of a logically interleaved 100G (C=100) frame format | Total bandwidth / ODU size. e.g. 200G Channel support 4xODU3 and 4xODU2[7] | |||||||
The OTUk (k=1/2/2e/3/3e2/4) is an information structure into which another information structure called ODUk (k=1/2/2e/3/3e2/4) is mapped. The ODUk signal is the server layer signal for client signals. The following ODUk information structures are defined in ITU-T RecommendationG.709
| Signal | Data Rate (Gbit/s) | Typical Applications |
|---|---|---|
| ODU0 | 1.24416 | Transport of a timing transparent transcoded (compressed)1000BASE-Xsignal[8]or a stream of packets (such as Ethernet,MPLSor IP) usingGeneric Framing Procedure |
| ODU1 | 2.49877512605042 | Transport of two ODU0 signals or a STS-48/STM-16 signal or a stream of packets (such as Ethernet, MPLS or IP) usingGeneric Framing Procedure. |
| ODU2 | 10.0372739240506 | Transport of up to eight ODU0 signals or up to four ODU1 signals or a STS-192/STM-64 signal or aWAN PHY (10GBASE-W)or a stream of packets (such as Ethernet, MPLS or IP) usingGeneric Framing Procedure |
| ODU2e | 10.3995253164557 | Transport of a10 Gigabit Ethernetsignal or a timing transparent transcoded (compressed) Fibre Channel10GFCsignal |
| ODU3 | 40.3192189830509 | Transport of up to 32 ODU0 signals or up to 16 ODU1 signals or up to four ODU2 signals or a STS-768/STM-256 signal or a timing transparent transcoded40 Gigabit Ethernetsignal or a stream of packets (such as Ethernet, MPLS or IP) usingGeneric Framing Procedure |
| ODU3e2 | 41.7859685595012 | Transport of up to four ODU2e signals |
| ODU4 | 104.794445814978 | Transport of up to 80 ODU0 signals or up to 40 ODU1 signals or up to ten ODU2 signals or up to two ODU3 signals or a100 Gigabit Ethernetsignal |
| ODUflex (CBR) | 239⁄238x client bit rate[8] | Transport of aconstant bitratesignal such as Fibre Channel8GFC,InfiniBandorCommon Public Radio Interface |
| ODUflex (GFP) | any configured rate[8] | Transport of a stream of packets (such as Ethernet, MPLS or IP) usingGeneric Framing Procedure |
Equipment
editAt a very high level, the typical signals processed by OTN equipment at the Optical Channel layer are:
- SONET/SDH
- Ethernet/FibreChannel
- Packets
- OTN
A few of the key functions performed on these signals are:
- Protocol processing of all the signals:-
- Mapping and de-mapping of non-OTN signals into and out of OTN signals
- Multiplexing and de-multiplexing of OTN signals
- Forward error correction(FEC) on OTN signals
- Packet processing in conjunction with mapping/de-mapping of packet into and out of OTN signals
Switch Fabric
editThe OTN signals at all data-rates have the same frame structure but the frame period reduces as the data-rate increases. As a result, theTime-Slot Interchange(TSI) technique of implementing SONET/SDH switch fabrics is not directly applicable to OTN switch fabrics. OTN switch fabrics are typically implemented using Packet Switch Fabrics.
FEC Latency
editOn a point-to-point OTN link there is latency due toforward error correction(FEC) processing. Hamming distance of the RS(255,239) code is 17
See also
editReferences
edit- ^ITU-T OTN definitions
- ^"G.709 – The Optical Transport Network (White Paper)"(PDF).VIAVI Solutions Inc. 2021.Retrieved10 January2024.
The aim of the optical transport network (OTN) is to combine the benefits of SONET/SDH technology with the bandwidth expandability of DWDM.
- ^"G.709: Interfaces for the optical transport network".
- ^"G.Sup43: Transport of IEEE 10GBASE-R in optical transport networks (OTN)".www.itu.int.Retrieved31 October2021.
- ^OTN offers transparent service deliveryArchived2008-05-10 at theWayback Machine,Retrieved June 2, 2007
- ^"ITU-T G Suppl. 43 (02/2011)".ITU.Retrieved31 October2021.
- ^"200G OTN Optical Transponder/Muxponder for DCI Network".FS.com.Retrieved31 October2021.
- ^abc"ODU0 and ODUflex — A Future-Proof Solution for OTN Client Mapping"(PDF).TPACK A/S. February 2010. Archived fromthe original(PDF)on 12 March 2012.
External links
edit- Anritsu Poster- Details of all OTN areas including breakdown of the full frame[dead link]
- Anritsu Poster - Details of all OTN areas including breakdown of the full frameat theWayback Machine(archived 2014-05-17)
- Optical Transport Network (OTN) Tutorial,ITU-T, only covers G.709 (2003/03)
- [1]Hot topics in Optical Transport Networks, Steve Trowbridge (Nokia), Chairman, ITU-T Study Group 15