Optical Network Control

Transcription

1 Optical Network Control Jorge M. Finochietto Córdoba 2014 LCD EFN UNC Laboratorio de Comunicaciones Digitales Facultad de Ciencias Exactas, Físicas y Naturales Universidad Nacional de Córdoba, Argentina

2 Optical Layer Overview Control 2 / 59

3 Outline 1 Network Management 2 Network Protocols Control 3 / 59

4 Outline 1 Network Management Configuration Management Performance Management Fault Management 2 Network Protocols Control Network Management 4 / 59

5 Optical Layer Lightpath as a Service Provides lightpaths to upper layers (SONET, IP, ATM, ETH) Behaves as a server layer which provides services to client layers Control Network Management 5 / 59

6 Optical Layer Requirements Lightpaths need to be setup and taken down as required by the client layer provide the amount of bandwidth required by the client layer implement adaptation functions on the client layer to make it compatible with optical layer guarantee a level of preformance (e.g., BER ) offer some level of protection meet jitter requirements to offer transparency to the client layer support fault management to address failures and report root-cause alarms A management and control interface between the optical layer and the client layer is required allows to setup or tear down lightpaths with configuration parameters provides performance and fault management information to the client layer Control Network Management 6 / 59

7 Optical Layer Management and Control Today lightpaths are set up fairly infrequently and remained nailed down for longs periods of time In the future, lightpaths could be provisioned dynamically To this end, there is no need of a signaling interface between the optical layer and the client one A network management system (NMS) is used to communicate with the optical layer network elements (NE) NEs (e.g., OLT/TLE, ROADM, OXC) are managed by element management system (EMS) EMS connect to the managed NEs using a data communication network (DCN) Besides, NEs can communicate each other through a fast signaling channel (FSC) to exchange real-time control information EMSs communicate with a NMS through a management network Besides EMS, a local management system is usually provided to enable craftpeople to manage individual NEs Control Network Management 7 / 59

8 Optical Layer Management System Control Network Management 8 / 59

9 Optical Layer Data Communication Network (DCN) EMS communicates with NEs through the DCN DCN can be realized in several ways Out-of-band separate network outside the optical layer (e.g., existing TCP/IP network) In-band same network as the optical layer In-band implies associating a control overhead to a line (multiple wavelengths) optical domain a path (one lightpath) electronic domain Control Network Management 9 / 59

10 Optical Layer Optical Supervisory Channel (OSC) Available for optical equipment that process multiple wavelengths Makes use of a separate (dedicated) wavelength from where data are being transported Optical amplifiers (i.e., EDFAs) and ROADMs can be managed this way For WDM systems in the C-band, the popular choices for the OSC wavelength include 1310nm, 1480nm, 1510nm, or 1620nm. ITU-T has adopted the 1510nm as the preferred choice Control Network Management 10 / 59

11 Optical Layer Rate-Preserving Overhead Available for optical equipment that processes lightpaths Uses the same wavelengths where data are being transported OLT/LTE and OXC with regeneration can be managed this way Overhead is already required by protocols for other purposes which include forward error correction (FEC) overhead In this context, overhead can be processed at each regeneration stage (endpoints of a lightpath) Control Network Management 11 / 59

12 Optical Layer Network Management Functions Fault Management: detects failures and isolates failed components Configuration Management: tracks equipment, establishes connections (manually), and adapts signals to the optical layer Accounting Management: gathers billing and usage data Performance Management: monitors and measure performance metrics Security Management: authenticates users and assigns permissions Control Network Management 12 / 59

13 Outline 1 Network Management Configuration Management Performance Management Fault Management 2 Network Protocols Control Network Management Configuration Management 13 / 59

14 Configuration Management Overview Equipment Management Keep track of actual equipment on the network and its capabilities Connection Management Set up lightpaths. keep track of them and tear them down Adaptation Management Converts clients signals to a form that can be used inside the optical layer Control Network Management Configuration Management 14 / 59

15 Configuration Management Connection Management Lightpaths pass through multiple nodes Each lightpath has an unique end-to-end identifier: section trace Additional identifiers can be used to identify concatenated lighpaths through 3R regeneration tandem trace user-defined set of consecutive lighpaths path trace end-to-end connection where client signal travels These identifiers enables the NMS to identify, verify and manage lightpaths Control Network Management Configuration Management 15 / 59

16 Configuration Management Adaptation Management Client signals may need adaptation to enter the optical layer Wavelength conversion signal conversion from one wavelength to another one Encapsulation add/remove overhead to manage the signal inside the optical layer Justification add/remove stuffing to compensate bit rate mismatches Multiplexing subrate multiplexing of lower-speed client streams Adaptation is done at transponders / muxponders Control Network Management Configuration Management 16 / 59

17 Outline 1 Network Management Configuration Management Performance Management Fault Management 2 Network Protocols Control Network Management Performance Management 17 / 59

18 Performance vs. Fault Management Overview Performance Management Measures the performance of the network Monitors quality-of-service (QoS) provided to client layer Ensures client layer complies with requirements Provides input to detect anomalous conditions Fault Management Detects failures when they happen Reports root-cause alarm to supress other correlated alarms Isolates faults by replacing faulty signals with special ones Control Network Management Performance Management 18 / 59

19 Performance Management BER Measurement Besides signal measurements (power level, chromatic dispersion, etc) bit error rate (BER) is the key performance attribute associated to a lightpath Difficult to measure BER accurately on the optical domain (i.e., based on the SNR) BER can be computed when signal is available in the electrical domain Lightpaths use framing protocols which include overhead bytes which can be used for in-service BER estimation Errored Blocks: verifies whether a data block contains errors or not by means of parity checks Corrected Errors: counts the corrected errors by the Forward Error Correction (FEC) code Control Network Management Performance Management 19 / 59

20 Performance Management Bit-Error-Ratio (BER) Measurement Besides signal measurements (power level, chromatic dispersion, etc) bit error rate (BER) is the key performance attribute associated to a lightpath Difficult to measure BER accurately on the optical domain (i.e., based on the SNR) BER can be computed when signal is available in the electrical domain Lightpaths use framing protocols which include overhead bytes which can be used for in-service BER estimation Corrected Errors: counts the corrected errors by the Forward Error Correction (FEC) code Errored Blocks: verifies whether a data block contains errors or not by means of parity checks Control Network Management Performance Management 20 / 59

21 Performance Management Errored Block Measurements Measurements are based on one-second intervals but typically registered in 15-minute counters 24-hour counters A Severely Errored Second (SES) is thus a one-second period that contains at least 15 % of errored blocks, or one or more defects such as TIM, PLM, AIS, OCI (more later) Otherwise, block errors are considered as Background Block Errors (BBE) Both SES and BBE can be expressed as the ratio (SESR and BBER) in a time interval (15-minute, 24-hour) Control Network Management Performance Management 21 / 59

22 Outline 1 Network Management Configuration Management Performance Management Fault Management 2 Network Protocols Control Network Management Fault Management 22 / 59

23 Fault Management Alignment + Connectivity + Payload Alignment Lightpaths transport both data and overhead in a structure known as frame An alignment signal is inserted to delineates these frame and extract overhead bytes from the signal Connectivity Lighpaths are identified by traces at different levels It is possibe then to detect incorrect connections (i.e., trace mismatch) Payload Lighpaths carry client signals on their payload It is possibe then to detect incorrect payloads (i.e., payload mismatch) Control Network Management Fault Management 23 / 59

24 Fault Management Alarm Management A signal failure may cause multiple alarms all over the network When a link (fiber) fails, all lightpaths on that link fail Besides the nodes at the end of the failed link, all nodes through which these lightpaths traverse could detect the failure and issue alarms Alarm supression is acomplished by using forward defect indication (FDI) backward defect indication (BDI) Control Network Management Fault Management 24 / 59

25 Fault Management Alarm Supression When a link fails, the node downstream of the failed link detects it and generates a defect condition. A defect condition could be generated because of a high bit error rate on the incoming signal or an outright loss of light on the incoming signal. If the defect persists for a certain time period (typically a few seconds), the node generates an alarm and inserts an FDI signal downstream to the next node The FDI is also referred to as the alarm indication signal (AIS) A node detecting a defect also sends a BDI signal upstream to the previous node, to notify that node of the failure If this previous node did not send out an FDI, it then knows that the link to the next node downstream has failed. Control Network Management Fault Management 25 / 59

26 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols 26 / 59

27 Optical Transport Network Overview A set of NEs connected by optical fiber links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals Standarized mainly in ITU-T G G.798 OTN was designed to provide support for WDM unlike its predecessor SONET/SDH as well as to carry much more FEC overhead to provide monitoring of user-defined segments (tandem connections) to support protocol transparency (CBR service) for asynchronous timing (i.e., frames can be generated using free-running oscillators) Control Network Protocols 27 / 59

28 Optical Transport Network Optical Layers + Electronic Layers Control Network Protocols 28 / 59

29 Optical Transport Network Optical Transmission Section (OTS) Manages fiber segments between optical components such as between optical amplifiers, or optical amplifiers and WDM muxes. Made up of i) a payload signal (OTS-P), consisting of all wavelengths with data traffic, and ii) an overhead signal (OTS-O) conveying optical supervisory channel (OSC) Control Network Protocols 29 / 59

30 Optical Transport Network OTS Continuity Supervision Loss of Signal Payload (LOS-P) indicates that the incoming payload signal is absent or that the incoming power level has dropped below some critical threshold Loss of Signal Overhead (LOS-O) indicates that the incoming overhead signal is absent or that the incoming power level has dropped below some critical threshold These defects indicate either a transmitter / receiver failure a path break (e.g., fiber cut, amplifier shutdown) Control Network Protocols 30 / 59

31 Optical Transport Network Optical Multiplex Section (OMS) Each link between OLTs or (R)OADMs represents an OMS Consists of several OTS segements carrying multiple wavelengths Has access to the optical supervisory channel (OSC) Control Network Protocols 31 / 59

32 Optical Transport Network Optical Channel (Och) Takes care of end-to-end routing of the lightpaths A lightpath traverses many fiber links, wherein it is multiplexed with many other wavelengths carrying other lightpaths Manages optical connections between 3R regeneration (i.e., transponders) Control Network Protocols 32 / 59

33 Optical Transport Network Och Transport Unit (OTU) Manages lightpaths provided by the optical layer (OCh) in the electronic domain Delineates frames, provides identification of the lightpath, monitors its BER performance, carries alarm indicators, and provides a communication channel between the end points Adds the FEC to frames and scrambles them before transmission Control Network Protocols 33 / 59

34 Optical Transport Network Frame Structure Control Network Protocols 34 / 59

35 Optical Transport Network Control Overhead Control Network Protocols 35 / 59

36 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols Alignment Overhead 36 / 59

37 Alignment Overhead Overhead Fields Frame Alignment Signal (FAS) A fixed patter consisting of 6 bytes are used to delineate each frame Multiframe Alignment Signal (MFAS) Some of the overhead fields carry information that is dispersed over multiple frames, referred to as multiframes. The MFAS byte is incremented every frame providing 256 values indicating the number of the frame within a multiframe. Control Network Protocols Alignment Overhead 37 / 59

38 Alignment Overhead Loss Conditions (Defects) Loss of Frame (LOF) indicates that it has not been possible to detect framing for a period of time (3 ms) Loss of Multiframe (LOM) indicates that it has not been possible to detect multiframing for a period of time (3 ms) Alignment memory: even if in out-of-(multi)frame condition last alignment is mantained; thus, the system could enter and recover from these loss states without changing the actual alignment assumption. Control Network Protocols Alignment Overhead 38 / 59

39 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols FEC Overhead 39 / 59

40 FEC Overhead Coding Gain An forward error-correcting code is a technique for reducing the bit error rate on a communicaton channel It involves transmitting additional bits, called redundancy, along with the data bits These redundant bits are used by the receiver to correct errors in the data bits Increasing tx power may not decrease BER due to non-linear effects, FEC techniques are typically used for this purpose FEC codes can be characterized by the overhead, which represents the rate expansion to append redundancy coding gain, which is the difference (db) in the OSNR of the coded and uncoded systems Since the overhead introduces an OSNR penalty, the coding gain is typicaly defined as the Net Equivalent Coding Gain (NECG) which is the FEC coding gain minus the overhead penalty Control Network Protocols FEC Overhead 40 / 59

41 FEC Overhead Hard Decision FEC Hard Decision (HD) FEC operate on bits, which means that a decision has been made a priori related to whether an input signal is a 1 or 0 value Default HD FEC for OTN signal is Reed-Solomon RS(255,239), which adds 16 redundant bits every 239 ones; thus, resulting in an overhead of 6.7 % and a NECG of 5.6 1e-12 Others HD FEC known as super FEC have been proposed in ITU-T G Control Network Protocols FEC Overhead 41 / 59

42 FEC Overhead Super HDFEC Control Network Protocols FEC Overhead 42 / 59

43 FEC Overhead Soft Decision FEC Soft Decision (HD) FEC operate on probabilities, which means that a decision has not been made a priori related to whether an input signal is a 1 or 0 value but its probability is used for enhancing teh error correction capacity of the code An SD FEC is also proposed in ITU-T G for the 6.67 % overhead; however, most SD-FEC make use of larger overhead (20 %) to maximize the NECG (11-12dB) Control Network Protocols FEC Overhead 43 / 59

44 FEC Overhead Super SDFEC Control Network Protocols FEC Overhead 44 / 59

45 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols OTU Overhead 45 / 59

46 OTU Overhead Overhead Fields Section Monitoring (SM): 3 byte for monitoring at the section (lightpath) level General Communications Channel (GCC0) 2-byte field that provides a clear channel connection between OTU termination points for use as DCN RESERVED (RES): for future standarization (all zero) Control Network Protocols OTU Overhead 46 / 59

47 Section Monitoring Overhead Fields Control Network Protocols OTU Overhead 47 / 59

48 Section Monitoring Overhead Fields Trail Trace Identifier (TTI) 64 bytes for lighpath identification distributed over 64 frames (1 byte on each frame), where 16 bytes are used for endpoint ids and the remaining 32 bytes are operator specific BIP-8 Parity checksum to detect errored frames (i.e., blocks) Alarm signals BEI/BIAE (backward error indicator and backward incoming alignment error) indicates to upstream node the number of errored blocks (BIP-8 fails) or if there is an incoming alignment error BDI (backward defect indication (BDI) indicates to upstream node whether there is a signal defect IAE (incoming alignment error) indicates to downstream node that it has detected an alignment error Control Network Protocols OTU Overhead 48 / 59

49 Section Monitoring Trail-trace Identifier Mismatch (TIM) The TTI mismatch process reports the trail trace identifier mismatch defect (TIM) The process is based on the comparison of expected xapis (i.e., SAPI and DAPI) with the xapis in the incoming signal. An acceptance process is required to define the xapi values on the incoming signal, which typically is based on receiving 3 consecutive times the same value Control Network Protocols OTU Overhead 49 / 59

50 Section Monitoring Bit-Interleaved-Parity 8 (BIP8) Control Network Protocols OTU Overhead 50 / 59

51 Section Monitoring (Backward) Incoming Alignment Error) Control Network Protocols OTU Overhead 51 / 59

52 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols ODU Overhead 52 / 59

53 Optical Transport Network Och Data Unit (ODU) Manages connections resulting from one or more consecutive lightpaths (i.e., includes 3R regeneration) End-to-end paths (electropaths) or just ODU path (PM) Intermediate connections (tandem connections) or just ODU TC Supports path and up to 6 TC monitoring (i.e, connections identification, BER performance, alarm indicators, etc.) Control Network Protocols ODU Overhead 53 / 59

54 Path & TC Monitoring Ovehead Fields Control Network Protocols ODU Overhead 54 / 59

55 Och Data Unit (ODU) Maintenance Signals A status field (STAT) is used to indicate the presence of a maintenance signal ODU-AIS: an alarm indication signal (AIS) is a signal sent downstream as an indication that an upstream defect has been detected. Encoded as all 1s signal. ODU-OCI: an open connection indication (OCI) is a signal sent downstream as an indication that upstream the signal is not connected (i.e., provisioned) Encoded as 0110 signal. ODU-LCK: a locked signal is sent downstream as an indication that upstream the connection is locked, and no signal has passed through. Encoded as 0101 signal. Control Network Protocols ODU Overhead 55 / 59

56 Outline 1 Network Management 2 Network Protocols Alignment Overhead FEC Overhead OTU Overhead ODU Overhead OPU Overhead Control Network Protocols OPU Overhead 56 / 59

57 Optical Transport Network Och Paylod Unit (OPU) Adapts client signals to the OTN frames Control Network Protocols OPU Overhead 57 / 59

58 Optical Transport Network OPU Fields One-byte Payload Type (PT) is used to indicate the content of the OPU signal Control Network Protocols OPU Overhead 58 / 59

59 Optical Network Control Jorge M. Finochietto Córdoba 2014 LCD EFN UNC Laboratorio de Comunicaciones Digitales Facultad de Ciencias Exactas, Físicas y Naturales Universidad Nacional de Córdoba, Argentina