The control of jitter and wander within the optical transport network (OTN)
|Publication Date:||1 November 2018|
The scope of this Recommendation is to define the parameters and the relevant limits that satisfactorily control the amount of jitter and wander present at the OTN network-node interface (NNI).
OTN network interfaces, to which this Recommendation is applicable, are defined in terms of bit rates and frame structures in [ITU-T G.709]; the relevant equipment characteristics are described in [ITU-T G.798] and the optical characteristics in [ITU-T G.959.1] or [ITU-T G.693]. Additional information regarding the architecture of the OTN is found in [ITU-T G.872].
The network limits given in clause 6, OTN interface tolerance specifications given in clause 7.1, and OTN equipment interface specifications given in Annex A apply at or refer to the OTUk interface. The relevant bit rates for these specifications are the OTUk bit rates. Note that some of the other requirements in this Recommendation, e.g., the demapper clock (ODCp), asynchronous mapper clock (ODCa), and bit-synchronous mapper clock (ODCb) requirements in Annex A, apply to other interfaces and other bit rates (i.e., the demapper resides in the sink adaptation function between the ODUkP and CBR, ODUj or ODUkP/ODUj_A client, while the asynchronous and bit-synchronous mapper clocks reside in the source adaptation function between the ODUkP and client). In this Recommendation the term 'clock', when used in ODU clock (ODC), refers to a frequency source. Note that this Recommendation contains requirements for both non-OTN CBRx clients mapped into ODUk and ODUj clients multiplexed into ODUk (k > j).
The OTN physical layer is not required to transport network synchronization. More precisely, neither the ODUk nor any layers below it are required to transport synchronization. Network synchronization distribution is a function of the client layer, e.g., SDH.
[ITU-T G.825] specifies the jitter and wander requirements for SDH clients, and any SDH signal (which must meet [ITU-T G.825]) is suitable for providing synchronization (see [ITU-T G.803]). SDH clients must meet [ITU-T G.825] requirements for both asynchronous and bit-synchronous mappings.
[ITU-T G.8261] specifies the jitter and wander requirements of synchronous Ethernet for providing synchronization (see Annex D of [ITU-T G.8261]). Synchronous Ethernet clients must meet [ITU-T G.8261] requirements for both GMP and bit-synchronous mappings.
Jitter and wander requirements for SDH networks are specified in [ITU-T G.825]. Jitter and wander requirements for PDH and synchronization networks are specified in [ITU-T G.823], for networks based on the first level bit rate of 2048 kbit/s, and in [ITU-T G.824] for networks based on the first-level bit rate of 1544 kbit/s.
The jitter and wander control philosophy is based on the need:
- to recommend a maximum network limit that should not be exceeded at any relevant OTN NNI;
- to recommend a consistent framework for the specification of individual digital equipment (i.e., jitter and wander transfer, tolerance and generation requirements);
- to provide sufficient information and guidelines for organizations to measure and study jitter and wander accumulation in any network configuration.
Note that there may exist hybrid network element (NE) types that contain SDH, Ethernet, and/or OTN atomic functions. For such hybrid NEs, it may not be possible to access the respective ports to make measurements to verify compliance with the requirements in this Recommendation. Measurements to verify compliance for hybrid NE types is outside the scope of this Recommendation.