ITU-T G.709协议：定义下一代OTN骨干传送网

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"G.709协议标准是国际电信联盟(ITU-T)制定的一系列推荐标准，用于规范光传输网络(OTN)的接口和架构。这个标准旨在提升基于波分复用技术的骨干传送网的性能和效率，解决传统WDM网络在业务调度、组网和保护方面的局限性。OTN是一种融合了光层和数字层的新型传输系统，旨在提供更强大的网络功能和服务。" G.709协议标准详细涵盖了OTN的帧结构、复用和解复用过程、光通道数据单元(OCDU)、光通道净荷单元(OPU)以及光通道传送单元(OTU)等关键概念。这些单元是OTN中的基本构建块，允许不同速率和类型的信号在光网络中传输。例如，OPU用于封装各种客户信号，如SDH、Ethernet或ATM，而OTU则负责在光纤上传输这些封装后的信号，同时提供误码检测、同步和网络管理等功能。标准G.709定义了多个层次的映射和适配过程，以实现不同速率服务的透明传输。它包括了从低速到高速（如从STM-N到100Gbps及以上）的各种信号的适配，使得网络能够灵活地处理各种容量的需求。此外，G.709还引入了丰富的开销信息，用于网络监控、故障检测、性能管理和保护恢复。在保护和恢复机制方面，G.709提供了多种机制，如1+1线性保护、环网保护、ASON(智能光网络)支持等，增强了网络的生存性和可靠性。这些特性使得OTN在网络发生故障时能够快速自动恢复，确保服务的连续性。另外，G.709与一系列其他ITU-T标准一起工作，如G.872定义了OTN的总体架构，G.798则关注于物理层的接口。这些标准共同构成了一个完整的OTN规范框架，为构建高效、可扩展且灵活的光传输网络提供了基础。 G.709协议标准对于现代通信网络的发展至关重要，特别是在承载大数据量、高带宽需求的服务如云计算、视频流和物联网(IoT)应用中。通过实施G.709，运营商可以构建更加智能化、可管理的网络基础设施，满足未来网络服务的快速增长和多样化需求。

8 Rec. ITU-T G.709/Y.1331 (06/2016)

ppm parts per million

PRBS Pseudo Random Binary Sequence

PSI Payload Structure Identifier

PT Payload Type

QDR Quad Data Rate

RES Reserved for future international standardization

RF Remote Fault

RS Reed-Solomon

RS-Ack Re-sequence Acknowledge

SAPI Source Access Point Identifier

SBCON Single-Byte command code sets Connection

SDI Serial Digital Interface

SDR Single Data Rate

Sk Sink

SM Section Monitoring

SMOH Section Monitoring Overhead

SNC Subnetwork Connection

SNC/I Subnetwork Connection protection with Inherent monitoring

SNC/N Subnetwork Connection protection with Non-intrusive monitoring

SNC/S Subnetwork Connection protection with Sublayer monitoring

So Source

SOTU Single-OTU

SOTUm Single-OTU with management

TC Tandem Connection

TC-CMEP Tandem Connection-Connection Monitoring End Point

TCM Tandem Connection Monitoring

TCMOH Tandem Connection Monitoring Overhead

TS Tributary Slot

TSI Transmitter Structure Identifier

TSOH Tributary Slot Overhead

TTI Trail Trace Identifier

TTT Timing Transparent Transcoding

TxTI Transmitted Trace Identifier

UNI User-to-Network Interface

XC Cross Connect

XGPON 10 Gigabit-capable Passive Optical Networks

Rec. ITU-T G.709/Y.1331 (06/2016) 9

5 Conventions

This Recommendation uses the following conventions defined in [ITU-T G.870]:

– k

– m

– n

The functional architecture of the optical transport network as specified in [ITU-T G.872] is used to

derive the ONNI. The ONNI is specified in terms of the adapted and characteristic information present

in each layer as described in [ITU-T G.805].

Transmission order: The order of transmission of information in all the diagrams in this

Recommendation is first from left to right and then from top to bottom. Within each byte the most

significant bit is transmitted first. The most significant bit (bit 1) is illustrated at the left in all the

diagrams.

Mapping order: The serial bit stream of a constant bit rate signal is inserted into the OPU payload

so that the bits will be transmitted on the OPU/ODU in the same order that they were received at the

input of the AMP, BMP or GMP mapper function. If m bits b

, b

up to b

are client signal bits of

which b

is the bit that is received first and b

is the bit that is received last, then b

will be mapped

into bit 1 of a first OPU byte and b

will be mapped into bit 8 of an n

OPU byte (with n = m/8).

Value of reserved bit(s): The value of an overhead bit, which is reserved or reserved for future

international standardization shall be set to "0".

Value of non-sourced bit(s): Unless stated otherwise, any non-sourced bits shall be set to "0".

OTUk, OTUCn, ODUk, ODUCn, OPUk and OPUCn overhead assignment: The assignment of

an overhead in the optical transport/data/payload unit signal to each part is defined in Figure 5-1.

OTUk, ODUk, OPUk contain one instance of OTU, ODU, OPU overhead. OTUCn, ODUCn and

OPUCn contain n instances of OTU, ODU, OPU overhead, numbered 1 to n.

Interleaved versions of the OTU, ODU and OPU overhead may be present on OTUCn interfaces.

This interleaving is interface specific and specified for OTN interfaces with standardized application

codes in the interface specific Recommendations (ITU-T G.709.x series). Within the other clauses of

this Recommendation an OTUCn, ODUCn and OPUCn are presented in an interface independent

manner, by means of n OTUC, ODUC and OPUC instances that are marked #1 to #n.

......

G.709-Y.1331(12)_F5-1

Row #

Column #

Frame alignment area OTU specific overhead area

ODU specific overhead area

OPU

specific

overhead area

1 167 14 158

Figure 5-1  OTU, ODU and OPU overhead

6 Optical transport network interface structure

The optical transport network as specified in [ITU-T G.872] defines two interface types, each with

two sub-types:

– Single optical transport unit interfaces:

• without optical layer overhead (SOTU);

• with optical layer overhead (SOTUm).

10 Rec. ITU-T G.709/Y.1331 (06/2016)

– Multi optical transport unit interfaces:

• without optical layer overhead (MOTU);

• with optical layer overhead (MOTUm).

The OTN interfaces without optical layer overhead are defined with 3R processing at each end of the

interface.

The interfaces consist of digital and management information defined in this Recommendation as

carried by a physical interface, the specifications of which are outside the scope of this

Recommendation.

Each interface may be associated with one or more application identifiers. Each application identifier

represents either a standardized application code or a vendor specific identifier. An interface with an

application code may be used to interconnect (OTN) equipment from different vendors. An interface

with a vendor specific identifier is to be used to interconnect (OTN) equipment from the same vendor.

6.1 Basic signal structure

The basic structure is shown in Figures 6-1 and 6-2 and consists of a digital and an optical structure.

6.1.1 OTN digital structure

The OTN digital structure (see Figure 6-1) consists of two classes of optical transport units (OTU);

the OTUk and OTUCn. The OTUk signal consists of a 4080 column by 4 row frame, which includes

256 columns allocated to contain a forward error correction code (FEC) and is operated at various bit

rates that are represented by the value of k. The OTUCn signal consists of n interleaved 3824 column

by 4 row frames, which do not include a FEC area and is operated at n times a basic rate that is

represented by OTUC. FEC for the OTUCn signal is interface specific and not included in the OTUCn

definition.

The OTUk contains an optical data unit (ODUk) and the ODUk contains an optical payload unit

(OPUk). The OTUk and its ODUk perform digital section and path layer roles.

The OTUCn contains an optical data unit (ODUCn) and the ODUCn contains an optical payload unit

(OPUCn). The OTUCn and its ODUCn perform digital section layer roles only.

– The completely standardized OTUk or functionally standardized OTUk-v and OTUkV

provide supervision and conditions the signal for transport between 3R regeneration points

in the OTN.

– The ODUk which provides:

• tandem connection monitoring (ODUkT)

• end-to-end path supervision (ODUkP)

• adaptation of client signals via the OPUk

• adaptation of client ODUk signals via the OPUk.

– The OTUCn provides supervision for transport between 3R regeneration points in the OTN.

Note that the OTUCn does not condition the signal for transport between 3R regeneration

points because encapsulation and forward error correction are not included in the OTUCn

definition.

– The ODUCn provides supervision for transport between ODUk aware points in the OTN.

• tandem connection monitoring (ODUCnT)

• end-to-end section supervision (ODUCnP)

• adaptation of ODUk signals via the OPUCn.

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