GPON technical standard analysis I

1.       Standard specification

ITU-T G.984.1：GPON General characteristics of

ITU-T G.984.2：GPON Of PMD Sublayer specification

ITU-T G.984.3：GPON Of TC Sublayer

ITU-T G.984.4： GPONONT OMCI Interface

ITU-T G.984.5：GPON- Enhance bandwidth

ITU-T G.984.6：GPON- Distance extension

ITU-T G.987： 10G Passive optical network (XG-PON):

ITU-T G.987.1：10G Passive optical network (XG-PON): Aggregate demand

ITU-T G.987.2：10G Passive optical network (XG-PON): Physical media related

 

2.       The term

logicalreach： Regardless of light overhead , The longest distance that theory can reach

differentialfibre distance： lately ONU And farthest ONU Optical path difference between

physicalreach： The farthest physical distance actually reached

meansignal transfer delay： Average delay of uplink and downlink , The value is RTT/2

 

3.       abbreviation

BRI（Basic Rate Interface）： Basic rate interface

DSL（Digital Subscriber Line）： Digital subscriber line

FTTB（Fiber to the Building）： Optical fiber to building

FTTC（Fiber to the Curb）： Fiber to the side of the road

FTTCab（Fiber to the Cabinet）： Optical fiber to junction box

FTTH（Fiber to the Home）： Fiber to home users

ISDN （Integrated Services Digital Network）： Integrated services digital network

GPON（Gigabit-Capable Passive Optical Network）： Gigabit passive optical network

ODN（Optical Distribution Network）： Optical distribution networks

OLT（Optical Line Terminal）： Optical line terminal

OMCC（ONU Management and Control Channel）：ONU Manage the control channel

OMCI（ONU Management and Control Interface）：ONU Management control interface

ONT（Optical Network Terminal）： Optical network terminal

ONU（Optical Network Unit）： Optical network unit

PDH（Plesiochronous Digital Hierarchy）： Quasi synchronous digital system

SDH（Synchronous Digital Hierarchy）： Synchronous digital system

PMD（Physical Medium Dependent）： Physical media related （ Sublayer ）

TC（Transmission Convergence）： Transmission convergence

TDM（Time Division Multiplex）： Time division multiplexing

SNI（Service Node Interface）： Business node interface

T-CONT（Transmission Container）： Transport container

UNI   （User NetworkInterface）： User network interface

 

4.       General overview

And others PON The system is similar to ,GPON The system usually consists of OLT、 On the user side ONU or ONT、 as well as ODN form .OLT and ONU Point to multipoint network structure is adopted between , Through passive ODN Connect .

              The system reference configuration is as follows ：

 

4.1    Network structure

         Three network structures are defined in the standard ：FTTH、FTTB/C and FTTCab. The difference between them is that they support different businesses .

	FTTB		FTTC/FTTCab	FTTH
	MDU	business
Asymmetric business	Support	Support	Support	Support
Symmetric service	Support	Support	Support	Support
POTS and ISDN	Support	Support	Support	Support
A dedicated line		Support
xDSL			Support

 

4.2    basic feature

  4.2.1     Bit rate

Support 7 Two rate combinations , Including symmetric bandwidth and asymmetric bandwidth

Up speed （ Company bit/s）	Down speed （ Company bit/s）
155M	1.2G
622M	1.2G
1.2G	1.2G
155M	2.4G
622M	2.4G
1.2G	2.4G
2.4G	2.4G

         At present, the mainstream of the market is upward 1.2G, The downside 2.4G.

  4.2.2     Theoretical coverage

Regardless of the limitations of the physical layer ,GPON The theoretical coverage of 60KM.

 

  4.2.3     Physical coverage

stay GPON Two ranges are defined in ：10KM and 20KM.10KM For support 1.25Gbit/s Defined by the high rate of .

 

  4.2.4     Optical path difference

The maximum optical path difference is 20KM.

 

  4.2.5     Time delay

GPON The maximum average delay of the service specified in is 1.5ms.

 

  4.2.6     Spectroscopic ratio

Support 1：64, even to the extent that 1：128 Spectral ratio of .

 

  4.2.7     Protection switching

Support automatic switching and forced switching .

Protection switching is caused by OAM Function realization , Because of the support POTS Business , The switching time shall be less than 120ms. Support 4 Protection switching of three types of structures .

a）

b）

c）

d）

 

  4.2.8     Working wavelength

Downlink center wavelength 1490nm

Uplink center wavelength 1310nm

 

5.       PMD Layer requirements

5.1    Access signal rate

GPON The line transmission rate of the system shall be 8kHz Multiple , Its uplink and downlink speed is ：

Ø  1244.16Mbit/s,155.52Mbit/s;

Ø  1244.16Mbit/s,622.08Mbit/s;

Ø  1244.16Mbit/s,1244.16Mbit/s;

Ø  2488.32Mbit/s,155.52Mbit/s;

Ø  2488.32Mbit/s,622.08Mbit/s;

Ø  2488.32Mbit/s,1244.16Mbit/s;

Ø  2488.32Mbit/s,2088.32Mbit/s;

Its specific optical interface parameters refer to the standard .

 

5.2    Transmission direction

The signal is transmitted in the upstream and downstream directions of the transmission medium .

 

5.3    Transmission method

Bidirectional transmission can use wavelength division multiplexing on an optical fiber （WDM） Technical realization , It can also be realized by using the unidirectional transmission technology on two optical fibers

 

5.4    Line rate

5.4.1 The downside

OLT to ONU The nominal rate of the downlink signal of is 1244.16Mbit/s or 2488.32Mbit/s. When OLT When the end office is working in a normal state , The rate of downlink signal tracks one 1 Class clock （ Accuracy of 1×10^-11）. When the end office is running in free oscillation mode , The rate of downlink signal tracks one 3 Class clock （ Accuracy of 4.6×10^-6). When OLT When running in free oscillation mode , The rate accuracy of the downlink signal is one 4 Class clock （3.2×10^-5).

5.4.2 The upside

ONU to OLT The uplink signal rate of is 155.52、622.08、1244.16、2488.32Mbit/s. When ONU When it is running or authorized , It should send a signal with the same clock accuracy as the downlink signal it receives . When ONU When it is not running or not authorized , It can't send any signals .

 

5.5    Line code type

use NRZ code .

The commonly used optical signal logic is ：

u  Binary system “1” Indicates the transmitted highlight power ;

u  Binary system “0” It means sending low optical power .

 

5.6    Working wavelength

Downward direction , The working wavelength range of single optical fiber system shall be 1480～1500nm, The working wavelength range of the dual fiber system shall be 1260～1360nm; The working wavelength range in the upward direction should be 1260-1360nm.

 

5.7    Uplink physical layer overhead

GPON In the system, the physical layer overhead is used to realize the burst of upstream flow .

Up speed	Overhead bytes
155.52 Mbit/s	4
622.08 Mbit/s	8
1244.16Mbit/s	12
2488.32 Mbit/s	24