What's the GPON Frame Structure

GPON frame structure

Upstream GPON Frame

An upstream GPON frame has a fixed length of 125 µs. Each upstream frame contains the content carried by one or more T-CONTs. All ONUs connected to a GPON port share the upstream bandwidth

• All ONUs connected to a GPON port send their data upstream at their own timeslots according to bandwidth map (BWmap) requirements.
• Each ONU reports the status of data to be sent to the OLT using upstream frames. Then, the OLT uses DBA to allocate upstream timeslots to ONUs and sends updates in each frame.

In Figure an upstream GPON frame consists of the physical layer overhead upstream (PLOu), PLOAM upstream (PLOAMu), power level sequence upstream (PLSu), dynamic bandwidth report upstream (DBRu), and payload fields, as described below,

Field	Description	Function
PLOu	Upstream physical layer overhead	Used for frame alignment, synchronization, and identification for an ONU.
PLOAMu	PLOAM messages of upstream data	Used for reporting ONU management messages, including maintenance and management status. This field may not be contained in a frame but must be negotiated.
PLSu	Upstream power level sequence	Used by ONUs for adjusting optical port power. This field may not be contained in a frame but must be negotiated.
DBRu	Upstream dynamic bandwidth report	Used for reporting the T-CONT status to apply for bandwidth next time and for allocating dynamic bandwidths. This field may not be contained in a frame but must be negotiated.
Payload	Payload user data	Can be a DBA status report or data frame. If this field is a data frame, this field consists of a GEM header and frames.

 

Downstream GPON Frame

A downstream GPON frame has a fixed length of 125 µs and comprises physical control block downstream (PCBd) and payload. PCBd mainly consists of the GTC header and BWmap. The OLT broadcasts PCBd to all ONUs. Then, the ONUs receive the PCBd and perform operations based on the information contained in PCBd.

• The GTC header is used for frame delimitation, synchronization, and forward error correction (FEC).
• The BWMap field notifies every ONU of upstream bandwidth allocation. It specifies the start and end upstream timeslots for the T-CONTs of each ONU, ensuring that all ONUs send data using the timeslots specified by the OLT to prevent data conflict.

PCBd contains PSync, Ident, PLOAMd, BIP, PLend, and US BW Map fields, where US BW Map is the upstream bandwidth mapping sent by the OLT for each T-CONT.

Field	Description	Function
PSync	Physical synchronization domain, frame synchronization information	Used by ONUs to specify the start of each frame.
Ident	Identification domain	Used for sorting a frame in the frames of the same type in length sequence.
Downstream PLOAM (PLOAMd)	PLOAM messages of downstream data	Used for reporting ONU management messages, including maintenance and management status. This field may not be contained in a frame but must be negotiated.
BIP	Bit interleaved parity	Used for performing a parity check for all bytes between two BIP fields (excluding the preamble and delimit) to monitor error codes.
PLend	Length of downstream payloads	Used for specifying the length of the BWmap field.
Upstream bandwidth map (US BW Map)	Upstream bandwidth mapping	Used by the OLT for sending the upstream bandwidth mapping to each T-CONT. The BWmap specifies the start and end times for each T-CONT in transmitting data.

More related:

What’s the alarm on the OptiX OSN 1800II board restarts after power-off

How to Control Board Failure After an MxU Service Port Is Bound to a Rate Unlimited

Pay attention to Optical Power Reporting of Modules in WDM Products

How to deal with GPON Stacks

GPON Protocol Stacks

ITU-T Recommendation G.984.3 defines a new set of frame structures, which consider traditional voice, video, and Ethernet packets as payloads of GPON (GPFD) frames. 

GPON protocol stacks involve the physical medium dependent (PMD) layer and GPON transmission convergence (GTC) layer.

PMD Layer
The GPON PMD layer corresponds to the GPON interfaces between OLTs and ONUs. Parameter values of the GPON interfaces specify the maximum reach and split ratio for a GPON system.

GTC Layer
The GTA layer is used to encapsulate payloads using ATM cells or GEM frames, and GEM frames are commonly used in GPON systems. GEM frames can carry Ethernet, POTS, E1, and T1 cells.
GTC is the core GPON layer, where media access is controlled for upstream service flows and ONUs are registered. Ethernet frame payloads are encapsulated into GEM frames and then packetized as GTC frames. These GTC frames are converted to binary codes for transmission based on interface parameters configured at the physical layer. The process is reversal on the receive end. Specifically, the receive end decapsulates the data to obtain GTC frames, GEM frames, and then payloads for data transmission.

The GTC layer is classified as TC adaptation sub-layer and GTC framing sub-layer by structure.

• The TC adaptation sub-layer involves the ATM, GEM TC, and optical network terminal management and control interface (OMCI) adapters and dynamic bandwidth assignment (DBA) control module. ATM and GEM TC adapters identify OMCI channels by virtual path identifier (VPI)/virtual channel identifier (VCI) or GEM port ID. OMCI adapters can exchange OMCI channel data with the ATM and GEM TC adapters and send the OMCI channel data to OMCI entities. The DBA control module is a common functional module, which generates ONU reports and controls DBA allocation.
• On the GTC framing sub-layer, GTC frames include GEM blocks, PLOAM blocks, and embedded OAM blocks. The GTC framing sub-layer supports the following functions:
  • Multiplexes and demultiplexes data. Specifically, the GTC framing sub-layer multiplexes PLOAM and GEM data into downstream TC frames based on the boundary information specified in the frame header. In addition, the GTC framing sub-layer demultiplexes PLOAM and GEM data from upstream TC frames based on frame header instructions.
  • Generates frame headers and decodes data. The GTC framing sub-layer generates the TC header of downstream frames in a specified format and decodes the frame header of upstream frames. In addition, the GTC framing sub-layer terminates the embedded OAM data encapsulated into the GTC header and uses the OAM data to control this sub-layer.
  • Routes data internally based on alloc-IDs. The GTC framing sub-layer routes the data sent by or to the GEM TC adapters based on internal alloc-IDs.

The GTC layer consists of plane C/M and plane U based on functions.

• The protocol stacks of plane C/M include embedded OAM, PLOAM, and OMCI. Embedded OAM and PLOAM channels are used for managing PMD and GTC sub-layer functions. OMCI provides a unified system for upper-layer sub-layer management.
  • Embedded OAM channels are defined in GTC frame headers for determining bandwidths, exchanging data, and dynamically allocating bandwidths.
  • Dedicated space is reserved in GTC frames for format-based PLOAM channels. The PLOAM channels carry the PMD and GTC management information that does not pass through the embedded OAM block.
  • OMCI channels are used for managing services.
• Service flows on plane U are identified based on service flow types (ATM or GEM) and port ID/VPI. Port IDs identify GEM service flows and VPIs identify ATM service flows. In T-CONTs, bandwidths are allocated and QoS is controlled using the timeslots that can be adjusted.

More related:

What’s the alarm on the OptiX OSN 1800II board restarts after power-off

Technical Case: Optical Network

Pay Attention to Service Interruption on FPGAs Cross-Connect Boards

GPON Service Multiplexing

GPON encapsulation mode (GEM) ports and transmission containers (T-CONTs) divide a PON network into virtual connections for service multiplexing.

• Each GEM port can carry one or more types of service stream. After carrying service streams, a GEM port must be mapped to a T-CONT before upstream service scheduling. Each ONU supports multiple T-CONTs that can have different service types.
• A T-CONT can be bound to one or more GEM ports, depending on customers' data plan. On the OLT, GEM ports are demodulated from the T-CONT and then service streams are demodulated from the GEM port payload for further processing.

Service Mapping Relationships

• In the upstream direction,
• An ONU sends Ethernet frames to GEM ports based on configured mapping rules between service ports and GEM ports. Then, the GEM ports encapsulate the Ethernet frames into GEM packet data units (PDUs) and add these PDUs to T-CONT queues based on mapping rules between GEM ports and T-CONT queues. Then, the T-CONT queues use timeslots for upstream transmission to send GEM PDUs to the OLT.
• The OLT receives the GEM PDUs and obtains Ethernet frames from them. Then, the OLT sends Ethernet frames from a specified uplink port based on mapping rules between service ports and uplink ports.

• In the downstream direction,
• The OLT sends Ethernet frames to the GPON service processing module based on configured mapping rules between service ports and uplink ports. The GPON service processing module then encapsulates the Ethernet frames into GEM PDUs for downstream transmission using a GPON port.
• GPON transmission convergence (GTC) frames containing GEM PDUs are broadcast to all ONUs connected to the GPON port.
• The ONU filters the received data according to the GEM port ID contained in the GEM PDU header and retains the data only belonging to the GEM ports of this ONU. Then, the ONU decapsulates the data to Ethernet frames and sends them to end users using service ports.

More related:

How to Clear the DBMS_ERROR Alarm Reported After an Upgrade

Tips to buy the home broadband router

New- and Old-Model Boards on ASON Networks of WDM Products

Pay attention to GPON Networking Applications

GPON is a passive optical transmission technology that applies in FTTx solutions, including fiber to the building (FTTB), fiber to the curb (FTTC), fiber to the door (FTTD), fiber to the home (FTTH), fiber to the mobile base station (FTTM), fiber to the office (FTTO), and fiber to the WLAN (FTTW), for voice, data, video, private line access, and base station access services. Figure 1 shows FTTx networking applications.

The FTTx network applications in GPON access have the following in common: The data, voice, and video signals of terminal users are sent to ONUs, where the signals are converted into Ethernet packets and then transmitted over optical fibers to the OLT using the GPON uplink ports on the ONUs. Then, the Ethernet packets are forwarded to the upper-layer IP network using the uplink port on the OLT.

• FTTB/FTTC: The OLT is connected to ONUs in corridors (FTTB) or by the curb (FTTC) using an optical distribution network (ODN). The ONUs are then connected to user terminals using xDSL. FTTB/FTTC is applicable to densely-populated residential communities or office buildings. In this scenario, FTTB/FTTC provides services of certain bandwidth for common users.
• FTTD: uses existing access media at user homes to resolve drop fiber issues in FTTH scenarios.
• FTTH: The OLT connects to ONTs at user homes using an ODN network. FTTH is applicable to new apartments or villas in loose distribution. In this scenario, FTTH provides services of higher bandwidth for high-end users.
• FTTM: The OLT is connected to ONUs using an ODN network. The ONUs are then connected to wireless base stations using E1. The OLT connects wireless base stations to the core IP bearer network using optical access technologies. This implementation mode is not only simpler than traditional SDH/ATM private line technologies, but also drives down the costs of base station backhaul. FTTM is applicable to reconstruction and capacity expansion of mobile bearer networks. In this scenario, FTTM converges the fixed network and the mobile network on the bearer plane.
• FTTO: The OLT is connected to enterprise ONUs using an ODN network. The ONUs are connected to user terminals using FE, POTS, or Wi-Fi. QinQ VLAN encapsulation is implemented on the ONUs and the OLT. In this way, transparent and secure data channels can be set up between the enterprise private networks located at different places, and therefore the service data and BPDUs between the enterprise private networks can be transparently transmitted over the public network. FTTO is applicable to enterprise networks. In this scenario, FTTO implements TDM PBX, IP PBX, and private line service in the enterprise intranets.
• FTTW: The OLT connects to ONUs using an ODN network, the ONUs connect to access points (APs) using GE for WLAN traffic backhaul. FTTW is the trend in Wi-Fi construction.

More related:

What’s the IGMP Framework on the Device

How to Upgrade the LSW Chip of the H801SCUN Board

New- and Old-Model Boards on ASON Networks of WDM Products

What's GPON transmission?

Introduction to the GPON System

Mainstream PON technologies include broadband passive optical network (BPON), Ethernet passive optical network (EPON), and gigabit passive optical network (GPON). Adopting the ATM encapsulation mode, BPON is mainly used for carrying ATM services. With the obsolescence of the ATM technology, BPON also drops out. EPON is an Ethernet passive optical network technology. GPON is a gigabit passive optical network technology and is to date the most widely used mainstream optical access technology.

• In the GPON network, such as GPFD,  the OLT is connected to the optical splitter through a single optical fiber, and the optical splitter is then connected to ONUs. Different wavelengths are adopted in the upstream and downstream directions for transmitting data. Specifically, wavelengths range from 1260 nm to 1360 nm in the upstream direction and from 1480 nm to 1500 nm in the downstream direction.
• The GPON adopts WDM to transmit data of different upstream/downstream wavelengths over the same ODN. Data is broadcast in the downstream direction and transmitted in the TDMA mode (based on timeslots) in the upstream direction.

GPON Downstream Transmission

All data is broadcast to all ONUs from the OLT. The ONUs then select and receive their respective data and discard the other data.

Main features:

• Supports point-to-multipoint (P2MP) multicast transmission.
• Broadcasts the same data to all ONUs and differentiates ONU data by GEM port ID.
• Allows an ONU to receive the desired data by ONU ID.

GPON Upstream Transmission

In the upstream direction, each ONU can send data to the OLT only in the timeslot permitted and allocated by the OLT. This ensures that each ONU sends data in a given sequence, avoiding upstream data conflicts.

Main features:

• Supports time division multiple access (TDMA).
• Transits data on an exclusive timeslot.
• Couples optical signals on an optical splitter.
• Detects and prevents collisions through ranging.

More related:

Prewarning for Flash Space Exhaustion

Pay Attention to the Interruption of SNCP Service on OSN 9500

Huawei MA5620 Series Equipment Port Mirror Capture

What's GEM Frame and T-CONT of GPON?

GEM Frame

In the gigabit-capable passive optical network (GPON) system, a GPON encapsulation mode (GEM) frame is the smallest service-carrying unit and the basic encapsulation structure. All service streams are encapsulated into the GEM frame and transmitted over GPON lines. The service streams are identified by GEM ports and each GEM port is identified by a unique port ID. The port ID is globally allocated by the OLT. Therefore, the ONUs connected to the same OLT cannot use GEM ports that have the same port ID. A GEM port is used to identify the virtual service channel that carries the service stream between the OLT and the ONU. It is similar to the virtual path identifier (VPI)/virtual channel identifier (VCI) of the asynchronous transfer mode (ATM) virtual connection.

A GEM header consists of PLI, Port ID, PTI, and header error check (HEC) and is used for differentiating data of different GEM ports.

• PLI: indicates the length of data payload.
• Port ID: uniquely identifies a GEM port.
• PTI: indicates the payload type. It is used for identifying the status and type of data that is being transmitted, for example, whether the operation, administration and maintenance (OAM) message is being transmitted and whether data transmission is complete.
• HEC: ensures the forward error correction (FEC) function and transmission quality.
• Fragment payload: indicates the frame fragment.

The following section describes the GEM frame structure based on the mapping of the Ethernet service in GPON mode, as shown in Figure 2.

• The GPON system parses Ethernet frames and maps data into GEM payloads for transmission.
• Header information is automatically encapsulated into GEM frames.
• The mapping format is clear and has good compatibility.

T-CONT

Transmission container (T-CONT) is a service carrier in the upstream direction in the GPON system. All GEM ports are mapped to T-CONTs. Then service streams are transmitted upstream by means of OLT's dynamic bandwidth allocation (DBA) scheduling. T-CONT is the basic control unit of the upstream service stream in the GPON system. Each T-CONT is identified by Alloc-ID. The Alloc-ID is allocated by the GPON port of the OLT, and the T-CONTs used by ONUs connected to the same GPON port of OLT cannot have the same Alloc-IDs.kangyu.

There are five types of T-CONT. T-CONT selection varies during the scheduling of different types of upstream service streams. Each T-CONT bandwidth type has its own quality of service (QoS) feature. QoS is mainly represented by the bandwidth guarantee, which can be classified into fixed, assured, non-assured, best-effort, and hybrid modes.

Type 1:

• The fixed bandwidth is reserved for specific ONUs or specific services on ONUs. It cannot be used by other ONUs even if no upstream service streams are carried on the specific ONUs.
• It applies to services that are sensitive to service quality. The services can be TDM or VoIP services.

Type 2:

• The assured bandwidth is available at any time required by an ONU. When the bandwidth required by the service streams on the ONU is smaller than the assured bandwidth, the system can use the DBA mechanism to allocate the remaining bandwidth to services on other ONUs.
• Because DBA is required, this type provides a less real-time performance compared with the fixed bandwidth.

Type 3:

• This type is the combination of the assured bandwidth and maximum bandwidth. The system assures some bandwidth for subscribers and allows subscribers to preempt bandwidth. However, the total used bandwidth cannot exceed the maximum configured bandwidth.
• It applies to VoIP services.

Type 4:

• This type is the maximum bandwidth that can be used by an ONU, fully providing the bandwidth required by the ONU.
• It applies to IPTV and other high-speed Internet services.

Type 5:

This type is the combination of the fixed, assured, and maximum bandwidth. It supports the following functions:

• Reserves bandwidth for subscribers and the bandwidth cannot be preempted by other subscribers.
• Provides the bandwidth to an ONU at any time when required
• Allow subscribers to preempt some bandwidth. (The total used bandwidth cannot exceed the maximum configured bandwidth.)

More Related:

Optical attenuation is too large lead to ONU recovery failure

How to Configure the H.248-based Voice Service?

What’s the Service Interruption on the MA5616?

What Is GPON?

PON is a point to multi-point (P2MP) passive optical network. GPON, a type of PON technology, is defined by ITU-T Recommendation G.984.x. Figure 1 shows a GPON network.

IFgpon: GPON interface
SNI: service node interface
UNI: user to network interface
CPE: customer premises equipment

• The optical line terminal (OLT:MA5683T) is an aggregation device located at the central office (CO) for terminating the PON protocol.
• Optical network units (ONUs)/Optical network terminal (ONTs:HG8245H) are located on the user side, providing various ports for connecting to user terminals. The OLT and ONUs are connected using an optical distribution network (ODN) for communication.
• The ODN is composed of passive optical components (POS), such as optical fibers, and one or more passive optical splitters. The ODN provides optical channels between the OLT and ONUs. It interconnects the OLT and ONUs and is highly reliable.

As the wide use of broadband services and fiber-in and copper-out development, carriers require a longer transmission reach, higher bandwidth, reliability, and lower operating expense (OPEX) on services. GPON supports the following functions to meet these requirements:

• Longer transmission distance: The transmission media of optical fibers covers up to 60 km coverage radius on the access layer, resolving transmission distance and bandwidth issues in twisted pair transmission.
• Higher bandwidth: Each GPON port can support a maximum transmission rate of 2.5 Gbit/s in the downstream direction and 1.25 Gbit/s in the upstream direction, meeting the usage requirements of high-bandwidth services, such as high definition television (HDTV) and outside broadcast (OB).
• Better user experience on full services: Flexible QoS measures support traffic control based on users and user services, implementing differentiated service provisioning for different users.
• Higher resource usage with lower costs: GPON supports a split ratio up to 1:128. A feeder fiber from the CO equipment room can be split to up to 128 drop fibers. This economizes on fiber resources and O&M costs.

More related:

How to Troubleshoot Synchronous Ethernet Clocks For Huawei SDH

Application of Time-range In HUAWEI MA5600 Series Equipment

ARP Security Configuration Commands_part 2

Why is GPON required?

Broadband services require more bandwidth

Access network evolution

The Application of optical fibers resolving transmission distance and bandwidth issues in twisted pari transmission.

GPON technology development 

Low-cost network

• Saving of at least half of the fiber optic backbone
• Compared to P2P, saving nearly half of the optical module

Low maintenance costs

• Passive Network save maintenance costs
• Feature reduces the power consumption of passive cluster node
• OAM management system reduces management difficulties

Better quality of service 

• Features native support for multicast
• Access high-bandwidth, and can evolution to more high bandwidth.

More related:

MA5600T Backup Redundant of Configuration Smart Link

Implementation of TR069 protocol in MA5600 series

The Issue that the MA5600T H802GPBD Board Resets Repeatedly

How to authenticate 10G GPON?

Authentication

Context

In the PON system, downstream data is broadcast to all ONUs. As a result, downstream data destined for certain ONUs or all ONUs may be intercepted by illegal users.

Figure 1 Authentication process 

An optical line terminal (OLT) authenticates an optical network unit (ONU) based on the authentication information reported by the ONU (HG8240) and rejects unauthorized ONUs. Only authenticated ONUs can access a passive optical network (PON). This function enables carriers to manage and maintain devices on the PON network flexibly and conveniently.

Authentication Modes

10G GPON support three authentication modes:

• SN
• SN + Password
• Password

Authentication Process

The authentication process include six states:

• O1: Initial state.
• O2-3: Serial Number state.
• O4: Ranging state.
• O5: Operation state.
• O6: Intermittent LODS state.
• O7: Emergency Stop state.

The authentication process include two timers:

• TO1: Ranging timer.
• TO2: LODS timer.

More related:

The Feature of Huawei MA5600

Tips to buy the home broadband router

The Issue that the MA5600T H802GPBD Board Resets Repeatedly

What's the network planning of 10G GPON on Huawei OLT

Background Information

This section describes two common networking scenarios for evolving GPON to 10G GPON. You can select either of them based on the actual networking and service requirements.

Networking Scenario I — Pure 10G GPON Network

Description
A pure 10G GPON network contains only 10G GPON devices, including 10G GPON service board, 10G GPON optical network units (ONUs), and an optical distribution network (ODN). This scenario applies to a new 10G GPON FTTB or FTTC network. FTTB is the acronym for fiber to the building and FTTC is the acronym for fiber to the curb.
Network Diagram
Figure 1 shows a pure 10G GPON network.

Figure 1 Pure 10G GPON network 

Characteristics

• Advantage: Only one type of network element (NE) (10G GPON devices) is involved, and the maintenance is easy.
• Disadvantage: A new ODN is required.

Networking Scenario II — Hybrid 10G GPON and GPON Network

Description
A hybrid 10G GPON and GPON network contains 10G GPON and GPON NEs. These 10G GPON and GPON NEs share an ODN.
Network Diagram

Figure 2 shows a hybrid 10G GPON and GPON network.

Figure 2 Hybrid 10G GPON and GPON network 

On a hybrid 10G GPON and GPON network, an OLT(MA5680T) uses 10G GPON and GPON boards to receive services. 10G GPON and GPON NEs share an ODN but use different service wavelengths. Therefore, a passive wavelength multiplexing device (WDM1r) is required.

Characteristics

• Advantage: A GPON network is smoothly migrated to a 10G GPON network and the two networks share an ODN.
• Disadvantages:
• A WDM1r device is required on the ODN to multiplex wavelengths. This operation requires reconstruction for existing ODN networks and optical fiber connections, which interrupts services.
• Various types of NEs (10G GPON and GPON devices) are involved, and the maintenance is complicated.

10G GPON ONUs are compatible with GPON ONUs. During the usage, pay attention to the following points:

• On OLTs, 10G GPON access board support only 10G GPON ONUs.
• On OLTs, GPON access board support only GPON ONUs.

More related:

How to Configure the Internet Access Service?

How to change the MA5600T Boards

10GE LAN link flapping on customer router due to SNCP switch

What's the four Key Technologies of 10G GPON?

Ranging

The logic reaches from optical network units (ONUs) to an optical line terminal (OLT) vary. The round trip delays (RTDs) between an OLT and ONUs also vary depending on time and environment. Therefore, collisions may occur when ONU sends data in TDMA mode (in this mode, only one of the ONUs connecting to a PON port sends data at a moment), as shown in Figure 1.

To prevent the collisions, ranging is enabled when an ONU (HG8245) registers for the first time. The OLT (MA5683T) measures the RTD of each ONU in the ranging process and calculates the equalization delay
(EqD) of each ONU to ensure that the values of Teqd, which is equal to RTD plus EqD, of all
ONUs connected to the same PON port are the same. Therefore, the logic reaches from ONUs
to an OLT are the same, preventing collisions during upstream transmission.

Burst Optical/Electrical Technology

In 10G GPON upstream direction, Time Division Multiple Access (TDMA) is used. An optical
network unit (ONU) transmits data only within the allocated timeslots. In the timeslots that are not allocated to it, the ONU disables the transmission of its optical transceiver to prevent other
ONUs from being affected. The optical line terminal (OLT) then receives the upstream data
from each ONU in a burst manner based on timeslots. Therefore, to ensure normal running of
the 10G GPON system.

Ranging can be implemented to prevent cells transmitted by different ONUs from conflicting
with each other on the OLT. However, the ranging accuracy is ± 1 bit and the cells transmitted
by different ONUs have a protection time of several bits (not a multiple of 1 bit). If the ONU-
side optical modules do not support the burst transmit function, the transmitted signals overlap
and distortion occurs.

• The distance from each ONU to the OLT varies and therefore the optical signal attenuation varies for each ONU. As a result, the power and level of packets received by an OLT at different timeslots various.
• If the OLT-side optical modules do not support the burst receive function, the OLT may restore incorrect signals because only the level greater than the threshold is considered valid and the signals with the level lower than the threshold cannot be restored.

DBA

The OLT uses DBA to dynamically adjust the upstream bandwidth allocated to different ONUs
to address the burst traffic on the ONUs, meeting the ONU upstream bandwidth requirements
and improving the utilization of the PON upstream bandwidth.

In the preceding figure,

• The DBA module in the OLT consistently collects DBA reports and uses the DBA algorithm to calculate the upstream bandwidth allocated to each ONU.
• The OLT sends the calculated result to each ONU using a bandwidth (BW) map.
• Each ONU transmits burst upstream data using permitted timeslots defined in the BW map.

Highlights and Applications

• Based on ONUs' burst upstream service traffic, the OLT dynamically allocates an upstream bandwidth to each ONU in real time, improving upstream bandwidth utilization on PON ports.
• More users are supported on a PON port.
• Higher service bandwidths with burst requirements are supported than those before DBA is applied.

FEC

Forward error correction (FEC) is mainly used for improving transmission quality of a line.
No ideal digital channel is available in practice. As a result, bit errors and jitter occur when digital signals are being transmitted over any transmission medium, deteriorating transmission quality on lines.

To resolve the problem, error correction mechanism is introduced.

• The mechanism can check and correct errors after data is transmitted to the peer end. such as FEC.
• The mechanism can check errors after data is transmitted to the peer end but not correct errors.

Highlight and Application

• Does not require retransmission and provides a high real-time performance
• Requires an additional bandwidth (Users must balance the transmission quality and bandwidth.)
• Checks and corrects errors after data is transmitted to the peer end, but does not apply to services for which retransmission is enabled
• Applies to data transmission on the network that has a poor quality
• Applies to services that have a low requirement on delay (The delay is large if retransmission is configured for services.)

Configuration Guide

The FEC function of 10G GPON as follows:

• Supported only in the downstream direction.
• FEC is enabled by default.
• The FEC function cannot be configured manually.

More related:

How to precaution the using problem of Huawei MA5603T product?

Optical attenuation is too large lead to ONU recovery failure

What‘s 10 GPON?

10G GPON is evolved from the existing GPON technology, the factors promoting the technology
evolution to 10G GPON are as follows:

• Developing services require higher bandwidths and the GPON technology cannot meet bandwidth requirements.
• Innovative access technologies on the user side require higher bandwidths and the GPON technology will face bandwidth bottlenecks.
• A greater split ratio and a longer transmission distance increase network construction investments.

Specification Differences Between 10G GPON and GPON

The following table lists specification differences between the two technologies.

Specifications	10G GPON (G.987 and G.988)	GPON (G.984)
Wavelength	Downstream: 1575-1580 nm Upstream: 1260-1280 nm	Downstream: 1480-1500 nm Upstream: 1290-1360 nm
Center wavelength	Downstream: 1577 nm Upstream: 1270 nm	Downstream: 1490 nm Upstream: 1310 nm
Transmission rate	Downstream: 9.95328 Gbit/s Upstream: 2.48832 Gbit/s	Downstream: 2.48832 Gbit/s Upstream: 1.24416 Gbit/s
Frame structure	x GPON encapsulation mode (xGEM)	GEM

XGEM Frame

An XGEM frame is the minimum service carrying unit in an 10G GPON system and is also the basic encapsulation structure. All the services must be encapsulated in XGEM frames for transmission. An XGEM frame is composed of a header and payload, as shown in Figure 1.

Figure 1 XGEM frame structure

Service Multiplexing

GEM ports and T-CONTs divide a PON network into virtual connections for service multiplexing, as shown in Figure 2.

Figure 2 Working principles of service multiplexing in an 10G GPON system

GEM Port

A GPON encapsulation mode (GEM) port is a virtual service channel that carries a service flow between the OLT (MA5683T, MA5680T, MA5608T) and an ONU (HG8245, HG8240) in an 10G GPON system. The GEM port is similar to the virtual connection (identified by VPI/VCI) in asynchronous transfer mode (ATM). VPI is the acronym for virtual path identifier and VCI is the acronym for virtual channel identifier.

• Each GEM port is identified by a unique XGEM port ID.
• The XGEM port ID is globally allocated according to the 10G GPON port by the OLT.
• A GEM port can carry one or more types of services.

T-CONT

A transmission container (T-CONT) is the basic control unit of upstream service flows in an 10G GPON system, and is also the unit for carrying service flows in the upstream direction. All the GEM ports are mapped to T-CONTs, and the OLT uses dynamic bandwidth allocation (DBA) to schedule upstream transmission.

• A T-CONT can carry one or more GEM ports according to user configurations.
• A T-CONT is identified uniquely by Alloc-ID.
• The Alloc-ID is allocated according to the 10G GPON port by the OLT.
• An ONU supports multiple T-CONTs configured for various service types.

Networking Diagram

A 10G GPON network is of the point-to-multipoint (P2MP) type, which is the same as that of a GPON network. Figure 1 shows a 10G GPON networking diagram.

Figure 1 Networking Diagram 

The 10G GPON network contains an optical line terminal, optical network units, and an optical distribution network (ODN).

• The Optical line terminal (OLT) is an aggregation device located at the central office (CO) for terminating the PON protocol.
• Optical network units (ONUs) are located on the user side, providing various types of ports for connecting to user terminals. The OLT and ONUs are connected through a passive ODN for communication.
• The Optical distribution network (ODN) is composed of passive optical components (POS) such as optical fibers, and one or more passive optical splitters. The ODN provides optical channels between the OLT and ONUs. It interconnects the OLT and ONUs and is highly reliable.

Transmit Principles

10G GPON uses wavelength division multiplexing (WDM) to transmit data in different wavelengths on an ODN network. Figure 2 shows the working principles.

Figure 2 Transmit Principles 

• In the downstream direction, data is broadcast and the center wavelength is 1577 nm (the wavelength ranging from 1575 nm to 1580 nm).
• In the upstream direction, data is transmitted in time division multiple access (TDMA) mode and the center wavelength is 1270 nm (the wavelength ranging from 1260 nm to 1280 nm).

More related:

Some Abnormal OLT GPON CLASS B+ Optical Modules at High Temperature- 20130627-A

How To Reset Huawei OLT MA5600T Series Equipment Password