Feature Guide

This document describes the main features supported by ONUs and the applications, principle, specification, and the limitations of the features.

Features Specifications and Dependency and Limitation of ONUs

GPON: Gigabit passive optical network (GPON) is a PON technology that is standardized by the ITU-T Recommendations G.984.x. A GPON device supports high-bandwidth transmission. GPON effectively solves the bandwidth bottleneck problem in the twisted-pair access and meets users demands on high-bandwidth services.

Layer 2 Broadband: The Layer 2 broadcast feature, including multiple sub-features, refers to the link layer protocol management. This topic describes sub-features of Layer 2 broadband in details.

QoS: QoS refers to quality of service. The QoS technology provides end-to-end service quality assurance for users by setting a series of QoS parameters, such as service availability, time delay, jitter, and packet loss rate. It includes technologies such as priority processing, traffic policing, ACL policy, and congestion avoidance and management.

Layer 3 Features

IPv6: An update version of IPv4, which is designed by the Internet Engineering Task Force (IETF) and is also called IP Next Generation (IPng).

Multicast: Multicast is a communication mode in which data is transmitted to multiple receivers at the same time.

Voice: As the ONU access device in the FTTO buildup model, the ONU not only provides broadband services (including data services and video live/on demand services), but also provides high-quality voice services by using the built-in voice module for the end users directly over twisted pairs. Such voice features fit in with the trend of integrated data, voice, and video services. This topic describes voice features.

WLAN

System Security

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.

Figure 1 shows the working principle of the GPON network.

Figure 1 Working principle of the GPON network

In the GPON network, 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. Figure 2shows the details.

Figure 2 Downstream communication principle of GPON

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. Figure 3 shows the details.

Figure 3 Upstream communication principle of GPON

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.

GPON Networking Applications

GPON is a passive optical transmission technology that applies in FTTx solutions, including fiber to the office (FTTO), for voice, data, video, private line access. Figure 1 shows FTTO networking applications.

Figure 1 FTTO networking applications

The OLT is connected to enterprise ONUs using an ODN network. The ONUs are connected to user terminals using GE, POTS, E1, 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.

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.
Figure 1 shows GPON service mapping relationships in the upstream direction.
Figure 1 GPON service mapping relationships in the upstream direction
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.
Figure 2 shows GPON service mapping relationships in the downstream direction.
Figure 2 GPON service mapping relationships in the downstream direction

GPON Port Specifications

This topic describes specifications and standards compliance of the GPON interfaces.

**Table 1** GPON port specifications
Parameter	Specifications
Transmission rate	Rx: 2.488 Gbit/s Tx: 1.244 Gbit/s
Connector	SC/UPC
Maximum reach	20 km
Standard compliance	ITU-T G.984.2 CLASS B+
Center wavelength	Tx: 1310 nm Rx: 1490 nm
Tx optical power	0.5 dBm to 5.0 dBm
Extinction ratio	> 10 dB
Minimum receiver sensitivity	-27 dBm
Maximum overload optical power	-8 dBm

XG-PON Port Specifications

This topic describes specifications and standards compliance of the XG-PON interfaces.

**Table 1** XG-PON port specifications
Parameter	Specifications(CLASS N1)	Specifications(CLASS N2a)
Transmission rate	Rx: 10 Gbit/s Tx: 2.5 Gbit/s
Connector	SC/UPC
Maximum reach	40 km
Standard compliance	ITU-T G.987.2 CLASS N1	ITU-T G.987.2 CLASS N2a
Center wavelength	Rx: 1577 nm Tx: 1270 nm
Tx optical power	2.0 dBm to 7.0 dBm
Extinction ratio	> 8.2 dB
Minimum receiver sensitivity	-28 dBm	-28 dBm
Maximum overload optical power	-8 dBm	-8 dBm