3.0 Introduction
3.1 MTTplus-420 Overview
The MTTplus-420 GPON test module for the VeEX® MTTplus platform is designed for ONT/ONU service activation and
troubleshooting. It is only intended to be used at the customer site between the splitter and Optical Network Unit/Optical Network
Terminal (ONU/ONT). The unit passively monitors downstream and upstream GPON traffic and tests optical power levels for
compliance to standards. Advanced testing mode reports system errors/alarms statuses and captures and decode OMCI and
PLOAM messages exchanged between the Optical Line Terminal (OLT) and ONT, allowing technicians to perform advanced
troubleshooting beyond basic signal level.
The operator is assumed to have received basic training in fiber optics and related testing and measurement practices.
3.2 What is GPON
The International Telecommunications Union standard (ITU-T G.984) describes attributes of gigabit- capable passive optical network
(GPON) systems. GPON utilizes optical wavelength division multiplexing (WDM) so a single fiber from a provider’s central office can
be split to serve multiple homes and businesses for both downstream and upstream data transmission.
The Optical Line Terminal (OLT) sends 1490nm signal downstream at a rate of 2.488 Gbits/s. Every Optical Network Unit/Optical
Network Terminal (ONU/ONT) receives the same data but is able to recognize data targeted to a specific ONU/ONT. Each
ONU/ONT upstream 1310nm signal transmits at a rate of 1.244 Gbits/s using a time division multiplex (TDM) format as each
ONU/ONT is assigned a time slot in which it can transmit to the OLT. The total available bandwidth is divided between all ONUs so
each user only gets a fraction of available bandwidth, such as 100 Mbits/s, depending on how the OLT allocates it. The upstream
transmissions, called burst-mode operation, is allocated on an as need basis by the OLT for each ONU/ONT that needs to send
data. Because the TDM method involves multiple users on a single transmission, the upstream data rate is always less than the
maximum available bandwidth to support sharing of bandwidth.
The OLT determines the distance and time delay for each subscriber. The software provides a way to allot time slots to upstream
data for each ONU. The typical split of a single fiber is 1:32 or 1:64. That means each fiber can serve up to 32 or 64 subscribers.
However, split ratios up to 1:128 are possible on some systems.
As for data format, the original GPON packets could handle ATM packets directly. Recall that ATM packages everything in 53-byte
packets with 48 bytes for data and 5 bytes for overhead. In 2008, the GPON standard removed direct ATM and only called for the
use of a generic encapsulation method (GEM) frame to carry protocols. GEM can encapsulate Ethernet, IP, TCP, UDP, T1/E1,
video, VoIP, or other protocols as called for by the data transmission. Minimum packet size is 53 bytes, and the maximum is 1518
bytes. AES encryption is used downstream only.
3.3 Key Features
Basic Mode
Two Port pass through mode for measuring ONT upstream and downstream level measurements for 1310and 1490
Simultaneous display and measurement of calibrated PON signals
Automatic ODN class detection and power-level pass/fail analysis
Display OLT TX, PON Type, and Budget, and Class (if supported by OLT)
Indicate pass/fail status for signal and ODN link budget
Filtered, in-service loss measurements for each PON signal
Low insertion loss:
≤
1.5 dB type
User defined Pass/Fail thresholds
Automated pass/fail fiber inspection analysis with optional fiberscope
Easy Report generation and data transfer
Upstream/Downstream LED status indicators for signal, Frame, Err/Alarm, and TC Sync
MTTplus-420_User_Manual_RevC00
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