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 |
|
|
| Center wavelength |
|
|
| Transmission rate |
|
|
| 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.
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.
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.
- 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).
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