Today, I will explain current PON technologies – GPON and XG(S)-PON. These technologies are the most important PON technologies specified by the ITU-T organization.
GPON is an abbreviation from Gigabit Passive Optical Network. It was the third PON standard was developed by the ITU-T organization. GPON technology was developed after BPON. The limitations that existed in the BPON standard were resolved with GPON.
GPON technology is based on the ITU-T G.984 standard. Standard ITU-T G.984.1 describes network parameters and network requirements for protection switchover. ITU-T G.984.2 explains ODN parameter specifications, 2.5Gbps/1.25Gbps downlink/uplink optical port parameter specifications, and physical layer overhead allocation. Next to standard ITU-T G.984.3 describes GTC layer specifications, multiplexing architecture and protocol stack, layer frame structure, ONU registration and activation flows, DBA specifications, and alarm and performance. And the last ITU-T G.984.4 explains OMCI message structure, device management architecture, and principles.
In the next figure, we can see the architecture of the GPON.
Figure 1. Architecture of GPON
(https://forum.huawei.com/carrier/en/thread-445963.html)
GPON system is composed of OLT (Optical Line Terminal), ODN (Optical Distribution Network), and ONUs (Optical Network Unit). The maximum logical reach is 60km, but the maximum physical reach is 20km. The split ratio is from 32 to a maximum of 128. The typical split ratio is 32 or 64.
This technology uses 1490nm for downstream and 1310nm for upstream. These wavelengths are used for video – IPTV and data – HSI and VOIP. In the downstream direction, OLT sends data to all ONUs. It is the broadcast mode. ONUs receive data and know their data based on GEM port IDs. In the upstream direction, every ONU has a timeslot for transmitting. The OLT assigns timeslots to ONUs. The ONUs can transmit only in these timeslots. It is TDMA (Time Division Multiple Access) modes.
The maximum speed for downstream is 2.5 Gbps and the maximum speed for upstream is 2.5 Gbps/1.25Gbps. Typical speed 2.5/1.25Gbps per PON port.
The GPON supports network protection in downstream and upstream. For downstream network, there are type B single-homing protection, type B dual-homing protection, type C single-homing protection and type C dual-homing protection.
Key technologies of GPON are DBA (Dynamic Bandwidth Allocation), ranging, burst optical and electrical technology, FEC (Forward Error Correction), and AES (Advanced Encryption System).
The GPON technology can be implemented in these scenarios: FTTH, FTTB, FTTC, FTTD, FTTO, FTTW, etc.
The next table shows us the main features of GPON technology.
Standard | G.984 |
Frame | GEM |
Downstream wavelength | 1490 nm |
Upstream wavelength | 1310 nm |
Speed | Max 2.5/2.5 Gbps or typical 2.5/1.25 Gbps |
Number of fibers | 1 |
Split Ratio | Max 128 or typical 32 or 64 |
Distance | Max 60 km or typical 20 km |
Fiber Type | G.652, G.657 |
The next generation of PON is 10G-PON or XG(S)-PON. This “X” is the Roman number 10. The standard for this technology is G.987. The 10G-PON can be asymetric – XG-PON and symetric – XGS-PON. The XG-PON has 10/2.5 Gbps and the XGS-PON has 10/10 Gbps. The architecture of XG(S)-PON is the same as GPON.
The new technology works at other wavelengths (1578nm for downstream and 1270nm for upstream) and allows for a more split ratio (254+). Thanks to other wavelengths, it is possible that GPON and XG(S)-PON exist in the same ODN network. The most important features of this new PON technology are in the next table.
Standard | G.987 |
Frame | XGEM |
Downstream wavelength | 1578 nm |
Upstream wavelength | 1270 nm |
Speed | Symetric 10/10 Gbps or asymetric 10/2.5 Gbps |
Number of fibers | 1 |
Split Ratio | Max 254+ or typical 64 |
Distance | Max 60 km or typical 20 km |
Fiber Type | G.652, G.657 |
Thank you!
Reference:
Traning materials for HCIA-Access V2.0
Traning material for HCIP-Access V2.0
https://forum.huawei.com/carrier/en/thread-445963.html
