PON ( Passive Optical Network ) Types
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♦♦PON ( Passive Optical Network ) Types♦♦
♦ BPON – (Broadband PON) is an older version of PON technology which is based on ITU specifications and is characterized by an asymmetrical 622 Mbps downstream and a 155 Mpbs upstream optical line rate.
♦ GPON – (Gigabit PON) is the latest ITU specified PON network and is characterized by a 2.4 Gbps downstream and a 1.25 Gbps upstream optical line rate. The first significant commercial deployments of GPON began in early 2008. Most carrier implementations of GPON are in the U.S.
♦ EPON – (Gigabit Ethernet PON or GEPON) is an IEEE standards based PON system characterized by a symmetrical 1.25 Gbps optical line rate. EPON is the predominant PON solution since it has been commercially available since 2001. GEPON has been primarily deployed in Asian Pacific markets. Recently, 10Gbit/s EPON or 10G-EPON was ratified as an amendment (IEEE 802.3av) in the IEEE 802.3 standard and provides for an asymmetrical 10 Gbps downstream/1 Gbps upstream rate as well as a symmetrical 10 Gbps rate.
♦ WDM PON – (Wave Division Multiplexing PON) is an emerging technology which leverages the optical advances of dense wave division multiplexing (DWDM) to provide a dedicated wavelength to a single ONT. Implementations range from “tunable” optics which must be matched to the ONT’s optics to a dynamic optical locking capability which automatically assigns a wavelength to the ONT at the ranging phase. WDM PONs utilize an arrayed waveguide grating (AWG) to multiplex up to 32 wavelengths of light onto a single fiber in the same way a passive optical splitter does. Unlike a typical optical splitter however, an AWG utilizes a phase shift in the optical light to provide an output on each fiber that only receives a certain wavelength of light.
♦ Downstream Communication
The OLT transmits a signal downstream that all of the ONTs receive (point-to- multipoint). In the downstream direction, the information is broadcast on a specific color (wavelength) of laser light. The information is encoded into digital form and given a specific address that matches a specific ONT. The ONT that matches the address receives the signal and forwards the information to the end-user Ethernet port as depicted below.
♦ Upstream Communication
Since many ONTs are placed on the same fiber, each with their own laser, upstream communications must be coordinated so that they do not interfere with each other. This is done by synchronizing the ONTs and requiring each to send information to the OLT (Upstream) in a specific time window (TDM). The upstream laser color is different from the downstream laser, so the upstream signal will not interfere with other ONTs on the PON. Using the WDM technique, ONTs do not interfere with each other; the upstream signals do not interfere with downstream signals, and the upstream and downstream signals can communicate at the same time (full duplex).
Các loại Mạng Quang Tĩnh (PON)
BPON (Broadband PON): Công nghệ PON cũ, dựa trên tiêu chuẩn ITU, có tốc độ xuống 622 Mbps và tốc độ lên 155 Mbps.
GPON (Gigabit PON): Công nghệ PON mới nhất của ITU, có tốc độ xuống 2,4 Gbps và tốc độ lên 1,25 Gbps. Các triển khai thương mại lớn bắt đầu từ năm 2008.
EPON (Gigabit Ethernet PON): Hệ thống PON dựa trên tiêu chuẩn IEEE, có tốc độ đối xứng 1,25 Gbps. EPON là giải pháp PON phổ biến nhất từ năm 2001.
WDM PON (Wave Division Multiplexing PON): Công nghệ mới, sử dụng kỹ thuật đa sóng mang để cung cấp sóng mang riêng cho mỗi thiết bị ONT.
Truyền thông Downstream
OLT gửi tín hiệu xuống tất cả ONT (điểm-đa điểm).
Thông tin được mã hóa và truyền trên sóng mang laser cụ thể.
ONT nhận tín hiệu và chuyển tiếp đến cổng Ethernet của người dùng.
Truyền thông Upstream
Các ONT được đồng bộ hóa để tránh xung đột.
Mỗi ONT gửi thông tin lên OLT trong cửa sổ thời gian cụ thể (TDM).
Sóng mang laser lên khác với sóng mang xuống, tránh xung đột.
Sử dụng kỹ thuật WDM, các ONT không xung đột, cho phép truyền thông hai chiều (full duplex).
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