To understand EPON, GPON and other networks, we must first understand what is a PON network?
PON (Passive Optical Network):
A PON network refers to an optical distribution network (ODN) between an OLT (optical line terminal) and an ONU (optical network unit) without any active electronic equipment, and is a pure medium network. The PON network uses a single-fiber bidirectional optical access network with a point-to-multipoint structure. It consists of an optical line terminal (OLT) on the network side, an optical distribution network (ODN), and an optical network unit (ONU) on the user side.
Operators generally use point-to-multipoint mode networking (as shown in the figure below-taking EPON as an example):
Communicate in the broadcast mode on the downstream, assign a unique LLID to the ONU
1, The PON downstream data stream is transmitted in TDM (Time Division Multiplexing) broadcast mode, and the ONU is assigned a unique LLID after registration; the upstream data stream is transmitted in TDMA (Time Division Multiple Access) mode.
2, Before the downstream data of EPON OLT is sent out, the source will add a LLID (15bit), this LLID corresponds to one of the ONUs below, when the ONU receives the data, it will judge whether the LLID is the same as its own at the physical level The LLIDs are consistent. If the questions are met, the answer will be accepted. If the questions are not met, the question will be discarded. GPON distinguishes different ONU data by the ONU-ID (8bit) in PLOAMd in the downstream GTC frame.
Upstream and downstream directions at the service data level:
1. In the upstream direction, various service information from each ONU is coupled to the same optical fiber through the 1:N passive optical combiner in the ODN without interference, and finally sent to the receiving end of the OLT at the central office.
2. In the downstream direction, IP data, voice, video and other services are distributed by the OLT located in the central office to all ONU units on the PON through the 1:N passive optical distributor in the ODN.
The difference between EPON and GPON:
1. EPON (based on Ethernet PON, also known as Gigabit Ethernet PON, or GEPON):
Bandwidth: Provide 1.25Gbps bandwidth for upstream and downstream, the actual bandwidth is 1G, adopt 8b/10b line coding.
Optical split ratio (how many ONUs an OLT port carries): The split ratio of the EPON standard is 1:32.
2. GPON (Gigabit Passive Optical Network):
Bandwidth: Support multiple rate levels, downstream 2.488Gbps or 1.244Gbps, upstream 1.244Gbps or 622 Mbps (upstream and downstream can be asymmetric), we generally choose the former (2.488Gbits/s download rate and 1.244Gbits/s upload rate).
Optical split ratio (how many ONUs an OLT port carries): GPON split ratios of 1:32, 1:64, and 1:128 are fine.
We need to pay attention: PON insertion has optical attenuation (loss 15 ~ 18dB), so a large split ratio will reduce the transmission distance.
GPON provides multiple options, but the cost is not much different from EPON. The maximum physical distance that GPON can support. When the optical split ratio is 1:16, it can support the maximum physical distance of 20KM; when the optical split ratio is 1:32, it can support the maximum physical distance of 10KM.
The difference between 10G EPON and 10G GPON:
10G EPON (10-Gbit/s Ethernet version of 802.3av):
Bandwidth: The actual rate is 10.3125 Gbit/s, which is divided into two types: symmetric (10 Gbps uplink and downlink rates) and asymmetric (10 Gbps downlink and 1 Gbps uplink).
Split ratio: 1:128 split ratio, compared with EPON & GPON, the splitting capability is stronger and can carry more users
10G GPON (also called XGPON):
Bandwidth: Asymmetric upstream and downstream (upstream 2.5Gbps, downstream 10Gbps).
Split ratio: 1:128. Under the same split ratio, the maximum transmission distance of 10G GPON can reach 40KM.
It should be noted that 10 Gbit/s EPON uses different optical wavelengths on the optical fiber (downstream 1575-1580nm, upstream 1260-1280nm), so 10 Gbit/s EPON and standard 1Gbit/sEPON can be on the same fiber Perform wavelength multiplexing. This advantage is that the 10GEPON splitter can be connected to the ONU of EPON.
The current mainstream PON technology applied to FTTH (fiber entry) is EPON technology and GPON technology. 10G PON technology is mainly used in FTTB (fiber entry corridor) scenarios. This is because the ONU price of 10G PON is nearly 5 times that of EPON. When used in FTTH scenarios, there is no advantage in price.