1. OLT basic concept
OLT (Optical Line Terminal) optical line terminal, PON network consists of OLT, ODN and ONU. The OLT belongs to the service node side device of the access network, and is connected to the corresponding service node device through the SNI interface to complete the access service of the access network.
In the PON technology application, the OLT device is an important central office device, and its functions are as follows: 1. The front-end (aggregation layer) switch is connected by a network cable, converted into an optical signal, and interconnected by a single optical fiber and a splitter at the user end.
1) Realize the functions of control, management and ranging of the ONU of the user equipment. 3. The OLT device is the same as the ONU device.
The OLT is connected to the central office equipment. If the optical signal is too strong (sometimes because the short-distance optical signal loss is small), an attenuator is required. The OLT is connected to the ONU, and the optical splitter is connected before the two.
The PON network carries services such as voice, Internet access, IPTV video and data line.
2. OLT physical composition
The OLT usually consists of the following parts:
1) Control board (also called main control board or super control unit) Generally, one OLT has two main boards and two boards.
2) DC power supply board (from the negative 48 volts of the switching power supply) is generally two main boards
3) Fan unit (heat dissipation and environmental monitoring of main equipment, etc.)
4) Chassis (or business box)
5) Upstream board: GE optical interface board (including gusset), optical transceiver integrated module, generally one board is 2 GE ports (currently 10GE has been commercialized), and the upstream board is transmitted (OTN transmission is connected to BRAS) (Broadband remote access server) and other aggregation switches or directly connected to the BRAS and other devices and SR devices, if there is IPTV service, you need to access the corresponding BNG device. The upstream board is not the same as the optical module (no transmission in the middle) It reaches 10-40KM.
6) Downlink board (also called service version or PON board), general OLT equipment has multi-port PON board (for example, one board has 8 PON ports), each port goes through the optical splitter (no more than 1:64) ) Connect to the ONT terminal.
The transmission distance and attenuation of the downstream components have their limitations because of the distance measurement between the ONT and the OLT. For example, the 8-port GPON OLT interface board (including the pluggable ClassB+ optical module) requires the ODN attenuation to be within -28db, and the 8-port GPON OLT interface board (including the pluggable ClassC+ optical module) requires the ODN transmission loss to be within -32db; However, considering the post-maintenance factors and other comprehensive reasons: the board control of the ClassB+ optical module in the initial project is required to be within -25db, and the board of the ClassC+ optical module is controlled within -29db.
7) According to the business needs, the OLT can also insert (all can be mixed and inserted) TDM service version, Ethernet service version, 16-channel E1 service version and other boards.
8) New OLT equipment must consider the full configuration power consumption (calculated by 1400W) to calculate the size of the power line, and the size of the empty space (occupying 2 groups, one master and one standby). According to the previous experience, 63A is generally used for the open space; the wire diameter is 16mm2 copper core wire (flame retardant), and the ground wire is 16mm2 yellow and green copper wire.
9) Note that the OLT uplink occupied terminals are convenient for opening, and the downlink occupied terminals must be considered clearly. The length of the pigtail should be measured well (the optical fiber is provided by the manufacturer, the power cord manufacturer provides it, but pay attention to the length). And the optical fiber jumper (the OLT side is the SC head (downstream) and the LC head is up) on the ODF side flange type.
