14 Common Questions About Telephone Optical Terminals
Oct 10, 2012
14 Common Questions About Telephone Optical Terminals
- How to evaluate the performance of a telephone optical terminal
How many optical ports and optical directions.
How many E1 channels.
Whether it has an Ethernet interface.
Whether it has a V35 interface.
Whether it has a V11/V24 interface.
Whether it has an order wire phone.
Whether it has network management.
Networking mode: whether it can form a self-healing ring. - Number of optical ports 1: Point-to-point mode
The cheapest telephone optical terminal has only 1 optical interface and 1 pair of devices, forming a point-to-point working mode, also called terminal mode: TM. - Number of optical ports 2: Dual optical ports, single direction
Better telephone optical terminals have dual optical ports. Dual-optical-port optical terminals are further divided into: 1 or 2 optical directions. Dual optical ports with 1 optical direction provide 1+1 backup operation. Once the main fiber is broken, the auxiliary optical port ensures continued operation. - Number of optical ports 3: Dual optical ports, dual directions
Part of the signal from the left optical port terminates locally, while the other part continues to be transmitted from the right optical port. This working mode is called add/drop multiplexing mode: ADM. Optical terminals with ADM capability can form a dual-fiber self-healing ring. - Benefits of a dual-fiber self-healing ring
The benefit of a self-healing ring is that once the optical cable is broken, the entire communication will not be interrupted. When the optical cable is normal, information between stations travels via the outer ring. After the cable is cut, information from Station 1 toward Station 2 is rerouted via the inner ring. When the optical cable is repaired, the network automatically returns to normal. Only optical terminals with ADM capability can implement a self-healing ring. - Number of optical ports 4: Multiple optical ports, multiple optical directions
The best telephone optical terminal is SDH, which supports multiple optical directions, but the price is much higher. A detailed discussion of SDH equipment is provided later. A network diagram is given at the end, which is a collection of various modes. - Number of E1 channels 1: PDH system
The simplest optical terminal has 4 E1 ports, commonly called small 8M.
30 analog telephone channels can be multiplexed into one 2M, called a primary group E1.
4 E1s can be multiplexed into one 8M, called a second-order group, also called E2.
4 E2s can be multiplexed into one 34M, called a third-order group, also called E3.
4 E3s can be multiplexed into one 140M, called a fourth-order group, also called E4.
This system is called PDH, also known as the plesiochronous system. - Number of E1 channels 2: SDH system
The SDH system is a new system, born only 10 years ago. The smallest capacity SDH is 155Mb/s, called STM-1, with 63 E1s.
4 STM-1s are multiplexed into one STM-4, also called 622.
4 STM-4s are multiplexed into one STM-16, called 2.5G.
4 STM-16s are multiplexed into one STM-64, called 10G.
It can be seen that SDH optical terminals are large-capacity optical terminals.
155 and 622 are the most widely used SDH optical terminals in the SDH system. - Ethernet interface
Ordinary telephone optical terminals do not have an Ethernet interface. Optical terminals with an Ethernet interface are a new market demand in the past 2 years.
One E1 channel can transmit a 10M Ethernet signal.
Four E1 channels can transmit a 100M Ethernet signal. - Whether it has a V35 interface
Ordinary optical terminals do not have a V35 interface.
The V35 interface is also a market demand of the past 2 years.
The V35 interface is a synchronous data interface with a rate of NX64kb/s.
Usually one E1 is used to transmit one V35 interface. - Auxiliary channels and order wire
Ordinary optical terminals generally have auxiliary channels. Auxiliary channels are low-speed asynchronous data interfaces, such as RS232. The order wire phone is used for inter-station liaison, but is actually rarely used. Very cheap optical terminals do not have an order wire phone, and some do not even have asynchronous data. - Network management system
Network management means computer network management, also called centralized monitoring. Connecting the operating status information of all optical terminals at all stations to the network management computer in the central office's network management room is network management.
Generally, PDH optical terminals do not have a network management system.
Generally, SDH optical terminals all have a network management system. - Networking mode
Generally, PDH optical terminals can only operate in TM mode, i.e., point-to-point networking.
Generally, PDH optical terminals have only 1 optical port.
SDH optical terminals can operate in both TM mode and ADM mode, and therefore can form a self-healing ring network.
The working mode with more than 3 optical directions is called DXC, i.e., cross-connect mode. - Specifications of telephone optical terminals
Telephone optical terminals have many specifications, but none of them are critical. The slightly useful one is the transmission distance. Generally, optical terminals can transmit 20-60 km. When a longer distance is required, simply replace the optical port module. Another point is the connector type of the optical port. The most common types are FC (round) and SC (square). When ordering, it is necessary to consider whether pigtails are included.