1. Summary Our ZMUX-121 is a "1+1" E1 channel protection device, which is used to distribute the incoming E1 streams to 2 transmission routings through main and stand-by E1 interface, simultaneously, supervision informations of transmission quality is inserted, and the signal from "BETTER" transmission route will be transmitted to subscriber's equipments after the signal quality of transmission is analyzed. This device can calibrate the delay of two transmissions,the acceptable max delay is 32ms for main and stand-by E1 transmissions. When the switching level is 0, the switching time is ns (bit level),thus, damage (that is caused by routing transmission failure)on subscriber's signal can be eliminated to ensure that subscriber's devices work reliably. Our ZMUX-121 can automatically or manually switch 1 E1 channel between 1 main and 1 stand-by E1 channel without damage on transmitted data so as to protect 1 important E1 incoming streams from subscriber's device. 2. Function Description Concurrently, our ZMUX-121 can transmit incoming E1 stream from subscriber's device to 2 routing transmissions,automatically choose and send the BETTER E1 signal to subscriber's device after receiving the incoming E1 streams from 2 transmissions. In PCM30 framing format,our ZMUX-121 is suitable for PCM framing channel that complies with ITU-T G.703, G.704, G.823 recommendations. In PCM unframing format, our ZMUX-121 is suitable for PCM unframing E1 channels, such as IP circuit of multi-link layer protocols,point to point dedicated circuits of CISCO HDLC protocol, frame relay circuit of LAPF protocol, X.25 circuit of LAPB protocol. The two main functions of our ZMUX-121 are supervisions on performance of transmission channels and safe switching control. This device can supervise real-time signal quality(information of error and alarms)of two routing transmissions and choose one E1 incoming stream based on switching mode to make switching without damage. The max delay of two E1 links is up to 32ms, the subscriber's device is connected to main E1 channel directly when power failure occurs. This device can work in automatic switching mode, it can be switched manually to work on main or stand-by E1 channel when in manual switching mode.In automatic switching mode, this device can be set to varied switching levels based on actual requirements. The E1 switching will happen when the set level is met or surpassed. "Mandatory switching" is the highest level, and the switching levels are ranked from highest to the lowest in the following: The default PCM format: PCM30 framing format The default switching level: level 0 LOS AIS LOF MLOF SLOF 10E-4 error mode 10E-6 error mode single bit error mode level 7 level 6 level 5 level 4 level 3 level 2 level 1 Level 0 Notes: 1) The default setting of working mode is: PCM framing format. 2) The default setting of switching level is: level 0. 3. Technical Parameters a) Interface: conforms to the ITU-T G.703, G704 and G823 recommendations b) Bit Rate: 2048kbit/s±50ppm c) Line Code Type: HDB3 d) Line Impedance: 75Ω or 120Ω e) CRC-4 Insertion Time Delay: <250us f) System Time Delay: ≤600us(PCM framing) ≤10ms(PCM unframing) g) The switching delay of two channels: ≤32ms h) Switching Delay : 0(when the switch level is 0) i) Timescale Insertion: insert the timescale with Sa bits j) Input Voltage: -48V DC or 220V AC k) Power consumption: < 10W l) Working temperature: 0 °C～40°C m) Relative Humidity: ≤85%(25℃) n) Switching indicators: alarms－LOS, AIS, LOF, MLOF, SLOF. o) Error code－10-4,10-6,bit(for PCM framing format),pack loss rate(for PCM unframing format) 4. System Characteristics 1) Integration of monitoring transmission quality and automatic switching without damge; 2) When LOS, LOF, AIS alarms occurs on local inputs, AIS will be seen on the remote output; 3) Three switching levels available in PCM framing mode: 10E-4/10E-6/single bit error code; 4) Three switching levels available in PCM unframing mode: packet loss rate of 2%/, 1%, 0.5%; 5) High precision digital PLL technology is adopted to ensure accurate synchronization between devices; 6) The device features small size, low power power consumption and high reliability based on VLSI solution. 7) The alarms and working status of this device can be collected by connecting pc to the monitoring port on the device. 5. Scope of Applications This device can supervise real-time signal quality(information of error and alarms)of two routing transmissions and choose one E1 incoming stream based on switching mode to make switching without damage.