Abstract: This article was published in the October 2003 issue of "Electronic Products" magazine to discuss how to select the T1 / E1 / J1 single-chip transceiver (SCT).
Overview Since the introduction of T carrier in the 1960s, T carrier and E carrier networks have gone through a long development path. Today, designers will see more and more functions integrated into T1 / E1 / J1 single-chip transceiver Device (SCT).
The introduction of a large number of functions is easy to confuse designers. This article introduces the important performance that needs to be paid attention to in the design. T1, E, and J carrier networks work at 1.544Mbps. T1 is the lowest rate of the North American Public Switched Telephone Network (PSTN) digital multiplex transmission T carrier layer. It was originally designed for the transmission of digital voice signals. T1 uses pulse code modulation and time division multiplexing technology to transmit 24 channel-level voice signals, which is called DS0. Each DS0 or time slot carries 64kbps of information.
E1 is a European digital transmission format, which can carry 32 channels of voice, and the multiplexed clock rate is 2.048Mbps.
Now, T1 and E1 not only transmit voice signals, but also transmit data or a combination of both. T1 and E1 transmission lines have been widely used in cellular base stations, business access routers and personal branch exchanges. Figure 1 shows a typical functional block diagram of T1 / E1 / J1 SCT. J1 is a T1 variant dedicated to Japan.
Figure 1. Typical functional block diagram of a single-chip T1 / E1 / J1 transceiver. The line interface unit and the line interface unit (LIU) of the framer SCT are the physical layer interfaces to the copper cable loop. The framer and the receiver received from the LIU Data synchronization, and format the LIU data for transmission. The advantage of some SCTs is that LIU can provide both short-range and long-range operations, enabling SCT to be used for the first layer of digital signal cross-connection (DSX-1) of CSU (channel service unit) / DSU (data service unit).
In the traditional T1 / E1 / J1 design, LIU and framer are independent ICs. With the development of ultra-large-scale integration technology, they can be integrated into a single-chip IC. One function that needs to be checked in SCT is: Whether the signal can be directly connected to the framer to allow modification of the data stream or insertion of code from an external signal source. Another benefit is the ability to use bidirectional code streams for monitoring purposes. Software programmable line termination Within a given T1 / E1 / J1 device's internal characteristics, software programmable copper cable loop termination is a very useful function, and ICs introduced by Dallas Semiconductor since the DS2155 SCT have this function. Engineers can design a complete T1 / E1 / J1 board, and can change the line terminal matching impedance required by the copper cable loop through software without adding any external components. At present, as T1 / E1 / J1 equipment is becoming more and more demanding on cost, this function has become a standard in design. The jitter attenuator T / E carrier loop will appear instantaneous out of synchronization. This phenomenon is often caused by jitter. Jitter is defined as the amplitude of the phase change when the reference clock frequency changes by more than 10 Hz.
To ensure the reliability of the system and the repeatability of the clock, it is best to choose an SCT that can provide jitter suppression in the transmit and receive channels. Some devices also provide two jitter suppression buffers, which are suitable for applications with large jitter, high reliability, or low response time. Advanced data link control Advanced data link control (HDLC) is the layer 2 processing type of the ISO 7-layer model. Physical layer link maintenance and quality monitoring are typical applications of HDLC controllers. In order to improve the system's adaptability, you can choose HDLC controller capable of allocating single or multiple DSO or FDL bits. The bit error rate test circuit (BERT) communication channel requires a diagnostic Tool to test the link quality. Most SCTs include sending and receiving BERTs. Pseudo-random data templates can be injected from the sending end to the copper cable loop. Then, the receiver BERT can Synchronized to the injected signal, the BERT can attenuate the signal or inject noise into the copper cable loop during operation, which helps to describe the performance of the SCT, copper cable loop and higher software layers. If the BERT detects an error state, further research or testing of the communication channel may be required. The protection switch considers that the T / E transmission line provides vital data. Many designs require a backup solution when the copper cable loop is unreliable or the line card terminates. The protection switch allows the standby SCT to switch to the line without losing the frame synchronization to replace the failed SCT. Many chips can provide this function without the need for external relays or switches. LIU with a high-impedance input for the receiver and a tri-state output for the transmitter is ideal for this type of application. Multi-port density Most T / E carrier line cards use multiple ports. One of the reasons is to meet the bandwidth of 1.544Mbps or 2.048Mbps. In this case, T1 and E1 are bound together or logically combined into a unit. For example, in multi-link frame relay; another multi-port line card application is an inverse multiplexer (IMA). According to this demand of users, the newly launched SCT usually provides multi-port density in a single-chip package. Low-voltage power supply Traditional framers and LIU products require + 5V power supply. In order to ensure low power consumption, most newly launched products use a single 3.3V power supply to allow 5V input / output interfaces.
Overview Since the introduction of T carrier in the 1960s, T carrier and E carrier networks have gone through a long development path. Today, designers will see more and more functions integrated into T1 / E1 / J1 single-chip transceiver Device (SCT).
The introduction of a large number of functions is easy to confuse designers. This article introduces the important performance that needs to be paid attention to in the design. T1, E, and J carrier networks work at 1.544Mbps. T1 is the lowest rate of the North American Public Switched Telephone Network (PSTN) digital multiplex transmission T carrier layer. It was originally designed for the transmission of digital voice signals. T1 uses pulse code modulation and time division multiplexing technology to transmit 24 channel-level voice signals, which is called DS0. Each DS0 or time slot carries 64kbps of information.
E1 is a European digital transmission format, which can carry 32 channels of voice, and the multiplexed clock rate is 2.048Mbps.
Now, T1 and E1 not only transmit voice signals, but also transmit data or a combination of both. T1 and E1 transmission lines have been widely used in cellular base stations, business access routers and personal branch exchanges. Figure 1 shows a typical functional block diagram of T1 / E1 / J1 SCT. J1 is a T1 variant dedicated to Japan.
Figure 1. Typical functional block diagram of a single-chip T1 / E1 / J1 transceiver. The line interface unit and the line interface unit (LIU) of the framer SCT are the physical layer interfaces to the copper cable loop. The framer and the receiver received from the LIU Data synchronization, and format the LIU data for transmission. The advantage of some SCTs is that LIU can provide both short-range and long-range operations, enabling SCT to be used for the first layer of digital signal cross-connection (DSX-1) of CSU (channel service unit) / DSU (data service unit).
In the traditional T1 / E1 / J1 design, LIU and framer are independent ICs. With the development of ultra-large-scale integration technology, they can be integrated into a single-chip IC. One function that needs to be checked in SCT is: Whether the signal can be directly connected to the framer to allow modification of the data stream or insertion of code from an external signal source. Another benefit is the ability to use bidirectional code streams for monitoring purposes. Software programmable line termination Within a given T1 / E1 / J1 device's internal characteristics, software programmable copper cable loop termination is a very useful function, and ICs introduced by Dallas Semiconductor since the DS2155 SCT have this function. Engineers can design a complete T1 / E1 / J1 board, and can change the line terminal matching impedance required by the copper cable loop through software without adding any external components. At present, as T1 / E1 / J1 equipment is becoming more and more demanding on cost, this function has become a standard in design. The jitter attenuator T / E carrier loop will appear instantaneous out of synchronization. This phenomenon is often caused by jitter. Jitter is defined as the amplitude of the phase change when the reference clock frequency changes by more than 10 Hz.
To ensure the reliability of the system and the repeatability of the clock, it is best to choose an SCT that can provide jitter suppression in the transmit and receive channels. Some devices also provide two jitter suppression buffers, which are suitable for applications with large jitter, high reliability, or low response time. Advanced data link control Advanced data link control (HDLC) is the layer 2 processing type of the ISO 7-layer model. Physical layer link maintenance and quality monitoring are typical applications of HDLC controllers. In order to improve the system's adaptability, you can choose HDLC controller capable of allocating single or multiple DSO or FDL bits. The bit error rate test circuit (BERT) communication channel requires a diagnostic Tool to test the link quality. Most SCTs include sending and receiving BERTs. Pseudo-random data templates can be injected from the sending end to the copper cable loop. Then, the receiver BERT can Synchronized to the injected signal, the BERT can attenuate the signal or inject noise into the copper cable loop during operation, which helps to describe the performance of the SCT, copper cable loop and higher software layers. If the BERT detects an error state, further research or testing of the communication channel may be required. The protection switch considers that the T / E transmission line provides vital data. Many designs require a backup solution when the copper cable loop is unreliable or the line card terminates. The protection switch allows the standby SCT to switch to the line without losing the frame synchronization to replace the failed SCT. Many chips can provide this function without the need for external relays or switches. LIU with a high-impedance input for the receiver and a tri-state output for the transmitter is ideal for this type of application. Multi-port density Most T / E carrier line cards use multiple ports. One of the reasons is to meet the bandwidth of 1.544Mbps or 2.048Mbps. In this case, T1 and E1 are bound together or logically combined into a unit. For example, in multi-link frame relay; another multi-port line card application is an inverse multiplexer (IMA). According to this demand of users, the newly launched SCT usually provides multi-port density in a single-chip package. Low-voltage power supply Traditional framers and LIU products require + 5V power supply. In order to ensure low power consumption, most newly launched products use a single 3.3V power supply to allow 5V input / output interfaces.
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