Explanations on the interconnection between IP Routers and SDH devices in the IP transport network

China's IP routers have developed rapidly and their technology is also very mature. Many people may not understand the connection between IP Routers and SDH devices of the IP transport network, after reading this article, you must have gained a lot. I hope this article will teach you more things. In recent years, the broadband high-speed Internet, with the IP technology as the core and SDH or DWDM as the bearer, has developed rapidly. IP Over SDH is one of the common solutions to achieve IP Broadband transmission.

1 Overview of IP over SDH

The basic design concept of IP over SDH is IP/PPP/HDLC over SDH. The SDH transmission network is used as the physical bearer of the IP service, and IP packets are encapsulated through the Point-to-Point Protocol (PPP, then use the advanced Data Link Control HDLC) to define the frame, and then map it to the virtual kubernetes SDH container VC), and finally add the corresponding SDH overhead to form the SDH-N frame, go to the SDH physical transport layer for transfer.

2. Question proposal

In the IP over SDH mode, the combination of IP and SDH is implemented through Point-to-Point Protocol (PPP) in the IP router. Specifically, IP packets are directly mapped to SDH frames, after the IP packet is processed, the STM-N standard transmission module is formed and enters the SDH device. For SDH devices, you only need to transmit the signals sent from the IP router transparently. In this way, there should be no problem in connecting SDH devices to the IP router.

The SDH devices of multiple manufacturers are used in the SDH Transmission Network. During the process of IP over SDH implementation, we find that SDH devices of some manufacturers are interconnected smoothly with IP routers without special settings; some manufacturers need to reset or adjust the SDH device parameters before they can connect to the IP router. In the IP address transmission network, what should I pay attention to when connecting SDH devices with IP Routers?

3. Signal labels in SDH frame structure

ITU-T-related recommendations define a C2 byte in SDH's high-order channel overhead to indicate the signal type for virtual container VC-3/VC-4/VC-4-XC loading. According to ITU-T recommendations, C2 bytes of 8 bits of different encoding correspond to different signal types, such as TUG structure, PDH34M or 45 M, PDH140M, ATM, MANDQDB) and FDDI. Initially, the ITU-T did not define the IP signal label. With the development of IP address, the ITU-T makes additional provisions on C2 bytes, defining PPP/HDLC Protocol) The signal label byte C2 is "11001111 ".

4 SDH devices adapt to C2 bytes in several ways

SDH devices of different manufacturers adopt different methods to adapt the signal label of the business to C2 bytes. The analysis shows that the following three methods are generally used.

4.1 Adaptive Mode

In this way, the SDH device automatically adapts to the C2 bytes of the service. The C2 bytes of the high-order channel in the SDH device STM-1 frame structure are automatically adapted to the signal label that carries the business. For example, in the structure of the signal label C2 = "00000010" TUG) that carries the business, the C2 bytes of the high-order channel in the SDH device are automatically adapted to C2 = "00000010 ". Similarly, if the signal label C2 = "11001111" PPP protocol that carries the business), the C2 bytes of the high-order channel in the SDH device are automatically adapted to C2 = "11001111 ". In the adaptive mode, IP over SDH is implemented. SDH devices can interconnect SDH devices with IP routers without any special settings. Most SDH manufacturers use this method.

4.2 manual adaptation

In this way, the SDH device cannot automatically adapt to the C2 bytes of the Service carried by the device. Manual configuration is required. Take IP over SDH as an example. Generally, the default value of C2 byte in SDH device is "00000010". According to the ITU-T suggestion, for IP service, C2 = "11001111 ". In this way, to interconnect SDH devices with IP Routers, the C2 bytes of SDH devices must be configured through SDH network management or SDH local operation terminal, from the default "00000010" to the "11001111" identifier that can adapt to the bearer IP address, otherwise the SDH system will generate a high-order channel signal label mismatch HP-SLM) alarm, affects the interconnection between SDH devices and IP routers.

4.3 cannot be adaptive, and manual adaptation to C2 bytes is also limited

As mentioned above, In the ITU-T's initial recommendations for SDH signal label C2 bytes, there is no defined virtual container VC) loaded IPPPP protocol) C2 encoding. Therefore, in the current transmission network, SDH devices that use manual adaptation can configure C2 bytes through SDH network management or SDH local maintenance terminal, only the following manual adaptation options are provided, but C2 = "11001111" PPP protocol is not available, because the SDH device and IP router cannot be connected smoothly. In this case, you can only change the configurations on the IP router, change C2 = "11001111" of the ITU-T suggested expression PPP or PPP/HDLC protocol to the default C2 = "00000010" TUG structure of the SDH device) to interconnect the SDH device with the IP router. However, this is only an alternative because SDH actually carries an IP address, while C2 indicates that SDH carries a TUG structure signal, in this case, the meaning indicated by the signal label C2 is obviously not vacuum. Pay special attention to this point when using the meter for testing or SDH overhead analysis.