IP over SDH technology and IP overATM Comparison
A higher bandwidth requirements. Internet Service Provider (ISP) is actively exploring a variety of technologies to better connect its backbone router. Common method is to use asynchronous transfer mode (ATM) technology, using the 155M (STM-1) up to 622M (STM-4) high-speed link. Resulting in a lot of IPoverATM technologies, such as LANE, CIPOA, MPOA, etc..
However, due to the underlying carrier network connection based on fiber optic synchronous digital hierarchy (SDH) (North America for the Synchronous Optical Network SONET), which makes the ISP more likely to IPoverSDH technology to improve bandwidth efficiency, rather than the rule The IPoverATM technology. The two solutions in the industry caused a strong argument.
2SDH/SONET Overview SDH as the physical layer technology used to transmit and re-use, transfer rate up to 10Gbps, is the ITU (ITU) standard. The SONET is the American Standards Committee (ANSI) standard, but in the complex with two different mechanisms, while the other techniques are similar, so this paper to IPoverSDH example, the following brief SDH.
2.1SDH network elements SDH network elements are mainly synchronous optical line system, terminal multiplexer (TM), Add-Drop Multiplexer (ADM) and Synchronous Digital Cross Connect (DXC). TM mainly to slip into the STM signal multiplexing optical signals and complete the conversion and its inverse process, ADM has a flexible insertion and separation of the functions of the circuit, can be inserted and the separation of sources, such as ATM switches to the ring generated by the user payload in the SDH frame. DXC complete signal cross-connect. A typical application is in optical SDH loop on the application, double loop structure, automatic protection switching in order to achieve double-loop self-healing.
2.2SDH frame structure SDH transmission 8KSDH frames per second (STM-N), STM-N frame is based on STM-1 frame structure. Although the SDH frame structure to provide synchronization, but it does not force the user payload in SDH frames in a specific location, on the contrary, it allows the user payload frame floating in the use of overhead domain pointer that the beginning of the user payload. The user appears, SDH is the physical layer to provide medium-byte synchronization.
3ATM Overview ATM is a cell (CELL) as the basic unit of exchange and reuse of the connection-oriented transport mechanism, fixed-length 53-byte ATM cell to facilitate hardware-based exchange. ATM VCC or VPC connection to use, use of cell header VPI / VCI for each connection identity.
ATM is not only the data link layer, also has a complete network layer and transport layer of the various features, such as addressing, routing and flow control, ATM data stream to allow multiple users to share effective link bandwidth, but Each connection must be pre-set QoS. Voice, data, images and video streams and so can be used in ATM, but for different application streams require different ATM Adaptation Layer (AAL) to map the corresponding user data to the ATM cell.
ATM can run on different physical media, ATM layer cell and then produced by the complete physical layer to the physical media to send and receive the appropriate signal. SDH / SONET is the physical layer of ATM, SDH frame as the payload of 53 byte cell is not an integral multiple, ATM cell can directly and continuously sent to the SDH frame in the payload of. In acceptance, ATM cell header cell header error detection (HEC) field is used to describe the payload from the SDH to the ATM in the cell is correct.
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