《SDH第01章.ppt

等级 速率（Mbit/s） STM-1 155.520 STM-2 622.080 STM-3 2 488.320 STM-4 9 953.280 表1-1 SDH标准速率 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 三、 SDH帧结构 SDH的帧结构必须适应同步数字复用、交叉连接和交换的功能，同时也希望支路信号在一帧中均匀分布、有规律，以便接入和取出。ITU-T最终采纳了一种以字节为单位的矩形块状（或称页状）帧结构，如图1-7所示。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 图1-7 SDH帧结构 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 对于STM-1而言，帧长度为270×9＝2430个字节，相当于19440bit，帧周期为125μs，由此可算出其比特速率为270×9×8／125×10-6=155.520Mbit／s。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 由图1-7可见，整个帧结构可分为三个主要区域。 1.段开销区域 2.净负荷区域 3.管理单元指针区域 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 四、 段开销字节 有两大类开销：段开销（SOH）和通道开销（POH） 。 SOH中包含定帧信息，用于维护与性能监视的信息以及其他操作功能。SOH可以进一步划分为再生段开销（RSOH，占第1至第3行）和复用段开销（MSOH，占第5至第9行）。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 1. STM-1段开销字节的安排和功能 （1） STM-1段开销字节的安排 各种不同SOH字节在STM-1帧内的安排分别如图1-8所示。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 图1-8 STM-1 SOH字节安排 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. （2） SOH字节的功能 ① 帧定位字节A1和A2 SOH中的A1和A2字节可用来识别帧的起始位置。A1A2 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 帧失步及帧丢失示意图 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. ② 再生段踪迹字节J0 该字节被用来重复地发送“段接入点标识符”，以便使段接收机能据此确认其是否与指定的发射机处于持续连接状态。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 A