1:1到底是属于专用保护还是共享保护

tthaonao

G.841(10/98)关于这个问题有两段论述，我给看糊涂了，谁给讲讲：

第一段话：（第3页）
dedicated protection: A protection architecture that provides capacity dedicated to the protection of traffic-carrying capacity (1 + 1). See Recommendation G.803.

第二段话：（第26页）
Linear VC trail protection is a dedicated protection mechanism that can be used on any physical structure (i.e. meshed, ring, or mixed). It may be applied in any path layer in a layered network.
It is an end-to-end protection mechanism, and switches on server failures and client level information, including path performance information. It need not be used on all VCs within a multiplex section.
Linear VC trail protection switching can operate in a unidirectional or bidirectional manner. Bidirectional protection switching has the ability to carry extra traffic on the protection path.

第一段话说只有1+1是专用保护，第二段第一句说线性VC通道保护是专用保护，最后一句又说保护通道可以传额外业务，应该就是说可以是1:1的了，谁给解释一下！

还有一个问题，我一直以为VC级的保护都是1＋1的，这里怎么好像说还可以是1:1的，以前看到说VC4/3的K3字节和VC12的K4字节可以用作APS保护，实际中有这样用的吗？