在IOS接口规范（A.S0014-B_v1.0）上要求SSD更新必须在业务信道上进行。
3.3.3 SSD Update Request 描述如下：This DTAP message is sent from the MSC to the BS and is used to initiate the Shared Secret Data update procedure at the MS. This message is used to perform the SSD Update on a voice/traffic channel. The Authentication Challenge Parameter (RANDSSD) information element of this message is used to generate the new SSD at the MS.
3.3.4 SSD Update Response 描述如下：This DTAP message is used to complete the SSD Update procedure and is sent in response to the Base Station Challenge Response message. This message is sent from the BS to the MSC. This message is used to perform the SSD Update on a voice/traffic channel.
在空中接口规范（C.S0005-C_v1.0)上说SSD更新可以在业务信道上也可以在信令信道上进行。
2.3.12.1.5 Updating the Shared Secret Data (SSD) 描述如下： The base station sends an SSD Update Message on either the f-csch or the f-dsch. The RANDSSD field of the SSD Update Message contains the same value used for the HLR/AC computation of SSD.