短消息业务联网协议1.2版系统体系结构 - Translated by Marianne Wang
System Structure

SMG是具有短消息转发功能的短消息网关。全国可以有多个SMG网关，SMG网关之间通过互联网等方式实现网络互联。每一个SMG同时与多个SMSC以及多个SP连接。全网具有唯一有效的GNS，GNS负责全局路由表的维护与更新；为了确保路由表存储的安全性，网络中设置主备用GNS，两个GNS要保持一致性。每一个SMG都和GNS连接。SMG与SP、SMG与GNS以及SMG与SMG之间的通信协议为SGIP协议。SMG与SMSC之间的通信统一采用SMPP3.3协议。
SMG is a Short Message Gateway with the function of short message forwarding. There can be many SMGs in the nation, which are interconnected by means of Internet etc. Each SMG is connected with multiple SMSCs and multiple SPs at the same time. In the whole network there is only one valid GNS which is responsible for routing list maintenance and upgrading of the whole bureau. To ensure the safety of routing list storage, a principal standby GNS consistent with the first GNS shall be setup in the network. Each SMG is connected to GNS. The communication protocol between SMG and SP, between SMG and GNS as well between SMG and SMG is SGIP protocol, and SMPP3.3 protocol is the uniform communication protocol between SMG and SMSC.

和SMG平台之间相连的SMSC称作本地SMSC，和异地SMG平台相连的SMSC称作异地SMSC。
A SMSC connected to a SMG platform is called local SMSC; a SMSC connected to a foreign SMG platform is called foreign SMSC.

和SMG平台之间相连的SP称作本地SP，和异地SMG平台相连的SP称作异地SP。
A SP connected to a SMG platform is called local SP; a SP connected to a foreign SMG platform is called foreign SP.

从本地SMSC向本地SP以及从本地SP向本地SMSC发送的消息直接由SMG转发；从本地SMSC向异地SP以及从本地SP向异地SMSC发送的消息由本地SMG路由到异地SMG后，再由异地SMG转发。
Messages from a local SMSC to a local SP and from a local SP to a local SMSC are forwarded directly by SMG; messages from a local SMSC to a foreign SP and from a local SP to a foreign SMSC are forwarded by the foreign SMG after they are routed from the local SMG to the foreign SMG.

1 Messages from A Local SMSC to A Local SP
SMG从SMSC接收到短消息，直接发给SP。比如SMG receives a short message from SMSC and transmits it directly to SP. Following is an illustration:
SMSC1A—〉SMG1—〉SP1Y
SMSC1B—〉SMG1—〉SP1X

2 Messages from A Local SP to A Local SMSC
SMG从SP接收短消息，直接发给SMSC。比如SMG receives a short message from SP and transmits it directly to SMSC. Following is an illustration:
SP1X—〉SMG1—〉SMSC1A
SP1Y—〉SMG1—〉SMSC1B

3 Messages from A Local SMSC to A Foreign SP
SMG从本地SMSC接收短消息，再路由到异地SMG，由异地的SMG发送到目的SP，比如SMG receives a short message from the local SMSC, routes it to a foreign SMG, and the foreign SMG delivers the message to the destination SP. Following is an illustration:
SMSC1A—〉SMG1—〉SMG2—〉SP2Y
SMSC1B—〉SMG1—〉SMG3—〉SP3X

4 Messages from A Local SP to A Foreign SMSC
SMG从本地SP接收短消息，再路由到异地SMG，由异地的SMG发送到目的SMSC，比如 SMG receives a short message from the local SP, routes it to a foreign SMG, which delivers it to the destination SMSC. Following is an illustration:

SP1X—〉SMG1—〉SMG2—〉SMSC2A
SP1Y—〉SMG1—〉SMG3—〉SMSC3B

5 路由选择Route Selection
当消息在本地SMSC和异地SP，或者在本地SP和异地SMSC之间传输时，发送方必须要获取消息接收方的位置信息。这部分功能称为路由选择。
When a message is being transmitted between a local SMSC and a foreign SP, or between a local SP and a foreign SMSC, the sender must obtain the position information of the message receiver. This function is called Route Selection.

对于MO方向的命令(即命令接收方为SP)，其路由根据命令中的SP接入号码来选择。
For a MO-direction command (i.e. the command receiver is a SP), the route is selected according to the SP access number in the command.

对于MT方向的命令(即接收方为用户手机)，其路由根据命令中的付费号码和用户号码来综合判断。如果付费号码为空，或付费号码为SP接入号码，则根据用户号码来选择路由；否则根据付费号码所代表的手机号码来选择路由(这样做是考虑到了系统计费和用户鉴权的可行性，关于计费和用户鉴权的细节，请参见其它文档)。
For a MT-direction command (i.e. the receiver is a user’s handset), the route is determined comprehensively according to the payment number and user number in the command. If the payment number is null or is the SP access number, then the route will be selected according to the user number; otherwise the route is selected according to the handset number represented by the payment number (the reason for this is the consideration on the feasibility of system billing and user authentication. Please see other files for the particulars on billing and user authentication) .

由于SMG网关之间采用网状互联，网关之间不可能出现二次前转，因此接收前转消息的网关必须能判断前转的消息目的地址是否是本网关覆盖范围的用户，若不是，必须发送出错信息到前转网关。
Because of the reticular interconnections between SMGs, it is impossible that a secondary forwarding happens between gateways, therefore the gateway receiving the forwarded message must be able to determine whether the destination address of the forwarded message belongs to a user covered by the gateway, otherwise an error message must be delivered to the forwarding gateway.