[asterisk-dev] How is an SLS assigned?

[tian]

Dear all,

I am learning SS7 standards recently. I got confused with the Signaling Link 
Selection (SLS) field in MSU's. I know an SLS is used for traffic 
distribution among signaling links, but how does an SSP assign SLS's to its 
outgoing messages?

Is an SLS of only local significance or is it necessary for two adjacent 
signaling points to used the same SLS value for messages exchanged on the 
same signaling link (If this is the case, how do they negotiate the SLS 
value to be used)?

Hope you guys will kindly give me some hints or refer me to some materials 
that clarify my question, thank you very much and I do appreciate your help!

Tian