SUA : Query

Hello,

I have a query,

(a) Which layers of an SS7 incoming message (Say a MAP/ CAP Message)
does a Signaling Gateway open as a part of the decision making process
for determining its routing towards the IP world connected over SUA?

(b) Does it restrict itself only upto the SCCP layer or does it open
TCAP/MAP/CAP also ? It appears that the CISCO product - ITP does open
the upper layers {typically in the case where IP SCPs are in a Cluster
and the first message is routed to any of the eligible SCPs while
subsequent messages for the same call context are to be routed
(naturally) to the same SCP node as the first message} ? Is this
behavior only CISCO specific or is it mandated by the IETF ?

If  it does not open any layer above the SCCP layer, what is the
mechanism by which a general (non CISCO) Signaling Gateway achieves
the same routing methodology as described in para 'b' above ?

Thanks in anticipation for your response !
Ashima