correct me if I am wrong but after expiry of T200 the only thing that happens is sending again the message (for example ASS CMD on SDCCH). The channel is released with the error indication after N200+1 repetitions.
So yes the chance for SD blocking is higher if you increase the T200, because you keep the channel busy (for total of (N200+1)xT200…and there is no MS to respond.
Here is the Siemens opinion:
To achieve an optimum
radio interface performance (from the subscribers point of view), the
timer values for T200 should be set in such a way that
– a Um layer 2 frame retransmission should take place at the earliest
after a time period the MS needs for the transmission of an
acknowledgement of a received layer 2 frame
– a Um layer 2 frame retransmission should take place as early as
possible when the aforementioned time period has passed and no
acknowledgement was received from the MS
– unnecessary retransmissions are avoided.
so they recommend 145ms T200, and default is 220ms (N200 is 23 for SD)