What does the letter before the trip number denotes?

Ever wonder why there is a letter before every shipment ID/ trip ID in IDS?

That letter states which server the shipment was created on. Since we are a cloud based system, our clusters share shipments to handle load balance. So if one server is busy and another one is not, the less busy one will take over.

Possible server letters are:

E
D
U
T
P
S
R
D