The transfer protocol framework supports the formal specification and
verification of data transfer protocols. It consists of generic specif
ication modules and theorems. Compositions of specification module ins
tances result in well-structured specifications which describe a proto
col, the medium used, and the service provided by means of TLA formula
s. The protocol verification is based on the proof of the logical impl
ication between protocol and service specification. Due to the modular
structuring of the specifications, this proof can be decomposed into
a set of subimplications which correspond directly to theorems of the
framework. Therefore, the development of formal specifications as well
as the protocol verification can be reduced to the instantiation and
arrangement of framework elements. The flexibility of the framework op
ens its application for a broad spectrum of data transfer protocols. W
e outline the principles of the framework and concentrate on its appli
cation to the high-speed transfer protocol XTP. Because of the framewo
rk support, the formal modeling and analysis of this modem and functio
n-rich protocol was manageable and identifies deficiencies of the curr
ent protocol definition clearly.