The signaling system 7 (SS7)is a signaling system for the public switched telephone network (PSTN). SS7 network transports call setup, teardown messages, database queries, trunk status, instructions for remote phone switches and so on, in fact it acts as a glue for the circuit switched network. Telecommunication deregulation, liberalization of economies and convergence of telephone, IP and wireless networks has broken the trust enjoyed so long by PSTN as being considered a closed community network. The convergence results in increasing number of interfaces between SS7 and other networks, and each brings with it many vulnerabilities. This paper first analyzes existing security threats due to virtually non-existent authentication and integrity check process and then presents a MTPSec solution at the MTP3 layer in the SS7protocol stack which provides security services through cryptographic operations. It can be implemented at each signaling point (SP) throughout the network to provide link-by-link security or at least at the SPs residing at the interface between two networks or trust sets.