Two-way time and frequency transfer in SONET

We have built a two-way time-transfer device which can use any currently unused byte in the SONET/SDH overhead to effect time transfer. The hardware should allow time transfer over short distances (km) with stabilities less than 10 ps for integration times greater than 1000 s. Accuracy at the same level in a dedicated fiber should also be possible. Time transfer though telecommunications network equipment has not yet been investigated.