1. ITU Recommendation G.708. Network Node Interface for the Synchronous Digital Hierarchy. 1993.
2. ITU Recommendation G.709. Synchronous Multiplexing Structure. 1993.
3. ITU Recommendation G.707. Synchronous Digital Hierarchy Bit Rates. 1993.
4. Synchronous digital hierarchy optical metropolitan network ring traffic analysis;Owen;European Transactions on Telecommunications,1993
5. Bellcore Special Report SR-NWT-002514. Digital Cross-Connect Systems in Transport Network Survivability, Issue 1, January 1993.