Synchronous digital hierarchy
- SONET in US, SDH in Europe
- requires central strict time sync
- synchronize ≡ same frequency + delay is known = precise time is known
- syntonize ≡ same frequency only, no phase info
- PDH data can be encapsulated into SDH
- no bit stuffing → data can be arbitrary unpacked
- standardised
- no upper bound for speed increase
- TDM
- 2 directions in ring: primary and backup
- backup is used only after primary fails
- 50ms failover (L1 OSI)
level | Speed |
---|---|
STM-1 | 155520 |
STM-2 | 622080 |
STM-3 | 2488320 |
STM-4 | 9953280 |