Result: standard mapping
How many E1s are in an OC-1?
An OC-1 carries 21 E1s, per Telcordia GR-253.
21
E1s in an OC-1
Working
OC-1 (STS-1) → 21 × E1
- 21 × E1 in each OC-1 (STS-1) Telcordia GR-253Seven VT groups × three VT2 (E1).
- 21 E1s
Leftover capacity
8.832 Mbit/s of each OC-1 line rate (51.840 Mbit/s) sits outside 21 × 2.048 Mbit/s of E1 line rate (43.008 Mbit/s). That remainder is overhead, fixed stuff or justification. It is not another whole tributary.
By bit rate only
Dividing the line rates gives 25.31, which floors to 25 E1s by bit rate only. The standard mapping is 21. Use the mapping.