Result: standard mapping
How many E1s are in an OC-12?
An OC-12 carries 252 E1s, per Telcordia GR-253.
252
E1s in an OC-12
Working
OC-12 → 12 × OC-1 (STS-1) → 21 × E1
- 12 × OC-1 (STS-1) in each OC-12 Telcordia GR-25312 × OC-1 (STS-1). Channelized OC-12 is 12 STS-1s.
- 21 × E1 in each OC-1 (STS-1) Telcordia GR-253Seven VT groups × three VT2 (E1).
- 12 OC-1s
- 12 × 21 = 252 E1s
Leftover capacity
105.984 Mbit/s of each OC-12 line rate (622.080 Mbit/s) sits outside 252 × 2.048 Mbit/s of E1 line rate (516.096 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 303.75, which floors to 303 E1s by bit rate only. The standard mapping is 252. Use the mapping.