Exhibit 12.1



REDBACK NETWORKS INC.

Computation of Ratio of Earnings to Fixed Charges



Pursuant to Item 503

Regulation S-K

(in thousands)



|                                                            |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|----------------------------------------------------------- |  | ----------------------- | -------- | - | ---- | - | -------- | ---- |  | - | -------- | - |  | ---- | ---------- | - |  | - | ---------- | -
|                                                            |  | Year ended December 31, |         
|                                                            |  | 2004                    |          |   | 2003 |   |          | 2002 |  |   | 2001     |   |  | 2000 |           
|Net loss                                                    |  | $                       | (552,999 | ) |      | $ | (118,849 | )    |  | $ | (186,924 | ) |  | $    | (4,117,974 | ) |  | $ | (1,007,545 | )
|Interest                                                    |  |                         | 55       |   |      |   | 17,653   |      |  |   | 19,713   |   |  |      | 27,091     |   |  |   | 19,955     |  
|Amortization of interest expense related to warrants issued |  |                         | 1,915    |   |      |   | 19       |      |  |   | 45       |   |  |      | 177        |   |  |   | 264        |  
|Amortization of deferred financing costs                    |  |                         |         |   |      |   | 1,604    |      |  |   | 2,003    |   |  |      | 1,782      |   |  |   | 1,299      |  
|Lease rental expense representative of interest (1)         |  |                         | 1,059    |   |      |   | 2,500    |      |  |   | 3,001    |   |  |      | 5,500      |   |  |   | 1,932      |  
|                                                            |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|Net loss before fixed charges                               |  |                         | (549,970 | ) |      |   | (97,073  | )    |  |   | (162,162 | ) |  |      | (4,083,424 | ) |  |   | (984,095   | )
|Less: fixed charges                                         |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|Interest                                                    |  |                         | (55      | ) |      |   | (17,653  | )    |  |   | (19,713  | ) |  |      | (27,091    | ) |  |   | (19,955    | )
|Amortization of interest expense related to warrants issued |  |                         | (1,915   | ) |      |   | (19      | )    |  |   | (45      | ) |  |      | (177       | ) |  |   | (264       | )
|Amortization of deferred financing costs                    |  |                         |         |   |      |   | (1,604   | )    |  |   | (2,003   | ) |  |      | (1,782     | ) |  |   | (1,299     | )
|Lease rental expense representative of interest (1)         |  |                         | (1,059   | ) |      |   | (2,500   | )    |  |   | (3,001   | ) |  |      | (5,500     | ) |  |   | (1,932     | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|Total fixed charges                                         |  |                         | (3,029   | ) |      |   | (21,776  | )    |  |   | (24,762  | ) |  |      | (34,550    | ) |  |   | (23,450    | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|Net loss                                                    |  | $                       | (552,999 | ) |      | $ | (118,849 | )    |  | $ | (186,924 | ) |  | $    | (4,117,974 | ) |  | $ | (1,007,545 | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |          |   |  |      |            |   |  |   |            |  
|Ratio of earnings to fixed charges                          |  |                         | N/A      |   |      |   | N/A      |      |  |   | N/A      |   |  |      | N/A        |   |  |   | N/A        |  
|Deficiency in earnings                                      |  | $                       | (552,999 | ) |      | $ | (118,849 | )    |  | $ | (186,924 | ) |  | $    | (4,117,974 | ) |  | $ | (1,007,545 | )

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|(1) |  | Calculated as one-third of rental expense, which is a reasonable approximation of the interest factor.
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