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, |         
|                                                            |  | 2003                    |          |   | 2002 |   |          | 2001 |  |   | 2000       |   |  | 1999 |           
|Net loss                                                    |  | $                       | (118,849 | ) |      | $ | (186,924 | )    |  | $ | (4,117,974 | ) |  | $    | (1,007,545 | ) |  | $ | (7,919 | )
|Interest                                                    |  |                         | 17,653   |   |      |   | 19,713   |      |  |   | 27,091     |   |  |      | 19,955     |   |  |   | 319    |  
|Amortization of interest expense related to warrants issued |  |                         | 19       |   |      |   | 45       |      |  |   | 177        |   |  |      | 264        |   |  |   | 28     |  
|Amortization of deferred financing costs                    |  |                         | 1,604    |   |      |   | 2,003    |      |  |   | 1,782      |   |  |      | 1,299      |   |  |   |       |  
|Lease rental expense representative of interest (1)         |  |                         | 2,500    |   |      |   | 3,001    |      |  |   | 5,500      |   |  |      | 1,932      |   |  |   | 414    |  
|                                                            |  |                         |          |   |      |   |          |      |  |   |            |   |  |      |            |   |  |   |        |  
|Net loss before fixed charges                               |  |                         | (97,073  | ) |      |   | (162,162 | )    |  |   | (4,083,424 | ) |  |      | (984,095   | ) |  |   | (7,158 | )
|Less: fixed charges                                         |  |                         |          |   |      |   |          |      |  |   |            |   |  |      |            |   |  |   |        |  
|Interest                                                    |  |                         | (17,653  | ) |      |   | (19,713  | )    |  |   | (27,091    | ) |  |      | (19,955    | ) |  |   | (319   | )
|Amortization of interest expense related to warrants issued |  |                         | (19      | ) |      |   | (45      | )    |  |   | (177       | ) |  |      | (264       | ) |  |   | (28    | )
|Amortization of deferred financing costs                    |  |                         | (1,604   | ) |      |   | (2,003   | )    |  |   | (1,782     | ) |  |      | (1,299     | ) |  |   |       |  
|Lease rental expense representative of interest (1)         |  |                         | (2,500   | ) |      |   | (3,001   | )    |  |   | (5,500     | ) |  |      | (1,932     | ) |  |   | (414   | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |            |   |  |      |            |   |  |   |        |  
|Total fixed charges                                         |  |                         | (21,776  | ) |      |   | (24,762  | )    |  |   | (34,550    | ) |  |      | (23,450    | ) |  |   | (761   | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |            |   |  |      |            |   |  |   |        |  
|Net loss                                                    |  | $                       | (118,849 | ) |      | $ | (186,924 | )    |  | $ | (4,117,974 | ) |  | $    | (1,007,545 | ) |  | $ | (7,919 | )
|                                                            |  |                         |          |   |      |   |          |      |  |   |            |   |  |      |            |   |  |   |        |  
|Ratio of earnings to fixed charges                          |  |                         | N/A      |   |      |   | N/A      |      |  |   | N/A        |   |  |      | N/A        |   |  |   | N/A    |  
|Deficiency in earnings                                      |  | $                       | (118,849 | ) |      | $ | (186,924 | )    |  | $ | (4,117,974 | ) |  | $    | (1,007,545 | ) |  | $ | (7,919 | )



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