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, |        
|                                                            |  | 2005                    |         |   | 2004 |   |          | 2003 |  |   | 2002     |   |  | 2001 |         
|Net loss                                                    |  | $                       | (21,976 | ) |      | $ | (552,999 | )    |  | $ | (118,849 | ) |  | $    | (186,924 | ) |  | $ | (4,117,974 | )
|Interest                                                    |  |                         | 6       |   |      |   | 55       |      |  |   | 17,653   |   |  |      | 19,713   |   |  |   | 27,091     |  
|Amortization of interest expense related to warrants issued |  |                         | 1,596   |   |      |   | 1,915    |      |  |   | 19       |   |  |      | 45       |   |  |   | 177        |  
|Amortization of deferred financing costs                    |  |                         |        |   |      |   |         |      |  |   | 1,604    |   |  |      | 2,003    |   |  |   | 1,782      |  
|Lease rental expense representative of interest (1)         |  |                         | 938     |   |      |   | 1,059    |      |  |   | 2,500    |   |  |      | 3,001    |   |  |   | 5,500      |  
|                                                            |  |                         |         |   |      |   |          |      |  |   |          |   |  |      |          |   |  |   |            |  
|Net loss before fixed charges                               |  |                         | (19,436 | ) |      |   | (549,970 | )    |  |   | (97,073  | ) |  |      | (162,162 | ) |  |   | (4,083,424 | )
|Less: fixed charges                                         |  |                         |         |   |      |   |          |      |  |   |          |   |  |      |          |   |  |   |            |  
|Interest                                                    |  |                         | (6      | ) |      |   | (55      | )    |  |   | (17,653  | ) |  |      | (19,713  | ) |  |   | (27,091    | )
|Amortization of interest expense related to warrants issued |  |                         | (1,596  | ) |      |   | (1,915   | )    |  |   | (19      | ) |  |      | (45      | ) |  |   | (177       | )
|Amortization of deferred financing costs                    |  |                         |        |   |      |   |         |      |  |   | (1,604   | ) |  |      | (2,003   | ) |  |   | (1,782     | )
|Lease rental expense representative of interest (1)         |  |                         | (938    | ) |      |   | (1,059   | )    |  |   | (2,500   | ) |  |      | (3,001   | ) |  |   | (5,500     | )
|                                                            |  |                         |         |   |      |   |          |      |  |   |          |   |  |      |          |   |  |   |            |  
|Total fixed charges                                         |  |                         | (2,540  | ) |      |   | (3,029   | )    |  |   | (21,776  | ) |  |      | (24,762  | ) |  |   | (34,550    | )
|                                                            |  |                         |         |   |      |   |          |      |  |   |          |   |  |      |          |   |  |   |            |  
|Net loss                                                    |  | $                       | (21,976 | ) |      | $ | (552,999 | )    |  | $ | (118,849 | ) |  | $    | (186,924 | ) |  | $ | (4,117,974 | )
|                                                            |  |                         |         |   |      |   |          |      |  |   |          |   |  |      |          |   |  |   |            |  
|Ratio of earnings to fixed charges                          |  |                         | N/A     |   |      |   | N/A      |      |  |   | N/A      |   |  |      | N/A      |   |  |   | N/A        |  
|Deficiency in earnings                                      |  | $                       | (21,976 | ) |      | $ | (552,999 | )    |  | $ | (118,849 | ) |  | $    | (186,924 | ) |  | $ | (4,117,974 | )



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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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