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                                                                   EXHIBIT 31.1

                                  CERTIFICATION

I, Stephen Goggiano, certify that:

1. I have reviewed this quarterly report on Form 10-Q of CoSine Communications,
   Inc.;

2. Based on my knowledge, this report does not contain any untrue statement of a
   material fact or omit to state a material fact necessary to make the
   statements made, in light of the circumstances under which such statements
   were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial
   information included in this report, fairly present in all material respects
   the financial condition, results of operations and cash flows of the
   registrant as of, and for, the periods presented in this report;

4. The registrant's other certifying officer and I are responsible for
   establishing and maintaining disclosure controls and procedures (as defined
   in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

      a)    designed such disclosure controls and procedures, or caused such
            disclosure controls and procedures to be designed under our
            supervision, to ensure that material information relating to the
            registrant, including its consolidated subsidiaries, is made known
            to us by others within those entities, particularly during the
            period in which this report is being prepared;

      b)    evaluated the effectiveness of the registrant's disclosure controls
            and procedures and presented in this report our conclusions about
            the effectiveness of the disclosure controls and procedures, as of
            the end of the period covered by this report based on such
            evaluation; and

      c)    disclosed in this report any change in the registrant's internal
            control over financial reporting that occurred during the
            registrant's most recent fiscal quarter (the registrant's fourth
            fiscal quarter in the case of an annual report) that has materially
            affected, or is reasonably likely to materially affect, the
            registrant's internal control over financial reporting; and

5.  The registrant's other certifying officer and I have disclosed, based on our
    most recent evaluation of internal control over financial reporting, to the
    registrant's auditors and the audit committee of the registrant's board of
    directors (or persons performing the equivalent function):

      a)    all significant deficiencies and material weaknesses in the design
            or operation of internal control over financial reporting which are
            reasonably likely to adversely affect the registrant's ability to
            record, process, summarize and report financial information; and

      b)    any fraud, whether or not material, that involves management or
            other employees who have a significant role in the registrant's
            internal control over financial reporting.

                                 /s/ Stephen Goggiano
                                 ------------------------------
                                 Stephen Goggiano
                                 Director, President and Chief Executive Officer
                                 May 13, 2004