EXHIBIT A AGREEMENT OF JOINT FILING Pursuant to Rule 13d-1(k)(1), we, the undersigned, hereby agree that the attached Schedule 13D is filed on behalf of each of us. Dated: November 21, 2001 VANTAGEPOINT VENTURE PARTNERS III(Q), L.P.

                                    EXHIBIT A

                            AGREEMENT OF JOINT FILING

      Pursuant to Rule 13d-1(k)(1), we, the undersigned, hereby agree that the
attached Schedule 13D is filed on behalf of each of us.

Dated: November 21, 2001


                               VANTAGEPOINT VENTURE PARTNERS III(Q), L.P.

                               By: VantagePoint Venture Associates III, L.L.C.
                               its general partner
                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT VENTURE PARTNERS III, L.P.

                               By: VantagePoint Venture Associates III, L.L.C.
                               its general partner
                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT COMMUNICATION PARTNERS, L.P.

                               By: VantagePoint Communication Associates, L.L.C.
                               its general partner
                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT VENTURE PARTNERS 1996, L.P.

                               By: VantagePoint Associates, L.L.C.
                               its general partner
                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT VENTURE ASSOCIATES III, L.L.C.

                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT COMMUNICATIONS ASSOCIATES, L.L.C.

                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               VANTAGEPOINT ASSOCIATES III, L.L.C.

                               By: /s/ Xxxxx X. Xxxxxx
                                   ---------------------------------------------
                               Name: Xxxxx X. Xxxxxx,
                               Managing Member


                               /s/ Xxxxx X. Xxxxxx
                               -------------------------------------------------
                               Xxxxx X. Xxxxxx


                               /s/ Xxxx X. Xxxxxxx
                               -------------------------------------------------
                               Xxxx X. Xxxxxxx


                               /s/ Xxxxxxx X. Xxxxxxxx
                               -------------------------------------------------
                               Xxxxxxx X. Xxxxxxxx