def connectPeer(self, peer):
        """Establish a SIGMA connection to the given peer.

        @param peer: a Q2QAddress of a peer which has a file that I want

        @return: a Deferred which fires a SigmaProtocol.
        """
        return self.conns.connectCached(endpoint.Q2QEndpoint(self.svc,
                                                             self.addr,
                                                             peer,
                                                             PROTOCOL_NAME),
                                        self.clientFactory)
Establish a SIGMA connection to the given peer.

        @param peer: a Q2QAddress of a peer which has a file that I want

        @return: a Deferred which fires a SigmaProtocol.