} else if (request.getMethod().equals(Request.ACK)){
                st = requestEvent.getServerTransaction();
                String input = ((CallIdHeader) request.getHeader(CallIdHeader.NAME)).getCallId() + ((CSeqHeader) request.getHeader(CSeqHeader.NAME)).getSeqNumber();
                String branch = generateBranch(input);
                ClientTransaction ct = clientTransactionHashMap.get(branch);
                    Dialog dialog = ct.getDialog();
                    Dialog stdialog = st.getDialog();
                    if(stdialog != null){
                        Long cseq = stdialog.getRemoteSeqNumber();
                        Request ackRequest = dialog.createAck(cseq);
                        ViaHeader newViaHeader = headerFactory.createViaHeader(proxyIp, proxyPort, "UDP", branch);
                        ackRequest.addHeader(newViaHeader);
                        MaxForwardsHeader maxForwardsHeader = (MaxForwardsHeader) request.getHeader(MaxForwardsHeader.NAME);
                        if(maxForwardsHeader == null){
                            maxForwardsHeader = headerFactory.createMaxForwardsHeader(69);
                        } else {
                            maxForwardsHeader.decrementMaxForwards();
                        }
                        ackRequest.setHeader(maxForwardsHeader);
                        List<String> userAgent = Arrays.asList("SIP Proxy", "Version:0.0", "Author:Jan Trencansky");
                        UserAgentHeader newUserAgentHeader = headerFactory.createUserAgentHeader(userAgent);
                        ackRequest.removeHeader(UserAgentHeader.NAME);
                        ackRequest.addHeader(newUserAgentHeader);
                        dialog.sendAck(ackRequest);
                        Controller.messages.add(new SipMessage(ackRequest));
                    }
            }