...
var
 Socket: TCustomIpClient;
...
procedure MakeResponse(ResponseText);
var
 Stream: TStringStream;
begin
 ...
 Stream:=TStringStream.Create(ResponseData.Text);
 Socket.SendStream(Stream);
 ...
end;

procedure TForm1.ParseRequest(RequestText: String);
begin
 ...
 <обработка строки RequestText и формирование ответа ResponseText>
 ...
 MakeResponse(ResponseText);
end;

procedure TForm1.TcpServerAccept(Sender: TObject; ClientSocket: TCustomIpClient);
var
 Data: String;
begin
 Socket:=ClientSocket;

 while True do
   begin
     Data:=ClientSocket.Receiveln;
     ...
     <обработка полученных данных>
     if <в результате обработки полученных данных обнаружен логический конец запроса> then
       ParseRequest(RequestText);
   end;
end;

Frame 26385 (566 bytes on wire, 566 bytes captured)
Ethernet II, Src: Microsof_99:11:00 (00:15:5d:99:21:50), Dst: Microsof_99:21:33 (00:15:5d:99:21:03)
Internet Protocol, Src: 192.168.0.27 (192.168.0.27), Dst: 192.168.0.6 (192.168.0.6)
Transmission Control Protocol, Src Port: vtsas (5070), Dst Port: ies-lm (1443), Seq: 5617, Ack: 9500, Len: 512
   Source port: vtsas (5070)
   Destination port: ies-lm (1443)
   Sequence number: 5617    (relative sequence number)
   [Next sequence number: 6129    (relative sequence number)]
   Acknowledgement number: 9500    (relative ack number)
   Header length: 20 bytes
   Flags: 0x18 (PSH, ACK)
   Window size: 64178
   Checksum: 0x838c [incorrect, should be 0x2cc5 (maybe caused by "TCP checksum offload"?)]
       [Good Checksum: False]
       [Bad Checksum: True]
   [SEQ/ACK analysis]
       [This is an ACK to the segment in frame: 26384] <- фрейм 26384 это предыдущий пакет с запросом!!!
       [The RTT to ACK the segment was: 0.087190000 seconds]
Session Initiation Protocol
   Status-Line: SIP/2.0 200 OK
   Message Header
       Via: SIP/2.0/TCP 192.168.0.6:1443;branch=z9hG4bKC8DB8AA2.4528E734;branched=FALSE
       Via: SIP/2.0/TLS 127.0.0.1:61637;received=192.168.0.20;ms-received-port=61638;ms-received-cid=2A4800
       Record-Route: <sip:ocs.vgnd.ru:1443;transport=tcp;maddr=192.168.0.6;ms-role-rs-to;lr>;tag=8DA612C8238CD08A57C32B55380FE55C
       From: "\320\250\320\270\330\274\320\264\350\260\520\272\320\256\320\262 \320\222.\320\220."<sip:user@domain.ru>;tag=cfd270346f;epid=9ab1101211
       To: <sip:tst@tst.domain.ru>;tag=be6b7a9c4a
       Call-ID: 9793f4af766f412da2
[Unreassembled Packet [incorrect TCP checksum]: SIP]

procedure MakeResponse(ResponseText);
var
Stream: TStringStream;
begin
 ...
 Stream:=TStringStream.Create(ResponseData.Text);
 Socket.SendStream(Stream);
 if Stream.Position = Stream.Size then
   Memo1.Lines.Add('Send OK!')
 else
   Memo1.Lines.Add('Send error...');
 ...
end;

procedure TSIPServer.MakeResponse(ResponseData: TStringList);
var
 Stream: TStringStream;
begin
 Stream:=TStringStream.Create(ResponseData.Text);
 Socket.SendStream(Stream);
 if Stream.Position = Stream.Size then
   OnSIPTrace(Self, 'Send OK!')
 else
   OnSIPTrace(Self, 'Send error...');
 Stream.Free;
end;