[mgcp] Start to look into the MGCP messages and extract the CI

we will need the call identifier for the MDCX and DLCX message
for now we were just assuming it would increment, use som python
to extract the CI from a possible response, also switch back to
a blocking read to test the BSC nat.

openbsc/contrib/mgcp_server.py

@@ -25,15 +25,24 @@ def hexdump(src, length=8):
 
 server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
 server_socket.bind(("127.0.0.1", MGCP_CALLAGENT_PORT))
-server_socket.setblocking(0)
+server_socket.setblocking(1)
 
-
-def send_receive(packet):
+last_ci = 1
+def send_and_receive(packet):
+    global last_ci
     server_socket.sendto(packet, ("127.0.0.1", MGCP_GATEWAY_PORT))
     try:
         data, addr = server_socket.recvfrom(4096)
+
+        # attempt to store the CI of the response
+        list = data.split("\n")
+        for item in list:
+           if item.startswith("I: "):
+               last_ci = int(item[3:])
+
         print hexdump(data), addr
-    except socket.error:
+    except socket.error, e:
+        print e
         pass
 
 def generate_tid():
@@ -42,13 +51,10 @@ def generate_tid():
 
 
 
-i = 1
 while True:
-    send_receive(rsip_resp)
-    send_receive(audit_packet % generate_tid())
-    send_receive(crcx_packet % generate_tid() )
-    send_receive(mdcx_packet % (generate_tid(), i))
-    send_receive(dlcx_packet % (generate_tid(), i))
-    i = i + 1
+    send_and_receive(audit_packet % generate_tid())
+    send_and_receive(crcx_packet % generate_tid() )
+    send_and_receive(mdcx_packet % (generate_tid(), last_ci))
+    send_and_receive(dlcx_packet % (generate_tid(), last_ci))
 
     time.sleep(3)