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  4. <html xmlns="http://www.w3.org/1999/xhtml"><head><title xmlns:rf="java:org.jboss.highlight.XhtmlRendererFactory">Chapter 4. Media Server Architecture</title><link rel="stylesheet" href="css/jbossorg.css" type="text/css"/><meta xmlns:rf="java:org.jboss.highlight.XhtmlRendererFactory" name="generator" content="DocBook XSL Stylesheets V1.74.0"/><link rel="home" href="index.html" title="Media Server User Guide"/><link rel="up" href="index.html" title="Media Server User Guide"/><link rel="prev" href="chapter-Installing_the_Media_Server.html" title="Chapter 3. Installing the Mobicents Media Server"/><link rel="next" href="ctms-Configuring_the_Media_Server.html" title="Chapter 5. Configuring the Mobicents Media Server"/></head><body><p id="title"><a href="http://www.jboss.org" class="site_href"><strong>JBoss.org</strong></a><a href="http://docs.jboss.org/" class="doc_href"><strong>Community Documentation</strong></a></p><ul class="docnav"><li class="previous"><a accesskey="p" href="chapter-Installing_the_Media_Server.html"><strong>Prev</strong></a></li><li class="next"><a accesskey="n" href="ctms-Configuring_the_Media_Server.html"><strong>Next</strong></a></li></ul><div class="chapter" lang="en-US"><div class="titlepage"><div><div><h2 class="title"><a id="ittms-Architecture_the_Media_Server"/>Chapter 4. Media Server Architecture</h2></div></div></div><div class="toc"><dl><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoints">4.1. Endpoints</a></span></dt><dd><dl><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_DS0">4.1.1. Digital Channel DSO</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_AAP">4.1.2. Announcement Access Point</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_CNF">4.1.3. Conference bridge</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_PR">4.1.4. Packet Relay</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_IVR">4.1.5. Interactive Voice Response</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_Soundcard">4.1.6. Soundcard</a></span></dt></dl></dd><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Endpoint_Local_Names">4.2. Endpoint local identifiers</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Calls_and_Connections">4.3. Calls and Connections</a></span></dt><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#ittms-Controller-Modules">4.4. Controller Modules</a></span></dt><dd><dl><dt><span class="section"><a href="ittms-Architecture_the_Media_Server.html#d0e1556">4.4.1. Media Gateway Control Protocol</a></span></dt></dl></dd></dl></div><p>
    5. 

  5.   A media gateway can be represented as a collection of endpoints. An endpoint 
    6. 

  6.   is a logical representation of a physical entity, such as an analog phone or 
    7. 

  7.   a channel in a trunk.
    8. 

  8.   </p><p>
    9. 

  9.   Endpoints are sources or sinks of data, and can be physical or virtual. 
    10. 

  10.   Physical endpoint creation requires hardware installation, while software is 
    11. 

  11.   sufficient for creating virtual endpoints.
    12. 

  12.   </p><p>
    13. 

  13.   An interface on a gateway that terminates at a trunk connected to a PTSN 
    14. 

  14.   switch would be an example of a physical endpoint. An audio source in an 
    15. 

  15.   audio content server would be an example of a virtual endpoint.
    16. 

  16.   </p><p>
    17. 

  17.   The Media Server assumes a connection model where the basic constructs are 
    18. 

  18.   endpoints and connections.
    19. 

  19.   </p><p>
    20. 

  20.   Connections are grouped in calls. One or more connections can belong to one 
    21. 

  21.   call. Connections and calls are set up at the initiation of one or several 
    22. 

  22.   Call Agents.
    23. 

  23.   </p><p>
    24. 

  24.   Controller Modules allow external interfaces to be implemented for the Media 
    25. 

  25.   Server. Each controller module implements an industry standard control 
    26. 

  26.   protocol, and uses a generic SPI to control processing components or 
    27. 

  27.   endpoints.
    28. 

  28.   </p><div class="figure"><a id="d0e1431"/><div class="figure-contents"><div class="mediaobject" align="center"><a id="ittms-mms-MMSArchictecture-dia-MMS"/><img src="images/mms-MMSArchictecture-dia-MMS2.jpg" align="middle" alt="Media Server Architecture"/></div></div><p class="title"><b>Figure 4.1. Media Server Architecture</b></p></div><br class="figure-break"/><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title"><a id="ittms-Endpoints"/>4.1. Endpoints</h2></div></div></div><p>
    29. 

  29. 	There are a number of basic endpoint types:
    30. 

  30. 	</p><div class="itemizedlist"><ul><li><p>Digital signal (DS0).</p></li><li><p>Announcement server access point.</p></li><li><p>Conference bridge access point.</p></li><li><p>Packet relay.</p></li><li><p>Interactive Voice Response.</p></li><li><p>Sound card.</p></li></ul></div><div xmlns:rf="java:org.jboss.highlight.XhtmlRendererFactory" class="note"><h2>Note</h2><p>
    31. 

  31.       This list is not final - other endpoint types may be defined in the 
    32. 

  32.       future, such as test endpoints which could be used to check network 
    33. 

  33.       quality, or frame-relay endpoints that could be used to manage audio 
    34. 

  34.       channels multiplexed over a frame-relay virtual circuit.
    35. 

  35.       </p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_DS0"/>4.1.1. Digital Channel DSO</h3></div></div></div><p>
    36. 

  36.       Digital channels provide an 8Khz*8bit service. Such channels are found in 
    37. 

  37.       the trunk and ISDN interfaces. They are typically part of digital 
    38. 

  38.       multiplexes, such as T1, E1, T3 or E3 interfaces. Media gateways that 
    39. 

  39.       support such channels are capable of translating the digital signals 
    40. 

  40.       received on the channel, which may be encoded according to A or mu-law, 
    41. 

  41.       using either the complete set of 8 bits or only 7 of these bits, into 
    42. 

  42.       audio packets. When the media gateway also supports a NAS service, the 
    43. 

  43.       gateway will be capable of receiving either audio-encoded data (modem 
    44. 

  44.       connection) or binary data (ISDN connection), and converting them into 
    45. 

  45.       data packets.
    46. 

  46.       </p><p>
    47. 

  47.       In some cases, like SS7 "F" links, or ISDN "D" channels, digital channels 
    48. 

  48.       are used to carry signalling. Media gateways that support these 
    49. 

  49.       signalling functions are able to send and receive the signalling packets 
    50. 

  50.       to and from a call agent, using the "back haul" procedures defined by the 
    51. 

  51.       SIGTRAN working group of the IETF.
    52. 

  52.       </p><p>
    53. 

  53.       Digital channels are sometimes used in conjunction with channel 
    54. 

  54.       associated signalling, such as "MF R2".
    55. 

  55.       </p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_AAP"/>4.1.2. Announcement Access Point</h3></div></div></div><p>
    56. 

  56.       An Announcement Server Endpoint provides access to an announcement 
    57. 

  57.       service. After a request from the call agent, the announcement server 
    58. 

  58.       will "play" a specified announcement. A given announcement endpoint is 
    59. 

  59.       not supposed to support more than one connection at a time. If several 
    60. 

  60.       connections were established to the same endpoint, then the same 
    61. 

  61.       announcements would be played simultaneously over all the connections.
    62. 

  62.       </p><p>
    63. 

  63.       Connections to an Announcement Server are typically one way, or "half 
    64. 

  64.       duplex" - the Announcement Server is not expected to listen the audio 
    65. 

  65.       signals from the connection.
    66. 

  66.       </p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_CNF"/>4.1.3. Conference bridge</h3></div></div></div><p>
    67. 

  67. 		A Conference Bridge Endpoint is used to provide access to a specific 
    68. 

  68. 		conference. The Media Server establishes several connections between the 
    69. 

  69. 		endpoint and the packet networks, or between the endpoint and other 
    70. 

  70. 		endpoints in the same server instance. The precise number of connections 
    71. 

  71. 		that an endpoint supports is a characteristic of the server's 
    72. 

  72. 		configuration, and may in fact vary according with the used hardware.
    73. 

  73. 		</p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_PR"/>4.1.4. Packet Relay</h3></div></div></div><p>
    74. 

  74. 	A Packet Relay Endpoint is a specific form of conference bridge, that 
    75. 

  75. 	typically only supports two connections. Packets relays can be found in 
    76. 

  76. 	firewalls between a protected and an open network, or in transcoding 
    77. 

  77. 	servers used to provide interoperation between incompatible gateways, 
    78. 

  78. 	such as gateways that do not support compatible compression algorithms, 
    79. 

  79. 	or gateways that operate over different transmission networks.
    80. 

  80. 	</p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_IVR"/>4.1.5. Interactive Voice Response</h3></div></div></div><p>
    81. 

  81.       An Interactive Voice Response (IVR) endpoint provides access to an IVR 
    82. 

  82.       service. Under requests from the call agent, the IVR server will "play" 
    83. 

  83.       announcements and tones, and will "listen" to responses from the user.
    84. 

  84.       </p><p>
    85. 

  85.       A given IVR endpoint is not supposed to support more than one connection 
    86. 

  86.       at a time. If several connections were established to the same endpoint, 
    87. 

  87.       then the same tones and announcements would be played simultaneously over 
    88. 

  88.       all the connections.
    89. 

  89.       </p></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="ittms-Endpoint_Soundcard"/>4.1.6. Soundcard</h3></div></div></div><p>
    90. 

  90. 	The sound card gives access to both the Analogue-to-Digital Converter 
    91. 

  91. 	(ADC) and the Digital-to-Analogue Converter (DAC). Data transmission over 
    92. 

  92. 	the Internet is done digitally. In order for voice to be transmitted it 
    93. 

  93. 	must be converted to digital using an ADC and be converted into analog 
    94. 

  94. 	again using a DAC so the voice it can be heard on the other end.
    95. 

  95. 	</p></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title"><a id="ittms-Endpoint_Local_Names"/>4.2. Endpoint local identifiers</h2></div></div></div><p>
    96. 

  96. 	The syntax of the local name depends on the type of endpoint being named. 
    97. 

  97. 	However, the local name for each of these types is naturally hierarchical, 
    98. 

  98. 	beginning with a term which identifies the physical gateway containing the 
    99. 

  99. 	given endpoint and ending in a term which specifies the individual endpoint 
    100. 

  100. 	concerned.
    101. 

  101. 	</p><p>
    102. 

  102. 	The following rules for construction and interpretation of the local 
    103. 

  103. 	identifier for these entity types MUST be supported:
    104. 

  104. 	</p><div class="itemizedlist"><ul><li><p>
    105. 

  105. 			The individual terms of the naming path MUST be separated by a single 
    106. 

  106. 			slash ("/", ASCII 2F hex).
    107. 

  107. 			</p></li><li><p>
    108. 

  108. 			The individual terms are character strings composed of letters, digits 
    109. 

  109. 			or other printable characters, with the exception of characters used as 
    110. 

  110. 			delimitors ("/", "@"), characters used for wildcarding ("*", "$") and 
    111. 

  111. 			white spaces.
    112. 

  112. 			</p></li><li><p>
    113. 

  113. 			Wild-carding is represented by square brakets and range using the 
    114. 

  114. 			following pattern: [a..b] where a and b are integer numbers.
    115. 

  115. 			</p></li><li><p>
    116. 

  116. 			In the ISUP protocol, trunks are grouped into trunk groups, identified 
    117. 

  117. 			by the SS7 point codes of the switches that the group connects. 
    118. 

  118. 			Circuits within a trunk group are identified by a circuit number (CIC 
    119. 

  119. 			in ISUP).
    120. 

  120. 			</p></li></ul></div></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title"><a id="ittms-Calls_and_Connections"/>4.3. Calls and Connections</h2></div></div></div><p>
    121. 

  121. 	Connections are created on the call agent for each endpoint that will be 
    122. 

  122. 	involved in the "call."  Connections may be either point to point or 
    123. 

  123. 	multipoint.
    124. 

  124. 	</p><p>
    125. 

  125. 	A point to point connection is an association between two endpoints with 
    126. 

  126. 	the purpose of transmitting data between those endpoints. Once this 
    127. 

  127. 	association is established for both endpoints, data transfer between these 
    128. 

  128. 	endpoints can take place.
    129. 

  129. 	</p><p>
    130. 

  130. 	A multipoint connection is established by connecting the endpoint to a 
    131. 

  131. 	multipoint session.
    132. 

  132. 	</p><p>
    133. 

  133. 	Connections can be established over several types of bearer networks:
    134. 

  134. 	</p><div class="itemizedlist"><ul><li><p>
    135. 

  135. 			Transmission of audio packets using RTP and UDP over a TCP/IP network.
    136. 

  136. 			</p></li><li><p>
    137. 

  137. 			Transmission of packets over an internal connection, such as the TDM 
    138. 

  138. 			backplane or the interconnection bus of a gateway. This is particularly 
    139. 

  139. 			used for "hairpin" connections - connections that terminate in a 
    140. 

  140. 			gateway but are immediately rerouted over the telephone network.
    141. 

  141. 			</p></li></ul></div><div class="example"><a id="d0e1540"/><p class="title"><b>Example 4.1. Connections Example</b></p><div class="example-contents"><p>
    142. 

  142. 		In the classic example of a connection between two "DS0" endpoints (EP1 
    143. 

  143. 		and EP2), the call agents controlling the end points will establish two 
    144. 

  144. 		connections (C1 and C2).
    145. 

  145. 		</p><p>
    146. 

  146. 		Each connection will be designated locally by a connection identifier, 
    147. 

  147. 		and will be characterized by connection attributes.
    148. 

  148. 		</p><p>
    149. 

  149. 		Once established, the connection parameters can be modified at any time 
    150. 

  150. 		by a "modify connection" command. The call agent may, for example, 
    151. 

  151. 		instruct the gateway to change the compression algorithm used on a 
    152. 

  152. 		connection, or to modify the IP address and UDP port to which data should 
    153. 

  153. 		be sent, if a connection is "redirected."
    154. 

  154. 		</p><p>
    155. 

  155. 		The call agent removes a connection by sending to the gateway a "delete 
    156. 

  156. 		connection" command. The gateway may also, under some circumstances, 
    157. 

  157. 		inform a gateway that a connection could not be sustained.
    158. 

  158. 		</p></div></div><br class="example-break"/></div><div class="section" lang="en-US"><div class="titlepage"><div><div><h2 class="title"><a id="ittms-Controller-Modules"/>4.4. Controller Modules</h2></div></div></div><p>
    159. 

  159. 	Controller Modules allow external interfaces to be implemented for the 
    160. 

  160. 	Media Server. Each controller module implements an industry standard 
    161. 

  161. 	control protocol, and uses a generic SPI to control processing components 
    162. 

  162. 	or endpoints. One such controller module is the Media Gateway Control 
    163. 

  163. 	Protocol.
    164. 

  164. 	</p><div class="section" lang="en-US"><div class="titlepage"><div><div><h3 class="title"><a id="d0e1556"/>4.4.1. Media Gateway Control Protocol</h3></div></div></div><p>
    165. 

  165. 		The Media Gateway Control Protocol (MGCP) is designed as an internal 
    166. 

  166. 		protocol within a distributed system that appears on the outside as a 
    167. 

  167. 		single VoIP gateway. The MGCP is composed of a Call Agent and a set of 
    168. 

  168. 		gateways, including at least one "media gateway" which performs the 
    169. 

  169. 		conversion of media signals between circuits and packets, and at least 
    170. 

  170. 		one "signalling gateway" when connected to an SS7 controlled network. The 
    171. 

  171. 		Call Agent can be distributed over several computer platforms.
    172. 

  172. 		</p><p>
    173. 

  173. 		MGCP is used for controlling telephony gateways from external call 
    174. 

  174. 		control elements called Media Gateway controllers or call agents. A 
    175. 

  175. 		telephony gateway is a network element that provides conversion betweekn 
    176. 

  176. 		the audio signals carried on telephone circuits and data packets carried 
    177. 

  177. 		over the Internet or over other packet networks.
    178. 

  178. 		</p><p>
    179. 

  179. 		MGCP assumes a call control architecture where the call control 
    180. 

  180. 		intelligence is outside the gateways and handled by external call control 
    181. 

  181. 		elements. The MGCP assumes that these call control elements, or Call 
    182. 

  182. 		Agents, will synchronize with each other to send coherent commands to the 
    183. 

  183. 		gateways under their control. MGCP is, in essence, a master/slave 
    184. 

  184. 		protocol, where the gateways are expected to execute the commands send by 
    185. 

  185. 		the Call Agents.
    186. 

  186. 		</p></div></div></div><ul class="docnav"><li class="previous"><a accesskey="p" href="chapter-Installing_the_Media_Server.html"><strong>Prev</strong>Chapter 3. Installing the Mobicents Media Server</a></li><li class="up"><a accesskey="u" href="#"><strong>Top of page</strong></a></li><li class="home"><a accesskey="h" href="index.html"><strong>Front page</strong></a></li><li class="next"><a accesskey="n" href="ctms-Configuring_the_Media_Server.html"><strong>Next</strong>Chapter 5. Configuring the Mobicents Media Server</a></li></ul></body></html>
    187.