Grouping protocol in soft exchange
Softswitch is the core of the next generation network (NGN), is the coordination center of the circuit switched network and the IP network. It implements the business layer between different networks by controlling the media gateway. In the communication system, control is implemented by negotiation, so there must be a corresponding protocol. In the NGN architecture, soft exchange is the control center, which supports H. 248 / Megaco, SIP, MGCP, H.323 and other multi-scale protocols. 1 mgcp protocol 1.1 MGCP basic concept MGCP protocol and H. 223 and SIPs, H.323 and SIP propose two sets of IP phone architectures, both of which are completely independent, and cannot be compatible with each other. The MGCP does not involve the architecture of the IP phone, which only involves the problem of gateway decomposition, but it can be used not only for H. 323 IP telephony systems can also be used in the SIP IP telephone system. The gateway can break down into the media gateway (MG) and the Media Gateway Controller (MGC), MG to implement cross-network media services under the control of MGC (or softswitch). It is very simple to look at logically, and the gateway consists of MG and MGC. It is not so simple from physical viewing. So far, the decomposition of the gateway has not been determined, and can be decomposed according to different needs. The MGCP protocol is the media gateway control protocol established by the Internet Engineering Task Group (IETF) in 1999, and the Connection model defined by the MGCP protocol includes two main concepts of endpoints (Connection). The endpoint is a data source or data, which can be a physical endpoint or a virtual endpoint. The endpoint type includes digital channels, analog lines, recording server access points, and interactive voice response access points. The endpoint identifies consists of two parts of the gateway domain name and gateway in the gateway. The connection can be a point-to-point connection or a multi-point connection. Point-to-point connection is an association between two endpoints that transfers data, which can start transmitting data after both endpoints are established. Multi-point connection is the link between multiple endpoints. The connection can be built on different types of bearer networks. The call agent may request an endpoint to issue a notification to it when some events (such as picking, hang up, tilt or dialing) can also request some signals (such as dial tone, ring tones, busy tone, etc.) Add it to the endpoint. Events and signal combination are packaged, each package supports a particular endpoint. Each event (including signal) can be represented by "Package / Event Name", each type of endpoint has a specific package, each package contains regular events and signals, with digital alphanumeric serial names. 1.2 Protocol Structure and Command MGCP uses a text protocol, the protocol message is divided into commands and responses, each command requires the recipient return response and uses three handshake methods to confirm. Command messages consist of command lines and several parameters, responding messages with 3 digits of response code. MGCP describes the connection parameters to the gateway using the Media Description Protocol (SDP). In order to reduce signaling transmission delays, the MGCP is transmitted using the User Dataset Protocol (UDP).
The protocol command includes: (L) endpointconfiguration, from the call agent to the gateway; (2) Notification Request command (NotificationRequest), from the call agent to the gateway; (3) Notify command (Notify), from the gateway to the call agent ; (4) Creating a CreateConnection, from the call agent to the gateway, call agent uses this command to associate a terminal with the specified IP address and UDP port, and also send a creative connection command to the remote endpoint, establish two endpoints Connection; (5) Modify the connection command, from the call agent to the gateway, modify the parameters of the previously established connection; (6) Delete the connection command (deleteConnection), from the call agent to the gateway (you can also customize from gateway to call agents) ), Delete previously established connections; (7) AuditEndPoint, from the call agent to the gateway; (8) AuditConnection, from the call agent to the gateway; (9) Restart in the command (RestartInProgress ), From the gateway to the call agent. 2 H.248 protocol 2.1 definition H. The 248 protocol is the media gateway control protocol proposed by ITU-T 16 Working Group 2000, which is improved on the early MGCP protocol. The H.248 / MeGaco protocol is used to connect the gateway control protocol of MGC and MG, which is applied to media gateways and soft exchanges and soft exchange and H. The 248 / MeGaco terminal is an important protocol that is supported by soft exchange. The Connection model defined by the H.248 protocol includes two main concepts of terminal (Termination) and context. The terminal is a logic entity in the MG, can transmit and receive one or more media, at any time, one terminal belongs and can only belong to one context, which can represent the slot, analog line, and the RTP (Real Time Protocol) stream. The terminal type mainly has a semi-permanent terminal (TDM channel or simulation line, etc.) and a temporary terminal (e.g., an RTP stream for carrying speech, data, and video signals or various mixed signals). With attributes, events, signals, statistical representation terminal features, in order to solve the problem of blocking terminal diversity, the package (Package) concept is introduced to the protocol, and various characteristic parameters of the terminal are combined. A context is a connection between some terminals, which describes the topology relationship between the terminals and the parameters of the media mixing / exchange. Lucent's first proposes the Context concept in the MGCP protocol, so that the protocol has better flexibility and scalability, the H.248 / MeGaco protocol extends this concept, it can be created with the add command, with the subtract or move command delete. 2.2 Main Features The H.248 protocol is the protocol of MGC control MG, also known as Megaco. The CNNText concept is introduced in H.248, increasing a number of Package definitions, thereby greatly promoting MGCP. It can be said that H.248 recommends that MGCP has been replaced, which is a protocol standard between MGC and MG. Decomposing the gateway into MG and MGC is the need to develop large telecommunication level IP telephone gateways. The function of MGC is: (L) H.225 Ras message with the gatekeeper; (2) Handling NO. 7 signaling (optional); (3) Processing H. 323 Signaling (optional).
The function of the MG is: (1) IP network endpoint interface; (2) circuit switched network endpoint interface; (3) processing H. 323 Signaling (in a certain type of decomposition); (4) Processes circuit exchange signaling with the RAS (Registenance Admission Status) (in a certain type of decomposition); (5) Handling the media stream. 2.3 Protocol Messages and Command Messages are the information unit sent by the protocol, and a message contains a message header and version number, the message header contains the sender's ID. Transactions in the message have nothing to do with each other and can be handled independently. The encoding format of the protocol message is the text format and binary format. MGC must support these two formats, MG can support any of these formats. When the MG initiates a call, the MGC creates a new context and use the add command to add the two terminals of the R7RP stream and analog line to the context. After the MG ends the call, the MGC uses the Subtract command to remove the terminal from the context, Release the resource. Use the modify command to modify the properties and signal parameters of the terminal. H.248 also defines: (l) Move command, move a terminal from one context to another; (2) AUDITVALUE command, return the current state of the terminal characteristics; (3) Auditcapabilities command, return to terminal characteristics (4) notify command, allows MG to notify the MGC; (5) serviceChange command, allowing MG to notify MGC one or more terminals will be detached or joined to the business, or for MG registration to MGC representability, and MGC's hang and MGC's master, and preparation notifications, etc. H. 248 and MGCP have a lot of similarities between protocol concepts and structures, but there is also different. The H.248 / MeGaco protocol is simple, powerful, and has a good scalability, allowing multiple partition gateways to be established in the call control layer; MGCP is H. 248 / Megaco Previous version, its flexibility and scalability is not as good as H.248 / MeGaco. H. 248 support multimedia, MGCP does not support multimedia. When applied to multi-party meetings, H.248 is easy to implement than MGCP. MGCP is based on UDP transmission, and H.248 is based on Transmission Control Protocol (TCP), UDP, etc. The message encoding of H.248 is based on text and binary, and MGCP message encoding is based on text. 3 H.323 protocol 3.1 H. Basic concept of 323 H. 323 The proposal of the protocol is designed for multimedia conferencing systems, not for IP phones, but IP phones (phones that are calling through gateway) can be used. 323 protocol, so H. 323 The protocol is borrowed as an IP telephone standard. IP phones also adopt other recommendations, including H.225, H.245, H.235, H.450, H.341, etc., but H. The 323 protocol is the overall technical requirement, usually referred to as H. 323 IP phone. H. 323 is mainly used for VoIP / FoIP (IP Phone / IP Fax), desktop conferencing television system, collaborative work and distance teaching / medical system. 3.2 H.323 Architecture H.323 The protocol mainly includes terminal, gateway, multi-point control unit (MCU), gatekeep. Terminal initiates or accepts calls, realizing media stream bearer and transmission capabilities, such as Netmeeting, video conferencing terminals, IP phones. The gateway is a heterogeneous network interworking device, completes signaling message format, content conversion, communication protocol process conversion, and media stream format conversion, such as IP telephone gateways, H.323 / h. 320 conference TV gateway.
MCUs can achieve multi-point meeting management and control, with meeting terminal management, media stream control (such as mixing and multi-screen), including multi-point control (MC) and multi-point processing (MP). The gatekeeper is a system-seek, mainly completing access authentication, address resolution, bandwidth management, bill management, regional management, and call management. 4 SIP Protocol 4.1 SIP Basic Concept SIP (Session Initiation Protocol) protocol is an application layer control protocol, with H. 323 Agreement side. The starting point of the SIP protocol is the existing Internet-based architecture IP telephone service network, so SIP design ideas and H. 323 is completely different, it is a decentralized protocol that pushes the complexity of the network device to the network edge. Unlike IP phones based on the H.323 protocol, the SIP protocol requires intelligent terminals. If the user terminal is a non-intelligent terminal, the SIP protocol can also be used as call signaling, but will greatly weaken the SIP protocol unique advantage, so the SIP protocol is more suitable for intelligent user terminals. In addition, the front machine can be added to the user telephone, replaced the gateway device, but the user's expenses have been added to purchase the expenditure. 4.2 SIP Features The SIP protocol has a simple, extended, and closely combined with the Internet. Simple refers to only 3 messages (INVITE, BYE and ACK) and 4 heads (TO, FORM, CALL-ID, and CSEQ) can implement simple Internet phones. The spreadability means that the network server has the characteristics of STATEFUL and STATELESS. Tightly combined with existing Internet is mainly referring to the SIP protocol to closely integrate with the Web and E-mail business. Click-to-Dial (Click-to-Fax "in the IETF PINT Working Group The protocol is based on SIP. 4.3 The basic function of the SIP protocol is mainly composed of two parts: user agent and network servers. User agent includes a User Agent Client (UAC) and User Agent Server (UAS), the user agent client is used to initiate a call, and the user proxy server is used to respond to calls. The User Agent Client and User Proxy Server constitutes the user-ended application, which is initiated and received by the call. SIP protocol is used to create, modify, and end multimedia sessions and calls, and multimedia sessions include Internet multimedia conferences, distance education and internet calls. 5 Subside points of the small knot MGCP are simplicity and reliability, which is limited to uninstalling media stream control and call processing, etc., so that the media gateway is a simple device, simplifies the design of the local access device, only burden The necessary access to the hardware and the MGCP user side function, transfer network management and interoperability costs to the network. MGCP is a key protocol for soft exchange, media gateway, and signaling gateway, which enables IP telephone network to access PSTN, implement end-to-end telephone service. The Media Equipment Control Association (MDCP) is proposed to merge the above protocol into a Megaco protocol (also known as H.248). Megaco adapts both for connected media (TDM and ATM), which adapts to the connectionless media (IP), which is a full set of media gateway control standards. The MGCP protocol is lacking in the description ability, making it unable to apply to large gateways, and the H.248 protocol is a very good choice for large gateways. Compared to MGCP users, H248 / MeGaco users have more choices for transport protocols, providing more application layer support, and management is also simpler. As a multimedia networking standard, h. 323 Application is relatively wide, it is a core protocol for IP gateways / terminals to transmit voice and multimedia services, including point-to-point, point-to-multi-point conference, call control, multimedia management, bandwidth management, LAN and other networks Interface, etc. The ITU's H.323 protocol defines the protocols and procedures for multimedia communication on the Internet or other grouping networks that have no business quality assurance.
