Five protocols involved in implementing Softswitch

NGN features a complex converged network based on multiple IP technology vendors, multiple technologies, and different architectures. Softswitch plays an extremely important role in controlling such a heterogeneous network.

Control is implemented through protocols. The main Protocols involved in implementing Softswitch include H.323, H.248/MEGACO, SIP, SIGTRAN, and BICC.

Check five major protocols

H.323 Protocol

H.323 is a set of standards that provide real-time audio, video, and data communication on the group network and is part of the series of protocols H.32x developed by the ITU-T to provide multimedia communication on a variety of networks. The H.323 protocol is widely recognized as the most mature protocol for supporting voice, image, and data services on the group network. Using the H.323 protocol, multimedia products and applications of different vendors can interact with each other, so users do not have to consider compatibility issues. This Protocol laid the foundation for collaborative development of multimedia products based on LAN and MAN for commercial and individual users.

H.323 is an umbrella protocol, which consists of a series of protocols. Figure 1 lists the basic content of the H.323 protocol stack.

H.225.0: call signaling protocol and media segmentation of the H.323 group Multimedia Communication System;

H.245: Communication Control Protocol between H.323 multimedia communication terminals;

RTP/RTCP: uses the capabilities provided by the Resource Reservation Protocol RSVP to control Resource Reservation and QoS service quality;

G.711: pulse coding modulation of voice frequency;

G.723.1: multimedia communication 5.3/6.3 kbit/s dual-Rate Speech Encoder;

G.729: 8 kbit/s Speech Encoding inspired by digital linear prediction using a bounded structure;

G.729a: low-complexity CS-ACELP8kbit/s speech encoding.

H.248/MEGACO Protocol

H.248/MEGACOMediaGatewayControlProtocol is a media gateway control protocol developed by IETF and ITU-T for communication between the media gateway controller and the media gateway. The H.248/MEGACO Protocol is a product of the concept of gateway separation. The core of gateway separation is business and control separation, control and bearer separation. In this way, the business, control, and bearer can develop independently. While making full use of new technologies, operators can also provide a wide range of services to enhance network value through innovative services. H.248/MEGACO is a protocol developed based on the MGCP protocol RFC2705 and combined with the features of other media gateway control protocols. It provides a mechanism for establishing, modifying, and releasing control media, at the same time, it can carry some along-the-way call signals to support calls from traditional network terminals. This Protocol plays an important role in building an open and multi-network integrated NGN.

SIP protocol

SIPSessionInitiationProtocol) the Session Initiation Protocol is developed by IETF and used for multi-party multimedia communication. According to the definition of IETFRFC2543, SIP is a text-based Application Layer Control Protocol Independent of the underlying transmission protocol TCP/UDP/SCTP, it is used to establish, modify, and terminate multi-party or multi-party multimedia sessions on the IP network. The SIP protocol uses HTTP, SMTP, and other protocols to support proxy, redirection, user registration, and other functions, and supports user mobility. Through cooperation with RTP/RTCP, SDP, RTSP, and other protocols and DNS, SIP supports voice, video, Data, E-mail, status, IM, chat, and games. The SIP protocol can be transmitted over TCP or UDP. Because the SIP itself has a handshake mechanism, UDP is preferred.

SIGTRAN Protocol

SIGTRAN protocol signaling Transfer Protocol) is a set of protocols developed by IETFSIGTRAN to transmit PSTN/ISDN Signaling over IP networks. SIGTRAN transmits circuit exchange signaling in the IP network, which is mainly the No. 7 signaling. The protocol is implemented through the signaling gateway SG. In our country's specifications, the signaling gateway is used to connect the No. 7 network and the IP network, and relay, translate or terminate signaling information.

The SIGTRAN protocol includes SCTP Traffic Control Transfer Protocol), M2UAMTP2 user adaptation), and M3UAMTP3 user adaptation. It provides the same functions as SS7MTP, as shown in protocol stack 2.

SCTP: used for reliable transmission of PSTN signaling over an IP network, which can replace TCP and UDP protocols;

M2UA: supports MTP3 intercommunication and link status maintenance, and provides the same functions as MTP2;

M3UA: supports MTP3 user intercommunication and provides signaling point encoding and IP address conversion;

SUA signaling user adaptation): supports SCCP user intercommunication, equivalent to TCAPoverIP;

M2PAMTP2 user peer-to-peer Adaptation Layer Protocol): supports MTP3 intercommunication, local MTP3, and M2PASG signaling gateway. It can be used as STP.

BICC Protocol

The BICCBearerIndependentCallControl protocol is a bearer-independent call control protocol developed by the ITU-TSG11 team. The main purpose of BICC protocol is to solve the problem of separation of Call Control and bearer control, so that call control signaling can be carried on various networks, including the MTP message transmission part) SS7 network, ATM network, and IP network. BICC protocol evolved from ISUPISDN user segments, and is an important supporting tool for the evolution of traditional telecom networks to integrated multi-service networks.

Protocol Comparison and development

H.323, H.248/MEGACOVsSIP

H.323, H.248, MEGACO, and SIP are implementation protocols for voice, multimedia, and other communication services on the group exchange network. Among them, H.323 appeared earlier and has a complete definition. Its biggest advantage is its maturity, which ensures the stability of devices and facilitates interoperability between devices of different vendors. Its disadvantage is that the standards are too complex, the product is too expensive and cannot be integrated with SS7. the upgrade and scalability are poor. At present, ITU-T group 16th focuses on how to further expand the H.323 protocol to expand its ability to support multimedia services and mobility management capabilities.

H.248/MEGACO is the product of H.323 gateway decomposition. It is advantageous for gateway interconnection. It is suitable for building a large-scale network and can work with SS7 signaling gateway. It can be well integrated with SS7 and has good protocol scalability. In addition, the separation of Call Control and Media Processing makes it possible for devices from multiple vendors to communicate with each other. Its disadvantage is that it is still immature. The H.248/MEGACO Protocol is a gateway control protocol that the ITU and IETF have agreed and jointly promoted. After resolving the complexity and poor scalability of H.323, H.248/MEGACO is widely supported by manufacturers and becomes a key media gateway control protocol for the Next Generation Network.

The SIP protocol is based on the client-server concept in the computer world. SIP is very similar to other Internet protocols and suitable for applications in the Internet environment. It supports user positioning, terminal capability detection, and multicast. Because the SIP protocol is simple, common, and easy to expand, it is becoming more and more popular in the industry. It is gradually becoming an important protocol in the NGN and 3G Multimedia subsystems, in addition, there are more and more client software and smart Multimedia Terminals supporting SIP, as well as servers and SoftSwitch devices using the SIP protocol. Although the SIP protocol is not yet mature, it is foreseeable that the SIP protocol will be the core protocol for businesses and Applications in network multimedia communication in the future.

BICCVsSIP/STP-T

One notable feature of NGN is its ability to achieve separation of Call Control and bearer control. In terms of communication call control, two protocols are worth noting, namely BICC and SIP-T, from the Standard Research of ITU-T and IETF.

BICC is directly oriented to telephone applications. It comes from the traditional telecom camp and has a more rigorous system architecture, therefore, it can provide good transparency for implementing services in the existing circuit switching telephone network in NGN. In contrast, the SIP architecture is not as complete as BICC defines. SIP is mainly used to support multimedia and other new services, and has more flexible and convenient features in multiple service applications based on IP networks.

SIP-T is an extension protocol of SIP, which increases support for telephone applications, inherits the flexibility of SIP, and is more suitable for IP networks. The extended SIP-T enables SIP messages to carry ISUP signaling, providing a mechanism for communication between SS7-based PSTN network users and SIP-based IP phone network users.

BICC is a mature standard protocol that makes it extremely easy for manufacturers of different devices to communicate with each other, and the use of SIP-T intercommunication has some problems. And from the perspective of system architecture, SIP-T is more complex.

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