Shulou(Shulou.com)11/24 Report--

In today's popularity of 5G, why mention 4G's darling again-IMS (IP Multimedia Subsystem,IP Multimedia Subsystem)?

Newton said, "I succeeded because I stood on the shoulders of giants." 5G is also a wise wave rider, he knows how to find a giant, find a shoulder to stand on, that is-- IMS.

What is the face of IMS, which has experienced several years of peak experience? What kind of transformation has transformed it into a right-hand man of the new overlord 5G?

As early as 2004, 3GPP introduced IMS in R5 as the architecture of 3G core network.

The goal of IMS is to enable various types of terminals to establish IP connections. Through this IP connection, terminals can transmit all kinds of information to each other, including voice, pictures, videos, files and so on. It can be said that IMS realizes end-to-end multimedia services through IP network.

IMS has rich services and a variety of access methods, as shown in the figure.

The terminal of IMS system can be mobile terminal, fixed telephone terminal, multimedia terminal, PC machine and so on. The access mode is not limited to cellular radio frequency interface, it can be wireless WCDMA, or wired LAN, xDSL and other technologies. Therefore, as a future-oriented communication architecture, IMS is of great significance for the integration of fixed and mobile access.

The IMS network contains many network elements, just like a huge feudal dynasty, which requires officials of all parties (corresponding to the network elements in the IMS) to perform their respective duties and cooperate with each other in order to ensure normal operation. There are many officials, so in order to facilitate management, they are divided into six parts: etiquette Ministry, Household Ministry, official Ministry, Engineering Ministry, Criminal Ministry, and military Ministry.

Similarly, if there are more network elements in the IMS network, it is necessary to divide them into six layers: service layer, operation support layer, control layer, interworking layer, access and bearer control layer, and access network layer.

If IMS is regarded as a dynasty, what are the responsibilities of the six parts of IMS? Let's see one by one.

The important function of the Ministry of Etiquette is diplomacy, while the diplomacy of IMS is an open and diversified business. The business layer of IMS is completely separated from the control layer. The service layer is mainly composed of a variety of different application servers. In addition to implementing a variety of basic services and supplementary services in the IMS network, the traditional narrowband intelligent network services can be connected to the IMS network, and provide a standard open application programming interface for the development of third-party services.

The economy of IMS is billing, and the population is the end user.

The operation support layer of IMS is mainly composed of home user server (HSS), online billing system (OCS), billing gateway (CG), etc., which provides support for the normal operation of IMS network.

The control layer is the core of IMS, and its status is important, just like the official department, which is the foundation of the feudal dynasty. The IMS control layer completes the signaling control functions in the process of IMS multimedia call session, including user registration, authentication, session control, routing, service trigger, bearer QoS, media resource control and network interworking and other functions.

The Ministry of Engineering is responsible for building roads leading to all directions. Like the interworking layer of IMS, it completes the interworking function between IMS network and other networks, such as connecting public switched telephone network (PSTN), public land mobile network (PLMN), and other IP networks.

The access and bearer control layer is comparable to the penalty department: to achieve access control, QoS control, dosage control, billing control and other functions, these control functions are like the criminal department, there are laws to abide by, there are laws to abide by. The Policy and Billing rules functional entity (PCRF) is the only network element in this layer.

The access network is located at the boundary of IMS, like the troops stationed in the border defense, to prevent wanton intrusion, such as: mobile phones are accessed by A-SBC (access session Border Controller), and A-SBC ensures network security. Moreover, the access network supports multiple access types (open diplomatic relations), such as xDSL / LAN, WiMAX / WiFi.

Among the six departments of the IMS dynasty, there are several key positions (that is, network elements), which are so important that they have to be introduced to you:

The Ministry of Household is in charge of the population in the country, the HSS (home user server) in IMS, and the communication equipment in the hands of everyone. HSS stores user-related data in the IMS network, including user identity, authentication data, service data, access parameters, service trigger information and roaming information.

CSCF (call conversation Control function), as the core part of IMS, is in charge of the Ministry of officials and the official residence Shangshu.

CSCF is responsible for handling the user's multimedia session. According to the function, it can be divided into P-CSCF, I-CSCF and S-CSCF.

Since the position of the clerk of the Ministry of officials has been occupied by CSCF, MRF can only be subordinated to the waiter.

MRF mainly completes the functions of multi-party call and multimedia conference. MRF consists of MRFC and MRFP:

MRFC: responsible for maintaining and controlling media resources in MRFP. To achieve playback, transceiver number, multi-party conference, IVR and voice codec conversion and other functions.

MRFP: completes the function of media resources within the IMS domain under the control of MRFC. Provide playback and reception resources and conference resources.

At this point, we have a general understanding of IMS.

The time comes to the end of 2008-4G will be available. Voice service is still one of the main services of 4G. The solution of 4G voice service is VoLTE (VoLTE:Voice over LTE).

VoLTE uses IMS for its own use: provides voice services based on IMS network, and makes voice services transmit as data streams in LTE data bearer networks.

In 2019, 5G fresh meat made its debut, whether it is time for IMS veterans to retire-No! The rise of the younger generation of 5G is still immature and needs to be honed. How can IMS retire?

In addition to 4G VoLTE,5G also launched EPS Fallback, VoNR (listen to the sound of 5G! ) and other voice programs.

As the 5G network matures, the 5G voice scheme will change:

At the initial stage of the establishment of 5G network, 5GC (5G core network) has not been deployed and the coverage of 5G base station is not complete. At this time, the voice service mainly adopts VoLTE scheme.

After the deployment of 5GC, the coverage of 5G base station is discontinuous. In order to avoid frequent handover of 4G / 5G, EPS Fallback voice scheme is recommended.

After the 5G base station is continuously covered, the voice is carried on the NR (5G wireless network), and the voice adopts the VoNR scheme, as shown in the figure.

The above three 5G voice schemes are all without the participation of IMS.

The stage of history is rapidly changing, and IMS can't be invincible all over the world, so how does he adapt to the new role?

Since its birth, IMS has inherent advantages: separation of control and business, separation of control and bearer. Entering the 5G era, EPC is busy with the evolution to 5GC (network element split, reorganization, etc., etc.), and IMS has inherently adapted to the business needs of 5G.

In order to implement the 5G voice solution, IMS needs to be changed, but not much:

Function: in the case of final call access domain selection (T-ADS), the policy executed by SCC AS needs to be enhanced for dual registration scenarios.

In terms of interfaces, parameters such as access type and location information need to be added for Rx, Sh and Gm / Mw / ISC, while 5G billing information needs to be transmitted through the Rf interface.

IMS has made changes to adapt to 5G, and it can be said that those who keep abreast of the times are outstanding.

Jiangshan generation of talented people, you sing and I take the stage-5G as the protagonist in the next few years, we look forward to its highlight moment. IMS is ready for solid backing!

This article comes from the official account of Wechat: ZTE documents (ID:ztedoc), by Yuan

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