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

"Hello, President Wang... Okay wait a minute, let me check... "

The weather is sunny, suitable for outings, is playing games in the bus worker Li, received a phone call from the boss, the boss asked about work-related content.

Xiao Li hung up the game while logging in to the company mailbox with his mobile phone. During this period, he also checked a data on the Internet. Finally, he successfully completed the boss's "inquiry" and continued the game without panic.

This wave of operation shocked the small editors on the side, telephone, games, Internet access, email... It turns out that mobile phones are so powerful that they can really be described as "one machine for multiple uses." How did this happen? After several days of research, I finally got the answer_in order to let you "multi-use," mobile phone is not hard work. Today, I will have a good chat with you about the secret script of "one machine for multiple uses," which is also another major function of the core network-session management.

The word "session" is not the conversation we usually talk about, but the logical connection established between two node devices in the network for data exchange.

Is it too deep to understand? Let's take a simple example:

As we all know, the early telephone was manually operated by the operator, using a manual switch, and the wiring and disconnection operations in the telephone exchange process were completely completed manually by the operator.

Today, although artificial switches are long gone, the nature of communication has always been similar. The only telephone function in the past has long been expanded to today's one-stop telephone and Internet service, so the original manual operator will naturally progress with the times.

Then, in mobile communication networks, there are also roles such as "operators." In the EPC (Evolved Packet Core) network of 4G, MME, SGW and PGW jointly complete the session management function, while in 5GC, SMF is responsible for independently completing the session management function, that is, establishing a data connection between UE and data network, so that UE can use data service and become a full-time "operator."

Below, we will recognize the changes in session management functions under the transition from 4G to 5G networks from two aspects: concept and service continuity.

In an EPS (Evolved Packet System) network, session management refers to establishing a PDN data connection between a UE and a PDN, and using the PDN connection as a data channel for session management. For example, when we go online, we create an EPS default bearer to access web pages. Halfway through the visit, another call comes, and at this point, there will be a proprietary bearer responsible for voice to meet the demand for making the call. In addition, a UE can also simultaneously create multiple PDN connections to access different PDN networks. This way, whether you want to make a phone call while browsing the web, or want to browse the web while watching videos, it is not a problem.

In the 5G era, a PDU (Packet Data Unit) session is used as a data channel to establish a data connection between a UE and a DN (Data Network).

EPS bearer in 4G network is replaced by QoS Flow (data path in 5G) in 5G network. Similar to 4G, a PDU session in a 5G network can be controlled by multiple QoS flows. If the default QoS Flow cannot meet the service requirements, a dedicated QoS Flow will be established to ensure the quality of the service. 5G networks support simultaneous creation of multiple PDU sessions to access different data networks. The difference is that in 5G, default QoS Flow will not be forcibly established, but whether to establish PDU session will be determined according to service requirements.

After saying so much, did he learn to be useless? Let's summarize the conceptual comparison of session management under 4G and 5G.

Business continuity over 4/5G Phone, video, gaming... Today, we need more and more types of business, business scenarios are more diverse. In order to let you surf the Internet smoothly, how many things have your mobile phone done silently behind your back? We already know that within the network coverage, no matter where the user moves, the network can track and record the user's location information, that is, mobility management functions.

SMF, as an "operator," one of its main responsibilities is to ensure business continuity, even if the user moves, the original ongoing business cannot be interrupted. So how does this happen? This brings us to the relationship between session and business continuity.

In order to meet the different requirements of different services for continuity, the 5G system provides three SSC modes relative to SSC Mode1 (Session and Service Continuity) in 4G. What are the meanings and differences of different SSC modes? Let's continue to take the daily life of workers as an example to see how different SSC modes work.

SSC Mode1: Always anchor the original UPF, suitable for applications with high service continuity requirements.

During the day of working people, work calls are absolutely indispensable. No matter where you go on the phone, you can't have a pause. Otherwise, if you make a phone call and don't hear the content clearly, it's better to type it clearly... What do I need this phone for?

Don't worry, with the support of SSC Mode1, even if you call from Yuhuatai to Xinjiekou (you found it, Xiaobian is in Nanjing), the business address will not change. Since the coverage of Yuhuatai UPF does not include Xinjiekou, Xinjiekou UPF will be accessed, and Xinjiekou UPF will be inserted in front of Yuhuatai UPF, which is actually still accessed through anchor point UPF (i.e. Yuhuatai UPF). "Voice communication is clearer", not a problem at all ~

SSC Mode2: Break-before-connect, suitable for applications that do not require high service continuity and allow short service interruptions.

After work, workers also need to catch up with drama to relax their hearts after a tense day.

After leaving work at Yuhuatai, turn on the video, and walk to Xinjiekou, SMF will find that the current user plane path of Yuhuatai is not the optimal path, and will request the user (that is, the mobile phone you use to watch the video) to release the original PDU session and establish a new PDU session to connect to the current Xinjiekou network (break first). The process of disconnecting from Yuhuatai UPF and reconnecting to Xinjiekou UPF may cause a small network jam. But it doesn't matter, relying on the previous cache, you can't even feel it in front of the screen.

SSC Mode3: Connect first and then disconnect, applicable to services with low requirements for service continuity but high requirements for delay.

After a busy week, the workers who finally looked forward to the weekend, of course, had to find a small partner to start a black game together! Even if you're not home, you want to play on the road. SSC Mode3 is now available.

You play games on the subway, unconsciously from Yuhuatai to Xinjiekou (don't ask me why I always go to Xinjiekou, ask is like). Long-distance movement causes the original user plane path of Yuhuatai not to be the optimal path. What should I do? SMF asks the user (i.e., the phone you are playing on) to reestablish a new PDU session connected to the current network and selects Xinjiekou UPF. After the service is transferred to the PDU session at Xinjiekou, the user is requested to release the PDU session at Yuhuatai (connect first and then disconnect). Compared with SSC Mode1, SSC Mode3 can reduce the delay while ensuring continuity, so that you can experience the pleasure of "smooth to take off" when playing games in front of the screen.

In actual work, which SSC Mode is selected is also the main work of SMF operator. When a user initiates a service, the operator may provide the user with SSC Mode selection policies, including one or more SSC Mode selection rules, from which the user determines the SSC Mode type for each application. Whether it is to maintain the initial anchor point UPF, or to break the connection first, to connect first and then break, it is to bring the most comfortable service experience to users.

It can be seen from this that a small mobile phone can realize the powerful function of "one machine for multiple uses" and bring a clear and smooth user experience, which cannot be separated from the efforts of our "operator"SMF.

Whether 4G or 5G, although the data channel and bearer granularity have changed, the essence of session management has not changed. It is initiated by UE to establish connection to external data network to realize network communication. The changes in 5G are nothing more than decoupling NF functions, PDU sessions and new SSC Mode to better serve increasingly diverse services.

Do you see how much effort the phone has made to make you "multi-use"?

This article comes from Weixin Official Accounts: ZTE Document (ID: ztedoc)

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