Hardcore science! Analysis of the technical principle of car
On November 11, the Ministry of Industry and Information Technology issued the "Regulations on the Management of Portable Number Transfer Service", marking the official operation of the "portable number transfer network" business of the three major operators in China. According to the plan, starting from December 1st, the “Portable Number Transfer” business will be officially launched nationwide.
This article was authorized to reprint from the fresh jujube classroom (ID: xzclasscom) these days, the news about "carrying the number to the net" repeatedly screen, I believe everyone has seen. The author also came to join in the fun today, and talked with everyone about "carrying the number to the net." However, what I want to say is not the business handling of “carrying the number to the network”, but the deeper content – the technical principle of “carrying the number to the net”. I want to use this article to help you understand the specific implementation behind this particular business. More importantly, I took the opportunity to introduce knowledge about mobile communication user numbers and call flows. Ok, no more nonsense, let's get started!
First of all, let me explain what is "portable number transfer". "Carrying the number to the network", as the name suggests, is to exchange the number with the network.
For example: You are now the China Mobile number at the beginning of 139. After the "portable number transfer", the number remains unchanged, but the operator's affiliation has changed - it has become telecommunications or China Unicom. The network and packages you use also become telecommunications or China Unicom. This kind of telecommunication service is "portable number transfer". In industry terminology, the real name of “portable number transfer” should be called “number portability” or “number portability”.
This business is not complicated on the surface, it is to change the operator, and then carry the number. But in fact, for mobile communication systems, it is not easy to implement. There are actually two mobile phone numbers, namely IMSI and MDN. The full name of IMSI is International Mobile Subscriber Identity, International Mobile Subscriber Identity. It is a "permanent user identity", each mobile phone SIM card, corresponding to an IMSI number. The IMSI number consists of three parts, namely:
MCC (Mobile Country Code) Mobile Country Code
MNC (Mobile Network Code) mobile network code
MSIN (Mobile Subscriber Identity) Mobile Subscriber Identity
The MCC is 3 digits (China is 460), the MNC is 2-3 digits, and the MSIN is 10-11 digits. The combined IMSI is generally no more than 15 digits, usually 15 digits (for example, our country).
Everyone in the phone dialing interface, enter *#*#4636#*#*, you can see your IMSI number.
Everyone noticed that in addition to the IMSI number, there is an IMEI number, so don't confuse the two.
IMEI is International Mobile Equipment Identity, International Mobile Equipment Identity (approximately 15-17 digits). That is to say, the mobile phone serial number (mobile phone serial number) is the "identity card" of each mobile phone hardware (there are 2 IMEI numbers in 2 card slots).
Then what are the numbers that we usually use at the beginning of 139, 153, and 189? These numbers, the real scientific name is MDN, Mobile Directory Number. The MDN is composed of a country code (CC), a mobile access number (MAC), an HLR identification code, and a mobile subscriber number.
Introduced the code of this code, everyone did not faint?
If you are not dizzy, let's continue! When it comes to this, everyone should understand it. The so-called "number portability", the MDN number is unchanged, and the IMSI number is changed. And IMSI is your "real" number.
After finishing the number, let's talk about the processing on the network side. At present, the mobile communication services we use are mainly talking, texting, and surfing the Internet. Everyone knows that surfing the Internet is a matter for individual users. A user's mobile phone initiates a data service request, obtains resources such as IP, and then connects to the carrier network to access the Internet. As long as your IMSI is legal, the business is normally opened, and there is no arrears, you can go online. But the call and the text message are different. This is the business between the two users. There are "calling" and "called".
The calling user has no big problem, anyway, his number is just a number. But when you are called, the trouble comes. The number is like the house number. Others are looking for you through the house number. You moved the house and took the house number. Is this a whole? Let’s take a look. When there was no number to carry the business, once. What is the normal call process: (Note: For ease of understanding, the call flow description is abbreviated.) Assume that the calling user A is the number starting with China Mobile 139. When he dials the called number, the local network core equipment (MSC, Mobile Switching Center) where it is located will perform "number analysis" on the called number according to the designed rules.
Number analysis is an important basis for telephone connection. Different analysis results mean different processing procedures:
According to the previous design, if the number starting with 138 is dialed, the MSC will analyze the number of China Mobile, which is processed according to the internal call process of the operator. (Specifically, MSC will go to China Mobile's own HLR, ask the location of the called party, and then look for it all the way. HLR is the home location register, which stores the data and information of China Mobile users.)
If the called party is "self-family", if the Unicom number starting with 185 is dialed, the local office equipment will analyze it as "its network number", which will be routed to the gateway between the operators, and then sent to Unicom to find Called, all the way to complete the phone connection.
If the called party is "other's family", now, if you want to carry the number, the trouble is coming. Or for example, A at the beginning of 139, dial B at the beginning of 138. B is the user who has carried the number. Although the number is 138, it cannot be processed according to the internal call process of China Mobile, otherwise the destination will be sent incorrectly. China Mobile's MSC must treat the B number as a special case and handle it separately.
If there is only one special case, then it is better to say that the problem is that this business is open to users all over the country, and there will be thousands of exceptions. In this case, the number analysis becomes very large and burdens the system capacity. So, in our country's current network, the solution is this: If a called number handles the number portability service (for example, jumping from mobile to Unicom). Then, the mobile HLR adds a special prefix number to the already carried number and returns it to the calling MSC, telling it that the number is not ours.
The China Mobile MSC on the calling side will perform special processing on the prefix number and directly process it according to other carrier numbers. If this number is Unicom's jump to mobile: the operator will first add an NP-HLR, that is, the number carries the HLR, and put all the incoming numbers in this HLR. The calling MSC will check the NP-HLR first for the "called number of all other carrier segments".
If you are carrying a number, follow your own number and check your home HLR.
If you are not carrying a number (that is, someone else's normal number), then check the HLR of someone else's home.
All in all, it is equivalent to checking the HLR twice. The above solution, although the process is more complicated, but the speed is very fast, user perception is not affected. This is the number portability implementation that is currently used in our country. Did you understand it?
Haha, can insist on watching, are all warriors, Xiaozaojun free recommended core network engineer offer! Finally, make a summary. The port number transfer service is undoubtedly a good thing for ordinary users. After all, it has increased the bargaining power and increased the autonomy. However, from the perspective of the communications engineer, this business adds some minor difficulties and minor problems - when we deal with the fault, we can no longer quickly judge the user attributes of the complainant through the number segment as before. Different user attributes mean completely different troubleshooting processes and ideas. That is to say, the popularity of the number portability service will “slightly” increase the difficulty of the communication engineer in handling the failure and the time of failure recovery. Well, the main content above is the technical analysis of the port number transfer service. You are welcome to make a brick discussion in the message area.
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