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Original address: http://blog.sina.com.cn/s/blog_4a0823ca010004ye.html in a TCP/IP based network, our information, including mail, Im,web and so on all PCs---to---pc transmission, I think most people still understand that. Because each host has a separate IP address, they pass certain devices, such as switches, and then routed, looking for the next node of different network segments, until the message is transferred to the address they want to reach the destination. Of course, the premise is that the source and destination address, the communication between the two require the same protocol, so you can be ready to reach the other side.
Such a seemingly simple thing, it is really condensed the wisdom of countless people. Although complex, I think a lot of people can really understand, but, for now there is a very popular industry, is VoIP (VOICE over Ip,voip is to achieve through the TCP/IP network of all the technology of voice communications collectively. There is a young hero who leads this trend, as you probably know, Skype, a business that grew more than two years, attracts tens of millions of people and is said to grow at a rate of 10 tens of thousands of people a day. Last year, they sold the ebay for E-commerce to a 2.6 billion dollar high, creating a classic myth in it history.
I am here simply a little bit, because the specific technical situation is very complex.
Send a question first, just like the title, is two seemingly completely different things, how they communicate, that is, we are on the computer network phone, why can directly hit the agreement can be said to be completely different from the other type of terminal, such as ordinary landline, and mobile phone. I think. There are still a large majority of people who are not clear. Here is a simple mention: there is a very important thing, to fulfill this: is the PSTN;
PSTN (Public switched telephone network), which is the phone company's model-building infrastructure, cabling, and so on. It handles your phone and has a complete set of techniques to make sure you are able to speak normally. The basic mode of the PSTN is the mainframe/terminal mode. The telephone company provides all the telephone service. Your phone is just a trivial terminal device, and the function is very simple. Even though some telephones have the function of call waiting, call forwarding, and call keeping keys, the implementation of these functions still relies on the support of the switch. The switch provides everything (even power) to the phone, and any signal sent on the phone, whether it is a button operation or your voice, must be managed and converted by the switch. As a result, all telephone connections are directly connected to these switches, and in low densities, such as residential connections, connections to the switch are called lines. If you need to connect multiple telephones, such as an office, it is obviously impractical to connect each phone directly to the switch, so the PBX (Private Branch Exchange) appears. This is a small switch installed in the user, and the connection between the PBX and the main switch is called trunk. One of the great advantages of a PBX is that internal calls can be handled entirely by the PBX, without the need to go through the phone company's switch, and therefore completely free.
But the rapid development of the Internet, enough to subvert all of this, or more prepared, is to use this with some of the impending elimination of resources, to start an unprecedented revolution in human communication.
Now let's take a look at the secret code.
The ordinary telephone uses the line Exchange method, but the Internet telephone takes the message exchange way, therefore when the Internet telephone passes through the PSTN, in the Internet and the PSTN need to pass through the Voice gateway conversion, transforms into conforms to the Internet transmission IP data message, and follow the TCP/IP protocol transfer. --internet telephone communication methods are divided into 3 kinds:
PC-TO-PC, Pc-to-phone and Phone-to-phone. After the voice is passed through the PSTN, the Connection Gateway (CG) and the Voice Gateway (VG) are connected with the No.7 signaling system (SS7) network and the IP network respectively. The CG completes the interconnection between IP protocol (such as H.323 and SIP) and PSTN protocol (such as IsUp, PRI), and the SS7 network acts as its intermediary; VG completes the conversion between the time division Multiplexing (TDM) signal and the TP packet. Gatekeeper In addition to the management of CG and VG two kinds of network customs, but also the implementation of SS7 and IP conferencing (session) management protocol between the conversion function, for the transmission of voice business Dynamic establishment of the Conference business. IP routers, including IP edge routers and IP center routers, are used primarily for routing. 1 TCP/IP protocol--internet telephony systems use standard Internet TCP/IP protocols to transmit real-time voice. TCP/IP not only refers to Internet Protocol IP and Transmission Control protocol TCP, but also includes many protocols and applications related to it, which are structured as follows: Application layer TELNET FTP SNMP SMTP HTTP DNS RPS NFS XDR
Transport layer TCP and UDP
Network Layer IP
Network interface Layer lan,wan,x.25,isdn,fr--telnet: Telnet protocol--ftp: File Transfer Protocol--SNMP: Simple Network Management Protocol--SMTP: Simple Mail Transfer Protocol--http: Overrun this transport protocol--dns : Domain Name System--rpc: Remote process Debugging--NFS: Network File system--xdr: External Data Representation--UDP: User Datagram Protocol
The Voice gateway in--internet belongs to the network layer in TCP/IP, completes the data conversion and IP addressing, and the network interface layer receives the IP data to form the data frame and sends it through the network. The application layer above the network layer and the network interface layer provides a variety of application services that meet the TCP/IP standards, including file transfer, remote login, etc. while the transport layer provides end-to-end communication between applications 2 signaling interconnection
Signaling interconnection refers to the interconnection of the ISUP protocol in the PSTN network and the H.323 protocol in the IP network via the No.7 Signaling System (SS7). Only when the two different protocols are interconnected can the voice messages be transmitted in the PSTN and the IP network. Rationale: When a call begins, an Integrated Services Digital network (ISDN) setup information is sent by a private packet switch (PBX) to an overlapping local switch bearer (ILEC)/internal switch bearer (IXC), ILEC/IXC will send a SS7 initial address information (IAM) to the Connection Gateway (CG), CG to Voice Gateway (VG) reserve channel resources, VG received CG reservation channel Resource Information, immediately informed (ACK) CG, CG then sends a H.323 setup message to the called Terminal PBX. The call Terminal PBX responds with a pager message and sends it back to CG for a standby signal that is converted into an address-access information (ACM) when it passes through the SS7 network. When the ILEC/IXC receives the ACM, ILEC/IXC sends a standby ISDN signal to the PBX (source), the signaling interconnection completes, the call begins. When the call is complete, a H.323 has been sent to CG, Billing began. This prompts the answer message (ANS) to be sent to ILEC/IXC, and then to the PBX, where the billing is complete.
3 Voice Gateway--Voice gateway is the key device to provide Phone-to-phone communication over the Internet, and is the interface device between Internet and PSIN/ISDN/PBX network. Before the telephone enters the internet is the analog signal, cannot transmit directly in the Internet, therefore must pass the Voice gateway conversion, transforms the analog signal to the digital signal, then compresses, packs, finally transforms into the suitable Internet transmission IP message data; At the receiving end, the Voice gateway completes the reverse process. Figure 3 is essentially only the core of the Internet Telephony Gateway-Voice compression codec, voice gateways and automatic control, synchronous transmission signal interface and ECHO cancellation platform line interface, and so on, not detailed here. 4 Network managers-network managers in the Internet Telephony system responsible for user registration and management, and the gateway to complete the IP addressing function. The role of the specific performance is as follows: ——. address mapping: Map the e.164 address of the telephone network to the IP address of the corresponding gateway; ——. call authentication and management: Authenticate the identity of the access user (dial-up user), prevent the access of illegal users; ——. Call log: Make the operator have detailed data to charge; ——. Zone Management: Multiple gateways can be managed by a network administrator. --ip addressing, the user through the ordinary telephone dial-up to the gateway, the gateway after the confirmation, network managers based on the user's dial-up phone number to find the best route (IP address), through the Internet to reach the nearest destination phone gateway, and then by the gateway to the destination user dial-up, This ultimately enables Internet telephony communication. --IP addresses can be divided into two types: static and dynamic. Static IP address refers to each user through the PSTN directly connected to the Internet, when his IP address is fixed; Dynamic IP address refers to the user through the Internet Service Provider (ISP), and then through the PSTN connected to the Internet, The IP address of each user is kept unchanged during the call, and the IP address is reassigned when the call ends. The advantage of dynamic IP addresses, compared with static IP addresses, is that IP addresses can be used by multiple users. The static IP address, whether or not the user is talking, is occupied by it, which is obviously a waste of resources. --ip address addressing methods are both online and not online, and internet telephony is an online addressing method. Dynamic online IP Addressing methods include the World Wide Web (WWW) addressing scheme, the switching server (ES) addressing scheme, and the dynamic Domain Name System (DDNS) addressing scheme. Summary: It is the above roughly mentioned that we can take headphones from the computer, and distant phone calls directly.
In fact, there are quite a lot of things, quite complex, but, including Skype, a large number of achievements have been placed in front of us, of course, the development of space is very big.
VoIP is a practical technology, is an unprecedented broad prospects of the industry, but also for everyone to bring convenience and real benefits, and ISP win the cause. Expect him to popularize that day.
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