Communication terms of proof of concept

POC (push-to-talk over wireless) is also called PTT (push-to-talk over wireless).

PTT: Push-to-talk function is a brand-new mobile technology, which can make "one-to-one" or "one-to-many" calls quickly, just like using a walkie-talkie. This function is suitable for small and medium-sized enterprises that need frequent intermediate contact and individual users who need to chat with relatives and friends.

In fact, PTT is the evolution of early walkie-talkies. PTT first became the hot spot of 3GSM conference, and then became the highlight of CTIA exhibition. It is very convenient for special industries and specific people, and has become a hot spot for major mobile operators to invest. As early as World War II, American troops stationed in Hawaii used loudspeakers scattered on various islands to communicate. When any speaker broadcasts, the other speakers must be silent. This is the earliest mode of modern communication, from which Ethernet comes. PTT service also uses this principle to establish communication. Because Hawaii's greeting is Aloha, this way of communication is also called Aloha.

● Mobile phone requirements: ordinary mobile phones cannot use PTT function. However, some mobile phones supporting Qualcomm BREW can support PTT technology through software upgrade in the future.

● Use: After the mobile phone is enabled for PTT, you can make one-to-one or one-to-many calls with the selected group by pressing the corresponding key of the mobile phone. The PTT service of Nextel, an American CDMA operator, requires the owner to hold down the button before calling, and after releasing it, the other party can not call until it hears the beep.

● Application: One-to-many push-to-talk function, suitable for colleagues who need to coordinate their working relationship from time to time, such as courier companies and community security guards. Push-to-talk has the characteristics of "push-to-talk", and friends can chat instantly like QQ and MSN through push-to-talk, and only need to send a short message at a time.

● Scope: Unlike walkie-talkies, which can only make short-distance calls, push-to-talk service can reach places that can be covered by mobile phone networks, with almost no distance limit.

● Billing: PTT business can be charged according to the time length, time period and traffic, or it can be charged on a monthly basis, depending on the operator. According to the business precedent of Qualcomm and CDMA operator Nextel, Nextel adopts monthly subscription system, and the cost is between $65,438+$05-$30.

● Interconnection: The possibility of using push-to-talk across operators is very small. At present, operators, equipment manufacturers and mobile phone manufacturers have not yet issued a unified standard. The PTT services of China Mobile and China Unicom are based on GPRS network and CDMA 1X network respectively. So far, operators have not tried to communicate with each other.

● Call delay: In the PTT service based on GPRS, the theoretical call delay time is 1 to 2 seconds, which may be as long as several seconds due to the change of conditions; The access delay of PTT service based on CDMA 1X is about 3 seconds theoretically, and the call delay is about 1 second.

In addition, PoC can also be used as a metaphor for the trigger code of a vulnerability.

As far as network security is concerned, PoC (Proof of Concept of Attack) files are aimed at vulnerabilities with great threats. These files contain codes or information that trigger vulnerabilities for the reference of developers of vulnerable products and make corresponding patches. In 3GPP R6, push-to-talk over cellular (PoC) service has been listed as one of the important applications of IP multimedia subsystem (IMS) of the third generation mobile communication in the future. In fact, the concept of PoC is not unfamiliar to people. It originated from trunking communication technology to realize wireless intercom. As early as 1995, Motorola Corporation of the United States launched a PTT intercom solution on its iDEN cluster system. 1 year later, Nextel, the operator, purchased iDEN trunk network and began to provide a service called Direct Connect. Practice has proved that Nextel is wise. The successful commercialization of Push-to-Talk has enabled Nextel to have the highest average revenue per user (ARPU) and the lowest user connection rate in the industry, and at the same time, it has little impact on traditional voice traffic. It can be predicted that PoC will become another "killer" service after SMS.

The PoC service discussed in this paper is based on 2.5G and 3G networks, which is different from the wireless intercom in the traditional trunking communication professional network, but they have many similarities in function. PoC technology combines the functions of mobile phone and walkie-talkie, and it is a half-duplex communication mode. On the user terminal supporting PoC service, users can make one-to-one (or one-to-many) instant calls with other users only by pressing a key, and the call connection is almost immediately connected, and the receiver does not need additional connection operation, which facilitates communication. At present, public mobile phones have to dial the number 1 1 first, and it takes several seconds or even longer to make a call. If the other party is on the phone, wait patiently no matter how urgent it is. However, this phenomenon will be greatly changed if PoC function is added to the existing mobile communication system. In addition, because the application of PoC technology is based on IP network, the cost is much lower than that of ordinary mobile phone voice service, and its potential business income and new profit growth point are also important reasons why this technology is increasingly favored by operators and equipment providers.

1 PoC service implementation plan

Before the promulgation of the industry standard and international standard of PoC, various manufacturers put forward many private solutions, which enabled PoC services to be realized in GSM/GPRS and CDMA2000 1x networks, and were called solutions based on packet domain (PS). However, due to the poor interoperability of technologies, it is extremely difficult to achieve business interoperability between different operators unless they use the PoC equipment of the same manufacturer, which makes the standardization of PoC technology an urgent matter.

In August, 2003, Ericsson, Motorola, Nokia and Siemens jointly launched the PoC V 1.0 specification [1 2], which is based on the third generation mobile communication cooperation project (3GPP) and the IMS defined by 3GPP2, emphasizing the openness and standardization of the system. It consists of six sub-specifications: user requirements, architecture, signaling flow, user group/contact list, do not disturb management and user platform (transmission and wireless access). At present, these four companies are actively cooperating with international organizations such as Open Mobile Organization Alliance (OMA) and 3GPP to make this specification an international standard. PoC V 1.0 specification can be called "IMS domain-based scheme" [3,4].

The specific PoC system structure based on IMS domain is shown in figure 1. The mobile user terminal with PoC client function accesses the packet domain/multimedia subdomain of the mobile communication network through the wireless access network, and connects to the PoC server based on the Session Initiation Protocol (SIP) and the Real-time Transport Protocol (RTP). Among them, IMS core includes several SIP agents and registration servers, which realize SIP signaling routing, SIP signaling decompression, authorization, user terminal maintenance registration, SIP session status and billing system interface. The site server can provide access to the reachable status information of the user terminal to the SIP core server, which is similar to the status presentation function in instant chat software. In addition, there is a group management list server (GLMS), which, together with the PoC terminal and PoC server, constitutes the core functional entity of PoC implementation (the bold wireframe part in figure 1).

2 PoC business characteristics

6.5438+0 POC basic service

According to the specification of PoC V 1.0, PoC service can provide users with four communication modes, the most important of which is one-to-one personal communication. In the one-to-one personal communication mode, user A can select the user B to contact from the contact list, and then press the PoC call function key on the terminal to start the call. This call connection is almost instantaneous. When the one-to-one call ends, the PoC function key can be released, so that user B can get the right to talk, and so on. In addition, there are three different one-to-many group communication modes. According to the different establishment methods, it can be divided into chat group chat, instant group chat and Ad-hoc group chat. Chat group calls can be divided into open chat groups and restricted chat groups. The former has no membership restrictions, and everyone can join; The latter must be a member of the specified group to join. Real-time group call is communication within a group, and group members can join or leave the group session at any time. Ad hoc group call is an ad hoc call group between users. After the meeting, the group will cease to exist. Members in the group can invite others to join, while those outside the group cannot join themselves without invitation.

Users can also choose two answering modes: automatic answering mode and manual answering mode. Automatic answering mode means that the terminal plays the incoming call directly when it is called for the first time (session establishment), while manual answering mode means that the user needs to answer manually when it is called for the first time to establish a connection. No matter which mode is adopted, subsequent calls will be played immediately.

2. Typical business processes

The typical process of PoC service is shown in Figure 2. Fig. 2 takes one-to-one instant communication with pre-media processing technology as an example, and describes the SIP signaling, voice and control flow in the communication process. Fig. 2 assumes that all user terminals adopt the automatic answer mode. In order to simplify the process, all SIP 100 attempt response messages are omitted.

In the signaling process of one-to-one telephone answering, firstly, user A selects the user B who needs to talk from the address book and presses the PoC talking function key on the terminal. This will trigger the terminal A to send a SIP invitation request to the PoC server A of its home network (step 1). Then, the server A generates a new SIP request and sends it to the user B (step 2). This request (step 2) is intercepted by PoC server B of user B's home network and used to ask whether user A is included in the call rejection list or automatic answer list of user B.. Here we assume that it is in the automatic answer list. In this way, when PoC server B sends a SIP Invite request to terminal B (step 3), corresponding to message step 2, a SIP session processing response will be sent back to server A (step 4). When server A receives this message, it indicates that user B is willing to make a call connection, so it will send a SIP 202 acceptance response (step 5) and allocate a call channel to user A (step 6).

When the terminal receives the messages of steps 5 and 6 at the same time, it will send a prompt tone to user A to start the call. Here, it can be noted that when the session channel has not been established end-to-end, user A begins to speak, which is a communication mode called media preprocessing, so the PoC server must buffer the voice stream until the session channel is established (steps 10, 15 and 16). When terminal A receives the SIP Notify message (step 1 1), it indicates that the call channel has been established. At the same time, terminal B receives the SIP invitation request (step 3) and is informed that user A will start talking immediately. Since the automatic response mode is adopted, corresponding to the request step 3, terminal B will send back a message to indicate acquiescence in step 9.

When user A stops talking and releases the PoC function key on the terminal, the right to talk is also released (step 19- step 22). Message steps 20- 22 indicate that the floor is in an idle state. In fig. 2, the user B also presses the PoC call function key on the terminal and starts the call until the call right returns to the idle state after releasing the PoC function key (step 3 1- step 35). If there is no further call demand between users, there is no need to manually end the call connection. After a certain time interval, the PoC server will automatically send a SIP BYE request message to end the call (steps 36- 39).

Advantages and disadvantages of 3 PoC technology

Undeniably, there are still some problems to be solved in PoC technology. First of all, compared with the PTT service provided by the trunking communication system (such as Motorola's iDEN system), the call setup time of PoC is relatively long, especially the initial call setup time, which is generally 7 ~10 s. Under the same circumstances, the call setup time of PTT service based on trunking communication system will not exceed 1 s, because in iDEN system, the mobile phone contacts the base station once every second, while in IDEN system, Because PoC adopts packet switching technology, there are a series of processes in voice message transmission, such as voice coding, information encapsulation, data transmission, reorganization and conversion, so the efficiency of data transmission is much lower than that of circuit switching. Similarly, when realizing cross-operator interoperability, its performance will be greatly reduced. This will undoubtedly reduce users' feelings and limit the popularity of business to some extent.

Of course, as a new service that attracts much attention, PoC has its special advantages. First of all, PoC covers a wide range. Because PoC calls through the mobile communication network, it can be used anywhere covered by the operator's network, which is different from the traditional walkie-talkie. Secondly, PoC adopts packet switching technology, so that users do not occupy separate channel resources when talking, which greatly improves the utilization rate of wireless channels; Thirdly, because PoC adopts VoIP transmission mode, operators can flexibly set tariffs, such as monthly subscription system and charging according to call duration. Finally, the most important advantage is low tariffs. Once PoC is put into commercial use, the tariff will be about 30% lower than that of existing mobile phones, which will be the key to whether PoC can be accepted by the majority of users.

4 PoC service user positioning

As far as the market positioning of PoC service is concerned, this paper thinks that PoC service should be different from PTT service provided by existing trunking communication private network. This is because the call setup time of PTT service in professional trunking communication network is very short (generally less than 1 s), and it can quickly communicate between groups in the face of emergencies, so it is more suitable for special industries such as military, armed police, electric power, traffic control, emergency and disaster relief. In this way, real-time, voice quality and security are reliably guaranteed, and these customers don't care much about auxiliary functions (such as online status and location information). In addition, in order to ensure the initial investment, usage habits and other reasons, it can be expected that such users are unlikely to switch to new PoC technologies.

PoC business should focus on ordinary enterprise users, community users and individual users mainly white-collar workers and teenagers. Considering that these users do not have high requirements for real-time call, are sensitive to the cost of using services, and show strong interest in auxiliary functions (online status, etc.). ), there is great market space and potential to promote PoC service among these users.

5 concluding remarks

It is envisaged that PoC will not only provide voice transmission, but also become a value-added service platform. Nokia, the communication equipment giant, not only claims that all its GPRS/CDMA mobile terminals will support PoC function from 2005, but also actively invests in the research of using PoC as a multimedia platform, which is expected to be applied in 1 ~ 2 years. Now there is no problem in the transmission of PoC text and voice. The future PoC service platform will be a colorful platform, which can carry multimedia services such as push viewing and push media. PoC can be used as an integration tool for many new services, such as MMS, instant messaging, status presentation, picture sending and receiving, etc. At that time, like SMS service, it will form a win-win PoC industry value chain for terminal manufacturers, equipment manufacturers, service providers and operators, and create a brand-new PoC era.