What are SIP AGs and PBXs, and what are the differences between them

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Access devices on the IP Multimedia Subsystem (IMS) provide various access modes and convert various services into a uniform format that can be transmitted. On the IMS, an access device is called access gateway (AG). AGs play an important role on the IMS and are connected to users.

AGs and media gateway controllers (MGCs) use Session Initiation Protocol (SIP). SIP-based AGs are called SIP AGs.

A traditional private branch exchange (PBX) manages the incoming and outgoing calls of an enterprise. It connects the enterprise to the Public Switched Telephone Network (PSTN) and provides services for devices such as telephones, fax machines, and modems. It allows users in the enterprise to call each other using extension phones and routes inter-office calls to the PSTN through a trunk line. Traditional PBXs cannot meet the requirements of computer telephony integration (CTI) and voice over IP (VoIP). In addition, these PBXs are expensive and do not use standard and open platforms, creating difficulties in interconnecting PBXs of different vendors. IP PBXs overcome the limitations of traditional PBXs. IP PBXs are based on the IP protocol and provide both local exchange and IP user access functionality. IP PBXs integrate the voice communications system of an enterprise into the enterprise's data network so that the enterprise can build a uniform voice and data network connecting branches, offices, and staff around the world.

The AR1200/2200/3200 can function as a PBX to provide traditional PBX functions and IP PBX functions.

SIP AGs and PBXs have the following differences:
-PBXs have two functions. PBXs can serve as switching devices on a private network to locate voice users' addresses and process other services. PBXs also allow users on the private network to access the IMS or PSTN through SIP trunks.
-SIP AGs provide only the second function of PBXs. SIP AGs can be considered to be a plain old telephone service (POTS) that can register with the IMS using SIP trunks. PBXs use SIP trunks to register with other SIP servers. SIP AGs register with the IMS using POTS user numbers. PBXs and SIP AGs provides the same services. However, PBXs provide the services by themselves.

Other related questions:
Differences between the AG and PBX
The differences between the access gateway (AG) and PBX are as follows: - A PBX can function as the switching layer device of the private network and provides address positioning and other services for voice users. It can also connect private network users to the IMS or PSTN through trunks such as SIP trunks. - An AG refers to a media access gateway. Compared with the PBX, the AG can only connect private network users to the IMS or PSTN through trunks such as SIP trunks. - The SIP AG is based on SIP. - The H248 AG is based on H248.

A SIP AG user fails to call a PBX user
A SIP AG is similar to a voice gateway connected to a PBX, and a SIP AG user is registered with the SIP server on the PBX. That is, the SIP AG user is similar to a SIP UE user on the PBX. When a SIP AG user calls a PBX user, you need to correctly configure call prefixes. The inter-office trunk does not need to be configured. Assume that a SIP AG user's number is 2200 and a PBX user's number is 1100. The local call prefixes 11 and 22 need to be set. Check the SIP AG configuration. 1. Check whether the SIP AG interface configuration is correct and whether the registration status is normal. 2. Check whether the user configuration on the SIP AG interface is correct. 3. Check whether the FXS interface on the SIP AG is normal. Check the PBX configuration. 1. Check whether the SIP server configuration is correct and whether the SIP server status is normal. 2. Check whether the prefix configuration is correct. 3. Verify that the SIPAG server has registered. 4. Verify that the SIPAG user on the PBX has been configured correctly. 5. Verify that the license is valid.

Why a SIP AG user communicate fail with a PBX user
A SIP AG is similar to a voice gateway connected to a PBX, and a SIP AG user is registered with the SIP server on the PBX. That is, the SIP AG user is similar to a SIP UE user on the PBX. When a SIP AG user calls a PBX user, you need to correctly configure call prefixes. The inter-office trunk does not need to be configured. Assume that a SIP AG user's number is 2200 and a PBX user's number is 1100. The local call prefixes 11 and 22 need to be set. - Check the SIP AG configuration. 1. Check whether the SIP AG interface configuration is correct and whether the registration status is normal. 2. Check whether the user configuration on the SIP AG interface is correct. 3. Check whether the FXS interface on the SIP AG is normal. - Check the PBX configuration. 1. Check whether the SIP server configuration is correct and whether the SIP server status is normal. 2. Check whether the prefix configuration is correct. 3. Check whether the SIP AG user is registered. 4. Check whether the SIP AG user configuration on the PBX is correct. 5. Check whether the license is valid.

LPT/ALS functions and differences between them
After ALS is enabled, when a fault occurs on the client or WDM side, the laser on the optical port in the corresponding transmit direction will be turned off. The laser will be recovered after signals in the receive direction are restored to normal. With the ALS function enabled, fault information can be sent to notify client equipment of the link status. The LPT function applies to scenarios in which WDM equipment receives FE, GE, or 10GE LAN services. With the LPT function, lasers on WDM equipment are alternately turned on and off. The on/off status of the lasers enables devices to know the link status. The devices will trigger service protection when detecting an unexpected link state, and switch services to the working or protection link to avoid service interruption. From the network layer perspective, the ALS function is similar to the LPT function. The main differences lie in applicable services, fault information transmission modes, and the laser restart mechanisms.

What are benefits of using SIP AGs as voice gateways
The AR router supports the SIP AG function to provide VoIP services, which brings the following benefits: -Lower costs: Traditional call and fax services use the circuit switching mode, in which each call session occupies a circuit. Therefore, fees are high, especially when users make long-distance calls. VoIP services use the packet switching mode, and call fees are much lower. -High call quality: SIP AGs ensure call completion rate, voice quality, and service types by configuring QoS. -Smooth upgrade/capacity expansion: A VoIP system is compatible with the existing telephony systems and office platforms, and the service capacity can be increased when the enterprise scale expands.

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