Difference and connection between three access methods: PPPT, PPPoE, and PPPoA

Presumably, you should be familiar with ADSL and other access methods. We have learned that PPPT, PPPoE, and PPPoA should be available. So what are the differences and associations between the three access methods? Let's take a look at it in detail. First, let's look at the concept of the Bridge CPE method.

1) Bridging Mode: equivalent to connecting to a HUB. IP addresses must be set at both ends. For example, if the adsl modem works with the computer and a fixed IP address is assigned to the computer, the local device can be connected to the Internet at startup.

RFC1483 is designed to encapsulate and transmit multi-protocol packets on the network layer on the ATM network. It is widely used in ATM technology, it becomes the encapsulation standard for processing multicast packets on an ATM network.

RFC1483 simulates the Ethernet bridging function. It encapsulates packets at the network layer on the data link layer through LLC/SNAP. After the RFC1483 ATM encapsulation of the Ethernet frame is completed in the ADSL Modem, the transparent transmission of data packets is completed through the PVC permanent virtual circuit of the client and the local network.

2) RFC 2364--PPP over ATM Access Method

This access method is used by the PC terminal to directly initiate a PPP call. After the pc atm 25 Nic receives the PPP package from the upper layer, the AAL5 layer encapsulation is performed on PPP packets according to RFC 2364 encapsulation standard to form an ATM Cell stream. ATM cells are transmitted to the broadband Access Server on the network side through ADSL ModemCPE, and requests and responses are received through standard negotiation processes), so that the PC and BRASBroadBand Remote Access Server, broadband remote access server) establishes a mutual trust PPP Point-to-Point Protocol) connection or Session, Session ), at the same time, there is a reliable mechanism to detect, maintain, and handle Session interruptions. Then, the user can initiate a request requesting to log on to an ISP using FQDN through the Session, for example, the use of USER1@163.GD + password, and then BRAS will forward the request to the RADIUS Server, to perform the relevant authentication, authorization, RADIUS began to charge records and return IP addresses and sessions to the PC.

In terms of implementation, the ADSL Modem is only an intermediate point for transmitting ATM cells. At the same time, to achieve PPPoA access, the user side must use an expensive ATM 25 Nic, And the NIC supplier must also provide the corresponding dedicated PPPoA client software. Because one VC in a CPE only supports one unique session, multi-user access becomes a problem, even if NAT or Proxy is used to solve this problem, however, this allows all users after CPE to access and use the same set of services. Due to the above reasons, the broadband access method PPPoA has not been widely applied.

3) PPTP-PPP-Point-to-Point Tunneling Technology to PPPoA or PPPoEPPP over Ethernet) Access Method

On the ADSL user side, the PPTP technology is used to establish an IP tunnel between the ADSL Modem and the user PC through the internal Ethernet and send PPP requests sent by the user terminal. ADSL ModemCPE) End the IP tunnel, extract the PPP package from the PC terminal, and use RFC 2364 or RFC 2516 standard for encapsulation, it is then transferred to the remote Broadband Access Server and completed a series of processes based on PPP technology, such as authentication, authorization, billing, and dynamic IP Address allocation. It can be seen that the PPTP-PPP access on the network side is completely consistent with PPPoA or PPPoE. The user-side IP tunneling technology can not only effectively use existing LAN resources to achieve simultaneous access for multiple users, in addition, some special settings can be used in the ADSL Modem to complete simple VPN selection. In terms of drivers, the user's PC terminal can use the virtual private network adapter provided by the existing Windows 98/NT operating system to achieve PPTP access without further purchase, which is highly practical.

From the perspective of its protocol stack structure and working principle, the protocol stack of this access method is too complex, thus affecting the actual performance of access. In terms of functionality, the ADSL Modem should not only terminate the IP Tunnel of PPTP, but also initiate a PPP connection to the network side. As an ADSL terminal device, the adsl cpe has limited packet processing capabilities. This will greatly reduce the actual rate of user access, and almost cannot implement services with high bandwidth and high quality requirements such as VOD.

Second, this access technology also limits the number of users supported. Finally, from the actual networking perspective, to complete PPP access for each end user, the corresponding PVC for transmitting the PPP package must be created in the ADSL Modem and ATM networks, network implementation is too complex. But in general, the PPTP-PPP access technology is combined with the product of Ethernet and PPPoA technology, and further promote the practical process of broadband access. In the realization of Internet user access and the simple intercommunication of ordinary enterprise network, PPTP-PPP is still an ideal choice.

4) RFC 2516 -- PPPoE access method

In this way, the ADSL Modem is interconnected with the user's PC over an Ethernet network. In the adsl cpe, the RFC 1483 bridging encapsulation is used to encapsulate the PPP packets sent by the PC through LLC/SNAP, the protocol stack works in principle 3, as shown in figure 3.

The advantages of this method are as follows:

◆ PPPoE uses PAPPassword Authentication Protocol and password verification Protocol for each process) or CHAPChallenge-Handshake Authentication Protcol to challenge the Handshake Verification Protocol) to overcome common security vulnerabilities in the bridging mechanism.

◆ Fees can be charged for each connection process, NSP or NAP) based on the duration of the process, or a minimum access fee.

◆ For CPE that cannot run PPPoA or that does not support PPP, this method will not be affected because it uses a bridge-based PPP protocol.

◆ PPPoE allows a PC to be connected to multiple destinations at the same time, that is, multiple processes can be deployed on each PVC.

◆ NSP can control each user using the standard RADIUS protocol, such as setting idle or timeout attributes.

◆ Configuration is very simple.

The disadvantage of this method is:

◆ Proprietary PPPoE client software must be installed.

◆ Due to the RFC 1483 bridging method, it is prone to broadcast storms and DoS attacks. However, since only one PVC is set for each CPE device to reach the BRAS device, the BRAS side often uses the RBERouted Bridged Encapsulation mechanism to effectively overcome this weakness.

In general, this method is practical and convenient, and the actual networking method is also very simple, the requirement for CPE is very simple, greatly reducing the complexity of the network, is currently the most common access mode for home users.

Router CPE Mode

In terms of system operation, the Router CPE can be understood as Bridge CPE + small-sized Router.

1) PPPoE is used. The call and establishment of PPPoE are all handled by the CPE, And the BRAS dynamically assigns the public IP address to the CPE. At the same time, the CPE can complete the NAT Function, the gateway on the PC points to the user-side port private IP address of the CPE,

2) In PPPoA mode, the call and establishment of PPPoA are all handled by the CPE, And the BRAS dynamically assigns the public IP address to the CPE. At the same time, the CPE can complete the NAT Function, the gateway on the PC points to the user-side port private IP address of the CPE

This removes the need to purchase a vro and allows you to use PPP dialing for a long time,