How PPPoE and VLAN used in Broadband

How PPPoE and VLAN works in Broadband modem and DSLAM. What is 802.1Q,802.1QinQ

This is your Broadband   Modem.  This is 512port DSLAM at   your ISP. Here,each Port is mapped to a separate   vlan from id-128 onwards.  Your modem is terminated at Port No.2 of this   DSLAM. Because of this your VLAN ID is 129.   All the 512vlans are aggregated as a single trunk link and goes to next Switch. Here I have shown ;your traffic in red dots. Your traffic is shown here in red dots. You belong to DSLAM1. A single link from your DSLAM comes and terminated in VLAN1 of this L2/L3 Switch (shown in pink line) . In the switch, VLAN ID starts from 3000 onwardsYour vlan gets the   VLAN ID3000  Because of this YOU have a unique id 3000-129.  Here all vlans are again aggregated and sent out as a single link and sent to BRAS.. Your data is encapsulated in PPP frame. Again this PPP frame is encapsulated in Ethernet Frame (That is why it is called as   PPP Over Ethernet. This ethernet frame, with the vlan id 3000-129 reaches the BRAS. The BRAS is now satisfied that the data has come from a specific port with vlan id 3000-129,   and it is able to bill the user correctly. It takes out the the packet from this encapsulation and sent it on Internet. . When an ethernet frame is sent out of the switch through a Trunk port, It get its VLAN ID. The VLAN ID is available in the field known as VLAN TAG. A frame which is having vlan tag is known as 802.1Q. 802.1Q is designed to have only one vlan id. But we need second level aggregation. So this protocol was slightly modified to accommodate the second vlan tag also. This modified protocol got the name 8021QinQ. This frame enters into BRAS. The BRAS gets the PPP frame which is encapsulated in 8021.QinQ ethernet frame. how ppp frame works: The PPP frame first reaches LCP (Link Control Protocol). It checks for any Error. The frame goes to NCP. NCP decides, to which network layer, the data should be forwarded. How router mode or pppoe works ?In the above diagram, the modem works as a Router. When modem works as a router, you are able to have two networks. In one end your Office computers with Private IP addresses. In another end is the Public IP Address of your ISP. When modem works in Router mode, you are able to NAT. When modem works in Router mode, this router will communiate with the ISP end and make connection. For this purpose, you have to store the username and password given by your isp, in this router. How bridge mode works in broadband modem?When the broadband is configured to work in BRIDGE MODE, the Layer 2 ethernet frames enter into this modem, it simply forwards them towards ISP end. No Network layer work is involved inside the modem. Modem will NOT negotiate with the ISP side devices. Only your computer has to send the username and password and setup the Internet connection. In this case, the computer to which the modem is connected get the public ip address. (this public ip address can be viewed by ipconfig command)