Implementation of multicast in mpls vpn Network

1 Introduction
As people's living standards continue to improve, the public's consumption of information increases sharply, various broadband network applications such as ip TV, video conferencing, Network Audio applications, network video applications, and multimedia distance education have broad market prospects. At the same time, a large amount of bandwidth consumption poses a challenge for network operators to provide efficient and stable services based on existing network resources.
Simply increasing bandwidth is not the key to solving the problem. We should seek a one-to-many Model Technology to relieve the pressure on bandwidth. multicast is the technology. In a multicast network, the network bandwidth in the backbone network does not need to increase even if the number of multicast users doubles. MPLSMultiProtocol Label Switching, Multi-Protocol Label exchange technology) is the next-generation Wan transmission technology since the IP technology, it is a new technology that makes full use of data tags to guide data packets through high-speed and efficient transmission in an open communication network. It introduces the connection mode in a connectionless network, this reduces network complexity and is compatible with various mainstream network technologies, greatly reducing network costs while improving IP service performance, it ensures the service quality of network communication and the security of data transmission. The combination of multicast technology and mpls vpn technology will provide operators with an unprecedented space for multi-service development.
Introduction to multicast and MPLS VPN 
IP data is transmitted in three ways in the network:
Unicast) transmission: the sender and each receiver need a separate data channel. In this mode, the Source IP host sends data packets to the specified target IP host. Each data packet sent from one host can only be sent to one target host, send these IP packets from the source host to the target host through a vro or vswitch. In unicast mode, it is impossible for another user to copy the data packet at the same time. The host that sends the information must send a separate copy of the data packet to each user who wants to receive the data packet. This huge redundancy will bring a huge price. First, it will impose a heavy burden on the source host that sends data, because it must respond to every requirement, this greatly extends the host response, and puts forward higher requirements on the Performance of routers and switches, management Personnel are forced to purchase unnecessary hardware and bandwidth to ensure certain service quality.
Broadcast) transmission: the sender and each receiver share a data channel. In this mode, the Source IP host sends data packets to a direct broadcast address, which means that all hosts in the target network must process the broadcast data packets, whether or not the data is required, it is a burden for hosts that do not need this data. Multicast) transmission: Implements point-to-point network connection between the sender and each receiver. If a sender transmits the same data to multiple receivers at the same time, only one identical packet needs to be copied. It improves data transmission efficiency, reduces the possibility of congestion on the backbone network, and does not affect other hosts.
In summary, compared with unicast, the use of IP multicast technology to distribute information often reduces the overall network bandwidth needs in essence. Compared with broadcast, the IP multicast technology can effectively reduce the impact on the performance of networked hosts, especially in multimedia stream applications.
One is the bandwidth advantage: for audio and video networks, a large number of users often need to access the same information at roughly the same time. If IP Unicast is used, the consumption of network bandwidth will increase linearly, because the typical MPEG-2 video information flow needs about 1 ~ 5 Mbps bandwidth is used for smooth and realistic images. Obviously, it is wise to use IP multicast to send programs. Because repeated data streams are replaced by a single transmission, network bandwidth can be used more effectively.
Second, server load advantages: If network operators of the audio and video networks continue to use the unicast transmission mechanism, as users grow, it will need to constantly increase the capabilities and quantity of its real-time audio servers to meet the increasing needs of connected users. When the server load increases to a certain extent, the server cannot send out information streams. If carriers use IP multicast to publish their programs, they do not need to purchase more and more high-performance servers to meet the increasing number of customers. Obviously, the main advantage of IP multicast is to greatly reduce the data volume to be forwarded and processed, thus reducing the required server performance.
Third, the advantages of distributed applications: in the case of IP Unicast, as demand and applications grow, multi-point applications are unlikely, because the number of customers in Unicast communication cannot grow infinitely. However, multicast is almost not limited by the increase in the number of customers. From the comparison of the above three transmission modes, we can see that multicast transmission is the best choice for multimedia stream applications.
Currently, mpls vpn is the most popular technology and application. It can be divided into two types: L2 mpls vpn and L3 mpls vpn. L2 mpls vpn: L2 mpls vpn is designed to provide dedicated Connections similar to ATM and FR over an IP network. Service providers only provide users with traditional L2 links such as ATM, FR, ethernet, etc.), and map the corresponding link ID (atm vpi/VCI, fr dlci, and Ethernet vlan id) to an mpls lsp to traverse the carrier's core network, the user organizes the Routing Structure on such a VPC connection.
Layer-3 mpls vpn: A layer-3 mpls vpn is an ip vpn based on MPLS technology. It uses MPLS technology on network routes and exchange devices to simplify the route selection method of the core router, IP Virtual Private Network (VPC) implemented by tag switching combined with traditional routing technologies. Mpls vpn is suitable for VPN services that require high service quality, service level, network resource utilization, and network reliability.
MPLS is currently the only network technology that can implement QoS and traffic engineering in the IP network. Therefore, when the network to be established has requirements for these functions, especially for real-time services with high service quality requirements, MPLS should be used as the Tunneling Protocol to implement ip vpn. Implementation of multicast in mpls vpn Networks
In the past, the only way to implement multicast communication in a VPN is to encapsulate multicast traffic in Unicast data packets through the GREGeneric Route Encapsulation, Generic Routing Encapsulation) tunnel for transmission. In this way, the sites involved in multicast communication must complete point-to-point GRE tunnel connections. When sites are added, the sites must establish point-to-point connections with each site, which leads to scalability problems. The mpls vpn that provides multicast support does not have this problem.
Multicast mpls vpn supports multicast by bringing Multicast Route information into the route forwarding table. When the customer's border CE) vro forwards multicast traffic or multicast control information to the provider's border PE) vro, the PE router queries the multicast VPN route forwarding table MVRF) for forwarding decision. How does the network of a service provider distinguish different VPNs to transmit multicast traffic and multicast control information?
A group of multicast traffic MVRF forms a multicast domain. For example, a customer's multicast domain can cover all the customer's edge routers that deliver specific multicast traffic. Multicast VPN creates a static default multicast allocation tree (MDT) for each multicast domain. This MDT defines the path between the provider's border routers that transmit multicast traffic in the multicast domain. For high-bandwidth application multicast types such as videos, a dynamic MDT is also provided, called the data multicast distribution tree Date MDT ), when the multicast traffic exceeds a set value, the dynamic MDT is established, so that the multicast traffic can flow along an optimized path. The following example describes the transmission process of multicast in mpls vpn. As shown in figure 1, the provider's MPLS core consists of four routers, namely P1, P2, P3, and P4, which are connected to their respective provider's border routers, the customer's VBR is connected through the VPN channel provided by the PE router. VPN Customer A is composed of Site a, B, and c, and VPN Customer B is composed of Site a and B. The default multicast distribution tree (MDT) of Customer A includes P1, P2, and P4, and the connected PE router, because the P3 router is not included only for other customers. In the multicast application of Customer A, site B connects to the multicast server O. Assume that A member of Site a of Customer A wants to join the multicast instance. As shown in figure 1, host M sends an IGMP group addition request, and the customer's border router CE1 forwards the request to PE1, the provider's border router PE1 forwards the multicast request to the provider's border router PE2 along the default multicast distribution tree of the multicast domain, when PE2 adds a request to the customer's border router CE2, CE2 starts to forward multicast data to PE2, and PE2 forwards multicast data along the default multicast distribution tree. When the multicast data is forwarded, PE2 detects that the multicast traffic exceeds the established data group.
Set the value of the multicast distribution tree. PE2 notifies all PE routers in the multicast domain of Customer A of the information created by the multicast distribution tree along the default multicast distribution tree. After A short interval, PE2 begins to distribute the multicast traffic along the data multicast tree. Because only PE1 sends multicast requests, only PE1 is added to the data multicast distribution tree and receives traffic.