The rapid growth of the Internet has brought equally rapid growth in all types of network data, voice, and video information. New services, such as e-commerce, online conferencing and auctions, video on demand, and e-learning, have also quickly emerged in the global market. These new services are point to multi-point (P2MP) compliant and offer high levels of security, bandwidth, and profit.
IP data transmission is based on IP addresses. The Internet uses IP addresses to identify and distinguish various devices on the network.
IP packets use IP addresses to identify the sending objectives, that is, the destination addresses of packets.
Hosts receive only the IP packets with the IP addresses they can identify.
Switchs search the next hop according to the destination address of an IP packet to forward the packet.
The process of transmitting IP data is as follows:
A source sends an IP packet. The destination address field carried in the packet is the IP address that can be identified by the destination host.
Switchs forward the packet to the network segment where the destination host resides. The network segment can be connected to multiple hosts.
Each host checks the destination addresses of all the packets in the network segment and receives only the IP packets whose destination addresses it can identify. If the IP addresses identified by each host in the network segment are different, the packets received by each host are different.
IP addresses identified by hosts are classified into the following types:
Unicast IP address
A unicast IP address can identify only one host and a host can identify only one unicast IP address. An IP packet that uses a unicast IP address as the destination address can be received by only one host.
Broadcast IP address
A broadcast IP address can identify all hosts in a network segment, but a host can identify only one broadcast IP address. An IP packet that uses a broadcast IP address as the destination address can be received by all hosts in a network segment. IP broadcast packets cannot be transmitted across network segments.
Multicast IP address
A multicast IP address can identify multiple hosts at different locations and a host can identify multiple multicast IP addresses. An IP packet that uses a multicast IP address as the destination address can be received by multiple hosts at different locations throughout the network.
Based on the three preceding types of IP addresses, IP transmission is classified into the following modes:
IP unicast
IP broadcast
IP multicast
The three types of transmission modes are used for P2MP data transmission. IP multicast is the most suitable for IP transmission of P2MP.
Unicast transmission
Features of unicast transmission
A unicast packet uses a unicast address as the destination address. The source sends a separate unicast packet to each receiver. If several receivers exist on the network, the source sends the unicast packets to each receiver.
Unicast packets are forwarded independently in an exclusive transmission path on the network. The source sends one copy of unicast packets for each receiver on the network.
Disadvantages of unicast transmission
In unicast mode, the data transmitted is in direct proportion to the number of users that request the data. If several users request the data, copies of the data flow appear on the network. This wastes processor resources and network bandwidth.
Unicast transmission is suitable for the network for a small number of users. If there are many, transmission quality cannot be ensured.
Broadcast transmission
Features of broadcast transmission
A broadcast packet uses a broadcast address as the destination address. The source sends only one packet to the broadcast address.
The source copies the packet and sends it to all hosts in the network segment, regardless of whether the hosts need it.
Disadvantages of broadcast transmission
In broadcast mode, the source and hosts must be in the shared network segment, and all hosts in the network segment can receive the packets sent by the source.
The broadcast transmission is suitable only for the shared network segment and cannot meet the requirements for information security and payment of services.
Multicast transmission
Figure 1 shows a network using multicast transmission. The network has a source, and User A and User C request information from the network.
Figure 1 Multicast transmission
Features of Multicast Transmission
A multicast packet uses a multicast address as the destination address. As shown in Figure 1, the source sends only one packet to the multicast address: packets for the multicast group.
The multicast protocol deployed in the network establishes a tree-shaped route for the packet. The root of the tree connects to the source, and the branches of the tree connect to all multicast receivers. As shown in Figure 1: Source→ Switch B → Switch E [ →Switch D → User A | → Switch F → User C ].
Advantages of multicast
In multicast mode, a single flow of information is sent to a group of users along the multicast distribution tree. A maximum of one data flow copy exists on each link. Unlike unicast mode, an increase in the number of users does not heavily load the network in multicast mode. This lightens the loads of the server and CPU.
Multicast packets can be transmitted across network segments. Users who do not request a packet cannot receive it. Unlike broadcast mode, information in multicast mode can be transmitted over long distances. The information is transmitted only to the place where there is a receiver, which guarantees the security of the information.
The multicast technology effectively solves the problem of one source and multiple receivers and implements the efficient data transmission of P2MP on the IP network.
Applications of multicast
Multicast is applicable to any P2MP data transmission, including the following:
Multimedia and stream media
Communications for training and telelearning
Data storage and finance (stock) applications
IP multicast technology applies to Internet information services provided by an Internet Service Provider (ISP), such as online broadcasts, network TV, distance learning, remote medicine, and real-time video and audio conferencing.
