Differences between broadcast, multicast, and Multicast

Source: Internet
Author: User

The terms unicast, multicast, and broadcast are used to describe the communication methods between network nodes. So what exactly do these terms mean? What is the difference ?.

1. unicast: communication between network nodes is like a conversation between people. If a person speaks to another person, the network technology is used to describe "unicast". At this time, information is received and transmitted only between two nodes. Unicast has been widely used in the network, and most of the data on the network is transmitted in the form of unicast, but the network users do not know it. For example, when sending and receiving emails and Browsing webpages, you must establish a connection with the mail server and web server. At this time, the unicast data transmission mode is used. However, "point-to-point communication" is usually used instead of "unicast", because "unicast" is generally used in comparison with "Multicast" and "broadcast.

2. multicasting: "multicasting" can also be called "multicast". There are not many applications in network technology, and online video conferences and on-demand videos are particularly suitable for multicasting. Because if the single-play mode is used for transmitting data one by one node and how many target nodes are there, there will be many transmission processes. This method is obviously extremely inefficient and is not desirable; if you use a broadcast method that does not differentiate the target and sends all data, although the data can be transferred at one time, it is clear that the purpose of distinguishing specific data receiving objects is not achieved. Multicast can be used to transmit data from all target nodes at a time, or to transmit data only to specific objects. Multicast over an IP network is generally achieved through multicast IP addresses. Multicast IP address is a Class d ip address, that is, the IP address between and Windows
The DHCP manager in 2000 supports automatic allocation of multicast IP addresses.

3. Broadcasting: "broadcasting" has many applications in the network. For example, the client can automatically obtain the IP address through DHCP through broadcasting. However, compared with unicast and multicast, broadcast occupies almost all the bandwidth of the network in the subnet. Let's take a meeting as an example. Only one person can speak at the venue. Imagine that if everyone uses a microphone to speak at the same time, it will turn into a box of porridge. The working principle of the hub determines that it is impossible to filter broadcast storms. General switches do not have this function. However, some network switches (such as omnidirectional QS series switches) as well as the broadcast storm filter function, the router itself has the function of isolating the broadcast storm. Broadcast storms cannot be completely eliminated, but they can only be transmitted within the same subnet, just as the sound of speakers can only be transmitted within the same venue, therefore, in a large and medium-sized LAN consisting of hundreds or even thousands of computers, subnets are generally divided, just like isolating a hall from many small halls by walls, to isolate broadcast storms.
In an IP address, the broadcast address is represented by the IP address "". This IP address represents all IP addresses in the same subnet.

There are three communication modes in the current network: unicast, broadcast, and multicast. Among them, multicast occurs at the latest time, but it also has the advantages of unicast and broadcast, it has the most promising future.

I. unicast:

One-to-one communication mode between hosts. vswitches and routers in the network only forward data and do not copy the data. If 10 clients need the same data, the server needs to transmit the data one by one and repeat the same work for 10 times. However, because it can respond to each customer in a timely manner, all current web browsing uses the IP Unicast protocol. Vrouters and vswitches in the network select a transmission path based on the target address, and transmit the IP Unicast data to the specified destination.
Advantages of unicast:

1. The server responds to client requests in a timely manner.

2. The server can easily implement personalized services by sending inaccessible data to requests of each customer.

Disadvantages of unicast:

1. the server sends data streams to each client. The server traffic is equal to the number of clients × client traffic. The server is overwhelmed in streaming media applications with a large number of customers and high traffic per client.

2. The existing network bandwidth is a pyramid structure. The inter-city backbone bandwidth is only equivalent to 5% of the total bandwidth of all its users. If all the unicast protocols are used, the network trunk will be overwhelmed. Now, P2P applications have frequently congested the trunk. As long as 5% of customers use the network at full speed, no one else needs to play. It is almost impossible to expand the trunk by 20 times.

Ii. Broadcast:

One-to-all communication mode between hosts. The network copies and forwards signals from each host unconditionally, all Hosts can receive all the information (whether or not you need it). Because you do not need to select a path, the network cost can be very low. A cable TV network is a typical broadcast network. Our TV actually receives signals from all channels, but only restores signals from one channel to a screen. Broadcast is also allowed in the data network, but it is restricted within the LAN of a layer-2 switch. Broadcast Data is prohibited from passing through the router to prevent broadcast data from affecting hosts in a large area.
Broadcast advantages:

1. Simple network equipment, simple maintenance, and low network deployment cost

2. Because the server does not need to send data separately to each client, the server traffic load is extremely low.

Disadvantages of broadcast:

1. Unable to provide personalized services in a timely manner based on the requirements and time of each customer.

2. The bandwidth allowed by the server to provide data is limited. The maximum bandwidth of the client = the total bandwidth of the service. For example, the cable TV client line supports 100 channels (IF digital compression technology is used, 500 channels can be provided theoretically ), even if the service provider has more financial resources to configure more sending devices and change them to the fiber trunk, the limit cannot be exceeded. That is to say, it is impossible to provide more diversified and personalized services to many customers.

3. Broadcasting is prohibited from being transmitted over the Internet broadband network.

Iii. Multicast:

One-to-one communication mode between hosts, that is, hosts added to the same group can accept all data in the group, vswitches and vrouters in the network only copy and forward the required data to the demanders. A host can send a request to a vro to join or exit a group. The vro and vswitch in the network can copy and transmit data, that is, only the data in the group is transmitted to those hosts in the group. In this way, data can be transmitted to multiple hosts that need to be added to the group at a time, and other communications between hosts that do not need to be added to the group are not affected.
Advantages of Multicast:

1. clients with the same data stream need to join the same group to share a data stream, saving the server load. It has the advantages of broadcast.

2. Because the multicast protocol replicates and forwards data streams based on the receiver's needs, the total service bandwidth of the server is not limited by the bandwidth of the client access end. The IP protocol supports over 0.2 billion 268435456 () multicast packets, so it provides a wide range of services.

3. This protocol is the same as the unicast protocol that allows transmission over the internet broadband network.

Disadvantages of Multicast:

1. Compared with the unicast protocol, there is no error correction mechanism and it is difficult to make up for packet loss errors, but it can be compensated through a certain Fault Tolerance Mechanism and QoS.

2. although the current network supports multicast transmission, it still needs to be improved in terms of customer authentication and QoS. These shortcomings have mature solutions theoretically, it only needs to be gradually applied to existing networks.

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