"Unicast", "Multicast", and "Multicast"

From "Baidu Knows", I don't know!

 

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 mannerAll 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.

Cable TV networks are typical broadcast networks.Our TV actually receives signals from all channels, but only restores signals from one channel to the screen.

InData NetworkThe existence of broadcast is also allowed, but itsRestricted within the LAN of L2 Switches,Prohibit broadcast data from passing through vroTo prevent large-area hosts from being affected by broadcast data.

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.Broadcast cannot be transmitted over the Internet Broadband Network. (Yang Guo Note: should this be for cable TV ?)

 

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.