Unicast, broadcast, and Multicast

Unicast, broadcast, and Multicast

 

I. Introduction

1. Three IP addresses are available: unicast address, broadcast address, and multicast address.

2. broadcast and multicast are only applied to UDP. TCP is a connection-oriented protocol that means two processes (determined by the port number) run on two hosts (determined by the IP address) there is a connection between them.

3. How is a packet transmitted to a process on the host?

1> the host Nic only receives packets whose destination address is the physical address or broadcast address of the NIC. (Currently, most NICs are configured to receive packets from multicast addresses or some subnet multicast addresses ).

2> after the network adapter receives the packet, it delivers the packet to the IP layer. The IP layer determines whether the destination IP address is a local IP address or multicast address. If yes, it receives the packet. Otherwise, it discards the packet.

3> the IP layer transmits the received packets to the transport layer, and the transport layer transmits the packets to a process at the application layer through the port number.

2. unicast, multicast, and broadcast

1. unicast: one-to-one communication mode between hosts. vswitches and vrouters 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.

1> advantages of unicast:

The server responds to client requests in a timely manner.

The server can send data that is not accessible to each customer for personalized services.

2> disadvantages of unicast:

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.

The existing network bandwidth is in a pyramid structure, and 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.

2. Broadcast: Sometimes a host sends frames to all other hosts on the Internet. This is broadcast. (A common ARP protocol is broadcast ). The physical MAC addresses of multicast targets are 0xff, 0xff, 0xff, 0xff, 0xff, and 0xff.

1> broadcast advantages:

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

Server traffic load is extremely low because the server does not need to send data separately to each client.

2> disadvantages of broadcast:

It is impossible to provide personalized services in a timely manner based on the requirements and time of each customer.

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.

Ø broadcast cannot be transmitted over the Internet Broadband Network (preventing broadcast storms)

4. multicast (Multicast) is between unicast and broadcast: frames are transmitted only to multiple hosts in multicast groups.

1> 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.

2> advantages of Multicast:

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.

The multicast protocol replicates and forwards data streams based on the receiver's needs. Therefore, the total 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.

The same as the unicast protocol, this protocol allows transmission over the internet broadband network.

3> disadvantages of Multicast:

Compared with unicast protocols, 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.

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.