what is multicast in computer networking?

Answer 1

Here it is in a sentence: Unicast is "one to one", broadcast is "one to all", multicast is "one to some", where "some" can be from one to all. Huh!? Here's what it means. A unicast packet is destined for a single host, so it's one to one, meaning one sender to one receiver. A broadcast packet is for everybody, one to all, one sender to all possible receivers. A multicast packet is meant to be delivered to some SUBSET of all the hosts, usually more than one host but much less than every single host.

Suppose for example you have a video surveillance application, say a bunch of video cameras connected to a DVR in the lobby of a bunch of banks. Suppose there are 10 executives at the headquarters who want to watch video from one of the banks where there was a robbery. Without multicasting, they would have to create 10 individual unicast streams over the network and this multiplies the network traffic by 10 times. With multicasting, it would only have to cross the network one time, and if the 10 people are on different LANs or in different sites, the multicast stream would only get replicated where necessary, instead of flooding every link of every network.

Within a single LAN, multicasting works much like broadcasting, and frames get sent out every port on the lan (every port in the broadcast domain) unless there is some type of multicast optimization turned on like IGMP snooping. Across larger networks, it is up to the routers to run a multicast routing protocol like PIM.

Answer 2

Multicasting is sending information out to multiple PCs. Normally when a packet of information is sent on a network, it is address to one PC, and only that PC will accept the packet. All other PCs simply pass in on until it reachs the right one. With multicasting, the packet is sent with a general address. Any PC receiving it can and accept, and also pass it on. Multicasting is used for streaming live video and similar things where many computers are expected to receive it all at the same time.

Answer 3

Multicast is like broadcast but it can be sent from multiple segments (the router does not block it--as long as its not programmed to do so) in broadcast the request can be sent so that all listening nodes can recieve the message (servers use this). the only problem with broadcast is that it could create broadcast storms if it passed rotuer to router (think the internet) the problem with this of course was with huge compaines that may have routers to segment thier network may need a service server to tranverse all these points. The following will explain it futher:

Multicast

What is Multicast?

Multicast is a set of technologies that enables efficient delivery of data to many locations on a network. In today's Internet, the dominant model of communication is "unicast" - the data source must create a separate copy of the data using for each recipient. When there are too many recipients, and when large amounts of data (e.g., streaming video) are being sent, unicast becomes prohibitively wasteful bandwidth. The key behind multicast is to create each recipient's copy of the data at a point close to that recipient as possible, thus minimizing the bandwidth consumed.

P network multicasting

The ability of SLP to automatically discover services that are available on the network, without a lot of setup or configuration, depends in a large part on the use of IP multicasting.
Multicasting methods
There are three methods to send messages across an IP network:

* Unicast
* Broadcast
* Multicast

Unicast method

The unicast method is the most common method, which requires that a sender of a message identifies one and only one target for that message. The target IP address is encoded within the message packet, and is used by the routers along the network path to route the packet to the proper destination. If a sender wants to send the same message to multiple recipients, then multiple messages must be generated and placed on the network, one message per recipient. When there are many potential recipients for a particular message, this places an unnecessary strain on the network resources because the same data is duplicated many times. The only difference is the target IP address encoded within the messages.
Broadcast method

In cases where the same message must be sent to many targets, the broadcast method is a much better choice than unicast because it puts much less strain on the network. Broadcasting uses a special IP address, 255.255.255.255, which indicates that the message packet is intended to be sent to all nodes in a network. As a result, the sender of a message only needs to generate a single copy of that message and transmit it to multiple recipients, that is, to all members of the network. The routers, in essence, multiplex the message packet because it is sent along all possible routes in the network to reach all possible destinations.

This method puts much less strain on the network bandwidth because only a single message stream enters the network, as opposed to one message stream per recipient. However, it puts much more strain on the individual nodes (and routers) in the network because every node receives the message even if every node is not interested in the message. This means that those members of the network that were not the intended recipients but who received the message anyway, must receive and then discard the unwanted message. Due to this inefficiency, in most network configurations, routers are configured to not forward any broadcast traffic, which means that any broadcast messages can only reach nodes on the same subnet as the sender.
Multicasting method

Multicasting can be thought of as a more sophisticated broadcast method, which aims to solve some of the inefficiencies inherent in the broadcasting mechanism. With multicasting, as with broadcasting, the sender of a message only has to generate a single copy of the message, saving network bandwidth. However, unlike broadcasting, with multicasting not every member of the network receives the message; only those members who have explicitly expressed an interest in the particular multicast stream receive the message.

Multicasting introduces a concept called a multicast group in which each multicast group is associated with a specific IP address. A particular network node (host) can join one or more multicast groups, which notify the associated routers that there is an interest in receiving multicast streams for those groups. When the sender, who does not necessarily have to be part of the same group, sends messages to a particular multicast group, that message is routed appropriately to only those subnets that contain members of that multicast group. This process avoids the entire network being flooded with the message, as is the case for broadcast traffic.

* IP network multicast addresses
Service Location Protocol (SLP) uses address 239.255.255.253 for all its multicast traffic. The port number for SLP is 427, for both unicast and multicast.
* IP router configuration
Routers send messages from a source to a destination along a network path. This topic discusses the most common router configurations for unicast and multicast messages.

Parent topic: MDM device discovery

Answer 4

to use multicast in networking, you must have access to large harddrives in more than one country.

Answer 5

What Is Multicast