Kindly explain this to me. First of all, services like Netflix and Youtube are not streaming services. They are video on demand services. This means that they implicitly require unicast functionality. The video that you watch on Youtube is being watched only by you at that specific time and no one else. Someone else may click on it a few seconds before or after you, but this is a uniquely separate event. Streaming services that are candidates for using multicast include online radio and the broadcasting of live events over the Internet.
However there are two reasons w. Ask a question or join the discussion by visiting our Community Forum. Skip to content Search for: Search. You are here: Home » Multicast. Lesson Contents. What about the Internet? Since multicast is so much more efficient than unicast, large companies like Netflix and Youtube must be using this to stream videos right?
Unfortunately multicast on the Internet has never really been implemented. These large video companies use LOTS of unicast traffic to deliver videos to their customers.
The only place where you might see multicast on the Internet is your local ISP. They typically use multicast for IPTV to deliver video to their own customers. Forum Replies Very clear explanation Rene. Solid information as usual.
Thanks for the breakdown. Hello Ashutosh First of all, services like Netflix and Youtube are not streaming services. The following multicast packet was sent from my NetWare server.
Notice the destination MAC address it's a multicast :. Analysis of a multicast destination MAC address:. So now you should be able to understand how computers can differentiate between a normal or unicast packet and a multicast packet. Again, the destination MAC address E is not the MAC address of a particular host-computer but the MAC address that can be recognised by computers that are part of the multicast group. I should also note that you will never find a source address that is a multicast MAC address, the source address will always be a real one, to identify which computer the packet came from.
This Rule is covered in the last section of this page, but you don't need to know it now in order to understand Hardware multicasting. The IP Multicast is the second part of multicasting which, combined with the hardware multicasting, gives us a multicasting model that works for our Ethernet network. If hardware multicasting fails to work, then the packet will never arrive at the network layer upon which IP multicasting is based, so the whole model fails.
Once Layer 2 Datalink picks the multicast packet from the network because it recognises it, as the destination MAC address is a multicast it will strip the MAC addresses off and send the rest to the above layer, which is the Network Layer. At that point, the Network Layer needs to be able to understand it's dealing with a multicast, so the IP address is set in a way that allows the computer to see it as a multicast datagram. A host may send multicast datagrams to a multicast group without being a member.
Multicasts are used a lot between routers so they can discover each other on an IP network. The OSPF router must send this "hello" packet to an assigned multicast address, which is The picture below is a screenshot from my packet sniffer, it shows a multicast packet which was sent from my NetWare server, notice the destination IP address:.
The screenshot above shows the packet which was captured, it's simply displaying a quick summary of what was caught. But, when we look on the left, we see the above packet in much more detail.
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There are many different multicast protocols and modes of operation, each optimized for a particular scenario. Many of these are still at an early stage of standardization. However, they all operate in the same general way, as follows.
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