The Internet Multicast

By Raul Bernardino

Introduction:

In today technology we have two options in sending packets over internet simultaneously. They are broadcasting and repeating the transmission. The broadcasting will be higher cost because we have to invest in the bandwidths. It is real-time broadcasting. If we compare to the traditional broadcasting it will count have many recipients and geographical location or the recipients. The repeating transmission will be lower cost because it is transmitted to the target and as it is needed.

“The broadcasting routing in the network will be transmitting from one source node to the rest of the nodes in the network. While, the multicasting routing is sending a copy of the packet from one node to the rest of the nodes”, Kurose J.F., Ross K.W., (2010, P.433).

The broadcast routing algorithms is transmitting N copy of the packet to N destination numbers. The packet duplication number as per destination number. However it is inefficient because not all notes are willing to receive the packets. And it is uncontrolled network flooding.

The multicast routing is only transmitting to a subnet of the network nodes. This is requiring packets to deliver to the nodes as follows: One or more sender sends the packets to the destination group of the receivers. For instance developers update software update to the users, streaming multimedia such as audio and video. Here we face to issues: How we identifier the receiver and how to address the packets sent to the receivers. In the case of the uni-cast the data-grams identified users with IP source and IP destination in the data-grams. In the case of the broadcast it broadcast from one single point to every node in the networks so it does not need destination address.

How do multicast works? The multicast packets are using addresses of the indirection. That is a single address to identify recipients group to send all packets to the group members. In the internet address the single identifier is class D which is multicasting IP address. The group op address that classifies in the class D is called multicast group. Below is the diagram on how the one single source making multicast session data to send the same information to the different location or nodes.

It can be shared also the resource of the multicasting to the different nodes in the group. Where, two or more sources of the multicast use one rendezvous point (RP) to distribute the same information to the rest of the group. Below diagram show how it distributes from RP to the rest of the group.

The following questions what may raise are? How do we join the sessions, when it start and terminate? Is there a group member restricted? And so on so for. The answers for those questions is IGMP which is stand for Internet Group Management Protocol.  The IGMP ver. 3 is operating between the hosts and router. And it is operating directly to attach host information to the router. The IGMP sent membership_query message from the router to the rest of the hosts that attached to the router. The host respond to the message and sent IGMP membership report to the router. In this way router can update the host membership information. If the host has been register before and it is not responding the IGMP membership_query message then message in IGMP would be leave_group.

References list:

• Kurose J.F., Ross K.W., 2010: Computer Networking; A Top-Down Approach: 5^th Edition’; Boston, Addison-Wesley
• Lecture notes, CPCOMM_week4_lecture
• Handley, M. Internet Multicast Today, [on-line]. Available from: http://www.cisco.com/web/about/ac123/ac147/ac174/ac198/about_cisco_ipj_archive_article09186a00800c851e.html  (Accessed date: August 27, 2011)
• Köhler, W.,( January, 2009),The Internet multicast service model, [on-line]. Available from: http://ce-gmbh.com/ComputerCommunication/multicast.htm (Accessed date: August 27, 2011)