Different types of node to node communications used in Computer Networks

Basically, there are four types of node to node communication used in Computer Networking. They are Unicasting, Multicasting, Broadcasting and Anycasting.

Unicasting :

When a source node sends a packet or frame destined to exactly one machine node, then it is termed as Unicast communication. This is basically point to point communication. Unicasting can be done at the physical layer (point to point links) or at the data link layer or at the network layer. Most of the standard application layer protocols are from a source node to a single destination node. Examples include HTTP, FTP, SMTP etc.


When a source node sends a packet or frame to a group address, destined only to a set of nodes that are part of a specific group, then it is termed as multicast communication. The group is termed as a multicast group. Multicasting is a form of point to multi-point communication, where communication is from a source node to multiple end nodes, but not to all end nodes of a network. It is communication from a source node confined to all the members of a specific group. Multicasting can be done at both data link and network layers. Multicasting is used for real-time applications like Voice over IP, audio/video conferencing, video or audio broadcasting to specific groups, Video On Demand (VOD) etc.


When a source node sends a packet or frame destined to all  nodes in a network, then it is termed as broadcast communication. Broadcasting is point to multi-point communication. Due to the increased amount of network traffic created by broadcasting, it is normally used only within a network, when it is essential to address all nodes of a network. Broadcasting can be done at the physical (bus lines),  data link and network layers. Examples of broadcasting include routing protocol update packets, DHCP address negotiation packets, Layer 2 flooded frames, spanning tree protocol frames etc.


Anycasting :

When a source node sends a packet or frame to a special destination IP address known as Anycast IP address,  then it is termed as Anycast communication. Anycasting has been introduced only in IPV6 and is not present in IPV4. It is a form of point to point communication, where a source node tries to reach any one instance of a server machine. Normally, for load balancing and redundancy purposes, there could be multiple instances of the same server machine, running at different points in the network (e.g. HTTP or DHCP or DNS servers). In such cases, all instances of the server machine are given the same Anycast IP address. Source nodes trying to contact the server would send IP packets to the common Anycast IP address. The network would then route the IP packet to that instance of the server machine that is closest to the source node. Anycasting is normally used only at the network layer, that too only if IPV6 is the network layer protocol under use.

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