Communications Protocols: Overview
Packet Switching
All the data transported over the Internet, such as files, messages, etc., is split into individual atomic “units of transportation,” called packets, that have certain well defined formats and structure. Packet switching protocols divide messages into packets before they are sent and transmit the packets across the internet.
Each packet is transmitted individually and can even follow different routes to its destination visavis other packets from the same stream of data transmitted over the Internet. Once all the packets forming a message arrive at the destination, they are recompiled into the original message. The communications method that splits and groups the transmitted data into suitably sized packets is called packet switching, and the communications protocol that is used to split, transmit, keep track of, and assemble packets over the Internet is called the Internet Protocol (IP). Every device on the Internet (and devices that are connected to the Internet) has a unique IP address.
As stated earlier, a packet is the smallest unit of information transmitted over the internet. It consists of protocol headers and payload. Headers contain control information or metadata about the data that they are actually carrying. This includes information such as the destination and source IP addresses, length of the packet, priority of the packet, as well as the sequence of the packet in the data stream that is later used in assembling the packets in order. The actual data being transferred is stored in the Payload.
To summarize, packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets.
In Connectionless Packet Switching, each packet of a message is transmitted independently of other packets. They may be routed along different paths between the source and the destination. Note that since different packets can travel along different routes, they may arrive out of order. When all the packets arrive at the destination, they are all reassembled in the proper order by the protocol in order so as to recreate the original message at the destination. This type of packet switching is a connectionless switching method since it does not require a dedicated connection between the source and destination. This type of switching is also known as Datagram Switching.
Connectionless Packet switching is useful for transferring data and it maximizes the usage of network bandwidth since different packets can travel along different paths. It also makes Internet more reliable since packet transmission from one destination to another is less sensitive to the failures of individual nodes of the Internet. However, since packets can arrive out of sequence at the destination, packet switching does not work very well for high performance applications such as realtime video transfers (streaming video).
With Connection Oriented Packet Switching a virtual connection is defined and preallocated in each device along the path during a connection setup phase before any packet is transferred. The packets include a connection identifier rather than address information and are delivered in order. This type of packet switching is also called Virtual Circuit Switching because a virtual circuit is set up between the source and destination.
After considering how communication protocols enable data to traverse our simplified internet model, it is helpful to look at an example of real network such as Verizon to get a sense of the massive infrastructure that exists to manage actual internet traffic including the complex and sophisticated topology of pipes that vary in size and capacity as well as the routers and hubs that connect them.
Explore the Interactive Verizon Global Network Website for an illustration of the size and complexity of their infrastructure.