Packetswitching

Packet switching is a method of breaking down digital data into smaller units called packets for transmission over a shared network. Each packet contains a header with addressing, sequencing, and control information, and a payload with a portion of the user data. Packets may take different routes from source to destination and are reassembled into the complete message at the destination. This approach contrasts with circuit switching, which reserves a dedicated path for the duration of a communication session.

Operation: In packet-switched networks, routers examine the header and forward packets toward the destination using routing tables and algorithms. Packets may experience variable delays and may arrive out of order, requiring reassembly and error handling by higher-layer protocols. In datagram networks, each packet is routed independently; in virtual-circuit networks a logical path is established before data transfer, and packets follow that path with potentially less per-packet routing.

Types and technologies: The Internet primarily uses datagram packet switching with IP, relying on protocols like TCP or UDP for transport and reliability. Other approaches such as virtual circuits are used in MPLS, ATM, and some older networks. Fragmentation may occur when a packet is larger than the next link's maximum transmission unit; reassembly occurs at the destination.

Advantages and limitations: Packet switching makes efficient use of network resources, supports multiple communications concurrently, and provides resilience to link failures. It introduces overhead from packet headers, potential delays due to queuing, and the possibility of out-of-order delivery. Reliability is typically provided by transport-layer protocols rather than the network itself in modern IP networks; quality of service can be implemented through resource management and signaling in certain systems.

History and impact: The concept was independently proposed by Paul Baran and Donald Davies in the 1960s. It became the basis of ARPANET and the modern Internet, which use packet switching to route data across heterogeneous networks.