When a device on a packet switching network sends information to another device, it takes a certain amount of time for that information, or data, to travel across the network and be received at the other end. Normally, before data is sent, it is separated into pieces commonly called packets, which are small enough to be handled by a network. As these information chunks traverse the network, they are examined and manipulated by devices called routers, which help direct and manage data flow. The time it takes for a routing device to take a packet in and decide what to do with it is called processing delay.
Processing delay is a part of the total network delay, which occurs during end-to-end transmissions. Other delays that might occur include transmission delay, propagation delay and queuing delay. Routers are computing devices that are specialized to make quick decisions about what to do with and where to send packets, and they use programs and hardware logic to perform these tasks. The fields of computer engineering and network engineering strive to develop and use concise software and optimized circuitry in routers. This reduces the time it takes for routers to make choices, thus reducing the processing delay.
Although endpoints also process incoming packets by examining and stripping away packet headers, the primary focus of processing delay typically concentrates on routers and somewhat on switches. This is because there can be many routers and a lesser amount of switches between two endpoints. Routers normally cause the most significant portion of processing delay. If one were to issue a traceroute command to a website from a command prompt or shell, one would see that there are indeed quite a few routers along the pathway. Non-routing switches that do not manipulate packet headers cause far less processing delay because they examine only the open systems interconnection (OSI) model layer two header.
When a router takes in a packet, it could be required to make many decisions that contribute to the overall processing delay. Packet-switched networks can be like a spider web of networks all hooked together with routers, so a router must choose which network it needs to send a packet to next. This action is generally called routing.
A router might also have to act as a gatekeeper and use access lists to allow or disallow packets to continue on their journey. Network address translation, which changes numbers called Internet protocol (IP) addresses on a packet, might need to be performed. Processing delay takes into account all of these procedures. There are other processes as well, and they can be included in the total time for processing delay if they are used.
As one can see, processing delay can be a large contributor toward total network delay. Reducing delay is very important for assuring quality network functionality. This helps to ensure that the Internet and other networks remain fast and effective.