Stands for “Time to Live.”
TTL can consult with considered one of a number of ideas in pc networking. It can consult with the a part of the TCP/IP protocol that units an expiration timer for each knowledge packet despatched over a network. It may consult with how lengthy a server shops cached info earlier than refreshing it.
TCP/IP
When an information packet is shipped from one pc to a different over the Internet, it travels by transferring from one network to a different till it reaches its vacation spot. Each step alongside the journey is known as a “hop.” Each knowledge packet touring alongside a network provides a small quantity of overhead, so packets unable to succeed in their vacation spot hopping round indefinitely would decelerate network efficiency considerably. To stop this, each knowledge packet is given a TTL depend when despatched to stop it from hopping round without end.
An information packet’s TTL depend is an 8-bit quantity (between 1 and 255, usually set within the center between 32 and 128) that specifies the utmost variety of hops it could actually take earlier than expiring and being discarded. Every time {that a} knowledge packet hops from one router to the subsequent, the TTL depend is decreased by 1. If the TTL depend reaches 0 earlier than it reaches its vacation spot, it is discarded by the router.
Cache
TTL may consult with the period of time {that a} server retains a cache of information for retrieval earlier than refreshing it. For instance, a DNS server may have a TTL worth for every file, measured in seconds, that controls how lengthy it could actually serve a file earlier than refreshing it. These TTL entries will be set as little as 30 seconds, however lower-priority information will be set so long as 86,400 seconds (24 hours).
A CDN server may have a TTL worth for each asset it shops that controls how lengthy it retains a cached copy earlier than it checks the origin server for adjustments. This permits the CDN to examine frequently-updated information usually, whereas different property will be cached for days or even weeks between updates.
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