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time to live (TCP/IP) (TTL)

Time to Live(TTL) is a lifetime information for messages. The TTL information is used so that data packets or messages do not circulate indefinitely in the networks and unnecessarily load the transmission capacities. The TTL algorithm exists in the header of the IP protocol and in Bluetooth networks.

  1. In the IP header, the TTL (Time to Live) field is a 1- byte counter field used to limit the lifetime of datagrams. The counter is located in the IP header and is decremented by the value "1" from each network node that the datagram passes through, starting at 255 (8 bits). When the IP packet has passed through 255 network nodes, the value "0" is reached and the datagram is discarded. This is done in order not to load the network unnecessarily with datagrams circling in the network. With the decrementing also the checksum is changed.
    TTL field in the IP header

    TTL field in the IP header

    Since the datagram can also stay in a router for a longer time, the TTL value is decremented by both the hop and the time. The second is defined as the time unit. For example, if the datagram is in a network node for 5 seconds, the TTL value is reduced by 5. The relative lifetime of a datagram is thus a maximum of 255 seconds or it corresponds to the time the datagram needs to pass through 255 routers.
  2. In Bluetooth networks, each radio node stores the received messages in a list. When the messages are received, the node compares whether the message has already been stored and sent. If the message is not in the list, the node sends the message. By checking the message, it is ensured that the message is not sent repeatedly. The TTL method of Bluetooth works like that of the IP protocol with decrementation. A TTL value can be set when the message is generated. This value is reduced by the value 1 when passing through each individual node. Theoretically, the message can pass through a maximum of 127 nodes before it is no longer forwarded.
Englisch: time to live (TCP/IP) - TTL
Updated at: 24.08.2017
#Words: 330
Links: through the lens (photo camera) (TTL), lifetime, information, data, transmission
Translations: DE

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