Keepalive
Encyclopedia
A keepalive is a message sent by one device to another to check that the link
between the two is operating, or to prevent this link from being broken.
. After a signal is sent, if no reply is received the link
is assumed to be down and future data will be routed via another path until the link is up again. A keepalive signal can also be used to indicate to Internet infrastructure that the connection should be preserved. Without a keepalive signal intermediate routers can drop the connection after timeout.
Since the only purpose is to find links that don't work or to indicate links that should be preserved, keepalive messages tend to be short and not take much bandwidth
. However, their precise format and usage terms depend on the communication protocol.
supports explicit means for maintaining an active connection between client and server.
(TCP) keepalives are an optional feature, and if included must default to off. The keepalive packet contains null data. In an Ethernet
network, a keepalive frame length is 60 bytes, while acknowledge to this, also a null data frame, is 54 bytes. There are three parameters related to keepalive:
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
between the two is operating, or to prevent this link from being broken.
Description
A keepalive signal is often sent at predefined intervals, and plays an important role on the InternetInternet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
. After a signal is sent, if no reply is received the link
Data link
In telecommunication a data link is the means of connecting one location to another for the purpose of transmitting and receiving information. It can also refer to a set of electronics assemblies, consisting of a transmitter and a receiver and the interconnecting data telecommunication circuit...
is assumed to be down and future data will be routed via another path until the link is up again. A keepalive signal can also be used to indicate to Internet infrastructure that the connection should be preserved. Without a keepalive signal intermediate routers can drop the connection after timeout.
Since the only purpose is to find links that don't work or to indicate links that should be preserved, keepalive messages tend to be short and not take much bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
. However, their precise format and usage terms depend on the communication protocol.
HTTP keepalive
Hypertext Transfer ProtocolHypertext Transfer Protocol
The Hypertext Transfer Protocol is a networking protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web....
supports explicit means for maintaining an active connection between client and server.
TCP keepalive
Under Transmission Control ProtocolTransmission Control Protocol
The Transmission Control Protocol is one of the core protocols of the Internet Protocol Suite. TCP is one of the two original components of the suite, complementing the Internet Protocol , and therefore the entire suite is commonly referred to as TCP/IP...
(TCP) keepalives are an optional feature, and if included must default to off. The keepalive packet contains null data. In an Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
network, a keepalive frame length is 60 bytes, while acknowledge to this, also a null data frame, is 54 bytes. There are three parameters related to keepalive:
- Keepalive time is the duration between two keepalive transmissions in idle condition. TCP keepalive period is required to be configurable and by default is set to no less than 2 hours.
- Keepalive interval is the duration between two successive keepalive retransmissions, if acknowledgement to the previous keepalive transmission is not received.
- Keepalive retry is the number of retransmissions to be carried out before declaring that remote end is not available.