In packet switching networks, traffic flow, packet flow or network flow is a sequence of packets from a source computer to a destination, which may be another host, a multicast group, or a broadcast domain. RFC 2722 defines traffic flow as "an artificial logical equivalent to a call or connection."[1] RFC 3697 defines traffic flow as "a sequence of packets sent from a particular source to a particular unicast, anycast, or multicast destination that the source desires to label as a flow. A flow could consist of all packets in a specific transport connection or a media stream. However, a flow is not necessarily 1:1 mapped to a transport connection."[2] Flow is also defined in RFC 3917 "a set of IP packets passing an observation point in the network during a certain time interval."[3]
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Conceptual description [link]
A TCP/IP flow can be uniquely identified by the following parameters within a certain time period:
-
- Source and Destination IP address
- Source and Destination Port
- Layer 4 Protocol (TCP/UDP/ICMP)
UDP and ICMP flows [link]
All packets with the same source address/port and destination address/port within a time period are considered as one flow.
Since UDP is uni-directional, it causes one flow. ICMP is bi-directional, so it causes two flows.
TCP flow [link]
Establishing a TCP connection begins with a three-way handshake and creates two flows. One from A to B, the other from B to A, where A and B are IP-Port source and destinations.
1. . (A) --> [SYN] ------>(B) 2. . (A) <-- [SYN/ACK] <--(B) 3. . (A) --> [ACK] ------>(B)
The two TCP flows end with a four-way handshake or a time-out.
1. . (A) --> ACK/FIN ---->(B) 2. . (A) <-- ACK <--------(B) 3. . (A) <-- ACK/FIN <----(B) 4. . (A) --> ACK -------->(B)
Other protocols [link]
Packets from other protocols can be grouped into flows as well. There are other transport protocols, and some protocols use layer 4 as a transport. E.g. HTTP traffic is carried by TCP/IP and creates a flow as the connection is built and torn down.
Utility for network administration [link]
The concept is important, since it may be that packets from one flow need to be handled differently from others, by means of separate queues in switches, routers and network adapters, to achieve traffic shaping, fair queueing or Quality of Service. It is also a concept used in network analyzers or in packet tracing.
Applied to Internet routers, a flow may be a host-to-host communication path, or a socket-to-socket communication identified by a unique combination of source and destination addresses and port numbers, together with transport protocol (for example, UDP or TCP). In the TCP case, a flow may be a virtual circuit, also known as a virtual connection or a byte stream.
In packet switches, the flow may be identified by IEEE 802.1Q Virtual LAN tagging in Ethernet networks, or by a Label Switched Path in MPLS tag switching.
Packet flow can be represented as a path in a network to model network performance. For example a water flow network can be used to conceptualize packet flow. Channels can be thought of as pipes, with the pipe capacity corresponding to bandwidth and flows corresponding to data throughput. This visualization can help to understand bottlenecks, queuing, and help understand the unique requirements of tailored systems.
See also [link]
- Cisco NetFlow
- Communication channel
- Data flow (software engineering)
- Data stream
- Flow control
- Traffic shaping
- Traffic policing
- Flow network in graph theory
- IP Flow Information Export
- Path (graph theory)
- Stream (computing)
- Telecommunication connection
- Traffic generation model
References [link]
- ^ N. Brownlee, C. Mills, and G. Ruth (1999-10). "RFC 2722 - Traffic Flow Measurement: Architecture". IETF. https://www.ietf.org/rfc/rfc2722.txt. Retrieved 2010-02-11.
- ^ J. Rajahalme, A. Conta, B. Carpenter and S. Deering (2004-03). "RFC 3697 - IPv6 Flow Label Specification". IETF. https://www.ietf.org/rfc/rfc3697.txt. Retrieved 2010-02-11.
- ^ J. Quittek, JT. Zseby, B. Claise, and S. Zander (2004-10). "RFC 3917 - IPFIX Requirements". IETF. https://www.ietf.org/rfc/rfc3917.txt. Retrieved 2010-02-11.
https://wn.com/Traffic_flow_(computer_networking)
Flow (mathematics)
In mathematics, a flow formalizes the idea of the motion of particles in a fluid. Flows are ubiquitous in science, including engineering and physics. The notion of flow is basic to the study of ordinary differential equations. Informally, a flow may be viewed as a continuous motion of points over time. More formally, a flow is a group action of the real numbers on a set.
The idea of a vector flow, that is, the flow determined by a vector field, occurs in the areas of differential topology, Riemannian geometry and Lie groups. Specific examples of vector flows include the geodesic flow, the Hamiltonian flow, the Ricci flow, the mean curvature flow, and the Anosov flow. Flows may also be defined for systems of random variables and stochastic processes, and occur in the study of ergodic dynamical systems. The most celebrated of these is perhaps the Bernoulli flow.
Formal definition
A flow on a set X is a group action of the additive group of real numbers on X. More explicitly, a flow is a mapping
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Track listing
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Personnel
References
External links
Rain (2006 film)
Rain is a 2006 film directed by Craig DiBona. The screenplay was written by Andrew Neiderman, based on the novel by V. C. Andrews. It premiered at the Palm Beach International Film Festival, although it did not receive further domestic distribution.
Plot
A talented young pianist named Rain (Brooklyn Sudano) is attacked by a vicious street gang which kills her sister. The gang sets out to find Rain while she hides in the care of a woman who is her natural grandmother. Rain was put up for adoption because the father of the baby was black and the mother was from a rich white family. Her adoptive mother (Khandi Alexander) sends her back because she is in danger for having witnessed her adoptive sister's murder.
Cast
Availability
The film is available to watch on such sites as Netflix to both rent and to watch on their online streaming option.
Rain (SWV song)
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Track listing
US Promo
US CD
UK CD
Rain (Status Quo song)
"Rain" is a single released by the British Rock band Status Quo in 1976. It was included on the album Blue for You.
The track "Rain" was originally intended to be included on the album On The Level, but at the time of the recording sessions Rick Parfitt had not completed the song and so it was held over to the band's next release.
