Cut-through switching
Encyclopedia
In computer networking, cut-through switching is a method for packet switching
systems, wherein the switch starts forwarding a frame
(or packet) before the whole frame has been received, normally as soon as the destination address is processed. This technique reduces latency through the switch, but decreases reliability.
The alternative to cut-through switching is store and forward
.
Adaptive switching
dynamically selects between cut-through and store and forward behaviors based on current network conditions.
Pure cut-through switching is only possible when the speed of the outgoing interface is equal to the incoming interface speed.
, because the frame check sequence
appears at the end of the frame
, the switch is not able to verify the integrity of an incoming packet before forwarding it. A cut-through switch will forward corrupted packets where a store and forward switch will drop them.
The technology was developed by Kalpana
the company that introduced the first Ethernet switch.
Fragment free is a variation on cut-through switching that partially addresses this problem by assuring that collision fragments are not forwarded. Fragment free will hold the frame until the first 64 bytes are read from the source to detect a collision before forwarding. This is only useful if there is a chance of a collision on the source port.
s since the edge routers of the ATM network were able to use cell switching through the core of the network with low latency at all points. With higher speed links, this has become less of a problem since packet latency has become much smaller.
networks, since these are often deployed in environments where latency is a prime concern, such as supercomputer
clusters.
Packet switching
Packet switching is a digital networking communications method that groups all transmitted data – regardless of content, type, or structure – into suitably sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams over a shared network...
systems, wherein the switch starts forwarding a frame
Data frame
In computer networking and telecommunication, a frame is a digital data transmission unit or data packet that includes frame synchronization, i.e. a sequence of bits or symbols making it possible for the receiver to detect the beginning and end of the packet in the stream of symbols or bits...
(or packet) before the whole frame has been received, normally as soon as the destination address is processed. This technique reduces latency through the switch, but decreases reliability.
The alternative to cut-through switching is store and forward
Store and forward
Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in a networking context, verifies the integrity of...
.
Adaptive switching
Adaptive switching
An adaptive switch is designed to operate in cut-through mode normally but if a port's error rate jumps too high, the switch automatically reconfigures the port to run in store-and-forward mode...
dynamically selects between cut-through and store and forward behaviors based on current network conditions.
Pure cut-through switching is only possible when the speed of the outgoing interface is equal to the incoming interface speed.
Use in Ethernet
When cut-through switching is used in EthernetEthernet
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....
, because the frame check sequence
Frame Check Sequence
A frame check sequence refers to the extra checksum characters added to a frame in a communication protocol for error detection and correction. Frames are used to send upper-layer data and ultimately the user application data from a source to a destination. The data package includes the message...
appears at the end of the frame
Ethernet frame
A data packet on an Ethernet link is called an Ethernet frame. A frame begins with Preamble and Start Frame Delimiter. Following which, each Ethernet frame continues with an Ethernet header featuring destination and source MAC addresses. The middle section of the frame is payload data including any...
, the switch is not able to verify the integrity of an incoming packet before forwarding it. A cut-through switch will forward corrupted packets where a store and forward switch will drop them.
The technology was developed by Kalpana
Kalpana (company)
Kalpana was a computer networking equipment manufacturer, located in Silicon Valley during the 1980s and 1990s.Kalpana is considered to be the inventor of Ethernet switching as the company was the first to introduce the concept of a multi-port network switch with its seven-port EtherSwitch in 1990...
the company that introduced the first Ethernet switch.
Fragment free is a variation on cut-through switching that partially addresses this problem by assuring that collision fragments are not forwarded. Fragment free will hold the frame until the first 64 bytes are read from the source to detect a collision before forwarding. This is only useful if there is a chance of a collision on the source port.
Use in ATM
Cut-through routing was one of the important features of IP networks using ATM networkAsynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
s since the edge routers of the ATM network were able to use cell switching through the core of the network with low latency at all points. With higher speed links, this has become less of a problem since packet latency has become much smaller.
Use in InfiniBand
Cut-through switching is very popular in InfiniBandInfiniBand
InfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
networks, since these are often deployed in environments where latency is a prime concern, such as supercomputer
Supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...
clusters.