EthernetCutthroughInterface¶

Package: inet.linklayer.ethernet.modular

compound module EthernetCutthroughInterface

Represents an Ethernet network interface with Ethernet cut-through switching support. In contrast with store-and-forward switching, Ethernet cut-through switching can begin the transmission of the outgoing packet before the reception of the corresponding incoming packet ends. Ethernet cut-through switching can significantly reduce end-to-end delay in the network.

There are some important limitations with the current Ethernet cut-through switching implementation:

FCS is not checked for cut-through packets in Ethernet switches
packet data cannot be changed for cut-through packets in Ethernet switches
Ethernet frame preemption is not supported with cut-through packets

The Ethernet FCS is simply forwarded as it is for cut-through packets. Moreover, the packet data cannot be changed inside the Ethernet switch, because it would imply changing the FCS of the packet. Changing the FCS of the packet would require checking the current FCS and aborting incorrect frames. The Ethernet cut-through implementation also assumes that transmissions are not updated on the channel as is the case for Ethernet frame preemption. The packet contents at the start of the reception are the same as the packet contents at the end of the reception.

The main reason for these limitations is that with Ethernet cut-through switching a received packet can reach far away both inside the network node and also in the network, and the current architecture doesn’t support updating this process.

Usage diagram¶

Inheritance diagram¶

Used in compound modules¶

Name	Type	Description
EthernetSwitch	compound module	EthernetSwitch models a Layer 2 Ethernet switch with support for various IEEE 802.1 protocols and features. It provides frame forwarding based on MAC addresses and implements multiple switching technologies.

Extends¶

Name	Type	Description
LayeredEthernetInterface	compound module	Implements an Ethernet network interface.

Parameters¶

Name	Type	Default value	Description
displayStringTextFormat	string	“%a (%i)\n%m”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
recordPcap	bool	false
numPcapRecorders	int	recordPcap ? 1 : 0
protocol	string	“ethernetmac”
broadcast	bool	true
multicast	bool	true
address	string	“auto”
bitrate	double
mtu	int	1500B
interfaceTableModule	string
macTableModule	string

Properties¶

Name	Value	Description
class	NetworkInterface
display	i=block/ifcard
lifecycleSupport
networkInterface

Gates¶

Name	Direction	Size	Description
upperLayerIn	input
upperLayerOut	output
cutthroughIn	input
cutthroughOut	output
phys	inout

Signals¶

Name	Type	Unit	Description
packetDropped	inet::Packet

Statistics¶

Name	Title	Source	Record	Unit	Interpolation Mode	Description
packetDropInterfaceDown	packet drops: interface down	packetDropReasonIsInterfaceDown(packetDropped)	count,sum(packetBytes),vector(packetBytes)		none
packetDropNoCarrier	packet drops: no carrier	packetDropReasonIsNoCarrier(packetDropped)	count,sum(packetBytes),vector(packetBytes)		none

Unassigned submodule parameters¶

Name	Type	Default value	Description
pcapRecorder.displayStringTextFormat	string	“rec: %n pks”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
pcapRecorder.verbose	bool	true	Whether to log packets on the module output
pcapRecorder.recordEmptyPackets	bool	true	Specifies if zero length packets are recorded or not
pcapRecorder.enableConvertingPackets	bool	true	Specifies if converting packets to link type is allowed or not
pcapRecorder.pcapFile	string	“”	The PCAP file to be written, suggested value: pcapFile = “${resultdir}/${configname}-#${runnumber}” + fullpath() + “.pcap”
pcapRecorder.fileFormat	string	“pcapng”
pcapRecorder.snaplen	int	65535	Maximum number of bytes to record per packet
pcapRecorder.timePrecision	int	6	Time precision in recorded file. pcap supports only 6 (usec) or 9 (nanosec), pcapng supports more values (see ‘if_tsresol’ option in pcapng file format).
pcapRecorder.dumpBadFrames	bool	true	Enable dump of frames with hasBitError
pcapRecorder.sendingSignalNames	string	“transmissionEnded”	Space-separated list of outbound packet signals to subscribe to
pcapRecorder.receivingSignalNames	string	“receptionEnded”	Space-separated list of inbound packet signals to subscribe to
pcapRecorder.dumpProtocols	string	“ethernetmac ppp ieee80211mac”	Space-separated list of protocol names as defined in the Protocol class
pcapRecorder.packetFilter	object	“*”	Which packets are considered, matches all packets by default
pcapRecorder.helpers	string	“”	Usable PcapRecorder::IHelper helpers for accept packettype and store/convert packet as specified linktype
pcapRecorder.alwaysFlush	bool	false	Flush the pcapFile after each write to ensure that all packets are captured in case of a crash
macLayer.queue.displayStringTextFormat	string	“contains %p pk (%l) pushed %u\npulled %o removed %r dropped %d”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
macLayer.queue.packetCapacity	int	-1	Maximum number of packets in the queue, no limit by default
macLayer.queue.dataCapacity	int	-1b	Maximum total length of packets in the queue, no limit by default
macLayer.queue.dropperClass	string	“”	Determines which packets are dropped when the queue is overloaded, packets are not dropped by default; the parameter must be the name of a C++ class which implements the IPacketDropperFunction C++ interface and is registered via Register_Class
macLayer.queue.comparatorClass	string	“”	Determines the order of packets in the queue, insertion order by default; the parameter must be the name of a C++ class which implements the IPacketComparatorFunction C++ interface and is registered via Register_Class
macLayer.queue.bufferModule	string	“”	Relative module path to the IPacketBuffer module used by this queue, implicit buffer by default
macLayer.server.displayStringTextFormat	string	“served %p pk (%l)”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
macLayer.server.serveSchedulingPriority	int	0	Specifies the FES scheduling priority for the extra event that is pulling the packet, -1 means no extra event
macLayer.outboundEmitter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
macLayer.outboundEmitter.packetFilter	object	“*”	Which packets are considered, matches all packets by default
macLayer.outboundEmitter.direction	string	“undefined”
macLayer.outboundEmitter.signalName	string
macLayer.fcsChecker.displayStringTextFormat	string	“dropped {numDroppedPackets}/{numProcessedPackets} pk ({droppedTotalLength}/{processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
macLayer.fcsChecker.backpressure	bool	false
macLayer.fcsChecker.popFcs	bool	false
macLayer.inboundEmitter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
macLayer.inboundEmitter.packetFilter	object	“*”	Which packets are considered, matches all packets by default
macLayer.inboundEmitter.direction	string	“undefined”
macLayer.inboundEmitter.signalName	string
phyLayer.phyHeaderInserter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.interFrameGapInserter.displayStringTextFormat	string	“delayed %p pk (%l)\nifg: %g”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.interFrameGapInserter.clockModule	string	“”	Relative path of a module that implements IClock(1,:ref:2 <neddoc-msg-inet-iclock>); optional
phyLayer.interFrameGapInserter.initialChannelBusy	bool	false	Assume that the channel was busy before the simulation started
phyLayer.interFrameGapInserter.duration	double	96s / dropUnit(parent.bitrate)
phyLayer.outboundEmitter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.outboundEmitter.packetFilter	object	“*”	Which packets are considered, matches all packets by default
phyLayer.outboundEmitter.direction	string	“undefined”
phyLayer.outboundEmitter.signalName	string
phyLayer.transmitter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.transmitter.clockModule	string	“”	Relative path of a module that implements IClock(1,:ref:2 <neddoc-msg-inet-iclock>); optional
phyLayer.transmitter.datarate	double	parent.bitrate
phyLayer.phyHeaderChecker.displayStringTextFormat	string	“dropped {numDroppedPackets}/{numProcessedPackets} pk ({droppedTotalLength}/{processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.phyHeaderChecker.backpressure	bool	false
phyLayer.inboundEmitter.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.inboundEmitter.packetFilter	object	“*”	Which packets are considered, matches all packets by default
phyLayer.inboundEmitter.direction	string	“undefined”
phyLayer.inboundEmitter.signalName	string
phyLayer.receiver.displayStringTextFormat	string	“processed {numProcessedPackets} pk ({processedTotalLength})”	Determines the text that is written on top of the submodule, supports displaying pars, watches, and module-specific information
phyLayer.receiver.datarate	double	parent.bitrate

Source code¶

//
// Represents an Ethernet network interface with Ethernet cut-through
// switching support. In contrast with store-and-forward switching, Ethernet
// cut-through switching can begin the transmission of the outgoing packet before
// the reception of the corresponding incoming packet ends. Ethernet cut-through
// switching can significantly reduce end-to-end delay in the network.
//
// There are some important limitations with the current Ethernet cut-through
// switching implementation:
//  - FCS is not checked for cut-through packets in Ethernet switches
//  - packet data cannot be changed for cut-through packets in Ethernet switches
//  - Ethernet frame preemption is not supported with cut-through packets
//
// The Ethernet FCS is simply forwarded as it is for cut-through packets. Moreover,
// the packet data cannot be changed inside the Ethernet switch, because it would
// imply changing the FCS of the packet. Changing the FCS of the packet would
// require checking the current FCS and aborting incorrect frames. The Ethernet
// cut-through implementation also assumes that transmissions are not updated on
// the channel as is the case for Ethernet frame preemption. The packet contents
// at the start of the reception are the same as the packet contents at the end of
// the reception.
//
// The main reason for these limitations is that with Ethernet cut-through
// switching a received packet can reach far away both inside the network node
// and also in the network, and the current architecture doesn't support updating
// this process.
//
module EthernetCutthroughInterface extends LayeredEthernetInterface
{
    parameters:
        string macTableModule;
        *.bitrate = default(this.bitrate);
        *.macTableModule = default(this.macTableModule);
        phyLayer.typename = default("EthernetStreamThroughPhyLayer");
        phyLayer.cutthroughSource.typename = default("EthernetCutthroughSource");
        phyLayer.cutthroughSink.typename = default("EthernetCutthroughSink");
}

File: src/inet/linklayer/ethernet/modular/EthernetCutthroughInterface.ned