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.

Inheritance diagram

The following diagram shows inheritance relationships for this type. Unresolved types are missing from the diagram.

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
networkInterface
lifecycleSupport
display	i=block/ifcard

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 currently available: "inet::AckingMacToEthernetPcapRecorderHelper"
pcapRecorder.alwaysFlush	bool	false	Flush the pcapFile after each write to ensure that all packets are captured in case of a crash

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

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