File: NetworkInterfaces/Ethernet/EtherMAC.ned
C++ definition: click here
Ethernet MAC layer. MAC performs transmission and reception of frames. Doesn't do encapsulation/decapsulation; see EtherLLC and EtherEncap for that. Also does not perform interface registration in RoutingTable -- that task is delegated to ARP, which makes it possible to use EtherMAC independent of the IP framework.
Supported variations:
Supports all three Ethernet frame types. (It handles EtherFrame message class; specific frame classes (Ethernet-II, IEEE 802.3) are subclassed from that one.) RAW mode (only used by the IPX protocol) is not supported.
Expected environment:
Operation
Processing of frames received from higher layers:
Processing of frames incoming from the network:
The module does not perform encapsulation or decapsulation of frames -- this is done by higher layers (EtherLLC).
When a frame is received from the higher layers, it must be an EtherFrame with message kind set to ETH_FRAME, and with all protocol fields filled out (including the destination MAC address). The source address, if left empty, will be filled in. Then frame is queued and transmitted according to the CSMA/CD protocol.
Data frames received from the network are EtherFrames, with message kind set to ETH_FRAME. They are passed to the higher layers without modification. Also, the module properly responds to PAUSE frames, but never sends them by itself -- however, it transmits PAUSE frames received from upper layers. See PAUSE handling for more info.
Autoconfiguration
A very short period at the beginning of the simulation is spent on all EtherMAC's exchanging autoconfiguration messages, during which the selection of transmission rate and full duplex/half duplex mode takes place.
For more info see Ethernet Model Overview.
Disabling and disconnecting
If the EtherMAC is not connected to the network ("cable unplugged"), it will start up in "disabled" mode. A disabled MAC simply discards any messages it receives. It is currently not supported to dynamically connect/disconnect an EtherMAC.
Queueing
In routers, EtherMAC relies on an external queue module (see OutputQueue) to model finite buffer, implement QoS and/or RED, and requests packets from this external queue one-by-one.
In hosts, no such queue is used, so EtherMAC contains an internal queue named txQueue to queue up packets waiting for transmission. Conceptually, txQueue is of infinite size, but for better diagnostics one can specify a hard limit in the txQueueLimit parameter -- if this is exceeded, the simulation stops with an error.
Physical layer messaging
Please see Messaging on the physical layer.
Statistics
Output vectors and WATCHes:
Output scalars (written in the finish() function) include the final values of the above variables and throughput.
See also: EthernetInterface, EthernetInterface, OutputQueue, EtherEncap, EtherLLC
See also: EtherFrame, EthernetIIFrame, EtherFrameWithLLC, Ieee802Ctrl
The following diagram shows usage relationships between modules, networks and channels. Unresolved module (and channel) types are missing from the diagram. Click here to see the full picture.
If a module type shows up more than once, that means it has been defined in more than one NED file.
EtherHost | Example host model with one Ethernet port and several traffic generators to create traffic in the test network. |
EthernetInterface | Ethernet network interface. Corresponds to the prototype NetworkInterface. Complements EtherMAC and EtherEncap with an output queue for QoS and RED support. |
EthernetInterfaceNoQueue | Ethernet network interface. Assumes inifinite queue. |
EtherSwitch | Model of an Ethernet switch. |
Name | Type | Description |
---|---|---|
promiscuous | bool | if true, all packets are received, otherwise only the ones with matching destination MAC address |
address | string | MAC address as hex string (12 hex digits), or "auto". "auto" values will be replaced by a generated MAC address in init stage 0. |
txrate | numeric | maximum data rate supported by this station (bit/s); actually chosen speed may be lower due to auto- configuration. 0 means fully auto-configured. |
duplexEnabled | bool | whether duplex mode can be enabled or not; whether MAC will actually use duplex mode depends on the result of the auto-configuration process (duplex is only possible with DTE-to-DTE connection). |
txQueueLimit | numeric | maximum number of frames queued up for transmission; additional frames are dropped. Only used if queueModule=="" |
queueModule | string | name of external queue module |
writeScalars | bool | enable/disable recording statistics in omnetpp.sca |
Name | Direction | Description |
---|---|---|
physIn | input | to physical layer or the network |
physOut | output | to physical layer or the network |
upperLayerIn | input | to EtherLLC or MACRelayUnitPP |
upperLayerOut | output | to EtherLLC or MACRelayUnitPP |
simple EtherMAC parameters: promiscuous : bool, // if true, all packets are received, otherwise only the // ones with matching destination MAC address address : string, // MAC address as hex string (12 hex digits), or // "auto". "auto" values will be replaced by // a generated MAC address in init stage 0. txrate : numeric, // maximum data rate supported by this station (bit/s); // actually chosen speed may be lower due to auto- // configuration. 0 means fully auto-configured. duplexEnabled : bool, // whether duplex mode can be enabled or not; whether // MAC will actually use duplex mode depends on the result // of the auto-configuration process (duplex is only // possible with DTE-to-DTE connection). txQueueLimit : numeric, // maximum number of frames queued up for transmission; // additional frames are dropped. Only used if queueModule=="" queueModule: string, // name of external queue module writeScalars: bool; // enable/disable recording statistics in omnetpp.sca gates: in: physIn; // to physical layer or the network out: physOut; // to physical layer or the network in: upperLayerIn; // to EtherLLC or MACRelayUnitPP out: upperLayerOut; // to EtherLLC or MACRelayUnitPP endsimple