ns3::CsmaNetDevice Class Reference

A Device for a Csma Network Link. More...

#include <csma-net-device.h>

Inheritance diagram for ns3::CsmaNetDevice:
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List of all members.

Public Types

enum  EncapsulationMode { ILLEGAL, DIX, LLC }

Public Member Functions

 CsmaNetDevice ()
virtual ~CsmaNetDevice ()
void SetInterframeGap (Time t)
void SetBackoffParams (Time slotTime, uint32_t minSlots, uint32_t maxSlots, uint32_t maxRetries, uint32_t ceiling)
bool Attach (Ptr< CsmaChannel > ch)
void SetQueue (Ptr< Queue > queue)
void SetReceiveErrorModel (Ptr< ErrorModel > em)
void Receive (Ptr< Packet > p, Ptr< CsmaNetDevice > sender)
bool IsSendEnabled (void)
void SetSendEnable (bool enable)
bool IsReceiveEnabled (void)
void SetReceiveEnable (bool enable)
void SetAddress (Mac48Address addr)
void SetFrameSize (uint16_t frameSize)
uint16_t GetFrameSize (void) const
void SetEncapsulationMode (CsmaNetDevice::EncapsulationMode mode)
CsmaNetDevice::EncapsulationMode GetEncapsulationMode (void)
virtual void SetName (const std::string name)
virtual std::string GetName (void) const
virtual void SetIfIndex (const uint32_t index)
virtual uint32_t GetIfIndex (void) const
virtual Ptr< ChannelGetChannel (void) const
virtual bool SetMtu (const uint16_t mtu)
virtual uint16_t GetMtu (void) const
virtual Address GetAddress (void) const
virtual bool IsLinkUp (void) const
virtual void SetLinkChangeCallback (Callback< void > callback)
virtual bool IsBroadcast (void) const
virtual Address GetBroadcast (void) const
virtual bool IsMulticast (void) const
virtual Address GetMulticast (Ipv4Address multicastGroup) const
 Make and return a MAC multicast address using the provided multicast group.
virtual bool IsPointToPoint (void) const
virtual bool IsBridge (void) const
virtual bool Send (Ptr< Packet > packet, const Address &dest, uint16_t protocolNumber)
virtual bool SendFrom (Ptr< Packet > packet, const Address &source, const Address &dest, uint16_t protocolNumber)
virtual Ptr< NodeGetNode (void) const
virtual void SetNode (Ptr< Node > node)
virtual bool NeedsArp (void) const
virtual void SetReceiveCallback (NetDevice::ReceiveCallback cb)
virtual Address GetMulticast (Ipv6Address addr) const
 Get the MAC multicast address corresponding to the IPv6 address provided.
virtual void SetPromiscReceiveCallback (PromiscReceiveCallback cb)
virtual bool SupportsSendFrom (void) const

Static Public Member Functions

static TypeId GetTypeId (void)
 This method returns the TypeId associated to ns3::CsmaNetDevice.

Protected Member Functions

virtual void DoDispose (void)
Ptr< QueueGetQueue (void) const
void AddHeader (Ptr< Packet > p, Mac48Address source, Mac48Address dest, uint16_t protocolNumber)
bool ProcessHeader (Ptr< Packet > p, uint16_t &param)

Private Types

enum  TxMachineState { READY, BUSY, GAP, BACKOFF }

Private Member Functions

CsmaNetDeviceoperator= (const CsmaNetDevice &o)
 CsmaNetDevice (const CsmaNetDevice &o)
void Init (bool sendEnable, bool receiveEnable)
uint32_t MtuFromFrameSize (uint32_t frameSize)
uint32_t FrameSizeFromMtu (uint32_t mtu)
void TransmitStart ()
void TransmitCompleteEvent (void)
void TransmitReadyEvent (void)
void TransmitAbort (void)
void NotifyLinkUp (void)

Private Attributes

uint32_t m_deviceId
bool m_sendEnable
bool m_receiveEnable
TxMachineState m_txMachineState
EncapsulationMode m_encapMode
DataRate m_bps
Time m_tInterframeGap
Backoff m_backoff
Ptr< Packetm_currentPkt
Ptr< CsmaChannelm_channel
Ptr< Queuem_queue
Ptr< ErrorModelm_receiveErrorModel
TracedCallback< Ptr< const
Packet > > 
m_rxTrace
TracedCallback< Ptr< const
Packet > > 
m_dropTrace
Ptr< Nodem_node
Mac48Address m_address
NetDevice::ReceiveCallback m_rxCallback
NetDevice::PromiscReceiveCallback m_promiscRxCallback
uint32_t m_ifIndex
std::string m_name
bool m_linkUp
Callback< void > m_linkChangeCallback
uint32_t m_frameSize
uint32_t m_mtu

Static Private Attributes

static const uint16_t DEFAULT_FRAME_SIZE = 1518
static const uint16_t ETHERNET_OVERHEAD = 18

Detailed Description

A Device for a Csma Network Link.

The Csma net device class is analogous to layer 1 and 2 of the TCP stack. The NetDevice takes a raw packet of bytes and creates a protocol specific packet from them.

Each Csma net device will receive all packets written to the Csma link. The ProcessHeader function can be used to filter out the packets such that higher level layers only receive packets that are addressed to their associated net devices

Definition at line 57 of file csma-net-device.h.


Member Enumeration Documentation

Enumeration of the types of packets supported in the class.

Enumerator:
ILLEGAL 

Encapsulation mode not set

DIX 

DIX II / Ethernet II packet

LLC 

802.2 LLC/SNAP Packet

Definition at line 66 of file csma-net-device.h.

Enumeration of the states of the transmit machine of the net device.

Enumerator:
READY 

The transmitter is ready to begin transmission of a packet

BUSY 

The transmitter is busy transmitting a packet

GAP 

The transmitter is in the interframe gap time

BACKOFF 

The transmitter is waiting for the channel to be free

Definition at line 574 of file csma-net-device.h.


Constructor & Destructor Documentation

ns3::CsmaNetDevice::CsmaNetDevice (  ) 
ns3::CsmaNetDevice::~CsmaNetDevice (  )  [virtual]

Destroy a CsmaNetDevice

This is the destructor for a CsmaNetDevice.

Definition at line 116 of file csma-net-device.cc.

References m_queue, and NS_LOG_FUNCTION_NOARGS.

ns3::CsmaNetDevice::CsmaNetDevice ( const CsmaNetDevice o  )  [private]

Copy constructor is declared but not implemented. This disables the copy constructor for CsmaNetDevice objects.


Member Function Documentation

void ns3::CsmaNetDevice::AddHeader ( Ptr< Packet p,
Mac48Address  source,
Mac48Address  dest,
uint16_t  protocolNumber 
) [protected]

Adds the necessary headers and trailers to a packet of data in order to respect the packet type

Parameters:
p Packet to which header should be added
source MAC source address from which packet should be sent
dest MAC destination address to which packet should be sent
protocolNumber In some protocols, identifies the type of payload contained in this packet.

Definition at line 314 of file csma-net-device.cc.

References ns3::EthernetTrailer::CalcFcs(), DIX, ILLEGAL, LLC, m_encapMode, m_frameSize, m_mtu, NS_ASSERT_MSG, NS_FATAL_ERROR, NS_LOG_FUNCTION, NS_LOG_LOGIC, ns3::EthernetHeader::SetDestination(), ns3::EthernetHeader::SetLengthType(), ns3::EthernetHeader::SetSource(), and ns3::LlcSnapHeader::SetType().

Referenced by SendFrom().

bool ns3::CsmaNetDevice::Attach ( Ptr< CsmaChannel ch  ) 

Attach the device to a channel.

The function Attach is used to add a CsmaNetDevice to a CsmaChannel.

See also:
SetDataRate ()
SetInterframeGap ()
Parameters:
ch a pointer to the channel to which this object is being attached.

Definition at line 558 of file csma-net-device.cc.

References ns3::DataRate::CalculateTxTime(), m_bps, m_channel, m_deviceId, m_tInterframeGap, NotifyLinkUp(), NS_LOG_FUNCTION, and ns3::Seconds().

void ns3::CsmaNetDevice::DoDispose ( void   )  [protected, virtual]

Perform any object release functionality required to break reference cycles in reference counted objects held by the device.

Reimplemented from ns3::Object.

Definition at line 123 of file csma-net-device.cc.

References m_channel, m_node, and NS_LOG_FUNCTION_NOARGS.

uint32_t ns3::CsmaNetDevice::FrameSizeFromMtu ( uint32_t  mtu  )  [private]

Calculate the value for the frame size that would be required to be able to set the MTU to the given value.

Definition at line 165 of file csma-net-device.cc.

References DIX, ETHERNET_OVERHEAD, ns3::LlcSnapHeader::GetSerializedSize(), ILLEGAL, LLC, m_encapMode, NS_FATAL_ERROR, and NS_LOG_FUNCTION.

Referenced by SetMtu().

Address ns3::CsmaNetDevice::GetAddress ( void   )  const [virtual]
Returns:
the current Address of this interface.

Implements ns3::NetDevice.

Definition at line 775 of file csma-net-device.cc.

References m_address, and NS_LOG_FUNCTION_NOARGS.

Referenced by ProcessHeader(), and Receive().

Address ns3::CsmaNetDevice::GetBroadcast ( void   )  const [virtual]
Returns:
the broadcast address supported by this netdevice.

Calling this method is invalid if IsBroadcast returns not true.

Implements ns3::NetDevice.

Definition at line 803 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

Referenced by ProcessHeader().

Ptr< Channel > ns3::CsmaNetDevice::GetChannel ( void   )  const [virtual]
Returns:
the channel this NetDevice is connected to. The value returned can be zero if the NetDevice is not yet connected to any channel.

Implements ns3::NetDevice.

Definition at line 768 of file csma-net-device.cc.

References m_channel, and NS_LOG_FUNCTION_NOARGS.

CsmaNetDevice::EncapsulationMode ns3::CsmaNetDevice::GetEncapsulationMode ( void   ) 

Get the encapsulation mode of this device.

Returns:
The encapsulation mode of this device.

Definition at line 205 of file csma-net-device.cc.

References m_encapMode, and NS_LOG_FUNCTION_NOARGS.

uint16_t ns3::CsmaNetDevice::GetFrameSize ( void   )  const

Get The max frame size of packets sent over this device.

Returns:
The max frame size of packets sent over this device.

Definition at line 255 of file csma-net-device.cc.

References m_frameSize.

Referenced by GetTypeId().

uint32_t ns3::CsmaNetDevice::GetIfIndex ( void   )  const [virtual]
Returns:
index ifIndex of the device

Implements ns3::NetDevice.

Definition at line 761 of file csma-net-device.cc.

References m_ifIndex, and NS_LOG_FUNCTION_NOARGS.

uint16_t ns3::CsmaNetDevice::GetMtu ( void   )  const [virtual]
Returns:
the link-level MTU in bytes for this interface.

This value is typically used by the IP layer to perform IP fragmentation when needed.

Implements ns3::NetDevice.

Definition at line 235 of file csma-net-device.cc.

References m_mtu, and NS_LOG_FUNCTION_NOARGS.

Address ns3::CsmaNetDevice::GetMulticast ( Ipv6Address  addr  )  const [virtual]

Get the MAC multicast address corresponding to the IPv6 address provided.

Parameters:
addr IPv6 address
Returns:
the MAC multicast address
Warning:
Calling this method is invalid if IsMulticast returns not true.

Implements ns3::NetDevice.

Definition at line 950 of file csma-net-device.cc.

References GetMulticast(), and NS_LOG_LOGIC.

Address ns3::CsmaNetDevice::GetMulticast ( Ipv4Address  multicastGroup  )  const [virtual]

Make and return a MAC multicast address using the provided multicast group.

RFC 1112 says that an Ipv4 host group address is mapped to an Ethernet multicast address by placing the low-order 23-bits of the IP address into the low-order 23 bits of the Ethernet multicast address 01-00-5E-00-00-00 (hex).

This method performs the multicast address creation function appropriate to an EUI-48-based CSMA device. This MAC address is encapsulated in an abstract Address to avoid dependencies on the exact address format.

Parameters:
multicastGroup The IP address for the multicast group destination of the packet.
Returns:
The MAC multicast Address used to send packets to the provided multicast group.
See also:
Ipv4Address
Mac48Address
Address

Implements ns3::NetDevice.

Definition at line 817 of file csma-net-device.cc.

References NS_LOG_FUNCTION, and NS_LOG_LOGIC.

Referenced by GetMulticast().

std::string ns3::CsmaNetDevice::GetName ( void   )  const [virtual]
Returns:
name name of the device (e.g. "eth0")

Implements ns3::NetDevice.

Definition at line 747 of file csma-net-device.cc.

References m_name, and NS_LOG_FUNCTION_NOARGS.

Ptr< Node > ns3::CsmaNetDevice::GetNode ( void   )  const [virtual]

Get the node to which this device is attached.

Returns:
Ptr to the Node to which the device is attached.

Implements ns3::NetDevice.

Definition at line 903 of file csma-net-device.cc.

References m_node, and NS_LOG_FUNCTION_NOARGS.

Ptr< Queue > ns3::CsmaNetDevice::GetQueue ( void   )  const [protected]

Get a copy of the attached Queue.

This method is provided for any derived class that may need to get direct access to the underlying queue.

Returns:
a pointer to the queue.

Definition at line 721 of file csma-net-device.cc.

References m_queue, and NS_LOG_FUNCTION_NOARGS.

TypeId ns3::CsmaNetDevice::GetTypeId ( void   )  [static]

This method returns the TypeId associated to ns3::CsmaNetDevice.

This object is accessible through the following paths with Config::Set and Config::Connect:

  • /NodeList/[i]/DeviceList/[i]/$ns3CsmaNetDevice

Attributes defined for this type:

  • Address: The MAC address of this device.
  • FrameSize: The maximum size of a packet sent over this device.
  • EncapsulationMode: The link-layer encapsulation type to use.
    • Set with class: ns3::EnumValue
    • Underlying type: Dix|Llc
    • Initial value: Dix
    • Flags: construct write
  • SendEnable: Enable or disable the transmitter section of the device.
    • Set with class: BooleanValue
    • Underlying type: bool
    • Initial value: true
    • Flags: construct write read
  • ReceiveEnable: Enable or disable the receiver section of the device.
    • Set with class: BooleanValue
    • Underlying type: bool
    • Initial value: true
    • Flags: construct write read
  • ReceiveErrorModel: The receiver error model used to simulate packet loss
  • TxQueue: A queue to use as the transmit queue in the device.

Attributes defined in parent class ns3::NetDevice:

  • Mtu: The MAC-level Maximum Transmission Unit

TraceSources defined for this type:

  • Rx: Trace source indicating reception of packet destined for broadcast, multicast or local address.
  • Drop: Trace source indicating packet discarded due to receiver disabled or error model decision.

Reimplemented from ns3::NetDevice.

Definition at line 43 of file csma-net-device.cc.

References ns3::TypeId::AddAttribute(), ns3::TypeId::AddTraceSource(), DEFAULT_FRAME_SIZE, DIX, GetFrameSize(), LLC, m_address, m_dropTrace, m_queue, m_receiveEnable, m_receiveErrorModel, m_rxTrace, m_sendEnable, ns3::MakeEnumAccessor(), ns3::MakeEnumChecker(), ns3::MakeTraceSourceAccessor(), SetEncapsulationMode(), SetFrameSize(), and ns3::TypeId::SetParent().

void ns3::CsmaNetDevice::Init ( bool  sendEnable,
bool  receiveEnable 
) [private]

Initialization function used during object construction.

bool ns3::CsmaNetDevice::IsBridge ( void   )  const [virtual]

Is this a bridge?

Returns:
false.

Implements ns3::NetDevice.

Definition at line 841 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

bool ns3::CsmaNetDevice::IsBroadcast ( void   )  const [virtual]
Returns:
true if this interface supports a broadcast address, false otherwise.

Implements ns3::NetDevice.

Definition at line 796 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

bool ns3::CsmaNetDevice::IsLinkUp ( void   )  const [virtual]
Returns:
true if link is up; false otherwise

Implements ns3::NetDevice.

Definition at line 782 of file csma-net-device.cc.

References m_linkUp, and NS_LOG_FUNCTION_NOARGS.

Referenced by SendFrom().

bool ns3::CsmaNetDevice::IsMulticast ( void   )  const [virtual]
Returns:
value of m_isMulticast flag

Implements ns3::NetDevice.

Definition at line 810 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

bool ns3::CsmaNetDevice::IsPointToPoint ( void   )  const [virtual]

Is this a point to point link?

Returns:
false.

Implements ns3::NetDevice.

Definition at line 834 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

bool ns3::CsmaNetDevice::IsReceiveEnabled ( void   ) 

Is the receive side of the network device enabled?

Returns:
True if the receiver side is enabled, otherwise false.

Definition at line 289 of file csma-net-device.cc.

References m_receiveEnable, and NS_LOG_FUNCTION_NOARGS.

Referenced by Receive().

bool ns3::CsmaNetDevice::IsSendEnabled ( void   ) 

Is the send side of the network device enabled?

Returns:
True if the send side is enabled, otherwise false.

Definition at line 282 of file csma-net-device.cc.

References m_sendEnable, and NS_LOG_FUNCTION_NOARGS.

Referenced by SendFrom(), and TransmitStart().

uint32_t ns3::CsmaNetDevice::MtuFromFrameSize ( uint32_t  frameSize  )  [private]

Calculate the value for the MTU that would result from setting the frame size to the given value.

Definition at line 132 of file csma-net-device.cc.

References DIX, ETHERNET_OVERHEAD, ns3::LlcSnapHeader::GetSerializedSize(), ILLEGAL, LLC, m_encapMode, NS_ASSERT_MSG, NS_FATAL_ERROR, and NS_LOG_FUNCTION.

Referenced by CsmaNetDevice(), SetEncapsulationMode(), and SetFrameSize().

bool ns3::CsmaNetDevice::NeedsArp ( void   )  const [virtual]

Does this device need to use the address resolution protocol?

Returns:
True if the encapsulation mode is set to a value that requires ARP (IP_ARP or LLC).

Implements ns3::NetDevice.

Definition at line 937 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

void ns3::CsmaNetDevice::NotifyLinkUp ( void   )  [private]

Notify any interested parties that the link has come up.

Definition at line 728 of file csma-net-device.cc.

References ns3::Callback< R, T1, T2, T3, T4, T5, T6, T7, T8, T9 >::IsNull(), m_linkChangeCallback, m_linkUp, and NS_LOG_FUNCTION_NOARGS.

Referenced by Attach().

CsmaNetDevice& ns3::CsmaNetDevice::operator= ( const CsmaNetDevice o  )  [private]

Operator = is declared but not implemented. This disables the assigment operator for CsmaNetDevice objects.

bool ns3::CsmaNetDevice::ProcessHeader ( Ptr< Packet p,
uint16_t &  param 
) [protected]

Removes, from a packet of data, all headers and trailers that relate to the packet type

Parameters:
p Packet whose headers need to be processed
param An integer parameter that can be set by the function to return information gathered in the header
Returns:
Returns true if the packet should be forwarded up the protocol stack.

Definition at line 371 of file csma-net-device.cc.

References ns3::EthernetTrailer::CheckFcs(), DIX, GetAddress(), GetBroadcast(), ns3::EthernetHeader::GetDestination(), ns3::EthernetHeader::GetLengthType(), ns3::LlcSnapHeader::GetType(), ILLEGAL, LLC, m_encapMode, NS_FATAL_ERROR, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::Receive ( Ptr< Packet p,
Ptr< CsmaNetDevice sender 
)
bool ns3::CsmaNetDevice::Send ( Ptr< Packet packet,
const Address dest,
uint16_t  protocolNumber 
) [virtual]

Start sending a packet down the channel.

Implements ns3::NetDevice.

Definition at line 848 of file csma-net-device.cc.

References m_address, NS_LOG_FUNCTION, and SendFrom().

bool ns3::CsmaNetDevice::SendFrom ( Ptr< Packet packet,
const Address source,
const Address dest,
uint16_t  protocolNumber 
) [virtual]

Start sending a packet down the channel, with MAC spoofing

Implements ns3::NetDevice.

Definition at line 855 of file csma-net-device.cc.

References AddHeader(), ns3::Mac48Address::ConvertFrom(), IsLinkUp(), IsSendEnabled(), m_currentPkt, m_queue, m_txMachineState, NS_ASSERT, NS_LOG_FUNCTION, NS_LOG_LOGIC, READY, and TransmitStart().

Referenced by Send().

void ns3::CsmaNetDevice::SetAddress ( Mac48Address  addr  ) 

Set the MAC address of the the network device.

Parameters:
addr The Mac48Address to use as the address of the device.

Definition at line 261 of file csma-net-device.cc.

References m_address, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetBackoffParams ( Time  slotTime,
uint32_t  minSlots,
uint32_t  maxSlots,
uint32_t  maxRetries,
uint32_t  ceiling 
)

Set the backoff parameters used to determine the wait to retry transmitting a packet when the channel is busy.

See also:
Attach ()
Parameters:
slotTime Length of a packet slot (or average packet time)
minSlots Minimum number of slots to wait
maxSlots Maximum number of slots to wait
maxRetries Maximum number of retries before packet is discard
ceiling Cap on the exponential function when calculating max slots

Definition at line 303 of file csma-net-device.cc.

References m_backoff, ns3::Backoff::m_ceiling, ns3::Backoff::m_maxRetries, ns3::Backoff::m_maxSlots, ns3::Backoff::m_minSlots, ns3::Backoff::m_slotTime, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetEncapsulationMode ( CsmaNetDevice::EncapsulationMode  mode  ) 

Set the encapsulation mode of this device.

Parameters:
mode The encapsulation mode of this device.
See also:
SetFrameSize

Definition at line 192 of file csma-net-device.cc.

References m_encapMode, m_frameSize, m_mtu, MtuFromFrameSize(), NS_LOG_FUNCTION, and NS_LOG_LOGIC.

Referenced by GetTypeId().

void ns3::CsmaNetDevice::SetFrameSize ( uint16_t  frameSize  ) 

Set The max frame size of packets sent over this device.

Okay, that was easy to say, but the details are a bit thorny. We have a MAC-level MTU that is the payload that higher level protocols see. We have a PHY-level MTU which is the maximum number of bytes we can send over the link (cf. 1500 bytes for Ethernet). We also have a frame size which is some total number of bytes in a packet which could or could not include any framing and overhead. There can be a lot of inconsistency in definitions of these terms. For example, RFC 1042 asserts that the terms maximum transmission unit and maximum packet size are equivalent. RFC 791, however, defines MTU as the maximum sized IP datagram that can be sent. Packet size and frame size are sometimes used interchangeably.

So, some careful definitions are in order to avoid confusion:

In real Ethernet, a packet on the wire starts with a preamble of seven bytes of alternating ones and zeroes followed by a Start-of-Frame-Delimeter (10101011). This is followed by what is usually called the packet: a MAC destination and source, a type field, payload, a possible padding field and a CRC. To be strictly and pedantically correct the frame size is necessarily larger than the packet size on a real Ethernet. But, this isn't a real Ethernet, it's a simulation of a device similar to Ethernet, and we have no good reason to add framing bits. So, in the case of the CSMA device, the frame size is equal to the packet size. Since these two values are equal, there is no danger in assuming they are identical. We do not implement any padding out to a minimum frame size, so padding is a non-issue. We define packet size to be equal to frame size and this excludes the preamble and SFD bytes of a real Ethernet frame. We define a single (MAC-level) MTU that coresponds to the payload size of the packet, which is the IP-centric view of the term as seen in RFC 791.

To make this concrete, consider DIX II (Digital Equipment, Intel, Xerox type II) framing, which is used in most TCP/IP stacks. NetWare and Wireshark call this framing Ethernet II, by the way. In this framing scheme, a real packet on the wire starts with the preamble and Start-of-Frame-Delimeter (10101011). We ignore these bits on this device since it they are not needed. In DIX II, the SFD is followed by the MAC (48) destination address (6 bytes), source address (6 bytes), the EtherType field (2 bytes), payload (0-1500 bytes) and a CRC (4 bytes) -- this corresponds to our entire frame. The payload of the packet/frame in DIX can be from 0 to 1500 bytes. It is the maxmimum value of this payload that we call the MTU. Typically, one sees the MTU set to 1500 bytes and the maximum frame size set to 1518 bytes in Ethernet-based networks.

Different framing schemes can make for different MTU and frame size relationships. For example, we support LLC/SNAP encapsulation which adds eight bytes of header overhead to the usual DIX framing. In this case, if the maximum frame size is left at 1518 bytes, we need to export an MTU that reflects the loss of eight bytes for a total of 1492.

Another complication is that IEEE 802.1Q adds four bytes to the maximum frame size for VLAN tagging. In order to provide an MTU of 1500 bytes, the frame size would need to increased to 1522 bytes to absorb the additional overhead.

So, there are really three variables that are not entirely free at work here. There is the maximum frame size, the MTU and the framing scheme which we call the encapsulation mode.

So, what do we do since there are be three values which must always be consistent in the driver? Which values to we allow to be changed and how do we ensure the other two are consistent? We want to actually allow a user to change these three variables in flexible ways, but we want the results (even at intermediate stages of her ultimate change) to be consistent. We certainly don't want to require that users must understand the various requirements of an enapsulation mode in order to set these variables.

Consider the following situation: A user wants to set the maximum frame size to 1418 bytes instead of 1518. This user shouldn't have to concern herself that the current encapuslation mode is LLC/SNAP and this will consume eight bytes. She should not have to also figure out that the MTU needs to be set to 1392 bytes, and she should certainly not have to do this in some special order to keep intermediate steps consistent.

Similarly, a user who is interested in setting the MTU to 1400 bytes should not be forced to understand that (based on encapsulation mode) the frame size may need to be set to eighteen + eight bytes more than what he wants in certain cases (802,3 + LLC/SNAP), twenty-two + zero bytes in others (802.1Q) and other inscrutable combinations

Now, consider a user who is only interested in changing the encapsulation mode from LLC/SNAP to DIX. This is going to change the relationship between the MTU and the frame size. We've may have to come up with a new value for at least one of the these? Which one? There are too many free variables.

We could play games trying to figure out what the user wants to do, but that is typically a bad plan and programmers have a long and distinguished history of guessing wrong. We'll avoid all of that and just define a flexible behavior that can be worked to get what you want. Here it is:

  • If the user is changing the encapsulation mode, the PHY MTU will remain fixed and the MAC MTU will change, if required, to make the three values consistent;
  • If the user is changing the MTU, she is interested in getting that part of the system set, so the frame size will be changed to make the three values consistent;
  • If the user is changing the frame size, he is interested in getting that part of the system set, so the MTU will be changed to make the three values consistent;
  • You cannot define the MTU and frame size separately -- they are always tied together by the emulation mode. This is not a restriction. Consider what this means. Perhaps you want to set the frame size to some large number and the MTU to some small number. The largest packet you can send is going to be limited by the MTU, so it is not possible to send a frame larger than the MTU plus overhead. The larger frame size is not useful.

So, if a user calls SetFrameSize, we assume that the maximum frame size is the interesting thing for that user and we just adjust the MTU to a new "correct value" based on the current encapsulation mode. If a user calls SetMtu, we assume that the MTU is the interesting property for that user, and we adjust the frame size to a new "correct value" for the current encapsulation mode. If a user calls SetEncapsulationMode, then we take the MTU as the free variable and set its value to match the current frame size.

Parameters:
frameSize The max frame size of packets sent over this device.

Definition at line 242 of file csma-net-device.cc.

References m_encapMode, m_frameSize, m_mtu, MtuFromFrameSize(), NS_LOG_FUNCTION, and NS_LOG_LOGIC.

Referenced by GetTypeId().

void ns3::CsmaNetDevice::SetIfIndex ( const uint32_t  index  )  [virtual]
Parameters:
index ifIndex of the device

Implements ns3::NetDevice.

Definition at line 754 of file csma-net-device.cc.

References m_ifIndex, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetInterframeGap ( Time  t  ) 

Set the inteframe gap used to separate packets. The interframe gap defines the minimum space required between packets sent by this device. As in Ethernet, it defaults to 96 bit times.

Parameters:
t the interframe gap time

Definition at line 296 of file csma-net-device.cc.

References m_tInterframeGap, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetLinkChangeCallback ( Callback< void >  callback  )  [virtual]
Parameters:
callback the callback to invoke

Register a callback invoked whenever the link status changes to UP. This callback is typically used by the IP/ARP layer to flush the ARP cache whenever the link goes up.

Implements ns3::NetDevice.

Definition at line 789 of file csma-net-device.cc.

References m_linkChangeCallback, and NS_LOG_FUNCTION.

bool ns3::CsmaNetDevice::SetMtu ( const uint16_t  mtu  )  [virtual]
Parameters:
mtu MTU value, in bytes, to set for the device
Returns:
whether the MTU value was within legal bounds

Override for default MTU defined on a per-type basis.

Implements ns3::NetDevice.

Definition at line 212 of file csma-net-device.cc.

References FrameSizeFromMtu(), m_encapMode, m_frameSize, m_mtu, NS_LOG_FUNCTION, NS_LOG_LOGIC, and NS_LOG_WARN.

void ns3::CsmaNetDevice::SetName ( const std::string  name  )  [virtual]
Parameters:
name name of the device (e.g. "eth0")

Implements ns3::NetDevice.

Definition at line 740 of file csma-net-device.cc.

References m_name, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetNode ( Ptr< Node node  )  [virtual]

Set the node to which this device is being attached.

Parameters:
node Ptr to the Node to which the device is being attached.

Implements ns3::NetDevice.

Definition at line 910 of file csma-net-device.cc.

References m_name, m_node, NS_LOG_FUNCTION, and ns3::PeekPointer().

void ns3::CsmaNetDevice::SetPromiscReceiveCallback ( PromiscReceiveCallback  cb  )  [virtual]
Parameters:
cb callback to invoke whenever a packet has been received in promiscuous mode and must be forwarded to the higher layers.

Enables netdevice promiscuous mode and sets the callback that will handle promiscuous mode packets. Note, promiscuous mode packets means _all_ packets, including those packets that can be sensed by the netdevice but which are intended to be received by other hosts.

Implements ns3::NetDevice.

Definition at line 959 of file csma-net-device.cc.

References m_promiscRxCallback, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetQueue ( Ptr< Queue queue  ) 

Attach a queue to the CsmaNetDevice.

The CsmaNetDevice "owns" a queue. This queue may be set by higher level topology objects to implement a particular queueing method such as DropTail or RED.

See also:
Queue
DropTailQueue
Parameters:
queue a Ptr to the queue for being assigned to the device.

Definition at line 584 of file csma-net-device.cc.

References m_queue, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetReceiveCallback ( NetDevice::ReceiveCallback  cb  )  [virtual]

Set the callback to be used to notify higher layers when a packet has been received.

Parameters:
cb The callback.

Implements ns3::NetDevice.

Definition at line 944 of file csma-net-device.cc.

References m_rxCallback, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetReceiveEnable ( bool  enable  ) 

Enable or disable the receive side of the network device.

Parameters:
enable Enable the receive side if true, otherwise disable.

Definition at line 275 of file csma-net-device.cc.

References m_receiveEnable, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetReceiveErrorModel ( Ptr< ErrorModel em  ) 

Attach a receive ErrorModel to the CsmaNetDevice.

The CsmaNetDevice may optionally include an ErrorModel in the packet receive chain to simulate data errors in during transmission.

See also:
ErrorModel
Parameters:
em a pointer to the ErrorModel

Definition at line 591 of file csma-net-device.cc.

References m_receiveErrorModel, and NS_LOG_FUNCTION.

void ns3::CsmaNetDevice::SetSendEnable ( bool  enable  ) 

Enable or disable the send side of the network device.

Parameters:
enable Enable the send side if true, otherwise disable.

Definition at line 268 of file csma-net-device.cc.

References m_sendEnable, and NS_LOG_FUNCTION.

bool ns3::CsmaNetDevice::SupportsSendFrom ( void   )  const [virtual]
Returns:
true if this interface supports a bridging mode, false otherwise.

Implements ns3::NetDevice.

Definition at line 966 of file csma-net-device.cc.

References NS_LOG_FUNCTION_NOARGS.

void ns3::CsmaNetDevice::TransmitAbort ( void   )  [private]

Aborts the transmission of the current packet

If the net device has tried to transmit a packet for more times than the maximum allowed number of retries (channel always busy) then the packet is dropped.

Definition at line 486 of file csma-net-device.cc.

References m_backoff, m_currentPkt, m_queue, m_txMachineState, NS_ASSERT_MSG, NS_LOG_FUNCTION_NOARGS, NS_LOG_LOGIC, READY, ns3::Backoff::ResetBackoffTime(), and TransmitStart().

Referenced by TransmitStart().

void ns3::CsmaNetDevice::TransmitCompleteEvent ( void   )  [private]

Stop Sending a Packet Down the Wire and Begin the Interframe Gap.

The TransmitCompleteEvent method is used internally to finish the process of sending a packet out on the channel. During execution of this method the TransmitEnd method is called on the channel to let it know that the physical device this class represents has finished sending simulated signals. The channel uses this event to begin its speed of light delay timer after which it notifies the Net Device(s) at the other end of the link that new bits have arrived (it delivers the Packet). During this method, the net device also schedules the TransmitReadyEvent at which time the transmitter becomes ready to send the next packet.

See also:
CsmaChannel::TransmitEnd ()
TransmitReadyEvent ()

Definition at line 507 of file csma-net-device.cc.

References BUSY, GAP, ns3::TimeUnit< 1 >::GetSeconds(), m_channel, m_currentPkt, m_tInterframeGap, m_txMachineState, NS_ASSERT, NS_ASSERT_MSG, NS_LOG_FUNCTION_NOARGS, NS_LOG_LOGIC, ns3::Simulator::Schedule(), TransmitReadyEvent(), and ns3::TRANSMITTING.

Referenced by TransmitStart().

void ns3::CsmaNetDevice::TransmitReadyEvent ( void   )  [private]

Cause the Transmitter to Become Ready to Send Another Packet.

The TransmitReadyEvent method is used internally to re-enable the transmit machine of the net device. It is scheduled after a suitable interframe gap after the completion of the previous transmission. The queue is checked at this time, and if there is a packet waiting on the queue, the transmission process is begun.

If a packet is in the queue, it is extracted for the queue as the next packet to be transmitted by the net device.

See also:
TransmitStart ()

Definition at line 530 of file csma-net-device.cc.

References GAP, m_currentPkt, m_queue, m_txMachineState, NS_ASSERT_MSG, NS_LOG_FUNCTION_NOARGS, READY, and TransmitStart().

Referenced by TransmitCompleteEvent().

void ns3::CsmaNetDevice::TransmitStart (  )  [private]

Start Sending a Packet Down the Wire.

The TransmitStart method is the method that is used internally in the CsmaNetDevice to begin the process of sending a packet out on the channel. A corresponding method is called on the channel to let it know that the physical device this class represents has actually started sending signals, this causes the channel to enter the BUSY state. An event is scheduled for the time at which the bits have been completely transmitted.

If the channel is found to be BUSY, this method reschedules itself for execution at a later time (within the backoff period).

See also:
CsmaChannel::TransmitStart ()
TransmitCompleteEvent ()

Definition at line 410 of file csma-net-device.cc.

References BACKOFF, BUSY, ns3::DataRate::CalculateTxTime(), ns3::Backoff::GetBackoffTime(), ns3::TimeUnit< 1 >::GetSeconds(), ns3::IDLE, ns3::Backoff::IncrNumRetries(), IsSendEnabled(), m_backoff, m_bps, m_channel, m_currentPkt, m_deviceId, m_txMachineState, ns3::Backoff::MaxRetriesReached(), NS_ASSERT_MSG, NS_LOG_FUNCTION_NOARGS, NS_LOG_LOGIC, NS_LOG_WARN, READY, ns3::Backoff::ResetBackoffTime(), ns3::Simulator::Schedule(), ns3::Seconds(), TransmitAbort(), and TransmitCompleteEvent().

Referenced by SendFrom(), TransmitAbort(), and TransmitReadyEvent().


Member Data Documentation

const uint16_t ns3::CsmaNetDevice::DEFAULT_FRAME_SIZE = 1518 [static, private]

Definition at line 701 of file csma-net-device.h.

Referenced by CsmaNetDevice(), and GetTypeId().

const uint16_t ns3::CsmaNetDevice::ETHERNET_OVERHEAD = 18 [static, private]

Definition at line 702 of file csma-net-device.h.

Referenced by FrameSizeFromMtu(), and MtuFromFrameSize().

The MAC address which has been assigned to this device.

Definition at line 668 of file csma-net-device.h.

Referenced by GetAddress(), GetTypeId(), Receive(), Send(), and SetAddress().

Holds the backoff parameters and is used to calculate the next backoff time to use when the channel is busy and the net device is ready to transmit

Definition at line 614 of file csma-net-device.h.

Referenced by SetBackoffParams(), TransmitAbort(), and TransmitStart().

The data rate that the Net Device uses to simulate packet transmission timing.

See also:
class DataRate

Definition at line 600 of file csma-net-device.h.

Referenced by Attach(), and TransmitStart().

The CsmaChannel to which this CsmaNetDevice has been attached.

See also:
class CsmaChannel

Definition at line 628 of file csma-net-device.h.

Referenced by Attach(), CsmaNetDevice(), DoDispose(), GetChannel(), TransmitCompleteEvent(), and TransmitStart().

Next packet that will be transmitted (if transmitter is not currently transmitting) or packet that is currently being transmitted.

Definition at line 621 of file csma-net-device.h.

Referenced by SendFrom(), TransmitAbort(), TransmitCompleteEvent(), TransmitReadyEvent(), and TransmitStart().

uint32_t ns3::CsmaNetDevice::m_deviceId [private]

Device ID returned by the attached functions. It is used by the mp-channel to identify each net device to make sure that only active net devices are writing to the channel

Definition at line 559 of file csma-net-device.h.

Referenced by Attach(), and TransmitStart().

The trace source for the packet drop events that the device can fire.

See also:
class CallBackTraceSource

Definition at line 658 of file csma-net-device.h.

Referenced by GetTypeId(), and Receive().

The type of packet that should be created by the AddHeader function and that should be processed by the ProcessHeader function.

Definition at line 593 of file csma-net-device.h.

Referenced by AddHeader(), CsmaNetDevice(), FrameSizeFromMtu(), GetEncapsulationMode(), MtuFromFrameSize(), ProcessHeader(), Receive(), SetEncapsulationMode(), SetFrameSize(), and SetMtu().

uint32_t ns3::CsmaNetDevice::m_frameSize [private]

The frame size/packet size. This corresponds to the maximum number of bytes that can be transmitted as a packet without framing. This corresponds to the 1518 byte packet size often seen on Ethernet.

Definition at line 709 of file csma-net-device.h.

Referenced by AddHeader(), CsmaNetDevice(), GetFrameSize(), SetEncapsulationMode(), SetFrameSize(), and SetMtu().

uint32_t ns3::CsmaNetDevice::m_ifIndex [private]

The interface index (really net evice index) that has been assigned to this network device.

Definition at line 683 of file csma-net-device.h.

Referenced by GetIfIndex(), and SetIfIndex().

Callback to fire if the link changes state (up or down).

Definition at line 699 of file csma-net-device.h.

Referenced by NotifyLinkUp(), and SetLinkChangeCallback().

Flag indicating whether or not the link is up. In this case, whether or not the device is connected to a channel.

Definition at line 694 of file csma-net-device.h.

Referenced by IsLinkUp(), and NotifyLinkUp().

uint32_t ns3::CsmaNetDevice::m_mtu [private]

The Maxmimum Transmission Unit. This corresponds to the maximum number of bytes that can be transmitted as seen from higher layers. This corresponds to the 1500 byte MTU size often seen on IP over Ethernet.

Definition at line 717 of file csma-net-device.h.

Referenced by AddHeader(), CsmaNetDevice(), GetMtu(), SetEncapsulationMode(), SetFrameSize(), and SetMtu().

std::string ns3::CsmaNetDevice::m_name [private]

The human readable name of this device.

Definition at line 688 of file csma-net-device.h.

Referenced by GetName(), SetName(), and SetNode().

The Node to which this device is attached.

Definition at line 663 of file csma-net-device.h.

Referenced by DoDispose(), GetNode(), and SetNode().

The callback used to notify higher layers that a packet has been received in promiscuous mode.

Definition at line 677 of file csma-net-device.h.

Referenced by Receive(), and SetPromiscReceiveCallback().

The Queue which this CsmaNetDevice uses as a packet source. Management of this Queue has been delegated to the CsmaNetDevice and it has the responsibility for deletion.

See also:
class Queue
class DropTailQueue

Definition at line 637 of file csma-net-device.h.

Referenced by GetQueue(), GetTypeId(), SendFrom(), SetQueue(), TransmitAbort(), TransmitReadyEvent(), and ~CsmaNetDevice().

Enable net device to receive packets. True by default

Definition at line 569 of file csma-net-device.h.

Referenced by GetTypeId(), IsReceiveEnabled(), and SetReceiveEnable().

Error model for receive packet events

Definition at line 642 of file csma-net-device.h.

Referenced by GetTypeId(), Receive(), and SetReceiveErrorModel().

The callback used to notify higher layers that a packet has been received.

Definition at line 673 of file csma-net-device.h.

Referenced by Receive(), and SetReceiveCallback().

The trace source for the packet reception events that the device can fire.

See also:
class CallBackTraceSource

Definition at line 650 of file csma-net-device.h.

Referenced by GetTypeId(), and Receive().

Enable net device to send packets. True by default

Definition at line 564 of file csma-net-device.h.

Referenced by GetTypeId(), IsSendEnabled(), and SetSendEnable().

The interframe gap that the Net Device uses insert time between packet transmission

See also:
class Time

Definition at line 607 of file csma-net-device.h.

Referenced by Attach(), CsmaNetDevice(), SetInterframeGap(), and TransmitCompleteEvent().

The state of the Net Device transmit state machine.

See also:
TxMachineState

Definition at line 586 of file csma-net-device.h.

Referenced by CsmaNetDevice(), SendFrom(), TransmitAbort(), TransmitCompleteEvent(), TransmitReadyEvent(), and TransmitStart().


The documentation for this class was generated from the following files:
Generated on Thu Dec 3 14:10:41 2009 for NS-3 by  doxygen 1.6.3