Public Types | Public Member Functions | Static Public Member Functions | Protected Member Functions

ns3::CsmaNetDevice Class Reference

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

#include <csma-net-device.h>

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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 SetFrameSize (uint16_t frameSize)
uint16_t GetFrameSize (void) const
void SetEncapsulationMode (CsmaNetDevice::EncapsulationMode mode)
CsmaNetDevice::EncapsulationMode GetEncapsulationMode (void)
virtual void SetIfIndex (const uint32_t index)
virtual uint32_t GetIfIndex (void) const
virtual Ptr< Channel > GetChannel (void) const
virtual bool SetMtu (const uint16_t mtu)
virtual uint16_t GetMtu (void) const
virtual void SetAddress (Address address)
virtual Address GetAddress (void) const
virtual bool IsLinkUp (void) const
virtual void AddLinkChangeCallback (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< Node > GetNode (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< Queue > GetQueue (void) const
void AddHeader (Ptr< Packet > p, Mac48Address source, Mac48Address dest, uint16_t protocolNumber)

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.

Member Enumeration Documentation

enum ns3::CsmaNetDevice::EncapsulationMode

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

Constructor & Destructor Documentation

ns3::CsmaNetDevice::CsmaNetDevice (  ) 

Construct a CsmaNetDevice

This is the default constructor for a CsmaNetDevice.

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

Destroy a CsmaNetDevice

This is the destructor for a CsmaNetDevice.

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

Add 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 and by IPv6 stack to flush NDISC cache whenever the link goes up.

Implements ns3::NetDevice.

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.
virtual 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.

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

Implements ns3::NetDevice.

virtual 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.

virtual 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 or if the underlying NetDevice has no concept of a channel. i.e., callers _must_ check for zero and be ready to handle it.

Implements ns3::NetDevice.

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

Get the encapsulation mode of this device.

Returns:
The encapsulation mode of this device.
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.
virtual uint32_t ns3::CsmaNetDevice::GetIfIndex ( void   )  const [virtual]
Returns:
index ifIndex of the device

Implements ns3::NetDevice.

virtual 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.

virtual 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.

virtual 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.

virtual 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.

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.
static 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]/$ns3::CsmaNetDevice

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:

  • MacTx: Trace source indicating a packet has arrived for transmission by this device
  • MacTxDrop: Trace source indicating a packet has been dropped by the device before transmission
  • MacPromiscRx: A packet has been received by this device, has been passed up from the physical layer and is being forwarded up the local protocol stack. This is a promiscuous trace,
  • MacRx: A packet has been received by this device, has been passed up from the physical layer and is being forwarded up the local protocol stack. This is a non-promiscuous trace,
  • MacTxBackoff: Trace source indicating a packet has been delayed by the CSMA backoff process
  • PhyTxBegin: Trace source indicating a packet has begun transmitting over the channel
  • PhyTxEnd: Trace source indicating a packet has been completely transmitted over the channel
  • PhyTxDrop: Trace source indicating a packet has been dropped by the device during transmission
  • PhyRxEnd: Trace source indicating a packet has been completely received by the device
  • PhyRxDrop: Trace source indicating a packet has been dropped by the device during reception
  • Sniffer: Trace source simulating a non-promiscuous packet sniffer attached to the device
  • PromiscSniffer: Trace source simulating a promiscuous packet sniffer attached to the device

Reimplemented from ns3::NetDevice.

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

Is this a bridge?

Returns:
false.

Implements ns3::NetDevice.

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

Implements ns3::NetDevice.

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

Implements ns3::NetDevice.

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

Implements ns3::NetDevice.

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

Is this a point to point link?

Returns:
false.

Implements ns3::NetDevice.

bool ns3::CsmaNetDevice::IsReceiveEnabled ( void   ) 

Is the receive side of the network device enabled?

Returns:
True if the receiver side is enabled, otherwise false.
bool ns3::CsmaNetDevice::IsSendEnabled ( void   ) 

Is the send side of the network device enabled?

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

void ns3::CsmaNetDevice::Receive ( Ptr< Packet >  p,
Ptr< CsmaNetDevice >  sender 
)

Receive a packet from a connected CsmaChannel.

The CsmaNetDevice receives packets from its connected channel and forwards them up the protocol stack. This is the public method used by the channel to indicate that the last bit of a packet has arrived at the device.

See also:
CsmaChannel
Parameters:
p a reference to the received packet
sender the CsmaNetDevice that transmitted the packet in the first place
virtual bool ns3::CsmaNetDevice::Send ( Ptr< Packet >  packet,
const Address &  dest,
uint16_t  protocolNumber 
) [virtual]

Start sending a packet down the channel.

Parameters:
packet packet to send
dest layer 2 destination address
protocolNumber protocol number
Returns:
true if successfull, false otherwise (drop, ...)

Implements ns3::NetDevice.

virtual 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

Parameters:
packet packet to send
source layer 2 source address
dest layer 2 destination address
protocolNumber protocol number
Returns:
true if successfull, false otherwise (drop, ...)

Implements ns3::NetDevice.

virtual void ns3::CsmaNetDevice::SetAddress ( Address  address  )  [virtual]

Set the address of this interface

Parameters:
address address to set

Implements ns3::NetDevice.

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

Implements ns3::NetDevice.

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
virtual 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.

virtual 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.

virtual 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.

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.
virtual 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.

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

Implements ns3::NetDevice.

The documentation for this class was generated from the following files:
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