/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */

 /*

  * Copyright (c) 2007, 2008 University of Washington

  *

  * This program is free software; you can redistribute it and/or modify

  * it under the terms of the GNU General Public License version 2 as

  * published by the Free Software Foundation;

  *

  * This program is distributed in the hope that it will be useful,

  * but WITHOUT ANY WARRANTY; without even the implied warranty of

  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

  * GNU General Public License for more details.

  *

  * You should have received a copy of the GNU General Public License

  * along with this program; if not, write to the Free Software

  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

  */

 #ifndef POINT_TO_POINT_NET_DEVICE_H

 #define POINT_TO_POINT_NET_DEVICE_H

 #include <string.h>

 #include "ns3/address.h"

 #include "ns3/node.h"

 #include "ns3/net-device.h"

 #include "ns3/callback.h"

 #include "ns3/packet.h"

 #include "ns3/traced-callback.h"

 #include "ns3/nstime.h"

 #include "ns3/data-rate.h"

 #include "ns3/ptr.h"

 #include "ns3/mac48-address.h"

 namespace ns3 {

 class Queue;

 class PointToPointChannel;

 class ErrorModel;

 /**

  * \class PointToPointNetDevice

  * \brief A Device for a Point to Point Network Link.

  *

  * This PointToPointNetDevice class specializes the NetDevice abstract

  * base class.  Together with a PointToPointChannel (and a peer 

  * PointToPointNetDevice), the class models, with some level of 

  * abstraction, a generic point-to-point or serial link.  

  * Key parameters or objects that can be specified for this device 

  * include a queue, data rate, and interframe transmission gap (the 

  * propagation delay is set in the PointToPointChannel).

  */

 class PointToPointNetDevice : public NetDevice 

 {

 public:

   static TypeId GetTypeId (void);

   /**

    * Construct a PointToPointNetDevice

    *

    * This is the constructor for the PointToPointNetDevice.  It takes as a

    * parameter a pointer to the Node to which this device is connected, 

    * as well as an optional DataRate object.

    */

   PointToPointNetDevice ();

   /**

    * Destroy a PointToPointNetDevice

    *

    * This is the destructor for the PointToPointNetDevice.

    */

   virtual ~PointToPointNetDevice ();

   /**

    * Set the Data Rate used for transmission of packets.  The data rate is

    * set in the Attach () method from the corresponding field in the channel

    * to which the device is attached.  It can be overridden using this method.

    *

    * @see Attach ()

    * @param bps the data rate at which this object operates

    */

   void SetDataRate (DataRate bps);

   /**

    * Set the inteframe gap used to separate packets.  The interframe gap

    * defines the minimum space required between packets sent by this device.

    *

    * @param t the interframe gap time

    */

   void SetInterframeGap (Time t);

   /**

    * Attach the device to a channel.

    *

    * @param ch Ptr to the channel to which this object is being attached.

    */

   bool Attach (Ptr<PointToPointChannel> ch);

   /**

    * Attach a queue to the PointToPointNetDevice.

    *

    * The PointToPointNetDevice "owns" a queue that implements a queueing 

    * method such as DropTail or RED.  

    *

    * @see Queue

    * @see DropTailQueue

    * @param queue Ptr to the new queue.

    */

   void SetQueue (Ptr<Queue> queue);

   /**

    * Attach a receive ErrorModel to the PointToPointNetDevice.

    *

    * The PointToPointNetDevice may optionally include an ErrorModel in

    * the packet receive chain.

    *

    * @see ErrorModel

    * @param em Ptr to the ErrorModel.

    */

   void SetReceiveErrorModel(Ptr<ErrorModel> em);

   /**

    * Receive a packet from a connected PointToPointChannel.

    *

    * The PointToPointNetDevice 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 PointToPointChannel

    * @param p Ptr to the received packet.

    */

   void Receive (Ptr<Packet> p);

   /**

    * Assign a MAC address to this device.

    *

    * @see Mac48Address

    * @param addr The new address.

    */

   void SetAddress (Mac48Address addr);

   /**

    * 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 serial channel (HDLC, for example), the wire idles (sends all ones) until the channel begins sending a packet.

    * A frame on the wire starts with a flag character (01111110).  This is followed by what is usually called the packet: 

    * address, control, payload, and a Frame Check Sequence (FCS).  This is followed by another flag character.  If the flag

    * characters are used, then bit stuffing must be used to prevent flag characters from appearing in the packet and confusing

    * the link.  Som to be strictly and pedantically correct the frame size is then necessarily larger than the packet size on 

    * a real link.  But, this isn't a real link, it's a simulation of a device similar to a point-to-point device, and we have

    * no good reason to add framing bits and therefore to do bit-stuffing.  So, in the case of the point-to-point device, the 

    * frame size is equal to the packet size.  Since these two values are defined to be equal, there is no danger in assuming

    * they are identical.  We define packet size to be equal to frame size and this excludes the flag characters.  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 PPP framing on a synchronous link.  In this framing scheme, a real serial frame on the 

    * wire starts with a flag character, address and control characters, then a 16-bit PPP protocol ID (0x21 = IP).  Then we 

    * would see the actual payload we are supposed to send, presumably an IP datagram.  At then we see the FCS and finally 

    * another flag character to end the frame.  We ignore the flag bits on this device since it they are not needed.  We 

    * aren't really using HDLC to send frames across the link, so we don't need the address and control bits either.  In fact,

    * to encapsulate using unframed PPP all we need to do is prepend the two-byte protocol ID.

    *

    * Typically the limiting factor in frame size is due to hardware limitations in the underlying HDLC controller receive 

    * FIFO buffer size.  This number can vary widely.  For example, the Motorola MC92460 has a 64 KByte maximum frame size; 

    * the Intel IXP4XX series has a 16 KByte size.  Older USARTs have a maximum frame size around 2KBytes, and typical PPP

    * links on the Internet have their MTU set to 1500 bytes since this is what will typically be used on Ethernet segments

    * and will avoid path MTU issues.  We choose to make the default MTU 1500 bytes which then fixes the maximum frame size

    * as described below.

    *

    * So, there are really two related variables at work here.  There is the maximum frame size that can be sent over the

    * link and there is the MTU.

    *

    * So, what do we do since these values must always be consistent in the driver?  We want to actually allow a user to change 

    * these variables, 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 details of PPP encapsulation in order to set these 

    * variables.

    *

    * Consider the following situation:  A user wants to set the maximum frame size to 16 KBytes.  This user shouldn't have to

    * concern herself that the PPP encapsulation will consume six bytes.  She should not have to figure out that the MTU needs

    * to be set to 16K - 2 bytes to make things consistent.

    *

    * Similarly, a user who is interested in setting the MTU to 1500 bytes should not be forced to understand that the frame 

    * size will need to be set to 1502 bytes. 

    *

    * 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 MTU, she is interested in getting that part of the system set, so the frame size

    * will be changed to make it 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 it consistent;

    *

    * - You cannot define the MTU and frame size separately -- they are always tied together by the overhead of the PPP 

    * encapsulation.  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.  Having the ability to set a  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.

    *

    * \param frameSize The max frame size of packets sent over this device.

    */

   void SetFrameSize (uint16_t frameSize);

   /**

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

    *

    * \returns The max frame size of packets sent over this device.

    */

   uint16_t GetFrameSize (void) const;

 //

 // Pure virtual methods inherited from NetDevice we must implement.

 //

   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<Channel> GetChannel (void) const;

   virtual Address GetAddress (void) const;

   virtual bool SetMtu (const uint16_t mtu);

   virtual uint16_t GetMtu (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;

   virtual bool IsPointToPoint (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;

   virtual void SetPromiscReceiveCallback (PromiscReceiveCallback cb);

   virtual bool SupportsSendFrom (void) const;

 private:

   virtual void DoDispose (void);

   /**

    * 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 Ptr to the queue.

    */

   Ptr<Queue> GetQueue(void) const; 

 private:

   /**

    * Calculate the value for the MTU that would result from 

    * setting the frame size to the given value.

    */

   uint32_t MtuFromFrameSize (uint32_t frameSize);

   /**

    * Calculate the value for the frame size that would be required

    * to be able to set the MTU to the given value.

    */

   uint32_t FrameSizeFromMtu (uint32_t mtu);

   /**

    * \returns the address of the remote device connected to this device

    * through the point to point channel.

    */

   Address GetRemote (void) const;

   /**

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

    * respect the protocol implemented by the agent.

    */

   void AddHeader(Ptr<Packet> p, uint16_t protocolNumber);

   /**

    * Removes, from a packet of data, all headers and trailers that

    * relate to the protocol implemented by the agent

    * \return Returns true if the packet should be forwarded up the

    * protocol stack.

    */

   bool ProcessHeader(Ptr<Packet> p, uint16_t& param);

   /**

    * Start Sending a Packet Down the Wire.

    *

    * The TransmitStart method is the method that is used internally in the

    * PointToPointNetDevice to begin the process of sending a packet out on

    * the channel.  The corresponding method is called on the channel to let

    * it know that the physical device this class represents has virually

    * started sending signals.  An event is scheduled for the time at which

    * the bits have been completely transmitted.

    *

    * @see PointToPointChannel::TransmitStart ()

    * @see TransmitCompleteEvent ()

    * @param p a reference to the packet to send

    * @returns true if success, false on failure

    */

   bool TransmitStart (Ptr<Packet> p);

   /**

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

    *

    * The TransmitComplete method is used internally to finish the process

    * of sending a packet out on the channel.

    */

   void TransmitComplete(void);

   void NotifyLinkUp (void);

   /**

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

    */

   enum TxMachineState

     {

       READY, /**< The transmitter is ready to begin transmission of a packet */

       BUSY   /**< The transmitter is busy transmitting a packet */

     };

   /**

    * The state of the Net Device transmit state machine.

    * @see TxMachineState

    */

   TxMachineState m_txMachineState;

   /**

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

    * timing.

    * @see class DataRate

    */

   DataRate       m_bps;

   /**

    * The interframe gap that the Net Device uses to throttle packet

    * transmission

    * @see class Time

    */

   Time           m_tInterframeGap;

   /**

    * The PointToPointChannel to which this PointToPointNetDevice has been

    * attached.

    * @see class PointToPointChannel

    */

   Ptr<PointToPointChannel> m_channel;

   /**

    * The Queue which this PointToPointNetDevice uses as a packet source.

    * Management of this Queue has been delegated to the PointToPointNetDevice

    * and it has the responsibility for deletion.

    * @see class Queue

    * @see class DropTailQueue

    */

   Ptr<Queue> m_queue;

   /**

    * The trace source for the packet reception events that the device can

    * fire.

    *

    * @see class CallBackTraceSource

    */

   TracedCallback<Ptr<const Packet> > m_rxTrace;

   /**

    * The trace source for the packet drop events that the device can

    * fire.

    *

    * @see class CallBackTraceSource

    */

   TracedCallback<Ptr<const Packet> > m_dropTrace;

   /**

    * Error model for receive packet events

    */

   Ptr<ErrorModel> m_receiveErrorModel;

   Ptr<Node> m_node;

   Mac48Address m_address;

   NetDevice::ReceiveCallback m_rxCallback;

   NetDevice::PromiscReceiveCallback m_promiscCallback;

   uint32_t m_ifIndex;

   std::string m_name;

   bool m_linkUp;

   Callback<void> m_linkChangeCallback;

   static const uint16_t DEFAULT_MTU = 1500;

   static const uint16_t PPP_OVERHEAD = 2;

   static const uint16_t DEFAULT_FRAME_SIZE = DEFAULT_MTU + PPP_OVERHEAD;

   /**

    * 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.

    */

   uint32_t m_frameSize;

   /**

    * 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.

    */

   uint32_t m_mtu;

 };

 } // namespace ns3

 #endif // POINT_TO_POINT_NET_DEVICE_H