Add Delivery Rate Estimation

Details

• A PrrtReceiver is equivalent to a BBR "Connection".

ToDo (Common)

• Introduce new type:

typedef uint32_t prrtByteCount_t;

ToDo (Sender)

• Make PrrtReceiver thread-safe (add a mutex that is locked upon changes). Extend it as follows:

typedef struct PrrtReceiver {
    ...
    pthread_mutex_t lock;
    prrtByteCount_t delivered; // tracked in octets
    prrtTimestamp_t delivered_time;
    prrtTimestamp_t first_sent_time;
    bool app_limited;
    BPTreeNode* outstandingPacketStates; // PrrtPacketStates are managed here
}

• Introduce a PacketState structure:

typedef struct PrrtPacketState {
   prrtByteCount_t delivered;
   prrtTimestamp_t expiry_time;
   prrtPacketLength_t payload_length;
   prrtTimestamp_t delivered_time;
   prrtTimestamp_t first_sent_time;
   bool is_app_limited;
   prrtTimestamp_t sent_time;
} PrrtPacketState;

• For each Receiver, we add a B-tree to keep track of PrrtPacketStates. The process works as follows:

  • Upon sending of the packet, the PrrtPacketState is added to the outstandingPacketStates.
  • When a feedback is received, and a packet is ACKed, the PacketState is removed and the rate sample is generated https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/tcp_rate.c.

• Introduce a PrrtRateSample structure (see http://elixir.free-electrons.com/linux/latest/source/include/net/tcp.h:

typedef struct PrrtRateSample {
   ...
   prrtTimedelta_t interval;
   prrtByteCount_t delivered;
   bool is_app_limited;
} PrrtRateSample;

• For now, printing out rate samples is sufficient.

ToDo (Receiver)

• Extend send_feedback() method to also include the packet sequence number that is to be acked.
• Extend feedback packet to include a prrtSequenceNumber to ACK a certain packet.