3.2 Receiver Module

Module Name:

rami_receiver

Purpose:

The Receiver module performs the necessary processes on a Receiver in order to implement the new window size algorithm.

Responsibilities:

The Receiver module is responsible for:

• Calculating and modifying the window size (by the Client's algorithm specified in section A) of received packets that contain a representation of $p(q)$.
• Enabling the user to provide values for the algorithm-specific variables:
  • $\tau$ - A constant which affects the rate at which the window increases. It has units of packets/sec, and a default value of 1.
  • $\alpha$ - A smoothing factor, normalised to the interval [0,1], but given to the module on the interval [0,100] as an integer. Default value is 25.
  • PS_THRESH - A constant used to determine when to end the prime start phase of the window size updating.
• Keeping a representation of $p(q)$ from the Router.
• Updating the representation of $p(q)$ whenever this information is present in a packet received on the Receiver.
• Ensuring altered packets are valid TCP/IP packets as specified by reference [7], including the extensions in reference [3].

Collaboration:

The Receiver module collaborates with:

• sch_qsize (the router module)

SRS References:

3.1.2.1, 3.1.2.2, 3.1.2.3, 3.1.2.4, 3.1.2.5, 3.1.2.6

3.2.1 Internal Data Structures

struct rami_info

This data structure holds information needed by the receiver to calculate the window size for a particular connection. It is kept between packets in a connection, and one is kept for each connection.

It has the following definition:

struct rami_info  {
        struct rami_info *next;
        struct sock *sk;
        __u32 previous_win;
        int mu;
        int prime_start;
        unsigned long tstamp;
        int timestamps[ALPHA];
        int counter;
};

Each field has the following use:

*next

A pointer to the next structure of this type within a list, or NULL if there is no other structure.

*sk

A pointer to the local socket structure (as maintained by the kernel) for the connection.

previous_win

The window size used for the previous packet transmitted for this connection.

mu

The value of $\mu$ as calculated when the previous packet was received.

prime_start

Determines whether or not the prime start phase of the connection is occurring. This should be initialised to a non-negative value (such as 1), and changed to 0 when the prime start phase has ended.

tstamp

The value of the kernel jiffies counter at the time the last packet for this connection was transmitted.

timestamps

A list of the last ALPHA timestamps for packets transmitted for this connection. This is used to determine the received rate.

counter

A counter which keeps a record of the number of packets transmitted modulus $\alpha$, which is used to maintain the list of the $\alpha$ most recent timestamps.

rami_hash_table

A hash table used to hold the rami_info structures for different connections. Separate chaining will be used to prevent collisions. The table will be FCM_HASH_SIZE long, as defined by a #define.