Introduction

Specifically, the project consists of two interacting programs, Client and Server. The Client consists of three components (each being one or more threads): ClientTester, ClientEntity, and NetworkSocket. The Server consists of three components (each being one or more threads): ServerTester, ServerEntity, and NetworkSocket. You are to implement ClientEntity and ServerEntity. You will be provided the others. ClientTester and ServerTester are the users of the transport entities. The pair of NetworkSockets provide the LRD channels and are as in Project 3.

Transport Service

Class ClientEntity must have the following interface:

• Constructor ClientEntity( local IP address and port, remote IP address and port, timeout value )
  Constructs the client of a transport protocol. Timeout signifies that the remote site is not reachable (in this case, due to congestion in LRD channels or due to the remote site closing).
• RequestConnection()
  Initiates a connection establishment attempt with server. Blocks until either connection is established (returns OPEN), connection is rejected (returns CLOSED), or times out (returns TIMEOUT).
  With respect to Note 4, an invocation of RequestConnection corresponds to a ConnectRequest event followed by the reception of an appropriate CRR, the reception of an appropriate REJ, or an Abort event.
• RequestDisconnection( )
  Initiates a disconnection attempt with server. Blocks until connection is either closed normally or disconnect request times out. With respect to Note 4, an invocation of RequestDisconnection corresponds to a DisconnectRequest event followed by the reception of an appropriate message (DRACK, REJ, ...), or an Abort event.
• SendData( byte sequence )
  Accepts byte string from local user (i.e., ClientTester) to be transferred to remote user. Iflocal resources cannot handle byte string, it blocks until resources become free or until timeout. Assume this is called only when open.
• DataAcked( )
  Returns when all data has been acked or timeout. (Allows local user to determine that all data sent has been acked.) Assume this is called only when open.
• ReceiveData( byte sequence )
  Returns byte string or timeout. Blocks until data available to be delivered to local user or time out occurs. Assume this is called only when open.
• At any time at most one call of any of the above methods is outstanding; i.e., an above method is called only when all previous calls of these methods have returned.

• Constructor ServerEntity( local IP address and port, remote IP address and port, timeout value )
  Constructs the server of the transport protocol, starting in closed (not accepting connections) state. Timeout signifies that the remote client is not reachable (in this case, due to congestion in LRD channels or due to the remote site closing).
• AcceptConnection()
  Puts the server in a state where it accepts a connection request. Blocks until a connection is established with client (returns OPEN), or time out occurs (i.e., returns TIMEOUT, indicating that no connectin attempt was observed before time out), or StopAcceptingConnection() occurs.
• StopAcceptingConnection()
  Puts the server in a state where it does not accept connections. Never blocks. Assume it is called only when AcceptConnection() is blocked; it unblocks AcceptConnection().
• AwaitDisconnection()
  Called only when server is open. Blocks until the client requests disconnection (returns CLOSED), or time out occurs (i.e., returns TIMEOUT, indicating that no disconnection attempt was observed before time out).
• SendData( byte sequence )
  Accepts byte string from local user (i.e., ClientTester) to be transferred to remote user. If local resources cannot handle byte string, it blocks until resources become free or until timeout. Assume this is called only when open.
• DataAcked( )
  Returns when all data has been acked or timeout. (Allows local user to determine that all data sent has been acked.) Assume this is called only when open.
• ReceiveData( byte sequence )
  Returns byte sequence or timeout. Blocks until data available to be delivered to local user or time out occurs. Assume this is called only when open.
• At any time at most one call of any of the above methods is outstanding, except for StopAcceptingConnection(); i.e., except for StopAcceptingConnection(), an above method is called only when all previous calls of these methods have returned.

Consider the execution of a corresponding pair of Client and Server entities. At the client, the activity consists of a sequence of RequestConnection, SendData, ReceiveData, Acked, and RequestDisconnection calls (issued by ClientTester). At the server, the activity consists of a sequence of AcceptConnection, StopAcceptingConnection, SendData, ReceiveData, Acked, and AwaitDisconnection calls (issued by ServerTester).

Your protocol must satisfy the requirements stated in section 2 of Note 4.

For example, Each RequestConnection call starts a new incarnation of the Client. Each AcceptConnection call starts a new incarnation of the Server. An incarnation x may or may not become open. If it does, then it becomes open to a corresponding incarnation y at the other site, and that incarnation y must become open to this incarnation x.

Data sent by an incarnation in a connection should be delivered in sequence to the other incarnation.

Transport Protocol