Orbit > OTG > Function Specifications > Class Gate

Gate

Gate is an abstract class for the interface to receive a packet, whether UDP, TCP Socket, or LIBMAC inteface. The most basic virtual funciton for a gate is defined here:

• receivePacket

Genereally, the OTR architrecture assume one OTR could have more than one gates. Each gate is bound to only one port number. Thus, if there are multiple ports used to receive packets, there are multiple gates. There is only one thread associated with each gate. One gate, one thread. The gate could have multiple flows, but unlike Port, "Gate" is in charge of reception, and Flow is passive, associated with one sender address.

Demultiplexing incoming packets

A link table data structure is used to store the sender information of all received packets. Each entry of sender information is defined as a class Flow. there are three points are defined to browse this data structure.

• rlhead_ : This points to the head of Incoming flow List.
• rltail_ : This points to the tail of incoming flow List.
• rlcurr_ : This points to the current position of incoming flow list

List of functions in Gate class to handle this flow list.

• createFlow
• addFlow
• deleteFlow
• searchFlowbyFd
• searchFlowbyAddress
• getFlowNum

Functions to prepare Gate opertion

To initialize the Gate object, there are two functions need to be called.

• init: the implemenatation of this depends on different child classes.
• configGate: this is used to bind the Gate object to the OrbitApp and Sink objects.
• startReceive: when a Gate thread (receiving thread) is initialzied by the OTR main function, this function is called to do final preparations.

Receive Operation

receivePacket is a virtual function for packet reception operation. In general, receivePacket are occured in a per-packet basis. After it is called, for TCP sockets, recv() functons. For UDP and RAW sockets, recvfrom() functions are used to receive data. It is in the default blocking socket mode. So, when recv and recvfrom socket functuon is called, unless some packets or bytes are retrieved, this thread is blocked.