Define Acknowledgment Protocol

Applications on a network node are typically of one of the following types. A TCP-based session with elastic data transfer using a closed-loop control, Web browsing. B over HTTP over TCP. Another class of application could be a streaming session, such. B a packet voice application, also known as Voice over IP (VoIP). Now that we have analyzed the throughput behavior of the 802.11 protocol, let`s use the information gained from this analysis to understand what happens to applications when they run on 802.11 WLANs. We will look at a single-hop Wi-Fi in which a number of STA are connected to an access point, which in turn allows access to the Internet to the STA via an uplink. This is by far the most widely used configuration for 802.11-based access. When a host needs to send TCP data, it must first establish a session with the opposite end (remember that a feature of connection-oriented protocols is that a session or call must be established before the data can be transmitted, and must be terminated or canceled at the end).

The session configuration process is initiated by the host, which sends a connection request message to the intended recipient. The intended recipient then returns a connection confirmation message, after which the sender returns a confirmation message. Once this so-called three-way handshake is complete, the connection is established and the data can be transferred. Similarly, when information is transmitted, the connection must be closed in each direction.20–22 The 802.11 MAC layer uses positive acknowledgements: a node that receives a packet from another node must respond by forwarding an acknowledgement packet. The purpose of the acknowledgement packet is to inform the sending node that the packet has been received. If the sending node does not receive the acknowledgement packet, the data packet is perceived as lost. Even if the data packet was successfully received but the acknowledgement packet was lost, the data packet is considered lost. The confirmation process is illustrated in Figure 12.13. TCP retransmission A device retransmits the TCP frame if it has not received confirmation for a certain period of time. Packet loss usually occurs with saturated or unreliable connections.

We`re not going to do a full review of how TCP/IP works here, but briefly consider a few relevant parts as a quick reminder. Remember that a TCP connection starts with the default three-way TCP negotiation: the client sends a SYN packet (synchronization), the server sends a SYN-ACK packet, and the client responds with an ACK (acknowledgement) packet, then starts sending data or waits for the server to send. When exchanging information, the sequence counters are increased on both sides and the receipt of packets must be confirmed with ACK packets. The connection ends either with an END packet exchange, similar to the three-way start negotiation, or more abruptly with RST (reset) packets. The legal provisions on the concept of acknowledgement of receipt vary from one country to another. However, in most states, the recipient must sign a form after receiving the package. Nowadays, this procedure is carried out electronically, the signature being made on a touch screen that even records the date and document number of the correspondence sent. If the recipient rejects the shipment and refuses to sign the CKA, a rejection record is entered. If the courier sending the parcel loses the ACK, the customer is not entitled to compensation. However, a duplicate may be issued if the issuer so requests and must be resigned by the consignee or include a written statement from the postman who made the delivery. Acknowledgement of receipt (ACK): If the second bit is set, the confirmation number is valid The voice payload per VoIP packet (Voice over IP) is rTP bits, where the encoding rate of the codec is located.

In addition, there are other protocols that need to be used, and each adds its overhead to form the VoIP packet that is transmitted over the 802.11 network. Real Time Transport Protocol (RTP) is used to transmit synchronization information to the listener. It introduces a 12-byte overload. The transport protocol is usually the User Datagram Protocol (UDP) and comes with an 8-byte overload. .