Question

Imagine that a two-way handshake rather than a three-way handshake were used to set up connections. In other words, the third message was not required. Are deadlocks now possible? Give an example or show that none exist.

Short answer

Yes, deadlocks can occur due to incomplete connection confirmation.

Step-by-step solution

Understanding Two-Way Handshake

In a two-way handshake, only two messages are exchanged between the communicating parties to establish a connection. Unlike the three-way handshake, where an ACK for the initial message is required, the two-way handshake omits this final acknowledgment.

Identifying the Role of Three-Way Handshake

The three-way handshake helps prevent potential issues such as deadlocks and ensures reliable communication. It confirms that both parties are ready to transmit and receive data, as it includes a round-trip verification of the connection setup.

Exploring Deadlock Possibility with Two-Way Handshake

Without the third message, also known as the ACK message, both parties might assume different states. If Party A sends a message expecting a response from Party B, and Party B believes the connection setup is complete but doesn’t send further acknowledgment, both parties could end up waiting indefinitely for a message from the other—resulting in a deadlock.

Example of Possible Deadlock

Consider the scenario where Party A sends a SYN message to Party B to initiate the connection. Party B responds with SYN-ACK. However, in a two-way handshake, Party A would not provide an ACK for Party B's response. Party B might wait for an ACK that never comes, thinking Party A hasn't received its message. Meanwhile, Party A waits to start communication, leading to a deadlock.

Conclusion on Deadlocks

The removal of the third message in the handshake sequence introduces potential for deadlocks, as each party might end up waiting indefinitely for responses that never arrive, due to the lack of final confirmation.

Key concepts

Deadlock

A deadlock happens when two or more parties are stuck waiting for each other to take an action. In computer networks, this situation can occur during a connection setup if the communication protocol doesn't handle confirmation steps robustly. When a deadlock occurs, the involved parties are effectively frozen, as each waits for the other to proceed. This often happens due to a lack of synchronization or proper acknowledgment signals.
During a two-way handshake, the chance for a deadlock is higher. Without a clear confirmation that each party has received and acknowledged the messages, both sides might end up waiting indefinitely for the other to act. When Party A sends an initial message and Party B is ready but doesn't send a confirming message back, Party A is left in a state of uncertainty. It may continue to wait for a response that never arrives, leading both parties to be stuck indefinitely.
To avoid deadlocks, protocols need mechanisms to ensure all parties are synchronized in their communication states. Otherwise, parties might enter a waiting pattern, assuming the other side doesn't respond appropriately, thus locking the setup process.

Three-Way Handshake

The three-way handshake is a crucial communication protocol that establishes a reliable connection between two parties on a network. It is used primarily in TCP/IP networks to make sure both sides are ready to send and receive data. This protocol involves three steps where two parties exchange short "SYN" and "ACK" messages.

How Does It Work?

First, the initiator, let's call it Party A, sends a "SYN" (synchronize) message to Party B to start the communication protocol. Party B responds with a "SYN-ACK" message, indicating that it has received the "SYN" and is itself ready to start communication. Finally, Party A sends an "ACK" message back to Party B, confirming the receipt of "SYN-ACK" and completing the handshake sequence. This ensures that both parties are synchronized and that the connection setup is entirely successful.
Without the third message, the communication could be left in limbo. The acknowledgment ("ACK") message is what prevents assumptions and gives parties the go-ahead to proceed with data transmission. This step effectively resolves any uncertainty about the other party's readiness and prevents deadlocks.

Connection Setup

Connection setup is the initial phase in communication protocols where two machines prepare to transmit data to each other. It's a fundamental step for establishing a reliable communication channel in network systems.

The Importance of a Clear Setup

A well-defined connection setup process guarantees that both parties are knowledgeable about each other's presence and readiness. It involves the critical preparation of "handshaking," which ensures no data is lost and the network communication is synchronized.
Connection setup typically involves steps where initial messages, checks, and confirmations are exchanged. An incomplete or improperly executed setup can result in errors, miscommunications, or inefficiencies. The three-way handshake is only one example of an established method for implementing a reliable connection setup. This process's goal is to ensure both sides agree on the starting parameters for the session, eliminating confusion and preventing deadlocking situations.

Communication Protocols

Communication protocols are rules governing data exchange across networks, ensuring that different network devices communicate efficiently and effectively. These protocols define how messages are formatted, transmitted, received, and acknowledged.
Effective communication protocols are crucial for network security and integrity, allowing different systems and devices to interact without conflicts. They define several components, such as how connections are established, data integrity checks, error handling, and termination of the communication.
Protocols like TCP/IP use the three-way handshake to ensure reliable connections, which is key to preventing deadlocks. These handshakes ensure both participating parties are in sync before proceeding to the data-transfer phase. By following these standard rules, communication protocols help maintain network functionality, prevent data loss, and avoid uncertainties in transmission. Properly designed protocols ensure systematic communication, minimizing delays and preventing potential deadlocks by confirming every stage of a data exchange.