The following figure shows the control messages sent among the client and the server under normal operations using the three-way handshake protocol. (Note: in SYNACK(y,x) and ACK(x,y), the first number is the sequence number of the message, the second number is the acknowledgment number, i.e., the sequence number of the message being acknowledged.)

a. Consider the following scenario (see Figure 3) where the SYNACK(y,x) message sent by the server is lost during the transmission. What will happen at either the client or the server side?

b. Suppose that by now the connection in a. (where the client used the initial sequence no. x, and the server used the initial sequence no. y) has been closed. An old, duplicate message SYNACK(y,x) now pops up at the client side (see Figure 4). First, can this scenario happen at all? Second, in response to this SYNACK(y,x) message, what will the client do? Briefly explain your answers to both questions

figure 4

Client Server established ACK(x established Figure 2: TCP 3-way handshake. Client Server SYN(x) SYNACK(VX) connection established lost Figure 3: Figure for Question 6a