TCP/IP Protocol Suite, Slides of Computer Networks

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Program Name :B.Tech

Semester :ECE 6th Sem

Course Name: Computer Network

Course Code:EC 602

Facilitator Name: Megha Dewan

13-2 TRANSPORT-LAYER PROTOCOLS

We can create a transport-layer protocol by

combining a set of services described in the

previous sections. To better understand the

behavior of these protocols, we start with the

simplest one and gradually add more

complexity. The TCP/IP protocol uses a

transport layer protocol that is either a

modification or a combination of some of

these protocols.

Figure 13.16 Simple protocol

Figure 13.17 FSMs for simple protocol

Figure 13.18 shows an example of communication using this protocol. It is very simple. The sender sends packets one after another without even thinking about the receiver. Example 13.

In the Stop-and-Wait protocol, we can use a 1-bit field to number the packets. The sequence numbers are based on modulo- arithmetic.

Note

In the Stop-and-Wait protocol, the acknowledgment number always announces in modulo-2 arithmetic the sequence number of the next packet expected.

Note

Figure 13.21 shows an example of Stop-and-Wait protocol. Packet 0 is sent and acknowledged. Packet 1 is lost and resent after the time-out. The resent packet 1 is acknowledged and the timer stops. Packet 0 is sent and acknowledged, but the acknowledgment is lost. The sender has no idea if the packet or the acknowledgment is lost, so after the time-out, it resends packet 0, which is acknowledged. Example 13.

• Figure 13.18 Example 13.
• Figure 13.21 Example 13.

What is the utilization percentage of the link in Example 13.5 if we have a protocol that can send up to 15 packets before stopping and worrying about the acknowledgments? Solution The bandwidth-delay product is still 20,000 bits. The system can send up to 15 packets or 15,000 bits during a round trip. This means the utilization is 15,000/20,000, or 75 percent. Of course, if there are damaged packets, the utilization percentage is much less because packets have to be resent. Example 13.

In the Go-Back-N Protocol, the sequence numbers are modulo 2 m , where m is the size of the sequence number field in bits.

Note

Figure 13.23 Send window for Go-Back-N

The send window is an abstract concept defining an imaginary box of maximum size = 2 m − 1 with three variables: S f , S n , and S size .

Note