Reliable stream transport service
- 1. ASSIGNMENT TOPIC – “RELIABLE STREAM TRANSPORT SERVICE” Submitted by, Ajay.v.j IT
- 3. Previous chapters: unreliable, connectionless, packet delivery service; defined by IP This chapter: reliable network level service stream delivery defined by TCP
- 4. At the lowest level, computer communication networks provide unreliable packet delivery. Packet can be lost or destroyed. when transmission errors interfere with data, when network hardware fails, when networks become too heavily loaded
- 5. Networks that route packets dynamically can Deliver them out of order Deliver them after a substantial delay or Deliver duplicates underlying network technologies may dictate an optimal packet size or pose other constraints needed to achieve efficient transfer rates. At the highest level, application programs often need to send large volumes of data from one computer to another.
- 6. unreliable connectionless delivery system for large volume transfers becomes tedious and annoying, it requires programmers to build error detection and recovery into each application program. Because it is difficult to design, understand, or modify software that correctly provides reliability.
- 7. goal of network protocol research has been to find general purpose solutions to the problems of providing reliable stream delivery, making it possible for experts to build a single instance of stream protocol software that all application programs use. Single general purpose protocol isolate application programs from the details of networking, and makes it possible to define a uniform interface for the stream transfer service.
- 8. Stream orientation Virtual circuit connection Buffered transfer Unstructured stream Full duplex connection
- 9. When user processes transfers data ,data as stream of bits divided into 8 bit octets which are called bytes. The stream delivery service on the destination machine passes to the receiver exactly the same sequence of octets that the sender passes to it on the source machine.
- 10. Protocol software modules in the two operating systems communicate by sending messages across an internet, verifying that the transfer is authorized, and that both sides are ready. Once all details have been settled, the protocol modules inform the application programs that a connection has been established and that transfer can begin. During transfer, protocol software on the two machines continue to communicate to verify that data is received correctly. If the communication fails for any reason ( e.g., because network hardware along the path between the machines fails), both machines detect the failure and report it to the appropriate application programs. We use the term virtual circuit to describe such connections because although application programs view the connection as a dedicated hardware circuit, the reliability is an illusion provided by the stream delivery service.
- 11. The protocol software is free to divide the stream into packets. Application program generates stream one octet at a time. if the application program chooses to generate extremely large blocks of data, the protocol software can choose to divide each block into smaller pieces for transmission. For those applications where data should be delivered even though it does not fill a buffer, the stream service provides a push mechanism that applications use to force a transfer. At the sending side, a push forces protocol software to transfer all data that has been generated without waiting to fill a buffer. When it reaches the receiving side, the push causes TCP to make the data available to the application without delay.
- 12. It is important to understand that the TCP/IP stream service does not honour structured data streams. Application programs using the stream service must understand stream content and agree on stream format before they initiate a connection.
- 13. Connections provided by the TCP/IP stream service allow concurrent transfer in both directions. Such connections are called full duplex. It consists of two independent streams flowing in opposite directions, with no apparent interaction. The stream service allows an application process to terminate flow in one direction while data continues to flow in the other direction, making the connection half duplex.
- 14. Advantage is that underlying protocol software can send control information for one stream back to the source in datagrams carrying data in opposite direction. Such piggybacking reduces the network traffic.