Your TCP has to know the port number used by the other end as well. (It finds out when the connection starts, as we will explain below.) It puts this in the “destination” port field. Of course if the other end sends a datagram back to you, the source and destination port numbers will be reversed, since then it will be the source and you will be the destination. This is used so that the other end can make sure that it gets the datagrams in the right order, and that it hasn’t missed any.
(SMTP is “simple mail transfer protocol.) We assume that a computer called TOPAZ.RUTGERS.EDU wants to send the following message. Note by the way that the terms “datagram” and “packet” often seem to be nearly interchangeable. Technically, datagram is the right word to use when describing TCP/IP. A datagram is a unit of data, which is what the protocols deal with. A packet is a physical thing, appearing on an Ethernet or some wire. In most cases a packet simply contains a datagram, so there is very little difference.
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TCP is a connection-based protocol, offering error correction and guaranteed delivery of data via what is known as flow control. Flow control determines when the flow of a data stream needs to be stopped, and previously sent data packets should to be re-sent due to problems such as collisions, for example, thus ensuring complete and accurate delivery of the data. TCP is typically used in the exchange of important information such as database transactions. TCP/IP is the driving force of the Internet, and thus it is the most popular set of network protocols on Earth.
- In many cases, the Gateway Address will be that of a router on the same network, which will in turn pass traffic on to other networks or hosts, such as Internet hosts.
- Flow control determines when the flow of a data stream needs to be stopped, and previously sent data packets should to be re-sent due to problems such as collisions, for example, thus ensuring complete and accurate delivery of the data.
- However in many applications, we have messages that will always fit in a single datagram.
- Because TCP and IP take care of all the networking details, the applications protocols can treat a network connection as if it were a simple byte stream, like a terminal or phone line.
- We are not going to describe the application protocols in detail in this document.
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However with most media, there are efficiency advantages to sending one datagram per packet, and so the distinction tends to vanish. Note that some of the protocols described above were designed by Berkeley, Sun, or other organizations. Thus they are not officially part of the Internet protocol suite. However they are implemented using TCP/IP, just as normal TCP/IP application protocols are. Since the protocol definitions are not considered proprietary, and since commercially-support implementations are widely available, it is reasonable to think of these protocols as being effectively part of the Internet suite.
Another alternative protocol is ICMP (“Internet control message protocol”). ICMP is used for error messages, and other messages intended for the TCP/IP software itself, rather than any particular user program. For example, if you attempt to connect to a host, your system may get back an ICMP message saying “host unreachable”. ICMP can also be used to find out some information about the network.
He has written textbooks on computer science topics such as operating systems, computer networks, computer organization, and cryptography. He also maintains a website titled Computer Science Student Resource. He has authored 17 titles, and counting revised editions, a total of over 40 books on various aspects of these subjects. In over crossgrid.org 20 years in the field, he has been a technical contributor, technical manager, and an executive with several high-technology firms. Currently he is an independent consultant whose clients have included computer and networking manufacturers and customers, software development firms, and leading-edge government research institutions.
Comprehensive survey of network security and network management covers the requirements and design issues involved in managing and safe guarding distributed systems. Reporting on next-generation Internet protocols explains RSVP, MPLS, SIP and RTP and how they fit together. Password protected instructor resources can be accessed here by clicking on the Resources Tab to view downloadable files. Protocols establish how two computers send and receive a message. Once the handshaking process is complete, the data transfer can begin.