Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Transmission Control Protocol shopping experience:
1. Compare - without doubt the biggest advantage that the Transmission Control Protocol offers shoppers today is the ability to compare thousands of Transmission Control Protocol at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.
2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about
3. Testimonials - don't know anybody that has bought a Transmission Control Protocol? Wrong! If the Transmission Control Protocol is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.
4. Questions - Got a question about Transmission Control Protocol then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
5. Reputation - Never heard of the company selling Transmission Control Protocol? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Transmission Control Protocol and build up a picture of their reputation for sales, returns, customer service, delivery etc.
6. Returns - still worried that even after all of the above your Transmission Control Protocol wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.
7. Feedback - happy with your Transmission Control Protocol then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.
8. Security - check for the yellow padlock on the Transmission Control Protocol site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Transmission Control Protocol, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Transmission Control Protocol, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
The
Transmission Control Protocol (
TCP) is one of the core protocols of the Internet protocol suite. TCP provides reliable, in-order delivery of a stream of bytes, making it suitable for applications like file transfer and e-mail. It is so important in the Internet protocol suite that sometimes the entire suite is referred to as "the TCP/IP protocol suite."
Reason for TCP
The Internet Protocol (IP) works by exchanging groups of information called packets. Packets are short sequences of bytes consisting of a header and a body. The header describes the packet's destination, which
routers on the Internet use to pass the packet along, in generally the right direction, until it arrives at its final destination. The body contains the application data.
In cases of congestion, the IP protocol can discard packets, and, for efficiency reasons, two consecutive packets on the internet can take different routes to the destination. Then, the packets can arrive at the destination in the wrong order.
The TCP protocol's software libraries use the IP protocol and provides a simpler interface to applications by hiding most of the underlying packet structures, rearranging out-of-order packets, minimizing network congestion, and re-transmitting discarded packets. Thus, TCP very significantly simplifies the task of writing networked applications.
Applicability of TCP
TCP is used extensively by many of the Internet's most popular application protocols and resulting applications, including the World Wide Web,
E-mail, File Transfer Protocol, Secure Shell, and some streaming media applications.
However, because TCP is optimized for accurate delivery rather than timely delivery, TCP sometimes incurs long delays while waiting for out-of-order messages or retransmissions of lost messages, and it is not particularly suitable for real-time applications such as
Voice over IP. For such applications, protocols like the Real-time Transport Protocol (RTP) running over the
User Datagram Protocol (UDP) are usually recommended instead.
Using TCP
Using TCP, applications on networked hosts can create
connections to one another, over which they can exchange streams of data using
Stream Sockets. TCP also distinguishes data for multiple connections by concurrent applications (
e.g., Web server and e-mail server) running on the same host.
In the Internet protocol suite, TCP is the intermediate layer between the Internet Protocol (IP) below it, and an
software application above it. Applications often need reliable
Pipes and filters-like connections to each other, whereas the Internet Protocol does not provide such streams, but rather only best effort delivery (
i.e., unreliable packets). TCP does the task of the transport layer in the simplified
OSI model of computer networks. The other main transport-level Internet protocols are
User Datagram Protocol and
Stream Control Transmission Protocol.
Applications send streams of octets (8-bit
bytes) to TCP for delivery through the network, and TCP divides the byte stream into appropriately sized TCP segment (usually delineated by the
MTU (networking) (MTU) size of the
data link layer of the network to which the computer is attached). TCP then passes the resulting packets to the Internet Protocol, for delivery through a network to the TCP module of the entity at the other end. TCP checks to make sure that no packets are lost by giving each packet a
sequence number, which is also used to make sure that the data is delivered to the entity at the other end in the correct order. The TCP module at the far end sends back an
acknowledgment for packets which have been successfully received; a timer at the sending TCP will cause a
timeout if an acknowledgment is not received within a reasonable round-trip time (or RTT), and the (presumably) lost data will then be
re-transmitted. The TCP checks that no bytes are corrupted by using a checksum; one is computed at the sender for each block of data before it is sent, and checked at the receiver.
Protocol operation
Unlike TCP's traditional counterpart, User Datagram Protocol, which can immediately start sending packets, TCP provides connections that need to be established before sending data. TCP connections have three phases:
connection establishment
data transfer
connection termination
Before describing these three phases, a note about the various
State (computer science) of a connection end-point or
Internet socket:
LISTEN
SYN-SENT
SYN-RECEIVED
ESTABLISHED
FIN-WAIT-1
FIN-WAIT-2
CLOSE-WAIT
CLOSING
LAST-ACK
TIME-WAIT
CLOSED
LISTEN represents waiting for a connection request from any remote TCP and port. (usually set by TCP servers)SYN-SENT represents waiting for the remote TCP to send back a TCP packet with the SYN and ACK flags set. (usually set by TCP clients)SYN-RECEIVED represents waiting for the remote TCP to send back an acknowledgment after having sent back a connection acknowledgment to the remote TCP. (usually set by TCP servers)ESTABLISHED represents that the port is ready to receive/send data from/to the remote TCP. (set by TCP clients and servers)TIME-WAIT represents waiting for enough time to pass to be sure the remote TCP received the acknowledgment of its connection termination request. According to RFC 793 a connection can stay in TIME-WAIT for a maximum of four minutes.
Connection establishment
To establish a connection, TCP uses a three-way Handshaking.Before a client attempts to connect with a server, the server must first bind to a port to open it up for connections: this is called a passive open.Once the passive open is established, a client may initiate an active open.To establish a connection, the three-way (or 3-step) handshake occurs:
The active open is performed by the client sending a SYN to the server.
In response, the server replies with a SYN-ACK.
Finally the client sends an ACK back to the server.
At this point, both the client and server have received an acknowledgment of the connection.
Example:
The initiating host (client) sends a synchronization (SYN flag set) packet to initiate a connection. Any SYN packet holds a Sequence Number. The Sequence Number is a 32-bit field in TCP segment header. Let the Sequence Number value for this session be x.
The other host receives the packet, records the Sequence Number x from the client, and replies with an acknowledgment and synchronization (SYN-ACK). The Acknowledgment is a 32-bit field in TCP segment header. It contains the next sequence number that this host is expecting to receive (x + 1). The host also initiates a return session. This includes a TCP segment with its own initial Sequence Number of value y.
The initiating host responds with the next Sequence Number (x + 1) and a simple Acknowledgment Number value of y + 1, which is the Sequence Number value of the other host + 1.
Vulnerability to Denial of Service:
By using a spoofed IP address and repeatedly sending SYN packets attackers can cause the server to consume large amounts of resources keeping track of the bogus connections.Proposed solutions to this problem include
SYN cookies and Cryptographic puzzles
Data transfer
There are a few key features that set TCP apart from User Datagram Protocol:
- Ordered data transfer
- Retransmission of lost packets
- Discarding duplicate packets
- Error-free data transfer
- Congestion/Flow control
Ordered data transfer, retransmission of lost packets and discarding duplicate packets
In the first two steps of the 3-way handshaking, both computers exchange an initial sequence number (ISN).This number can be arbitrary.This sequence number identifies the order of the bytes sent from each computer so that the data transferred is in order regardless of any fragmentation or disordering that occurs during transmission.For every byte transmitted the sequence number must be incremented.
Conceptually, each byte sent is assigned a sequence number and the receiver then sends an acknowledgment back to the sender that effectively states that they received it.What is done in practice is only the first data byte is assigned a sequence number which is inserted in the sequence number field and the receiver sends an acknowledgment value of the next byte they expect to receive.
For example, if computer A sends 4 bytes with a sequence number of 100 (conceptually, the four bytes would have a sequence number of 100, 101, 102, & 103 assigned) then the receiver would send back an acknowledgment of 104 since that is the next byte it expects to receive in the next packet.By sending an acknowledgment of 104, the receiver is signaling that it received bytes 100, 101, 102, & 103 correctly.If, by some chance, the last two bytes were corrupted then an acknowledgment value of 102 would be sent since 100 & 101 were received successfully.
However, a problem can occasionally arise when packets are lost. For example, 10,000 bytes are sent in 10 different TCP packets, and the first packet is lost during transmission. The sender would then have to resend all 10,000 bytes; the recipient cannot say that it received bytes 1,000 to 9,999 but only that it failed to receive the first packet, containing bytes 0 to 999. In order to solve this problem, an option of
selective acknowledgment (SACK) has been added. This option allows the receiver to acknowledge isolated blocks of packets that were received correctly, rather than the sequence number of the last packet received successively, as in the basic TCP acknowledgment. Each block is conveyed by the starting and ending sequence numbers. In the example above, the receiver would send SACK with sequence numbers 1,000 and 10,000. The sender will thus retransmit only the first packet.
The SACK option is not mandatory and it is used only if both parties support it. This is negotiated when connection is established. SACK uses the optional part of the TCP header. See
#TCP segment structure. The use of SACK is widespread - all popular TCP stacks support it. Selective acknowledgment is also used in
Stream Control Transmission Protocol.
Error-free data transfer
Sequence numbers and acknowledgments cover discarding duplicate packets, retransmission of lost packets, and ordered-data transfer.To assure correctness a checksum field is included (
see #TCP segment structure for details on checksumming).
The TCP checksum is a quite weak check by modern standards. Data Link Layers with a high probability of bit error rates may require additional link error correction/detection capabilities. If TCP were to be redesigned today, it would most probably have a 32-bit cyclic redundancy check specified as an error check instead of the current checksum. The weak checksum is partially compensated for by the common use of a CRC or better integrity check at layer 2, below both TCP and IP, such as is used in Point-to-Point Protocol or the
Ethernet frame. However, this does not mean that the 16-bit TCP checksum is redundant: remarkably, surveys of Internet traffic have shown that software and hardware errors that introduce errors in packets between CRC-protected hops are common, and that the
end-to-end principle 16-bit TCP checksum catches most of these simple errors. This is the end-to-end principle at work.
The
Transmission Control Protocol (
TCP) is one of the core protocols of the Internet protocol suite. TCP provides reliable, in-order delivery of a stream of bytes, making it suitable for applications like file transfer and e-mail. It is so important in the Internet protocol suite that sometimes the entire suite is referred to as "the TCP/IP protocol suite."
Reason for TCP
The Internet Protocol (IP) works by exchanging groups of information called packets. Packets are short sequences of
bytes consisting of a header and a body. The header describes the packet's destination, which
routers on the Internet use to pass the packet along, in generally the right direction, until it arrives at its final destination. The body contains the application data.
In cases of congestion, the IP protocol can discard packets, and, for efficiency reasons, two consecutive packets on the internet can take different routes to the destination. Then, the packets can arrive at the destination in the wrong order.
The TCP protocol's software libraries use the IP protocol and provides a simpler interface to applications by hiding most of the underlying packet structures, rearranging out-of-order packets, minimizing network congestion, and re-transmitting discarded packets. Thus, TCP very significantly simplifies the task of writing networked applications.
Applicability of TCP
TCP is used extensively by many of the Internet's most popular application protocols and resulting applications, including the World Wide Web, E-mail,
File Transfer Protocol,
Secure Shell, and some streaming media applications.
However, because TCP is optimized for accurate delivery rather than timely delivery, TCP sometimes incurs long delays while waiting for out-of-order messages or retransmissions of lost messages, and it is not particularly suitable for real-time applications such as Voice over IP. For such applications, protocols like the
Real-time Transport Protocol (RTP) running over the User Datagram Protocol (UDP) are usually recommended instead.
Using TCP
Using TCP, applications on networked hosts can create
connections to one another, over which they can exchange streams of data using
Stream Sockets. TCP also distinguishes data for multiple connections by concurrent applications (
e.g., Web server and e-mail server) running on the same host.
In the Internet protocol suite, TCP is the intermediate layer between the Internet Protocol (IP) below it, and an
software application above it. Applications often need reliable
Pipes and filters-like connections to each other, whereas the Internet Protocol does not provide such streams, but rather only best effort delivery (
i.e.,
unreliable packets). TCP does the task of the transport layer in the simplified OSI model of computer networks. The other main transport-level Internet protocols are
User Datagram Protocol and Stream Control Transmission Protocol.
Applications send streams of octets (8-bit bytes) to TCP for delivery through the network, and TCP divides the byte stream into appropriately sized TCP segment (usually delineated by the MTU (networking) (MTU) size of the data link layer of the network to which the computer is attached). TCP then passes the resulting packets to the Internet Protocol, for delivery through a network to the TCP module of the entity at the other end. TCP checks to make sure that no packets are lost by giving each packet a
sequence number, which is also used to make sure that the data is delivered to the entity at the other end in the correct order. The TCP module at the far end sends back an
acknowledgment for packets which have been successfully received; a timer at the sending TCP will cause a
timeout if an acknowledgment is not received within a reasonable
round-trip time (or RTT), and the (presumably) lost data will then be
re-transmitted. The TCP checks that no bytes are corrupted by using a
checksum; one is computed at the sender for each block of data before it is sent, and checked at the receiver.
Protocol operation
Unlike TCP's traditional counterpart,
User Datagram Protocol, which can immediately start sending packets, TCP provides connections that need to be established before sending data. TCP connections have three phases:
connection establishment
data transfer
connection termination
Before describing these three phases, a note about the various State (computer science) of a connection end-point or
Internet socket:
LISTEN
SYN-SENT
SYN-RECEIVED
ESTABLISHED
FIN-WAIT-1
FIN-WAIT-2
CLOSE-WAIT
CLOSING
LAST-ACK
TIME-WAIT
CLOSED
LISTEN represents waiting for a connection request from any remote TCP and port. (usually set by TCP servers)SYN-SENT represents waiting for the remote TCP to send back a TCP packet with the SYN and ACK flags set. (usually set by TCP clients)SYN-RECEIVED represents waiting for the remote TCP to send back an acknowledgment after having sent back a connection acknowledgment to the remote TCP. (usually set by TCP servers)ESTABLISHED represents that the port is ready to receive/send data from/to the remote TCP. (set by TCP clients and servers)TIME-WAIT represents waiting for enough time to pass to be sure the remote TCP received the acknowledgment of its connection termination request. According to RFC 793 a connection can stay in TIME-WAIT for a maximum of four minutes.
Connection establishment
To establish a connection, TCP uses a three-way
Handshaking.Before a client attempts to connect with a server, the server must first bind to a port to open it up for connections: this is called a passive open.Once the passive open is established, a client may initiate an active open.To establish a connection, the three-way (or 3-step) handshake occurs:
The active open is performed by the client sending a SYN to the server.
In response, the server replies with a SYN-ACK.
Finally the client sends an ACK back to the server.
At this point, both the client and server have received an acknowledgment of the connection.
Example:
The initiating host (client) sends a synchronization (SYN flag set) packet to initiate a connection. Any SYN packet holds a Sequence Number. The Sequence Number is a 32-bit field in TCP segment header. Let the Sequence Number value for this session be x.
The other host receives the packet, records the Sequence Number x from the client, and replies with an acknowledgment and synchronization (SYN-ACK). The Acknowledgment is a 32-bit field in TCP segment header. It contains the next sequence number that this host is expecting to receive (x + 1). The host also initiates a return session. This includes a TCP segment with its own initial Sequence Number of value y.
The initiating host responds with the next Sequence Number (x + 1) and a simple Acknowledgment Number value of y + 1, which is the Sequence Number value of the other host + 1.
Vulnerability to Denial of Service:
By using a spoofed IP address and repeatedly sending SYN packets attackers can cause the server to consume large amounts of resources keeping track of the bogus connections.Proposed solutions to this problem include SYN cookies and Cryptographic puzzles
Data transfer
There are a few key features that set TCP apart from User Datagram Protocol:
- Ordered data transfer
- Retransmission of lost packets
- Discarding duplicate packets
- Error-free data transfer
- Congestion/Flow control
Ordered data transfer, retransmission of lost packets and discarding duplicate packets
In the first two steps of the 3-way handshaking, both computers exchange an initial sequence number (ISN).This number can be arbitrary.This sequence number identifies the order of the bytes sent from each computer so that the data transferred is in order regardless of any fragmentation or disordering that occurs during transmission.For every byte transmitted the sequence number must be incremented.
Conceptually, each byte sent is assigned a sequence number and the receiver then sends an acknowledgment back to the sender that effectively states that they received it.What is done in practice is only the first data byte is assigned a sequence number which is inserted in the sequence number field and the receiver sends an acknowledgment value of the next byte they expect to receive.
For example, if computer A sends 4 bytes with a sequence number of 100 (conceptually, the four bytes would have a sequence number of 100, 101, 102, & 103 assigned) then the receiver would send back an acknowledgment of 104 since that is the next byte it expects to receive in the next packet.By sending an acknowledgment of 104, the receiver is signaling that it received bytes 100, 101, 102, & 103 correctly.If, by some chance, the last two bytes were corrupted then an acknowledgment value of 102 would be sent since 100 & 101 were received successfully.
However, a problem can occasionally arise when packets are lost. For example, 10,000 bytes are sent in 10 different TCP packets, and the first packet is lost during transmission. The sender would then have to resend all 10,000 bytes; the recipient cannot say that it received bytes 1,000 to 9,999 but only that it failed to receive the first packet, containing bytes 0 to 999. In order to solve this problem, an option of
selective acknowledgment (SACK) has been added. This option allows the receiver to acknowledge isolated blocks of packets that were received correctly, rather than the sequence number of the last packet received successively, as in the basic TCP acknowledgment. Each block is conveyed by the starting and ending sequence numbers. In the example above, the receiver would send SACK with sequence numbers 1,000 and 10,000. The sender will thus retransmit only the first packet.
The SACK option is not mandatory and it is used only if both parties support it. This is negotiated when connection is established. SACK uses the optional part of the TCP header. See
#TCP segment structure. The use of SACK is widespread - all popular TCP stacks support it. Selective acknowledgment is also used in
Stream Control Transmission Protocol.
Error-free data transfer
Sequence numbers and acknowledgments cover discarding duplicate packets, retransmission of lost packets, and ordered-data transfer.To assure correctness a checksum field is included (
see #TCP segment structure for details on checksumming).
The TCP checksum is a quite weak check by modern standards. Data Link Layers with a high probability of bit error rates may require additional link error correction/detection capabilities. If TCP were to be redesigned today, it would most probably have a 32-bit cyclic redundancy check specified as an error check instead of the current checksum. The weak checksum is partially compensated for by the common use of a CRC or better integrity check at layer 2, below both TCP and IP, such as is used in
Point-to-Point Protocol or the
Ethernet frame. However, this does not mean that the 16-bit TCP checksum is redundant: remarkably, surveys of Internet traffic have shown that software and hardware errors that introduce errors in packets between CRC-protected hops are common, and that the
end-to-end principle 16-bit TCP checksum catches most of these simple errors. This is the
end-to-end principle at work.
Transmission Control Protocol from FOLDOC
Transmission Control Protocol < networking, protocol > (TCP) The most common transport layer protocol used on Ethernet and the Internet. It was developed by DARPA.
Transmission Control Protocol (TCP)
Transmission Control Protocol (TCP) The Transmission Control Protocol (TCP) is a connection-oriented reliable protocol. It provides a reliable transport service between pairs of ...
Transmission Control Protocol - Wikipedia, the free encyclopedia
The Transmission Control Protocol (TCP) is one of the core protocols of the Internet Protocol Suite. TCP is so central that the entire suite is often referred to as "TCP/IP.
Transmission Control Protocol (Client-Server)
Transmission Control Protocol Simulator (Client-Server) See the download page to obtain this program Protocol Description TCP (Transmission Control Protocol) is a connection ...
What is TCP? - a definition from Whatis.com - see also: Transmission ...
TCP (Transmission Control Protocol) is a set of rules (protocol) used along with the Internet Protocol (IP) to send data in the form of message units between computers over the ...
TCP, Transmission Control Protocol
TCP is typically used by applications that require guaranteed delivery. It is a sliding window protocol that provides handling for both timeouts and retransmissions.
Transmission Control Protocol (Peer-Peer)
Transmission Control Protocol Simulator (Peer-Peer) See the download page to obtain this program Protocol Description TCP (Transmission Control Protocol) is a connection-oriented ...
Transmission Control Protocol
The Free Online Dictionary of Computing (http://foldoc.doc.ic.ac.uk/) is edited by Denis Howe < dbh@doc.ic.ac.uk >. Previous: Translation Look-aside Buffer Next: transparent
RFC 793 - Transmission Control Protocol
Transmission Control Protocol. J. Postel. September 1981.
Rfc793 Transmission Control Protocol
