What is Data Transport protocol mechanisms

[Ander K]

I have just started to learn about data transmissions in networks. We have been given an assignment on Transport Protocol mechanisms. Now frankly speaking, I am not having much knowledge about it. I am just aware about some basic things of it. Like, I know that Transportation services are those functions and data supplied by the user protocol (either applications or other entities) from the upper layer. The main thing for me is know what is Data Transport protocol mechanisms? Any other information about the Transport protocol mechanisms would be really very grateful.

[Gefry]

There is connection-oriented services (through general datagrams) and connectionless (may be virtual circuits). Generally, a connection-oriented service is safer and provides error detection and sequencing (as in lower layers). But there are cases where a connectionless service is most appropriate, for example:

• Collection of input data: no need for constant connection and also a loss of data is not very significant, as new data arrive later.
• Disseminate output: do not need a continuous connection when you are only notified to users or other entities of certain events.
• Request-response: when a Server provides data requested by many users do not need continuous connection.
• Real-time applications.

[Rover]

Service quality is a function that the user of the transport layer can request this. For example, priorities, minimum delay, low error, etc. These functions may request the end user and must be addressed by the transport layer, and if not, they should be asking the next layer (the Internet and so on down). For example, the file transfer protocol (FTP) requires high performance, the transaction protocol requires a low delay (database queries), e-mail protocol requires priority levels, etc.. TCP implements this ability to choose various qualities of service, but OSI chose to provide different protocols for different types of traffic. TCP must provide duplex mode, but also must provide simplex and half duplex. Although it is not appropriate standardization of the user interface with TCP (as it is better adapted to the user's particular environment), it prevents the user interface overload or collapse the data transport protocol.

[Joko]

Handles TCP (connection-oriented services) of the facility and cut the connection, but it is desirable that the user may to some extent take the reins and cut home connection, as long as no data for user interrupts. This is a service that lets you send data urgently, so that later in their arrival to other less urgent. TCP should implement this service in addition to the typical priorities. TCP must provide the user with information on connection services, network addresses, protocol type in use, state of the machine, etc. TCP can provide access control checks, connection, encryption and decryption of data, etc.

[Aanand]

Suppose a network service accepts data blocks of arbitrary size and send 100% safe. If so, TCP is very simple:

• Address: as a user who wants to send data to another but never connect. To do this, you specify the destination address, user ID, end user port, etc. TCP takes the data needed last block by the user and then, after processing its part of work, and passes control data to the next layer. One question to be answered is how the user knows the address of the destination user? While the user knows the address, the address is well established and known in advance, either by using a name server or the destination is a general service is known and when required, gives the address of the requested destination.
• Multiplexing: TCP can allow multiple users to use identified through multiple ports. The multiplexing can be also down, establishing several points of contact with the network layer to allow sending of data by multiple virtual circuits, increasing performance.
• Flow Control: Flow control in TCP is highly complex, involving users (without predicting its rate of emission data). To control the flow, TCP recipient can do 4 things: do nothing, in which case all data received after that will be discarded saturated TCP (not confirmed) and the broadcast transmitter (situation very inefficient and unreliable) , reject the segments of network service, which this layer will control the flow (since it has mechanisms for it) letting you know the sender's network layer that will not accept more data (this mechanism is coarse), using protocol sliding window, but in some types of unsecured networks, the TCP layer of the sender does not know whether the lack of confirmation is because they have lost or flow control and a loan scheme is similar to the sliding window but no confirmations imply an acceptance of new segments.
• Establishing and closing the connection: a user reports that its TCP wants to establish a connection with another user, then TCP sends a synchronization signal to the TCP layer of the receiver and if the recipient accepts, the TCP receiver informs its user that connection, then sends a synchronization signal to the TCP sender and is put into connection. A time TCP sender receives the TCP signal receiver, also in connection gets established. Either TCP may close the connection. This type of connection is very robust and allows a lot of freedom on both sides of the connection. To avoid loss of data, to end a connection, requesting the order that informs the other end of connection requests and expects to receive confirmation of this request, so no data is lost and route.

[S_Asnodkar]

I would like to discuss about the Insurance Services Network. Security implies that the segments are not lost and they arrive in the correct sequence. In this layer is difficult to ensure the arrival and sequencing of segments. To understand this, consider seven issues:

1. Transportation in order: TCP segments with the numbers the serial number of the data it contains, ie the first segment is numbered 0 and contains 1200 bytes, the next segment is numbered 1200.
2. Retransmission strategy: use a strategy of positive confirmation that the recipient notify the sender of the correct arrival of a segment (confirmed on 4 confirms all the above.) When a segment is not confirmed before a timer expires, it must be retransmitted. To set the timer can be provided with a fixed value, but this does not solve the problem when changing traffic conditions in the network using a timer to suit the conditions of the network also has its drawbacks.
3. Duplicate Detection: when a segment is lost, the issuer received no confirmation sent a duplicate, but suppose that what happened was not to be lost but the timer expired or lost the confirmation, then the receiver will arrive two duplicates , so you should be able to keep one and discard the other. One problem to consider is that the numbering of the segments should form a very large number so that no two segments are numbered with the same number and both are in the network at the same time. An additional problem is that there are segments circulating even when the connection is closed, if for a moment then opens again, the receiver could get these segments that are no longer valid and confuse them with new ones in the new transmission, and to solve this The receiver should remember the last segment received in the last connection.
4. Flow Control: d control type is more robust flow of credit. This system is that when the receiver gets a segment, where confirmation is included in this segment and all of the above and also tells the sender that there is willingness to accept a certain number of new segments (credit). This system means that if you lose a confirmation, the next confirms the earlier loss and also, when a sender timer expires, it will resend the segment.
5. Establishing the connection: it requires a dialogue between the two systems to communicate and for that you use a synchronization signal. There is a mechanism for synchronization signals repeat if they do not arrive. To avoid confusion in the repetition of sync signals, these are numbered, and they have a field confirmation of receipt.
6. Closing the connection: can be a situation in which a signal connection to anticipate one or more data segments, then these segments will be lost, to avoid this situation adds a field to pass the last segment in the segment signaling the end of transmission, so the receiver will wait for the remaining segments.
7. Crash recovery: It is possible that one system fails, in which case it turns itself off, losing all the data contained in its configuration. But the other connected system ignores this is a problem, so it will continue sending data until its timer expires. Then shall be terminated disconnection.