Chapter 9 Transport layer

What are ACK used for

Acknowledgments are used to notify a sending device that a stream of data packets has or has not been received.

Which two services or protocols use the preferred UDP protocol for fast transmission and low overhead?

Both DNS and VoIP use UDP to provide low overhead services within a network implementation.

During a TCP session, a destination device sends an acknowledgment number to the source device. What does the acknowledgment number represent?

the next byte that the destination expects to receive

What is a characteristic of a TCP server process?

Each application process running on the server is configured to use a port number. An individual server cannot have two services assigned to the same port number within the same transport layer services. There can be many ports open simultaneously on a server, one for each active server application.

What does TCP do if the sending source detects network congestion on the path to the destination?

If the source determines that TCP segments are either not being acknowledged or not acknowledged in a timely manner, then it can reduce the number of bytes it sends before receiving an acknowledgment

Network congestion has resulted in the source learning of the loss of TCP segments that were sent to the destination. What is one way that the TCP protocol addresses this?

If the source determines that the TCP segments are either not being acknowledged or are not acknowledged in a timely manner, then it can reduce the number of bytes it sends before receiving an acknowledgment.

What are port number

Port numbers are used to pass data streams to their proper applications.

What kind of port must be requested from IANA in order to be used with a specific application?

Registered ports (numbers 1024 to 49151) are assigned by IANA to a requesting entity to use with specific processes or applications. These processes are primarily individual applications that a user has chosen to install

A host device is receiving live streaming video. How does the device account for video data that is lost during transmission?

Since live streaming video applications use UDP as the transport protocol, the receiver will continue showing the video although there may be a slight delay or reduction in quality.

Which three application layer protocols use TCP

Some protocols require the reliable data transport that is provided by TCP. In addition, these protocols do not have real time communication requirements and can tolerate some data loss while minimizing protocol overhead. Examples of these protocols are SMTP, FTP, and HTTP.

What is a socket?

A socket is a combination of the source IP address and source port or the destination IP address and the destination port number.

Which number or set of numbers represents a socket?

A socket is defined by the combination of an IP address and a port number, and uniquely identifies a particular communication.

What happens if part of an FTP message is not delivered to the destination

Because FTP uses TCP as its transport layer protocol, sequence and acknowledgment numbers will identify the missing segments, which will be re-sent to complete the message.

Which action is performed by a client when establishing communication with a server via the use of UDP at the transport layer?

Because a session does not have to be established for UDP, the client selects a random source port to begin a connection. The random port number selected is inserted into the source port field of the UDP header.

Which transport layer feature is used to guarantee session establishment?

TCP uses the 3-way handshake. UDP does not use this feature. The 3-way handshake ensures there is connectivity between the source and destination devices before transmission occurs.

Which two flags in the TCP header are used in a TCP three-way handshake to establish connectivity between two network devices?

TCP uses the SYN and ACK flags in order to establish connectivity between two network devices.

What information is used by TCP to reassemble and reorder received segments

TCP uses the sequence numbers in the header of each TCP segment to reassemble the segments into the correct order.

Which two characteristics are associated with TCP sessions?

TCP: · Provides tracking of transmitted data segments · Destination devices will acknowledge received data. · Source devices will re transmit unacknowledged data.

What is the purpose of the TCP sliding window?

The TCP sliding window allows a destination device to inform a source to slow down the rate of transmission.

What happens if the first packet of a TFTP transfer is lost?

The TFTP protocol uses UDP for queries, so the TFTP application must implement the reliability, if needed. The TFTP application will retry the request if a reply is not received.

Which flag in the TCP header is used in response to a received FIN in order to terminate connectivity between two network devices?

The connected device that receives the segment will respond with an ACK to acknowledge that segment. The device that sent the ACK will then send a FIN message to close the connection it has with the other device

Which factor determines TCP window size?

The initial window is agreed upon during the session startup via the three-way handshake between source and destination. It is determined by how much data the destination device of a TCP session is able to accept and process at one time.

What is the purpose of using a source port number in a TCP communication?

The source port number in a segment header is used to keep track of multiple conversations between devices. It is also used to keep an open entry for the response from the server. The incorrect options are more related to flow control and guaranteed delivery.

What OSI layer is responsible for establishing a temporary communication session between two applications and ensuring that transmitted data can be reassembled in proper sequence?

The transport layer of the OSI model has several responsibilities. One of the primary responsibilities is to segment data into blocks that can be reassembled in proper sequence at the destination device.

What is the complete range of TCP and UDP well-known ports?

The well-know range of port numbers is from 0 - 1023.

Which two characteristics are associated with UDP sessions?

UDP · Destination devices will not acknowledge received data · Headers use very little overhead and cause minimal delay.​

When is UDP preferred to TCP?

UDP can be used when an application can tolerate some data loss. UDP is the preferred protocol for applications that provide voice or video that cannot tolerate delay.

What is an advantage of UDP over TCP?

UDP has less overhead than TCP because the UDP header has fewer bytes and UDP does not confirm the receipt of packets.

What is a characteristic of UDP

UDP has no way to reorder the datagrams into their transmission order, so UDP simply reassembles the data in the order it was received and forwards it to the application.​

What type of applications are best suited for using UDP?

UDP is not a connection-oriented protocol and does not provide retransmission, sequencing, or flow control mechanisms. It provides basic transport layer functions with a much lower overhead than TCP. Lower overhead makes UDP suitable for applications which are sensitive to delay.

What does a client do when it has UDP datagrams to send?

When a client has UDP datagrams to send, it just sends the datagrams.

Why does HTTP use TCP as the transport layer protocol?

When a host requests a web page, transmission reliability and completeness must be guaranteed. Therefore, HTTP uses TCP as its transport layer protocol.

What is window size

Window size is used to slow down the rate of data communication.

A PC is downloading a large file from a server. The TCP window is 1000 bytes. The server is sending the file using 100-byte segments. How many segments will the server send before it requires an acknowledgment from the PC?

With a window of 1000 bytes, the destination host accepts segments until all 1000 bytes of data have been received. Then the destination host sends an acknowledgment. 10 segments

When developing an IP addressing scheme for an enterprise network, which devices are recommended to be grouped into their own subnet or logical addressing group?

hosts accessible from the Internet

What type of information is included in the transport header?

includes the source and destination process, or port numbers

A network administrator needs to monitor network traffic to and from servers in a data center. Which features of an IP addressing scheme should be applied to these devices?

predictable static IP addresses for easier identification

A client application needs to terminate a TCP communication session with a server. Place the termination process steps in the order that they will occur

In order to terminate a TCP session, the client sends to the server a segment with the FIN flag set. The server acknowledges the client by sending a segment with the ACK flag set. The server sends a FIN to the client to terminate the server to client session. The client acknowledges the termination by sending a segment with the ACK flag set.

Which two reasons generally make DHCP the preferred method of assigning IP addresses to hosts on large networks?

It eliminates most address configuration errors. It reduces the burden on network support staff

Which three fields are used in a UDP segment header?

Length Source Port Checksum

What are three responsibilities of the transport layer

Meeting the reliability requirements of applications if any Multiplexing multiple communications streams from many users or applications on the same network Identifying the application and services on the client and server that should handle transmitted data

A host device needs to send a large video file across the network while providing data communication to other users. Which feature will allow different communication streams to occur at the same time, without having a single data stream using all available bandwidth?

Multiplexing is useful for interleaving multiple communication streams.