The Bits and Bytes of Computer Networking. Week 3: The Transport and Application Layers

Ports 1-1023 are known as ______ ports.

system; System ports are used for very well-known services.

A connection, at which layer, implies that every segment of data sent is acknowledged?

transport; A connection at the transport layer implies that every segment of data sent is acknowledged.

Ports that are generally used to establish outbound connections are known as ______ ports.

ephemeral; The exact ports used are different, depending on the operating system, but they're all known as ephemeral ports.

A device involved in a Transmission Control Protocol (TCP) connection is ready to close the connection. The other device in the connection agrees. What has occured?

four-way handshake; A four-way handshake occurs when the session is closed.

Transport layer protocols, like TCP and UDP, introduce the concept of a port. How many bits is a port field?

16 bits; A TCP or UDP port is a 16-bit number, meaning there are theoretically 65,535 possible values it can have.

How many bits are used to direct traffic to specific services running on a networked computer?

16; A port is a 16-bit number that's used to direct traffic to specific services running on a networked computer.

What port does the File Transfer Protocol (FTP) typically listen on?

21; FTP typically listens on port 21.

How many Transmission Control Protocol (TCP) control flags are there?

6

What's the standard number for a TTL field?

64; While this value can be set to anything from 0 to 255, 64 is the recommended standard.

How many bits are reserved for the Transmission Control Protocol (TCP) flags?

6; 6 bits are reserved for the 6 TCP control flags.

A device receives a Transmission Control Protocol (TCP) packet. The device understands where the actual data payload begins. Which portion of the TCP header provides this information?

Data offset; The data offset field communicates how long the TCP header for a segment is. This causes the receiving network device to understand where the actual data payload begins

A device that blocks traffic that meets certain criteria is know as a ________.

Firewall; A firewall is used to block certain defined types of traffic.

A network has the ability to direct traffic toward all of the receiving services. What provides this ability in the transport layer?

Multiplexing; Multiplexing in the transport layer means that nodes on a network have the ability to direct traffic toward many different receiving services.

If the transmitting device would like for the receiving device to push currently buffered data to the application on the receiving end immediately, it would set the ____ flag.

PSH; The PSH flag ensures that the receiving end doesn't wait for any further data.

You are sending a very small amount of information that you need the listening program to respond to immediately. Which Transmission Control Protocol (TCP) flag will be used?

PSH; The PSH flag will be used to push the information immediately.

Please select all valid TCP control flags. WAIT, URG, ACK, LISTEN, RST, CLOSE

RST, ACK, URG

What ordering of TCP flags makes up the Three-way Handshake?

SYN, SYN/ACK, ACK; The computer that wants to establish a connection sends a packet with the SYN flag set. Then, the server responds with a packet with both the SYN and ACK flags set. Finally, the original computer sends a packet with just the ACK flag set.

Unlike our five-layer model, the OSI network model adds two more layers on top of the Application Layer. Select examples of these new layers below.

The presentation layer; The presentation layer might handle things like compression or encryption. the session layer; The session layer handles delivery of data from the transport layer to applications themselves.

An example of something that operates at the application layer is:

a web browser; Web browsers and server operate at the application layer.

Connection-oriented protocols protect against dropped data by forming connections and using what type of constant stream?

acknowledgements; Connection-oriented protocols protect against dropped data with a constant stream of acknowledgements.

HTTP is an example of a(n) ______ layer protocol.

application; There are lots of application layer protocols, but HTTP is one of the most common ones.