OSI Model

Identify the well-known UDP port number for NTP.

123 The Network Time Protocol (NTP) relies on port 123.

User Datagram Protocol (UDP)

A connection-less transport protocol. Connectionless transport protocols provide unreliable transport, in that if a segment is dropped, the sender is unaware of the drop, and no retransmission occurs.

Transmission Control Protocol (TCP)

A connection-oriented transport protocol. Connection-oriented transport protocols provide reliable transport, in that if a segment is dropped, the sender can detect that drop and retransmit the dropped segment. Specifically, a receiver acknowledges segments that it receives. Based on those acknowledgements, a sender can determine which segments were successfully received.

Cyclic redundancy check (CRC)

A mathematical algorithm that is executed on a data string by both the sender and the receiver of the data string. If the calculated CRC values match, the receiver can conclude that the data string was not corrupted during transmission.

application layer (TCP/IP stack)

Addresses concepts described by Layers 5, 6, and 7 (that is, the session, presentation, and application layers) of the OSI model.

TCP/IP stack

Also known as the DoD model, this four-layer model (as opposed to the seven-layer OSI model) targets the suite of TCP/IP protocols.

data link layer

As Layer 2 of the OSI model, this layer is concerned with the packaging of data into frames and transmitting those frame on a network, performing error detection, correction, uniquely identifying network devices with an address, and handling flow control.

transport layer (OSI model)

As Layer 4 of the OSI model, it acts as a dividing line between the upper layers and the lower layers. Specifically, messages are taken from the upper layers (Layers 5-7) and encapsulated into segments for transmission to the lower layers (Layers 1-3). Similarly, data streams coming from lower layers are decapsulated and sent to Layer 5 (the session layer) or some other upper layer, depending on the protocol.

session layer

As Layer 5 of the OSI model, it's responsible for setting up, maintaining, and tearing down sessions.

Which approach to bandwidth usage consumes all the available frequencies on a medium to transmit data?

Baseband Baseband technology uses the entire medium to transmit. You should contrast this to broadband technology, which can divide the medium up into different channels. A great example of broadband is the use of coaxial cable you might have in your home, which carries cable television signaling as well as high-speed Internet.

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

Below 1024 The well-known port numbers are all below 1024. An example would be HTTP at port 80.

Open Systems Interconnection (OSI) reference model

Commonly referred to as the OSI model or the OSI stack. This seven-layer model categorizes various network technologies.

Which layer of the OSI reference model contains the MAC and LLC sublayers?

Data link layer The data link layer of the OSI model is the only layer of the famous model that we typically divide into sublayers (the MAC and LLC sublayers).

physical layer

Layer 1 of the OSI model. This layer is concerned with the transmission of bits on a network.

network layer

Layer 3 of the OSI model. This layer is primarily concerned with forwarding data based on logical addresses.

presentation layer

Layer 6 of the OSI model. This layer is responsible for the formatting of data being exchanged and securing the data with encryption.

application layer (OSI model)

Layer 7 of the OSI model. This layer provides application services to a network. An important yet often-misunderstood concept is that the end-user applications do not reside at the application layer. Instead, the application layer supports services used by end-user applications. Another function of the application layer is advertising available services.

IP addresses reside at which layer of the OSI reference model?

Network Layer An IP address is a typical ingredient of at the network layer (Layer 3) of the OSI model. Routers use these addresses to route traffic through an internetwork.

State transition modulation

One way to electrically or optically represent a a binary 1 or 0 is to use the transition between a voltage level (ex, going from a state of no voltage to a state of voltage, or vice versa, on a copper cable) or the transition of having light or no light on a fiber-optic cable to represent a binary 1. Similarly, a binary 0 is represented by having no transition in a voltage level or light level from one time period to the next. This approach of representing binary digits is called state transition modulation.

current state modulation

One way to electrically or optically represent a binary 1 or 0 is to use current state modulation, which represents a binary 1 with the presence of voltage (on a copper cable) or the presence of light (on a fiber-optic cable). Similarly, the absence of light or voltage represents a binary 0.

Identify 3 mail protocols:

SMTP, POP3, IMAP4 SMTP, POP3, and IMAP4 are all examples of email protocols. Note that it is very easy to confuse SMTP with SNMP. Simple Network Management Protocol aids in the robust management of network devices.

Which protocol supports a secure connection to a remote host via terminal emulation software?

SSH Secure Shell (SSH) provides a secure alternative to Telnet when it comes to remotely accessing a network device for management of that device.

time-division multiplexing (TDM)

Supports different communication sessions (for example, different telephone conversations in a telephony network) on the same physical medium by allowing sessions to take turns. For a brief period of time, defined as a time slot, data from the first session is sent, followed by data from the second session. This continues until all sessions have had a turn, and the process repeats itself.

Protocol data unit (PDU)

The name given to data at different layers of the OSI model. Specifically, the PDU for layer 4 is segment. The layer 3 PDU is packet, the layer 2 PDU is frame, and the Layer 1 PDU is bit.

network interface layer

The network interface layer of the TCP/IP stack (also known as the network access layer) encompasses the technologies addressed by Layers1 and 2 (that is, the physical and data link layers) of the OSI model.

transport layer (TCP/IP stack)

The transport layer of the TCP/IP stack maps to Layer 4 (transport layer) of the OSI model. The two primary protocols found at the TCP/IP stack's transport layer are TCP and UDP.

Internet layer

This layer of the TCP/IP stack maps to Layer 3(network layer) of the OSI model. Although multiple routed protocols (for example, IPv4 and IPv6) may reside at the OSI model's network layer, the Internet layer of the TCP/IP stack focuses on IP as the protocol to be routed through a network.

Windowing is provided at what layer of the OSI model?

Transport layer The transport layer offers TCP and UDP. With TCP, a connection-oriented protocol, windowing can be used to dictate how much data is sent at one time.

What are the four layers of the TCP/IP stack?

Transport layer, Internet layer, Application layer, Network interface layer.

Which of the following is a connectionless transport layer protocol?

UDP User Datagram Protocol (UDP) sacrifices reliability for speed and efficiency in the transport of data.