The OSI Model

What does multiplexing do?

Allows multiple communication sessions to share the same physical medium.

What two major protocols are used on the Transport Layer?

TCP and UDP

What are the concerns of the LLC sub-layer of the Data Link Layer?

1. Connection Services 2. Flow Control 3. Error Control 4. Synchronizing transmissions

What happens at the Data Link Layer?

1. Packaging data into frames 2. Transmitting frames on the network 3. Performing Error detection/correction 4. Uniquely identifying network devices with an address 5. Handling Flow Control

What is a MAC Address?

A 48-bit address assigned to a device's network interface card (NIC) The first 24-bits are collectively referred to as the vender code.

When is Data called a 'frame' at the Data Link Layer of the OSI Model?

A frame is the network layer packet with the MAC address of the source and destination devices added. A frame also includes Cyclic Redundancy Check (CRC)

What is a Cyclic Redundancy Check?

A mathematical value that helps the receiving device identify any errors that may have occurred during transmission.

What is the function of error control at the Data Link Layer?

Allows the recipient of data to let the sender know whether the expected data frame was not received or whether it was received but is corrupted.

How is data represented at the Physical Layer?

Binary Expressions (Series of 1s and 0s)

What are the two main functions provided by acknowledgment messages, in regard to connection services?

Flow Control & Error Control

What are some protocols associated with the Application Layer?

HTTP 80 FTP TFTP SMTP 25

What are examples of devices defined by Physical Layer standards?

Hubs Wireless Access Points Network Cabling

What is the Network Layer of the OSI Model responsible for?

Layer 3 Responsible for moving data between systems throughout the internetwork and is where routing happens. Also responsible for assignment of IP addresses Routing protocols specify how each router identifies destination networks and the path data should take to arrive at that destination network.

What is the Presentation Layer of the OSI Model responsible for?

Layer 6 Thought of as the formatting layer; this layer deals with syntax, encryption and compression.

What is the Application Layer of the OSI Model responsible for?

Layer 7 Integrating network services with the operating system; provides an interface between an application running on the system and the rest of the network. DOES NOT REFER TO THE APPLICATION ITSELF

What two sub-layers make up the Data Link Layer

Media Access Control (MAC) & Logical Link Control (LLC)

What is the MAC sub-layer of the Data Link Layer concerned with?

Physical Addressing Logical Topology Method of Transmitting on the media

What does the Logical- Link Control sub-layer of the Data Link Layer responsible for?

Provides the interface between the lower layers and the upper layers of the OSI Model.

What does Time Division Multiplexing (TDM) strategy do?

Supports different communication sessions on the same physical medium by causing the session to take turns. Each session receives its own slot, even if one of the sessions does not have any data to transmit at the moment.

What occurs at the Physical layer when using Synchronous synchronization?

Synchronizes the internal clocks of both the sender and the receiver to ensure that they agree on when bits begin and end. A common approach is to use an external clock which is referenced by both the sender and receiver.

T/F: Layer 1 devices view a network as a physical topology.

True

What is the chronological process of sending data on the OSI Model

1. First it will compress and encrypt the data at the presentation layer, then append the session ID at the session layer; the data then goes on to the transport layer 2. The Transport layer breaks the data into blocks called segments and appends a port number to identify which top-layer application need to receive the data on the destination device; each segment then goes to the network layer. 3. The Network Layer appends the source and destination IP addresses to create a packet; the packets are then, sent to the Data Link layer 4. The Data Link Layer adds the source and destination MAC addresses and the CRC; the packet is now called a frame. 5. The frames are then sent to the Physical layer, in which they become signals that represent a series of zeros and ones; each data point in this string is called a bit.

T/F: Baseband technologies divide the bandwidth available on a medium into different channels, and different communication streams are then transmitted over the various channels.

False. This is an example of Broadband technologies.

What is the Physical Layer of the OSI Model concerned with?

How bits are represented on the medium Wiring standards for connectors and jacks Physical Topology Synchronizing bits Bandwidth usage Multiplexing strategy

What is the Physical Layer of the OSI Model responsible for?

Layer 1 Responsible for the Physical hardware, as well as protocols that identify the cables, connectors, and devices that can be used on the network. This layer deals with data in bits, electrical impulses, light impulses, or radio signal depending on the physical medium used.

What is the function of flow control at the Data Link Layer?

Limits the amount of data a sender can send at one time; this prevents the receiver from being overwhelmed with too much information.

What is UDP in terms of networking protocols and how does it operate within the Transport Layer of the OSI Model?

User Datagram Protocol Referred to as a connectionless protocol; more concerned with moving data through the network without necessarily ensuring that everything arrives at the destination device.

What is a common example of a Layer 2 address?

MAC Address

What are bits grouped together known as, in reference to the OSI Model?

Protocol Data Unit ( PDU) OR Data Service Unit OR Packets

What does the Media Access Control sub-layer of the Data Link Layer responsible for?

Responsible for identifying how devices can access the physical medium. A MAC address is assigned to data packets received from the Network Layer of the OSI Model

What is TCP in terms of networking protocols and how does it operate within the Transport Layer of the OSI Model?

Transmission Control Protocol Referred to as a connection-oriented protocol because it takes advantage of sequencing, error corrections, and flow control to ensure that data sent from upper layers is received at the receiving device.

T/F: Baseband technologies use all the available frequencies on a medium to transmit data.

True Ethernet is an example.

How do we describe protocols within the OSI Model? **Needs Work**

We describe protocols by the highest layer the protocol functions at.

How is data transmitted using current state modulation?

A presence or absence of voltage represents a 1 or 0; the same with light in fiber-optic cabling

What are the two fundamental approaches to bandwidth usage on a network at the Physical Layer?

Broadband & Baseband

How does a recipient know whether data received is missing or corrupted?

By mathematically calculating a checksum received; if the calculated checksum does not match the checksum received with the data frame, the recipient of the data draws the conclusion that the data frame is corrupted and can then notify the sender via an acknowledgment message.

What does Statistical Time-Division Multiplexing (StatTDM) do?

Dynamically assigns time slots to communications sessions on an as-needed basis.

In what form are MAC addresses commonly written?

Hexadecimal Notation

What is the Data Link Layer of the OSI Model responsible for?

Layer 2 Responsible for interfacing between the physical transmission media (the physical device) and the network layer. Also defines the logical topology of the network, or how devices access the media. MAC addresses are assigned to data packets from the Network Layer of the OSI Model. This layer is divided into two sub-layers: the Logical-Link Control and the Media Access Control sub-layer.

What is the Transport Layer of the OSI Model responsible for?

Layer 4 Delivering data on the network by segmenting the data into smaller blocks and identifies each block with a sequence number. Also responsible for flow control between two hosts as well as retransmission of lost segments or blocks. Also assigns port numbers, which identifies an upper later service running on a server; by using a port number, the transport layer can identify the upper layer protocol that the data is intended for.

What is the Session Layer of the OSI Model responsible for?

Layer 5 Creating & Terminating Sessions between communication devices; each client is connection is called a session. Uses a Session ID to identify unique sessions; this keeps the data stream separated so that information requested by one client isn't sent to another client.

What occurs at the Physical layer when using Asynchronous synchronization?

1. A sender indicates it about to start transmitting by sending a start bit to the receiver. 2. When the receiver sees this, it starts its own internal clock to measure the subsequent bits. 3. After the sender transmits its data, it sends a stop bit to indicate that it has finished its transmission.

What are the two basic approaches to bit synchronization?

Asynchronous & Synchronous

What does Frequency-Division Multiplexing do?

Divides a medium's frequency range into channels, and different communication sessions transmit their data over different channels This approach to bandwidth usage is called broadband.