OSI & TCP/IP Model

Session Layer (Layer 5)

The session layer is responsible for managing and controlling the synchronization of data between applications on two devices. It does this by establishing, maintaining, and breaking sessions. Whereas the transport layer is responsible for setting up and maintaining the connection between the two nodes, the session layer performs the same function on behalf of the application.

Layer 3: The Network Layer

This layer is responsible for routing, which does not specify how the data is passed, but rather provides the mechanisms to do so. Responsible for route selection. At this layer, the logical grouping of data is referred to as a packet.

Example of real world Physical Layer

* Ethernet, DSL, ISDN, modems * 568A/B standards * Bus, Ring, Star, Mesh * 10BASE-T, 10BASE2, etc. * 802.11x standards * T1 and other T-carrier links * SONET/SDH * Optical Transport Network (OTN)

What Layer of the OSI model does a AP operate

Access point (AP) operate at the Data link (Layer 2)

Layers Of The OSI model

Layer 1 - Physical Layer 2 - Data link Layer 3 - Network Layer 4 - Transport Layer 5 - Session Layer 6 - Presentation Layer 7 - Application

What Layer of the OSI model does a Router operate

Network (Layer 3)

Transport Layer of The TCP/IP model

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

What other Name does the TCP/IP model go by

This model is known as the DoD model, as it was developed by the department of defence or the TCP/IP stack .

Three Characteristics of the MAC sub-layer @ level 2.

Assigns a 48-bit address assigned to a device's network interface card (NIC). Devices at this layer view a network as a logical topology, like a bus or a ring. Implement some strategy for determining when a device is allowed to transmit on the media, to minimize signal interference/collision.

What happens at the Physical Layer

At this layer, binary expressions (that is, a series of 1s and 0s) represent data. A binary expression is made up of bits, where a bit is a single 1 or a single 0. How bits are represented on the medium Wiring standards for connectors and jacks Physical topology Synchronizing bits Bandwidth usage Multiplexing strategy

What Layer of the OSI model does a Bridge operate

Data link (Layer 2)

What Layer of the OSI model does a NIC operate

Data link (Layer 2)

What Layer of the OSI model does a Switch operate

Data link (Layer 2) or network (Layer 3) for a multi-function switch

Application services at layer 7

Examples of the application services residing at the application layer include file sharing and e-mail.

Example other than TCP/UDP protocol at layer4

Internet Control Message Protocol (ICMP) is another transport layer protocol you are likely to encounter. ICMP is used by utilities such as ping and traceroute

What are the layers of TCP/IP model

Network Interface Layer ( aka Network Access or Link layer) Internet Layer Transport Layer Application Layer

What does OSI abbreviation stand for?

Open Systems Interconnect

What Layer of the OSI model does a Hub operate

Physical (Layer 1)

Service addressing at the Transport Layer

Protocols such as TCP/IP support many network services. The transport layer ensures that data is passed to the right service at the upper layers of the OSI model.

Characteristics of the Logical Link Control (LLC) sub-layer @ layer 2.

Provides an acknowledgement to the other device to confirm the message was sent Prevents the user from being overwhelmed with data by limiting the volume of data that can be sent at any one time. Informs the sender if any sent data was corrupted or not sent completely. Coordinates the transmission of data, so both sides know what to expect and when.

Service advertisement at Layer 7

Service advertisement: Some applications' services (for example, some networked printers) periodically send out advertisements, making the availability of their service known to other devices on the network. Other services, however, register themselves and their services with a centralized directory (for example, Microsoft Active Directory), which can be queried by other network devices seeking such services.

Internet layer of TCP/IP model

The Internet layer of the TCP/IP stack maps to Layer 3 (the network layer) of the OSI model. Although multiple routed protocols (for example, IP, IPX, and AppleTalk) 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

Network Interface Layer of TCP/IP stack

The TCP/IP stack's network interface layer encompasses the technologies addressed by Layers 1 and 2 (physical and data link layers) of the OSI model.

Application Layer Of The TCP/IP model

The biggest difference between the TCP/IP stack and the OSI model is found at the TCP/IP stack's application layer. This layer addresses concepts described by Layers 5, 6, and 7 (the session, presentation, and application layers) of the OSI model. Application layer protocols in the TCP/IP stack are identifiable by unique port numbers .

Application Layer ( Layer 7)

The function of the application layer is to take requests and data from the users and pass them to the lower layers of the OSI model. Incoming information is passed to the application layer, which then displays the information to the users. Some of the most basic application-layer services include file and print capabilities. Two basic services include • Application services and Service advertisement

Presentation Layer (Layer 6)

The presentation layer's basic function is to convert the data intended for or received from the application layer into another format. Such conversion is necessary because of how data is formatted so that it can be transported across the network. Applications cannot necessarily read this conversion. Some common data formats handled by the presentation layer include the following: Graphics files: JPEG, TIFF, GIF, and so on are graphics file formats that require the data to be formatted in a certain way. Text and data: The presentation layer can translate data into different formats, such as American Standard Code for Information Interchange (ASCII) and Extended Binary Coded Decimal Interchange Code (EBCDIC). Sound/video: MPEG, MP3, and MIDI files all have their own data formats to and from which data must be converted. Another important function of the presentation layer is encryption, which is the scrambling of data so that it can't be read by anyone other than the intended recipient. Given the basic role of the presentation layer—that of data-format translator—it is the obvious place for encryption and decryption to take place.

Segmentation at the Transport Layer

To traverse the network, blocks of data need to be broken into packets of a manageable size for the lower layers to handle. This process, called segmentation, is the responsibility of the transport layer.

Two common transport layer protocols

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 that dropped segment. Specifically, a receiver acknowledges segments that it receives. Based on those acknowledgments, a sender can determine which segments were successfully received and which segments need to be transmitted again. User Datagram Protocol (UDP): A connectionless 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.

Transport Layer (Layer 4)

This layer acts as a dividing line between the upper layers and lower layers of the model. Data is encapsulated or decapsulated, and sent on the appropriate path. Provide mechanisms to transport data between network devices. Incorporates error checking, service addressing, and segmentation.

What happens at the Data Link Layer ?

This layer is concerned with packaging data into frames and transmitting those frames on the network, performing error detection/correction, uniquely identifying network devices with an address, and handling flow control.

Two common flow control approaches at Layer 4

Windowing: Data is sent in groups of segments that require only one acknowledgment. The size of the window (that is, how many segments fit into one acknowledgment) is defined when the session between the two devices is established. As you can imagine, the need to have only one acknowledgment for every, say, five segments can greatly reduce overhead. Buffering: With buffering, a device (for example, a router) allocates a chunk of memory (sometimes called a buffer or a queue) to store segments if bandwidth is not currently available to transmit those segments. A queue has a finite capacity, however, and can overflow (that is, drop segments) in the event of sustained network congestion. When buffering flow control is used, data is temporarily stored and waits for the destination device to become available. Buffering can cause a problem if the sending device transmits data much faster than the receiving device can manage.