Application -File, printing, message, database, and application services.

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Presentation -Data encryption / decryption, compression, and also translating services.
Session -Dialog control.
Transport -End to end connection.
Network -Routing.
Data Link -Framing.
Physical -Physical topology.
Advantages of making use of a Layered ModelAllows a layer to be changed without impacting the remainder of the model.Interoperability between network applications is boosted by making use of a standard interface.Design and breakthrough efforts can be do in a modular fashion.Network operations and also troubleshooting have the right to be simplified. Five Conversion procedures of Data Encapsulation Data >> Segments >> Packets >> Frames >> BitsUpper layers convert and format the information into data and also send it come the deliver Layer.The transfer layer transforms the data right into segments and also adds headers then sends out them come the Network layer.The Network layer receives the segments and converts them into packets and also adds header information (logical addressing) and sends them come the Data link Layer.The Data link layer obtain the packets and converts them right into frames and adds header information (physical source and destination addresses) and also sends the frames come the physical Layer.The physical layer receive the frames and also converts them right into bits to be placed on the network medium.

Application Layer

The applications layer is the OSI class closest to the finish user, which means that both the OSI applications layer and the user connect directly with the software application application. This great interacts with software application applications that implement a interacting component. Such application programs fall external the limit of the OSI model. Application-layer functions typically include identifying communication partners, determining source availability, and synchronizing communication.

When identifying interaction partners, the applications layer identify the identification and access of communication partners for an application through data to transmit. Once determining source availability, the applications layer have to decide whether adequate network resources for the requested communication exist. In synchronizing communication, every communication between applications requires cooperation that is regulated by the application layer.Two key types of application-layer implementations room TCP/IP applications and OSI applications. TCP/IP applications are protocols, such as Telnet, paper Transfer Protocol (FTP), and simple Mail carry Protocol (SMTP), that exist in the internet Protocol suite. OSI applications space protocols, such as record Transfer, Access, and Management (FTAM), virtual Terminal Protocol (VTP), and Common Management info Protocol (CMIP), the exist in the OSI suite.

Internetworking Applications


-Connects many servers presenting diverse formats: multimedia, graphics, text, sound, and video. Applications such as Netscape Navigator, web Explorer, and Mosaic leveling accessing and also viewing internet sites.


-Versatile have the right to use SMTP or X.400 to deliver messages in between different email applications.

Electronic Data Interchange

-Composite of devoted standards the facilitates the circulation of jobs such as accounting, shipping / receiving, and also order and also inventory tracking between business.

Bulletin Boards

-Includes internet chat rooms, and sharing windy domain software.

Internet navigation Utilities

-Includes Gopher, WAIS, and search engines, e.g. Yahoo, Excite, and Alta Vista. Helps users locate resources and also information on the Internet.

Financial Transaction Services

-They gather and sell info pertaining to investments and also credit data to their subscribers.

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Presentation Layer

The presentation layer gives a selection of coding and also conversion attributes that are used to application layer data. These attributes ensure that information sent native the application layer the one mechanism will it is in readable through the application layer of another system. Some examples of presentation-layer coding and conversion schemes include usual data depiction formats, switch of character depiction formats, common data compression schemes, and common data encryption schemes.Common data representation formats, or the use of typical image, sound, and video clip formats, permit the interchange of application data in between different varieties of computer systems. Switch schemes are offered to exchange info with equipment by using different text and data representations, such as EBCDIC and ASCII. Typical data compression schemes allow data that is compressed at the source machine to be appropriately decompressed in ~ the destination. Typical data encryption schemes permit data encrypted at the source machine to be correctly deciphered in ~ the destination. Presentation-layer implementations are not typically linked with a particular protocol stack. The complying with serve to direct graphic and also visual image presentations:


-Picture style used through Mac and also PowerPC programs for delivering Quick attract graphics.


-Tagged Image record Format, a traditional graphics format for high-resolution bitmapped images.


-Joint Photographic experts Group standards.


-Musical instrument Digital Interface, supplied for digitized music.


-Moving picture Experts Group, standard for compression and also coding of movement video. Digital storage and bit rates up to 1.5 Mbps.


-Mac and PowerPC audio and video clip applications.

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Session Layer

The conference layer establishes, manages, and also terminates communication sessions in between presentation layer entities. Interaction sessions consists of organization requests and also service responses that occur in between applications situated in various network devices. This requests and responses room coordinated by protocols implemented at the session layer. Some instances of session-layer implementations incorporate Zone details Protocol (ZIP), the AppleTalk protocol that collaborates the surname binding process; and also Session manage Protocol (SCP), the DECnet phase IV session-layer protocol. Also provides dialog control between devices or nodes. Coordinates and also organizes communications between system by offering three different modes: simplex, half-duplex, and also full-duplex. The layer basically keeps different applications" data different from various other applications" data.

Session great Protocols and Interfaces


-Network paper System, developed by sunlight Microsystems and also used v TCP/IP and also Unix workstations to enable transparent access to far resources.


-Developed through IBM to administer users through a simpler way to define their info requirements top top both local and remote systems.


-A broad client / server redirection tool used for disparate business environment. Its actions are created on clients and also performed on servers.

X Window

-Widely offered by smart terminals for interactions with far Unix computers, permitting them to operate as though they were locally attached monitors.

AppleTalk conference Protocol

-A customer / server mechanism which establishes and also maintains sessions between AppleTalk customer and server machines.

Digital Network style Session control Protocol

-A DECnet conference layer protocol.

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Transport Layer

The carry layer implements trusted internetwork data transport solutions that room transparent to upper layers. Transport-layer functions generally include flow control, multiplexing, virtual circuit management, and also error checking and recovery. Services situated in move layer both segment and reassemble data from upper layer applications and also unite it onto the exact same data stream. They provide end-to-end data transport services and also can create a reasonable connection in between the sending host and destination hold on an Internetwork. It also hides details of any type of network dependent details from the greater layer by giving transparent data transfer.

Flow Control

-Data truth is guarantee by keeping flow control and allowing users the option to request dependable data transport in between systems. Flow manage manages data transmission between devices so that the transmitting machine does no send an ext data than the receiving an equipment can process. Trusted data transport employs a connection-oriented interaction session in between systems. The protocols ensure that the adhering to are achieved:

-segments delivered are recognized to sender top top delivery.

-non acknowledged segments space re-sent.

-segments space put back in sequence upon come at their destination.

-a controlled data flow is preserved to avoid congestion, overloading, and also data loss.


The carry layer is responsible for providing mechanisms because that multiplexing top layer applications. Multiplexing allows data from several applications to be transmitted onto a solitary physical link.

Virtual Circuits

Virtual circuits room established, maintained, and also terminated through the transfer layer.

Error Checking and Recovery

Error checking involves producing various mechanisms because that detecting infection errors, while error recovery involves taking one action, such together requesting the data be retransmitted, come resolve any errors that occur.


-Positive acknowledgement v retransmission guarantee that reliable data distribution by inquiry a receiving machine to send an acknowledgment post tothe sender once it receive data. The sending device documents every segment sent and also waits because that an acknowledgment prior to sending the nextsegment. Using windowing, the maker will carry an agreed upon variety of segments. If the receiving device receives every the segment intact, itwill request the following segment that the following window. If it misses a segment, it will certainly request the lacking segment and also will transmit a request for the nextsegment that the next window, once the very first window"s segments space all received.

-During a transfer, congestion have the right to occur since high speed computers can generate data faster that the network deserve to transfer that or because many computersare utilizing the network and also sending datagrams v a solitary gateway. Once a machine receives a overwhelming of datagrams, it stores them in a buffer. Ifthe buffer fills, all extr datagrams room discarded. Carry can issue a "not ready" signal to protect against a maker from transmittingadditional segments. When the buffer is emptied, it sends a "ready" carry indicator. When the waiting device receives this"go" signal, it proceeds where that left off. To prevent failures in data transfers, the receiving host acknowledges every segment the receives.

Connection-Oriented Communications

-In reputable transport operations

One device very first establishes a link oriented session through is peer (Initiation) Both host"s applications programs begin by notifying their individual Operating equipment that a connection is around to it is in initiated. (Synchronization) The two Operating Systems communicate by sending messages end the network confirming the the move is approved and both political parties are all set for the to take place. (Negotiating) as soon as the synchronization is complete, a connection is fully established and also data move begins. (Established) The data transfers. While the details is gift transferred between hosts, the two makers periodically check in through each other, connecting through your protocol software program to ensure the all is walk well and that data is being got properly.


-A home window is the number of segments that have the right to be sent without receiving an acknowledgement. Windowing deserve to increase the throughput because that data exchangesby limiting the variety of acknowledgments essential for complete segments transferred. Example: if the home window size is three then an acknowledgment is forced afterthe 3rd segment is transferred.

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Network Layer

The Network layer gives routing and also related features that allow multiple data web links to be combined into an internetwork. This is accomplished by the logical addressing (as opposed to the physics addressing) of devices. The network layer supports both connection-oriented and also connectionless organization from higher-layer protocols. Network-layer protocols frequently are routing protocols, yet other types of protocols are imposed at the network layer as well. Routers work-related at this level and administer the routing solutions for an internetwork.

Routing a Packet

The router receives the packet and also looks increase the location IP address. If the packet isn"t destined for the router, the router looks because that the destination deal with in the routing table. Once the destination interface is found, the packet will be sent to the interface. In ~ the destination interface, the packet is framed and sent the end on the local network.

-There room two varieties of packets in ~ the Network layer.

Data Packets

-Used to deliver user data with internetwork.

-Uses routed protocols together as: IP and also IPX.

Router upgrade Packets

-Used to upgrade neighbor routers about networks connected to routers ~ above the internetwork.

-Routing protocols: RIP, EIGRP, OSPF.

-Builds and also maintains routing tables on each router.

Routing Table

Network Address

-Protocol certain network addresses. A table is preserved for individual routing protocols since each protocol keeps track of a network v a various addressing scheme.


-The interface the packet is sent on once destined for a specific network.


-The distance to the remote network.

-Routers breakup broadcast domains by no forwarding transfer or multicast packets through a router. They likewise breakup collision domain names as eachinterface is a separate network.

-Routers use logical addresses in a network class header to determine the next hop router to front the packet to.

-Routers can use access lists to regulate security ~ above packets entering or leaving an interface.

-Routers can administer layer 2 bridging and also can simultaneously course through the exact same interface

-Routers administer connections between Virtual LANs. (VLANs)

-Routers can provide Quality of company for specific species of network traffic.

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Network vs. Data connect Layer AddressesNetwork layer addressing is described as reasonable addressing, conversely, Data connect layer addressing supplies physical addresses. The physical address of a maker can"t be adjusted without remove or replacing the hardware (physical attend to is shed into a NIC"s ROM); if a logical resolve is configured in software and can be adjusted as needed.

Data attach Layer

The Data connect layer provides reliable transit the data throughout a physical network link. Various Data link layer specifications specify different network and also protocol characteristics, including physical addressing, network topology, error notification, sequencing that frames, and also flow control. The Data attach layer converts messages native the Network layer into bits for the physics layer to transmit. It styles messages right into data frames and also adds a customized header include the resource and location hardware addresses. Data link layer is responsible because that uniquely identify each device on a local network.

Physical addressing (as protest to network addressing) specifies how devices are addressed at the data link layer. Network topology is composed of the data link layer specifications that often define how tools are to it is in physically connected, such together in a bus or a ring topology.Error notification alerts upper-layer protocols that a infection error has actually occurred, and the sequencing of data frames reorders frames that are transmitted out of sequence. Flow control moderates the infection of data so the the receiving machine is not overwhelmed with much more traffic than it have the right to handle at one time.

-When a packet is sent in between routers, that is framed with control information in ~ the Data attach layer. The details is eliminated at the location router and only the initial packet remains. If the packet is to walk to one more router, the framing procedure is repetitive until it it s okay to the receivinghost. The packet is never ever altered, just encapsulated with control information to it is in passed on to the different media type.

The IEEE has actually subdivided the data attach layer into two sublayers: Logical connect Control (LLC) and also Media access Control (MAC).

MAC (Media access Control)

The Media accessibility Control (MAC) sublayer of the data link layer manages protocol access to the physical network medium. The IEEE MAC specification specifies MAC addresses, which enable multiple devices to uniquely identify one an additional at the data attach layer.--The MAC describes how a station schedules, transmits and also receives data ~ above a mutual media environment.

--Ensures trusted transfer of information throughout the link, synchronizes data transmission, establish errors (doesn"t exactly them), and controls the flow of data.

--Defines just how packets are put on the media.

--Physical addressing is identified here as well as local topologies.

--MAC example is Ethernet/802.3 and Token Ring/802.5

--Line discipline, error notification, ordered shipment of frames, and also optional flow control can be provided at this layer.

--In General, MACs are only vital in mutual medium atmospheres where many nodes can affix to the very same transmission medium.

LLC (Logical attach Control)

The Logical attach Control (LLC) sublayer the the data connect layer manages communications in between devices over a solitary link that a network. Gmbh is characterized in the IEEE 802.2 specification and supports both connectionless and also connection-oriented services offered by higher-layer protocols. IEEE 802.2 specifies a variety of fields in data link layer frames that allow multiple higher-layer protocols come share a solitary physical data link.

--Responsible because that identifying Network class protocols and encapsulating them.

--A gmbh header tells the Data attach layer what to carry out with a packet once it is received.

Switches and also Bridges

Work in ~ Data attach layer and also filter network making use of MAC addresses. Great 2 switching is hardware based switching because it supplies an ASIC (Application specific Integrated Circuit).Switches and Bridges review each structure as it overcome through, it then puts the resource address in a filter table and keeps monitor of which harbor it was got on. This speak the switch wherein that device is located.After a filter table is built, the machine will only forward frames come the segment where the destination resolve is located. If the destination an equipment is on the very same segment together the frame, the great 2 machine will block the from being forwarded. If the location is on one more segment, the frame will just be forwarded to the segment (transparent bridging).When a class 2 an equipment receives a frame and also the destination is unknown come the device"s filter table, it will forward the structure to all connected segments. If the unknown device replies, the filter table is updated v that device"s location.

-Layer 2 gadgets (Switches / Bridges) propagate transfer storms and also the only way to protect against them is through a router.

-Each port on a move is in its very own collision domain.

-Switches enable all segment to transmit simultaneously.

-Switches can"t translate various media types.

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Physical Layer

The physics layer defines the electrical, mechanical, procedural, and functional specifications because that activating, maintaining, and deactivating the physics link between communicating network systems. Physical layer specifications define qualities such together voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and also physical connectors. Physical-layer implementations deserve to be categorized as either LAN or WAN specifications.

-The physical layer has actually two responsibilities, send and also receive bits (bits have actually a value of 1 or 0).

-The interface between DCEs and DTEs is characterized at the physics layer.

-The DCE is top top the organization provider side.

-The DTE is the fastened device, the services available to a DTE are accessed with a CSU/DSU.

-HSSI Peer-based interactions assumes intelligence in DCE and also DTE devices.

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Hubs and also Repeaters

-Hubs room multiple harbor repeaters. A repeater receives a signal, regenerates the digital signal, and forwards the on all energetic ports. An active hub walk the same thing. All devices plugged right into a hub room on the same collision and also the same broadcast domains. Hubs don"t look at at any traffic the enters, it just forwards all website traffic to all ports. Every maker connected to the hub must listen if a device transmits.