Question

You want to transfer a document from one computer to another, and you want the document to be encrypted. The destination computer is on another network, so you know data has to travel through one or more routers. The network technology on your network is Token and ring, but the technology on the destination network is Wi-Fi. From what you have learned about networking, should this document transfer work? Why or why not? Which layers of the OSI model are involved in the italicized parts of this description?

Answer 1

Did you find an ENCRYPTED file on your computer and wonder what program should open it ?

May be someone emailed you an ENCRYPTED file but you're not sure how to use it. Perhaps you tried to open ENCRYPTED file but Windows told you that it could not open it.

Before you can open an ENCRYPTED file (assuming it's even a file format that's intended to be viewed or edited),you"ll need to determine what kind of file the .ENCRYPTED file extension refers to.

Enncrypting File System(EFS) only works on computers that use the NTFS file system. If the file you want to encrypt is on a volume that uses the FAT or FAT32 file system, you need to convert the volume to NTFS to make the Advanced button appear.For more information,

The OSI model defines internet working in terms of a vertical stack of seven layers. The upper layers of OSI model represent software that implements network services like encryption and connection management. The lower layers of OSI model implement more primitive, hardware-oriented functions like routing, addressing, and flow control.

The OSI model was introduced in 1984. Although it was desinged to be an abstract model, the OSI model remains a practical framework for today's key network technologies like Ethernet and protocols like IP.

The OSI model should be used as a guide for how data is transmitted over the network. It is an abstract representation of the data pathway and should be treated as such.

The OSI model was specifically made for connecting open systems. These systems are desinged to be open for communication with almost any other system. The model was made to breakdown each functional layer so that overall design complexity should be lessened. The model was constructed with seven layers for the flow of information. These are:

1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data link layer
7. Physical layer

1.1 Application layer : Provides a means for the user to access information on the network through an apllication. This layer is the main interface for the user to interact with the application the therefore the network.

The application layer is the OSI layer closest to the end user, which means that both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. Such apllication programs fall outside the scope of the OSI model. Application layer functions typically include identifying communication partners, and synchronizing communication. When identifying communication partners, the application layer determines the identity and availability of communication partners, the application layer must decide whether sufficient network resources for the requested communication exist. In synchronizing communication, all commication between applications requires cooperation that is managed by the application layer.

1.2 Presentation layer : Manages the presentation of the information in an ordered and meaningful manner. This layer's primary function is the syntax and semantics of the data transmission. It converts local host computer data representations into a standard network format for transmission on the network. On the recieving side, it changes the network format into the appropriate host computer. ASCII and EBCDIC conversions, cryptography, and the like are handled here.

The presentation layer provides a variety of coding and conversion functions that are applied to application layer data. These functions ensure that infornation sent from the application layer of one system would be readable by the application layer of another system. Some examples of presentation layer coding and conversation schemes include common data representation formats, common data compression schemes, and common data encryption schemes.

Common data representation formats, or the use of standard image, sound, and video formats, enable the interchange of apllication data between different types of computer systems. Using different text and data representations, such as EBCDIC and ASCII, uses conversion schemes to exchange information with systems. Standard data compression schemes enable data that is compressed. or encrypted at the source device to be properly decompressed, or deciphered at the destination.

Presentation layer implementations are not typically associcated with a particular protocol stack. Some well known standards for video include QuickTime and Motion Pictures Experts Groups (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

Among well known graphic image formats are graphics interchange format (GIF), joint photographic experts group (JPEG), and tagged image file format(TIFF), GIF is a standard for compressing and coding graphic images, and TIFF is a standard coding format for graphic images.

1.3. Session layer : Coordinates dialogue/session/connection between devices over the network. This layer manages communications between connected sessions. Examples of this layer are token management (the session layer manages who has the token) and network time synchronization.

The session layer establishes, manages, and terminates communication sessions. Communication sessions consist of service requests and service responses that occur between applications located in different network devices. These requests and responses are coordinated by protocols implemented at the session layer. Some examples of session-layer implementations include Zone Information Protocol (ZIP), the AppleTalk protocol that coordinates the name binding process; and Session Control Protocol (SCP), the Decent Phase IV session layer protocol.

1.4. Transport layer: Responsible for reliable transmission of data and service specification between hosts. The major responsibility of this layer is data integrity--that data transmitted between hosts is reliable and timely. Upper layer data grams are broken down into network-sized data grams if needed and then implemented using appropriate transmission control. The transport layer creates one or more than one network connection, depending on conditions. This layer also handles what type of connection will be created. Two major transport protocols are the TCP (Transmission Control Protocol) and the UDP (User Data gram Protocol).

Important features of Transport layer:

Transport layer ensures reliable service.
Breaks the message (from sessions layer) into smaller packets, assigns sequence number and sends them.
Reliable transport connections are built on top of X.25 or IP.
In case IP, lost packets arriving out of order must be reordered.
Important features of TCP/UDP:

TCP/IP Widely used for network/transport layer (UNIX).
TCP (Transport Control Protocol): This is a connection oriented protocol.
UDP (Universal Data gram Protocol): This is a connectionless transport layer protocol.
Application programs that do not need connection-oriented protocol generally use UDP.
1.5 Network layer : Responsible for the routing of data (packets) through the network; handles the addressing and delivery of data. This layer provides for congestion control, accounting information for the network, routing, addressing, and several other functions. IP (Internet Protocol) is a good example of a network layer protocol. Network layer does not deal with lost messages.

Important features of Network layer protocols:

Concerned with the transmission of packets.
Choose the best path to send a packet (routing).
The routing may be complex in a large network (e.g. Internet).
Routing packets through a network may be accomplished by using simple static routes or by using complex dynamic routing algorithms.
1.6 Data link layer : Provides for the reliable delivery of data across a physical network. This layer deals with issues such as flow regulation, error detection and control, and frames. This layer has the important task of creating and managing what frames are sent out on the network. The network data frame, or packet, is made up of checksum, source address, destination address, and the data itself. The largest packet size that can be sent defines the maximum transmission Unit (MTU).

Important features of Data link layer:

Handles errors in the physical layer.
Groups bits into frames and ensures their correct delivery.
Adds some bits at the beginning and end of each frame plus the checksum.
Receiver verifies the checksum.
If the checksum is not correct, it asks for retransmission. (Send a control message).
Consists of two sub layers:
Logical Link Control (LLC) defines how data is transferred over the cable and provides data link service to the higher layers.

Medium Access Control (MAC) defines who can use the network when multiple computers are trying to access it simultaneously (i.e. Token passing, Ethernet [CSMA/CD]).

The data link layer provides reliable transit of data across a physical network link. Different data link layer specifications define different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control. Physical addressing (as opposed to network addressing) defines how devices are addressed at the data link layer. Network topology consists of the data link layer specifications that often define how devices are to be physically connected, such as in a bus or a ring topology. Error notification alerts upper-layer protocols that a transmission error has occurred, and the sequencing of data frames reorders frames that are transmitted out of sequence. Finally, flow control moderates the transmission of data so that the receiving device is not overwhelmed with more traffic than it can handle at one time.

The protocols used in Data link layer are SLIP, PPP, MTU, and CSLP.
1.7 Physical layer : Handles the bit-level electrical/light communication across the network channel. The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between communicating network systems. Physical layer specifications define characteristics such as media, voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors.

Basically, this layer ensures that a bit sent on one side of the Network is received correctly on the other side.

Data travels from the application layer of the sender, down through the levels, across the nodes of the network service, and up through the levels of the receiver

To keep track of the transmission, each layer "wraps" the preceding layer's data and header with its own header. A small chunk of data will be transmitted with multiple layer headers attached to it. On the receiving end, each layer strips off the header that corresponds to its respective level.

Physical layer is concerned with the following:

Physical interface characteristics like electrical, and mechanical specifications,
Number of bits of second to be transmitted,
Transmission type like duplex or half-duplex etc.
Frequently used Physical layer protocols:

Some of the important standards that deal with physical layer specifications are:

RS-232(for serial communication lines), X.21, EIA 232, and G730.

Physical layer and Data link layer implementations can be categorized as either LAN or WAN specifications.