Why Networking Standards are Needed

• Keeps equipment interchangeable. No more need for specific equipment for specific machines.
• IBM stepped away from secrecy, so that add-ons could be developed for its PC.
• Beware of nonstandard equipment still available on the market.

Types of Standards

• There are many types of standards for computer equipment. These standards affect the following:

• Bus Design
• CPU Design
• Serial Port Design
• Parallel Port Design
• Keyboard Architecture
• Display Architecture
• Printer Communications
• Network Communications

• Standards create a common ground for transmitting data, manufacturing compatible network equipment, and designing operating systems for use on networks.
• Influences of networking standards include:

• What communications media are used and specifications for those media.
• How communications are established and maintained between nodes.
• How to determine if a communications error has occurred.
• What to do if a communications error has occurred.
• How fast and how far packets can travel on a network.
• How a network can be designed for reliable communications.
• What communications are used to manage a network.
• What equipment can be attached to a network and how.

Key Networking Standards Organizations

• American National Standards Institute

• ANSI
• http://www.ansi.org

• Institute of Electrical and Electronics Engineers

• IEEE
• http://standards.ieee.org
• 802 standards:

• Consultative Committee on International Telegraph and Telephone

• CCITT
• E-mail standards

• Mail service and user interface elements
• Guidelines for encoding and decoding mail objects
• Syntax for mail transfer
• Methods to ensure reliable mail transfer
• Guidelines for message transfer layer
• Messaging protocol for telex

• International Standards Organization

• Scientific
• Technological
• Economic
• Intellectual

OSI Layered Communications

• The ISO and ANSI have jointly developed a seven-layer network communications model known as OSI.
• The OSI is not a device or a set of software routines; it is a theoretical framework for understanding network communications.
• OSI guidelines apply to the following issues:
  • How network devices contact each other and how devices using different languages communicate.
  • How a network device knows when to transmit or not to transmit data.
  • How the physical network devices are arranged and connected.
  • Methods to ensure that network transmissions are received correctly.
  • How network devices maintain a consistent rate of data flow.
  • How electronic data is represented on the network media.
• The OSI model has seven distinct layers stacked on top of one another.

The Physical Layer

• Protocols in the physical layer are responsible for generating and detecting voltage to transmit and receive signals that carry data.
• Network cabling and equipment is also included in the physical layer.
• Interference is caused by nearby electrical motors, high voltage lines, lightning, and other electrical devices.

The Data Link Layer

• Responsible for the construction of frames.
• Each frame is formatted in a specified way so that data transmissions are synchronized from node to node.
• Errors are handled by the use of a cyclic redundancy check. This calculates a value for the total size of the information fields contained in a frame.
• LANs that follow IEEE specifications, the data link layer incorporates the logical link control and media access control sub-layers.

• The LLC is a data link sub-layer of the OSI model that initiates the communication link between nodes and ensures that the link is not unintentionally broken.

• Two types of services are used for communication between the LLC sub-layer and the network layer, which is the next layer up in the stack.

• Type 1 operation is a connectionless service.

• Does not establish a logical connection between the sending and receiving nodes.
• The success of data transmission is simply chance.
• Most commonly used LLC class for protocols employed by:

• Microsoft NetBEUI
• Novell IPX/SPX
• Internet TCP/IP

• Type 2 operation is a connection-oriented service.

• Logical connection is established between sending and receiving nodes before a full communication begins.
• Error recovery is possible.

The Network Layer

• The third layer which controls the passage of packets along the network.

• Physical routes which are cable paths.

• Routers are used to help the packet along it’s path.
• Routers are physical devices that contain software to enable packets formatted on one network to reach a different network in a format that the second network understands.

• Logical routes which are software paths.

• Virtual circuits are logical communication paths set up to send and receive data.

• This layer is responsible for tracking the situation and re-sequencing the frames before they are transported to the next layer.

Transport Layer

• Ensures that data is sent reliably from the sending node to the destination node.
• Flow control is used to make sure one device does not send information faster than can be received by another device.

The Session Layer

• Responsible for the continuity of the communications link between two nodes.
• It establishes the link and ensures that the link is maintained for the duration of the nodes.
• Also provides for orderly communication between nodes.

The Presentation Layer

• This layer takes care of data formatting.
• Each type of network uses a particular formatting scheme, which is accomplished in the presentation layer.

• EBCDIC- 256 character set
• ASCII- 96 upper and lowercase characters, and 32 nonprinting characters

• Responsible for data compression.

Application Layer

• Highest level of OSI model.
• Represents computer user’s most direct access to applications and network services on the computer.
• Provides network services for application software, such as databases.
• Some of the services are:

• The redirector is what allows remote access to another computer on a network.

Communication Between Stacks

• For two computers to communicate on a network, they both must be operating under the same theoretical model, such as the OSI model.
• Peer protocols allows and OSI layer on a sending node to communicate with the same layer on the receiving node.
• Information is transferred from one level to the next by means of commands called primitives. The information transferred is called a protocol data unit, or PDU.

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Node A sends packet to Node B

Applying the OSI Model

• Accessing a shared drive on another network computer is a good example of how layered communications work.

• The redirector at the application layer locates the shared drive.
• The presentation layer ensures that the data format is in the right format.
• The session layer establishes the link, and keeps it from being interrupted.
• The transport layer makes sure it is interpreted in the same order it was sent.
• The network layer make sure packets are sent along the fastest route.
• The data link layer constructs and makes sure packets go to the right station.
• The physical layer converts it into electrical signals to be sent over the network.