Author: Neftaly Malatjie

We shall now look at various standards that exist in the networking industry. We shall look at some of them

1. ISO

Short for International Organization for Standardization. Note that ISO is not an acronym; instead, the name derives from the Greek word iso, which means equal. Founded in 1946, ISO is an international organization composed of national standards bodies from over 75 countries. For example, ANSI (American National Standards Institute) is a member of ISO. ISO has defined a number of important computer standards, the most significant of which is perhaps OSI (Open Systems Interconnection), a standardized architecture for designing networks.

2. OSI

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to their underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers. The original version of the model defined seven layers.

A layer serves the layer above it and is served by the layer below it. For example, a layer that provides error-free communications across a network provides the path needed by applications above it, while it calls the next lower layer to send and receive packets that comprise the contents of that path. Two instances at the same layer are visualized as connected by a horizontal connection in that layer.

3. SNA

(Systems Network Architecture) IBM’s mainframe network standards introduced in 1974. Originally a centralized architecture with a host computer controlling many terminals, enhancements, such as APPN and APPC (LU 6.2), adapted SNA to modern peer-to-peer communications and distributed computing environments. SNA has mostly been replaced with TCP/IP as the world has migrated to the IP protocol. Following are some of SNA’s basic concepts.

Cell relay systems break variable-length user packets into groups of fixed-length cells, that add addressing and verification information. Frame length is fixed in networking hardware, based on time delay and user packet-length considerations. One user data message may be segmented over many cells.

Cell relay systems may also carry bitstream-based data such as PDH traffic, by breaking it into streams of cells, with a lightweight synchronization and clock recovery shim. Thus cell relay systems may potentially carry any combination of stream-based and packet-based data. This is a form of statistical time division multiplexing.

Cell relay is an implementation of fast packet-switching technology that is used in connection-oriented broadband integrated services digital networks (B-ISDN, and its better-known supporting technology ATM) and connectionless IEEE 802.6 switched multi-megabit data service (SMDS).

At any time there is information to be transmitted; the switch basically sends the data units. Connections don’t have to be negotiated like circuit switching. Channels don’t have to be allocated because channels do not exist in ATM, and on condition that there is an adequate amount of bandwidth to maintain it, there can be indefinite transmissions over the same facility.

Cell relay utilizes data cells of a persistent size. Frames are comparable to data packets; however they contrast from cells in that they may fluctuate in size based on circumstances. This type of technology is not secure for the reason that its procedures do not support error handling or data recovery. Per se, all delicate and significant transmissions may perhaps be transported faster via fixed-sized cells, which are simpler to transmit compared to variable-sized frames or packets.

Cell relay is data transmission service that uses transmission technology referred to as Asynchronous Transfer Mode (ATM). As the name suggests, the data transmission unit is a fixed length of data known as a cell. High-speed transmission compared to other services like frame relay is possible with the cell relay method. The cell relay is considered by most to be the transport service of the future.

Frame relay is a packet-switching telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between endpoints in wide area networks (WANs). The service, once widely available and implemented, is in the process of being discontinued by major Internet service providers. Sprint ended its frame relay service in 2007, while Verizon said it plans to phase out the service in 2015. AT&T stopped offering frame relay in 2012 but said it would support existing customers until 2016.

Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the endpoints, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service provider figures out the route each frame travels to its destination and can charge based on usage. Switched virtual circuits (SVC), by contrast, are temporary connections that are destroyed after a specific data transfer is completed.

An enterprise can select a level of service quality, prioritizing some frames and making others less important. A number of service providers, including AT&T, offer frame relay, and it’s available on fractional T-1 or full T-carrier system carriers. Frame relay complements and provides a mid-range service between ISDN, which offers bandwidth at 128 Kbps, and Asynchronous Transfer Mode (ATM), which operates in somewhat similar fashion to frame relay but at speeds of 155.520 Mbps or 622.080 Mbps.

In computer networking, a hop represents one portion of the full path between source and destination. When communicating over the Internet, for example, data passes through a number of intermediate devices (routers and switches) rather than flowing directly over a single wire. Each such device causes data to “hop” between one point-to-point network connection and another.

The hop count represents the total number of devices a given piece of data (packet) passes through. Generally speaking, the more hops data must traverse to reach their destination, the greater the transmission delay incurred.

Network utilities like ping can be used to determine the hop count to a specific destination.

Ping generates packets that include a field reserved for the hop count. Each time a capable device receives these packets, that device modifies the packet, incrementing the hop count by one. In addition, the device compares the hop count against a predetermined limit and discards the packet if its hop count is too high.

This prevents packets from endlessly bouncing around the network due to routing