In 1985, the Institute of Electrical and Electronic Engineers (IEEE) in the United States of America, produced a series of standards for Local Area Networks (LANs) called the IEEE 802 standards. These have found widespread acceptability and now form the core of most LANs. One of the IEEE 802 standards, IEEE 802.3, is a standard known as “Ethernet”. This is the most widely used LAN technology in the world today. Ethernet was developed by the Xerox Corporation’s Palo Alto Research Center (known colloquially as Xerox PARC) in 1972 and was probably the first true LAN to be introduced. The IEEE standards have been adopted by the International Standards Organization (ISO), and is standardized in a series of standards known as ISO 8802-3. ISO was created in 1947 to construct world-wide standards for a wide variety of engineering tasks. The name Ethernet comes from the physical concept of ether.
The ISO-OSI reference model specifies standards for describing “Open Systems Interconnection” with the term ‘open’ chosen to emphasize the fact that by using these international standards, a system may be defined which is open to all other systems obeying the same standards throughout the world.
The OSI layers may be summarized by:
- Physical layer: Provides electrical, functional, and procedural characteristics to activate, maintain, and deactivate physical links that transparently send the bit stream; only recognizes individual bits, not characters or multicharacter frames.
- Data link layer: Provides functional and procedural means to transfer data between network entities and (possibly) correct transmission errors; provides for activation, maintenance, and deactivation of data link connections, grouping of bits into characters and message frames, character and frame synchronization, error control, media access control, and flow control
- Network layer: Provides independence from data transfer technology and relaying and routing considerations; masks peculiarities of data transfer medium from higher layers and provides switching and routing functions to establish, maintain, and terminate network layer connections and transfer data between users.
- Transport layer: Provides transparent transfer of data between systems, relieving upper layers from concern with providing reliable and cost effective data transfer; provides end-to-end control and information interchange with quality of service needed by the application program; first true end-to-end layer.
- Session layer: Provides mechanisms for organizing and structuring dialogues between application processes; mechanisms allow for two-way simultaneous or twoway alternate operation, establishment of major and minor synchronization points, and techniques for structuring data exchanges.
- Presentation layer: Provides independence to application processes from differences in data representation, that is, in syntax; syntax selection and conversion provided by allowing the user to select a “presentation context” with conversion between alternative contexts.
- Application layer: Concerned with the requirements of application. All application processes use the service elements provided by the application layer. The elements include library routines which perform interprocess communication, provide common procedures for constructing application protocols and for accessing the services provided by servers which reside on the network.
The communications engineer is concerned mainly with the protocols operating at the bottom four layers (physical, data link, network, and transport) in the OSI reference model. These layers provide the basic communications service. The layers above are primarily the concern of computer scientists who wish to build distributed applications programs using the services
provided by the network.
Ethernet uses a scheme known as carrier sense multiple access with collision detection (CSMA/CD) governs the way the computers share the channel. When one computer wants to send some information, it obeys the following algorithm:
- Start – If the wire is idle, start transmitting, else go to step 4
- Transmitting – If detecting a collision, continue transmitting until the minimum packet time is reached (to ensure that all other transmitters and receivers detect the collision) then go to step 4.
- End successful transmission – Report success to higher network layers; exit transmit mode.
- Wire is busy – Wait until wire becomes idle
- Wire just became idle – Wait a random time, then go to step 1, unless maximum number of transmission attempts has been exceeded
- Maximum number of transmission
Strictly, “Ethernet” refers to a product, which predates the IEEE 802.3 Standard. However nowadays any 802.3 compliant network is referred to as an Ethernet. Over the years Ethernet has continued to evolve, with 10Base5 using thick coaxial cable approved in 1986, 10Base2 using cheaper thin coaxial cable approved in 1986. Twisted pair wiring was used in 10BaseT, approved in 1991 and fiber wire in 10BaseF, approved in 1994-95. In 1995 100Mbps Ethernet was released, increasing the speed of Ethernet, which has since been further increased with the release of Gigabit Ethernet in 1998-99. In the future, Ethernet will continue to increase in speed, with 10 Gigabit Ethernet recently ratified, with 40 Gigabit arriving soon and 100 Gigabit Ethernet technology demonstrations currently occurring. RJ-45 is a physical interface often used for terminating twisted pair type cables. “RJ” stands for Registered Jack which is part of the United States Code of Federal Regulations. It has eight “pins” or electrical connections per connector.
The protocols involved in Ethernet are IP, ICMP, MAC, TCP, UDP, FTP, SMTP, SNMP and ARP. The Internetwork Protocol (IP) provides a best effort network layer service for connecting computers to form a computer network. Each computer is identified by one or more globally unique IP addresses. Each packet carries the IP address of the sending computer and also the address of the intended recipient or recipients of the packet. Other management information is also carried. The IP address is 32-bit numbers. The center for allocating IP address is called Inter network information center (InterNIC). The IP addresses are divided into 5 classes class A, class B, class C, class D and class E.
ICMP protocol is used to report problems with delivery of IP datagrams within an IP network. It reports the problems such as when the end system is not responding, when IP network is not reachable, when the node is overloaded and when error occurs in the IP header. The 8-bit type code identifies the types of message. In this case two types of message are involved the ECHO request (sent by the client) and the ECHO reply (the response by the server). Each message may contain some optional data. When data are sent by a server, the server returns the data in the reply, which is generated. The address resolution protocol (ARP) is a protocol used by the IP, to map IP network addresses to the hardware addresses used by a data link protocol. The term address resolution refers to the process of finding an address of a computer in a network. The address is “resolved” using a protocol in which a piece of information is sent by a client process executing on the local computer to a server process executing on a remote computer. The information received by the server allows the server to uniquely identify the network system for which the address was required and therefore to provide the required address. The address resolution procedure is completed when the client receives a response from the server containing the required address.