IEEE LAN STANDARD

IEEE LAN Standards

Institute of Electrical and Electronic Engineers (IEEE) has published a set of standards for LANs. The standards are collectively known as the IEEE 802.x standards. These standards have gained industry acceptance in the development and implementation of LANs.

The commonly used IEEE 802.x standards for LANs are:

1. IEEE 802.1
2. IEEE 802.2
3. IEEE 802.3
4. IEEE 802.4
5. IEEE 802.5

IEEE 802.1

The IEEE 802.1 LAN standard provides information about the prerequisites for the interface of LAN standards. This standard is also known as the Higher Layer Interface (HILI).
An interface is a set of services that a layer offers to the layer above it in the protocol suite.

IEEE 802.2

The IEEE 802.2 LAN standard is a part of the Logical Link Control (LLC) sublayer of the Data Link layer. LLC compensates for the difference between the various 802 networks by providing a single format and interface to the Network layer.

IEEE 802.3

The IEEE 802.3 LAN standard is used for 1-persistent Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) LAN, which is commonly known as Ethernet. Using the CSMA protocol, a node transmits data packets when it finds the channel or the transmission media idle. Due to this, it is known as 1-persistent CSMA.

If the channel is free, the node transmits data; otherwise, the node waits for it to become idle. If there is a collision in the channel, all nodes terminate their transmission, wait for a random time, and retransmit the data.
The IEEE 802.3 LAN standard falls under the MAC sublayer of the Data Link layer and the OSI Physical layer.

IEEE 802.4

The IEEE 802.4 LAN standard, which is also known as the token bus, was developed to avoid collisions on a network.

The token bus comprises of nodes, which are physically arranged linearly but logically organized to form a ring. Each node on the ring knows the addresses of the nodes to its immediate left and right. The following figure shows a token bus.

Token Bus

The token bus is based on a principle of a calculated wait period for each node in the ring. If the token bus takes time t for each node to transmit a frame and there are y nodes in the ring, the wait period for each node would be at most t*y. Each node in the ring holds the token for an equal time, transmits its frames within that period, and then passes the token to its neighbor.

NB: A token is a special control frame required by a node to send the frames on the logical ring. A control frame carries the administrative information responsible for maintaining the ring or delivering data from the source to the destination.

IEEE 802.5

The IEEE 802.5 LAN standard is also known as the Token Ring. The standard defines the specification for ring networks.
When the ring is initially set up, all the nodes are idle and the token circulates in the ring. When a node needs to transmit data frames to the ring, it would need to acquire the token and remove it from the ring. There is only one token traversing the ring and only the token holder can transmit its frames to the ring.

   

NETWORK COMPONENTS OF A LAN

Network Components of a LAN

Any network requires four components so that the nodes within it can communicate with each other and exchange information. These components include the following:

1. The transmission medium over which the data is exchanged
2. Rules and standards or protocols that facilitate the communication on the network
3. Software components in the form of NOS and management applications
4. Hardware devices that make up the network

Transmission media and protocols have already been covered in the previous articless. This section consists of the hardware components that are used in a LAN. These components include the following devices:

• Media connectors
• Network Interface Cards
• Repeaters
• Hubs
• Bridges
• Switches

Media Connectors

Media connectors are devices that connect a node to the transmission medium. They correspond to the Physical layer of the OSI reference model.

The commonly used media connectors include the following:

• British Naval Connectors (BNCs): These connectors connect coaxial cables to the node. These connectors are commonly used to connect nodes in a bus topology.
• T-Connectors: These connectors connect a network card of a PC to a network through cables.
• RJ-45 connectors: These connectors connect a PC to the network socket in the wall.
• DB-9 connectors: These connectors are used with different interfaces, such as video interfaces.
• DB-25 connectors: These connectors are used in serial connections and parallel interfaces, such as printers.

Network Interface Cards

Network Interface Cards (NICs) are the internal components of nodes and connect each node to the network. NICs operate in the Data Link layer of the OSI model. As a result, they perform the functions corresponding to this layer. They supply the hardware or physical address to each node on the network.

Repeaters

The information traversing through the transmission media on a network is known as a signal. Each medium has a maximum range to carry data reliably. While traversing, the signal undergoes weakening, degradation, and distortion because the length of the network segment increases. As a result, the transmission media restricts the network segment's length.

This problem is overcome by the use of a hardware device known as repeaters. Repeaters amplify and regenerate the signal from one node to another on a network. As a result, repeaters allow you to extend the effective length of the transmission media. A repeater does not filter or interpret the signal. It only repeats or regenerates the signal. The repeaters operate at the Physical layer of the OSI reference model. If the distance between the segments to be connected is very large, multiple repeaters may be required.

The following figure shows the extension of a network segment between two floors of the same building and two different buildings using repeaters.

Network Setup Using Repeaters

Hubs

Hubs are the central point of connection on a network because they allow multiple nodes and devices to be attached to them at the same time. The point where a node or a network device is attached to the hub is referred to as a port.
Based on the number of ports, hubs can be 8-port, 10-port, 16-port, 24-port, and 32-port. Hubs with a higher port capacity are also available in the market.

The following figure shows a hub:

Network Setup Using Hub

Hubs are of the following types:

• Passive hubs: These hubs do not regenerate the signals that they receive. In addition, the signals are sent to all devices that are connected to them.
• Active hubs: These hubs are capable of signal regeneration. However, they also forward the signals that they receive to all the nodes attached to them.
• Intelligent hubs: Apart from signal regeneration, these hubs are capable of basic management-related activities, such as gathering statistics about network traffic and collisions. In addition, the signal that passes through the hub goes to the destination node and the other nodes do not receive the signal. As a result, these hubs actively participate in reducing network traffic.

Bridges

Bridges are devices to connect network segments to each other. Bridges not only extend a network, but also filter unnecessary traffic on the network.

In a large bus setup, network traffic is very high because the data packets are sent to all the nodes attached to the bus. As a result, excessive traffic is generated, which results in the low performance of the setup. The network device, bridge, is used to overcome this problem. The bridge operates on the MAC sublayer of the OSI Data Link layer.

The bridge between the two segments examines each packet for its destination information and forwards only those data packets that are specific to other segments instead of sending all the data packets. This helps reduce the network traffic between the two segments and the overall network traffic. The segregation of the network into segments and their connectivity by bridges enables the smooth functioning of the network in the event of a breakdown of a particular segment. The following figure shows the use of bridges to manage network traffic.

Network Setup Using Bridge

Bridges cannot join dissimilar network segments because it needs the physical address of the device to send the data packet. The physical address is the function of the Data Link layer that uses different protocols on each type of network.

Switches

Switches are intelligent network devices that provide universal connectivity. At the same time, switches make efficient use of network resources, especially transmission media and their bandwidth.

On receiving data packets, instead of forwarding the packets to all connected nodes or segments, switches forward the packets only to the node that is the intended recipient of the packets. As a result, switches prevent network bandwidth from being wasted.

Switches are capable of basic network management activities, such as gathering statistics about network traffic and collisions. In addition, switches can also perform advanced management activities, such as selecting the optimal path for signal delivery within a network. As a result, switches play an active role in bringing down the overall network traffic.
Switches can operate at the Data Link layer, the Network layer, or both. The switches that operate at both the Data Link layer and the Network layer are known as multilayer switches. The switches perform both the switching and routing function.

NB: Bandwidth is the range of frequencies that a signal, such as analog or digital, can occupy over a specific transmission medium. Bandwidth is measured in bits of data per second (bps) for a digital signal, while it is measured in kilohertz (kHz) for an analog signal.




   

HOW TO CHOOSE A PROTOCOL?

Choosing and Combining Protocols

The factors that govern the choice and implementation of protocols on a network are:


Physical layout of the network: The Physical layout is the topology of the network used. For example, the star topology typically uses the Ethernet protocol.

Span of the network: Networks can span a room, a floor, a building, a city, a country, or continents. The span of the network also dictates what protocols need to be implemented. For example, networks that span across cities, countries, and continents can use protocols, such as TCP/IP, while networks in a room or on a floor can use protocols, such as NetBIOS and NetBEUI.

Network operating system (NOS): NOSs also influence the choice of protocols largely. For example, Netware v3.2 uses the IPX/SPX protocol suite, while Windows 3.11 uses NetBEUI, by default.
Budget of the organization: This factor is possibly the most important factor because it influences the physical layout of the network and the choice of NOS, which, in turn, influences the choice of protocol.


The choice of a protocol to be used on a network depends on the requirements of the network. The requirements of a network may change over time.
To understand this, consider a scenario in which an organization had a LAN setup of 10 computers a decade ago. This network used the NetBEUI protocol. Now, the company wishes to connect the LAN to the Internet. Because the Internet uses TCP/IP, the company cannot use NetBEUI to communicate over the Internet.

Similarly, consider a scenario in which an organization with a TCP/IP-based network takes over another organization, which has two mainframes. In this case, the SNA protocol is required to implement connectivity between the two mainframes and TCP/IP-based hosts.
   

DLC & NETBEUI PROTOCOLS SUITES

DLC Protocol Suite  

The Data Link Control (DLC) protocol communicates between personal computers and mainframes (IBM Hosts). The DLC protocol provides services to the Data Link layer of the OSI reference model. It provides reliable data transfer across each connection on a network. The DLC protocol also defines frames and maintains flow control on the network.

NetBEUI Protocol Suite

NetBEUI stands for NetBIOS Extended User Interface. This protocol extends the functionality of the NetBIOS protocol. The NetBIOS protocol enables the transmission of data within a network. NetBEUI supplements this functionality of NetBIOS by formalizing the format of frames transmitted across the network. NetBEUI is best suited for small LANs because it is a nonroutable protocol that cannot route data packets across LANs.

       

SNA PROTOCOL SUITE

SNA Protocol Suite

IBM invented Systems Network Architecture (SNA) in the 1970s. The SNA protocol suite consists of the following:


Document Interchange Architecture (DIA): This specification controls file services, such as the storage and retrieval of files and file transfers among heterogeneous systems.

SNA Distribution Services (SNADS): This service controls the distribution of documents and messages.

Distributed Data Management (DDM): This service coordinates the execution of file requests locally or on a server. When DDM receives file requests, it executes them locally, if required resources are available. However, if required resources are not available on the node on which the request originated, the execution takes place at the server end, which can support the requirements.

Advanced Program-to-Program Communication (APPC): This service allows peer-to-peer communication among clients.

Information Management Systems (IMS): This service provides information management capabilities by scheduling priority transactions.

Customer Information Control Systems (CICS): This service provides multitasking capabilities, security, storage management, transaction management, and restart capabilities.


Advanced Peer-to-Peer Networking (APPN): This specification facilitates peer-to-peer communication among SNA-based networks.

Network Control Program (NCP): This specification provides routing and gateway functionality on SNA-based networks.

Virtual Telecommunication Access Methods (VTAM): This specification works with the NCP protocol to control network resources. In addition, it provides domain support on SNA-based networks.

Synchronous Data Link Control (SDLC): This specification supports remote connections through leased or dial-up connections. It provides point-to-point, multipoint, half duplex, and full duplex transactions.
Token Ring: This is the LAN specification for IBM Token Ring networks.

      

APPLE TALK PROTOCOL SUITE

AppleTalk Protocol Suite

Apple Computer, Inc. developed the AppleTalk protocol suite in the early 1980s. This protocol suite allows the integration of Macintosh computers on a network. It also provides interconnectivity between Apple computers and other networking technologies, such as IBM mainframes and VAX computers.
The following figure shows the AppleTalk protocol suite mapped to the seven layers of the OSI reference model:

In the preceding figure, the AppleTalk protocol suite consists of the following protocols:


AppleShare: This protocol is subdivided into three applications, AppleShare File Server (AFS), AppleShare Print Server (APS), and AppleShare PC (APC). AFS allows users to interact with a file server while APS allows users to send print commands to the print server. APC provides interconnectivity with MS-DOS-based nodes.

AppleTalk Filing Protocol (AFP): This protocol facilitates file sharing between network nodes.

AppleTalk Data Stream Protocol (ADSP): This protocol provides the services of the Session layer of the OSI reference model.

Zone Information Protocol (ZIP): This protocol divides an internetwork into zones and coordinates the interaction of these zones. In addition, ZIP assigns service providers to zones.

Printer Access Protocols (PAP): This protocol establishes connections between network nodes and various servers, such as print and file.

AppleTalk Session Protocol (ASP): This protocol optimises file service functions.

AppleTalk Transaction Protocol (ATP): This protocol provides a reliable delivery service for connection-oriented operations.

Name Binding Protocol (NBP): This protocol maps the names of nodes to their addresses.


Routing Table Maintenance Protocol (RTMP): This protocol manages routing information.

Datagram Delivery Protocol (DDP): This protocol provides routing services.

AppleTalk Address Resolution Protocol (AARP): This protocol maps the physical addresses of devices to their logical addresses.