LANARCHITECTURE

bY:Cathie M. Guinet

What is meant by LAN Architecture?3 Major Components of LANs

Media Access Control (MAC) Protocol Network Topology Network Operating System Software

Media Access Control (MAC) Protocol – a protocol found at the media access control (MAC) sub layer of the OSI reference model’s data link layer. defines how a station gains access to the media for data transmission.

Common MAC protocols Carrier Sense Multiple Access Collision DetectionNetwork Topology – the logical or physical arrangement of network nodes.

– a model for the way in which network nodes are connected Logical Topologies includes;

Broadcast or Sequential (ring)Physical Topologies includes;

Bus Ring Star

(CSMA/CD)

LAN Architecture – the overall design of a LAN. – includes hardware, software, topology and

Media Access Control (MAC) Protocol.LAN TOPOLOGIESTopology – derives from a mathematics field that deals with

points and surfaces in space.LANs 3 Basic Topologies

Bus Star RingBus Topology – a physical network topology in which all network attached devices connect to a common communication pathway or channel.

–in LANs the communication medium in a bus topology consist of a single wire or cable to which nodes are attached via connectors and/or transceivers.

BUS TOPOLOGY

Figure 8-1 (a)

Ethernet – a LAN implementation using the CSMA/CD protocol on a bus the IEEE 802.3 standard is based on Ethernet. A popular LAN implementation.

Institute of Electrical and Electronics Engineer (IEEE) – a professional society that establishes and publishes documents and standards for data communication.

– has established several standards for both cable-based and wire less LANs including;

IEEE 802.3 IEEE 802.5 IEEE 802.I I

IEEE 802.3 Standard – the IEEE standard that addresses Ethernet LANs.

– It covers a variety of physical implementations of Ethernet all of which use CSMA/CD as the MAC protocol.

LAN TOPOLOGIES

Ring Topology – a LAN topology in which stations are attached to one another in a logical or physical circle. A weakness of this physical topology is that communications for the entire network may be disrupted if one of the microcomputer or network adapters malfunction.

A

B

C D

E

F

RING TOPOLOGY In a physical ring the medium forms a loop to which workstations are attached. In both physical and logical rings, access to the medium is passed from one station to the next; also, data are transmitted from one station to the next around the ring. Generally, the access protocol used in a ring topology is token passing.

LAN TOPOLOGIES

Figure 8-1 (b)

Token Passing Within a Ring Topology

A

B

C

D

E

F

G

Data Flow

LAN TOPOLOGIES

Figure 8-3

Active node – a node capable of sending or receiving network messages.Inactive node – a node that may be powered down and is incapable of sending or receiving messages.IEEE 802.5 standard – an IEEE standard for token-passing networks including token ring LANs.Multistation Access Unit (MAU) –

LAN TOPOLOGIES

Multistation Access Unit (MAU)

Workstation Connection

Ring In Inbound Connection from other MAU

Ring Connection Created by MAU

Ring Out Outbound Connection

to other MAU

Figure 8-4

Star Topology – a physical network topology using a central station (typically a hub or a switch) to which all nodes have point-to-point in connections.

- all communication among nodes occurs through the central station.

- this is the most widely implemented LAN topology. That has been used today.

Wiring Hub

Star Topology

LAN TOPOLOGIES

Figure 8-1 (c)

ARCnet (Attached Resource Computer Network) – among the first LAN implementations capable of connecting up to 255 nodes in a star topology over twisted-pair wires or coaxial cable.

Logical Topology – a LAN’s logical topology is concerned with how messages are passed from node to node within the network rather than with how the nodes are physically connected to form a network. Two logical LAN Topologies exist:

Sequential Ring Broadcast

HUB

Star Topology

LAN TOPOLOGIESFigure 8-7

LAN TOPOLOGIES

Sequential (Ring) – also called a ring logical topology because data is passed from one node to another in a ring-like sequence.

Each node in the ring examines the destination address field of each data packet receives in order to determine if it is the intended recipient.

Broadcast – nodes in LANs that have a broadcast logical topology transmit each packet to all the other nodes in the network.

Each node receive all the packets transmitted by all other nodes and examines each packets that it receives to determine if it is the intended recipient.

2 Logical LAN Topologies

DATALINK AND MEDIA ACCESS CONTROL PROTOCOL

Data Link ProtocolsIn general, a data link layer protocol established the rules for gaining access to the medium and for exchanging messages.

Six Most Important Aspects of Data Link Protocol

Delineation of Data – a data link layer protocol must define or delineate where the data portion of the transmitted message begins and ends.

Octet- a group of 8 bits used in data communication protocol frame formats.

Error Control – is used to detect transmission errors. Common error detection techniques are parity and cyclic redundancy checks.

Addressing – communication between two network nodes is accomplished through the addressing scheme. Network addressing is similar to addressing used for postal mail.

Transparency – in the data link protocol, transparency is the ability of the data link to transmit any bit combination.

Preamble Destination Address

Source Address

Type Field Data Field 32-Bit CRC

Figure 8-9

Preamble Start Frame Delimeter

Destination Address

Source Address

Length Field

Data Field 32-Bit CRC

(a) Original Ethernet II Frame

(b) IEEE 802.3 Frame

Preamble Start Frame Delimeter

Destination Address

Source Address

Length Field

IEEE 802.2 Control

Data Field

32-Bit CRC

Preamble

Destination Address

Source Address

Length Field

DSAP SSAP CTRL Data Field

32-Bit CRC

(c) IEEE 802.2 Frame

(d) Ethernet SNAP (an 802.2 variant)

Ethernet Message Formats

Code Independence – the ability to transmit data regardless of the code, such as ASCII or EBCDIC.

- means that any data code, such as ASCII or EBCDIC, or Unicode, can be transmitted. This codes used different bit patterns to represent many of the character. Media Access – the way in which network device gains access to the communication medium . Thus is usually governed by a Media Access Control(MAC) protocol specifying how the device gains the right to transmit data on the medium.

MAC PROTOCOLS LAN technology adheres to two primary data link protocols:

Token Passing ContentionData Link layer is divided is divided into 2 sublayers:

The LLC (Logical Link Control) – provides the function of a flow control , message sequencing , message acknowledgement, and error checking

The MAC (Media Access Control) layer – describes token passing and contention.

Application Layer

Presentation Layer

Session Layer

Transport Layer

Physical Layer

Network Layer

Data Link Layer

Media Access Control(MAC)

Logical Link Control (LLC)

Media Signaling

Bus Interface Unit

Communication Interface UnitOSI Reference Model Layers

Medium

LLC and MAC Sublayers of the OSI Reference Models Data Link Layer

Contention - a media access control convention governing how devices obtain control of a communication link.

- in contention mode, devices compete for control of the line either by transmitting directly on an idle line or by issuing a request for line control.

- is typically follows a first-come, first -serve, methodology expect when two devices contend for the communication link at the same point in time.

Collision – in the CSMA/CD media access control protocol and other contention-based communication protocols, a collision occurs when two stations attempt to send a message at the same time. The message interfere with each other, so correct communication is not possible.

Carrier Sense Multiple Access and Collision Detection (CSMA/CD)- a media access control technique that resolves

contention between two or more stations by collision detection.

- it is used in Ethernet LANs and is often referred to as the

“Ethernet protocol”. Carrier Sense Multiple Access and Collision Avoidance (CSMA/CA)

- a LAN media access control method that attempts to avoid contention among stations and message collisions. It is widely used in wireless LANs.

MAC PROTOCOLS

MAC PROTOCOLS

Token Passing - the second major MAC protocol.- a media access control protocol in which a string

of bits called the token is passed from network node to network node in a logical ring. A computer that receives token is allowed to transmit data onto the network and after transmitting its data, the computer passes the token to the next computer in the ring.

Active Monitor – in a token ring network, the active monitor is the station that controls the token. It maintains clock synchronization, detects and corrects errors in the token frame format, and generates a new token in the case of token loss.

Kinds of Token Passing

Token-Passing Ring – in a token-passing LAN with a physical or logical ring topology, the token can become loss if node holding the token fails or if transmission errors occur. Recovery in such problems involves the active monitor.

Token-Passing Bus - token passing is slightly different on a token-passing bus.On a bus, the token is passed from one workstation to another based on station addresses. As mentioned earlier , the token can be passed in ascending or descending address order.

Address 55 Address 72 Address 45

Address 38 Address 10

Lowest AddressPasses to

Highest Address

Path of Token Based on Descending Station Address

D E FCBA

MAUPORTS

RI RO21 743 865UnusedUnused

Turned Off

Malfunctioning

Closed SwitchOpen Switch The 24-bit token is passed from node via circuits within the

MAU. In this MAU, the token would be passed from node A to node C. Node C would the pass the token to node D. Node D would pass the token to F. the token would not be passed to nodes B or E. Switches within the MAU prevent the token from being passed to powered down or malfunctioning nodes; they also are used to bypass unused ports.Token Passing Within a Token Ring MAU

Figure 8-12

Table 8-3 MAC Protocol Comparison

Access is equal for all nodes Access is equal for all nodes.

Access window is predictable. Access window can be unpredictable.

Maximum wait time to transmit is token circulation time.

Maximum time to transmit is unpredictable and depends on collisions.

Average wait time to transmit is predictable: half the maximum circulation time.

Average wait time to transmit is unpredictable.

Network congestion does not adversely affect network efficiency.

Network congestion may result in collisions and reduce network efficiency.

A node must wait for the token before being able to transmit.

A node may be able to transmit immediately.

One node cannot monopolize the network.

A node may be able to monopolize the network

Large rings can result in long delays before a node obtains token.

A node can transmit when the network is quiet.

Performance is consistent for large, busy networks.

Performance is unpredictable for large, busy networks because of possibility of collisions.

Token Passing CSMA/CD

Figure 8-13

11 11 10 0 0

Bit IntervalPhysical Layer Data Encoding Used in LANs

a) Bit Stream

b) Binary Encoded Bit System

c) Manchester Encoding –Manchester encoding is used in 10-mbps Ethernet LANs and requires a low to high mid bit transition to represent a 1 and high to low to 1 and a high to low transition to represent a 0 bit.

d) Differential Manchester Encoding – is used in token ring LANs. Like Manchester Encoding, Differential Manchester Encoding requires a mid bit transition. However, in this scheme, a 1 bit always starts at the same level as the previous bit ends ; a 0 bit always starts at the opposite level from where the previous bit ends.e) NRZI Encoding (Non-Return to Zero with Invert on Ones). NRZI Encoding is used in FDDI LANs. In this scheme, 1s have mid bit transitions, 0s do not. Both 1s and 0s start at the same level as the previous bit ends.

LAN Architectures

Aspects of LAN architecture. These include the ; LAN’s physical topology LAN’s logical topology LAN’s MAC protocol

Ethernet Frame FormatsFast Ethernet – refers to 100BaseT Ethernet implementations that comply with the IEEE 802.3u standard.

- 100BaseT transmits at 100 mbps. Like regular Ethernet, fast Ethernet is a shared media LAN that uses CSMA/CD as the media access control protocol.Gigabit Ethernet – evolved from ANSI’s X3TII Fibre Channel standard.

Fibre Channel – gigabit Ethernet evolved ANSI’s X3I I specifications for Fibre Channel include a medium speed of 1 GHz and a data rate of 800 mbps.

Fibre Channel often used to build storage area networks (SANs), and implementations that support speeds over 2 gbps. In the future, transmission speeds are expected to exceed 4 gbps.

Ethernet Frame Formats

Isochronous Ethernet – enables 10BaseT Ethernet LANs located at different geographic locations to be connected via ISDN . The IEEE 802.9a specifications addresses Isochronous Ethernet; also called Iso-Ethernet.

-This enhancement enables Ethernet to handle real-time voice and video by providing a total bandwidth of more than 6 mbps that can be used for video conferencing.

- Isochronous Ethernet can be integrated into the existing network through the addition of the isochronous. Token Ring

- networks use in a token-passing MAC protocol over a logical ring (sequential ) topology. Physically token ring networks look like a star.

Multistation Access Unit (MAU) – a central hub in a token ring LAN.

Location 1

ISDN Network

Figure 8-14

Using Iso-Ethernet to Connect Ethernet Lans at two Locations via ISDN

Location 2

Iso-Ethernet Access Units (AU’s) with ISDN Interfaces

ISDN Links

MAU1

MAU 2

MAU-to-MAU

Connection

MAU-to-MAU Connection

Figure 8-6

FDDI

Fiber Distributed Data Interface (FDDI) – an ANSI standard token passing network that used optical fiber cabling and transmits at 100 mbps up to 2 kilometers. Its heyday as a LAN and MAN access method was the

mid-1990’s .

- FDDI, being pronounced as “Fiddy”

Copper Distributed Data Interface (CDDI) – a version of FDDI that uses UTP (unshielded twisted pair) wires rather than optical fiber as the communication medium.

- has also been recognized in the TP-PMD (twisted pair-physical media dependent) standard based UTP.

DAS (DualAttachment

Station) Minicompute

r

FDDI Network Configuration and Key Technologies

File Server

FDDI toEthernet Bridge

Fiber Cable or STP

Figure 8-16

Secondary RingPrimary Ring

Minicomputer

FDDI Concentrato

rSingle

Attachment Station(SAS)

Fiber Distributed Data Interface (FDDI)

Single Attached Station (SAS) – some FDDI NICs enable a workstation to be attached only to the primary

data ring, often via a concentrator; workstations that connect to FDDI network in this fashion are called single attached stations (SASs).

Dual Attached Station (DAS) – workstations in FDDI networks that attached to both FDDI rings.

Direction of Token

Passing

A

B

C

X

Y

ZNode A has the token

T

T - Token

(a)

Figure 8-17

Message Passing in a FDDI LAN

A

B

C

X

Y

Z

(b)

T MESSAGE

A

Direction of Token Passing

T - Token

Direction of Token

Passing

A

B

C

X

Y

Z

T

(c)

Figure 8-17

Message Passing in a FDDI LAN

A

B

C

X

YZ

(d)

T MESSAGE

A

Direction of Token Passing

T - TokenMessage A

Message B

Message A

Message A

-Token

Node B’s message continues to circulate.

Node A receives message in

acknowledgement & removes it from the

ring

Node X keeps A’s message and sends

it back to A.

Figure 8-18

FDDI’s Self-Healing Capability

Primary

Secondary

PrimaryNormal Operation Rerouted Traffic After Line Break

Break in the line Between C and D

100 G-AnyLAN

100 G-AnyLAN – an IEEE specification for twisted-pair wire or fiber optic cable Ethernet LANs with speed of 100 mbps.

- is derived from a 100-mbps version of Ethernet developed by Hewlett-Packard that is capable of transporting both IEEE 802.3 and IEEE 802.5 (token ring) frames.

100VG Ethernet Hub

100VG ROUTER

100VG Token Ring

MAU

100 Mbps Token Ring

LAN

In this 100VG-AnyLANImplementation option, the 100VG router converts IEEE 802.5 frames to IEEE 802.3 frames, and vice versa.

Figure 8-20

An Example of a 100VG-AnyLAN Network

ATM LANs

Another LAN architecture that has a good job of supporting multimedia traffic is ATM (asynchronous transfer mode). ATM is a switched network architecture that employs 53-octet cells to transmit data . ATM is also used in LANs.

ATM LAN emulation – when ATM LAN emulation is employed, LAN MAC addresses are converted to ATM network addresses.

- enables virtual LANs to be created across an ATM backbone by using ATM switches to handle message exchange among logical work-group members.

ATM Switc

hATM

Switch

ATMSwitch

ATM WAN

ATM Access Gateway/

Switch

ATM Backbone Network

MAU

25-mps ATM LAN Switch

Ethernet LAN

Hub

Token Ring LAN

Figure 8-12

Interconnecting LANs via an ATM Backbone

Three-Tier Architectures and Virtual LANsTraditionally, LANs have been classified as having 2-tierred client/server architecture which clients located on one tier and servers on second .

Application Server

Middle-Tier Server

Client

Data Server(e.g., Oracle)

Data Server(e.g.,

Sybase)

Backend Servers

Figure 8-22

Three-Tier Client/Server Computing Architecture

Layer 2 switch – a network device that forwards traffic based on MAC layer(Ethernet or Token Ring ) Addresses .

Most LAN switches are called Layer 2 switches because the switched connection is based on the MAC layer destination address included in data link layer frames transmitted between LAN-attached devices.

Three-Tier Architectures

Layer 3 Switch – a network device that forward traffic based on Layer 3 information.

Layer 3 is the network layer of the OSI reference model. When network layer destination addresses (such as IP addresses) are used to establish switched connections instead of MAC layer addresses, the switch is called a layer 3 switch.

Figure 8-23

Layer 2 and Layer 3 Switches in LANs

Three-Tier Architectures

LAN 1:10 mbps

Layer 2 Switch

LAN 2:100 mbps

Layer 2 Switch

Layer 2 Switch

LAN 3:10 mbps

Wide Area Network

Router

100 mbps100 mbps

1 gbps1 gbps

Layer 3 Switch

Virtual LANs

Virtual LANs are logical network designs that are dependent upon LAN switches to provide functionality. Special virtual LAN software, supported in Layer 2 and Layer 3 LAN switches, enables virtual LANs to be created and maintained.

In essence , a virtual LAN is a logical grouping of work-group members that does not require each member of the group to be physically attached to the same switched.

WIRELESS LAN ARCHITECTUREInfrared LANs – LANs that rely on infrared lights as the communication medium transmits signals whose wavelengths fall between those of visible light and radio waves.

Spread –Spectrum Radio (SSR) LANs – the primary application of SSR for data communication is wireless LANs. SSR has a long history military use because of its ability to provide reliable communication in battlefield environments where signal jamming and other kinds of signal interference are likely; Two Transmission Methods :

Frequency-Hopping Spread Spectrum (FHSS)Direct Sequence Spread Spectrum (DSSS)

Frequency-Hopping Spread Spectrum (FHSS) – FHSS continuously changes the center frequency of a conventional carrier several times per second according to a pseudo-random pattern and set of channels.

Data is transmitted at one frequency then, then the frequency is charged and data are transmitted at once frequency, then the frequency is change and data is are transmitted at the new frequency , and so on.

This makes very difficult to illegally monitor the spread spectrum signals and increases the probability that the transmitted data will be successfully received.

Direct Sequence Spread Spectrum (DSSS) - sends data over several different spread spectrum radio frequencies simultaneously using the full bandwidth of the communication channel.

Frequency (Hz) Wavelength 1016 X rays, gamma rays 1015 Ultraviolet light1014 Visible light1013 Infrared light1012 Millimeter waves1011 Microwaves1010 UHF television109 VHF television 108 VHF TV (high band)

FM radio107 VHF TV (low band)

Shortwave radio106 AM radio105 Very low frequency104 Very low frequency103 Very low frequency102 Very low frequency101 Very low frequency

Table 8-5

Frequency Spectrum Classification

Wireless LAN Topologies

Wireless LANs are typically implemented as physical stars. Nodes connect to wireless hubs that are typically called access point. Access points can be stand-alone devices or can interface with cable-based networks in order to provide wireless segments for an otherwise wire-based called networks on order to provide wireless segments for an otherwise wire-based LAN.

Standard DescriptionIEEE 802.11 Original WLAN; supports 1- to 2-mbps transmission speedsIEEE 802.11b Currently the dominant WLAN standard; supports transmission

speeds of 11mbpsIEEE 802.11a High-speed WLAN standards for 5- to 6-GHz band; supports 54

mbpsHiperLAN2 Competing high-speed WLAN standard for 5- to 6-GHz band;

supports 54 mbpsIEEE 802.11g High-speed WLAN standard for 2..4-GHz band; supports 20+

mbps transmission speedsIEEE 802.1x Comprehensive security framework for all IEEE networks

including WLANs and EthernetIEEE 802.11i Wireless-specific WLAN security standard that complies with IEEE

802.11xIEEE 802.11e Quality of Service (QoS) mechanisms that support all IEEE WLAN

radio interfacesIEEE 802.11f Defines communication between WLAN access points

IEEE 802.11h Defines spectrum management techniques for IEEE 802.11a WLANs

WISPR Wireless ISP roaming standard recommended by the wireless Ethernet Compatibility Alliance to enable roaming among multiple public WLAN networks

Table 8-6 Important Wireless LAN Standard

MAKING THE DECISIONS

In making the decision you need to consider;

Cost - if cost were not a consideration, LAN selection would be easier. You could buy the fastest, biggest workstations and servers available and use the most comprehensive LAN network operating system and application software available .

Cost Number of workstations

Type of workstations

Number of concurrent users

Type of use Number of printers

Medium and distance Speed Applications

Expandability Device connectivity Connectivity with other networks

LAN software and Hardware

Vendor Adherence to established standards

Vendor Support Manageability Security

Table 8-7Major Factors Influencing LAN Selection

Immediate Costs

Equipment Costs Training (users, operators, administrators)

Documentation Installation of cabling Site preparation System software installation Hardware installation Creative user environment Installing application Space required for new equipment Testing Supplies and sparesRecurring Costs LAN management personnel costs

Hardware and software maintenance

Consumable supplies Training (new users, administrators)

Table 8-8 Immediate and Recurring LAN Costs

Total cost of ownership – includes all cost aspects of LAN/IT projects including ongoing cost for support, management, and maintenance over the entire expected life span of the network/system.

MAKING THE DECISIONS

Number of Concurrent Users and Type of UseThe number of concurrent users expected during normal peak network usage periods is often an important factor in selecting among LAN alternatives.

Overlay Module – a memory management technique wherein the program is divided into distinct segment types:

resident or main segment overlay segments Overlay segments share the same memory area.

Typically, only one of the overlays is in memory at any given time. When a different overlay segment is required, it replaces the memory resident overlay segment.

MAKING THE DECISIONS

Communication Speed

LAN speeds can be somewhat deceptive. A LAN speed quoted by the vendor is the speed in which data is transmitted over the medium. You cannot expect the LAN to maintain its speed at all times.

MAKING THE DECISIONS

Vendor and SupportWhen you are selecting a LAN, you are selecting much more than hardware and software, You also are selecting a vendor/s with whom you expect to have a long-term relationship.

ManageabilityNever underestimate the time and effort required to operate and manage LAN. Even small, static LAN requires some management once it has been installed and set up. Occasionally, a user might be added or deleted, applications must be added or updated, and so on.

Table 8-9 MAKING THE DECISIONS

User/Group Oriented Add, delete users and groups Set user/group security Set user environment Solve user problemsPrinter Oriented Install/removed printers Set-up user environment Maintain printersHardware/Software Oriented Add/change/delete software Add/change/delete hardware Diagnose problems Established connections w/ other

networks Plan and implement changesGeneral Make backups Maintain operating procedures Carry out recovery as necessary Educate users Plan capacity needs Monitor the network Serve as a liaison with other network administrators

LAN Management Task

Security

When stand-alone minicomputers, security generally is not an issue. Stand-alone microcomputer system usually single-user system, and system security features, such as passwords-controlled screen savers, are rarely used. As a result, access to the system is tantamount to access all data sorted on that system.

IEEE LAN STANDARDSThe IEEE established a standards group called the 802 Committee during the 1970’s . This group is divided into subcommittees, each of which addresses specific LAN issues and architectures. The subcommittees and their objectives are summarized here.802.1: High-Level Interface – high-level interface subcommittee addresses matters relating to network architecture, network management, network interconnection, and all other issues related to OSI layers above the data link layer, which are the network, transport, session, presentation, and application layers.802.2; Logical Link Control - IEEE has divided the OSI data link layer into two sub layers: Logical Link Control (LLC) and MAC sub layer implements protocols such as token passing CSMS/CD.

802.3: CSMA/CD – the IEEE 802.3 standard covers a variety of CSMA/CD architectures that are generally based on Ethernet.

802.4: token Bus – the IEEE 802.4 standard subcommittee sets standard for token bus networks.

802.5: Token Ring – the IEEE standards subcommittee sets standards for token ring networks.

802.6: Metropolitan Area Networks (MANs) – as noted previously the FDDI family of technologies was proposed as a standard for metropolitan are networks. The IEEE 802 LAN standards committee, however, chose a competing set of specifications, IEEE 802.6, for a MAN.

- The standard is also called the distributed queue dual bus (DQDB) standard.

802.7: Broadband Technical Advisory Group – this group provides guidance and technical expertise to other groups that are establishing broadband LAN standards, such as the 803.3 subcommittee for 10Broad36.

802.8: Fiber Optic Technical Advisory Group – this group provides guidance and technical expertise to other groups that are establishing standards for LANs using fiber optic cable.

IEEE LAN STANDARDS

Figure 8-24

Bus A, Unidirectional

Bus B, UnidirectionalDistributed Queue Dual Bus MAN Architecture

802.9: Integrated Data and Voice Networks – this committee sets standards for networks that carry both voice and data. Specifically, it is setting standards for interfaces to ISDN networks.

802.10 LAN Security – this committee addresses the implementation of security capabilities such as encryption, network management, and the transfer of data.

802.11: Wireless LANs – these standards cover multiple transmission methods to include infrared light, as well as a variety of broadcast frequencies to include spread spectrum radio waves and microwaves.

802.12: Demand Priority Access Method – this subgroup developed the specifications for the data link layer protocol in 100VG- AnyLAN networks.

IEEE LAN STANDARDS

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