Lan architecture

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 Detection
Network 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

LAN Architecture – the overall design of a LAN.
– includes hardware, software, topology and Media Access
Control (MAC) Protocol.
LAN TOPOLOGIES
Topology – derives from a mathematics field that deals with points and
surfaces in space.
LANs 3 Basic Topologies
 Bus  Star  Ring

Bus 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.
Figure 8-1 (a)

BUS TOPOLOGY

LAN TOPOLOGIES

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.
Figure 8-1 (b)
A F

B E

C D

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 8-3 A G

B F

C E

D
Data Flow

Token Passing Within a Ring Topology

LAN TOPOLOGIES

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) –
Figure 8-4

Workstation Ring Connection
Connection Created by MAU

Ring In Inbound
Connection Ring Out Outbound
from other MAU Connection
Multistation Access Unit (MAU) to other MAU

LAN TOPOLOGIES

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.
Figure 8-1 (c)

Wiring Hub

Star Topology

HUB
LAN TOPOLOGIES
Figure 8-7

Star Topology

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

LAN TOPOLOGIES

2 Logical 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.

DATALINK AND MEDIA ACCESS CONTROL PROTOCOL

Data Link Protocols
In 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.

Figure 8-9

Preamble Destination Source Type Field Data Field 32-Bit CRC
Address Address

(a) Original Ethernet II Frame

Preamble Start Frame Destination Source Length Field Data Field 32-Bit CRC
Delimeter Address Address

(b) IEEE 802.3 Frame

Preamble Start Destination Source Length IEEE 802.2 Data 32-Bit CRC
Frame Address Address Field Control Field
Delimeter

(c) IEEE 802.2 Frame

Preambl Destinati Source Length DSAP SSAP CTRL Data 32-Bit
e on Address Field Field CRC
Address

(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
 Contention
Data 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.

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

Application Layer

Presentation Layer
Logical Link Control
Session Layer (LLC)
Media Access Control
Transport Layer (MAC)

Network Layer
Media Signaling
Data Link Layer
Bus Interface Unit
Physical Layer

OSI Reference Model Layers Communication
Interface Unit

Medium

MAC PROTOCOLS

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

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

Lowest Address
Passes to
Highest Address

Address 38 Address 10

Path of Token Based on Descending Station Address

Figure 8-12 MAU
PORTS

RI 1 2 3 4 5 6 7 8 RO
Unused Unused

A B C D E F

Turned Malfunctioning
Open Switch Off
The 24-bit token is passed from node via circuits within the MAU. In
Closed Switch 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

Table 8-3 MAC Protocol Comparison

Token Passing CSMA/CD
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 Maximum time to transmit is unpredictable
circulation time. and depends on collisions.
Average wait time to transmit is predictable: Average wait time to transmit is
half the maximum circulation time. unpredictable.
Network congestion does not adversely affect Network congestion may result in collisions
network efficiency. and reduce network efficiency.

A node must wait for the token before being A node may be able to transmit immediately.
able to transmit.
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 can transmit when the network is
a node obtains token. quiet.
Performance is consistent for large, busy Performance is unpredictable for large, busy
networks. networks because of possibility of collisions.

Figure 8-13

1 1 0 1 0 0 1 1 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.

Bit Interval
Physical Layer Data Encoding Used in LANs

LAN Architectures

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

Ethernet Frame Formats
Fast 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.

Figure 8-14

Location 1

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

Location 2

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

Figure 8-6

MAU-to-MAU
Connection

MAU-to-MAU Connection

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.

Figure 8-16

Minicomputer

DAS (Dual FDDI
Attachment Concentrator
Station)
Single
Minicomputer Attachment
Station
(SAS)

Secondary Ring
FDDI to
Primary Ring Ethernet Bridge

File Server
Fiber Cable
or STP

FDDI Network Configuration and Key Technologies

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.

Figure 8-17

Z
Node A Z T
has the token M Y
Y E
S
S A
A X Direction of X
T A
Direction of Token
Token G Passing
Passing E B
B
A

- Token C
T C T - Token
(b)
(a)

Message Passing in a FDDI LAN

Figure 8-17
Node A receives message in Node B’s message
acknowledgement continues to circulate.
& removes it from the ring

Message B
Z Z

Y Y
Message A
A
A X Direction of X
Direction of Token
Token Passing Message A
Passing B
B

T
M C
E C Message A T - Token
S (d)
S
(c) Node X keeps A’s
message and sends
A
it back to A.
G
E
T -Token
A

Message Passing in a FDDI LAN

Figure 8-18

Normal Operation Rerouted Traffic After Line Break
Primary
Primary

Secondary

Break
in the line
Between
C and D

FDDI’s Self-Healing Capability

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.

Figure 8-20

100VG
Ethernet Hub

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

100 Mbps
Token Ring
100VG LAN
Token Ring
MAU

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.

Figure 8-12 ATM
Backbone
Ethernet LAN ATM Network
WAN

ATM
Switch

25-mps ATM
ATM LAN Switch
Switch

Hub
ATM
Switch

ATM Access
Gateway/Switch

MAU

Interconnecting LANs via an ATM Backbone Token Ring LAN

Three-Tier Architectures and Virtual LANs

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

Figure 8-22
Middle-Tier
Server

Application Server
Data Server
(e.g., Oracle)
Client

Backend Servers

Data Server
(e.g., Sybase)

Three-Tier Client/Server Computing Architecture

Three-Tier Architectures

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.

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.

Three-Tier Architectures
Figure 8-23

LAN 1:
10 mbps LAN 3:
10 mbps
100 mbps 100 mbps
Layer 2 Switch Layer 2 Switch

Layer 3 Switch
Layer 2 Switch
LAN 2: 1 gbps 1 gbps
100 mbps

Router

Wide Area Network

Layer 2 and Layer 3 Switches in LANs

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 ARCHITECTURE
Infrared 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.

Table 8-5 Frequency (Hz) Wavelength
1016 X rays, gamma rays
1015 Ultraviolet light
1014 Visible light
1013 Infrared light
1012 Millimeter waves
1011 Microwaves
1010 UHF television
109 VHF television
108 VHF TV (high band)
FM radio
107 VHF TV (low band)
Shortwave radio
106 AM radio
105 Very low frequency
Frequency Spectrum Classification
1

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.

Table 8-6 Important Wireless LAN Standard
Standard Description
IEEE 802.11 Original WLAN; supports 1- to 2-mbps transmission speeds

IEEE 802.11b Currently the dominant WLAN standard; supports transmission speeds of
11mbps
IEEE 802.11a High-speed WLAN standards for 5- to 6-GHz band; supports 54 mbps

HiperLAN2 Competing high-speed WLAN standard for 5- to 6-GHz band; supports 54
mbps
IEEE 802.11g High-speed WLAN standard for 2..4-GHz band; supports 20+ mbps
transmission speeds
IEEE 802.1x Comprehensive security framework for all IEEE networks including WLANs
and Ethernet
IEEE 802.11i Wireless-specific WLAN security standard that complies with IEEE 802.11x

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

MAKING THE DECISIONS
Table 8-7
Major Factors Influencing LAN Selection

Cost Number of workstations Type of workstations

Number of concurrent Type of use Number of printers
users
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

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 . 


Table 8-8 Immediate and Recurring LAN Costs

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 spares
Recurring Costs
LAN management personnel costs Hardware and software maintenance
Consumable supplies Training (new users, administrators)

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.


Number of Concurrent Users and Type of Use
The 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.


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.
Vendor and Support

When 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.

Manageability
Never 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 LAN Management Task
User/Group Oriented
Add, delete users and groups Set user/group security
Set user environment Solve user problems
Printer Oriented
Install/removed printers Set-up user environment
Maintain printers
Hardware/Software Oriented
Add/change/delete software Add/change/delete hardware
Diagnose problems Established connections w/ other networks
Plan and implement changes
General
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

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 STANDARDS
The 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.

IEEE LAN STANDARDS
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.

Figure 8-24

Bus A, Unidirectional

Bus B, Unidirectional

Distributed Queue Dual Bus MAN Architecture

IEEE LAN STANDARDS

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.

Lan architecture

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