Download Unit 2 Lesson 5

Lesson 5: Other Network Architectures
At a Glance
This lesson covers the basic characteristics of Token Ring, FDDI, ARCNet
and LocalTalk architecture.
What You Will Learn
After completing this lesson, you will be able to:
D

Describe the characteristics of Token Ring architecture.

Describe the characteristics of FDDI architecture.

Describe the characteristics of ARCNet architecture.

Describe the characteristics of LocalTalk architecture.

Design a Token Ring network

Select appropriate network architecture when given a set of
specifications.
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Unit 2
Student Notes
Tech Talk
2

Active Monitor – The computer device on a Token Ring network whose
responsibility is to ensure that the network is functioning properly.

ARCNet – A Token Ring network that runs over tine twisted pair RJ62/U cable at speeds of either 2.5 or 4 Mbs.

Beacon Frame – A specialized frame, or signal, used in both Token Ring
and FDDI networks. Beacon frames are used to indicate network
malfunctions, such as a break in the ring.

Claim Frame – A specialized frame, or signal, used in both Token Ring
and FDDI networks that indicates that a new computer device on the
ring has been designated the active monitor.

Fiber Distributed Data Interface (FDDI) Architecture – A high speed,
dual token passing access network that uses fiber optic cable.

Medium Interface Connector (MIC). 1. An IBM designed connector,
used for Type 1 and Type 2 cabling, that may be connected to another
like connector. Two connectors are attached simply by flipping one of
them over. 2. An interface used in FDDI networks, to connect fiber
optical cable to a computer device or another fiber optical cable
segment. The MIC is also used to terminate fiber optical cable.

Ring Wrap – The joining of the primary and secondary FDDI rings in
the even of a break in the primary ring. This process allows the
network to heal itself and continue to operate.

Timed Token Frame – Specialized data packet used in FDDI networks
that gives permission to a computer device to transmit data. The
rotation time around the ring is timed making it possible to determine
when a device should have token access.

Token Frame – Specialized data packet used in Token Ring networks to
give permission to computer devices to transmit data.

Token Ring Architecture – An IBM, IEEE 802.5 physical star, logical
ring topology technology that uses a token passing access method for
transmitting data.
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Lesson 5: Other Network Architectures
Token Ring Architecture
Token Ring architecture, introduced in the mid 80s by IBM and defined by
the IEEE 802.5 standard, is a physical star, logical ring topology. In Token
Ring networks, computer devices are connected logically in a ring with
each device connected separately to a specialized Token Ring hub called a
multistation access unit (MSAU or MAU). The function of this hub is to
ensure that the packets of data are transmitted around the ring and has
the ability to bypass a device in case of failure on one of the ports.
Token Ring Multistation Access Unit (MAU)
Traditional Token Ring networks transmit signals at a speed of either 4 or
16 Mbs using a token that is passed from computer to computer around a
network. [Recent Token Ring technology with speeds of 100 and 128 Mbs
is called fast Token Ring networks. These networks operate like
traditional Token Ring networks]. In order to send data, a computer
device must capture the token. The token, which is continuously
transmitted around the ring, is a 24-bit frame with three fields, a Start
Delimiter (SD), an Access Control (AC), and an Ending Delimiter (ED).
Token Frame Format
SD
AC
ED
The access field carries a signal, either a 0 or 1, that tells the computer
device whether or not it is available to carry data. If available, the access
control signal is a 0, and the computer device captures the token frame,
inserts the information being transmitted in between the access field and
the ending delimiter, and then sends the entire frame.
When workstation A transmits to workstation C, workstation A grabs a
free token and changes the AC to a 1 indicating that the token is no longer
available for use and encapsulates its data within the token frame
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Workstation A Captures the Free Token
D
Free
Token
A
C
B
The token with its encapsulated data travels around the network from one
computer to the next, where each device accepts the frame and checks the
destination address. If the hardware addresses match, the device
processes the data, if it does not match the data is retransmitted to the
next device until the token reaches its intended destination.
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Lesson 5: Other Network Architectures
Data Encapsulated in Token Frame
D
A
C
Data
B
The destination device accepts the frame and copies the data, verifies
receipt, and returns the token frame to the network where it continues
around the ring until it reaches the original sending device. The sending
device recaptures the token that contains information that the frame was
received and also contains error control information. After stripping the
original data from the frame, the sending device returns the available
token to the network and the process continues.
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Workstation C Accepts Data and Sends to Back to A to be Stripped
D
Data
Data
A
C
Token
B
Four Mbs Token Rings only allow one token on the ring at a time, sixteen
Mbs Token Rings allow multiple data frames to be on the ring at the same
time.
Token Ring networks are not as susceptible to signal degradation as other
network types, since each device acts like a repeater, regenerating the
signal before transmitting it to the next device. Token Ring networks fail
more gracefully than Ethernet networks when they are overloaded. Since
they are so reliable, diagnostic and troubleshooting measures are often
built into the hardware. Also, priority can be assigned in Token Ring
networks.
Although they work quite well, Token Ring networks are currently being
phased out for several reasons. They have very complicated protocols,
which makes them both difficult to troubleshoot and more expensive than
other technology. Token Ring is basically IBM, so there are compatibility
issues with equipment from other manufacturers who also are not as
interested in new Token Ring technology since the market isn’t as
profitable as the Ethernet market. Additionally, 4 Mbs networks are too
slow.
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Lesson 5: Other Network Architectures
Token Ring Frame Format
Token Ring frame format begins with the 8 bit Start Delimiter followed by
the 8 bit Access Control. The next field, is a Frame Control field, which
indicates whether the frame contains Media Access Control information for
all network devices or only data for only a single destination device. This
field is followed by the Destination Address field (either 16 or 48 bits), the
Source Address field (either 16 or 48 bits), the Data field (has no
determined size), the Frame Check Sequence field (32bits), the End
Delimiter field (8 bits), and finally the 8bit Frame Status field.
Token Ring Frame Format
SD
AC
Frame
Control
Destination
Address
Source
Address
Data
Field
FCS
ED
8
bits
8
bits
8
bits
16 or 48
bits
16 or 48
bits
>0
bits
32
bits
8
bits
Detecting Errors through Beaconing
One computer device on a Token Ring network, usually the first device
recognized when the LAN comes up, is designated the active monitor. It is
the responsibility of the active monitor to ensure that the network is
functioning properly. Every seven seconds the active monitor station sends
a signal, called a beacon, which checks for malfunctioning devices and
problems such as errors in delivery of frames. Each successive device on
the ring receives and forwards the beacon signal. If a device does not
receive the beacon announcement, it sends a message on to the network
indicating that there is a malfunction, and the Token Ring tries to selfcorrect the problem. If the active monitor malfunctions, its nearest active
upstream neighbor (NAUN) becomes the new active monitor and sends out
a Claim Token notifying all other devices of the change in active monitor
status.
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Token Ring Components
Cabling
The specified cable in the IEEE 802.5 Token Ring standard is 150 ohm
STP. IBM Token Ring networks use UTP, STP, and fiber optic cable types.
The chart below indicates the IBM cable types, their description, and
common uses.
IBM Cable Type
Description
Type 1
Two-pair 22 AWG STP wire used for conduits
and outside walls
Type 2
Two-pair 22 AWG STP wire for data and fourpair 26 AWG wire, outside the shield, used for
telephone (voice). Commonly used for trunk
cable.
Type 3
Four-pair 22 or 24 AWG UTP wire, which
requires a media filter for use in Token Ring
networks. Susceptible to EMI since it is
unshielded wire. Also can’t be used for 16 Mbs
Token Ring networks.
Type 5
100/140 micron two strand fiber optic cable,
which is used for the main ring of Token Ring
networks.
Type 6
26 AWG flexible STP wire used for patch or
extension cables.
Type 8
Single copper core 26 AWG STP specifically
designed for use under carpets.
Type 9
Single pair Plenum grade 26 AWG STP fire
resistant wire. Used in walls and ceilings.
Token Ring Network Interface Adapter Cards
Token Ring Network Adapter Cards, the specialized interface used to
connect devices on Token Ring networks are available for both 4Mbs and
16Mbs Token Ring networks. A 16 Mbs Token Ring NIC can be used on a
4 Mbs network; however a 16 Mbs network must use 16 Mbs adapter
cards.
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Multistation Access Units
Multistation Access Units (MAU or SMAU), are specialized hubs
(sometimes called concentrators) made specifically for Token Ring
networks. These hubs have an internal wiring arrangement that allows
the computers to be connected in a continuous ring. MAUs have the ability
to bypass failed computer devices connected to the ring. Typical MAUs
connect eight or more computer devices and, according to standards, up to
12 MAUs can be interconnected.
Adapter and Patch Cables
A Token Ring adapter cable typically has a nine-pin connector at one end
that attaches to the back of the NIC. and a special IBM data connector that
connects to the MAU at the other end. Adapter cables may also have
telephone-jack-type cable connectors.
Patch cables are Type 6 IBM cables that come in standard lengths of 8, 30,
75, or 150 feet. They are used to extend the distance of a computer device
from the MAU, or to attach two MAUs.
Media Filters
A media filter is used to connect a Token Ring adapter card to an RJ-11 or
RJ-45 wall jack. A media filter is required when Type 3 telephone cable is
used or when a NIC card with a DB-9 interface to connected to hub. The
media filter converts different signals and reduces noise interference.
Connectors
Many different types of connectors are supported within a Token Ring
network. The type of connector specifies the type of cabling that is
acceptable. If UTP cabling is used, both the cable and connectors must
have the same category rating.
Token Ring connectors include the following:

DB-9 Connector. Used for STP cable. May be used for trunk a
connection or device inaction. Most commonly found on the back of a
Token Ring NIC card. A DB-9 must have a media filter attached if used
with UTP cable.
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DB-9 and IBM Data Connector
DB-9 Connector
NIC
STP Cable
IBM Data Connector

Medium Interface Connector (MIC). An IBM designed connector, used
for Type 1 and Type 2 cabling. A MIC may be attached to another like
connector simply by flipping one of them over.
IBM Data Connector
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
RJ-45. An 8-pin standard telephone-jack-type connection used to
connect UTP or STP cables.

RJ-11. A 4-pin telephone-jack connector used for Type 3 cable
connections.
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
Straight Tip (ST). Connector used with fiber cable . Two connectors
are required per port, one transmits and one receives.
Straight Tip Connector
Check Your Understanding
 What are the advantages of a Token Ring Network?
 What is a token?
 What is a MAU?
Fiber Distributed Data Interface (FDDI)
Fiber Distributed Data Interface (FDDI) is a high speed (100 Mbs), fiber
optic LAN technology that uses the token passing method to access the
network. The American National Standards Institute (ANSI) developed
standards for FDDI networks (X3T9.5) that address the Physical and
Media Access (sub)layers of the OSI model. It assumes the use of IEEE
802.2 Logical Link Control sublayer standard above the MAC layer. FDDI
uses physical star, logical ring topology. Unlike Token Ring, which has
only one ring, FDDI is a dual ring topology. FDDI is commonly used
between LANs in metropolitan area networks to provide high speed
connections.
Like Token Ring, FDDI uses a token frame to pass data from one station to
the next around a ring until it returns to the source device; however, an
additional clocking field is added to the beginning of the token. This field
is added because FDDI transmissions may be synchronous and require a
clocking mechanism. Voice and video transmissions are examples of data
that require synchronization.
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When a free token is available, a computer device is allowed to transmit its
data. Unlike Token Ring, which can transmit only one frame at a time,
with FDDI the computer device can transmit as many frames as possible
until a predefined time limit is reached. When the device either has no
more frames to send or the time limit is reached, it stops transmitting data
and immediately releases an available token. In Token Ring, the free
token was not released until after the sending device received the frame it
sent indicating receipt and/or errors.
Because the token is transmitted as soon as a computer device is finished
transmitting frames, it is possible for a device on the ring to transmit new
frames while other frames are still circulating around the ring. It is
therefore possible for multiple frames from multiple devices to be on the
network simultaneously.
FDDI networks are commonly used to connect LANs where either EMI or
distance is problems. Computer devices can be as far apart as 2 kilometers
and FDDI networks can support up to 1000 devices per LAN.
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FDDI Rings
FDDI is able to send more than one frame at a time because it uses dual,
rings with data moving in opposite directions on each ring, as shown in the
illustration below. This also allows more than one computer to transmit at
the same time.
FDDI Dual Rings
Primary ring
Secondary ring
The dual rings are classified as primary or secondary. Devices on FDDI
networks may be connected to both primary and secondary rings or only
the primary ring. If there is a malfunction on the primary ring, the
secondary ring automatically wraps to the first ring forming a complete
ring once again. This is referred to as “ring wrap” and is an automatic
function of FDDI. A type of claim token frames is used in FDDI networks
to detect errors in transmission or timing.
A device connected to both the primary and secondary rings is classified as
a dual-attached station or Class A station. A single-attached or Class B
station, is attached to only the primary ring. Typically, a Class A station
would be a hub and a Class B, a computer workstation. The Class B device
would connect to the primary ring and through that connects to the hub.
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FDDI Frame Format
In addition to the four token fields FDDI network include the following
fields:
FDDI
The diagram below shows the FDDI Frame Format.
FDDI Frame Format
LLC-PDU
SSAP
Address
DSAP
Address
Frame
Control
Information
MAC Frame
Preamble
Starting
Frame
Delimiter
8 octets
1 octet
Frame
Control
Dest.
MAC
Address
Source.
MAC
Address
Information
2 or 6
octets
2 or 6
octets
0-4478
octets
1 octet
Frame
End
Check
Frame
Sequence Delimiter
4 octets
.5 octet

Preamble: this field, which consists of all 1s, is used as a clocking
mechanism and indicates the beginning of a frame.

Start Delimiter: designates the physical start of the FDDI frame.
 ES-AV0025000
Frame
5/33 control: indicates the length of the address and the transmission
type (synchronous/asynchronous and data/network information).
14

Destination Address field.

Source Address field.

Data: application and upper layer protocol data.

CRC: error checking frame.

End Delimiter: signifies the end of the data frame.

Frame Status field: offers further error checking.
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Frame
Status
1.5 octets
Unit 2
Lesson 5: Other Network Architectures
FDDI Media
Cabling
Fiber optic cable is specified as the standard for FDDI and may be single or
multi-mode fiber. Single mode fiber optic cable uses laser technology and
can transmit up to a maximum of 20 km without using repeaters. Multimode fiber is less expensive. Instead of laser technology, it employs LED,
light emitting diode technology, and can transmit signals of to a maximum
distance of 2 km.
STP Type 1 and UTP Category 5 copper cable may be used for the ring
device connections.
Dual Attachment Concentrator (DAC)
A dual attachment concentrator is a hub used in FDDI networks that are
capable of attaching to dual counter rotating rings. DACs have additional
ports, called trunk ports, used to connect to additional concentrators or
other FDDI computer devices.
FDDI Network Adapter Cards
The transceiver in FDDI networks in built into the FDDI NIC. It is a laser
transceiver used to convert digital data to light impulses and vice versa.
This conversion allows signals to travel over both copper and fiber optic
cabling thus enabling connections to PCs. It is not unusual for some types
of NICs to have more than one transceiver. For example, many Ethernet
NICs have more than one transceiver, but each transceiver must have its
own connector type on the card.
FDDI Connectors
The connectors used in FDDI networks are Media Interface Connectors
(MIC), Straight-tip Connectors (ST), and RJ-45 Connectors.
There are several types of MICs. They are typically color coded to assist in
allowing only desirable port connections. During installation and
troubleshooting when cable connections are often moved, it is important to
keep the color-coded key attached to the MIC connector. Occasionally fiber
cabling may use a combination of connectors with a MIC at one end and a
ST connector on the opposite end.
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LocalTalk
Since its introduction in 1984, Apple Computer has included a built-in
network interface on every Macintosh. LocalTalk is a low-speed network
that was designed to work in small workgroups with a few devices. The
network transmits data at 230 kilobits per second, about 40 times slower
than the slowest Ethernet network. In contrast to Ethernet use of
CSMA/CD, LocalTalk uses the CSMA/CA access method.
LocalTalk
Connector
module
8-pin plug
LocalTalk
cable
The original version of LocalTalk from Apple used a shielded 2-wire cable
to transmit data. The system used a bus topology in a fashion similar to
10Base2. Although LocalTalk is easy to install and use, it is very slow and
does not support more than 253 devices and is limited to a maximum of 32
devices per daisy chain.
Check Your Understanding
 What are differences between FDDI and Token Ring networks?
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LocalTalk Addressing
LocalTalk provides three levels of addressing: node, network, and socket.
Node ID
You'll remember that one of the requirements of a Data Link layer protocol
is to move data from device-to-device on a single LAN. To do so, each device
on the network requires a unique address. On Ethernet and Token Ring
network interface cards, this address is located in some form of nonvolatile memory. For the Macintosh, Apple chose a different approach.
Instead of storing a unique network address into every Macintosh
computer, an address is dynamically assigned each time the computer is
turned on. Apple calls this address a Node ID.
The Node ID is a Data Link layer address that uniquely identifies each
device on a single network. The Node ID is 8 bits and ranges from 0 to 255.
Node IDs 0, 254, and 255 are reserved resulting in a possible 253 addresses
per network.
Check Your Understanding
 Compare the speed of LocalTalk with Ethernet:
 How is LocalTalk addressing different from Ethernet and Token
Ring?
Network ID
The Network ID is a Network layer address that uniquely identifies each
network on an internetwork. The Network ID is 16 bits and ranges from 0
to 65,535. This allows a maximum of 65,536 networks each with 253
devices for a total of 16,580,608 devices.
DIN type connectors for STP SSTP connectors generally must be soldered
during installation, LocalTalk originated as STP but can now use UTP
with RJ-45 connectors.
The Datagram Delivery Protocol (DDP) is LocalTalk's Network layer
protocol. DDP provides connectionless, best-effort data delivery and
provides no acknowledgement sent to the receiver
ARCNet
Attached Resource Computer network was developed in the late 70s for
small LANs is a token passing media access control network topology, that
transmits data at speeds 2.5 Mbs. Tokens in ARCNet networks are passed
according the MAC address rather than in succession from one computer to
the NAUN computer device.
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Topology is either bus, star, or a combination. If bus topology is used, the
maximum distance per segment is 305 meters. With the addition of an
active hub that repeats the signals, the maximum distance between the
computer device and the hub is 610 meters when using BNC connectors
and coaxial cable and 244 meters when using twisted pair and RJ-11 or
RJ-45 connectors.
ARCNet Media
ARCNet networks use coaxial, UTP, STP, and fiber optic cable although
the standard cable is 93-ohm, RG-62A/U coaxial.
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Lesson 5: Other Network Architectures
Hybrid Architectures
Incorporating more than one type of architecture when connecting and
expanding LANs is not uncommon. A specialized bridge, called a
translating bridge, must be used when interconnecting LANs using
different data link layer protocols and different physical network media
(for example, Token Ring to FDDI). It must be able to convert the frame
format of one media type into the frame format of another media type.
Translating Bridge
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U2L5 Supplemental #1
Ethernet or Token Ring?
Write a one half -page scenario for two companies that includes the
following information:

Type of company

Number of employees

Network access requirements

Network reliability needs

Physical layout requirements

Type of equipment

Type and amount of data to be transmitted
Make one scenario company use an Ethernet network (so make up
company characteristics to fit that architecture) and one scenario to use
an IBM Token Ring network (again, make up company charactoristics to
fit token ring strengths) Your two scenarios should emphasis the strength
of both architectures. Don’t make guesses. From the reading what did you
learn? Include in your analysis your reasons for the choice. Defend as
many aspects of your choice as possible based on facts about each type.
U2L5 Supplemental #2
Give the answers to the following blank spaces. Also, after each question tell
where you found the answer. Some will be from the lesson reading in which
case give the page number. Others will be found on the net so give the URL
where you found it.
1.
uses a physical star, logical ring topology with each network
device connected separately to a multistation access unit.
2. This network technology designed by
is a low-speed network
(230 Kbps) that was designed to work in small workgroups with a few devices.
3. This network technology can use either a bus, star or combination topology and was
designed in the late 70s for small LANs. The original version used token passing at
2.5Mbps.
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Lesson 5: Other Network Architectures
4. The most commonly installed Token Ring networks run at
5.
.
networks are not as susceptible to signal degradation as other network
types since each device acts as a repeater.
6. Token Ring networks use a
devices.
signal to check for malfunctioning
7. The IEEE Token Ring specification is
8. A 16 Mbps Token Ring NIC
.
be used on a 4 Mbps Token Ring network.
9. A Token Ring hub is commonly referred to as a
.
10. MAU is an acronym for _______________________________________.
11. A DB-9 connector used in a Token Ring network must have a
attached for device connection if used with a UTP network.
12. According to Token Ring standards, up to ______ MAUs may be interconnected.
13. _________ can be used between LANs in metropolitan area networks to provide high
speed connections.
14. A ________ FDDI device is connected to both the primary and secondary rings.
15. Multi-mode fiber optic cable can transmit to a maximum of ________ on a FDDI
network without using repeaters.
16. The hub used in FDDI networks that allows attachment to the dual rings is called
a
.
17. LocalTalk devices use ________ addresses for network communications:
18. A ___________ is used to interconnect LANs using different data link layer protocols
and different physical network media (example: Ethernet to FDDI).
19. Here is the format for a Token Frame:
And here is the format for an Ethernet Frame:
When compared the three most obvious differences are:
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U2L5 Supplemental #3
Other Networking Architectures Review Questions
Part A
1. Token Ring networks operate at
a. 10, 100 or 1000 Mbps
b. 4, 16, 100 or 128 Mbps
c. 1 Gbps
d. 10, 16 or 1000 Mbps
e. 4 or 10 Mbps
2. A device may use the token frame to send data if
a. The Start Delimiter is 0
b. The End Delimiter is 1
c. The hardware addresses match
d. The Access Control signal is 0
e. The Start Delimiter is 1
3. The token frame size is
a. 16 bits
b. 24 bits
c. 32 bits
d. 48 bits
e. 64 bits
4. After copying data from the token frame, a receiving device
a. Releases the token
b. Reads error control information from the frame
c. Uses the token frame to send new data
d. Destroys the token frame
e. Send the frame back to the sending device
5. Token Ring networks
a. Fail more often than Ethernet networks
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b. Fail more gracefully than Ethernet networks
c. Never fail
d. Cannot accept priority assignments
e. Must use fiber optic cabling
6. To detect and correct errors
a. Every device on a Token Ring network is an active monitor
b. Each device on a Token Ring network diagnoses its own errors
c. Each device gives control to its nearest active upstream neighbor
d. One device is designated as the active monitor
e. All devices send out a Claim Token
7. An MAU
a. Connects Token Ring devices into a ring
b. Turn off the ring when any connected device fails
c. Route power to connected devices
d. Switch traffic to neighboring networks
e. Cannot connect to other MAUs
Part B
1. FDDI operates at
a. 10 Mbps
b. 4 or 16 Mbps
c. 100 Mbps
d. 1000 Mbps
e. 4.5 Mbps
2. To transport streaming media data, FDDI
a. Opens a switched circuit
b. Can synchronize data with a clocking field
c. Can only transmit one frame when the token has been captured
d. Uses fiber optic cabling
3. When an FDDI sending device has captured a token
a. It can only transmit one frame
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b. It can transmit as many frames as it wants
c. It can only transmit error diagnostics
d. It can transmit frames until a time limit expires
e. It releases the token
4. A secondary ring in FDDI
a. Automatically steps in if the primary ring fails
b. Allows priority communication to select devices
c. Doubles communication speed
d. Connects to Token Ring networks
Part C
1. Which computer manufacturer uses local talk?
a. IBM
b. Digital Equipment Corporation
c. Intel Corporation
d. Motorola
e. Apple Computer
2. AppleTalk operates at
a. 230 Kbps
b. 1 Mbps
c. 10 Mbps
d. 100 Mbps
e. 1 Gbps
3. AppleTalk Node Id’s are assigned
a. By the manufacturer
b. By the user
c. By the computer when the device is powered up
d. By the computer when the device is installed
e. By the server
4. AppleTalk connects using
a. Fiber optic cable
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Lesson 5: Other Network Architectures
b. Coaxial cable
c. Twisted pair cable
d. Microwave radio
e. Photonic switches
Part D
1. ARCNet operates at
a. 230 Kbps
b. 1 Mbps
c. 2.5 Mbps
d. 10 Mbps
e. 1 Gbps
2. ARCNet tokens are passed by
a. nearest active upstream neighbor
b. nearest active downstream neighbor
c. Random walk
d. MAC address
e. NAUN computer device
3. ARCNet connects using
a. Twisted pair or coaxial cable
b. Fiber optic cable
c. Infrared light
d. Microwave radio
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