Token Ring Basic Concepts

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COPYRIGHT
©1996 Madge Networks, Inc. All rights reserved. No part of this publication may be reproduced, transmitted, transcribed,
stored in a retrieval system, or translated into any language or computer language, in any form or by any means, electronic,
mechanical, photocopying, manual or otherwise, in whole or in part, without the prior written consent of Madge Networks,
Inc.
NOTICE
The information contained in this document is subject to change without notice. Madge Networks, Inc., reserves the right to
revise this publication and to make changes from time to time in the content hereof without notice.
DISCLAIMER
While every precaution has been taken in the preparation of this self study, Madge Networks, Inc. assumes no responsibility
for any errors or omissions that may appear in this document. Nor does it assume any liability for any damages resulting from
the use of the information contained herein.
TRADEMARKS
©1996 Madge Networks, Inc., All rights reserved. Madge and the Madge logo are trademarks, and in some jurisdictions, may
be registered trademarks of Madge Networks. All other brand and product names are trademarks or registered trademarks of
their respective holders.
Printed in USA
Publication TRSSVer 2. 1996

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INTRODUCTION TOKEN RING BASIC CONCEPTS SELF-STUDY 5
Course Objectives 5
MODULE ONE TOKEN RING BASICS 7
Objectives 7
Overview 7
Token Ring Evolution 8
Token Ring Operation 8
Early Token Release 12
The Token and Frame Formats 15
Starting Delimiter 15
Access Control 15
Frame Control 16
Destination Address 16
Source Address 16
Routing Information 16
Information Field 16
FCS (Frame Check Sequence) 17
Ending Delimiter 17
Frame Status 17
Module One Summary 18
Module One Self-study 19
MODULE TWO RING MAINTENANCE 21
Objectives 21
Overview 21
The Active Monitor 21
The Master Clock 22
Ring Delay 22
Token Circulation 22
Orphaned Frames 22
Neighbor Notification 23
Ring Purge 23

II Table of Contents
Standby Monitors 24
Joining the Ring 24
Lobe Test 24
Physical Insertion and Monitor Check 25
Duplicate Address Check 25
Ring Poll Participation 25
Request Initialization 25
Error Detection 26
Hard Errors 26
Sample Hard Errors 26
Hard Error Detection 26
Soft Errors 28
Sample Soft Errors 28
Soft Error Recovery 28
Module Two Summary 29
Module Two Self-test 30
MODULE THREE TOKEN RING NETWORK COMPONENTS 33
Objectives 33
Overview 33
Token Ring Network Components 33
Token Ring Adapter 33
Wiring Hub 34
Ring-In 34
Ring-Out 35
Lobe Connection 35
Phantom Current 35
Trunk Connection 35
Primary and Secondary Paths 36
Primary Path 36
Secondary Path 36
Token Ring Cabling Options 38
Shielded Twisted Pair (STP) 38
Unshielded Twisted Pair (UTP) 38
Fiber Optic 38
Token Ring Topology 39
Logical Ring/ Physical Star 39
Module Three Summary 40
Module Three Self-study 41

Table of Contents III
Token Ring Basic Concepts
MODULE FOUR BUILDING TOKEN RING NETWORK
INFRASTRUCTURES 45
Objectives 45
Overview 45
Source Route Bridging 45
Single Route versus All Routes Broadcasts 47
Transparent Bridging 48
Source Route Transparent Bridging 48
Module Four Summary 50
Module Four Self-test 51
MODULE FIVE TOKEN RING SWITCHING 53
Objectives 53
Overview 53
Cut-Through Switching 53
Store and Forward Switches 54
Contention and Buffering 54
Switching by Source Routing 55
Full Duplex Token Ring 55
Virtual LANs 56
Token Ring Switching and ATM 57
Module Five Summary 59
Module Five Self-study 60
APPENDIX A - ANSWERS TO SELF-STUDY QUESTIONS 61
Module One Self-study Answers 61
Module Two Self-study Answers 62
Module Three Self-study Answers 63
Module Four Self-test Answers 64
Module Five Self-test Answers 65

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Welcome to Token Ring Basic Concepts Self-study.
This course introduces Token Ring concepts and
terminology that will provide you with the background
you need to sell Token Ring products from Madge
Networks.
Course Objectives{ XE Welcome }
By the end of this self-study, you will be able to:
N Discuss the evolution of Token Ring.
N Describe the theory of operation for Token Ring.
N Describe the function of token passing and explain
its importance.
N Explain Token Ring’s basic ring management
functions.
N Describe the function of Token Ring bridges,
including source routing and source route
transparent bridging.
N Explain Token Ring frame switching.

7
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This module provides an introduction to basic Token
Ring concepts you will need to understand the
applications and benefits of Token Ring technology.
Objectives{ XE Assumptions made for manual }
By the end of the Token Ring Basics module, you will
be able to:
N Discuss the evolution of Token Ring.
N Describe the theory of operation for Token Ring.
N Describe the function of token passing and explain
its importance.
N Describe the token and data frame formats.
Overview
A Token Ring network can be described as baseband
network that simplifies network resource sharing by
providing a standardized architecture. The Token Ring
network derives its name from its method of operation
and the way its stations are linked together. The nodes
or stations on the network are connected to create a
“ring” path for the data frames to travel from one
station to the next. The ring is made up of ring stations
that are connected via cabling. Each station has a
Token Ring adapter card and access to the logical link
control (LLC) and media access control (MAC)
service access point functions. A token (a specific
pattern of data) is used on the Token Ring network to
decide which node can use the ring at any one time.
Let’s take a brief look at the evolution of Token Ring
and then the specific operation of a Token Ring
network.

8 Module 2- Ring Maintenance
Token Ring Evolution
Token Ring technology was originally proposed in
1969 and was known as the Newhall ring, after one of
its developers. Even though this technology was being
worked on before Ethernet, it wasn’t until the mid
1980s, when IBM endorsed the Token Passing Access
Method, that Token Ring emerged as another LAN
enabling technology. The IEEE 802.5 standard was a
direct outgrowth of research done by IBM. In fact,
IBM’s Token Ring Network is an implementation of
the 802.5 standard.
Token Ring continued the trend of sharing media, but
it differs significantly from Ethernet in the way the
media is accessed. When a station wishes to transmit
data on a Token Ring network to another station, the
sending station must first get possession of the
“token.”
The token is a unique 24-bit message (control signal)
that controls access to the ring. The token continuously
circulates the ring, passing from one station to the next
until a station wishes to transmit. The transmitting
station takes possession of the token until transmission
of the data frame travels a ring path. This method
ensures that no two stations can transmit at the same
time, thus avoids the possibility of a data collision.
Let’s take a more detailed look at Token Ring
operation.
Token Ring Operation
We will be using a four-node network as our sample
Token Ring network. (See Figure 1) In our sample
network, station “A” would like to send information to
station “C.” Station “A” has possession of the token
and has sent a data frame out onto the ring. Station “C”
is the destination station.

9
Sending
Station
Data frame
being sent to
station “C”
A
B
C
D
Receiving
Station
Figure 1 Sample Token Ring network
The data frame will be received by the next station in
line, station “B.” ( See Figure 2.) Station “B” will
check the destination address to see if the data frame is
for station “B.” In this case, the data frame is not
addressed to station “B” and therefore “B” sends the
data frame back out onto the ring without making any
changes.

Sending
Station
A
B
C
D
Receiving
Station
Data frame
being sent on to
station “C”
Figure 2 Data frame being sent to station “C”
Next, the data frame will be received by station “C.”
( See Figure 3.) Station “C” will read the destination
address. Because the data frame is addressed to station
“C,” station “C” will copy the data frame; after
changing bits in the frame to indicate the frame was
copied, station “C” passes the original frame back out
on to the ring. The modified data frame goes through
station “D” the same way it went through station “B,”
without changes being made.

11
Copy
Sending
Station
A
B
C
D
Receiving
Station
Data frame is
copied and original
is sent back to “A”
Figure 3 Data frame is copied by Station C
When station “A” receives the original data frame
back, it reads the destination and source addresses. It
recognizes its source address and checks the frame-
copied bits to make sure the data frame was received.
(If the frame-copied bits are not changed, the station
waits for the token again and retransmits the data
frame.) The frame-copied bits are changed, so station
“A” will release the token out onto the ring. (See
Figure 4.)
Sending
Station
A
B
C
D
Token is
sent back out
onto the ring

Figure 4 The token is sent back out on the ring
The Token Ring operation just described is specifically
that of 4 Mbps Token Ring. The next station must
wait for the transmission to complete before it can get
possession of the token. This means the delay on the
ring grows as more stations are added. To alleviate this
problem, Early Token Release (ETR) was made
available with 16 Mbps Token Ring operation in the
late 1980s.
Early Token Release
Early Token Release operation releases a token after
the data frame has been released. This allows multiple
data frames to be out on the ring at the same time. (The
number of data frames supported by a particular ring
depends upon the size of the ring.)
All of the data is synchronously clocked once it is on
the ring. Data goes around the ring in only one
direction and data frames never meet. All data frames
include the source and destination addresses, so each
node is able to tell whether it should copy the data
frame or send it on.
Let’s use the same example to demonstrate 16 Mbps
operation and Early Token Release.
Station “A” is about to transmit data to station “C.”
After the data frame has been released, station “A”
also releases a token. (See Figure 5.)

13
Data frame
being sent to
station “C”
Token is released
a short time
after the last bit of
data has left
the station
Sending
Station
A
B
C
D
Receiving
Station
Figure5 Early token release
The data frame is received at station “B.” Station “B”
checks the destination address to see if the data frame
is for station “B.” In this case the data frame is not
addressed to station “B,” and therefore “B” sends the
data frame back out onto the ring without making any
changes, as before. But this time station “B” would
like to transmit, too. In this case, station “B” grabs the
token that follows the data frame destined for station
“C” and sends a data frame to station “D.” A short
time after the last bit of data has left station “B,”
station “B” releases a token. This token is available for
the next station in line that wishes to transmit.
Let’s check and see what happens when station “A’s”
original data frame returns. When station “A” receives
the original data frame back, it reads the destination
and source addresses just like before. It recognizes its
source address and checks the frame copied bits to
make sure the data frame was received. The frame
copied bits are changed, so station “A” strips the data
frame off the ring.

In this case, station “A” does NOT release a token as it
did before, on the 4 Mbps ring. Because a token is
released after every transmission, there is no need to
release a token after the data frame returns to the
originating station. It is important to note that at any
one time there is only ONE token available on the ring.
After a station grabs the token and begins to transmit
its data, the grabbed token is a “busy” token.
Next, let’s take a detailed look at the token and data
frame structures.

15
The Token and Frame Formats
The token is a 24-bit frame that is composed of the
starting delimiter, ending delimiter, and access control
fields.
SD AC ED
1 Byte 1 Byte 1 Byte
Figure 6 The token structure
SD AC FC DA SA RI Information FCS ED FS
1
byte
1
byte
1
byte
1
byte
1
byte
2 or 6 bytes
each
0 - 4999
bytes
4 bytes
Figure 7 The IEEE 802.5 frame format
Starting Delimiter
The starting delimiter is 1 byte or 8 bits. This field is
used to synchronize the transmission of the token or
frame.
Access Control
The access control field is a status byte that occurs in
both the token and the data frame. The access control
field contains bits that indicate whether the frame is a
token or a data frame, what the priority of the frame is,
and bits used by the active monitor for control
purposes. (We will discuss the active monitor function
in Module Two.)

Frame Control
The frame control field indicates whether the frame is
a MAC control frame or a data frame. MAC control
frames are frames that have to do with ring operation
and may need special handling. The requirement for
special handling is indicated in the frame control field.
If the MAC frame needs to be processed immediately
by the destination station, the frame control field has
bits that indicate this; the MAC frame is copied into an
express buffer and processed immediately at the MAC
level. These MAC frames stay on their local ring and
are not sent to any other rings.
Destination Address
The Destination Address field is next. According to the
802.5 specification, it is 6 bytes long and specifies
which station(s) receives and copies the frame.
Source Address
The source address identifies the address of the
originating station and must correspond to the size of
the destination address.
Routing Information
The routing information field is an optional field used
if the frame is addressed to a station on another ring.
Information Field
The information field contains LLC (logical link
control) or MAC (media access control) data. If the
frame is an LLC frame the information field holds end
user data. If the frame is a MAC frame the information
field holds MAC control information.
This is a variable length field. On a 4 Mbps Token
Ring network, the data field can be a maximum of
4,472 bytes long. On a 16 Mbps network, the data
field can be a maximum of 17,800 bytes long.

17
FCS (Frame Check Sequence)
The FCS, or Frame Check Sequence, contains a 32-bit
CRC, or Cyclic Redundancy Check value, that is the
result of error checking done by the originating station.
The transmitting station calculates this value based
upon the frame control field, source and destination
address fields, routing information fields (if present),
and the data field. The receiving station recalculates
the value based upon the received data and compares it
to the FCS to confirm that the frame was copied
without error. If the two do not match, the frame is
rejected.
Ending Delimiter
The ending delimiter is also 1 byte in length. Its
purpose is to mark the end of a token or data frame.
Frame Status
The frame status field contains the bits changed by the
receiving station to indicate it recognized its address
and copied the frame. The originating station checks
this field when the frame returns. If the address is
recognized and frame-copied bits are unchanged, it
resends the frame when it gets possession of the token
again.

Module One Summary
£ Token Ring emerged as a LAN enabling
technology in the mid 1980s.
£The Token Ring network derives its name from its
method of operation and the way its stations are linked
together.
£ The nodes or stations on the network are connected
to create a “ring” path for the data frames to travel
from one station to the next. A token (a specific pattern
of data) is used on the Token Ring network to decide
which node can use the ring at any one time.

19
Module One Self-study
Complete the following self-test by answering the following questions. Use the
answer key located in Appendix A to check your answers.
1. The 802.5 standard is a direct outgrowth of the research done by _________.
a) DEC
b) IBM
c) IEEE
d) Proteon
2. When a station on a Token Ring network wishes to transmit, it must first possess
the ____________.
a) ring
b) token
c) baton
d) none of the above
3. The frame control field indicates whether the frame is a(n) _______ control frame
or a data frame.
a) MAC
b) error
c) beacon
4. The maximum data field for 16 Mbps Token Ring is _____________.
a) 4,472 bytes
b) 17,800 bytes
c) 1,518 bytes
5. If the address-recognized and frame-copied bits are unchanged in the frame status
field, the originating station will resend the frame around the ring.
T or F?

21
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This module provides an introduction to Ring
Maintenance concepts you will need to understand the
benefits of Token Ring technology.
By the end of the Ring Maintenance module, you will
be able to:
N Explain Token Ring’s basic ring management
functions.
N List the functions of the active and standby
monitor.
N Describe the phases a station must go through to
join a ring.
N Describe how errors are detected on a ring and the
function of the beacon MAC frame.
Overview
Token Ring technology incorporates extensive error
detection capabilities. The access method has many
built-in functions for dealing with errors on the ring.
The Active Monitor
The active monitor is responsible for maintaining ring
operations. The active monitor performs the following
functions:

N Provides master clock for the ring
N Maintains proper ring delay
N Ensures a token is circulating at regular intervals
N Monitors the ring for orphaned frames
N Initiates the neighbor notification process
N Ensures the neighbor notification process operates
correctly
N Purges and cleans up the ring when necessary
The Master Clock
The active monitor is responsible for maintaining the
master clock for the ring. Stations on the ring
synchronize their clocks to the master clock.
Ring Delay
Ring delay, also known as minimum ring latency, is
required to ensure that delay on the ring is long enough
to accommodate the token. The active monitor ensures
the proper ring delay exists by introducing at least a
24-bit delay on the ring, when necessary.
Token Circulation
The active monitor is responsible for making sure a
token is always circulating the ring. If the active
monitor has not detected a token or frame within 10
milliseconds, it clears the ring and releases a new
token.
Orphaned Frames

23
Frames can become “orphaned” if the originating
station is no longer active on the ring. To make sure
this frame doesn’t circulate the ring endlessly, the
active monitor sets the monitor bit in the access control
field in every frame that passes. This changed monitor
bit indicates the frame has circled the ring once. If the
monitor sees a frame that has the monitor bit changed,
it knows the frame is orphaned and will take it off the
ring.
Neighbor Notification
Each station on a Token Ring network needs to know
the address of its nearest active upstream neighbor
(NAUN). The address of the NAUN is used when
there is an error on the ring. If a station on the ring has
not received a transmission from its NAUN within a
certain period of time, the station notifies the other
stations of a problem on the ring.
The neighbor notification or ring poll process is
initiated by the active monitor on a regular basis to
update the upstream neighbor’s address in all stations
on the ring. This ring poll process also communicates
the presence of the active monitor on the ring. The
active monitor transmits an active monitor present
(AMP) MAC frame every seven seconds.
Ring Purge
When the Token Ring network does not operate
properly, the active monitor transmits a ring purge
frame, which clears the ring.

Standby Monitors
Every station on the ring except the active monitor is
considered a standby monitor. The standby monitors
are responsible for making sure there is an active
monitor on the ring. In the event that an AMP frame is
not detected within a certain time interval, a standby
monitor initiates the active monitor contention process.
The station with the highest MAC address becomes the
active monitor, and all other stations become standby
monitors.
Joining the Ring
Before a station joins the ring, it must perform some
tests so the ring-joining process is smooth and error-
free.
The station wishing to join the ring must perform the
following checks or functions:
N Lobe test
N Physical insertion and monitor check
N Duplicate address check
N Ring poll participation
N Request initialization
Lobe Test
The first check a station must complete is the lobe
media test. (The lobe refers to the length of cable from
the station to the wiring hub.) The lobe media test is
designed to test the integrity of the cable attached to
the station and the wiring hub.
The station transmits a series of lobe test MAC frames
that test the continuity of the cable. If the cable is not
connected, or if there is a cable fault or a fault at the
hub port, the station does not join the ring.

25
Physical Insertion and Monitor Check
If the lobe test MAC frames are transmitted
successfully, the hub relay is opened. This activates the
port, and the station is physically connected to the ring.
The station then listens to see if there is an active
monitor present. The station sets a timer, and if the
timer expires and none of the active monitor frames are
detected the station assumes there is no active monitor
and initiates the monitor contention process. When the
presence of the active monitor is confirmed, the
physical insertion and monitor check is complete.
Duplicate Address Check
When the station is part of the ring, it sends a frame
with its address as the destination address. When it
receives this frame back, it checks the frame status
field to see if the address-recognized bit has been
changed. A changed bit indicates there is another
station with the same address. In this case, the station
leaves the ring.
Ring Poll Participation
As soon as the duplicate address test is complete, the
station participates in the ring poll process. This lets
the new station learn its NAUN’s address and make its
address known to its nearest downstream neighbor.
Request Initialization
The station joins the ring using default parameters or
parameters that have been provided by a ring
parameter server.

Error Detection
Token Ring errors are categorized as either hard or soft
errors. All stations on the ring can detect both types of
errors.
Hard Errors
Hard errors are those errors on the Token Ring
network that can not be remedied by the Token Ring
protocol. These errors require human intervention via
manual or automatic network management.
Sample Hard
Errors
x “bad” cable
x 4 Mbps adapter trying to insert into 16 Mbps ring
or visa versa
x Faulty adapter card
x Other internal hardware errors
Table 1 Sample hard errors
Hard Error Detection
When a station has not received a transmission from its
neighbor within a certain period of time, it signals the
rest of the ring that there is a problem by continuously
sending beacon frames. In Figure 8, station “A” has
not received anything from station D and its timer has
elapsed. It will begin to send beacon frames. The
beaconing station and its NAUN, as well as the cable
between them, make up the fault domain. The fault
domain assists with isolation of the fault, which could
be the adapters in station A or D or the cable between
them. Station “A” will continue to send beacon frames
until it receives a beacon frame back with its own
address. When it receives this frame, it is assured that
the fault has been removed.

27
A
B
C
D
Beaconing
Station
Beacon
frame
Cable
Fault
Figure 8 Beaconing ring

Soft Errors
Soft errors are those errors on the Token Ring network
that are remedied by the Token Ring protocol.
Sample Soft
Errors
x Lost frame
x Lost monitor
x Corrupted token
x Continuously circulating frame or token
Table 2 Sample soft errors
Soft errors occur on a regular basis and are a normal
event. For example, burst errors occur when a station
joins the ring.
Soft Error Recovery
There are four types of soft errors. Each type of soft
error requires a different process for ring recovery.
Soft Error
Type
Error Example Ring Recovery Procedures
Type 1 Burst error No ring recovery function is required.
Type 2 Lost frame Ring recovery requires the ring purge
to be executed.
Type 3 Lost monitor Ring recovery requires the monitor
contention and ring purge processes.
Type 4 Monitor contention cannot
be resolved
Ring recovery requires the beacon,
monitor contention, and ring purge
processes to be executed.
Table 3 Soft error ring recovery procedures

29
Module Two Summary
£ Token Ring technology incorporates extensive error
detection capabilities.
£ The active monitor is responsible for maintaining
ring operations.
£ Every station on the ring except the active monitor
is considered a standby monitor.
£ Before a station joins the ring it must perform some
checks so that the ring joining process will be a smooth
one.
£ Token Ring errors are categorized as either hard or
soft errors. All stations on the ring can detect both
types of errors.

Module Two Self-test
1. The standby monitor is responsible for setting the clock speed for the ring.
T or F?
2. The active monitor is responsible for making sure a _____________ is always
circulating around the ring.
a) ring
b) token
c) baton
3. If the __________________ has not detected a token or frame within 10
milliseconds, it clears the ring and releases a new token.
a) network administrator
b) standby monitor
c) active user
d) active monitor
4. If the active monitor sees a changed monitor bit it knows the frame has circled the
ring once and it will _________________.
a) repeat the frame on the next station
b) mark it as orphaned and send it on to the next station
c) take the frame off the ring
5. A Token Ring station transmits a series of _______ test MAC frames that test the
continuity of the cable.
a) port
b) lobe media
c) trunk media

33
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This module provides an introduction to the basic
Token Ring network components.
By the end of the Token Ring Network Components
module, you will be able to:
N List and describe the function of each of the
required Token Ring network components.
N Describe the star-wired ring topology.
Overview
Token Ring networks use adapters, cabling, and wiring
hubs. This module provides the specific Token Ring
terminology and concepts related to these network
components.
Token Ring Network Components
The physical components of a Token Ring network
are:
x The network adapter.
x Wiring hub.
x Cabling.
Token Ring Adapter
Any device that is to be connected to a Token Ring
LAN requires a Token Ring adapter. The adapter
manages the physical-and MAC-layer functionality.

34 Module 3- Token Ring Network Components
Wiring Hub
Token Ring wiring hubs use ring-in and ring-out
expansion ports. These ports enable the hubs to be
connected together. Wiring hubs use relay to allow
stations to access the ring via the lobe cables. The
relays receive a DC voltage (3.4-7.0 v) from the station
through the lobe cable to the wiring hub. This is called
the phantom current. The presence of the phantom
current opens the relay at the hub port and allows the
station to insert itself. The relays provide ring
continuity; when the station is not actively part of the
ring, the signal is routed through the relay (the relay is
closed because there is not phantom current) and
effectively bypasses the inactive station.
Lobes
Wiring Hub
Ring-In
Ring-Out
Figure 9 Single wiring hub configuration
Ring-In The trunk receive port on the wiring hub.

35
Ring-Out The trunk transmit port on the wiring hub.
Lobe Connection The interconnection cable that runs between the station
and the wiring hub port.
Phantom Current The wiring hub relays receive a DC voltage (3.4-7.0 v)
from the station through the lobe cable.
Trunk
RIRI RO RO
Figure 10 Multiple wiring hubs
Trunk Connection The wiring that interconnects wiring hubs together.

Primary and Secondary Paths
Trunk cables connecting wiring hubs create primary
and secondary paths for data transmission. In the event
of a cable break, transmissions can traverse the
secondary path. (See Figure 11.)
Primary Path The Token Ring path used under normal ring
operations.
Secondary Path The Token Ring path used when the trunk cable
breaks, or a hub loses power.

37
Secondary
Path
RIRI RO RO
Primary
Path
Figure 11 Primary and secondary paths
RI RO
Cable
Break
RI RO
Figure 12 Transmission using secondary path

Token Ring Cabling Options
Token Ring uses two pairs of wires—one pair for
transmitting the data and one pair for receiving it.
Originally Token Ring networks operated using
shielded twisted pair media. Today, Token Ring
networks can operate over unshielded twisted pair and
fiber optic media in addition to shielded twisted pair.
Shielded Twisted
Pair (STP)
Shielded twisted pair cable is the original cable type
used with early Token Ring networks. The shielding
protects the signal from interference and provides a
robust cabling solution.
Unshielded
Twisted Pair
(UTP)
Unshielded twisted pair cable is made of copper
strands twisted together to form pairs. The pairs are
covered with a sheath, and there is no shielding.
Category 3, 4, and 5 UTP cabling are acceptable
building wiring. Usually UTP is used for lobe and
patch cables.
Fiber Optic Fiber optic cabling supports long connections. This
type of cabling is not susceptible to electromagnetic
interference, because the signal is transmitted as light
rather than electricity. Fiber is usually used for Token
Ring trunk connections.

39
Token Ring Topology
Logical Ring/
Physical Star
The Token Ring network uses a logical ring/physical
star topology. Physically, the stations are connected to
the hubs in a star topology. However, if we were to
trace the path the frames travel, we would see it is a
ring.
RI RO
Figure 13 Logical ring path

Module Three Summary
£Token Ring networks use adapters, cabling, and
wiring hubs.
£ Token Ring uses two pair of wires—one pair for
transmitting the data and one pair for receiving it.
£ Token Ring networks can operate over unshielded
twisted pair, shielded twisted pair, and fiber optic
cabling.
£The Token Ring network uses a logical
ring/physical star topology.

41
Module Three Self-study
1. __________________ cabling is used most often for lobe and patch cables.
a) STP
b) UTP
c) Coax
d) Fiber optic
2. Fiber optic cabling supports long distances and is not susceptible to
_________________.
a) electromagnetic interference
b) breakage
c) sunspots
3. Physically, Token Ring stations are connected to wiring hubs in a ___________
topology.
a) star
b) bus
c) ring
d) tree
4. ______________ cables connecting wiring hubs create primary and secondary
paths for data transmission.
a) Lobe
b) Patch
c) Trunk
d) None of the above
5. The relays in a Token Ring hub provide ring continuity because when the station
is not actively part of the ring, the signal is routed through the relay and in effect
________________ the station.
a) shuts down
b) bypasses
c) wraps

45
0RGXOH)RXU %XLOGLQJ7RNHQ5LQJ1HWZRUN
,QIUDVWUXFWXUHV
This module provides an overview of internetworking
techniques used with Token Ring networks. We will
focus on source routing, bridging, and source route
transparent bridging. Routers can also be used to
interconnect rings, but routing is beyond the scope of
this self-study.
By the end of the Building Token Ring Network
Infrastructures module, you will be able to:
N Discuss how bridges improve performance through
microsegmentation.
N Define source route bridging.
N Describe the difference between source route
bridging and source route transparent bridging.
Overview
Large networks have always consisted of multiple
segments, because there are practical limits on the
number of stations that can be attached to a single
segment. With Token Ring, the maximum permitted is
255 stations on one ring, but in practice few users load
rings up with more than about 100 stations.
The traditional method for interconnecting Token
Rings is the source route bridge. Let’s take a look at
this method of connecting Token Ring networks.
Source Route Bridging

46 Module 4- Building Token Ring Network Infrastructures
In a multiple Token Ring network, each ring has a
unique number and each bridge has an identification
number that is not necessarily unique. The bridging
technique typically used in Token Ring is source route
bridging. Source route bridging is designed so the
originating station determines the path to the
destination. The path is encoded into the data frame’s
routing information field and used by source route
bridges to make forwarding decisions.
The routing information field includes a ring and
bridge number for each segment the frame must
traverse to reach its destination. Refer to the
configuration shown in Figure 14.
Station “A” wishes to send information to station “Z.”
Station “A” first attempts to reach station “Z” on its
own ring. If the frame returns unanswered—frame
copied bits are unchanged—station “A” assumes
station “Z” is located on another ring, and attempts to
determine a route to station “Z.” Station “A” does this
by sending a discovery frame. A discovery frame or
XID packet is a broadcast message that determines a
path to the destination address.
On its way to station “Z,” each bridge that receives the
frame adds its bridge number and the ring number of
the next segment to the routing information field of the
frame. When station “Z” receives the frame, it copies
the frame and sends it back to the originating station.
The source route bridges use the route that is now
located in the routing information field.

47
Sending
Station
Data frame
being sent to
station “Z”
A
B C
D
B 1
Ring 1
K
H I
J
Ring 2
Y
W X
Z
Ring 4
Destination
Station
B 4
O
L
Ring 3B 3
B 2
Figure 14 Bridged Token Ring network
In our example, there is more than one path between
the originating station and the destination. The two
possible paths to Station “Z” are: ring 1, bridge 1, ring
2, bridge 2, ring 3, bridge 3; or ring 1, bridge 4, ring 4.
Station “A” uses the path in the first discovery frame
that returns, assuming this is the most efficient route.
Single Route versus All Routes Broadcasts

In source route bridging, stations use two broadcast
methods for route discovery, single-route broadcast,
and an all-routes broadcast. Because source routing
broadcast overhead can become unacceptable in highly
meshed topologies, networks typically use the single-
route broadcast method and a designated bridge. When
this method is used, only the designated bridge on each
ring appends its routing information to the frame and
forwards the frame to the next segment. This method
reduces the amount of overhead traffic on the ring.
Transparent Bridging
Transparent bridging is used in Ethernet networks.
Transparent bridges learn the addresses of all devices
on each of their ports and build address tables to keep
track of that information. A transparent bridge then
uses the address table to make forwarding decisions. A
bridge reads all frames on the network, examines the
source and destination addresses, and decides whether
to forward or discard the frame. If the source and
destination are in different address tables, the frame is
forwarded to the appropriate network.
This process is called transparent bridging because
unlike source route bridging, the end stations have no
role in this activity. The end station is not aware that
its frame is being bridged to another ring segment. The
bridge has all the responsibility of forwarding the
frames. Optimally, a bridge performs at line speeds so
it does not lose data or become a bottleneck.
Source Route Transparent Bridging
Source route transparent (SRT) bridging evolved to
meet the need for interoperability between networks
using transparent bridge and networks using source
route bridging. The goal of SRT is to provide for this
interoperability by having the source routing stations
interpret and understand the functions of the
transparent bridge station.
When a frame is received by the bridge, the bridge
checks to see if there is routing information in the
frame. If there is, the bridge uses source route bridging
to forward the frame. If the routing information
indicator bit is not set, the bridge uses the transparent
method to decide if the frame needs to be forwarded.

49
SRT bridges implement spanning tree with the other
SRT stations and transparent bridges the same way that
spanning tree is implemented in a pure transparent
network. SRT stations will use the source routing path
if one exists or fall back on the spanning tree path.
SRT stations use a single on segment route explorer
frame. This route explorer mechanism results in one
single route broadcast frame at the destination station.
The destination frame responds with one single route
broadcast message containing no routing information.
The originating station will pick the route or use the
spanning tree path. Transparent bridging stations do
not respond to frames that contain routing information.

Module Four Summary
£In multiple Token Ring networks, each ring has a
unique number and each bridge has an identification
number.
£The bridging technique typically used in Token
Ring networks is source route bridging.
£Source route bridging is designed such that the
originating station determines the path to the
destination.
£ The path is encoded into the routing information
field in the data frame and used by the source route
bridge to make forwarding decisions.
£In source route bridging, stations use two broadcast
methods for route discovery, single-route broadcast
and an all-routes broadcast.

51
Module Four Self-test
1. In a multiple ring Token Ring network, each __________ has a unique number.
a) ring
b) bridge
c) station
d) router
2. Source route bridging is designed such that the originating station determines the
path to the destination station.
T or F?
3. The traditional method for connecting Token Ring networks together is via
T or F?
4. In transparent bridging, stations use two broadcast methods.
T or F?
5. The Routing information field contains the ring and bridge numbers that make up
the path the frame must take to reach its destination.
T or F?

53
0RGXOH)LYH 7RNHQ5LQJ6ZLWFKLQJ
This module provides an introduction to Token Ring
switching. Token Ring switching offers an alternative
means of interconnecting multiple Token Rings.
By the end of the Token Ring Switching module, you
will be able to:
N Define Token Ring switching.
N List the benefits of Token Ring switching.
N Describe cut-through switching.
Overview
Switching offers an alternative means of
interconnecting multiple Token Rings that is both
simpler and more efficient than routing or bridging. In
a switch, packets are transferred from one ring to
another with negligible latency, because the packets
are neither buffered nor processed within the switch.
Let’s, take a closer look at how Token Ring switching
works.
Cut-Through Switching
Instead of reading packets in their entirety into buffer
memory before making a decision about where to
forward the frame, a cut-through switch takes action
as soon as the first 20-30 bytes of the frame have been
received. Information in the frame header is analyzed
almost instantly, and the required destination port is
deduced. At this point, a connection is effectively
made between the input port and the output port, and
the packet immediately starts transmitting onto the
destination ring. This technique is sometime known as
cut-through switching or on-the-fly switching.

54 Module 5- Token Ring Switching
The total time that a frame is held up within a switch is
as little as 30 microseconds. Compared to the 500-
4,000 microseconds of delay that store and forward
devices (see below) introduce, This is a significant
reduction in latency.
By virtually eliminating latency, cut-through
switching allows clients on one ring to communicate
with servers on another ring with the same
performance as if they were both attached to the same
ring.
Store and Forward Switches
LAN internetworks devices are available which use the
same layer 2 forwarding technique as cut-through
switches, but are based on store and forward designs.
The devices are known as store and forwarded devices
or “buffered” switches.
Architecturally, these devices are multiport bridges and
suffer from the same high latency as traditional routers
and bridges. When used in Token Ring networks, these
devices deliver only limited performance
improvements and users will see a degradation in
performance when communicating with servers located
on different rings.
Contention and Buffering
Although switching involves the transfer of frames
from one ring to another without buffering frames in
memory, there are circumstances in which buffering is
needed. A switch cannot transmit a frame onto a ring if
the ring is busy. If the ring is busy, the frame must be
buffered until the destination ring has gone quiet and
the token can be grabbed. Likewise, if frames arrive
simultaneously at two input ports of the same switch
and require onward transmission to the same ring, the
switch must buffer one of the packets until it has
finished forwarding the other.
Thus, a Token Ring switch must be equipped with
sufficient buffer memory to deal with these
circumstances without dropping frames. This is true
for any kind of LAN switch.

55
Switching by Source Routing
The standard method for interconnecting Token Rings
is source routing. With this technique, clients first
establish a route to a server using a route discovery
process and then insert information that defines this
route in each packet they send.
Source routing operates at Layer 2, the data link layer,
and is, therefore, applicable to all upper layer protocols
whether they include Layer 3 (Network Layer)
addressing or not. A Token Ring switch can use source
routing information to make forwarding decisions on
each frame received. Because the source routing
information explicitly identifies the ring the frame
should be passed to next. The switch can make very
rapid forwarding decisions with minimal processing.
With transparent switching, forwarding decisions are
made on the MAC address information in the header of
each packet. The switch must learn which MAC
addresses are attached to each port and maintain tables
of this information. As each packet enters the switch,
the address tables must be updated, and the destination
MAC address must be looked up to determine which is
the correct destination port.
Switching based on source routing has a number of
advantages compared to the transparent technique.
Less work is required for each packet; therefore, less
processing power is required, leading to lower costs.
All Token Ring applications are compatible with
source routing, whereas some will not work with
transparent switching.
Full Duplex Token Ring
Token Ring switching provides a means to
interconnect multiple Token Rings with very high
performance. A switch can act as a collapsed
backbone, connecting workgroup rings to other rings
that support centrally-based servers.

In almost all LAN environments, many users access a
few servers, and the server connection can therefore
easily become a bottleneck. Switching helps with this
problem. By placing only a few servers on a dedicated
ring, it enables the server rings to be segmented to
reduce the number of machines on each ring.
The most heavily loaded servers may well justify
having a private ring all to themselves. In this special
case, the server is the only device connected to a port
on a switch. Instead of running the full token-passing
protocol of Token Ring between these two devices, it
is possible to dispense with the token and operate this
link as a full duplex serial link running at 16 Mbps in
both directions at once.
Full duplex Token Ring provides double the
bandwidth to any station that handles concurrent
bidirectional traffic, it offers a clear 16 Mbps channel
in each direction. Heavily loaded servers can take
advantage of this, because their operating systems deal
with multiple concurrent read and write operations.
Video-equipped workstations can also benefit from full
duplex Token Ring.
Token Ring is inherently capable of operating in full
duplex mode. To provide full duplex operation, the
software controlling the Token Ring chipset simply
needs to be changed.
Virtual LANs
LAN switches direct traffic so packets are only sent to
the segments that need them. This is fine for
individually addressed packets, but what about
broadcast frames? There are additional benefits with
switching if the forwarding of broadcast traffic is
controlled in the switch. With the appropriate
intelligence applied to the filtering of broadcast frames,
switches can help network administrators with moves
and changes by allowing the creation of “virtual
LANs.”

57
A virtual LAN is a collection of LAN segments
connected by switches in which all broadcast traffic
originating from any of the segments is seen by all
stations on the other segments. By either blocking or
enabling the flow of broadcast traffic between
designated ports on the switch, virtual LANs can be
defined to include or exclude specified LAN segments
attached to the switch.
All stations on a virtual LAN can see all broadcast
packets, including service advertisement, address
resolution, and route discovery packets, that originate
within the virtual LAN. Likewise, stations cannot see
any broadcast packets that originate on segments that
are defined as belonging to other virtual LANs. The
result is stations can only make connections to other
stations, servers, or gateways that are part of the same
virtual LAN.
Virtual LANs provide the additional benefit: they
confine the propagation of broadcast traffic within the
set of rings that must receive the broadcasts. This
ensures that broadcast traffic occupies only a small
proportion of each segment’s bandwidth. It also
overcomes any concern about “broadcast storms” in a
source routed environment.
Token Ring Switching and ATM
Token Ring switches need a high speed interconnect so
large volumes of traffic can be carried between
switches. Both FDDI and ATM are considered
appropriate technologies for the switch interconnect.
FDDI offers 100 Mbps capacity between switches,
and will support the connection of servers at 100
Mbps. Thus eliminating another potential source of
network bottlenecks. ATM, at 155 Mbps, also
provides ample capacity for inter-switch traffic. But
when ATM is used with Token Ring switching, it
offers far more than just a means to interconnect
switches.

When integrated with a LAN environment, ATM
operates in a mode known as “LAN emulation.” The
idea behind this is to make an ATM network behave
like a LAN, even though traffic is being carried on
point-to-point connections across the network. With
LAN emulation, additional services within the ATM
network support LAN-like functions such as address
resolution and broadcast packets.
ATM can emulate Token Ring LANs. Token Ring
packets can be carried across an ATM network just as
if they were being carried on a ring–even though in
reality they go point-to-point.
The idea of virtual LANs embracing both the Token
Ring and ATM domains is extremely powerful and
flexible. It provides network administrators with
complete freedom to configure and reconfigure the
linkages between rings and servers in any size
network. This can all be done from the network
management console. And it allows large networks to
be built entirely on the basis of switching, largely
eliminating the need for slow and inefficient routing.

59
Module Five Summary
£ Token Ring switching offers an alternative means of
interconnecting multiple Token Rings that is both
simpler and more efficient than routing or bridging.
£A Token Ring switch can make use of source route
information to make forwarding decisions on each
frame it receives.
£ Because the source routing information explicity
identifies the ring the frame should be passed to next,
the switch can make very rapid decisions with minimal
processing.
£Full duplex Token Ring provides double the
bandwidth to any station that handles concurrent
bidirectional traffic, as it offers a clear 16 Mbps
channel in each direction.

Module Five Self-study
1. Full duplex Token Ring doubles the bandwitdth of a Token Ring connection.
T or F?
2. In almost all LAN environments, users can access only a few servers, and the
server connections can easily create bottlenecks. Servers can be connected via full
dulplex Token Ring to reduce the incidence of bottlenecks.
T or F?
3. Switching is less efficient than using a router to microsegment the network.
T or F?
4. Token Ring switches always use store and forward switching method.
T or F?
5. In Token Ring switches that use source routing, the source routing information
identifies the ring the frame should be passed to next.
T or F?

61
$SSHQGL[$$QVZHUVWR6HOIVWXG4XHVWLRQV
Module One Self-study Answers
1. The 802.5 standard is a direct outgrowth of the research done by ___b______.
a) DEC
b) IBM*
c) IEEE
d) Proteon
2. When a station on a Token Ring network wishes to transmit, it must first possess
the _____b_______.
a) ring
b) token*
c) baton
3. The frame control field indicates whether the frame is a ___a____ control frame or
a data frame.
a) MAC*
b) error
c) beacon
4. The maximum data field for 16 Mbps Token Ring is ____b_________.
a) 4,472 bytes
b) 17,800 bytes*
c) 1,518 bytes
5. If the address-recognized and frame-copied bits are unchanged in the frame status
field, the originating station will resend the frame around the ring.
T or F?
T

62 Appendix - A
Module Two Self-study Answers
1. The standby monitor is responsible for setting the clock speed for the ring.
T or F?
F
2. The active monitor is responsible for making sure a _____b________ is always
circulating around the ring.
a) ring
b) token*
c) baton
3. If the _______d___________ has not detected a token or frame within 10
milliseconds, it clears the ring and releases a new token.
a) network administrator
b) standby monitor
c) active user
d) active monitor*
4. If the active monitor sees a changed monitor bit, it knows the frame has circled the
ring once and it will _______c__________.
a) repeat the frame on the next station
b) mark it as orphaned and send it on to the next station
c) take the frame off the ring*
5. A Token Ring station transmits a series of __b_____ test MAC frames that test
the continuity of the cable.
a) port
b) lobe media*
c) trunk media

63
Module Three Self-study Answers
1. _______b___________ cabling is used most often for lobe and patch cables.
a) STP
b) UTP*
c) Coax
d) Fiber optic
2. Fiber optic cabling supports long distances and is not suseptible to
________a_________.
a) electromagnetic interference*
b) breakage
c) sunspots
3. Physically, Token Ring stations are connected to wiring hubs in a ____a_______
topology.
a) star*
b) bus
c) ring
d) tree
4. ______c________ cables connecting wiring hubs create primary and secondary
paths for data transmission.
a) Lobe
b) Patch
c) Trunk*
d) None of the above
5. The relays in a Token Ring hub provide ring continuity because when the station
is not actively part of the ring, the signal is routed through the relay and in effect
______b__________ the station.
a) shuts down
b) bypasses*
c) wraps

64 Appendix - A
Module Four Self-test Answers
1. In a multiple ring Token Ring network, each ____a______ has a unique number.
a) ring*
b) bridge
c) station
d) router
2. Source route bridging is designed such that the origingating station determines the
path to the destination station.
T or F?
T
3. The traditional method for connecting Token Ring networks together is via
T or F?
F
4. In transparent bridging, stations use two broadcast methods.
T or F?
F
5. The Routing information field contains the ring and bridge numbers that make up
the path the frame must take to reach its destination.
T or F?
T

65
Module Five Self-test Answers
1. Full duplex Token Ring doubles the bandwitdth of a Token Ring connection.
T or F?
T
2. In almost all LAN environments, users can access only a few servers, and the
server connections can easily create bottlenecks. Servers can be connected via full
dulplex token ring to reduce the incidence of bottlenecks.
T or F?
T
3. Switching is less efficient than using a router to microsegment the network.
T or F?
F
4. Token Ring switches always use store and forward switching method.
T or F?
F
5. In Token Ring switches that use source routing, the source routing information
identifies the ring the frame should be passed to next.
T or F
T

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