Token Ring Basic Concepts

A self study for Token Ring from Madge Networks. Historical Documentation.

1. Token Ring Basic Concepts
Self-Study

2. O0 Male ees At. pf i pn m neni tant
‘hea eal ten ene apa rer gen oor me et
ia loro ih bp store

‘elton tain uma hn it ace Ma as lors eo
Re pm A

SSSI o o am a ay ge an on

OP ale wen A geo ste Me ie em ns ji my
Sen sas Alo cd pr red aa

3. Table of Contents

INTRODUCTION TOKEN RING BASIC CONCEPTS SELF-STUDY

Course Objectives

MODULE ONE TOKEN RING BASICS
Obeines
One
“oben Ring solo

‘Token Ring Operation
Fary Token Reine

“The Token and Frame Formats
ring Deli
Acces Cont
FES (Frame Check Sequence)

Module One Summary

MODULE TWO RING MAINTENANCE
bicis

Orne Frames

4. " Table of Contents

Standby Monitors

ving he Ring

Error Detection
rd Ks
Sample Hard Eos
Simple Sat nen

Module Two Summary

Module Two Self

MODULE THREE TOKEN RING NETWORK COMPONENTS

Obcines
vente

“Token Ring Network Components
oben Ring Adapter
Wiig Hab
Ringe
Ring Oa
La Connection
Phao Curent
rary Pah

“Token Ring Cabling Options
‘Shed Twist Par (STP)
siehe Twisted Par (UTP)
Fier Opie

“Token Ring Topology
ogi Ring! Pic Siar

Module Three Summary

Module Three Slt

26

»

3

a

5. Table of Contents

MODULE FOUR BUILDING TOKEN RING NETWORK

INFRASTRUCTURES
Obie
Siglo Rute venas A Rows sad
Transparent Bnding
Sau Roue Teangare Badge
Module Fou Summary

Module Four Slt

MODULE FIVE TOKEN RING SWITCHING
Objects
Owen
Cu Through Shi

Fa Dpls Token Ring
Vital LAN
Token Ring Switching and ATM

Module Five Summary

Module Five Steud

APPENDIX A - ANSWERS TO SELF-STUDY QUESTIONS

Module One Sttstudy Answers
Module Two Selfstudy Answers,
Module Three Study Answers
Module Four Sl Answers

Module Five Stes Answers

s
s

s

6
a
e

e

‘Token Ring Base Con

6. Introduction Token Ring Basic Concepts
Self-study

Welcome to Token Ring Basic Concepts Self-study
‘This course introduces Token Ring concepts and
teminology that will provide you with the background
ou need to sell Token Ri

Networks

Course Objectives{ XE "Welcome" }

By the end of this self-study. y

+ Discuss the evolution of Token Ring.
‘+ Describe the theory of operation for Token Ring.

‘+ Describe the function of token passing and explain
its importance.

‘+ Explain Token Ring's basic ring management
functions

‘+ Describe the function of Token Ring bridges,
including source routing and souree route
transparent bridging.

+ Explain Token Ring frame switching

7. Module One__ Token Ring Basics

“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

+ Discuss the evolution of Token Ring.
‘+ Describe the theory of operation for Token Ring.

‘+ Describe the Function of token passing and explain
its importance.

‘+ Describe the token and daa 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 is method of operation
“and the way its stations are liked together, The nodes
‘or stations on the network are connected to cre

“ring” path forthe data frames o travel from one
station tothe nex. The rng is made up of ring stations
that are connected via cabling. Each station has a
‘Token Ring adapter card and access to the logica ink
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 o
decide which node can use the ring at any one time.
Let's take a brief look atthe evolution of Token Ring
and then the specific operation of a Token Ring
network,

8. 8 Module 2- Ring Maintenance

Token Ring Evolution

‘Token Ring technology was originally proposed in
1969 and was known asthe Newhall ing, after one of
its developers. Even though this technology was being
‘worked on before Ethernet, it wasnt until the mid
1080s, 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 isan implementation of
the 8025 standard

‘Token Ring continued the trend of sharing media, but
dies significa from Ethernet in the way the
media is accessed. When a sation wishes to transmit
data on a Token Ring network to another station, the
sending station must fist get possession ofthe
“token.”

“The token is a unique 24-bit message (control signal)
that controls access 1 the ring. The token continuously
circulates the ring, passing from one station to the next
‘nti a station wishes 1 transmit. The transmitting
Station takes possession ofthe token uni transmission
ofthe data frame travels a ring path. This method!
{ensues that no two stations can transmit atthe same
time, thus avoids the possibility of data collision.
Let's take a more detailed look at Token Ring
operation,

Token Ring Operation

We will be using a fou.node network as our sample
‘Token Ring network, (See Figure 1) In our sample

X ike to send information to
station “C” Station “A” has possession of he token
nd has sen a data frame out onto the ring. Station °C”
is the destination ation,

9. Receiving
Station

Station

“The daa frame willbe received by the next station in
lin, station “B." (See Figure 2) Staion “B" will
check the destination address to see if he data frame is
for station “B." In this case, the data frame is not
addressed 1 station “B” and therefore "B" sends the
data frame back out onto the ring without mal

changes.

‘Token Ring Base Cones

10. 10

Module 2- Ring Maintenance

Data frame
being sen
station:

Pe Da fre in sn

Next te data frame will be received by station “C.
{See Figure 3.) Station "C” wil read the destination
address, Because the data frame is addressed to sation
“Catón °C” will copy the data frame: after
changing bits in the frame to indicate the frame was
copied, station "C passes the original frame hack 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. "

Receiving
Station

‘it a ia —

Staton

When station “A” receives the original data frame
buck, treads the destination and source addresses. It
ies its source address and checks the frame

‘copied bits 10 make sure the data frame was received,
(OF the frame-copied bits are not changed, the tation
waits for the token again and retrnsmits the data
frame.) The frame-copied bits are changed, so station
“A” will release the token out onto the ring. (See
Figure 4.)

Tokens
sent back out
foto the ring.

‘Token Ring Base Cones

12. 12

Early Token Release

Module 2- Ring Maintenance

‘The Token Ring operation just described is specifically
that of 4 Mbps Token Ring. The next station must

‘wait for the transmission o complete before it can got
possession ofthe token, This means the delay on the
ing grows as more tations are aed. To alleviate this
problem, Early Token Release (ETR) was made
available with 16 Mbps Token Ring operation inthe
Tate 1980s.

Early Token Release operation releases a token after
the data frame has been released. This allows multiple
data frames tobe out on the ring atthe same time. (The
‘number of data frames supported by a particular ing
depends upon the size of the ring)

All of the data is synchronously clocked once ts on
the ring. Data goes around te ring in only one
direction and data Frames never met, All data frames
include the source and destination addresses, o each
node is able to tell wheiherit should copy the data
Tame or send iton.

Let's use the same example to demonstrate 16 Mbps
‘operation and Early Token Release.

Station “Ais about to transmit data o station °C."
After the data frame has been released, station "A"
also releases token, (See Figur 5.)

13. 13

Data frame
being sent to

‘Tokens released
a short time

after the last bit of
fata has left
‘the station

“The data frame is received at station “B.” Station “B”
checks the destination address to se ithe data Frame
is for sion "B." In this case the data frame isnot
‘addressed o station “B,” and therefore "B” sends the
data frame back out ont the ring without making à
changes, as before, But this time station “B” would
Tike 1 transmit, oo, In this case, station “B" grabs the
token that follows the data frame destined for station |
“C* and sends a data frame to sation “D. À short
time after the last bit of data has lft station “B,

station “B” releases token, This token is availabe for
the next station in ine that wishes 0 transmit,

Let’ check and see what happens when station “A's”
‘original data frame retums, When station “A” receives
the original data frame back, it reads the destination
and source addresses jus ike before. It ecognizes its
source address and checks the frame copied bits to
make sure the data frame was received, The fram
copied bits are changed, s station “A” sis the data
frame off the ving.

‘Token Ring Base Cones

14. 4

Module 2- Ring Maintenance

In this case, station "A" does NOT release a token as it
id before, on the 4 Mbps ring. Because a token is
released after every transmission, thee is no need to
release a token afer the data frame retums to the
¿riginating sation. 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 sa “busy” token

[Next let's take a detailed look atthe token and data
frame structures.

15. 15

‘The Token and Frame Formats

“The token isa 24-bit frame that is composed ofthe

starting delimiter, ending delimiter, and acces
Fields,

1Bye 1Byte 1Byte

SD AC ED
IR BEL 0-49 ai
byte byte byte bytes

byte_byte

Starting Delimiter

‘The stating delimiter i 1 byte or 8 bits. This field is
used to synchronize the transmission ofthe token or
frame

Access Control

“The access control field is a stats byt that occurs in
both the token and the data frame, The acces control
Field contains bits that indicate whether the Frame ia
token ora 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.)

‘Token Ring Base Cones

16. 16

Module 2- Ring Maintenance

Frame Control
‘The frame contol field indicates whether the frame is
a MAC control frame ora data frame. MAC control
rames are frames hat have to do with ring operation
and may need special handling. The requirement for
special handling is indicated in the frame control fie
Ifthe MAC frame needs to be processed immediately
by the destination station, the frame control feld has
bits hat indicate this; the MAC frame is copied into an
express buffer and processed immediately at the MAC
level. These MAC frames stay on ther local ing and
are not sent to any other rings,

Destination Address
‘The Destination Address field is next. According tothe
802.5 specification, itis 6 bytes long and specifies
‘which station(s) receive and copies the frame,
Source Address

“The source address identifies the address ofthe
‘originating station and must correspond to the size of
the destination address

Routing Information

‘The routing information field is an optional Field used
if he frame is addressed 1 a station on another ring

Information Field
‘The information field contains LLC (logical link
control) or MAC (media access contol) data. Ifthe
frame isan LLC frame the information field holds end
user data If the frame isa MAC frame the information
field holds MAC control information.

‘This is variable length field. On ad Mbps Token
Ring network, the daa field can be a maximum of

4.472 bytes long. On a 16 Mbps network. the data
Field can be a maximum of 17500 bytes long.

17. 7

FCS (Frame Check Sequence)

Ending Delimiter

Frame Status

“The FCS, or Frame Check Sequence, contains a 32-bit
(CRC, or Cyclic Redundancy Check value, thats the
resulto enor 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 (i presen),
and the data field. The receiving station recalculate
the value based upon the received data and compares it
tothe FCS to confirm that the frame was copied
without errr. Ifthe two do not match, the Frame i
rejected

‘The ending delimiters also 1 byte in length ts
purpose is to mark the end ofa token oF dat frame.

“The frame satus field contains the bits changed by the
receiving station to indicat it recognized its address
and copied the frame. The originating ation checks.
this feld when the frame retums I the address is
recognized and frame-copied bits are unchanged, it
resends the frame when it ets possession of the token
again

‘Token Ring Base Cones

18. 18 Module 2- Ring Maintenance

Module One Summary

> Token Ring emerged as a LAN enabling
technology inthe mid 1980s,

> The Token Ring network derives its name fom ts
‘method of operation andthe way its stations are linked
together.

> The nodes or stations on the network are connected
Lo create “ring” path fr 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 onetime

19. 19

Module One Self-study

‘Complete the following slftet by answering the following questions, Use the
answer Key located in Appendix A to check your answers

1. The 802.5 standard isa direct outgrowth ofthe research done by

a DEC
>) IBM
©) IEEE
9) Proteon

2. When a station on a Token Ring network wishes 0 transmit it must Fist possess
the

a) ing
b) token
©) baton
© none ofthe above

3. Te frame control field indicates whether the Frame is an) control frame

ora data frame.

a MAC
b) error
©) beacon
{none ofthe above

4. The maximum daa field for 16 Mbps Token Ring is

a) 4472 bytes
by 17.800 bytes
©) 1518 bytes

© none of the above

5. Ae address-recognized and frame-copied
Field, the originating station will resend the fan

ts are unchanged in the frame status
around the tng.

Tor

Token Ring Base Cones

20. Module Two

2

‘This module provides an introduction 10 Ring
Maintenance concepts you will need to understand the
benefits of Token Ring technology

Objectives{ XE "Assumptions made for manual" }

Overview

By the end of the Ring Main
be able wo:

enance module, you will

‘+ Explain Token Ring's base ring management
funcions

+ List the functions of the active and standby

+ Describe the phases a station must go through to
join a rng

‘+ Describe how errors are detected on a ring and the
function ofthe beacon MAC

The Active Monitor

‘Token Ring technology incorporates extensive error
detection capabilites. The access method has many
‘built-in functions for dealing with errors on te rng.

‘The active monitor is responsible for maintaining ring
‘operations. The active monitor performs the following
functions

21. ‘The Master Clock

Ring Delay

‘Token Circulation

(Orphaned Frames

Module 2- Ring Maintenance

+ Provides master clock forthe ring
+ Maintains proper ing delay
+ Ensures token is circulating at regular intervals

“Mi

ys the ring for orphaned frames
+ Intists the neighbor notification process

+ Ensures be neighbor notification process operates
correctly

‘+ Purges and cleans up the ring when necessary

‘The ative monitors responsible for maintaining the
master clock forthe ing. Stations on the ring
synchronize their clocks 10 the master lock

Ring delay, lso known as minimum ring latency, is
required o ensure that delay on the ring is long enough
to accommodate the token, The ative monitor ensures
the proper ring delay exists y introducing at east a
24-bit delay on the ing, when necessary

‘The active monitors responsible For making sure a
token is always circulating the ring. Ifthe active
‘monitor as not detected a token or frame within 10
nilliseconds, it clears the ring and releases a new
token

22. 2

Frames can become “orphaned” i the originating
‘Station is no longer active onthe ring. To make sure
this frame doesnt circulate the ring endlessly, the
active monitor sets the monitor Dit in the acces control
Field in every frame that pases. This changed monitor
bi indicates the frame has cirled the ring once, Ifthe
monitor sees a frame that has the monitor bit changed,
itknows the frame i orphaned and will ake it off the

Each station on a Token Ring network needs to know
the address ofits nearest active upstream neighbor
(NAUN). The address of the NAUN is used when
there is an emor on the ring. Ka station on the ring has
not received a transmission from its NAUN within a
certain period of time, the station notifies the other
‘ations ofa problem on the rng.

“The neighbor notification or ring poll process is
iniited by the active monitor on à regular basis 10
update the upstream neighbor's address in all stations
‘on the ring. This ing poll process also communicates
the presence ofthe active monitor on the ring. The
active monitor transmits an ative monitor present
(AMP) MAC frame every even seconds.

Ring Purge

‘When the Token Ring network does not operate
propery, the active monitor transmits a ring purge

‘Token Ring Base Cones

23. 24

Standby Monitors

Module 2- Ring Maintenance

Joining the Ring

Every station on the ring except the active monitor is
considered a standby monitor. The standby monitors
A responsible for making sure there is an active
‘monitor on the rng. Inthe event that an AMP frame is.
ot 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

Lobe Test

Before a station joins the ing, it must perform some
tests so the ring-jining process is smooth and eror-
free.

‘The station wishing to join the ing must perform the
following checks or functions:

+ Lobetes

+ Physical insertion and monitor check
‘+ Duplicate address check
+ Ring poll participation

‘The first check à station must completes the lobe
‘media test. (The lobe refers o the length of cable from
the sation tothe wiring hub.) The lobe media testis
designed to tex the integrity ofthe cable attached to
the sation and the wiring hub,

‘The tation transmits a series of lobe test MAC frames
(hat test the continuity of the cable, the cable is not
connected, or if there is a cable fault oF a fault atthe
hub port the station does not join the ring,

24. 25

Physical Insertion and Monitor Check
I the lobe test MAC frames ac transmitted
successfully, the hub relay is opened. This activates the
pon, and the station is physically connected o the ing.
‘The station then listens o sce if there is an active
monitor presen, The station sets timer, and ifthe
timer expires and none ofthe active monitor frames are
detected the sation assumes there is no active monitor
and initiates the monitor contention process. When the
presence ofthe active monitor is confirmed, the
Physical insertion and monitor check is complet.

Duplicate Address Check
Wien the station is part of the ring it send a frame
with its address as the destination address, When it
receives this frame back, it checks the frame status
Field to sce ifthe addres-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 asthe duplicate address es is complete, the
‘Station participates in the ring poll process, This lets
the new station learn its NAUN’s address and make it
address known 10 is nearest downstream neighbor.

lization
“The station joins the ing using default parameters or
parameters that have been provided by à ing
parameter server.

Request Initi

‘Token Ring Base Cones

25. 26 Module 2- Ring Maintenance

Error Detection
‘Token Ring errors are categorized as either hard or soft
‘rors Al stations on the ring ean detect both types of
Hard Errors
Hard errors are those errors onthe Token Ring
network that can not be remedied by the Token Ring
protocol These errors require human intervention via
manual or automate network management
‘Sample Hard + “bad cable
Errors
+ 4MbpS adapter trying 0 insert into 16 Mbps ing
+ Faulty adapter card
+ Other internal hardware errors
Tate ame ante,
Hard Error Detection

When a tation has not received a transmission from its
eighbor within a certain period of time, it signals the
rest of the ring that there ia problem by continuously
sending beacon frames, In Figure 8, station “A” has
‘not received anything from station D. and its timer has.
lapsed. I will begin o 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 receive a beacon frame back with its own
address, When it receives this frame, itis assured that
the fault has been removed.

27. Module 2- Ring Maintenance

Soft Errors
Soft errors are those errors onthe Token Ring network
that are remedied by the Token Ring protocol.

‘Sample Soft Lost frame
Errors
Lost monitor
+ Comupted token
‘© Continuously circulating frame or token
Tale? Sample er
Soft errors occur on a regular bass and area normal
event. For example, burst errors occur when a station
joins the ring.
Soft Error Recovery
‘There are four types of soft eros. Each type of sot
or requires a different proces for ring recovery.

Soft Error Error Example | Ring Recovery Procedures

‘Type

Type | Burst enor No ring recovery Function To require.

Type? | Lost frame Ring recovery requires the ring purge
to be executed

Types | Lostmonior Ring recovery requires ihe monitor
‘contention and ring purge processes

Type | Monitor contention cannot | Ring recovery requires the beacon,

be resolved monitor contention, and ring purge

processes to be executed.

Table eo ing reser pes

28. 29

Module Two Summary

> Token Ring technology incorporates extensive error
detection capabilites,

> The active monitor is responsible for maintaining
ring operations.

Every station onthe ring except the active monitor
is considered a standby monitor

> Before a station joins the ring it must perform some
checks so that the ing joining process will De a smooth
> Token Ring emors are categorized as either hard or
soft eros. All stations onthe ring can detect both
types of errors

‘Token Ring Base Cones

29. 30 Module 2- Ring Maintenance

Module Two Self-test

Complete the following selftest by answering the following questions. Use the
answer key located in Appendix A to check your answers.

1. The standby monitor is responsible for setting the clock speed forthe rng.
TorF?

2, The active monitors responsible for making sure a is always
<irculaing around the ring.

a) ring

b) token

©) baton

© none of the above

3, Ifibe has not detected a token or frame within 10
‘milliseconds clears the ring and releases a new token,

a) network administrator
D) standby monitor

©) active user

© active monitor

4. Ifthe active monitor sees a changed monitor bit it knows the frame has circled the
ring once and it will

) repeat the fame on
'b) mark ias omphaned and send ito to the next station
©) take the frame off the ring

© none of the above

5. A Token Ring station transits a series of est MAC frames that test the

continuity of the cable

a) port
») lobe media
©) trunk media

none of the above

30. E]

ase Comps

31. Module 2- Ring Maintenance

32. 33

Module Three Token Ring Network
Components

“This module provides an introduction to the basic
‘Token Ring network components.
Objectives{ XE "Assumptions made for manual" }

By the end of the Token Ring Network Components
module, you wil be able to:

+ Lis
requ

1 describe the function of each ofthe
. Token Ring network components.

+ Deseribe 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

+ The network adapter.
+ Wiring hub
+ Cabling

Token Ring Adapter
Any device that is o be connected toa Token Ring

LAN requires a Token Ring adapter. The adapte
‘manages the physial-and MAC layer functionality

33. 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 1 access the ring via the lobe cables. The
relays receive a DC voltage (3.47. y) from the station
{through the lobe cable tothe wiring hub. This is called
the phantom current The presence ofthe phantom
current opens the relay atthe hub port and allows the
Station 10 insert itself. The elas provide ing
‘continuity; when the station is not actively part of the
sing, the signal is routed through the relay (he relay is
closed because there i no phantom current) and
effectively bypasses the inactive station,

Ring-In

Ring-In The trunk receive por on the wiring hub.

34. 35

Ring-Out ‘The trunk transmit port on the wiring hub.

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¥)
from the station trough the lobe cable

Trunk

WE

Trunk Connection The wiring tht interconnects wiring hubs together

35. Module 3- Token Ring Network Components

Primary and Secondary Paths
‘Trunk cables connecting wiring hubs erate primary
and secondary paths for data transmission, Inthe event
fof a cable brea, 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.

36. Primary Secondary
Path Path
ral

7 Ñ À D =
E |
LLL LO

37. 38

Module 3- Token Ring Network Components

Token Ring Cabling Options

Shielded Twisted
Pair (STP)

Unshielded
‘Twisted Pai
(UTP)

mc

‘Token Ring uses two pairs of wires—one pair for
transmiting the data and one par for receiving it.
Originally Token Ring networks operated using
shielded twisted pair media. Today, Token Ring
networks can operate over unshielded twisted pair and
fiberoptic media in addition to shielded twisted pair

‘Shiclled twisted pair cable isthe original cable type
used with early Token Ring networks, The shielding
from interference and provides a

Uns

clded twisted pair cable is made of copper
strands twisted together o form pairs. The pairs are
covered with a sheath, and there is no shielding,
Category 3,4, and S UTP cabling are acceptable
building wiring. Usually UTP is used for lobe and
patch cables

Fiber opti cabling support ong connections, This
type of cabling is not susceptible o electromagnetic
interference, because the signal is transmitted as I
rather than electricity. Fiber is usually used for Token
Ring trunk connections.

38. 39

Token Ring Topolog)

Logical Ring/ ‘The Token Ring network uses logics ring/physical
Physical Star star topology. Physically, the stations are connected to
{he hubs in a star topology. However, if we w
trace the path the frames travel, we would see itis a
ring

39. 40 Module 3- Token Ring Network Components

Module Three Summary

> Token Ring networks use adapter, cabling, and
wiring hubs

> Token Ring uses two pair of wires—one pai for
ransmiting the data and one par for receiving it.

> Token Ring networks can operate over unshielded
twisted par, shielded twisted pai, and fiber opti
cabling.

> The Token Ring network uses a logical
ring/physical sar topology

40. a

Module Three Self-study

‘Complete the following sete by answering the following questions. Use the
answer key located in Appendix A to check your answers.

1 cabling is used mos often for lobe and patch cables.

a STP
b) UTP
©) Com
9) Fiber optic

2. Fiber optic cabling supports long distances and is ot susceptible to

a) electromagnetic interference
+) breakage

©) sunspots

4) none ofthe above

3. Physically, Token Ring stations are connected to wiring hubs in a

topology

a) star
) bus
©) ting
9 me

a. cables connecting wiring hubs create primary and secondary
pas Tor data transmission,

a) Lobe
b) Patch
©) Trunk
© None ofthe above

5. The relays in a Token Ring hub provide ing continuity because when the tation
is not aetvely part ofthe ring, the signal is routed through the relay and in effect
the sation.

a) shuts down
D) bypasses

©) wraps

© none ofthe above

‘Token Ring Base Cones

41. “2

Module 3- Token Ring Network Components

42. 43

ask Comets

43. 45

Module Four Building Token Ring Network
Infrastructures

“This module provides an overview of intemetworking
techniques used with Token Ring networks. We will
focus on source outing, bridging, and source route
transparent bridging, Routers can also be used to
interconnect rings, hut routing is beyond the scope of
this self-study

Objectives{ XE "Assumptions made for manual" }

By the end of the Building Token Ring Network
Infrastructures module, you willbe able o:

+ Discuss how bridges improve performance through
microsegmentatio,

+ Define source route bridging.
+ Describe the difference between source route

bridging and source route transparent bridging.

Overview

Large networks have always consisted of multiple
segments, because thee are practical limits on the
number of stations that can be attached toa single
‘segment. With Token Ring the maximum permitted is
255 stations on one ring, but in practice few users load
Fings up with more than about 100 sation.

‘The traditional method for interconnecting Token
Rings isthe source route bridge, Lets take a lok at
this method of connecting Token Ring networks.

Source Route Bridging

44. 46

Module 4 Bug Token ing Network nrastucures

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 othe
destination. The path is encoded into the data frame's
‘outing information field and used by source route
bridges to make forwarding decisions.

“The routing information field includes a sing and
bridge number or 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 aempts to reach station “2” on it
‘wn ring If the frame returns unanswered —frame
copied bits are unchanged station “A” assumes
Station “Z" is located on another ring, and atempts to
determine a route to station "Z." Station “A” does his
by sending a discovery frame. A discovery frame or
XID packet i a broadcast message that determines a
path tothe destination address.

On ts way to station "2," each bridge that receives the
frame add its bridge number and the ring number of
the next segment tothe routing information field ofthe
frame. When sation "Z" reeives the frame, it copies
the frame and sends it back tothe originating station
‘The source route bridges use the route that is now
located in the routing information field.

45. Ring 1

Ring?
Data frame Br B2
being sent to
station “2°
FR Rings

Station

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 L bridge I. ing
2, bridge 2, ing 3, bridge 3: or ring I bridge 4.
Staton “A” uses the path inthe first discovery fram
that returns, assuming this is the most efficient rot

Single Route versus All Routes Broadcasts

Token Ring Base Cones

46. Module 4 Bug Token ing Network nrastucures

In source route bridging, stations use two broadcast
methods for route discovery, single-route broadcast,
and an allroutes 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
forward the frame to the next segment, This method
reduces the amount of overhead traffic on the in.

‘Transparent Bridging
Transparent bridging is used in Ethemet networks,
“Transparent bridges learn the addresses of al devices
‘on each oftheir ports and build adress tables to Keep
truck ofthat information. A transparent bridge then
uses the address able to make forwarding decisions. A
bridge reads al frames on the network, examines the
source and destination addresses, and decides whether
o forward or discard the frame. If the source and
destination ae in different address tales, the frame is
forwarded tothe appropriate network,

‘This process is called transparent bridging because
unlike source route bridging. the end stations have no
ole inthis activity. The end station is not aware that
its frame is being bridged to another ring segment. The
bridge as all the responsiblity of forwarding the
frames. Optimally, a bridge performs at ine speeds so
does not lose daa or become a botleneck

Source Route Transparent Bridging
Source route transparent (SRT) bridging evolved to
meet the need for interoperability between networks
‘sing transparent bridge and networks using source
route bridging. The goal of SRT isto provide for his.
interoperability by having the source routing tations
interpret and understand the functions of the
transparent bridge station,

When a frame is received by the bridge, the bridge
checks tose if thee is routing information inthe
frame, Ihre i, the bridge uses source route bridging
to forward the frame, If the outing information
indicator bi is not et, the bridge uses the transparent
method to decide if the frame needs to be forwarded,

47. 49

‘SRT bridges implement spanning tree with the ther
SRT stations and transparent bridges the same way that
‘panning tree is implemented in a pure transparent
network. SRT stations will use the source routing path
itone exist or fall back on the spanning tee path
SRT stations use a single on segment route explorer
frame, This route explorer mechanism results in one
Single route broadcast frame atthe destination sation.
“The destination frame responds with one single route
broadcast message containing no routing information
“The originating sation will pick the route or use the
spanning tee path, Transparent bridging stations do
not respond t frames that contain routing information,

‘Token Ring Base Cones

48. 50 Module 4 Bug Token ing Network nrastucturos

Module Four Summary

+ In multiple Token Ring networks, each ring has a
unique number and each bridge has an identification
number

> The bridging technique ypiclly used in Token
Ring networks is source route bridging,

> Source route bridging is designed such thatthe
‘originating station determines the path othe
destinaron

> The path is encoded into th routing information
field in the data fame and used by the source route
bridge to make Forwarding decisions

> In source route bridging, stations use two broadcast
methods for route discover, single-route broadcast
and an allroutes broadeas.

49. st

Module Four Self-test

‘Complete the following slftet by answering the following questions, Use the
answer Key located in Appendix A to check your answers

Lin a multiple ring Token Ring network, each has a unique number.

a) sing
D) bridge
©) station
© router

2. Source route bridging is designed such that the originating tation determines the
Path to te destination sation.

Torr?

3. The traditional method for connecting Token Ri
transparent bridging.

networks togethers via

Tork?
4. In transparent bridging, stations use to broadcast methods,
Torr?

5. The Routing information field contains the ring and bridge numbers that make up
the path the frame must take to reach its destination

Torr?

‘Token Ring Base Cones

50. Module 4 Bug Token ing Network nrastucures

51. Module Five__ Token Ring Switching

“This module provides an introduction to Token Ring
‘switching. Token Ring switching offers an alternative
means of interconnecting multiple Token Rings.

Objectives{ XE "Assumptions made for manual" }

By the end of the Token Ring Swi
willbe able o:

1g module, you

+ Define Token Ring switching.
+ Listthe benefits of Token Ring switching
+ Describe cutabrough switching.

Overview

‘Switching offers an altemative means of
interconnecting multiple Token Rings that is both
‘Simpler and more efficient than routing or bridging. In
a switch, packets are transfered from one ring 10
another with negligible latency, because the packets
fare neither buffered nor procesced within the switch,

Lets, take a closer look at how Token Ring switching
works

Cut-Through Switching

Instead of reading packets in their entirety ino buffer
memory before making a decision about where to
forward he frame, a cut-through switch takes action
as oom asthe First 20-30 bytes ofthe frame have been
received, Information in the frame header is analyzed
almost instantly. and the required destination por is
Seduced. At this point a connection is effectively
made between the input port andthe output pon and
the packet immediately starts transmitting onto the
destination ring, This technique is sometime known as
ceut-through switching or on-the-fly switching,

52. 54 Modulo 5- Token Ring Switching

‘The total time hat a frame is held up within a switch is
as lle as 30 microseconds. Compared 1 the 500-
4,000 microseconds of delay that store and forward
devices (sce below) introduce, This isa significant
reduction in latency.

By virally eliminating latency, cut-through
switching allows cients on one ring o communicate
‘with servers on another ring with the samme
performance a 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-hrough
switches, but are based on store and forward designs.
‘The devices are known as store and forwarded devices
‘or bullered” 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
Ämprovements and users will see a degradation in
performance when communicating with servers located
‘on diferent rings.

Contention and Buffering
Although switching involves the transfer of Frames.
{rom one ring to another without buffering frames in
memory, there ae circumstances in which buffering is
needed, A switch cannot transmita frame onto a ring if
the ring is busy. [the ing is busy. the frame must be
‘buffered until the destination ring has gone quiet and
the token can be grabbed. Likewise, if frames ative
simultaneously a two input ports ofthe same switch
and require onward transmission tothe same ring, the
‘witch 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

circumstances without dropping fran
forany kind of LAN switch.

53. 55

Switching by Source Routing

“The standard method for interconnecting Token
is source routing. With his technique, lents fist
establish a route 104 server using a route discovery
process and then insert information tha defines ts
route in each packet hey send

‘Source routing operates at Layer 2 the data link layer,
Andis, 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
‘ach frame received, Because the source routing
information explicitly idemúfic the ring the frame
should be passed o next. The switch can make very
rapid forwarding decisions with minimal processing.

With transparent switching, Forwarding decisions ae
made on the MAC address information inthe header of
‘ach packet. The switch must leam which MAC
addresses ae attached to each port and maintain tables
‘of is 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 por.

‘Switching based on source routing has a number of
advantages compared tothe transparent techni
Less work is required for each packet: therefore, los
processing power i required, leading to lower cos.
Al 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 colapsed
‘backbone, connecting workgroup rings to other rings
‘that support cenrall-based servers.

‘Token Ring Base Cones

54. Virtual LANs

Module 5- Token Ring Switching

In almost all LAN environment, many users access a
few servers and the serve connection can therefore
easly become a bottleneck. Switching helps with this
problem, By placing only a few servers on a dedicated
ring, itenables the server ings 1 be segmented 10
reduce the number of machines on cach ring

‘The most heavily loaded servers may well justify
having a private ring all to themselves In his special
case, the server i the only device connected 10 port
on a switch, Instead of running the full oken-passing.
protocol of Token Ring between these two devices,
is possible to dispense with the token and operate this
link as a fll duplex serial link running at 16 Mbps in
both directions at once,

Pull duplex Token Ring provides double the
‘bandwidth to any station that handles concurrent
bidirectional trafic, it offers a clar 16 Mbps channel
in each direction. Heavily loaded servers can take
advantage ofthis, because their operating systems deal
‘with muliple 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 controling the Token Ring chipset simply
red tobe changed,

LAN switches direct trafic so packets are only sent to
the segments that need them. This fin for
individually addressed packets, but what about
broadcast frames? There are additional benefits with
switching ifthe forwarding of broadcast waffi is
controlled in the switch, With the appropriate
intelligence applied to he Filtering of broadcast frames,
Switches can help network administrators with moves
and changes by allowing the creation of "viral
LANs.”

55. 87

A viral LAN is collection of LAN segments
connected by switches in which al broadcast trafic
‘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
‘esignated ports on he switch, virtual LANS can be
defined to include or exclude specified LAN segments
attached tothe switch

All stations on a vinual LAN can see all broadcast
packets including service advertisement, address
resolution, and route discovery packets, hat originate
within the vital LAN. Likewise, stations cannot see
any broadcast packets that originate on segments that
fare 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
viral LAN,

Virtual LANs provide the ational benefit: they
confine the propagation of broadcast trafic within the
‘Set of rings that must receive the broadcast, This
ensures that broadeast traffic occupies only a small
proportion of each segment' bandwidth. It also
‘overcomes any concem about “broadcast corms” ina
‘source routed environment

‘Token Ring Switching and ATM

‘Token Ring switches need a high speed interconnect so
large volumes of traffic ean be carried between
‘witches. Both FDDI and ATM are considered
appropriate technologies for he 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 interswith traffic, But
When ATM is used with Token Ring switching, it
“offers far more than just a means to interconnect
‘witches.

‘Token Ring Base Cones

56. Module 5- Token Ring Switching

Wen integrated with a LAN environment, ATM
‘operates in a mode known as “LAN emulaion.” The
‘dea behind this i to make an ATM network behave
like a LAN, even though trafic is being carried on
point-to-point connections across the network. With
LAN emulation, additional services within the ATM
network support LAN Ike functions such as address
resolution and broadeast packets,

ATM can emulate Token Ring LANs. Token Ring
packets an be carried across an ATM network just as
if they were being carried on a ring-even though in
realty they go poin-to-poin.

‘The idea of viral LANs embracing both the Token
Ring and ATM domains i extremely powerful and
exible, It provides network administrators with
complete freedom to configure and reconfigure the
linkages between rings and servers in any size
network, This ean all be done from the network
‘management console. And it allows large networks 10
be built emirely on the basis of switching, largely
eliminating the need for low and inefiien rot

ing

57. 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 expliciy
idemilis 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 sation that handles concurren
bidirectional trafic, as i offers a clear 16 Mbps
channel in each direcion.

‘Token Ring Base Cones

58. 60 Module 5- Token Ring Switching

Module Five Self-study

Complete the following slftest by answering the following questions. Use the

answer key located in Appendix A to check your answers.

1. Full duplex Token Ring doubles the bandwidth ofa Token Ring connection.
Tork?

2. In almost al LAN environment, users can access only a few servers, andthe
Server connections can easily create botenecs, Servers can be connected via ull
Alpes Token Ring to reduce the incidence of botlenecks.

Tork?

5 Switching i ess efficient than sing a router to microsegment the network
Tork?

4. Token Ring switches always use tore and forward switching method,

Tork?

5. In Token Ring switches that use source routing, dhe source routing information
‘denies the ring the frame shouldbe passed to next.

TorF?

59. st

Appendix A - Answers to Self-study Questions

Module One Self-study Answers
1. The 802.5 standard sa direct outgrowth ofthe research done by —1

a DEC
D) IBMe
©) IEEE
4) Proteon

2. When a station on a Token Ring network wishes to transmit, it must ist possess
the

a) ring
D) token"
©) baton
© none ofthe above

3. Te frame control field indicates whether the frame is a
à dat frame,

1 control frame or

a) Mac
b) error

©) beacon

© none ofthe above

4. The maximum data field for 16 Mbps Token Ring is _b,

a) 4472 bytes
D) 17,500 bytes
©) 1518 bytes

) none of the above

5. the address-secognized and frame-copied bits are unchanged inthe frame status
Ad, the originating station wil resend the frame around the ing,

Torr?

7

60. 62 Appenóx=A

Module Two Self-study Answers.
1. The standby monitor is responsible for setting he clock speed for the ring
TorF?

E

2. The active monitors responsible for making sure a is always

<irculaing around the ring,

a) ring
b) token?

©) baton

4) none of the above

3, fido a has not detected a token or frame within 10

‘milliseconds, i clears the ring and releases a new token

a) network administrator
) standby monitor

©) active us

à) active monitor

4, Ifthe active monitor sees a changed monitor bit it knows the frame has cirled the
ring once and it wi

a) repeat the frame on the next station
b) mark tas omphaned and send it on to
©) take the frame off the ring?

© none of the above

5. A Token Ring sation transmits a series of test MAC frames that test

the continuity of the cable

a port
D) lobe mediar
©) trunk media

© none of the above

61. 63

Module Three Self-study Answers

cabling is used most often for lobe and patch cables

a) STP
by UTPe
©) Coax
4) Fiber optic

ber optic cabling supports long distances and is not susepúbl to

a) electromagnetic interference?
D) breakage

©) sunspots

© none of the above

3. Physically, Token Ring stations are connected to wiring hubs in a
‘opotogy.

a) sur
b) bus
©) ting
© we

4
paths Tor data an

cables connecting wring hubs ereate primary and secondary

a) Lobe
b) Patch

9 Trunke

4 None ofthe above

5. The relaysina Token Ring hub provide ring continuity because when the station
is not atively part ofthe ing, he signal is routed through the relay and in effect
the station

a) shuts down
D) bypasses
©) wraps

‘Token Ring Base Cones

62. 64 Appenóx=A

& none ofthe above

Module Four Self-test Answers

1. Ina multiple ring Token Ring network, each__ a has a unique number.

a) rings
D) bridge
©) station
© router

2. Source route bridging is designed such thatthe origingaing station determines the
path tothe destination tation.

Torr?
T

3. The traditional method for connecting Token Ring networks together is via
Transparent bridging,

TorF?
F
4. In transparent bridging, stations use two broadcast methods.

TorF?

5. The Routing information feld contains the ring and bridge numbers that make wp
the path the frame must take 0 reach ts destination

TorF?

T

63. 65

Module Five Self-test Answers

1. Full duplex Token Ring doubles the bandwidth of a Token Ring connection
Torr?

1

2. In almost all LAN environments, users can access only a few servers and the
server connections an caily create bottlenecks, Servers can be connected via ll
<ulplex token ring to reduce the incidence of Dotlenecs

Torr?

1

5. Switching sles ffiien than using a router tomicroscgment the network
Tork?

F

4. Token Ring switches always ue store and forward switching method.
Tork?

F

5. In Token Ring switches that use source routing, the source routing information
identities the ring the frame should be passed to next.

Tork

‘Token Ring Base Cones

64. Aopen À