Comprehensive Report: Token Ring Network Functionality and Design

This report provides a comprehensive analysis of the Token Ring Network, a multiple access mechanism developed by IBM and standardized as IEEE 802.5. It details the network's operation, emphasizing the token passing method to avoid collisions and ensure deterministic behavior. The report covers the physical medium, frame formats, Media Access Control (MAC), and message transmission processes, including sending and receiving algorithms. It explores prioritized functionalities, ring management, and maintenance procedures, addressing potential issues such as token loss and busy tokens. The report also highlights advantages like collision-free operation and high performance, along with disadvantages such as the cost of Multiple Access Units (MAUs) and data frame flow. Finally, it concludes with a summary of the Token Ring Network's key features and its role in network communication.

Assignment No.
Title – Token Ring Network
Student Name –
Date of Submission –
Name of the Faculty, Affliation
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Table of Contents
1. Introduction to Token Ring 3
1.1 Operation of Token Ring Network 3
1.2 Prioritized Functionalities 4
1.3 Ring Management and Maintenance 5
1.4 Token Ring Physical Medium 5
1.5 Token Ring Network Frame Format 6
2. Media Access Control 7
2.1 Message Transmission an Example 8
2.2 Token Ring Send Algorithm 9
2.3 Token Ring Receive Algorithm 10
3. Protocol 11
4. Advantage of Token Ring 12
4.1 Collision Free Network Operation 12
4.2 High performance in any condition 12
4.3 No need of server to control and manage the network connectivity 12
5. Disadvantages of Token Ring Network 13
5.1 Cost of Multiple Access Unit (MAU) and Network Card 13
5.2 Data Frame Flow 13
5.3 Higher Wait for Sending the data 13
6. Conclusion 13
References 14
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1. Introduction to Token Ring
Token ring is multiple access mechanism used in network to communicate data. In 1980
International Business Machine (IBM) developed token ring multiple access mechanism for
Local Area Network. This token ring network access mechanism was developed as an alternative
to the Ethernet network. Later on, Institute of Electrical and Electronics (IEEE) specified the
standard for token ring network as IEEE 802.5. This IEEE 802.5 specification for shared
multiple access is dedicated for token ring network. The specification states that multiple stations
are connected with a ring network where a particular station is master station that provides a
token into the network. This token circulates in the network and if a station has to send the data
frame then it has to grab the token and add the data into the token to make complete data frame
and transmit. Now, this data frame circulates into the ring network and all stations listen to data
frame and one which address matches with the destination address of the frame grab the data
frame and releases the token again into the network. The station which address does not match
with the destination address of the data frame discards to grab and this way data frame circulates
into the ring network.
Star wire ring configuration is used under the token ring network. All the workstations and
networking equipments are connected physically with the ring. The signal travels in the ring and
all the workstations including the network devices listen the circulating signal.
Token ring network is also known as token passing network. A token ring network does not
introduce the problem of collision. This is due to fact that at a time either token is circulating or
complete data frame is circulating in the network.
1.1 Operation of Token Ring Network
A token ring network has small frame such as token passes in the ring by which all the
workstations are connected and formed a ring of network. Each workstation listen the token one
by one as token circulates in the ring. It is also the mechanism that each workstation has a turn to
send the data frame to destination workstation in the network. All the succeeding workstations
grab the token and if they have to send the data frame then attach the data with token to make
token as a data frame and push into the ring and wait for defined amount of time for
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acknowledgement. The workstation of token ring network is allowed to hold the token for a
fixed amount of time ("Broadcast Communication Networks", 2017).
When a workstation has to send the data it captures the circulating token at time token passes
through that workstation. After seizing the token the ring becomes empty and the workstation
that captures the token changes 1 bit of the token which makes the token to start of the frame
sequence. After changing 1 bit of token data is added under specified field of token to make the
complete data frame. Finally, the workstation releases the token into the ring network to reach to
the destination workstation of network. When the data frame circulates into the ring network
there is not any token circulates into the network so that other workstations are not able to send
data frame and collision does not occur. All the workstation have to wait for the token to send
the data to destination machine in the ring network.
At other end when the data frame is received by a workstation then the workstation first extracts
the data from the data frame and changes 1 bit of start of frame sequence to make the frame to
token. After making the token by changing 1 bit of frame the token is again released into the
network. Now token again circulates into the network. The workstation grabs the token with
respect to turn and if it has to send the data then token seized otherwise workstation releases
token immediately into the ring.
Token passing or token ring network is a deterministic network. Due to this property of token
ring network the calculation of maximum time which passes before a workstation may be
capable to transmit data. Token passing network is suitable for those application where the
predictable delay and robust network operation are needed.
1.2 Prioritized Functionalities
Token ring network allows its workstation to be assigned with priority for sending the data
frame. A priority scheme can be implemented with all the workstations or some of the
workstations of the network. The frame of token ring network has two fields for priority
management in network operation. These two fields are priority and reservation field.
With this prioritized operational scheme, only a workstation can seize the token which priority is
either equal to or higher than the priority of the token priority field. If this condition machos with
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a workstation then it captures the token and converts the token into data frame and inserts into
the ring to reach at the destination workstation. In next pass of the token after receiving the data
frame by destination workstation the token is seized by a station which priority is higher than
that of the previous workstation or station.
1.3 Ring Management and Maintenance
Token ring network is highly susceptible to failure of the ring network operation due to ring
breakdown. This is caused by two basic error conditions under the token ring network. First
cause is loss of the token from the ring and second is busy token under the token ring network. In
first error condition there is not any token circulates in the ring so that non of the workstation
becomes able to send data frame. In case of second problem the token circulates in the ring
endlessly.
This problem is solved by introducing a workstation as a active monitor. The active monitor
detects the lost token with respect to a timer time out and produces a new fresh token under the
ring. To detect the busy token the active monitor sets a bit which is known as monitor bit into
the busy token. In next round the active monitor checks the token and if found that monitor bit is
set then it remove that token and insert a fresh token into the ring.
1.4 Token Ring Physical Medium
A point to point connection by shielded twisted pair cable is taken to connect the adjacent
workstations in token ring network (Nilausen, 1992). The signaling process is baseband and
differential Manchester encoding is used. Wiring concentrator is used to avoid the ring network
down due to cable break or workstation down. Wiring concentrator creates a bypass system
under the star based token ring network. This bypass system protects the functioning of token
ring even the network cable breaks.
The physical layout of the connection between the adjacent stations in token ring network is
presented in figure 1.
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Figure 1. Bypass Relay in Token Ring Network Connectivity
This bypass relay system protects the ring network services even the workstation fails and cable
break. Two way communication is being established by wiring connector by connecting the
shielded twisted pair cable for the token ring star connected ring topology.
1.5 Token Ring Network Frame Format
Token ring LAN has two different categories of frame formats. These frame formats are for the
token and data frame or command frame of the token ring local area network. The length of
token frame is 3 bytes long that contains the fields like start delimiter, access control and end
delimiter. Each of the filed of token is of 1 byte.
Data and command frames of token ring network varies in size. This variation is due to size of
the information field of the data frame in token ring network. Command frame carries the control
information and data frame carries the upper layer data.
The token format is presented in figure 2.
Figure 2. Token Format
Start delimiter indicates the stations about the arrival of token. Access control filed of token
contains the priority information of the token. End delimiter contains the end of the token field.
Data and Command Frame Format is presented in figure 3.
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Data and command frame format of token ring network is presented in figure 3. The individual
field size in byte of data and command frame is also indicated.
Figure 3. Data and Command Frame Format of Token Ring Network
Start delimiter, end delimiter and access control fields are of 1 byte each taken from the token
frame and rest of the additional fields are detailed as follows.
Frame Control – This 1 byte filed indicates that the frame is either data frame or command
frame.
Destination and Source Address field – The destination and source address fields are 6 bytes
long field. The 6 bytes of source address filed indicates the source station address that sends the
given frame. Again 6 bytes of destination address field indicates the destination station address
for which the source sends the frame.
Frame Check Sequence (FCS) – The calculated frame sequence with the contents of the frame
data is placed under this 4 bytes field. The destination machine recalculates the FCS and
compare with existing under the FCS field. If both matches then frame is accepted by destination
station otherwise discarded.
Frame Status – Frame status is 1 bytes field indicates the termination of the data and command
frame. It also indicates the indicator of address recognition and indicator of frame copy.
2 Media Access Control
Media Access Control is very simple mechanism under the token ring network. Each station of
the token ring network is physically connected via the point to point connection. A station of the
network is configured as master station. When token ring boots, the master station generates a
fresh token of 3 bytes containing the three fields and insert the token into the ring. After inserting
the token into the ring the token circulates into the ring. Token is read by each succeeding station
in the ring. If a station has to send the data then it seizes the token and add data of upper layer
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and releases into the ring. When data frame is inserted into the ring and circulates into the ring to
reach the destination all stations listen it and token is not available into the ring. Therefore, rest
of the stations of the token ring network are not able to send data frame as there is need of token
to send the data. Once the data frame reaches to the destination station the data is grabbed and
token is released into the ring (Thakur, 2017). Further token circulates into the network by
passing through each succeeding station.
2.1 Message Transmission an Example
The medium access control in token ring network is very simple as it is based on the token to
send the data or command frame to destination. Once the token is captured by the station no
other stations of the token ring network can send the data frame as token is not available. For
example,
Let there are 5 stations in token ring network. These stations are a, b ,c, d and e. a is master
station. Station c has to send data to station e.
When this network boots master station a generates a token t and insert into the ring. Token t
reaches to station b, it reads the token and releases in the network ring. Again token reaches at
station c and c seizes the token and changes the start delimiter field to make the token a data
frame. Now, station c adds other fields such as source address, destination address, FCS, frame
control, data and frame status field into the token to make data frame. Station c inserts this data
frame into ring to reach at the destination. Each station reads the frame and checks the
destination address of data frame. Data frame reaches to station e and e grabs it and extracts the
data for its upper layer and removes all fields except the fields of token. Finally, station e
releases the token into the ring. Next station which has to send the data does the same operation
as done by station c in token ring network. This operation scenario is illustrated in figure 4.
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Figure 4. Token ring message flow example
In token ring network either a token or data frame can circulates into the ring so that its becomes
very simple in medium access control and this also ensures the collision free medium
accessibility. Multiple Station Access unit (MASU) or wiring center provides the medium access
control and management of the multiple access in token ring network. MASU detects any
problem or fault in the network and removes that problem in medium access.
2.2 Token Ring Send Algorithm
Token ring send algorithm is designed with simple mechanism of medium access control
("Networking Fundamentals - Unit 4 Sec 6", 2017). The algorithmic steps are as follows.
Step 1. Wait for token
Step 2. If data has to be sent, grab the token
Step 3. Format data frame and transmit data frame
Step 4. Start timer
Step 5. If time expires, and hold the token
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Step 6. Forward the token
Step 7. else wait for token
Step 8. Else forward token
The operational diagram is given under figure 5.
Figure 5. Token Ring Send algorithm diagram
2.3 Token Ring Receive Algorithm
The token ring network receive algorithm in stepwise algorithmic procedures is presented as
follows with detailed explanation and diagram.
Step 1. Wait for frame to receive
Step 2. If it is a token
Step 3. Enter the Xmit routine
Step 4. Elseif it is data frame
Step 5. Set A and C bits and repeat frame
Step 6. Pass frame to higher layer
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Step 7. Else repeat frame and goto step 1
Step 8 end
The receive frame diagram is presented in figure 6.
Figure 6. Diagram of Receive Frame Algorithm
3 Protocol
The token ring network has a protocol which is also known with its name token ring. A token
ring protocol works with the mechanism of token passing system where a station listen the token
and if it has to send the data, it seizes the token.
All the functions of the medium access control as mentioned in section 2 are governed by the
token passing protocol as IEEE 802.5 specification dictates the token passing mechanisms for
token ring network.
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Advanced version of token passing mechanism is employed by protocol Fiber Distributed Data
Interface (FDDI). This protocol also works like a token ring protocol but the physical medium is
Fiber Optic. There are two rings used under the FDDI. These two rings such as physical and
logical rings. These two rings of FDDI are opposites with each other such as one ring is
clockwise and other ring is anti clockwise. The operation mechanism of FDDI is same as the
token ring.
4 Advantages of Token Ring
Token ring or token passing network has many advantages. These all advantages are presented
pointwise as follows.
4.1 Collision free network operation
Token ring network provides the collision free network operation for local area network. The
reason behind this collision free is that a station of token ring network can transmit only when it
has a token and once the token is seized by a station then no token circulates into the ring till the
transmission completes (Sparrow, 2017).
Due to collision free network operation environment there is no need of the collision
management by deploying the different categories of medium access mechanisms that avoids and
manages the collision of the network.
4.2 High performance in any condition
The token ring network gives the better performances even the load in the network is being
increased. Other networks such Ethernet, token bus etc performances decreases if the load on the
network is increased (Sparrow, 2017). Other benefits of the token ring network with respect to
performance is that it becomes operative even the cable is disconnected through the bypass relay.
The structural configuration of the token ring network makes it robust in station failure by
enabling the network to make bypass of failed station to construct the ring by reducing the
number of stations in the ring.
4.3 No need of server to control and manage the network connectivity.
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Adjacent stations in token ring network is connected by point to point connectivity. All the
control management such as generation and release of token first time and whenever required is
taken by master station. Thus, expensive server configuration and setup is not required in token
ring network.
5. Disadvantages of Token Ring Network
There are so many disadvantages of token ring network. Some of main disadvantages of token
ring network are presented pointwise as follows.
5.1 Cost of Multiple Access Unit (MAU) and Network Card
The cost of the MAU and network cards are very high in comparison to Ethernet cards for
physical layer establishment (Sparrow, 2017). Due to this cost the setup of the token ring
network becomes expensive with the star network topology.
5.2 Data Frame Flow
Each of the data frame goes to each of the station in the ring network. This is major security
problem that intruder can intentionally read the frame data and disclose the transmitted
information. This security risk is very high with the token ring network.
5.3 Higher Wait for Sending the data
In a token ring network a station can send the data frame if it grabs the token (Sparrow, 2017).
When a network diameter is big and there are so many stations then turn time for a station to get
the token is high. This introduces the delay and data transmission rate is lower such as 4 Mbps to
16 Mbps under the LAN system.
6. Conclusion
Token ring network was developed by IBM in early 1970 and it became functional in LAN in
1980. A ring of the network by connecting the adjacent workstations or station such as
computing nodes is created. The first computing node is connected with last computing node
under the token ring network so this is called a ring network. A token ring network is also known
as token passing network. A token of 3 byte is essential for the operation of token ring network.
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A station can send the data when it gets the token otherwise it has to wait for its turn in the token
ring network. When a station grabs or seizes the token then there is no token in the network and
that station formats data frame by adding the other fields and data into the token. Once the data
frame is formatted in given time interval then station transmits the frame through the ring. All
the stations listen the data frame and a station receives the data frame if the destination address
of frame matches its 6 byte station or MAC address. After receiving the data frame the data of
the frame is supplied to upper layer of the station and all the added additional fields are removed
and token is again inserted into the network. A master station of the token ring network always
detects the faults and removes that faults. There are so many advantages and disadvantages of
token ring network. The common advantages of token ring network is high performance,
collision free network operation and server less network operation. The disadvantages of token
ring network is cost, frame flow and security and waiting time for token.
References
Broadcast Communication Networks. (2017). http://nptel.ac.in. Retrieved 18 July 2017, from
http://nptel.ac.in/courses/106105080/pdf/M5L4.pdf
Nilausen, J. (1992). Token ring networks. New York: Prentice Hall.
Thakur, D. (2017). IEEE 802.5 Token Ring. Ecomputernotes.com. Retrieved 18 July 2017, from
http://ecomputernotes.com/computernetworkingnotes/communication-networks/what-is-ieee-
8025-protocol
Networking Fundamentals - Unit 4 Sec 6. (2017). Webclasses.net. Retrieved 18 July 2017, from
http://www.webclasses.net/demo/intro/5.2/sp/units/unit4_sec6.html
Sparrow, P. (2017). Ring Topology : Advantages and Disadvantages. Ianswer4u.com. Retrieved
18 July 2017, from http://www.ianswer4u.com/2011/05/ring-topology-advantages-
and.html#axzz4nCiiweYZ
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