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Gaurav GuptaEmail
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| | Profile: I graduated from Manipal University with a Bachelor's in Information Technology [B.I.T]. I am currently pursuing an M.B.A. from Ansal Institute of Technology, affiliated to Tarleton State University [Texas A&M]. Prof. Ashay Dharwadker's Courses (1): | Course | Semester | Grade | | | Computer Networks | Spring 2004 | View | |
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Research Note ID: 65
Course: Computer Networks
Topic: Token Ring
| | Description: The Token Ring network was originally developed by IBM in the 1970s. It is still IBM's primary local-area network (LAN) technology. The related IEEE 802.5 specification is almost identical to and completely compatible with IBM's Token Ring network. In fact, the IEEE 802.5 specification was modeled after IBM Token Ring, and it continues to shadow IBM's Token Ring development. The term Token Ring generally is used to refer to both IBM's Token Ring network and IEEE 802.5 networks.
v TOKEN-RING NETWORK
Ø A type of computer network in which all the computers are arranged (schematically) in a circle. A token, which is a special bit pattern, travels around the circle. To send a message, a computer catches the token, attaches a message to it, and then lets it continue to travel around the network.
Ø (2) When capitalized, Token Ring refers to the PC network architecture developed by IBM. The IBM Token-Ring specification has been standardized by the IEEE as the IEEE 802.5 standard.
A Token Ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and a bit- or token-passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time. The Token Ring protocol is the second most widely-used protocol on local area networks after Ethernet. The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5. Both protocols are used and are very similar. The IEEE 802.5 Token Ring technology provides for data transfer rates of either 4 or 16 megabits per second.
Very briefly, here is how it works:
q Empty information frames are continuously circulated on the ring
§ . When a computer has a message to send, it inserts a token in an empty frame (this may consist of simply changing a 0 to a 1 in the token bit part of the frame) and inserts a message and a destination identifier in the frame.
§ The frame is then examined by each successive workstation. If the workstation sees that it is the destination for the message, it copies the message from the frame and changes the token back to 0.
§ When the frame gets back to the originator, it sees that the token has been changed to 0 and that the message has been copied and received. It removes the message from the frame.
§ The frame continues to circulate as an "empty" frame, ready to be taken by a workstation when it has a message to send.
§ The token scheme can also be used with bus topology LANs.
§ The standard for the Token Ring protocol is Institute of Electrical and Electronics Engineers (IEEE) 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol. 802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol.
802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol.
802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol.
802.5. The Fiber Distributed-Data Interface (FDDI) also uses a Token Ring protocol.
References:
searchnetworking.techtarget.com/sDefinition/ 0,,sid7_gci213154,00.html
www.webopedia.com/TERM/T/token_ring_network.html
www.cisco.com/univercd/cc/td/doc/ cisintwk/ito_doc/tokenrng.htm
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Research Note ID: 66
Course: Computer Networks
Topic: Token Ring
| | Description: Background
Token Ring is a Local Area Network (LAN) protocol. The Token Ring protocol was first developed by IBM. Token Ring is standardized in IEEE 802.5 that was published in 1985. The protocol deals with the problem of collision, which is defined as a state were two stations transmit at the same time. In order to avoid the situation of collision there was a need to control the access to the network. This kind of control is possible by the use of a control (permission) called token. The token is passed from one station to another according to a set of rules. The ring consists of ring stations and transmission medium. Data travels sequentially from station to station. Only the station in possession of the token is allowed to transmit data. Each station repeats the data, checks for errors, and copies the data if appropriate. When the data is returned to the sending station, it removes it from the ring . The token Ring protocol supports priorities in transmission. It is implemented setting the priority bits in the Token Ring Frame.
Token Ring is a first and second layer protocol in the OSI ( Open Systems Interconnection ) seven layer model. The First release of Token Ring version was capable of 4Mbs data transmission rate, the transmission rate was improved later to 16Mbs. Token Ring operates on many cable types.
Ring benefits:
High reliability, the Ring can continue normal operation despite any single fault.
Bypassing inactive stations.
Effective use, 95% in Token Ring only whilst 30-40% in Ethernet.
Excellent traffic handling (17.8 kb in TR, only 15kb in Ethernet.).
Large maximum frame length .
High bandwidth efficiency. 70% in Token Ring, 30% in Ethernet.
Many media choices: UTP STP coax fiber.
Supports transmission priority.
Token Format
The token is the shortest frame transmitted (24 bit)
MSB (Most Significant Bit) is always transmitted first - as opposed to Ethernet
SD AC ED
SD = Starting Delimiter (1 Octet)
AC = Access Control (1 Octet)
ED = Ending Delimiter (1 Octet)
Starting Delimiter Format:
J K O J K O O O
J = Code Violation
K = Code Violation
Access Control Format:
P P P T M R R R
T = “0” for Token
T = “1” for Frame
When a station with a Frame to transmit detects a token which has a priority equal to or less than the Frame to be transmitted, it may change the token to a start-of-frame sequence and transmit the Frame
P = Priority
Bits Priority Bits indicate tokens piority, and therefore, which stations are allowed to use it. Station can transmit if its priority as at least as high as that of the token.
M = Monitor
The monitor bit is used to prevent a token whose priority is greater than 0 or any frame from continuously circulating on the ring. If an active monitor detects a frame or a high priorety token with the monitor bit equal to 1, the frame or token is aborted. This bit shall be transmitted as 0 in all frame and tokens. The active monitor inspects and modifies this bit. All other stations shall repeat this bit as received.
R = Reserved bits
The reserved bits allow station with high priority Frames to request that the next token be issued at the requested priori ty.
Ending Delimiter Format:
J K 1 J K 1 1 E
J = Code Violation
K = Code Violation
I = Intermediate Frame Bit
E = Error Detected Bit
Frame Format
MSB (Most Significant Bit) is always transmitted first - as opposed to Ethernet
SD AC FC DA SA INFO FCS ED FS
SD = Starting Delimiter (1 Octet)
J K 0 J K 0 0 0
J = Code Violation
K = Code Violation
AC = Access Control (1 Octet)
P P P T M R R R
T = “0” for Token,
T = “1” for Frame.
When a station with a Frame to transmit detects a token which has a priority equal to or less than the Frame to be transmitted, it may change the token to a start-of-frame sequence and transmit the Frame.
P = Priority
Bits Priority Bits indicate tokens piority,and therefore, which stations are allowed to use it. Station can transmit if its priority as at least as high as that of the token.
M = Monitor
The monitor bit is used to prevent a token whose priority is greater than 0 or any frame from continuously circulating on the ring. if an active monitor detects a frame or a high priority token with the monitor bit equal to 1, the frame or token is aborted. This bit shall be transmitted as 0 in all frame and tokens. The active monitor inspects and modifies this bit. All other stations shall repeat this bit as received.
R = Reserved bits the reserved bits allow station with high priority Frames to request that the next token be issued at the requested priority
FC = Frame Control (1 Octet)
DA = Destination Address (2 or 6 Octets)
SA = Source Address (2 or 6 Octets)
INFO = Information 0 or more octets up to 4027 FCS = Frame Check Sequence (4 Octets)
ED = Ending Delimiter (1 Octet)
J K 1 J K 1 I E
J = Code Violation
K = Code Violation
I = Intermediate Frame Bit
E = Error Detected Bit
FS = Frame Status (1 Octet) this octet includes the address recognition bit & copy bit
References:
www.rad.com/networks/1996/toknring/toknring.htm
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Last updated on Sunday, 1st February 2004, 05:14:50 PM.
Prof. Ashay Dharwadker
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