Token Bus. Message Exchange in Token Bus. Example. Problems with Token Bus

Token us Token -procedure: Only someone who possesses a certain token (= bit sequence), may send. One example for a token network: IEEE 80. Token us All s should be treated equally, i.e. they have to pass
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Token us Token -procedure: Only someone who possesses a certain token (= bit sequence), may send. One example for a token network: IEEE 80. Token us All s should be treated equally, i.e. they have to pass on the token cyclically or this: logical ordering of all s to a ring In a bus topology, ordering is made regarding addresses: 9 Usage e.g. as a field bus (eldbus in German) in industrial environments with a high degree of noise. Purpose: e.g. roboter control; a few masters, many slaves (they only listen). Data rate is not that important, but guarantees in response times are necessary (not possible with Ethernet) Page Message Exchange in Token us Two types of messages are used: Token messages T ID, nextid ID Data messages M ID ID Data Token messages are used for passing on the sending permission from ID to nextid Data messages contain the data to be sent Having the token, a is allowed to send a message. After this (or if nothing is to be sent) the token is passed on. Traffic on the bus e.g.: T 5,7 M 7 T 7, M T, T, T,6 M 6 T 6,9 T 9,5 M 5 T 5,7 High overhead for token exchange: 5 it times for each token message (a full small size Ethernet frame)! In contrast to that, in Token Ring networks only one bit is to be switched from 0 to, i.e. only one bit time for a token message. Thus, the number of participating s should be low, or the number of masters should be low, you can tolerate very many slaves nextid Page Problems with Token us irst problem: a leaves the logical ring Easy solution: the leaving sends a message to its predecessor indicating the new successor Second problem: a comes into the logical ring To allow new s to join, in periodically intervals, a window is opened between neighbors, e.g. between 5 and 7. New s with IDs from 6 to 6 now can apply. Problem: conflict risk! Several s could apply to join in this window Conflict resolution: survival of the fittest. Consider last bits of the IDs: send a request to join with a duration specified by the last bits of your ID: 00 send short 0 send longer 0 send even longer send longest If you hear anybody else sending longer than you, give up. If you survive without conflict, join. If there is no resolution (two or more s are sending for the same time, no one is sending longer), repeat with the second-last bit pair, etc. Page Example Assume a global window. Competitors: Winner! In case of some configuration error, two identical IDs are present: after checking all pairs of the IDs, continue by adding random bit pairs. Page ut Industrial Ethernet Token Ring The Token-us approach is more and more displaced by Ethernet variants, e.g.: EtherCAT (since 00) ast Ethernet based on a bus, star or tree topology (very flexible) Uses TP or optical fiber as medium Synchronization necessary between all s A master polls the other s Ethernet Powerlink Introduction of time slots and a cyclic timing schedule Whole time axis is divided into isochronous and asynchronous phase Isochronous: for time-critical data transfer Asynchronous: for non-time-critical data transfer A managing node assigns time slots (in both phases!) Page 5 Token -procedure: Only someone who possesses a certain token (= bit sequence), may send. based on standard IEEE 80.5 Token Ring the s share a ring of point-to-point connections the token is cyclically passed on particularly suitable for rings Token Ring (/6/00 Mbit/s) Characteristics: guaranteed access, no collisions very good utilization of the network capacity, high efficiency fair, guaranteed response times possible: multiple tokens however: complex and expensive Passing on the token Page 6 Token Ring Sending and Receiving Characteristics Medium: twisted pair, coaxial cable or optical fiber Capacity of resp. 6 Mit/s (00Mb/s with optical fiber) Differential Manchester Code on layer The s are actively attached, i.e. received signals are regenerated (same principle as for repeaters, therefore no restriction of the ring s expansion) Station Point-to-Point Connection Active connector Initial state Data are received from the ring serially Data addressed to a connector s are copied Data are serially passed on along the ring Receiver from the ring to Transmitter from to the ring from the ring Receiver to Transmitter from to the ring Transmission state The ring is divided Own data are sent serially Data coming in from the ring are evaluated by the Receiver from the ring to Transmitter from to the ring Page 7 Page 8 Access within a Token Ring Access within a Multiple Token Ring Example: Station sends to. Station waits for free token (transmission authorization, -yte- Token).. Station changes free token into an occupied one (occupied token = frame header). Afterwards, sends the frame. (Station may send further frames, if the token holding timer (default 0 ms) is not exceeded). Station terminates the frame and waits until the frame passed the whole ring and arrives again.. Station copies the frame. Station removes it from the ring and produces a new, free token. remove entfernen kopieren copy Same example: Station sends to. Station waits for free token (transmission authorization).. Station changes free token into an occupied one (occupied token = frame header). Afterwards, sends the frame. (Station may send further frames, if the token holding timer (default 0 ms) is not exceeded). Station terminates the frame and produces a new, free token immediately.. Station copies the frame. Station removes it from the ring. remove entfernen kopieren copy Page 9 Page 0 rame ormat for Token Ring rame ormat for Token Ring If the ring is inactive, only the -yte-token (SD, AC, ED) circulates. If a wants to send, it sets a certain bit in this token from 0 to. ree token, if a certain bit within AC is set. /6 /6 any DA SA Data CS rame Control (C) Access Control (AC) Start Delimiter (SD) End Delimiter (ED) rame Status SD and ED serve for marking the frame. They contain invalid sequences of the Differential Manchester code. Access control contains the token bit, further a monitor bit, priority bits and reservation bits. rame control marks the kind of the frame: Data, control, yte rame status contains confirmation bits A and C. If a frame arrives at the with the destination address, bit A is set. If the processes the frame, also bit C is set. When the sending gets the frame back, it can see whether the receiving is not working (A = 0, C = 0), if the frame was not accepted (A =, C = 0), or whether the frame was received correctly (A =, C = ). To protect against bit errors, both bits are doubly present. The addresses and the checksum are identical to Ethernet. its of access control: Themonitor bit serves for recognition of a second frame circulation Thepriority bits make possible several priorities. They indicate the priority of the token. If a wants to send with priority n, it must wait for a token of priority n or higher. Thereservation bits permit a to reserve the next frame for itself. If a wants to do this, it registers its priority into the reservation bits. This is only possible, if not already a higher priority is registered. During the next token generation, the priority is copied into the priority bits. Page Page Ring Maintenance To check the correct function of the ring, a monitor is introduced. If this crashes, another is raised as monitor : if a recognizes that the monitor is inactive, this sends a certain token (CLAIM_TOKEN). This can be done by several s simultaneously. If such a message arrives with a smaller ID then suppress it. If a message arrives with larger ID then pass it on. If a CLAIM_TOKEN message arrives with own ID: this is the new monitor. iber Distributed Data Interface (DDI) DDI is a high performance token ring LAN based on optical fibers ANSI standard XT9.5 Data rates of 00 Mit/s Range of up to 00 km (MAN?) Support of up to 000 s, with distances of maximally km Often used as ackbone for small LANs Host ridge 80. LAN Tasks of the monitor : New generation of the token after a token loss Reaction to ring collapse Removal of frame fragments Deletion of old, circulating frames or each problem an own token is defined. Additionally if necessary also timers are used. Page 80.5 LAN ridge DDI ring Successor: DDI-II, supports besides normal data also synchronous circuit switched PCM data (speech) and ISDN traffic Variant: CDDI (Copper Distributed Data Interface), with 00 Mit/s over Twisted Pair Page Structure of DDI DDI Configurations Wiring within DDI: optical fiber rings with opposite transmission direction During normal operation, only the primary ring is used, the secondary ring remains in readiness Normaler asic double Doppel-Ring ring DAS DAS Double ring Doppelter with connected Ring mit Einzelring-Erweiterung single DAS DAS Einfacher Simple DDI DDI-Ring ring NAC If the ring breaks, the other one (also called protection ring) can be used. If both rings break or if a precipitates, the rings can be combined into only one, which has double length: DAS DAS DAS DAC SAC SAC DAS = Dual Attachment Station = Single Attachment Station Two classes of s exist: DAS (Dual Attachment Station) can be attached to both rings, the cheaper (Single Attachment Station) are only attached to one ring. DAC = Dual Attachment Concentrator NAC =Null Attachment Concentrator SAC = Single Attachment Concentrator y means of the concentrators several rings can be linked. Page 5 Page 6 Transmission within DDI Synchronous Transmission of Data Coding /5 code, thus coding of bits of data in 5 bits which are transferred Synchronization Transmission of a long preamble in order to synchronize the receiver to the sender clock pulse. The clocks of all s must run stable on at least 0.005%. With such a stability, frames with up to 500 byte of data can be transferred without the receiver losing the clock pulse. Protocols The fundamental protocols of DDI are similar to IEEE 80.5 (token ring): in order to transmit data, a must acquire the token. Then it transfers its frame and takes it from the ring when it returns to it. Due to the expansion of DDI, a single token is unpractical. Therefore, DDI transfers in the multiple token mode. Original transmission principle within DDI: Use of asynchronous frames, i.e. sending can be started any time. Additionally, with DDI-II also the use of synchronous frames for circuit switched PCM or ISDN data (telephony) is possible: every 5 µs a master produces synchronous frames for reaching the 8000 samples / second necessary for PCM. every frame consists of 6 byte for non-circuit-switched data and up to 96 byte for circuit switched data (up to 96 PCM channels per frame). if a once uses fixed slots in a frame, these are considered for it as reserved until the releases them expressly (implicit reservation). unused synchronous slots of the frame are assigned on request to any. Ring and management also are similar to IEEE 80.5, additionally a function for deviating traffic to the protection ring is included. Page 7 Page 8 Data frames with DDI The data frames are similar to those used in the token ring format: Conclusion: Local Area Networks 8 /6 /6 Up to 80 Preamble DA SA Data CS rame Control (C) Start Delimiter (SD) End Delimiter (ED) rame Status Thepreamble is used for the synchronization as well as for the preparation of the s to a following transmission Start and end delimiter are being used for marking the frame rame control specifies the type of the frame: data, control, synchronously/asynchronously, Here, also several tokens are differentiated for the possible traffic types. rame status contains confirmation bits as in IEEE 80.5 Addresses and the CS are as in IEEE 80.5 yte Token Preamble S D C E D Page 9 Three main approaches: Ethernet for networks sporadic, bursty traffic Token us for networks with a few sending s having timing guarantees Token Ring for networks with many s having timing guarantees. Also suited for MANs Today s trend: Ring networks (DDI) still in use in older MANs, no longer used in the LAN area ield busses still in use as field busses, but Ethernet variants take over the market Everything tends to Ethernet Page 0 Also RWTH is Ethernet-based Also RWTH is Ethernet-based Page Page One Step up: Germany Europe Router 0 Git/s, Git/s, Git/s 6 Mit/s Connection router of RWTH to the so-called GWIN ackbone in Germany Rostock Kiel Global Upstream Hamburg Oldenburg raunschweig Hannover Magdeburg erlin ielefeld Essen Göttingen Leipzig St. Augustin Marburg Ilmenau Dresden Aachen Würzburg rankfurt Erlangen GEANT Heidelberg Karlsruhe Regensburg Kaiserslautern Stuttgart Augsburg Garching Router in rankfurt is access node to the European network Géant urthermore in rankfurt and Hamburg: intercontinental connections Punkt-zu-Punkt-Verbindung Now: what techniques are used in such larger networks? Page Page
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