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Updated 1/20021 SMDS Nirmala Shenoy Information technology Department Rochester Institute of Technology.

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Presentation on theme: "Updated 1/20021 SMDS Nirmala Shenoy Information technology Department Rochester Institute of Technology."— Presentation transcript:

1 updated 1/20021 SMDS Nirmala Shenoy Information technology Department Rochester Institute of Technology

2 updated 1/20022 SMDS Scope –DQDB operation –SMDS Architecture

3 updated 1/20023 DQDB Uses MAN protocol – hence first briefly into DQDB DQDB – Distributed Queue Dual Bus –2 communication channels –Each station connects to both bus –Queues to use each bus –Queues carry information about other stations

4 updated 1/20024 DQDB Architecture

5 updated 1/20025 DQDB Architecture –Bus B With respect to Station 3, Stn 1, and 2 are downstream Stn 4, 5 are upstream –Bus A With respect to Station 3, stn 4, 5 are down stream Stn 1, 2 are upstream

6 updated 1/20026 DQDB Operation – On Bus A, head of bus A generates slots of 53 bytes which goes down bus A –On Bus B, head of Bus B generates slots which go down bus B –Empty slot travels down the bus, till a station wanting to transmit, sends its 53 bytes

7 updated 1/20027 DQDB Operation – Bus A: Stn 3 can send to 1 and 2 –Bus B, stn 3 can send to stn 4 and 5 –Upstream Node monopolization –Station to reserve for slots if they want to communicate to downstream nodes –Reservation goes in direction opposite to the direction you want to send

8 updated 1/20028 DQDB Operation – To book a downstream slot in Bus A, use the slots passing by in Bus B to the head of bus A –All upstream nodes in Bus A see the reservation going by –Keep an account of the number of reservations that go by –On empty slots going downstream A, the upstream station let that many slots go by

9 updated 1/20029 DQDB Operation –Distributed Queues Queue A for Bus A Queue B for Bus B –Queues hold the booking for slots –Each station puts a token in the queue when it sees a request going by –When it wants to send, it will put its token in the queue

10 updated 1/200210 DQDB Operation –As empty slots go by –Tokens are removed for each empty slot –Till – this station token is at HoQ –Empty slot comes by and is taken by this station Ring configuration possible

11 updated 1/200211 DQDB DQDB layers –Physical –MAC layer 48 byte payload 5 byte header

12 updated 1/200212 DQDB DQDB MAC PDU –5 byte Header Access Address Type Priority CRC

13 updated 1/200213 DQDB Access field – 8 bits –Busy bit – slot is carrying data –Slot type – pkt transmission, isochronous transmission –Reserved bit –PSR – (Previous Slot Read) 2 bits – set to 0 once the destination stn has read –RQ – 3 bits – 8 levels of priority on request

14 updated 1/200214 DQDB Address Field –20 bit VCI Type field – 2 bits –payload type, user data, management data Priority field – Priority of the slot DQDB – self healing Determination of upstream and downstream stations

15 updated 1/200215 SMDS –Packet switched datagram service for high speed MAN traffic –Switched service – pay for time of usage –Networks use Router to connect to SMDS switches using DQDB SMDS Interface protocol - SIP

16 updated 1/200216 SMDS SMDS topology

17 updated 1/200217 SMDS SMDS - SIP Level 3 –Adds header and trailer –Header has sender and receiver address –Packet is segmented into 44 bytes –Each 44 byte is given 2 bytes header, 2 bytes trailer –2 byte header -

18 updated 1/200218 SMDS SMDS - SIP Level 3 –header –ST – 2 bits – segment type –4 bits sequence count –Message ID – 10 bits –Trailer 6 bit length indicator 10 bit crc

19 updated 1/200219 SMDS SMDS - SIP Level 2 – DQDB SIP level 1 – physical layer

20 updated 1/200220 SMDS Summary –Ease on geographic limits –Offers Switched services –Addresses high speed interconnectivity –End Systems are routers –Real-time? –Bulk data


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