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Fiber Optic based Networks

FDDISMDSSONET. Items that will be covered. All three (FDDI,SMDS,SONET) use fiber as the transport mediumFiber is immune to Electric interferenceRadio interferenceCross-talkFiber can travel much longer distances before needing to be amplified or regenerated.. Fiber-Based Network Overview. F

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Fiber Optic based Networks

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    1. Fiber Optic based Networks Kevin Andersen Tel 660 2/2/2006

    2. FDDI SMDS SONET

    3. All three (FDDI,SMDS,SONET) use fiber as the transport medium Fiber is immune to Electric interference Radio interference Cross-talk Fiber can travel much longer distances before needing to be amplified or regenerated.

    4. Fiber Distributed Data Interface (FDDI) Developed in mid-1980’s “High Speed” LAN backbone technology 100 Mbps Ring Circumference Limitation – 124 Miles Max Distance Between Nodes – 124 Miles Max Nodes Per Ring - 1000 Dual Rings

    5. Operates on the Physical and Media-Access portions of the OSI reference model. Provides connectivity between upper layer protocols such as TCP/IP and the media ,fiber optic cable.

    6. 2 independent rings First ring is primary data path Second ring remains idle and provides an alternate path in case of failure Rings transmit in opposite directions

    7. Single Attachment Station (SAS) Dual-Attachment Station (DAS) Singe-attached Concentrator (SAC) Dual-attached Concentrator (DAC)

    8. An SAS attaches to only one ring through a concentrator. If a Node is disconnected or powered off there will be no effect on the FDDI ring

    9. Has 2 ports, designated A and B Connects to 2 FDDI rings DAS will effect a ring if powered down or disconnected

    10. DAC is also known as a “concentrator”. Attaches to both the primary and secondary rings and ensures that the powering down of any SAS does not bring down the network.

    11. FDDI provides a number of fault-tolerant features. Dual-ring environment Implementation of the optical bypass switch Dual-homing

    12. If a station on the dual ring fails or is powered down, or if the cable is damaged, the dual ring automatically wraps back onto itself to create a single ring. The ring continues to function without performance impact during the wrap condition

    13. Used to prevent ring segmentation and eliminate failed stations from the ring. Uses optical mirrors to pass light from the ring to the DAS during normal operation.

    14. Critical Devices , such as routers and servers, are attached to the ring in two access points, concentrators. One link is configured as a primary, the other a backup If a link or concentrator failure occurs the second link automatically takes over

    15. FDDI- Dual Homing

    16. FDDI frame format is similar to Token Ring. Frame size can be as large as 4,500 bytes

    17. FDDI uses a token passing protocol to move data around the ring and second protocol based on timers. Scheme is designed for delay-sensitive, synchronous data. Each ring has its own clock Each station retimes and regenerates the packets. When the token is seized, the ring is made idle briefly while the packet is being setup

    18. FDDI – Timed Token Approach Rotation Time = time it takes a signal to propagate around the ring Token rotation Timer (TRT) = Times the period between receipts of tokens Pre-Negotiated Target Time (PTT) = Coordinated for the transmission Each node measures the TRT A node compares the TRT to the PTT .A node is allowed to transmit as long as its full transmission stream does not exceed the PTT If the token returns sooner than the PTT, there is a light load on the network. If the token return later than the PTT, there is a heavy load on the network; low priority traffic must then be deferred.

    19. FDDI equivalent over copper cabling. Security and reliability are degraded in CDDI. Copper wiring is easily tapped Copper wiring is not immune to Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) like fiber is.

    20. Switched Multi-megabit Data Services Speeds for 1-45 Mbps Well suited for “bursty” LAN traffic Designed for originations with 4 or more locations Not common in USA. Some support in Europe. Supports connection and connection-less services

    21. SMDS - OSI Operates at Layer 1, Physical, and MAC sub-layer of Layer 2, Data Link.

    22. SMDS - DQDB Dual Queue Dual Bus Consists of two unconnected and independent fiber-optic buses. All nodes are connected to the same communications channels Reservation system used to manage data transmission.

    23. SMDS – DQDB Structure Each bus transmit traffic in only one direction Each bus is independent of the other in the transfer of traffic Both buses run at the same speed A queue is maintained for each bus.

    24. SMDS - Bus

    25. SMDS – Request Counter The Request Counter (RQ) is used to determine when a router can transmit. A Node X determines that it wants to transmit on Bus A When the Node X is idle it counts the requests to transmit on Bus B Node Y , upstream of X, reserves three time slots Node X increments its RQ by three. Node X decreases RQ for each empty time slot it receives Node X is transmit when the counter equals 0

    26. SMDS – Request Counter

    27. SMDS- Location Discovery Since each bus only transmit in one direction a node must determine where the destination node is located This is done by reading the source address of each packet.

    28. SMDS – Location Discovery

    29. SMDS Interface Protocol (SIP) Provides a connectionless service that allows the SMDS router to access the Carrier’s SMDS network. SIP is subdivided into three level (SIP1,SIP2,SIP3). SIP1 operates at Layer 1 SIP2 & SIP3 operate at Layer 2 , MAC sub layer

    30. SMDS - SIP3 SIP3 PDU receives data passed from upper layers, places the payload into “info” field and passes the following to SIP2

    31. SMDS – SIP2 SIP2 receives data from SIP3 and segmented into uniformly sized (53-octets). SIP2 then passes the frames to SIP1

    32. SMDS – SIP1 SIP1 operates at the Physical layer Receives cells from SIP2 SIP1 is responsible for the Physical Layer Convergency Protocol (PLCP) sub-layers

    33. SMDS – Network Components To connect to an SMDS network the following is needed: Router which supports SIP SMDS CSU/DSU Subscriber Network Interface (SNI), a circuit back to the carrier’s equipment

    34. SMDS Addressing SMDS Address are 10-digits similar to conventional phone numbers. 4 bit address type Variable length E.164 address- based on the ISDN global number addressing.

    35. SMDS Addressing Type Code The type code in the address field indicates one of two codes: Unicast transmission – only one destination multicast transmission – Addressing an entire sub-group of nodes or locations.

    36. SMDS – Security Source Address validation – verifies the source address is valid for that SNI circuit. This helps prevent “spoofing”. Address Screening – Traffic is filtered to prevent unwanted traffic . Traffic is filtered by source address.

    37. SONET - Overview Synchronous Optical Network Timing and Sync Muxing STS Frame Format SONET Hierarchy Rings Wave Division Multiplexing

    38. What is SONET ? Very high speed optical transport (10+ Gbps) Based on TDM. Interfaces such as T1 and T3s are allocated time slots for the optical transmission. Flexible enough to allow a wide range of services (ATM, Frame Relay, FDDI, SMDS,IP)

    39. SONET Asynchronous / Synchronous Async traffic often requires bit stuffing to achieve the required bandwidth for multiplexing. Sync traffic requires that all nodes are clocked together to accurately decode 0’s and 1’s. A Stratum 1,2, or 3E clock is required for a SONET network.

    40. SONET - Add / Drop Multiplexer (ADM) ADM provides an interface between the high speed optical connections and the slower speed electrical interfaces (DS1,DS3, Ethernet) ADM do not disrupt other optical signals that do not terminate at this node. A low speed circuit (i.e. T1) can be directly accessed without multiple levels of demuxing.

    41. SONET – Digital Cross Connect Digital Cross Connect (DCS) provide a method of switching and interconnection circuits in a SONET network. Needed to convert an optical signal to a electrical interface. Needed to combined multiple slower Optical rates.

    42. SONET – Digital Cross Connect

    43. SONET – STS-1 Frame STS frame is the building block of SONET Total frame size is equal to 51.84 Mbps 27 bytes for Transport overhead (TOH) 9 bytes for Section overhead (SOH) 18 bytes for Line overhead (LOH) 783 bytes for Synchronous Payload Envelope (SPE) 9 bytes of SPE are for Path overhead (POH)

    44. STS – 1 Frame Diagram

    45. SONET - Overheads

    46. SONET – VT & SPE A SPE is the total payload for that STS frame. The SPE can carry a T-3 A VT is used to subset the SPE for smaller payloads. A VT can carry a T-1 as the payload. 28 VT are used to create a SPE.

    47. SONET – Optical Carrier Optical Carrier (OC) is used to specify the speed of transmission for digital signals on optical fibers.

    48. SONET OC / STS Transmission Rates OC1/STS1 – 51.84 Mbps OC3/STS3c – 155.52 Mbps OC12/STS12c – 622.08 Mbps OC48/STS48c – 2488.32 Mbps OC192/STS192c – 9953.28 Mbps OC256 – 1327.1 Mbps OC768 – 4000 Mbps

    50. SONET - Concatenated STS-1 Concatenation allows SONET to carry larger payloads by combining multiple STS frames together. An STS-3c is 9 rows x 270 column frame that carries 3 (interleaved) concatenated STS-1s. (~155 Mbps) Only first frames overhead is used. Other overheads are disregarded.

    51. SONET - Rings Types of Ring applications BLSR – Signal is transmitted around the ring in only one direction but can double back if a fault is detected. UPSR – Signal is transmitted around the ring in both directions simultaneously

    52. SONET - UPSR UPSR – Unidirectional Path Switched Ring

    53. SONET - BLSR BLSR – Bidirectional Line Switched Ring

    54. SONET – Connection with ATM SONET does not provide any method for prioritizing circuits. Once configured the circuits are static in size and do not change based on congestion. ATM can run on top of SONET to prioritize circuits and detect congestion.

    55. Synchronous Digital Hierarchy SDH is the international version of SONET. The basic building block is an STM-1 which is roughly the size of SONET’s STS-3.

    56. Wave Division Multiplexing If separate light waves are used, 32+ optical signals can be combined to maximize valuable fiber optic cable throughput.

    57. Fiber Optic Based Networks Any questions?

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