Sonet fall2011
2 likes1,428 views
SONET/SDH is a standard developed for optical networks to transport telecommunication signals over optical fiber with synchronous timing. It uses synchronous transport signals and time division multiplexing to combine lower rate connections. SONET frames contain overhead bytes for management and a synchronous payload envelope containing client data. Higher rates are obtained by interleaving multiple lower rate frames. SONET provides advantages over older asynchronous standards through integral rate hierarchies and extensive performance monitoring capabilities.
Sonet fall2011
- 2. Op)cal Networks • Networks using op)cal fiber can be thought as client layers of op)cal layer – Backbone – Access – Metro • Backbone op)cal fiber client layers – SONET / SDH – Ethernet – Op)cal Transport Network
- 3. Other Client Layers -‐ Metro • Gigabit Ethernet • 10-Gigabit Ethernet • Fibre Channel (storage network) • Resilient Packet Ring (RPR) – packet traffic • SONET/SDH
- 4. SONET/SDH • SONET/SDH: first generation of optical networks deployed in backbone networks • Supports constant bit rate (CBR) connections • Multiplexes CBR connections into higher speed optical connections by using time division multiplexing • Originally designed for low speed voice and CBR connections, up to 51 Mb/s • Supports data network, packet traffic that can have link transmission rates in the tens of gigabits per second. • It provides carrier grade service of high availability
- 5. SONET Layers
- 6. SONET/SDH • Synchronous Op)cal Network – Transmission and multiplexing standard for high-speed signals within the carrier infrastructure in North America • SDH (Synchronous Digital Hierarchy), has been adopted in Europe and Japan
- 7. SONET Timing hHp://people.seas.harvard.edu/~jones/cscie129/nu_lectures/lecture12/sonet/sonet.html
- 8. Synchroniza)on vs. Plesiochronous • Plesiochronous digital hierarchy (PDH) – Known as asynchronous digital hierarchy in North America – Used for multiplexing digital voice circuits • 4KHz Bandwidth • Sampled at 8KHz • Bit rate of 64 kbps (basic stream) • Higher speeds are achieved by multiple of basic stream • In North America the basic voice rate is called digital signal – n – E.g., DS0, DS1, • In Europe this hierarchy is labeled as E0, E1, E2, E3, & so on
- 9. • Each system has its own clock (asynchronous) – nominal clock – Difference in clock can generate serious synch. Issues • 20 ppm difference between clocks à 1.8 kbps bit rate difference – Bit stuffing is typically used to compensate for difference in transmission rates • Transmission rates are not exactly integral mul)ple of the basic rate (64 kbps) • DS1 (1.544 Mbps) > 24 x 64 kbps ! – In order to extract lower rate the en)re signal has to be demul)plexed – expensive! • Provides liHle/no management informa)on including performance monitoring • Offers liHle standards for reliability Plesiochronous -‐ Issues
- 10. SONET / SDH Standards -‐ Advantages • Higher bit rates are integral mul)ples of lower rates • All clocks are perfectly synchronized (via a master clock) • Incorporate extensive management informa)on, e.g., performance monitoring • Provides interoperability between different devices by different vendors • Fast restora)on )me (much longer in PDH)
- 11. SONET / SDH Mul)plexing • SONET basic rate is 51.84 Mbps – Called the synchronous transport signal level-1 (STS-1) – STS is an electrical signal – It uses scrambling (to avoid long runs of 1s and zeros) – Higher rate signals (STS-N) are obtained by interleaving N frames • No need for bit stuffing • Simple demultiplexing process • Optical interfaces of STS-N are labeled as OC-N
- 12. SONET Hierarchy
- 13. SONET Frame • SONET frame – Overhead bytes called transport overhead – Payload – STS payload is carried in synchronous payload envelope (SPE) • SPE contains addi)onal path overhead • SONET uses pointers to indicate the loca)on of the payload data within the frame – Clock phase differences can be compensated using pointer adjustments (no bit stuffing) • Pointer processing is complex!
- 14. Framing
- 15. SONET Frame • Lower-speed non-SONET streams below the STS-1 rate are mapped into virtual tributaries (VTs) – Four VT sizes – SDH uses Virtual Container (VC) to accommodate for lower speed signals • SONET allows mul)plexing lower-‐speed asynchronous streams into Virtual Tributary
- 16. SONET Concatena)on • An STS-‐Nc signal with a locked payload is also defined in the standards – The “c” stands for concatenated – N is the number of STS-‐1 payloads • The concatenated or locked payload implies that this signal cannot be demul)plexed into lower-‐speed streams • Example: 150 Mb/s client signal can be mapped into an STS-‐3c signal How do we use SONET to carry Gigabit Ethernet?
- 17. Virtual Concatena)on • Virtual Concatenation (VCAT) allows noncontiguous payloads to be combined as a single connection • Such a grouping is referred to as a virtual concatenation group (VCG) • The VCAT notation for SONET – STS-N -M v – N is the size of a member & M is the number of members in a VCG • Example: How do we carry GigabitE STS-‐3-‐7V (155 Mbps x 7) about 1.05 (excluding the overhead) – 5 percent overprovisioning!
- 18. SONET Layers TM: terminal mul)plexer (end-‐to-‐end) connec)on ADM: Add/drop mul)plexer • SONET layer consists of four sublayers – path, line, section, and physical layers • Physical layer interfaces – Different rates – Electrical / optical – Distance (code): • Intraoffice (short reach) – I • Short haul 15km/1310 or 40km/1550 - S • Long haul 40km/1310 or 80km/1550 (400-600 km with Amplifiers) - L • Very long haul 60km/1310 or 120km/1550 • ultra long haul 160km • Fiber type – Standard single-mode fiber (G.652) – Dispersion-shifted fiber (G.653) – Nonzero dispersion-shifted fiber (G.655) • The transmitter types – LEDs or multilongitudinal mode (MLM), single-longitudinal mode (SLM) distances Different Physical Interfaces for SDH (similar for SONET)
- 19. Physical Layer
- 20. SONET Elements TM: terminal mul)plexer (end-‐to-‐end) connec)on ADM: Add/drop mul)plexer DCS: Digital crossconnect LTE: Line Termina)ng Element UPSR: Unidirec)onal path-‐switched rings BLSR: Bidirec)onal line-‐switched rings (with 2 / 4 fibers) ADM Is connected to TM
- 21. SONET Elements TM: terminal mul)plexer (end-‐to-‐end) connec)on ADM: Add/drop mul)plexer DCS: Digital crossconnect LTE: Line Termina)ng Element UPSR: Unidirec)onal path-‐switched rings BLSR: Bidirec)onal line-‐switched rings (with 2 / 4 fibers) Traffics with the same des)na)ons are groomed together Unidirec)onal Ring ADM Is connected to TM
- 23. SONET Frame Structure • STS-‐1 frame is 125 usec (1/8000 sec/frame) • There are 810 bytes per frame – Transmission row-‐by-‐row, lem-‐to-‐right, MSB first
- 24. Frame Structure -‐ Overhead
- 25. Use of Pointers – Pointer H2 Line Overhead
- 26. Frame Structure • A/A2: Network elements use these bytes to determine the start of a new frame • G1 is Yellow alarm to upstream nodes • K2 (FERF) alarm for upstream node • APS indicating automatic switching
- 27. BIP-‐8 Errors • Monitoring BIPs – Bit interleaved parity – Even parity – Calculated for the previous frame X/Y = X applies to the first STS-‐N; Y is remaining
- 28. Calcula)ng BIP-‐8 • Calculated BIP-‐8 (B1) is based on the previous STS-‐N frame amer scrambling – Odd parity means there is an error • B2 is based on calcula)ng line overhead of the line overhead – checked by the line termina)ng equipment
- 29. Client Layers of Op)cal Fiber
- 30. SONET Protec)on • Chapter 9 -‐ up to 9.3
- 31. SONET Protec)on • Availability: A common requirement that the connec)on will be available 99.999% • Thus network has to be survivable – continue providing service in the presence of failures • Protection switching is the key technique used to ensure survivability – The term restoration to schemes where traffic is restored • There are many failures – Human errors / disasters / AHacks / etc. – Component failures – Link failures: • There are estimates that long-haul networks annually suffer 3 fiber cuts for every 1000 miles of fiber • For a large network of 30,000 miles of fiber cable, that would be 90 cuts per year
- 32. Protec)on Key Parameters • Detect failures • Protect against failures (single failures) • Restora)on )me (60 msec – including detec)on and restora)on) • Topology (Ring / Mesh) • Signaling
- 33. Basic Protec)on Concepts • Failures must be protected! • Failure types: – Single / mul)ple / double (a series of shared links can fail) • Failure example: – Node / Link (Fiber) / Components • Protec)on type – Shared – Dedicated • Scheme – Rever)ve – when shared protec)on is used – Non-‐rever)ve – when 1+1 is used
- 34. Protec)on Switching • Automa)c Protec)on Switching (ASP) • Unidirec)onal – ASP Required – Signaling is required • Bidirec)onal – No ASP is required Case b: Only affected direc)on is switched: -‐ Unidirec)onal Protec)on switching (RED is working) Case c: Bidirec)onal protec)on
- 35. Traffic Rou)ng Due to Protec)on Switching – how the traffic is being rerouted due to link failure Path Switching Span Switching Ring Switching (rerou)ng on a ring)
- 36. Protec)on Techniques 1+1 Protec)on / Simultaneous TX & RX) 1:1 Protec)on / Signaling is required To ac)vate the protec)on / traffic must be switched / The protec)on links can carry EXTRA traffic – low priority
- 37. Protec)on Schemes 1:N Protec)on / Shared Protec)on / Signaling is required / Typically, must be rever)ve!
- 38. SONET Rings and Self-‐Healing Rings • Unidirec)onal path-‐switched ring (UPSR) • 1+1 Protec)on • Two Fibers only • Unidirec)onal • Simultaneous traffic (clockwise and counter CW) • Path Layer Protec)on • Simple / requires no signaling • No node limita)on / no length limita)on Note: It is important that the traffics are moving in DIFFERENT direc)ons to protect against any node failure
- 39. Four Fiber Bidirec)onal Lines Switched Ring (BLSR/4) • Mainly, line protec)on • Traffic is on both direc)ons – CW and CCW • Max of 16 notes are supported • Max length is 1600 km • Supports span switching or ring switching (next slide)
- 40. SPAN / RING Switching in BLSR/4
- 41. Two-‐fiber bidirec)onal line-‐ switched Ring (BLSR/2) • k • Each link has half BW • Very complex – uses APS (K1/K2 bytes) • 1:1 Switching • Used for long haul • Very common • Efficient use of special capacity
- 42. Example: BLSR/2 is much more efficient than UPSR (2 fiber)
- 43. Node Failure
- 44. Lab
- 45. Framing Review
- 47. Framing Bytes
- 48. Connec)on Setup Pseudo-‐random bit sequences – max 14 consecu)ve zeros
- 49. References • hHp://www.cisco.com/en/US/tech/tk482/ tk607/ technologies_tech_note09186a0080094313.s html • hHp://www.op)cus.co.uk/pdf/WhitePaper-‐ Understanding_Error_Checking_Using_Parity_ Bytes.pdf