Presentation is loading. Please wait.

Presentation is loading. Please wait.

SONET/SDH Yaakov (J) Stein Chief Scientist RAD Data Communications.

Similar presentations

Presentation on theme: "SONET/SDH Yaakov (J) Stein Chief Scientist RAD Data Communications."— Presentation transcript:

1 SONET/SDH Yaakov (J) Stein Chief Scientist RAD Data Communications

2 Y(J)S SONET Slide 2 Course Outline Background (analog telephony, TDM, PDH) SONET/SDH history and motivation Architecture (path, line, section) Rates and frame structure Payloads and mappings Protection and rings VCAT and LCAS Handling packet data

3 Y(J)S SONET Slide 3 Background

4 Y(J)S SONET Slide 4 The PSTN circa 1900 pair of copper wires “local loop” manual routing at local exchange office (CO) Analog voltage travels over copper wire end-to-end Voice signal arrives at destination severely attenuated and distorted Routing performed manually at exchanges office(s) Routing is expensive and lengthy operation Route is maintained for duration of call

5 Y(J)S SONET Slide 5 Telephony Multiplexing 1900: 25% of telephony revenues went to copper mines standard was 18 gauge, long distance even heavier two wires per loop to combat cross-talk needed method to place multiple conversations on a single trunk 1918: “Carrier system” (FDM) 5 conversations on single trunk later extended to 12 (group) still later supergroups (60), master groups (60)), … f channels 8 kHz 12 kHz 4 kHz 16 kHz 20 kHz

6 Y(J)S SONET Slide 6 The Digitalization of the PSTN Shannon (Bell Labs) proved that Digital communications is always better than Analog communications and the PSTN became digital Better means More efficient use of resources (e.g. more channels on trunks) Higher voice quality (less noise, less distortion) Added features After the invention of the transistor, in 1963 T-carrier system (TDM) 1 byte per sample – 8000 samples per second T1 = 24 conversations per trunk 2 groups per cable! t timeslots

7 Y(J)S SONET Slide 7 and switching became easier too Complexity increases rapidly with size Analog Crossbar switch Digital Cross-connect (DXC) processor t t 21543

8 Y(J)S SONET Slide 8 Optimized Telephony Routing Circuit switching (route is maintained for duration of call) Route “set-up” is an expensive operation, just as it was for manual switching Today, complex least cost routing algorithms are used Call duration consists of set-up, voice and tear-down phases

9 Y(J)S SONET Slide 9 The PSTN circa 1960 local loop subscriber line automatic routing through universal telephone network Analog voltages used throughout, but extensive Frequency Division Multiplexing Voice signal arrives at destination after amplification and filtering to 4 KHz Automatic routing Universal dial-tone Voltage and tone signaling Circuit switching (route is maintained for duration of call) trunks circuits

10 Y(J)S SONET Slide 10 The Present PSTN subscriber line Analog voltages and copper wire used only in “last mile”, but core designed to mimic original situation Voice signal filtered to 4 KHz at input to digital network Time Division Multiplexing of digital signals in the network Extensive use of fiber optic and wireless physical links T1/E1, PDH and SONET/SDH “synchronous” protocols Signaling can be channel/trunk associated or via separate network (SS7) Automatic routing Circuit switching (route is maintained for duration of call) Complex routing optimization algorithms (LP, Karmarkar, etc) PSTN Network class 5 switch tandem switch last mile

11 Y(J)S SONET Slide 11 TDM timing Time Domain Multiplexing relies on all channels (timeslots) having precisely the same timing (frequency and phase) In order to enforce this the TDM device itself frequently performs the digitization analog signals digital signals

12 Y(J)S SONET Slide 12 if the inputs are already digital If the TDM switch does not digitize the analog signals then there can be a problem the clocks used to digitize do not have identical frequencies we get byte slips! (well, actually, we can get bit slips first …) exaggerated pictorial example Numerical example: clock derived from 8000 Hz. quartz crystal typical crystal accuracy =  50 ppm So 2 crystals can differ by 100 ppm i.e. 0.8 samples / second So difference is 1 sample after 1 ¼ seconds component signals TDM

13 Y(J)S SONET Slide 13 The fix We must ensure that all the clocks have the same frequency Every telephony network has an accurate clock called a “stratum 1” or “Primary Reference Clock” All other clocks are directly or indirectly locked to it (master – slave) A TDM receiving device can lock onto the source clock based on the incoming data (FLL, PLL) For this to work, we must ensure that the data has enough transitions (special line coding, scrambling bits, etc.) 1 0 transitions no transitions

14 Y(J)S SONET Slide 14 Comparing clocks A clock is said to be isochronous (isos=equal, chronos=time) if its ticks are equally spaced in time 2 clocks are said to be synchronous (syn=same chronos=time) if they tick in time, i.e. have precisely the same frequency 2 clocks are said to be plesiochronous (plesio=near chronos=time) if they are nominally if the same frequency but are not locked

15 Y(J)S SONET Slide 15 PDH principle If we want yet higher rates, we can mux together TDM signals (tributaries) We could demux the TDM timeslots and directly remux them –but that is too complex The TDM inputs are already digital, so we must –insist that the mux provide clock to all tributaries (not always possible, may already be locked to a network) OR –somehow transport tributary with its own clock across a higher speed network with a different clock (without spoiling remote clock recovery)

16 Y(J)S SONET Slide 16 PDH hierarchies 64 kbps Mbps Mbps Mbps Mbps Mbps Mbps Mbps Mbps Mbps Mbps CEPT N.A. Japan level * 30 * 24 * 4 * 7 * 6 * 4 * 5 * 3 E1 E2 E3 E4 T1 T2 T3 T4 J1 J2 J3 J4

17 Y(J)S SONET Slide 17 Framing and overhead In addition to locking on to bit-rate we need to recognize the frame structure We identify frames by adding Frame Alignment Signal The FAS is part of the frame overhead (which also includes "C-bits", OAM, etc.) Each layer in PDH hierarchy adds its own overhead For example E1 – 2 overhead bytes per 32 bytes – overhead 6.25 % E2 – 4 E1s = Mbps out of 8.448Mbps so there is an additional Mbps = 3 % altogether 4*30*64 kbps = Mbps out of Mbps or 9.09% overhead What happens next ?

18 Y(J)S SONET Slide 18 PDH overhead Overhead always increases with data rate ! digital signal data rate (Mbps) voice channels overhead percentage T % T % T % T % E % E % E % E %

19 Y(J)S SONET Slide 19 OAM analog channels and 64 kbps digital channels do not have mechanisms to check signal validity and quality thus major faults could go undetected for long periods of time hard to characterize and localize faults when reported minor defects might be unnoticed indefinitely Solution is to add mechanisms based on overhead as PDH networks evolved, more and more overhead was dedicated to Operations, Administration and Maintenance (OAM) functions including: monitoring for valid signal defect reporting alarm indication/inhibition (AIS)

20 Y(J)S SONET Slide 20 PDH Justification In addition to FAS, PDH overhead includes justification control (C-bits) and justification opportunity “stuffing” (R-bits) Assume the tributary bitrate is B  T Positive justification payload is expected at highest bitrate B+T if the tributary rate is actually at the maximum bitrate then all payload and R bits are filled if the tributary rate is lower than the maximum then sometimes there are not enough incoming bits so the R-bits are not filled and C-bits indicate this Negative justification payload is expected at lowest bitrate B-T if the tributary rate is actually the minimum bitrate then payload space suffices if the tributary rate is higher than the minimum then sometimes there are not enough positions to accommodate so R-bits in the overhead are used and the C-bits indicate this Positive/Negative justification payload is expected at nominal bitrate B positive or negative justification is applied as required

21 Y(J)S SONET Slide 21 SONET/SDH motivation and history

22 Y(J)S SONET Slide 22 First step With the disvestiture of the US Bell system a new need arose MCI and NYNEX couldn’t directly interconnect optical trunks Interexchange Carrier Compatibility Forum requested T1 to solve problem Needed multivendor/ multioperator fiber-optic communications standard Three main tasks: Optical interfaces (wavelengths, power levels, etc) proposal submitted to T1X1 (Aug 1984) T1.106 standard on single mode optical interfaces (1988) Operations (OAM) system proposal submitted to T1M1 T1.119 standard Rates, formats, definition of network elements Bellcore ( Yau-Chau Ching and Rodney Boehm ) proposal (Feb 1985) proposed to T1X1 term SONET was coined T1.105 standard (1988)

23 Y(J)S SONET Slide 23 PDH limitations Rate limitations Copper interfaces defined Need to mux/demux hierarchy of levels (hard to pull out a single timeslot) Overhead percentage increases with rate At least three different systems (Europe, NA, Japan) –E 2.048, 8.448, , –T 1.544, 3.152, 6.312, , , –J 1.544, 3.152, 6.312, , , So a completely new mechanism was needed

24 Y(J)S SONET Slide 24 Idea behind SONET Synchronous Optical NETwork Designed for optical transport (high bitrate) Direct mapping of lower levels into higher ones Carry all PDH types in one universal hierarchy –ITU version = Synchronous Digital Hierarchy –different terminology but interoperable Overhead doesn’t increase with rate OAM designed-in from beginning

25 Y(J)S SONET Slide 25 Standardization ! The original Bellcore proposal: hierarchy of signals, all multiple of basic rate (50.688) basic rate about 50 Mbps to carry DS3 payload bit-oriented mux mechanisms to carry DS1, DS2, DS3 Many other proposals were merged into 1987 draft document (rate ) In summer of 1986 CCITT express interest in cooperation needed a rate of about 150 Mbps to carry E4 wanted byte oriented mux Initial compromise attempt byte mux US wanted 13 rows * 180 columns CEPT wanted 9 rows * 270 columns Compromise! US would use basic rate of Mbps, 9 rows * 90 columns CEPT would use three times that rate Mbps, 9 rows * 270 columns

26 Y(J)S SONET Slide 26 SONET/SDH architecture

27 Y(J)S SONET Slide 27 Layers SONET was designed with definite layering concepts Physical layer – optical fiber (linear or ring) –when exceed fiber reach – regenerators –regenerators are not mere amplifiers, –regenerators use their own overhead –fiber between regenerators called section (regenerator section) Line layer – link between SONET muxes (Add/Drop Multiplexers) –input and output at this level are Virtual Tributaries (VCs) –actually 2 layers lower order VC (for low bitrate payloads) higher order VC (for high bitrate payloads) Path layer – end-to-end path of client data (tributaries) –client data (payload) may be PDH ATM packet data

28 Y(J)S SONET Slide 28 SONET architecture SONET (SDH) has at 3 layers: path – end-to-end data connection, muxes tributary signals path section –there are STS paths + Virtual Tributary (VT) paths line – protected multiplexed SONET payload multiplex section section – physical link between adjacent elements regenerator section Each layer has its own overhead to support needed functionality SDH terminology Path Termination Path Termination Line Termination Line Termination Section Termination path line ADM regenerator section

29 Y(J)S SONET Slide 29 STS, OC, etc. A SONET signal is called a Synchronous Transport Signal The basic STS is STS-1, all others are multiples of it - STS-N The (optical) physical layer signal corresponding to an STS-N is an OC-N SONETOpticalrate STS-1OC M STS-3OC M STS-12OC M STS-48OC M STS-192OC M * 3 * 4

30 Y(J)S SONET Slide 30 rates and frame structure

31 Y(J)S SONET Slide 31 SONET / SDH frames Synchronous Transfer Signals are bit-signals (OC are optical) Like all TDM signals, there are framing bits at the beginning of the frame However, it is convenient to draw SONET/SDH signals as rectangles framing

32 Y(J)S SONET Slide 32 SONET STS-1 frame Each STS-1 frame is 90 columns * 9 rows = 810 bytes There are 8000 STS-1 frames per second so each byte represents 64 kbps (each column is 576 kbps) Thus the basic STS-1 rate is Mbps 90 columns 9 rows framing

33 Y(J)S SONET Slide 33 SDH STM-1 frame Synchronous Transport Modules are the bit-signals for SDH Each STM-1 frame is 270 columns * 9 rows = 2430 bytes There are 8000 STM-1 frames per second Thus the basic STM-1 rate is Mbps 3 times the STS-1 rate! 270 columns 9 rows …

34 Y(J)S SONET Slide 34 SONET/SDH rates STS-N has 90N columns STM-M corresponds to STS-N with N = 3M SDH rates increase by factors of 4 each time STS/STM signals can carry PDH tributaries, for example: STS-1 can carry 1 T3 or 28 T1s or 1 E3 or 21 E1s STM-1 can carry 3 E3s or 63 E1s or 3 T3s or 84 T1s SONETSDHcolumnsrate STS M STS-3STM M STS-12STM M STS-48STM M STS-192STM M

35 Y(J)S SONET Slide 35 SONET/SDH tributaries E3 and T3 are carried as Higher Order Paths (HOPs) E1 and T1 are carried as Lower Order Paths (LOPs) (the numbers are for direct mapping) SONETSDH T1 T3 E1 E3 E4 STS STS-3STM STS-12STM STS-48STM STS-192STM

36 Y(J)S SONET Slide 36 Synchronous Payload Envelope STS-1 frame structure 9 rows Transport Overhead TOH 6 rows 3 rows Section overhead is 3 rows * 3 columns = 9 bytes = 576 kbps framing, performance monitoring, management Line overhead is 6 rows * 3 columns = 18 bytes = 1152 kbps protection switching, line maintenance, mux/concat, SPE pointer SPE is 9 rows * 87 columns = 783 bytes = Mbps Similarly, STM-1 has 9 (different) columns of section+line overhead ! 90 columns 9 rows

37 Y(J)S SONET Slide 37 STM-1 frame structure Section Overhead SOH STM-1 has 9 (different) columns of transport overhead ! RS overhead is 3 rows * 9 columns Pointer overhead is 1 row * 9 columns MS overhead is 5 rows * 9 columns SPE is 9 rows * 261 columns … 270 columns RSOH MSOH

38 Y(J)S SONET Slide 38 Even higher rates 3 STS-1s can form an STS-3 4 STM-1s (STS-3s) can form an STM-4 (STS-12) 4 STM-4s (STS-12s) can form an STM-16 (STS-48) etc. for STM-N (STS-3N) The procedure is byte-interleaving

39 Y(J)S SONET Slide 39 Byte-interleaving...

40 Y(J)S SONET Slide 40 Scrambling SONET/SDH receivers recover clock based on incoming signal Insufficient number of 0-1 transitions causes degradation of clock performance In order to guarantee sufficient transitions, SONET/SDH employ a scrambler All data except first row of section overhead is scrambled Scrambler is 7 bit self-synchronizing X 7 + X Scrambler is initialized with ones A short scrambler is sufficient for voice data but NOT for data which may contain long stretches of zeros When sending data an additional payload scrambler is used modern standards use 43 bit X run continuously on ATM payload bytes (suspended for 5 bytes of cell tax) run continuously on HDLC payloads Z -43 XnXn Y n = X n + Y n-43

41 Y(J)S SONET Slide 41 STS-1 Overhead The STS-1 overhead consists of 3 rows of section overhead –frame sync (A1, A2) –section trace (J0) –error control (B1) –section orderwire (E1) –Embedded Operations Channel (Di) 6 rows of line overhead –pointer and pointer action (Hi) –error control (B2) –Automatic Protection Switching signaling (Ki) –Data Channel (Di) –Synchronization Status Message (S1) –Far End Block Error (M0) –line orderwire (E2) A1A2J0 B1E1F1 D1D2D3 H1H2H3 B2K1K2 D4D5D6 D7D8D9 D10D11D12 S1M0E2 section overhead line overhead

42 Y(J)S SONET Slide 42 STM-1 Overhead A1 A2 J0res B1mmE1mF1res D1mmD2mD3 B2 K1K2 D4D5D6 D7D8D9 D10D11D12 S1M1E2 RSOH MSOH SOH m – media dependent (defined for SONET radio) res – reserved for national use AU pointers

43 Y(J)S SONET Slide 43 A1, A2, J0 (section overhead) A1, A2 - framing bytes A1 = A2 = SONET/SDH framing always uses equal numbers of A1 and A2 bytes J0 - regenerator section trace (in early SONET - a counter called C1) enables receiver to be sure that the section connection is still OK enables identifying individual STS/STMs after muxing J0 goes through a 16 byte sequence MSBs are J0 framing (1000…00) Cs are CRC-7 of previous frame S are 15 7-bit characters section access point identifier SSSSSSS0 SSSSSSS0 C7C7 C6C6 C5C5 C4C4 C3C3 C2C2 C1C1 1 …

44 Y(J)S SONET Slide 44 B1, E1, F1, D1-3 (section overhead) B1 – Byte Interleaved Parity-8 byte even parity of bits of bytes of previous frame after scrambling only 1 BIT-8 for multiplexed STS/STM E1 – section orderwire 64 kbps voice link for technicians from regenerator to regenerator F1 – 64 kbps link for user purposes D1 + D2 + D3 – 192 kbps messaging channel used by section termination as Embedded Operations Channel (SONET) or Data Communications Channel (SDH)

45 Y(J)S SONET Slide 45 Pointers (line overhead) In SONET, pointers are considered part of line overhead For STS-1, H1+H2 is the pointer, H3 is the pointer action H1+H2 indicates the offset (in bytes) from H3 to the SPE (i.e. if 0 then J1 POH byte is immediately after H3 in the row) 4 MSBs are New Data Flag, 10 LSBs are actual offset value (0 – 782) When offset=522 the STS-1 SPE is in a single STS-1 frame In all other cases the SPE straddles two frames When offset is a multiple of 87, the SPE is rectangular To compensate for clock differences we have pointer justification When negative justification H3 carries the extra data When positive justification byte after H3 is stuffing byte

46 Y(J)S SONET Slide 46 SONET Justification If tributary rate is above nominal, negative justification is needed When less than 8 more bits than expected in buffer NDF is 0110 offset unchanged When 8 extra bits accumulate NDF is set to 1001 extra byte placed into H3 offset is decremented by 1 (byte) If tributary rate is below nominal, positive justification is needed When less than 8 fewer than expected bits in buffer NDF is 0110 offset unchanged When 8 missing bits NDF is set to 1001 byte after H3 is stuffing offset is incremented by 1 (byte) H1H2 extra … H1H2H3 stuff …

47 Y(J)S SONET Slide 47 B2, K1, K2, D4-D12 (line overhead) B2 – BIP-8 of line overhead + previous envelope (w/o scrambling) N B2s for muxed STM-N K1 and K2 are used for Automatic Protection Switching (see later) D4 – D12 are a 576 Kbps Data Communications Channel between multiplexers usually manufacturer specific OAM functions

48 Y(J)S SONET Slide 48 S1, M0, E2 (line overhead) S1 – Synchronization Status Message indicates stratum level (unknown, stratum 1, …, do not use) M0 – Far End Block Error indicates number of BIP violations detected E2 – line orderwire 64 kbps voice link for technicians from line mux to line mux

49 Y(J)S SONET Slide 49 Payloads and Mappings

50 Y(J)S SONET Slide 50 STS-1 HOP SPE structure We saw that the pointer the line overhead points to the STS path overhead POH (after re-arranging) POH is one column of 9 rows (9 bytes = 576 kbps)

51 Y(J)S SONET Slide 51 STS-1 HOP 1 column of SPE is POH 2 more (“fixed stuffing”) columns are reserved We are left with 84 columns = 756 bytes = Mbps for payload This is enough for a E3 (34.368M) or a T3 (44.736M)

52 Y(J)S SONET Slide 52 STS-1 Path overhead 1 column of overhead for path (576 Kbps) POH is responsible for –path type identification –path performance monitoring –status (including of mapped payloads) –virtual concatenation –path protection –trace J1 B3 C2 G1 F2 H4 F3 K3 N1 POH

53 Y(J)S SONET Slide 53 J1, B3, C2 (path overhead) J1 – path trace enables receiver to be sure that the path connection is still OK B3 – BIP-8 even bit parity of bytes (without scrambling) of previous payload C2 – path signal label identifies the payload type (examples in table) C2 (hex) Payload type 00unequipped 01nonspecific 02LOP (TUG) 04E3/T3 12E4 13ATM 16PoS – RFC LAPS X.85 1A10G Ethernet 1BGFP CFPoS - RFC1619

54 Y(J)S SONET Slide 54 G1, F2, H4, F3, K3, N1 (path overhead) G1 – path status conveys status and performance back to originator 4 MSBs are path FEBE, 1 bit RDI, 3 unused F2 and F3 – user specific communications H4 – used for LOP multiframe sync and VCAT (see later) K3 (4 MSBs) – path APS N1 – Tandem Connection Monitoring Messaging channel for tandem connections

55 Y(J)S SONET Slide 55 LOP To carry lower rate payloads, divide the 84 available columns into 7 * 12 interleaved columns, i.e. 7 Virtual Tributary (VT) Groups VT group is 12 columns of 9 rows, i.e. 108 bytes or Mbps VT group is composed of VT(s) there are different types of VT in order to carry different types of payload all VTs in VT group must be of the same type (no mixing) but different VT groups in same SPE can have different VT types A VT can have 3, 4, 6 or 12 columns VTGs

56 Y(J)S SONET Slide 56 SONET/SDH : VT/VC types VT/STSVC column rate payload VT 1.5VC DS1 (1.544) VT 2VC E1 (2.048) VT DS1C (3.152) VT 6VC DS2 (6.312) STS-1VC E3 (34.368) STS-1VC DS3 (44.736) STS-3cVC E4 ( ) LOP HOP standard PDH rates map efficiently into SONET/SDH ! 4 per group 3 per group 2 per group 1 per group

57 Y(J)S APS Slide 57 LO Path overhead LOP OH is responsible for timing, PM, REI, … LO Path APS signaling is 4 MSBs of byte K4 V5 J2 N2 K4 V1 pointer V2 pointer V3 pointer V4 pointer VC11 – 25B VC12 – 34B 125  sec 500  sec H4=XXXXXX00 H4=XXXXXX01 H4=XXXXXX10 H4=XXXXXX11 VC11 – 27B VC12 – 36B

58 Y(J)S SONET Slide 58 Payload capacity VT1.5/VC-11 has 3 columns = 27 bytes = Mbps but 2 bytes are used for overhead (V1/V2/V3/V4 and V5/J2/N2/K4) so actually only 25 bytes = 1.6 Mbps are available Similarly VT2/VC-12 has 4 columns = 36 bytes = Mbps but 2 bytes are used for overhead So actually only 34 bytes = Mbps are available

59 Y(J)S SONET Slide 59 LOP overhead V5 consists of BIP (2b) REI (1b) RFI (1b) Signal label (3b) (uneq, async, bit-sync, byte-sync, test, AIS) RDI (1b) J2 is path trace N2 is the network operator byte –may be used for LOP tandem connection monitoring (LO-TCM) K4 is for LO VCAT and LO APS

60 Y(J)S SONET Slide 60 SDH Containers Tributary payloads are not placed directly into SDH Payloads are placed (adapted) into containers The containers are made into virtual containers (by adding POH) Next, the pointer is used – the pointer + VC is a TU or AU Tributary Unit adapts a lower order VC to high order VC Administrative Unit adapts higher order VC to SDH TUs and AUs are grouped together until they are big enough We finally get an Administrative Unit Group To the AUG we add SOH to make the STM frame

61 Y(J)S SONET Slide 61 Formally … C-n n = 11, 12, 2, 3, 4 VC-n = POH + C-n TU-n = pointer + VC-n (n=11, 12, 2, 3) AU-n = pointer + VC-n (n=3,4) TUG = N * TU-n AUG = N * AU-n STM-N = SOH + AUG

62 Y(J)S SONET Slide 62 Multiplexing An AUG may contain a VC-4 with an E4 or it may contain 3 AU-3s each with a VC-3s with an E3 In the latter case, the AU pointer points to the AUG and inside the AUG are 3 pointers to the AU-3s J1 B3 C2 G1 F2 H4 F3 K3 N1 H1 H2 H3

63 Y(J)S SONET Slide 63 More multiplexing Similarly, we can hierarchically build complex structures Lower rate STMs can be combined into higher rate STMs AUGs can be combined into STMs AUs can be combined into AUGs TUGs can be combined into high order VCs Lower rate TUs can be combined into TUGs etc. But only certain combinations are allowed by standards

64 Y(J)S SONET Slide 64 All SDH mappings STM-N AU-3VC-3C3 VC-3TU-3TUG-3 C-4VC-4AU-4AUG … C2 C12 C11 TUG-2VC-2TU-2 VC-12TU-12 VC-11TU-11 STM-0 ATM M E M ATM 1.6 M ATM M ATM M ATM 6.874M E M T M T M E M T M * 3 *7*7 *7*7 * 4 * 3

65 Y(J)S SONET Slide 65 All SONET mappings STS-N STS-3 SPE STS-3c STS-1 VT6 SPE VT2 SPE VT1.5 SPE VT6 VT-2 VT1.5 ATM M E M ATM 1.6 M ATM M ATM M ATM 6.874M E M T M T M E M T M *N*N STS-1 SPE VTG *7*7 pointer processing * 3 * 4

66 Y(J)S SONET Slide 66 Tributary mapping types When mapping tributaries into VCs, PDH-like bit-stuffing is used For E1 and T1 there are several options Asynchronous mapping (framing-agnostic) Bit synchronous mapping Byte synchronous mapping (time-slot aligned) E4 into VC-4, E3/T3 into VC-3 are always asynchronous T1 into VC-11 may be any of the 3 (in byte synchronous the framing bit is placed in the VC overhead) E1 into VC-12 may be asynchronous or byte synchronous

67 Y(J)S SONET Slide 67 WAN-PHY (10 GbE in STM-64) There is a special case where the bit-rates work out relatively well GbE 10GBASE-R (64B/66B coding) can be directly mapped into a STM-64 (with contiguous concatenation - see later) without need for GFP MAC creates "stretched InterPacket Gap" to compensate for rate being < 10G This is the fastest connection commonly used for Internet traffic Complication: SDH clock accuracy is  4.6 ppm, GbE accuracy is  20 ppm 64*(270-9) = columns J1 63 columns of fixed stuff 10GBASE-W Clause 50

68 Y(J)S SONET Slide 68 Protection and Rings

69 Y(J)S SONET Slide 69 What is protection ? SONET/SDH need to be highly reliable (five nines) Down-time should be minimal (less than 50 msec) So systems must repair themselves (no time for manual intervention) Upon detection of a failure (dLOS, dLOF, high BER) the network must reroute traffic (protection switching) from working channel to protection channel The Network Element that detects the failure (tail-end NE) initiates the protection switching The head-end NE must change forwarding or to send duplicate traffic Protection switching is unidirectional Protection switching may be revertive (automatically revert to working channel) head-end NE tail-end NE working channel protection channel

70 Y(J)S SONET Slide 70 How does it work? Head-end and tail-end NEs have bridges (muxes) Head-end and tail-end NEs maintain bidirectional signaling channel Signaling is contained in K1 and K2 bytes of protection channel K1 – tail-end status and requests K2 – head-end status head-end bridge tail-end bridge working channel protection channelsignaling channel

71 Y(J)S SONET Slide 71 Linear 1+1 protection Simplest form of protection Can be at OC-n level (different physical fibers) or at STM/VC level (called SubNetwork Connection Protection) or end-to-end path (called trail protection) Head-end bridge always sends data on both channels Tail-end chooses channel to use based on BER, dLOS, etc. No need for signaling If non-revertive there is no distinction between working and protection channels BW utilization is 50% channel A channel B

72 Y(J)S SONET Slide 72 Linear 1:1 protection Head-end bridge usually sends data on working channel When tail-end detects failure it signals (using K1) to head-end Head-end then starts sending data over protection channel When not in use protection channel can be used for (discounted) extra traffic (pre-emptible unprotected traffic) May be at any layer (only OC-n level protects against fiber cuts) working channel protection channel extra traffic

73 Y(J)S SONET Slide 73 Linear 1:N protection In order to save BW we allocate 1 protection channel for every N working channels N limited to 14 4 bits in K1 byte from tail-end to head-end –0 protection channel –1-14 working channels –15 extra traffic channel working channels protection channel

74 Y(J)S SONET Slide 74 Two fiber vs. Four-fiber rings Ring based protection is popular in North America (100K+ rings) Full protection against physical fiber cuts Simpler and less expensive than mesh topologies Protection at line (multiplexed section) or path layer Four-fiber rings fully redundant at OC level can support bidirectional routing at line layer Two-fiber rings support unidirectional routing at line layer 2 fibers in opposite directions

75 Y(J)S SONET Slide 75 Unidirectional vs. bidirectional Unidirectional routing working channel B-A same direction (e.g. clockwise) as A-B management simplicity: A-B and B-A can occupy same timeslots Inefficient: waste in ring BW and excessive delay in one direction Bidirectional routing A-B and B-1 are opposite in direction both using shortest route spatial reuse: timeslots can be reused in other sections A B A-B B-A A B A-B C B-C C-B

76 Y(J)S SONET Slide 76 UPSR vs. BLSR (MS-SPRing) Of all the possible combinations, only a few are in use Unidirectional Path Switched Rings protects tributaries extension of 1+1 to ring topology Bidirectional Line Switched Rings (two-fiber and four-fiber versions) called Multiplex Section Shared Protection Ring in SDH simultaneously protects all tributaries in STM extension of 1:1 to ring topology Path switching Line switching Two-fiber Four-fiber Unidirectional Bidirectional UPSR BLSR

77 Y(J)S SONET Slide 77 UPSR Working channel is in one direction protection channel in the opposite direction All traffic is added in both directions decision as to which to use at drop point (no signaling) Normally non-revertive, so effective two diversity paths Good match for access networks 1 access resilient ring less expensive than fiber pair per customer Inefficient for core networks no spatial reuse every signal in every span in both directions node needs to continuously monitor every tributary to be dropped

78 Y(J)S SONET Slide 78 BLSR Switch at line level – less monitoring When failure detected tail-end NE signals head-end NE Works for unidirectional/bidirectional fiber cuts, and NE failures Two-fiber version half of OC-N capacity devoted to protection only half capacity available for traffic Four-fiber version full redundant OC-N devoted to protection twice as many NEs as compared to two-fiber Example recovery from unidirectional fiber cut

79 Y(J)S SONET Slide 79 VCAT and LCAS

80 Y(J)S SONET Slide 80 Concatenation Payloads that don’t fit into standard VT/VC sizes can be accommodated by concatenating of several VTs / VCs For example, 10 Mbps doesn’t fit into any VT or VC so w/o concatenation we need to put it into an STS-1 ( Mbps) the remaining Mbps can not be used We would like to be able to divide the 10 Mbps among 7 VT1.5/VC-11 s = 7 * = Mbps or 5 VT2/VC-12 s = 5 * = Mbps

81 Y(J)S SONET Slide 81 Concatenation (cont.) There are 2 ways to concatenate X VTs or VCs: Contiguous Concatenation (G ) –HOP – STS-Nc (SONET) or VC-4-Nc (SDH) or LOP – 1-7 VC-2-Nc into a VC-3 –since has to fit into SONET/SDH payload only STS-Nc : N=3 * 4 n or VC-4-Nc : N=4 n –components transported together and in-phase –requires support at intermediate network elements Virtual Concatenation (VCAT G ) –HOP – STS-1-Xv or STS-Nc-Xv (SONET) or VC-3/4-Xv (SDH) or LOP – VT-1.5/2/3/6-Xv (SONET) or VC-11/12/2-Xv (SDH) –HOP: X ≤ 256 LOP: X ≤ 64 (limitation due to bits in header) –payload split over multiple STSs / STMs –fragments may follow different routes –requires support only at path terminations –requires buffering and differential delay alignment

82 Y(J)S SONET Slide 82 Contiguous Concatenation: STS-3c 270 columns 9 rows … 9 columns of section and line overhead 3 columns of path overhead 258 columns of SPE STS columns 9 rows … 9 columns of section and line overhead 1 column of path overhead 260 columns of SPE STS-3c 258 columns * = Mbps 260 columns * = Mbps

83 Y(J)S SONET Slide 83 STS-N vs. STS-Nc Although both have raw rates of Mbps STS-3c has 2 more columns (1.152Mbps) available More generally, For STS-Nc gains (N-1) columns e.g. STS-12c gains 11 columns = 6.336Mbps vis a vis STS-12 STS-48c gains 47 columns = Mbps STS-192c gains 191 columns = Mbps ! However, an STS-Nc signal is not as easily separable when we want to add/drop component signals

84 Y(J)S SONET Slide 84 Virtual Concatenation VCAT is an inverse multiplexing mechanism (round-robin) VCAT members may travel along different routes in SONET/SDH network Intermediate network elements don’t need to know about VCAT (unlike contiguous concatenation that is handled by all intermediate nodes) … H4

85 Y(J)S SONET Slide 85 SDH virtually concatenated VCs So we have many permissible rates 1.600, 2.176, 3.200, 4.352, 4.800, 6.400, 6.528, 6.784, 8.000, … VCCapacity (Mbps)if all members in one VC VC-11-Xv1.600, 3.200, … 1.600X in VC-3 X ≤ 28 C ≤ in VC-4 X ≤ 64 C ≤ VC-12-Xv2.176, 4.352, … 2.176X in VC-3 X ≤ 21 C ≤ in VC-4 X ≤ 63 C ≤ VC-2-Xv6.784, , …, 6.784Xin VC-3 X ≤ 7 C ≤ in VC-4 X ≤ 21 C ≤

86 Y(J)S SONET Slide 86 SONET virtually concatenated VTs VTCapacity (Mbps)If all members in one STS VT1.5-Xv1.600, 3.200, … 1.600X in STS-1 X ≤ 28 C ≤ in STS-3c X ≤ 64 C ≤ VT2-Xv2.176, 4.352, … 2.176X in STS-1 X ≤ 21 C ≤ in STS-3c X ≤ 63 C ≤ VT3-Xv3.328, 6.656, … 3.328X in STS-1 X ≤ 14 C ≤ in STS-3c X ≤ 42 C ≤ VT6-Xv6.784, , … 6.784Xin STS-1 X ≤ 7 C ≤ in STS-3c X ≤ 21 C ≤ So we have many permissible rates 1.600, 2.176, 3.200, 3.328, 4.352, 4.800, 6.400, 6.528, 6.656, 6.784, …

87 Y(J)S SONET Slide 87 Efficiency comparison Using VCAT increases efficiency to close to 100% ! ratew/o VCATefficiencywith VCATefficiency 10STS-121% VT2-5v VC-12-5v 92% 100 STS-3c VC-4 67% STS-1-2v VC-3-2v 100% 1000STS-48c VC-4-16c 42%STS-3c-7v VC-4-7v 95%

88 Y(J)S SONET Slide 88 PDH VCAT Recently ITU-T G.7043 expanded VCAT to E1,T1,E3,T3 Enables bonding of up to 16 PDH signals to support higher rates Only bonding of like PDH signals allowed (e.g. can’t mix E1s and T1s) Multiframe is always per G.704/G.832 (e.g. T1 – ESF 24 frames, E1 16 frames) 1 byte per multiframe is VCAT overhead (SQ, MFI, MST, CRC) Supports LCAS (to be discussed next) TS0 1 st frame of 4 E1s VCAT overhead octet time each E1

89 Y(J)S SONET Slide 89 PDH VCAT overhead octet There is one VCAT overhead octet per multiframe, so net rate is T1: (24*24-1=) 575 data bytes per 3 ms. multiframe = kB/s E1: (16*30-1=) 495 data bytes per 2 ms multiframe = kB/s T3 and E3 can also be used We will show the overhead octet format later (when using LCAS, the overhead octet is called VLI) TS0 frames of an E1 VCAT overhead octet …

90 Y(J)S SONET Slide 90 Delay compensation 802.1ad Ethernet link aggregation cheats –each identifiable flow is restricted to one link –doesn’t work if single high-BW flow VCAT is completely general –works even with a single flow VCG members may travel over completely separate paths so the VCAT mechanism must compensate for differential delay Requirement for over ½ second compensation Must compensate to the bit level but since frames have Frame Alignment Signal the VCAT mechanism only needs to identify individual frames

91 Y(J)S SONET Slide 91 VCAT buffering Since VCAT components may take different paths At egress the members are no longer in the proper temporal relationship VCAT path termination function buffers members and outputs in proper order (relying on POH sequencing) (up to 512 ms of differential delay can be tolerated) VCAT defines a multiframe to enable delay compensation –length of multiframe determines delay that can be accommodated H4 byte in member’s POH contains : sequence indicator (identifies component) (number of bits limits X) MFI multiframe indicator (multiframe sequencing to find differential delay)

92 Y(J)S SONET Slide 92 Multiframes and superframes Here is how we compensate for 512 ms of differential delay 512 ms corresponds to a superframe is 4096 TDM frames (4096*0.125m=512m) For HOP SDH VCAT and PDH VCAT (H4 byte or PDH VCAT overhead) The basic multiframe is 16 frames So we need 256 multiframes in a superframe (256*16=4096) The MultiFrame Indicator is divided into two parts: MFI1 (4 bits) appears once per frame –and counts from 0 to 15 to sequence the multiframe MFI2 (8bits) appears once per multiframe –and counts from 0 to 255 For LOP SDH (bit 2 of K4 byte) –a 32 bit frame is built and a 5-bit MFI is dedicated –32 multiframes of 16 ms give the needed 512 ms

93 Y(J)S SONET Slide 93 L ink C apacity A djustment S cheme LCAS is defined in G.7042 (also numbered Y.1305) LCAS extends VCAT by allowing dynamic BW changes LCAS is a protocol for dynamic adding/removing of VCAT members –hitless BW modification –similar to Link Aggregation Control Protocol for Ethernet links LCAS is not a “control plane” or “management” protocol –it doesn’t allocate the members –still need control protocols to perform actual allocation LCAS is a “handshake” protocol –it enables the path ends to negotiate the additional / deletion –it guarantees that there will be no loss of data during change –it can determine that a proposed member is ill suited –it allows automatic removal of faulty member

94 Y(J)S SONET Slide 94 LCAS – how does it work? LCAS is unidirectional (for symmetric BW need to perform twice) LCAS functions can be initiated by source or sink LCAS assumes that all VCG members are error-free –LCAS messages are CRC protected LCAS messages are sent in advance –sink processes messages after differential compensation –message describes link state at time of next message –receiver can switch to new configuration in time LCAS messages are in the upper nibble of –H4 byte for HOS SONET/SDH –K4 byte for LOS SONET/SDH –VCAT overhead octet for PDH – VCAT and LCAS Information LCAS messages employ redundancy –messages from source to sink are member specific –messages from sink to source are replicated J1 B3 C2 G1 F2 H4 F3 K3 N1 POH

95 Y(J)S SONET Slide 95 LCAS control messages LCAS adds fields to the basic VCAT ones Fields in messages from source to sink: –MFI MultiFrame Indicator –SQ SeQuence indicator (member ID inside VCAT group) –CTRL ConTRoL (IDLE, being ADDed, NORMal, End of Sequence, Do Not Use) –GID Group Identification (identifies VCAT group) Fields in messages from sink to source (identical in all members) : –MST Member Status (1 bit for each VCG member) –RS-Ack ReSequence Acknowledgement Fields in both directions –CRC Cyclic Redundancy Code The precise format depends on the VCAT type (H4, K4, PDH) Note: for H4 format SQ is 8 bits, so up to 256 VCG members for PDH SQ is only 4 bits, so up to 16 VCG members

96 Y(J)S SONET Slide 96 H4 format MFI2 bits MFI2 bits CTRL GID CRC-8 bits CRC-8 bits MST bits more MST bits RS-ACK SQ bits SQ bits frame multiframe MFI1 reserved fields

97 Y(J)S SONET Slide 97 H4 format – some comments CRC-8 (when using K4 it is CRC-3) –covers the previous 14 frames (not sync’ed on multiframe) –polynomial x 8 + x 2 + x + 1 MST –each VCG member carries the status of all members –so we need 256 bits of member status –this is done by muxing MST bits –there are MST bits per multiframe –and 32 multiframes in an MST multiframe –no special sequencing, just MFI2 multiframe mod 32 GID –single bit indentifier –all members of VCG share the same bit –cycles through LFSR sequence –different VCGs use different phase offsets of sequence

98 Y(J)S SONET Slide 98 LCAS – adding a member (1) When more/less BW is needed, we need to add/remove VCAT members Adding/removing VCAT members first requires provisioning (management) LCAS handles member sequence numbers assignment LCAS ensures service is not disrupted Example: to add a 4 th member to group “1” Initial state: Step 1: NMS provisions new member source sends CTRL=IDLE for new member sink sends MST=FAIL for new member GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=NORM GID=g SQ=3 CTRL=EOS GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=NORM GID=g SQ=3 CTRL=EOS GID=g SQ=FF CTRL=IDLE

99 Y(J)S SONET Slide 99 LCAS – adding a member (2) Step 2: source sends CTRL=ADD and SQ sink sends MST=OK for new member if it has been provisioned if receiving new member OK if it is able to compensate for delay otherwise it will send MST=FAIL and source reports this to NMS Step 3: source sends CTRL=EOS for new member new member starts to carry traffic sink sends RS-ACK Note 1: several new members may be added at once Note 2: removing a member is similar Source puts CTRL=IDLE for member to be removed and stops using it All member sequence numbers must be adjusted GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=NORM GID=g SQ=3 CTRL=EOS GID=g SQ=4 CTRL=ADD GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=NORM GID=g SQ=3 CTRL=NORM GID=g SQ=4 CTRL=EOS

100 Y(J)S SONET Slide 100 LCAS – service preservation To preserve service integrity if sink detects a failure of a VCAT member LCAS can temporarily remove member (if service can tolerate BW reduction) Example: Initial state Step 1: sink sends MST=FAIL for member 2 source sends CTRL=DNU (special treatment if EoS) and ceases to use member 2 Note: if EoS fails, renumber to ensure EoS is active Step 2: sink sends MST=OK indicating defect is cleared source returns CTRL to NORM and starts using the member again Note: if NMS decides to permanently remove the member, proceed as in previous slide GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=NORM GID=g SQ=3 CTRL=NORM GID=g SQ=4 CTRL=EOS GID=g SQ=1 CTRL=NORM GID=g SQ=2 CTRL=DNU GID=g SQ=3 CTRL=NORM GID=g SQ=4 CTRL=EOS

101 Y(J)S SONET Slide 101 Handling Packet Data

102 Y(J)S SONET Slide 102 Packet over SONET Currently defined in RFC2615 (PPP over SONET) obsoletes RFC1619 SONET/SDH can provide a point-to-point byte-oriented full-duplex synchronous link PPP is ideal for data transport over such a link PoS uses PPP in HDLC framing to provide a byte-oriented interface to the SONET/SDH infrastructure POH signal label (C2) indicates PoS as C2=16 (C2=CF if no scrambler)

103 Y(J)S SONET Slide 103 PoS architecture PoS is based on PPP in HDLC framing Since SONET/SDH is byte oriented, byte stuffing is employed A special scrambler is used to protect SONET/SDH timing PoS operates on IP packets If IP is delivered over Ethernet –the Ethernet is terminated (frame removed) –Ethernet must be reconstituted at the far end –require routers at edges of SONET/SDH network IP PPP HDLC SONET/SDH

104 Y(J)S SONET Slide 104 PoS Details IP packet is encapsulated in PPP –default MTU is 1500 bytes –up to 64,000 bytes allowed if negotiated by PPP FCS is generated and appended PPP in HDLC framing with byte stuffing 43 bit scrambler is run over the SPE byte stream is placed octet-aligned in SPE –(e.g Mbps of STM-1) –HDLC frames may cross SPE boundaries

105 Y(J)S SONET Slide 105 POS problems PoS is BW efficient but POS has its disadvantages BW must be predetermined HDLC BW expansion and nondeterminacy BW allocation is tightly constrained by SONET/SDH capacities –e.g. GBE requires a full OC-48 pipe POS requires removing the Ethernet headers –so lose RPR, VLAN, 802.1p, multicasting, etc POS requires IP routers

106 Y(J)S SONET Slide 106 LAPS In 2001 ITU-T introduced protocols for transporting packets over SDH X.85 IP over SDH using LAPS X.86 Ethernet over LAPS Built on series of ITU “LAPx” HDLC-based protocols Use ISO HDLC format Implement connectionless byte-oriented protocols over SDH X.85 is very close to (but not quite) IETF PoS

107 Y(J)S SONET Slide 107 GFP architecture A new approach, not based on HDLC Defined in ITU-T G.7041 (also numbered Y.1303) originally developed in T1X1 to fix ATM limitations (like ATM) uses HEC protected frames instead of HDLC Client may be PDU-oriented (Ethernet MAC, IP) or block-oriented (GBE, fiber channel) GFP frames –are octet aligned –contain at most 65,535 bytes –consist of a header + payload area Any idle time between GFP frames is filled with GFP idle frames EthernetIPother GFP – client specific part GFP – common part SDHOTNother HDLC

108 Y(J)S SONET Slide 108 GFP frame structure Every GFP frame has a 4-byte core header –2 byte Payload Length Indicator PLI = 01,2,3 are for control frames –2 byte core Header Error Control X 16 + X 12 + X –entire core header is XOR’ed with B6AB31E0 Idle GFP frames –have PLI=0 –have no payload area Non-idle GFP frames –have ≥ 4 bytes in payload area –the payload has its own header –2 payload modes : GFP-F and GFP-T –optionally protect payload with CRC-32 PLI (2B) cHEC (2B) payload header (4-64B) payload optional payload FCS (4B) core header payload area

109 Y(J)S SONET Slide 109 GFP payload header GFP payload header has –type (2B) –type HEC (CRC-16) –extension header (0-60B) either null or linear extension (payload type muxing) –extension HEC (CRC-16) type consists of –Payload Type Identifier (3b) PTI=000 for client data PTI=100 for client management (OAM dLOS, dLOF) –Payload FCS Indicator (1b) PFI=1 means there is a payload FCS –Extension Header ID (3b) –User Payload Identifier (8b) values for Ethernet, IP, PPP, FC, RPR, MPLS, etc. type (2B) tHEC (2B) extension header (0-60B) eHEC (2B) UPI (8b) PTI (3b) EXI (3b) PFI

110 Y(J)S SONET Slide 110 GFP modes GFP-F - frame mapped GFP Good for PDU-based protocols (Ethernet, IP, MPLS) or HDLC-based ones (PPP) Client PDU is placed in GFP payload field GFP-T – transparent GFP Good for protocols that exploit physical layer capabilities In particular 8B/10B line code used in fiber channel, GbE, FICON, ESCON, DVB, etc Were we to use GFP-F would lose control info, GFP-T is transparent to these codes Also, GFP-T needn’t wait for entire PDU to be received (adding delay!)

Download ppt "SONET/SDH Yaakov (J) Stein Chief Scientist RAD Data Communications."

Similar presentations

Ads by Google