Transcript IP: Addresses and Forwarding

SONET:
Broadband Convergence at Layer 1
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
[email protected]
http://www.ecse.rpi.edu/Homepages/shivkuma
Based in part on slides of Nick McKeown (Stanford)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
1
Telephony: Multiplexing
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Telephone Trunks between central offices carry
hundreds of conversations: Can’t run thick bundles!
Send many calls on the same wire: multiplexing
Analog multiplexing
 bandlimit call to 3.4 KHz and frequency shift onto
higher bandwidth trunk
Digital multiplexing: convert voice to samples
 8000 samples/sec => call = 64 Kbps
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
2
Telephony: Multiplexing Hierarchy
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Pre-SONET:
 Telephone call: 64 kbps
 T1 line: 1.544 Mbps = 24 calls (aka DS1)
 T3 line: 45 Mbps = 28 T1 lines (aka DS3)
Multiplexing and de-multiplexing based upon strict
timing (synchronous)
 At higher rates, jitter is a problem
 Have to resort to bit-stuffing and complex
extraction => costly “plesiochronous” hierarchy
SONET developed for higher multiplexing aggregates
 Use of “pointers” like C to avoid bit-stuffing
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
3
Digital Telephony in 1984
DS1
M13
• Switches
• Leased Line
DS3
Fiber Optic
Transmission
Systems
M13
DS1
DS1 Cross
Connect
Fiber
M13
Central
Office
Central
Office
No Guaranteed
Timing
Synchronization
Key System Aspects:
• M13 Building Blocks
• Asynchronous Operation
• Electrical DS3 Signals
• Proprietary Fiber Systems
• Brute Force Cross Connect
• AT&T Network/Western
Electric Equipment
DS3
DS1
Central
Office
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
4
Digital Carrier Hierarchy (contd)
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Multiplexing trunk networks: called “carrier” systems (eg:
T-carrier):
 allowed fast addition of digital trunk capacity without
expensive layout of new cables
Time frames (125 us) and a per-frame bit in the T-carrier
for synchronization => TDM
 Each phone call (DS0) occupies same position in the
frame
Overhead bits: error control
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“robbed” bits in voice call for OAM information
Too many 0s => synch loss (max number = 15)
“yellow alarm”. 1s density etc => usable b/w = 7bits/frame => 56
kbps
Europe: E1; more streamlined framing & 2.048 Mbps
Variants: Concatenated T1, Un-channelized
(raw) T1
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
5
Digital Hierarchy (Contd)
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1980s: demand for bandwidth. But > T3s not available
except in proprietary form
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Public vs Private Networks:
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Fiber-optic interface for T3 was proprietary
Primitive online OAM&P capabilities (eg: robbed bits…)
Fewer operators: interoperability/mid-span meet not critical
Changed dramatically after 1984 deregulation!
Private: Customer operates n/w (eg: w/ private leased lines):
developed from PBX & SNA
Public: Provider operates n/w for subscribers
More public networks (eg: X.25) outside US
Drivers of SONET:
IBM SNA/mainframes => hub-and-spoke networking
 Increase of PCs => client-server & p2p computing => more
demands on long-distance trunks
 Polytechnic
T-carrier
evolution rate much slower than computing
trends
Shivkumar
Kalyanaraman
Rensselaer
Institute
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6
Digital Hierarchy (Contd)
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Digital streams organized as bytes (eg: voice samples,
data)
Byte interleaving: (eg: 24 DS0 -> DS1)
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service one byte from each input port into a transmission frame
Simple device: T1 mux a.k.a channel bank
Very convenient for processing, add-drop multiplexor (ADM) or
Digital Cross-connect System (DCS) functions (fig 3.8/3.10)
ADM/DCS does both mux (“add”) and demux (“drop”) functions
=> need to do this with minimal buffering, fast/scalable
processing
Bit-interleaving (eg: DS1 -> DS2 etc)
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Cant use buffers to mask jitter! => bit stuffing
Partly because high speed memory was costly then!
“Plesiochronous hierarchy” => harder to ADM/DCS because full
de-stuffing/de-multiplexing necessary before these functions
DS3s used to be muxed using proprietary optical methods (eg:
M13 mux): SONET solves all these problemsShivkumar Kalyanaraman
Rensselaer Polytechnic Institute
7
US Telephone Network Structure
(after 1984 divestiture)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
8
Post-AT&T Divestiture Dilemmas
• Switches
• Leased Line
• LAN Services
• Data Services
Different
Carriers,
Vendors
M13
DS1
Internal
DS3 Cross
Connect
Needs:
• Support Faster Fiber
• Support New Services
• Allow Other Topologies
• Standardize Redundancy
• Common OAM&P
• Scalable Cross Connect
Support
Other
Topologies,
Protect Fibers
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
9
The SONET Standards Process
Divestiture
CCITT Expresses
Interest in SONET
British and Japanese
Participation in T1X1
Exchange Carriers
Standards Associate (ECSA)
T1 Committee Formed
ANSI T1X1
Bellcore Proposed Approves
SONET Principles
Project
To ANSI T1X1
1984
1985
CCITT XVIII
Begins Study
Group
1986
SONET/SDH
Standards
Approved
CEPT Proposes
Merged ANSI/CCITT
Standard
1987
1988
SONET Concept Developed By Bellcore
US T1X1 Accepts
>400 Technical Proposals
Modifications
• Rate Discussions AT&T vs. Bellcore
(resolved w/ virtual tributary concept)
• International Changes For Byte/Bit ANSI Approves
SYNTRAN
Interleaving, Frames, Data Rates
• Phase I, II, III Separate APS, etc.
Shivkumar Kalyanaraman
• ITU’s
Rensselaer
PolytechnicSDH
Instituteinitiative…
10
SONET Standards Story
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SYNTRAN: pre-divestiture effort, no pointer concept.
SONET: primarily US (divestiture) driven
AT&T vs Bellcore debate: 146.432 Mbps vs 50.688 Mbps:
compromise at 49.94 Mbps
 Virtual tributary concept to transport DS-1 services
1986: CCITT (ITU) starts own effort (SDH)
June 1987: change SONET from bit-interleaved to byteinterleaved; and rate from 49.92 to 51.84 Mbps
Phased rollouts:
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1988 = Phase 1: signal level interoperability
Phase II: OAM&P functions: embedded channel & electrical I/f
specification, APS work initiated
Phase III: OSI network management adopted
Seamless worldwide connectivity (allowed Europe to
merge its E-hierarchy into SDH)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
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11
SONET: Achievements
1. Standard multiplexing using multiples of 51.84
Mbps (STS-1 and STS-N) as building blocks
 2. Optical signal standard for interconnecting
multiple vendor equipment
 3. Extensive OAM&P capabilities
 4. Multiplexing formats for existing digital signals
(DS1, DS2 etc)
 5. Supports ITU hierarchy (E1 etc)
 6. Accomodates other applications: B-ISDN etc
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Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
12
SONET Lingo
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OC-N: Optical carrier Nx51.84 Mbps
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STS-N: Synchronous Transport Signal (electronic
equivalent of OC)
Envelope: Payload + end-system overhead
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Approximate heuristic: bit rate = N/20 Gbps (eg: OC-48 => 48/20
= 2.4 Gbps)
Overhead percentage = 3.45% for all N (unlike PDH!)
OC signal is sent after scrambling to avoid long string of zeros
and ones to enable clock recovery
Synchronous payload envelope (SPE): 9 rows, 87 columns in
STS-1
Overhead: management OAM&P portion
Concatenation: “un-channelized” (envelope can carry
“super-rate” data payloads: eg: ATM): Eg: OC-3c
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Method of concatenation different from that of T-carrier
hierarchy…
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
13
SONET Multiplexing Possibilities
•Asynchronous
DS-3
•Virtual
Tributaries for
DS1 etc
•STS-3c for
CEPT-4 and BISDN
STS-1s are mutually synchronized irrespective of inputs
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
14
STS-1 Frame Format
90 Bytes
Or “Columns”
9
Rows
Small Rectangle =1 Byte
Two-dimensional frame representation (90 bytes x 9 bytes)…
Frame Transmission: Top Row First, Sent Left To Right
• Time-frame: 125 ms/Frame
• Frame Size & Rate:
810 Bytes/Frame * 8000 Frames/s * 8 b/byte= 51.84 Mbps
• For STS-3, only the number of columns changes (90x3 = 270)
STS = Synchronous Transport Signal
Rensselaer Polytechnic Institute
15
Shivkumar Kalyanaraman
STS-1 Headers
Section Overhead (SOH)
90 Bytes
Or “Columns”
9
Rows
Path Overhead (POH):
Line Overhead (LOH) Floating => can begin anywhere
Line + Section overhead = Transport Overhead (TOH)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
16
SONET Equipment Types
Path
Sections
PTE
Repeaters
• Section Termination (STE)
Line
SONET End
Device - I.e.
Telephony
Switch, Router
• Line Termination (LTE)
• Path Termination (PTE)
PTE
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
17
SONET Overhead Processing
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
18
Headers: Section Overhead (SOH)
Rcv
SOH
A1
=0xF6
B1
BIP-8
Xmt
SOH
A2
=0x28
J0/Z0
STS-ID
E1
Orderwire
F1
User
D1
D2
D3
Data Com Data Com Data Com
Section Overhead
• 9 Bytes Total
• Originated And Terminated By All
Section Devices (Regenerators,
Multiplexers, CPE)
• Other Fields Pass Unaffected
Selected Fields:
•A1,A2 - Framing Bytes
•BIP-8 - Bit Interleaved
Parity
• F1 User - Proprietary
OAM Management
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
19
Headers: Line Overhead (LOH)
H1
Pointer
Xmt
LOH
Xmt
SOH
Rcv
LOH
Rcv
SOH
Xmt
SOH
Rcv
SOH
B2
BIP-8
H2
H3
Pointer Pointer Act
K1
K2
APS
APS
D4
D5
D6
Data Com Data Com Data Com
D7
D8
D9
Data Com Data Com Data Com
D10
D11
D12
Data Com Data Com Data Com
S1
Sync
Line Overhead
• 18 Bytes Total
• Originated And Terminated By All
Line Devices (Multiplexers, CPE)
• LOH+SOH=TOH (Transport OH)
M0
REI
E1
Orderwire
Selected Fields:
•H1-3 - Payload Pointers
•K1, K2 - Automatic
Protection Switching
• D4-D12 - 576 kbps
OSI/CMIP
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
20
Floating Payload: SONET LOH Pointers
SPE is not frame-aligned: overlaps multiple frames!
Avoids buffer management complexity & artificial delays
Allows direct access to byte-synchronous lower-level signals
(eg: DS-1) with just one frame recovery procedure
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
21
SPE: Synchronous Payload Envelope
Synchronous Payload Envelope
• Contains POH + Data
• First Byte Follows First Byte Of POH
• Wraps In Subsequent Columns
• May Span Frames
• Up To 49.536 Mbps for Data:
•Enough for DS3
Defined Payloads
• Virtual Tributaries
(For DS1, DS2)
• DS3
• SMDS
• ATM
• PPP …
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
22
Headers: Path Overhead (POH)
PTE
PTE
STE
Frame N
Frame N+1
J1
Trace
B3
BIP-8
Frame N
Frame N+1
C2
Sig Label
Path Overhead
• H1,H2 fields of LOH points to
Beginning of POH
•POH Beginning Floats Within Frame
• 9 Bytes (1 Column) Spans Frames
• Originated And Terminated By All
Path Devices (I.e. CPE, Switches)
• End-to-end OAM support
G1
Path Stat
F2
User
H4
Indicator
Selected
fields:
•BIP-8 - Parity
• C2 - Payload
Type Indicator
• G1 - End End
Path Status
Z3
Growth
Z4
Growth
Z5
Tandem
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
23
STS-1 Headers: Putting it Together
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
24
Accommodating Jitter
Positive Stuff
Negative Stuff
• To Shorten/Lengthen Frame:
• Byte After H3 Ignored; Or H3 Holds Extra Byte
• H1, H2 Values Indicate Changes - Maximum Every 4 Frames
• Requires Close (Not Exact) Clock Synch Among Elements
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
25
Clock Synchronization
BITS
BITS
PTE
•Level
•Level
•Level
•Level
1: 10-11
2: 1.6x10-8
3: 4.6x10-6
4: 32x10-6
Primary
Reference
Building Integrated Timing System
• Hierarchical Clocking Distribution
• Normally All Synch’d To Stratum 1
(Can Be Cesium/Rubidium Clock)
• Dedicated Link Or Recovered
• Fallback To Higher Stratum In Failure
(Temperature Controlled Crystal)
Backup
Reference
BITS
PTE
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
26
STS-N Frame Format
90xN Bytes
Or “Columns”
N Individual STS-1 Frames
Composite Frames:
• Byte Interleaved STS-1’s
• Clock Rate = Nx51.84 Mbps
• 9 colns overhead
Examples
STS-1
51.84 Mbps
STS-3
155.520 Mbps
STS-12 622.080 Mbps
STS-48 2.48832 Gbps
STS-192 9.95323 Gbps
Multiple frame streams, w/ independent payload pointers
Note: header columns also interleaved
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
27
STS-N: Generic Frame Format
STS-N
STS-1
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
28
Example: STS-3 Frame Format
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
29
STS-Nc Frame Format
90xN Bytes
Or “Columns”
Transport Overhead: SOH+LOH
Concatenated mode:
• Same TOH Structure And Data Rates As STS-N
• Not All TOH Bytes Used
• First H1, H2 Point To POH
• Single Payload In Rest Of SPE
• Accommodates FDDI, E4, data
Current IP over SONET technologies use concatenated
mode: OC-3c (155 Mbps) to OC-192c (10 Gbps) rates
a.k.a “super-rate” payloads
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
30
Virtual Tributaries (Containers)
Opposite of STS-N: sub-multiplexing
 STS-1 is divided into 7 virtual tributary groups (12 columns ea),
which can be subdivided further
 VT groups are byte-interleaved to create a basic SONET SPE
 VT1.5: most popular quickly access T1 lines within the STS-1 frame
Shivkumar Kalyanaraman
 SDH
usesInstitute
the word “virtual containers” (VCs)
Rensselaer
Polytechnic
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31
Virtual Tributaries: Pointers
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VT payload (a.k.a VT SPE) floats inside the VT
One more level of pointer used to access it.
 Can access a T1 with just two pointer operations
 Very complex to do the same function in DS-3
 Eg: accessing DS0 within DS-3 requires FULL demultiplexing: a.k.a stacked multiplexing or muxmountains!
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
32
SONET Transmission Encoding
Electrical Transmission
Standard
• STS-1: B3ZS (BPV), 450’
• STS-3: Coded Mark
Inversion, 225’
• Useful Intra-Office
Connection
Scrambling
• Ensures Ones Density
• Does Not Include A1, A2, C1 Bytes
• Output Is NRZ Encoded
1+x6+x7
E O
OC-N Is Optical Carrier STS-N
Long Reach: 40 km
1310 or 1550 nm SM
Intermediate Reach: 15 km
1310 or 1550 nm SM
Short Reach:Long Reach 2 km
1310 nm MM
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
33
SONET Scrambling
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
34
Packet Over SONET (POS)
Special Data Scrambler
• 1+ x43 Polynomial
Standard PPP Encapsulation
• Protects Against Transmitted
• Magic Number Recommended
• No Address and Control Compression Frames Containing Synch Bytes
Or Insufficient Ones Density
• No Protocol Field Compression
PPP
FCS
Byte
Stuff
Scrambling
Standard CRC Computation
• OC3 May Use CRC-16
• Other Speeds Use CRC-32
SONET
Framing
SONET Framing
• OC3, OC12, OC48, OC192 Defined
• C2 Byte = 0x16 With Scrambling
• C2 Byte = oxCF Without (OC-3)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
35
Practical SONET Architectures
Today: multiple “stacked” rings over DWDM (different s)
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
36
SONET Network Elements
D+R
DS1s
TM
ADM
MN
MN
MN
MN
DCC
D+R
D+R
DS1s
Nonstandard, Functional Names
TM: Terminal Mux: (aka LTE: ends of pt-pt links)
ADM: Add-Drop Mux
DCC: Digital Cross Connect
(Wideband and Broadband)
MN: Matched Node
D+R: Drop and Repeat
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
37
Digital Cross Connects (DCS)
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Cross-connects thousands of streams under software
control (replaces patch panel)
Handles perf monitoring, PDH/SONET streams, and also
provides ADM functions
Grooming:
 Grouping traffic with similar destinations, QoS etc
 Muxing/extracting streams also
Narrow-/wide-/broad-band and optical crossconnects
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
38
Topology Building Blocks
ADM
DCC
ADM
ADM
ADM
2 Fiber Ring
DCC
Each Line Is
Full Duplex
ADM
ADM
ADM
DCC
Each Line Is
Full Duplex
ADM
ADM
ADM
4 Fiber Ring
DCC
Uni- vs. BiDirectional
ADM
ADM
All Traffic Runs Clockwise,
vs Either Way
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
39
APS
ADM
ADM
ADM
ADM
Line Protection Switching
Uses TOH
Trunk Application
Backup Capacity Is Idle
Supports 1:n, N=1-14
ADM
ADM
Path Protection Switching
Uses POH
Access Line Applications
Duplicate Traffic Sent On Protect
1+1
Automatic Protection Switching
• Line Or Path Based
• Revertive vs. Non-Revertive
• Mechanism For Intentional Cutover
• Restoration Times ~ 50 ms
• K1, K2 Bytes Signal Change
• Common Uses: 2 Fiber UPSR or ULSR,
4 Fiber BPSR
Shivkumar Kalyanaraman
Rensselaer Polytechnic Institute
40