1 chapter 8 transport networks: advanced concepts m. pickavet and c. develder
TRANSCRIPT
1
CHAPTER 8 Transport Networks:
Advanced concepts
M. Pickavet and C. Develder
Transport networks:Advanced concepts 2
Outline
1. Network management and control1.1 Network management1.2 Network control1.3 Interaction
2. Network recovery3. Optical packet/burst switching
Transport networks:Advanced concepts 3
Monitor, account and control
the network activities and resources
TMN or Telecommunications Management Network
FCAPS : Fault managementConfiguration managementAccounting managementPerformance managementSecurity management
Network Management
Transport networks:Advanced concepts 4
Data plane
XC
XC
XC XC
XC
Mgmt plane
MIB
MIBMIB
MIB
MIB
Network Mgmt System
Network ElementMgmt Agent
TelecommunicationMgmt Network
OXC or DXC
Customer Premise Equipment
Circuit (e.g. lightpath)
Network Management
Transport networks:Advanced concepts 5
NMS
Via signalling channels(SDH overhead)
DXCLTE
LTE
LTE
LTE
matrix
hard
ware
AGENTPROCESS
MANAGINGPROCESS
managedobject
managedobject
managedobject
softw
are
MIB
MIB
Conceptual architecture
Transport networks:Advanced concepts 6
Network Management: Pros and contras
Well-standardised Mature Widely used in practice (legacy) Centralised:
Efficient Scalable ? Vulnerable
Reconfiguration: slow (e.g. months) Semi-permanent connections Dynamic IP traffic ?
Transport networks:Advanced concepts 7
Outline
1. Network management and control1.1 Network management1.2 Network control1.3 Interaction
2. Network recovery3. Optical packet/burst switching
Transport networks:Advanced concepts 8
Network Control
Data plane
XC
XC
XC XC
XC
Circuit
Control plane
User-NetworkInterface
Network-NetworkInterface
ConnectionController
Connection ControlInterface
Request Agent
Transport networks:Advanced concepts 9
ASTN and GMPLS
Automatically Switched Transport Network (ASTN) E.g. ASON (Aut. Sw. Optical Netw.) Based on distributed control plane
architecture Enables fast reconfiguration
Protocol: GMPLS (Generalised MPLS) Standardisation by IETF Idea: MPLS concepts transport network
layer (OTN, SDH, SONET, …)
Transport networks:Advanced concepts 10
5
7A
B
C
D
IP Payload
IP Header
MPLS Label
IN IF IN LABEL OUT IF OUT LABELA 2 D 3B 5 C 7B 9 D 7
GMPLS exampleIP/MPLS router
MPLS:
OXC
A
B
C
D
IN
OUT
IN -->
OUT
GMPLS-capable OXCGMPLS:
Transport networks:Advanced concepts 11
OXC
A
B
C
D
IN
OUT
IN -->
OUT
GMPLS in general
GMPLS-capable OXC
GMPLS also applicable to other scales/technologies OTN label = fiber, waveband, wavelength, … SDH label = time slot, …
ASTN/GMPLS = efficient BW utilisation ? Longer time scale variations (s, min, …): reconfiguration
possible Shorter time scale (ms, s, …):
still circuit switching
Transport networks:Advanced concepts 12
Outline
1. Network management and control1.1 Network management1.2 Network control1.3 Interaction
2. Network recovery3. Optical packet/burst switching
Transport networks:Advanced concepts 13
Management and Control
Control plane
Data plane
OXC
OXC
OXC OXC
OXC
Mgmt plane
MIB
MIBMIB
MIB
MIB
Transport networks:Advanced concepts 14
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 15
1988 : fire in small switch in Hinsdale (Illinois) 35000 residential lines disconnected
37000 trunk lines disconnected118000 long-distance lines failed(500000 residential and business users affected, normally calling 3.5 million times a day, O’Hare airport closed)
1988 : two fuses of 600A blown (Massachusetts) 35000 users disconnected for whole day
banks closed for security reasons1990 : failure in signaling network (SS7) 65 million connections lost over US1991 : 3 wrong lines of software (on a total of 2.1 million lines) 1 week no telephone connections between Washington, Los Angeles
and Pittsburg
Examples of network failures
Transport networks:Advanced concepts 16
Examples of network failures1995 : Hanshin Earthquake in Kobe (Japan) 7.2 on Richter Scale, 5379 people died, 34626 people injured
Transport networks:Advanced concepts 17
Illustration of the effects of a failure on the telephone network
affected infrastructure:• 193.000 circuits• 3.500 leased lines (14%)• 3.600 poles• 330 km aerial cable• 20 km buried cable• 2.600 manholes• 210 km cable conduit
number of call attempts per call after the disaster
Examples of network failures1995 : Hanshin Earthquake in Kobe (Japan)
Transport networks:Advanced concepts 18
Typical failure rates
Web server 104-106 1IP interface card 104-105 2IP router itself 104-106 2ATM switch 105-106 1SDH DXC 105-106 4SDH ADM 105-106 4OTN OXC 105-106 4OTN OADM 105-106 41 km cable 106-107 48
Equipment type MTBF (hours) MTTR (hours)
(1 year 104 hours)
time
TBF
TTR TTR TTR
TBFTBF TBF
TTR = time to repairTBF = time between failures
Statistics:MTTR = mean TTRMTBF = mean TBF
Avail. MTBF-MTTR MTBF
Transport networks:Advanced concepts 19
Example: pan-European network
Oslo
Stockholm
Copenhagen
Amsterdam
Dublin
London
Brussels
Paris
Madrid
Zurich
Milan
Berlin
Athens
BudapestVienna
Prague
Warsaw
Munich
Rome
Hamburg
Barcelona
BordeauxLyon
Frankfurt
Glasgow
Belgrade
Strasbourg
28 nodes 20000 km cable
Cable break: every 4 days (!)Node failure: every month
Transport networks:Advanced concepts 20
Need for recovery ?
Plain Old Telephone service 5Voice over IP 5Video telephony 5Video-conferencing 5Tele-working 4TV broadcast 4Distance learning 5Movies on demand 3News on demand 2Internet access 2Tele-shopping 2
Application Need for recovery
(5 = crucial, 1 = not needed)
streaming
traffic
elastictraffic
Transport networks:Advanced concepts 21
Network Operator
Defect Duration
Compensation
Ameritech >1 min/ month 1 month credit
AT&T 1-60 min
>9 hours
5% month tariff pay back
50% month tariff pay back
BellSouth >2.5 sec 1 month credit
Nynex >1 min/ month 1 month tariff pay back
Pacifi c Bell >2 hours 1 month credit
Examples of availability guarantee
Transport networks:Advanced concepts 22
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 23
Improving network availability (e.g.
99.999 %)
working path
More reliable equipment (safer design, more testing, …)
Duplicate vulnerable network elements Network recovery mechanisms:
RHE
RTE
recovered segment
recovery path
Transport networks:Advanced concepts 24
Essential failure scenarios
single link failure
single node failure
(traffic terminated in affected node can not be recovered)
Transport networks:Advanced concepts 25
Recovery mechanism: goals
Stability Scope of failure coverage Recovery time Backup capacity requirements Guaranteed bandwidth ? Additional delay and jitter Packet reordering or duplication ? State overhead Signaling requirements Scalability Recovery classes ?
Transport networks:Advanced concepts 26
Steps in recovery process
time
fault detection timehold-off time
fault notification timerecovery operation time
traffic recovery time
failurefault detected
recovery time
operationaloperational
Transport networks:Advanced concepts 27
Backup capacity: dedicated
working paths
recovery paths
channel 1
channel 2
A B C
D E F
G H I
Transport networks:Advanced concepts 28
Backup capacity: shared
one commonchannel
A B C
D E F
G H I
working paths
recovery paths
Transport networks:Advanced concepts 29
Backup capacity: dedicated shared
Dedicated:• More simple• Backup capacity usage less efficient
Shared:• More complex: check whether resource available higher recovery time• Backup capacity used more efficiently
Transport networks:Advanced concepts 30
Recovery paths: preplanned dynamic
Preplanned: for all accounted failure scenarios, path of recovery flow is calculated in advance
• Allows fast recovery• No flexibility for unaccounted failure scenarios• Can be shared or dedicated backup capacity
Dynamic: path is computed on the fly once the failure is detected
• Additional time needed to identify suitable recovery path• Can search for recovery of unaccounted failure scenarios
too• Leads typically to shared backup capacity
Transport networks:Advanced concepts 31
Protection vs. restoration
Protection: all signaling occurs before failure• No time needed for after-failure signaling fast
Restoration: part of signaling occurs after failure
• Typically shared backup capacity requires less capacity
Transport networks:Advanced concepts 32
Protection variants
1+1 protection: dedicated protection• Traffic is permanently duplicated• Signal selection at RTE
1:1 protection: dedicated protection with extra traffic
• Traffic only on one path• Other path if available: other traffic
1:N protection: shared protection with extra traffic• One backup entity for N working entities
M:N protection• M backup entities for N working entities
Transport networks:Advanced concepts 33
Recovered segment: local recovery
working path
recovery path
RTERTE RHERHE
working path
recovery path
working path
recovery path
RTERTE RHERHE
Transport networks:Advanced concepts 34
Recovered segment: global recovery
working path
recovery path
RTERTE RHERHE
working path
recovery path
RTERTE RHERHE
Transport networks:Advanced concepts 35
working path
Recovered segment: local global
Choose possible recovery paths if• local recovery ?• global recovery ?
Exercise
Transport networks:Advanced concepts 36
Recovered segment: local global
RTERHE RTERHE
Local recovery: nodes close to failure faster recovery
Local recovery: inefficient total paths
consuming more capacity
Slightly different failure coverage
Other state and signaling requirementsRTERHE RTERHE
Transport networks:Advanced concepts 37
Control of recovery mechanism
Centralisede.g. TMN-based
Distributed e.g. control plane based (IP, GMPLS)
Pros and contras:• Centralised: good overall network view• Centralised: typically less complex• Centralised: typically more efficient capacity usage• Centralised: central point vulnerable point on its own• Distributed: more scalable
Transport networks:Advanced concepts 38
Network topology: mesh ring
ring 1ring 2ring 3
working path
recovery paths
Transport networks:Advanced concepts 39
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples
2.3.1 Ring protection2.3.2 Mesh protection2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 40
(O)MS-SPRing
(O)ADM
Connection
Working Capacity
Protection/backup capacity
A B C D
H G F E
(Optical) Multiplex Section Shared Protection Ring
Transport networks:Advanced concepts 41
(O)MS-SPRing
A B C D
H G F E
(O)ADM
Connection
Connectionlooped back
Working Capacity
Protection/backup capacity
B C
B C+
Transport networks:Advanced concepts 42
(O)MS-DPRing
A B C D
H G F E
Situation without failure
Connection Working Capacity
Protection/backup capacity
ADM
(Optical) Multiplex Section Dedicated Protection Ring
Transport networks:Advanced concepts 43
(O)MS-DPRing
Connection
Connectionlooped back
Working Capacity
Protection/backup capacity
ADM
A B C D
H G F E
Situation in case of a link failure
Transport networks:Advanced concepts 44
SNCP Ring
BridgeA B C
DF E
SubNetwork Connection Protection Ring
Switch/Selector
Bridge
Switch/Selector
Transport networks:Advanced concepts 45
Ring interconnection
A
B
C
D
H
E
G
F
J
I
Single point of failure
Transport networks:Advanced concepts 46
Ring interconnection
A
B
C
D
H
E
G
F
J
I
Drop & continu
e
Drop & continu
e
Drop & continu
e
Drop & continu
e
Transport networks:Advanced concepts 47
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples
2.3.1 Ring protection2.3.2 Mesh protection2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 48
1+1 Multiplex Section Protection
Cable W: working STM-N signalCable B: backup STM-N signal
Bridge
Selector Bridge
Selector
Transport networks:Advanced concepts 49
1+1 Mesh SNCP
A
B C
D
EF
Transport networks:Advanced concepts 50
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples
2.3.1 Ring protection2.3.2 Mesh protection2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 51
Path restoration
Working path 2
Working path 1 Working path 1
Working path 2
Recoverypath 1
Recoverypath 1
Recoverypath 2
Recoverypath 2
Transport networks:Advanced concepts 52
Comparison of capacity requirements
0
5000
10000
15000
20000
25000
no protection 1+1 path
protection, link
disjoint
1+1 path
protection, node
disjoint
path restoration link restoration
# o
f re
quir
ed w
avel
engt
hs
back- up path
working path
Transport networks:Advanced concepts 53
Outline
1. Network management and control2. Network recovery
2.1 Network failures2.2 General (single-layer) recovery
concepts2.3 SDH & OTN examples2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:Advanced concepts 54
Why multilayer recovery: Example 1
client layer
server layer
a
b
c
d
A
B
C
D
E working path
recovery path
Transport networks:Advanced concepts 55
Why multilayer recovery: Example 2
client layer
server layer
Transport networks:Advanced concepts 56
Why multilayer recovery: general
Trade-offs:• Lower layers will not notice failures of higher layer equipment
recovery at higher layer needed • Higher layer equipment can get isolated by lower layer
equipment failure (see example 1) recovery at higher layer needed
• Escalation of root failure (see example 2) recovery at lower layer preferred
• Native traffic injected in lower layer recovery at lower layer needed
• Multilayer recovery is complex (design, monitoring, operation)
Key questions:• In which layer(s) recovery ?• Which recovery mechanisms ?• How to coordinate the recovery mechanisms in multiple layers
?
Transport networks:Advanced concepts 57
Multilayer recovery: uncoordinated
A
D
B
C
E
client layer
server layer
a
d
b
c
Client Layer primary path
Client Layer recovery path Server Layer recovery path
Transport networks:Advanced concepts 58
Multilayer recovery: bottom-up
A
D
B
C
E
client layer
server layer
ad
b
c
Server layer recovery failed
A
D
B
C
E
client layer
server layer
ad
b
c
Client Layer primary path
Client Layer recovery path
Server Layer recovery path
Phase 1: recovery action in server layer
Phase 2: recovery action in client layer
• Hold-off timer• Recovery token
Transport networks:Advanced concepts 59
Outline
1. Network management and control
2. Network recovery3. Optical packet/burst switching
3.1 Introduction3.2 Node architectures3.3 Contention resolution
Transport networks:Advanced concepts 60
Optical switching:• direct light from an
input port to an output port• possibly wavelength conversion
circuit-switching:• continuous bit-stream• pre-established light-paths• set-up: “manual” or dynamic
packet/burst switching• chunks of bits, encapsulated in packets• packet header determines forwarding• e.g. label switching, GMPLS based
Optical packet/burst switching
f f
cc b
a
d
b
e
c
f
OPS/OBS:packet/burst (at least payload) stays in optical domain
Transport networks:Advanced concepts 61
Packet format
fixed/variable duration: pro variable = no
fragmentation/reassembly, no padding, less header overhead
contra = long packets can block many short ones
slotted/unslotted operation: pro slotted = easier packet
scheduling (synchronous switching)
contra = cost of synchronisation components
1
2
unslotted, variable length
1
2
slotted, fixed length
1
2
slotted, variable lengthpadding
single packet
OPS:
OBS:
Transport networks:Advanced concepts 62
Header format
1
2
3
4
1
2
3
4
1
2
3
4
phase
intensity
out-of-band: orthogonal channel (e.g. DPSK)
out-of-band: dedicated wavelength;
position of header: in-band: header and payload are sent sequentially,
separated in time
Transport networks:Advanced concepts 63
Typical operation of OPS fixed-length packets, slotted operation header accompanies payload
• contains necessary information to make forwarding decision
each timeslot:• inspect packets at input ports• decide which packets can be forwarded without
collisions
switch is “memory-less”• no knowledge of packets scheduled in past is necessary
OPSnode
Transport networks:Advanced concepts 64
Typical operation of OBS variable packet lengths, unslotted operation header is sent Toffset before payload
• contains necessary information to make forwarding decision• functions as one-way reservation (allows timely configuration
of switch fabric)• offset decreases by header processing time per hop• priority mechanism possible
on arrival of header:• decide whether burst can be forwarded without collisions• make necessary resource reservations if burst is accepted
switch needs “memory”:• keep track of reservations made in past
OBSnode
Toffset -
Toffset
Transport networks:Advanced concepts 65
Outline
1. Network management and control
2. Network recovery3. Optical packet/burst switching
3.1 Introduction3.2 Node architectures3.3 Contention resolution
Transport networks:Advanced concepts 66
Functionality of an OPS/OBS node input interface:
• header extraction (straightforward if out-of-band)• synchronisation: detect beginning of packet/burst• in OPS: align packets
switching matrix: fast reconfig. (s or ns) crucial• MEMS too slow• SOAs or fast TWCs possible
output interface• e.g. regeneration of optical signal; header re-writing…
synchr.control
switchcontrol
headerrewriting
inputinterface
switching matrix
outputinterface
payload
header
Transport networks:Advanced concepts 67
Header processing
Electronical header processing• Optics for capacity & switching (payload)• Electronics for routing & forwarding (header)
Optical header processing• Avoids O-E-O conversions for headers• Limited optical processing functionalities
synchr.control
switchcontrol
headerrewriting
inputinterface
switching matrix
outputinterface
optical processing
Electronic or opticalprocessing
Transport networks:Advanced concepts 68
Outline
1. Network management and control
2. Network recovery3. Optical packet/burst switching
3.1 Introduction3.2 Node architectures3.3 Contention resolution
Transport networks:Advanced concepts 69
Problem and possible solutions
Problem:two or more packets contend for same resource: destined
for same outgoing port at the same time
Solutions:
contention
deflection routing wavelength conversion optical buffer (Fiber Delay Lines)
Transport networks:Advanced concepts 70
Problem and possible solutions
contention
deflection routing wavelength conversion optical buffer (Fiber Delay Lines)
Try to predict the performance:• network throughput• packet loss rate as total network load increases
(cf. traffic jams)
Exercise
Transport networks:Advanced concepts 71
What solution to choose?
Deflection:• packets are “stored” in network:• increases load, increases delay• only works for low loads
Wavelength conversion:• no packet storage• allows high network throughput, no
increased delay
Buffering:• local packet storage at nodes• small delay penalty
Conclusion: Use combination of wavelength conversion and buffers figures © Yao et al., Opticomm’00
netw
ork
th
rou
gh
pu
tpack
et
loss r
ate
load (packet arrival rate, pkt/s)
load (packet arrival rate, pkt/s)
Transport networks:Advanced concepts 72
Buffer architectures
feed-forward vs feed-back• feed-forward: input or
output buffering• feed-back: shared,
recirculating FDLs
single stage vs multiple stage
• multiple stages separated by switching elements
• e.g.: each stage different delay resolution (“units”, “tens”, “hundreds”…)
choice of FDL lengths in stage
D-1
10
...
feed-forward vs feed-back
single vs multiple stages
D-1
10
D-1
10
...
...
Transport networks:Advanced concepts 73
OPS/OBS: fixed vs increasing FDLs
1.E-07
1.E-05
1.E-03
1.E-01
0 8 16 24 32 40 48 56 64nr. buffer ports (B)
ParetoOnOff, incr ParetoOnOff, fix
GeoOnoff, incr GeoOnoff, fix
Poisson, incr Poisson, fix
sample results for fixed-length, slotted OPS
Increasing FDL lengths give far lower PLRs (order of magnitude or more)
“penalty”: reordering of packets, higher delays
1
B
…1
1
1
B
…
…
1
B
Pack
et
loss
rate
Transport networks:Advanced concepts 74
“Network Recovery: Protection and Restoration of Optical, SONET-SDH, IP, and MPLS” by JP Vasseur, M. Pickavet, P. Demeester (July 2004, Morgan Kaufmann, ISBN 0-12-715051)
“Node Architectures for Optical Packet and Burst Switching” by C. Develder, J. Cheyns, E. Van Breusegem, E. Baert, A. Ackaert, M. Pickavet, P. Demeester, Invited - Technical Digest of PS 2002, the 2002 International Topical Meeting on Photonics in Switching, ISBN 89-5519-085-9, 21-25 July 2002, Cheju Island, Korea , pp. 104-106)
References