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CHAPTER 8
Transport Networks:
Advanced concepts
M. Pickavet and C. Develder
1
Outline
1. Network management and control
1.1 Network management
1.2 Network control
1.3 Interaction
2. Network recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 2
Network Management
Monitor, account and control
the network activities and resources
TMN or Telecommunications Management Network
FCAPS :
Fault management
Configuration management
Accounting management
Performance management
Security management
Transport networks:
Advanced concepts 3
Network Management
Telecommunication
Mgmt Network
MIB
MIB
MIB
MIB
Mgmt plane
Network Element
Mgmt Agent
MIB
Circuit (e.g. lightpath) XC
OXC or DXC
XC
XC
Data plane
Network Mgmt System
XC
XC
Transport networks:
Customer Premise Advanced
Equipment
concepts 4
Conceptual architecture
LTE
LTE
LTE
matrix
hardware
DXC
Via signalling channels
(SDH overhead)
NMS
LTE
MIB
managed
object
AGENT
PROCESS
managed
object
MIB
MANAGING
PROCESS
software
managed
object
Transport networks:
Advanced concepts 5
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 6
Outline
1. Network management and control
1.1 Network management
1.2 Network control
1.3 Interaction
2. Network recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 7
Network Control
Network-Network
Interface
User-Network
Interface
Connection
Controller
Request Agent
Connection Control
Interface
Control plane
XC
XC
XC
XC
XC
Data plane
Circuit
Transport networks:
Advanced concepts 8
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 9
GMPLS example
MPLS:
IP/MPLS router
IP Payload
IP Header
MPLS Label
5
A
C
B
D
7
IN IF IN LABEL OUT IF OUT LABEL
A
2
D
3
B
5
C
7
B
9
D
7
GMPLS:
GMPLS-capable OXC
A
C
OUT
IN
B
OXC
D
Transport networks:
Advanced concepts 10
GMPLS in general
 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
GMPLS-capable OXC
A
C
OUT
IN
B
OXC
D
Transport networks:
Advanced concepts 11
Outline
1. Network management and control
1.1 Network management
1.2 Network control
1.3 Interaction
2. Network recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 12
Management and Control
MIB
MIB
MIB
MIB
Mgmt plane
MIB
Control plane
OXC
OXC
OXC
Data plane
OXC
OXC
Transport networks:
Advanced concepts 13
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 14
Examples of network failures
1988 : fire in small switch in Hinsdale (Illinois)

35000 residential lines disconnected
37000 trunk lines disconnected
118000 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 reasons
1990 : failure in signaling network (SS7)

65 million connections lost over US

1 week no telephone connections between Washington, Los Angeles
and Pittsburg
1991 : 3 wrong lines of software (on a total of 2.1 million lines)
Transport networks:
Advanced concepts 15
Examples of network failures
1995 : Hanshin Earthquake in Kobe (Japan)

7.2 on Richter Scale, 5379 people died, 34626 people injured
Transport networks:
Advanced concepts 16
Examples of network failures
1995 : Hanshin Earthquake in Kobe (Japan)
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
Transport networks:
Advanced concepts 17
Typical failure rates
TBF
TTR
TTR
TTR
time
TTR = time to repair
TBF = time between failures
TBF
TBF
TBF
Statistics:
MTTR = mean TTR
MTBF = mean TBF
Avail. 
Equipment type
MTBF (hours)
MTTR (hours)
Web server
IP interface card
IP router itself
ATM switch
SDH DXC
SDH ADM
OTN OXC
OTN OADM
1 km cable
104-106
104-105
104-106
105-106
105-106
105-106
105-106
105-106
106-107
1
2
2
1
4
4
4
4
48
MTBF-MTTR
MTBF
(1 year  104 hours)
Transport networks:
Advanced concepts 18
Example: pan-European network
Oslo
Stockholm
Glasgow
Copenhagen
Dublin
28 nodes
20000 km cable
London
Berlin
Frankfurt
Brussels
Paris Strasbourg Munich
Cable break: every 4 days (!)
Node failure: every month
Warsaw
Amsterdam Hamburg
Zurich
Prague
Vienna
Lyon
Bordeaux
Belgrade
Milan
Madrid
Barcelona
Budapest
Rome
Athens
Transport networks:
Advanced concepts 19
Need for recovery ?
Application
streaming
traffic
elastic
traffic
Plain Old Telephone service
Voice over IP
Video telephony
Video-conferencing
Tele-working
TV broadcast
Distance learning
Movies on demand
News on demand
Internet access
Tele-shopping
Need for recovery
5
5
5
5
4
4
5
3
2
2
2
(5 = crucial,
1 = not needed)
Transport networks:
Advanced concepts 20
Examples of availability guarantee
Network
Operator
Defect
Duration
Compensation
Ameritech
>1 min/month
1 month credit
AT&T
1-60 min
5% month tariff
pay back
50% month tariff
pay back
>9 hours
BellSouth
>2.5 sec
1 month credit
Nynex
>1 min/month
1 month tariff pay
back
Pacific Bell
>2 hours
1 month credit
Transport networks:
Advanced concepts 21
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 22
Improving network availability
(e.g. 99.999 %)
 More reliable equipment (safer design, more testing, …)
 Duplicate vulnerable network elements
 Network recovery mechanisms:
RTE
working path
recovered segment
recovery path
RHE
Transport networks:
Advanced concepts 23
Essential failure scenarios
single link failure
single node failure
(traffic terminated in affected
node can not be recovered)
Transport networks:
Advanced concepts 24
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 25
Steps in recovery process
recovery time
failure
fault detected
time
operational
operational
traffic recovery time
recovery operation time
fault notification time
hold-off time
fault detection time
Transport networks:
Advanced concepts 26
Backup capacity: dedicated
A
B
C
channel 1
D
G
E
H
F
I
channel 2
working paths
recovery paths
Transport networks:
Advanced concepts 27
Backup capacity: shared
A
D
B
E
C
F
one common
channel
working paths
G
H
I
recovery paths
Transport networks:
Advanced concepts 28
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 29
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 30
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 31
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 32
Recovered segment: local recovery
Transport networks:
Advanced concepts 33
Recovered segment: global recovery
Transport networks:
Advanced concepts 34
Recovered segment: local  global
Exercise
working path
Choose possible recovery paths if
• local recovery ?
• global recovery ?
Transport networks:
Advanced concepts 35
Recovered segment: local  global
 Local recovery: nodes close to failure
 faster recovery
 Local recovery: inefficient
total paths
 consuming more capacity
 Slightly different failure
coverage
 Other state and signaling requirements Transport networks:
Advanced concepts 36
Control of recovery mechanism
 Centralised
e.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 37
Network topology: mesh  ring
working path
recovery paths
ring 1
ring 2
ring 3
Transport networks:
Advanced concepts 38
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.3.1 Ring protection
2.3.2 Mesh protection
2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 39
(O)MS-SPRing
(Optical) Multiplex Section Shared Protection Ring
(O)ADM
A
B
C
D
Connection
Working Capacity
Protection/backup capacity
H
G
F
E
Transport networks:
Advanced concepts 40
(O)MS-SPRing
B
B
C
+
C
(O)ADM
A
B
C
D
Connection
Connection
looped back
Working Capacity
Protection/backup capacity
H
G
F
E
Transport networks:
Advanced concepts 41
(O)MS-DPRing
(Optical) Multiplex Section Dedicated Protection Ring
A
B
C
D
Situation without failure
H
G
Connection
F
E
Working Capacity
Protection/backup capacity
ADM
Transport networks:
Advanced concepts 42
(O)MS-DPRing
A
B
C
D
Situation in case of a link failure
H
ADM
G
F
Connection
Working Capacity
Connection
looped back
Protection/backup capacity
E
Transport networks:
Advanced concepts 43
SNCP Ring
SubNetwork Connection Protection Ring
A
Bridge
B
C
Switch/
Selector
Switch/
Selector
F
E
Bridge
D
Transport networks:
Advanced concepts 44
Ring interconnection
Single point
of failure
B
G
C
H
A
F
D
E
I
J
Transport networks:
Advanced concepts 45
Ring interconnection
Drop &
continue
Drop &
continue
B
G
C
H
A
F
I
D
E
J
Drop &
continue
Drop &
continue
Transport networks:
Advanced concepts 46
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.3.1 Ring protection
2.3.2 Mesh protection
2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 47
1+1 Multiplex Section Protection
Selector
Bridge
Bridge
Cable W: working STM-N signal
Cable B: backup STM-N signal
Selector
Transport networks:
Advanced concepts 48
1+1 Mesh SNCP
F
E
A
D
B
C
Transport networks:
Advanced concepts 49
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.3.1 Ring protection
2.3.2 Mesh protection
2.3.3 Mesh restoration
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 50
Path restoration
Working path 1
Recovery
path 1
Recovery
path 2
Working path 2
Working path 1
Recovery
path 1
Recovery
path 2
Working path 2
Transport networks:
Advanced concepts 51
Comparison of capacity requirements
# of required wavelengths
25000
back-up path
working path
20000
15000
10000
5000
0
no protection
1+1 path
protection, link
1+1 path
protection, node
disjoint
disjoint
path restoration
link restoration
Transport networks:
Advanced concepts 52
Outline
1. Network management and control
2. Network recovery
2.1 Network failures
2.2 General (single-layer) recovery concepts
2.3 SDH & OTN examples
2.4 Multi-layer recovery
3. Optical packet/burst switching
Transport networks:
Advanced concepts 53
Why multilayer recovery: Example 1
b
a
d
c
client layer
B
D
A
E
server layer
C
working path
recovery path
Transport networks:
Advanced concepts 54
Why multilayer recovery: Example 2
client layer
server layer
Transport networks:
Advanced concepts 55
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 56
Multilayer recovery: uncoordinated
d
a
c
b
client layer
D
E
C
A
server layer
B
Client Layer primary path
Server Layer recovery path
Client Layer recovery path
Transport networks:
Advanced concepts 57
Multilayer recovery: bottom-up
Phase 1:
recovery action in server layer
Phase 2:
recovery action in client layer
d
a
c
client layer
a
D
b
D
E
C
A
B
c
client layer
b
E
server layer
d
Server layer
recovery failed
C
A
server layer
B
Client Layer primary path
Server Layer recovery path
Client Layer recovery path
• Hold-off timer
• Recovery token
Transport networks:
Advanced concepts 58
Outline
1. Network management and control
2. Network recovery
3. Optical packet/burst switching
3.1 Introduction
3.2 Node architectures
3.3 Contention resolution
Transport networks:
Advanced concepts 59
Optical packet/burst switching
 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
b
a
d
e
OPS/OBS:
c
f
f
f
Transport networks:
60
packet/burst (at least payload) stays in optical domain Advanced concepts
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
OBS: unslotted, variable length
single packet
1
2
padding
slotted, variable length
1
2
OPS:slotted, fixed length
Transport networks:
Advanced concepts 61
Header format
 position of header:
 in-band: header and payload are sent sequentially,
separated in time

out-of-band: dedicated wavelength;

out-of-band: orthogonal channel (e.g. DPSK)
phase
1
1
1
intensity
2
2
2
3
3
3
4
4
4
Transport networks:
Advanced concepts 62
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
OPS
node
Transport networks:
Advanced concepts 63
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
Toffset
OBS
node
Toffset - d
Transport networks:
Advanced concepts 64
Outline
1. Network management and control
2. Network recovery
3. Optical packet/burst switching
3.1 Introduction
3.2 Node architectures
3.3 Contention resolution
Transport networks:
Advanced concepts 65
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…
input
interface
switching
matrix
output
interface
synchr.
control
switch
control
header
rewriting
payload
header
Transport networks:
Advanced concepts 66
Header processing
input
interface
switching
matrix
output
interface
optical processing
synchr.
control
switch
control
header
rewriting
Electronic or optical
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
Transport networks:
Advanced concepts 67
Outline
1. Network management and control
2. Network recovery
3. Optical packet/burst switching
3.1 Introduction
3.2 Node architectures
3.3 Contention resolution
Transport networks:
Advanced concepts 68
Problem and possible solutions
 Problem:
two or more packets contend for same resource: destined for
same outgoing port at the same time
 Solutions:
deflection routing
wavelength conversion
optical buffer
(Fiber Delay Lines)
Transport networks:
Advanced concepts 69
Problem and possible solutions
Exercise
Try to predict the performance:
• network throughput
• packet loss rate
as total network load increases
(cf. traffic jams)
deflection routing
wavelength conversion
optical buffer
(Fiber Delay Lines)
Transport networks:
Advanced concepts 70
 Deflection:
• packets are “stored” in network:
• increases load, increases delay
• only works for low loads
network throughput
What solution to choose?
 Wavelength conversion:
 Buffering:
• local packet storage at nodes
• small delay penalty
Conclusion: Use combination of
wavelength conversion and buffers
packet loss rate
• no packet storage
• allows high network throughput, no
increased delay
load (packet arrival rate, pkt/s)
load (packet arrival rate, pkt/s)
figures © Yao et al., Opticomm’00
Transport networks:
Advanced concepts 71
Buffer architectures
 feed-forward vs feed-back
feed-forward vs feed-back
• feed-forward: input or output
buffering
• feed-back: shared,
recirculating FDLs
 single stage vs multiple
stage
 choice of FDL lengths in
0
1
0
1
D-1
D-1
0
1
...
...
stage
single vs multiple stages
...
• multiple stages separated by
switching elements
• e.g.: each stage different
delay resolution (“units”,
“tens”, “hundreds”…)
D-1
Transport networks:
Advanced concepts 72
OPS/OBS: fixed vs increasing FDLs
…
1
B
1
B
…
…
1
1
B
Packet loss rate
1
1.E-01
1.E-03
1.E-05
 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.E-07
0
8
16
24
32
40
nr. buffer ports (B)
48
56
64
ParetoOnOff, incr
ParetoOnOff, fix
GeoOnoff, incr
GeoOnoff, fix
Poisson, incr
Poisson, fix
Transport networks:
Advanced concepts 73
References
“Network Recovery: Protection and Restoration of Optical, SONETSDH, 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)
Transport networks:
Advanced concepts 74