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Outline
A brief Historical aside
Review of Transmission (Transport)
Technologies, Architectures and Evolution
Transporting Broadband across Transmission
Networks designed for Narrowband
Current Issues:
Broadband IP Transport Analysis
Ongoing Investigations in IP/OTN Networks
A Brief Historical Aside
Pre 1984 AT&T
BOCsLD Bell-Labs BCS WE ME
RBOCs circa 1984
US West
Bellcore
Ameritech
SouthWest Bell
Bell South
Nynex
Bell-Atlantic
Pac Bell
AT&T 1984 - 1997
LD Bell-Labs BCS WE ME
AT&T circa 1997
LD AT&T Labs
Lucent circa 1997
Bell-Labs BCS WE ME
The Bell System Legacy Today
Qwest
SBC
Verizon
Tellium
Bell South Telcordia
AT&T
Lucent
Avaya
Agere
Review of Transmission
(Transport) Technologies,
Architectures and Evolution
Opening Trivia Question
What is the difference between a DS3 (or DS1)
and a T3 (or T1)?
Asynchronous Data Rates
Digital Signal Level 0
internal to equipment
DS0
64 Kb/s
Digital Signal Level 1
intra office only (600 ft limit)
DS1
1.544 Mb/s
Digital Signal Level 3
intra office only (600 ft limit)
DS3
45 Mb/s
T1 Electrical (Copper) Version of DS1
1.544 Mb/s
repeatered version of DS1 sent out of Central Office
T3 Electrical (Copper) Version of DS3
45 Mb/s
repeatered version of DS3 sent out of Central Office
Asynchronous Digital Hierarchy
DS0 (a digitized analog
POTS circuit @ 64 Kbits/s)
24 DS0s = 1 DS1
28 DS1s = 1 DS3 Asynchronous Optical Line Signal
N x DS3s
Asynchronous Lightwave
Systems typically transport
traffic in multiples of DS3s
i.e.... 1, 3, 12, 24, 36, 72 DS3s
Asynchronous Networking
Manual DS1 Grooming/Add/Drop
LW
D
S
X
3
M13
D
S
X
1
D
S
X
1
DS3
DS3
DS1
• Manually Hardwired Central Office
• No Automation of Operations
• Labor Intensive
• High Operations Cost
• Longer Time To Service
M13
D
S
X
3
LW
Some Review Questions
What does the acronym SONET mean?
What differentiates SONET from
Asynchronous technology?
What does the acronym SDH mean?
The Original Goals of SONET/SDH
Standardization
Vendor Independence & Interoperability
Elimination of All Manual Operations Activities
Reduction of Cost of Operations
Protection from Cable Cuts and Node Failures
Faster, More Reliable, Less Expensive Service to
the Customer
SONET Rates
DS3s are STS-1 Mapped
DS0 (a digitized analog
POTS circuit @ 64 Kbits/s)
24 DS0s = 1
DS1
(= 1 VT1.5)
28 DS1s = 1 DS3 = 1 STS-1 SONET Optical Line Signal
OC-N = N x STS-1s
N is the number of STS-1s
(or DS3s) transported
SONET and SDH
OC level
OC-1
OC-3
OC-12
OC-48
OC-192
STM level
Line rate (MB/s)
STM-1
STM-4
STM-16
STM-64
51.84
155.52
622.08
2488.32
9953.28
SONET Layering for Cost
Effective Operations
DS-3
PTE
LTE
DS-3
PTE
STE
STE
LTE
DS-3
PTE
PTE
PTE
PTE
OC-3 TM
OC-3 TM
SONET Section
SONET Line
SONET Path
PTE = Path Terminating Element
LTE = Line Terminating Element
STE = Section Terminating Element
TM = Terminal Multiplexor
DS = Digital Signal
DS-3
DS-3
DS-3
SONET Point-to-Point Network
Repeater
Repeater
TM
TM
Section
Line
Path
STS-1
Frame
Format
Section
Overhead
Line
Overhead
Path
Overhead
STS-1 Synchronous
Payload Envelope
STS-1 SPE
SONET Ring Network Architectures
Unidirectional Path Switched Ring
A-B B-A
Bridge
Failure-free State
Path Selection
W
B
Bridge
fiber 1
P
A-B
C
A
B-A
Path
Selection
fiber 2
D
Bidirectional Line Switched Ring
Working
Protection
2-Fiber BLSR
B
AC
C A
C
A
D
AC
C A
Some Review Questions
Which SONET Ring Network is simpler?
Which SONET Ring Network is inefficient for
distributed demand sets?
Typical Deployment of UPSR and BLSR
in RBOC Network
Regional Ring (BLSR)
BB DACs
Intra-Regional Ring (BLSR)
Intra-Regional Ring (BLSR)
WB DACs
Access Rings (UPSR)
WB DACS = Wideband DACS - DS1 Grooming
BB DACS = Broadband DACS - DS3/STS-1 Grooming
Optical Cross Connect = OXC = STS-48 Grooming
DACS=DCS=DXC
Emergence of DWDM
Some Review Questions
What does the acronym DWDM mean?
What was the fundamental technology that
enabled the DWDM network deployments?
WDM NE
BLSR Fiber Pairs
WDM NE
First Driver for DWDM
Long Distance Networks
• Limited Rights of Way
• Multiple BLSR Rings Homing to a few Rights of Way
• Fiber Exhaustion
BLSR Fiber Pairs
Key Development for DWDM
Optical Fiber Amplifier
40km
40km
40km
40km
40km
40km
40km
40km
40km
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
1310
1310
1310
1310
1310
1310
1310
1310
TERM
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
RPTR
TERM
Conventional Optical Transport - 20 Gb/s
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
120 km
120 km
OLS
TERM
OLS
RPTR
120 km
OLS
RPTR
OLS
TERM
Fiber Amplifier Based Optical Transport - 20 Gb/s
Increased Fiber Network Capacity
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
OC-48
Transporting Broadband
across Transmission Networks
designed for Narrowband
Public/Private
Internet Peering
Data SP
Core
Core
Router
Router
RAS
RAS
EtherSwitch
Core
Access
Router
Router
RAS
RAS
RAS
Access
ATM
Switch
Core
ATM
Switch
RAS
Router
EtherSwitch
Router
RAS
RAS
RAS
ATM
Switch
Core
ATM
Switch
Router
RAS
ATM Access
Access
Router
RAS
RAS
Core
RAS
Router
Access
RAS
Router
ATM Access
RAS
RAS
Backbone
SONET/WDM
T1/T3/OC3
FRS and CRS
ATM
Access
Switch
Router
T1/T3 IP
Leased-Line
Connections
ATM
ATM
ATM
ATM
Access
Access
Access
Access
T1/T3 FR
and ATM IP
Leased-Line
Connections
RAS Farms
High Capacity Path Networking
IP router
IP router
STS-12c/48c/...
IP router
STS-3c
Existing SDH-SONET Network
Existing SONET/SDH networks are a BOTTLENECK for Broadband
Transport
Most Access Rings are OC-3 and OC-12 UPSRs while most
Backbone Rings are OC-48. Transport of rates higher than
OC-48 using the existing SONET/SDH network will require
significant and costly changes. Clearly upgrading the
SONET/SDH network everytime broadband data interfaces are
upgraded based increased IP traffic is not an appropriate
solution.
IP/SONET/WDM Network Architecture
OC-3/12
[STS-3c/12c]
OC-48
EMS
Access
Routers/
Enterprise
Servers
.
.
.
SONET
XC
SONET
NMS
SONET
ADM/LT
OC-3/12
[STS-3c/12c/48c]
SONET
ADM/LT
EMS
OC-12/48
SONET Transport Network
Core IP
Node
Core IP
Node
.
.
.
OTN
NMS
OC-3/12/48
[STS-3c/12c/48c]
WDM
LT
l1, l2, ...
WDM
LT
Pt-to-Pt WDM Transport Network
OC-3/12/48
[STS-3c/12c/48c]
LT = Line Terminal
IP = Internet Protocol
EMS = Element Management System
OTN = Optical Transport Network
NMS = Network Management System
ADM = Add Drop Multiplexor
WDM = Wavelength Division Multiplexing
Optical Network Evolution mirrors
SONET Network Evolution
Point-to-Point WDM
Line System
Multipoint Network
WDM Add/Drop
Optical Cross-Connect
WDM Networking
l1
l2
lN
l1
l2
lN
WDM
ADM
WDM
ADM
li
lk
OXC
IP/OTN Architecture
EMS
Core Data
Node
mc: multi-channel interface
(e.g., multi-channel OC-12/OC-48)
.
.
.
mc
OTN
NMS
OXC
EMS
Access Routers
Enterprise Servers
.
.
.
Core Data
Node
EMS
OXC
OXC
mc
mc
Optical Transport Network
mc
Core Data
Node
.
.
.
IP = Internet Protocol
EMS = Element Management System
OTN = Optical Transport Network
NMS = Network Management System
OXC = Optical Cross Connect
WDM = Wavelength Division Multiplexing
Broadband IP Transport Analysis
Credits to Debanjan Saha and Subir Biswas
Architectural Alternatives
IP-over-DWDM: IP routers connected directly over
DWDM transport systems.
IP-over-OTN: IP routers interconnected over a
reconfigurable optical transport network (OTN)
consisting of optical cross-connects (OXCs)
connected via DWDM.
Architectural Alternatives
Quadruple Redundant Configuration
of IP Routers at PoPs
Currently deployed by carriers to increase router reliability and
perform load balancing.
Upper two routers are service routers adding/dropping traffic from
the network side and passing through transit traffic.
Lower two routers are drop routers connected to client devices.
Two connections from the network port at the ingress upper
(service) router to two drop ports, one in each of the lower (drop)
routers. Client device sends 50% of the traffic on one of these drop
interfaces and 50% on the other (it is attached to both of the drop
routers).
Not required for OXCs.
IP-over-DWDM: Pros and Cons
Pros
IP-routers with OC-48c/OC-192c interfaces
and aggregate throughput reaching 100s of
Gbps.
Transport functions like switching,
configuration, and restoration are moved to
the IP layer and accomplished by protocols
like MPLS, thus providing a unifying
framework.
IP routers control end-to-end path selection
using traffic engineering extended routing
and signaling IP protocols.
Supports the peer-to-peer model where IP
routers interact as peers to exchange
routing information.
Cons
Can router technology scale to port
counts consistent with multi-terabit
capacities without compromising
performance, reliability, restoration
speed, and software stability ? A
big question mark.
IP-over-OTN: Pros and Cons
Pros
Reconfigurable optical backbone
provides a flexible transport infrastructure
Core OXC network can be shared with
other service networks such as ATM,
Frame Relay, and SONET/SDH private
line services.
Allows interconnection of IP routers in an
arbitrary (logical) mesh topology.
Not possible in architecture A since a
typical CO/PoP has two, in some cases
three, and in rare occasions four conduits
connecting it to neighboring PoPs.
Cons
Adding a reconfigurable optical backbone
introduces an additional layer between
the IP and DWDM layers and associated
overhead.
Traffic engineering occurs independently
in two domains -- (i) the IP router network
with its logical adjacencies spanning the
OXC backbone, and (ii) the optical
network which provisions physical
lightpaths between edge IP routers. Could
lead to inefficiency in traffic routing from a
global perspective.
Why Glass Through is not an Alternative?
Removes the flexibility of dynamic switching between incoming and
outgoing fibers at a PoP that comes with using a router or an OXC.
Prevents organic growth of the network. Dynamic switching allows local
capacity to be used to meet traffic demands between arbitrary PoPs. With
glass through, bandwidth is not available at the link level but only at the
segment level whose two end PoPs terminate glass through fiber paths.
Does not allow intelligent packet processing or performance monitoring of
transit traffic at a PoP.
Network Deployment Cost Analysis
Analysis of the two architectures from an economic standpoint.
Contrary to common wisdom, a reconfigurable optical layer can lead to
substantial reduction in capital expenditure for networks of even moderate
size.
Critical observation: Amount of transit traffic at a PoP is much higher than the
amount of add-drop traffic.
Hence, a reconfigurable optical layer that uses OXC ports (instead of router
ports) to route transit traffic will drive total network cost down so long as an
OXC interface is marginally cheaper than a router interface.
Savings increases rapidly with the number of nodes in the network and traffic
demand between nodes.
Assumptions: Network Model
Typical CO/PoP has two, in some cases
three, and in rare occasions four conduits
connecting it to neighboring PoPs. Average
degree = 2.5.
Routing uniform traffic (equal traffic demand
between every pair of PoPs) on networks of
increasing size.
Two traffic demand scenarios: uniform
demand of 2.5 Gbps (OC-48) and 5 Gbps
between every pair of PoPs.
Multiple routers/OXCs can be placed at each
PoP to meet port requirements for routing
traffic.
Core OXC network provides full grooming of
OC-192 ports into OC-48 tributaries.
Transit traffic uses router ports in IPover-WDM and OXC ports (only) in
IP-over-OTN.
Quadruple redundant configuration of
IP routers at a PoP to improve
reliability and perform load-balancing.
Shortest-hop routing of lightpaths.
IP routers have upto 64 ports and
OXCs have upto 512 ports (in keeping
with port counts of currently shipped
products).
With or without traffic restoration
(diverse backup paths).
Assumptions:Pricing
IP routers and OXCs have fixed costs and per-port costs for OC-48 and OC192 interfaces.
Ballpark list prices for currently shipped products.
IP router:
fixed cost of $200K and
per-port cost of $100K and $250K for OC-48 and OC-192 interfaces respectively.
OXC:
fixed cost of $1M and
per-post cost of $25K and $100K for OC-48 and OC-192 interfaces respectively.
2.5 Gbps of Traffic between PoP Pairs
Without Restoration
Total $-Cost (M)
2.5 Gbps uniform traffic
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
0
IP-over-WDM
IP-over-OTN
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of about 18 nodes.
50
60
5 Gbps of Traffic between PoP Pairs
Without Restoration
5 Gbps uniform traffic
Total $-Cost (M)
8000
7000
IP-over-WDM
IP-over-OTN
6000
5000
4000
3000
2000
1000
0
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of about 15 nodes.
50
60
% of Transit Traffic in the Network
Without Restoration
% of Transit Traffic
100
% Transit Traffic
degree = 2
degree = 3
80
60
40
20
0
0
10
20
30
40
Network size (nodes)
50
60
75-85% of the total traffic is transit traffic for a network size of 50 PoPs.
2.5 Gbps of Traffic between PoP Pairs
With Restoration
Total $-Cost (M)
2.5 Gbps uniform traffic
9000
8000
7000
IP-over-WDM
IP-over-OTN
6000
5000
4000
3000
2000
1000
0
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of less than 8 nodes.
50
60
5 Gbps of Traffic between PoP Pairs
With Restoration
Total $-Cost (M)
5 Gbps uniform traffic
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
IP-over-WDM
IP-over-OTN
0
10
20
30
40
Network size (nodes)
Cross-over point at network size of less than 4 nodes.
50
60
% of Transit Traffic in the Network
With Restoration
% Through Traffic
% of Transit Traffic
100
90
80
70
60
50
40
30
20
10
0
degree = 2
degree = 3
0
10
20
30
40
Network size (nodes)
50
60
80-95% of the total traffic is transit traffic for a network size of 50 PoPs.
Results and Discussion
Without restoration: Network cost breakeven point occurs at network sizes of
18 and 15 nodes for 2.5 Gbps and 5 Gbps of uniform traffic respectively.
With restoration: IP-over-OTN has lower cost beyond a network size of 4-6
nodes.
IP-over-OTN becomes increasingly attractive as amount of traffic and network
size grows. Savings is much more when we consider traffic restoration.
Amount of transit traffic in the network grows rapidly as network size
increases. For example, without restoration, 75-85% of the total traffic is
transit traffic for a network size of 50 PoPs, and with restoration, it is 80-95%.
Carrying transit traffic over OXC ports (instead of router ports) drives network
cost down so long as an OXC interface is marginally cheaper than a router
interface.
Results and Discussion contd. ...
With traffic restoration, the economies of scale reaped from IP-over-OTN is
further increased.
Each primary path in a network has a diversely routed backup path.
Transit port usage will increase substantially when we consider backup paths
while the number of terminating ports remains unchanged.
Case for Restoration at Optical Layer
Restoration in IP-over-WDM: Provided at the IP layer where backup paths
consume router ports (like primary paths).
Restoration in IP-over-OTN: Can be provided at the optical or IP layers. In
the former case, router ports are not consumed on intermediate PoPs.
Study shows substantial increase in savings for IP-over-OTN when
restoration is taken into consideration.
IP-over-OTN has lower cost beyond a network size of 4-6 nodes.
As much as 80-95% of the total traffic is transit traffic for a network size of 50
PoPs.
Ongoing Investigations in IP/OTN
Networks
Can IP layer provide reliable service?
How much Restoration is really required for
services?
Interaction of Routing Protocols with Optical
Layer Restoration
Optimal Routing with Topology of IP and
Optical Layers
And many more...