TELECOM ITALIA GROUP
MPLS World Congress 2007
Paris, February 2007
Telecom Italia: 5 years experience in MPLS-
TE Fast Reroute deployment
A. Capello, S. Mastropietro, P. Salamandra

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Agenda
TI’s vision and the PSTN “Class 4 Replacement” Project
MPLS-TE Fast Reroute: design and deployment
MPLS-TE: relevant issues
MPLS-TE: operational impact
MPLS-TE Fast Reroute: next steps

TELECOM ITALIA GROUP

MPLS World Congress 2007

Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment

TI’s vision and the PSTN “Class 4 Replacement” Project

Cost EfficiencyFocus

Revenue
Generation Focus

MANAGEMENT
MANAGEMENTMANAGEMENTPLATFORM
PLATFORMPLATFORM

VOICE
VOICVOIECE

VOICE
VOICEVOICE

OPTICAL
OPTICAOPTICLALACCESS
ACCESACCESSS

OPTICAL
OPTICALOPTICALPACKET VIDEO
PACKETVIDEOVIDEOPACKETVIDEOVIDEOBACKBONE
BACKBONEBACKBONExDSL
xDSLxDSLACCESS
ACCESACCESSS

DATA
DATADATADATADATA

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
The PSTN “Class 4 Replacement”
OPBBackboneOPB
Edge Router
IN
NAS
SGU
OLO
CoreINAP
P
R
A
ISUP
MGMGCOut of Band
Signaling
2001: TI decided to migrate the
Transit Telephone Traffic to IP
using OPB network for the
transport of voice traffic
The new technologies was first
activated between Rome and
Milan
It was progressively extended to
the rest of the network
OPBBackboneOPB
Edge Router
IN
NAS
SGU
OLO
CoreINAP
P
R
A
ISUP
ISUP
SGTPSTN/ISDN

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
The PSTN “Class 4 Replacement” Requirements
Ones of the requirements for the packet backbone was the ability to hide
telephone traffic from “public” IP traffic
Moreover, another important goal was to guarantee to the ToIP traffic a
level of availability comparable to the PSTN network, where the so-called
“Five Nines Avail-ability” was regularly achieved
MPLS-TE technology was chosen to satisfy these requirements since
tunnels were able to isolate traffic and Link Fast Reroute feature was
capable of guaranteeing recovery times in the order of 50-100 ms over a
layer 1 DWDM unprotected network

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Perception of a link fault by customers
A Link Fault in the IP network introduces a new perception by the customers. The
fault causes traffic losses in a “bursty” way can lead to call interruption directly
by customer… (the signaling plane and the phone plane are now disjointed)
500 ms 2,5 s
Temporally speech
interruption
Negligible speech
interruption
No phone call interruption Phone call interruption
depends on the user
Long speech
interruption
100 ms

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute Link Protection
POS STM-
MGX2
Rc-1 Rc-3
Rc-2 Rc-4
Re-1
Re-2
Re-3
Re-3
Lp-1 Lp-2 Lp-3
POS STM-16/64
MGX1
Rc-1Rc-3Rc-2Rc-4Re-1Re-2Re-3Re-3Lp-1Lp-2Lp-3Main tunnel -Path Option 10 Dynamic
Main tunnel -Path Option 10 Dynamic after recalculation
Fast Rerouting tunnel . Path Option 10 Explicit

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Design
At the beginning, the MPLS-TE technology was deployed adopting a full
mesh of MPLS-TE Tunnels among the involved PoPs
Voice traffic (only the bearer channel) was statically routed into the
Traffic Engineering Tunnels using private addressing (10.x.0.0), while the
ISUP signaling was still transported over TDM
Creating an overlay architecture intrinsically secure and independent from
Public control Plane (BGP)
The MPLS-TE FRR Link Protection was applied to Sonet/SDH interfaces
MPLS-TE deployment was not addressed to bandwidth optimization, but
a even distribution of tunnels across network resources is required to
optimize FRR performances and to limit faults impact

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Design: relevant issues
Tunnel configuration and manageability (e.g. Explicit Path configuration
vs. Dynamic Path configuration)
Balancing of tunnels across multiple equal-cost paths
Fast Reroute technique to be used (e.g. Link Protection vs. Node
Protection)

TELECOM ITALIA GROUP

MPLS World Congress 2007

Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment

Explicit Path Configuration vs Dynamic Path Configuration (I)

Simplify operational aspects
(configuration, debugging,
troubleshooting)
Choose a flexible configuration,
in order to not change everything


The fully meshed MPLS-TE in case of OPB topology changes

architecture required to
Strictly control the bandwidth
configure 2280 Tunnels
used by MPLS-TE traffic

Evenly distribute MPLS-TE
tunnels across available paths
and routers to speed up FRR
performances

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Explicit Path Configuration vs Dynamic Path Configuration (II)
The adopted solution: Dynamic path configuration
Advantages
Save at least 6-10 configuration lines for each tunnel
Simplify know-how sharing with NOC people
Speed-up deployment
Make easier management of tunnels
Update OPB topology with no need to re-configure every tunnel

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Balancing of tunnels across multiple equal-cost paths (1)
Need to evenly distribute network utilization across available resources
FRR performances were dependent on the number of tunnels traversing
the faulty link
Lab tests showed that rerouting events could disrupt tunnel distribution,
even after the fault had been repaired
FAULT FAULT

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Balancing of tunnels across multiple equal-cost paths (2)
Potential solutions (rejected):
Use bandwidth attribute: lab tests showed it wasn’t able to solve the
problem
Use affinity attribute: its usage was not flexible enough for TI purposes
The issue was solved by tuning
the OSPF-TE metrics
The applicability of the solution
was verified by lab tests and
offline tools (WANDL MPLS View
and TI IP Planner)
-1 -1
-1 -1
FAULT

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Balancing of tunnels across multiple equal-cost paths (3)
Open issues
The chosen solution represents a constraint for network deployment and an
additional complexity to be managed in case of network evolution
The solution cannot solve the issue of balancing across parallel links
TI contributed as coauthor to an Internet Draft which describes new IGP-TE
extensions for implementing efficient and automatic load-balancing algorithms:
draft-ietf-mpls-number-0-bw-te-lsps

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Fast Reroute techniques
Fast Reroute technique comes in different flavors, depending on which
network resources have to be protected: links, nodes or SRLG (Shared
Risk Logical Group).
In general, does not exist an absolute right solution, as it depends on
network properties, fault types and frequency
that’s important regarding the number of tunnels to be instantiated and
their routing through the network.
In this context, Telecom Italia choose to restore at IP level all
unprotected DWDM links

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute Link Protection (1)
In order to obtain fault recovery time comparable with traditional
SDH/SONET performances (~50 msec), the choice was to use MPLS-TE
Fast Rerouting functionality based on the following design
MGX2
Rc-1 Rc-3
Rc-2 Rc-4
Re-1
Re-2
Re-3
Re-3
MGX1
Rc-1Rc-3Rc-2Rc-4Re-1Re-2Re-3Re-3
Enable every primary tunnel belonging to the full mesh to
be protected by a bypass tunnel

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute Link Protection (2)
In order to obtain fault recovery time comparable with traditional
SDH/SONET performances (~50 msec), the choice was to use MPLS-TE
Fast Rerouting functionality based on the following design
For each IP link (STM-16 or STM-64), define a bypass NHOP tunnel for link
protection
In TI network scenario ~300 MPLS-TE bypass explicit tunnels were configured
MGX2
Rc-1 Rc-3
Rc-2 Rc-4
Re-1
Re-2
Re-3
Re-3
MGX1
Rc-1Rc-3Rc-2Rc-4Re-1Re-2Re-3Re-3Lp-2
Lp-5
Lp-3
Lp-6Lp-4
Lp-1

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute Link Protection (3)
In order to obtain fault recovery time comparable with traditional SDH/SONET
performances (~50 msec), the choice was to use MPLS-TE Fast Rerouting
functionality based on the following design
The path of the bypass tunnel must be Link diverse from the protected path. In
order to obtain that and control all the bypass tunnels path, it was decided to
configure every bypass tunnel with an explicit configuration defining the physical
hop-by-hop path to be used and avoiding some specific links
MGX2
Rc-1 Rc-3
Rc-2 Rc-4
Re-1
Re-2
Re-3
Re-3
MGX1
Rc-1Rc-3Rc-2Rc-4Re-1Re-2Re-3Re-3Lp-1
Fast Rerouting
Tunnel Best Path
Fast Rerouting
Tunnel After Recal.

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute Node Protection
Some analysis and testing activities were done regarding MPLS-TE Fast
Rerouting Node Protection:
High complexity owed to the high number of NNHOP tunnels to be used
Test Lab activities showed that Link Protection recovery times was shorter than Node
Protection
The Node Protection mechanism can be actually useful in case of:
Double power supply failure
Software bugs that impact the network control plane and leave active the Line
Card laser
In the last six years neither of them happened in the OPB network…
Considering the previous points, the impact on control plane was too high
compared to the real advantages and for this reason TI did not introduce the
MPLS-TE Fast Rerouting Node Protection on OPB Network

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
Tunnels rerouting in case of a node failure
MGX2
Rc-1 Rc-3
Rc-2 Rc-4
Re-1
Re-2
Re-3
Re-3
Lp-1 Lp-2 Lp-3
POS STM . 16/64
MGX1
Rc-1Rc-3Rc-2Rc-4Re-1Re-2Re-3Re-3Lp-1Lp-2Lp-3Main tunnel -Path option 10 dynamic
Main tunnel -Path option 10 dynamic -RECALCULATED
Fast Rerouting tunnel
Recovery depends on
OSPF convergence

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE: operational impact
A 5 years experience demonstrated that simple design choices make easier the
deployment and management of a new technology like MPLS-TE
No outages due to MPLS-TE deployment
Despite of a simple design, the management of ~2500 MPLS-TE tunnels required
the support of automatic tools (at the moment not for provisioning). In TI
deployment process, WANDL MPLS View tool helped in several situations:
Automatic generation of MPLS-TE tunnels configuration (e.g. at least 10 configuration
lines for each tunnel mean 25000 configuration lines to be compiled and managed)
Integrity check before deployment and definition of the new configuration of MPLS-TE
tunnels in case of network changes

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Telecom Italia: 5 years experience in MPLS-TE Fast Reroute deployment
MPLS World Congress 2007
TELECOM ITALIA GROUP
MPLS-TE Fast Reroute: next steps
At the moment, MPLS-TE Fast Reroute is the most effective recovery
technique (comparable to Sonet/SDH protections)
Alternative solutions (e.g. IP Fast Rerouting) have been evaluated but no
real advantage has been figured out with respect to the current MPLS-TE
FRR deployment
Encouraged by the good behavior of current deployment, TI is working on
a class 4 replacement project for the mobile core network based on the
same MPLS-TE architecture
One of current major concerns for SPs is related to the protection of IP
multicast traffic, a key building block in the deployment of IPTV services
MPLS-TE Point to Multipoint will be the first technique to tackle and solve
the problem (e.g. IP Fast Rerouting currently doesn’t offer any protection to
IP multicast traffic)