Graceful Label Numbering
in
Optical MPLS Networks
Ibrahim C. Arkut
ica@lefke.edu.tr
Refik C. Arkut
refik.arkut@alcatel.com.tr
Nasir Ghani
nghani@sorrentonet.com
What is MPLS?
Multi Protocol Label Switching
is a routing technique
that imitate connection
oriented forwarding
method in a connectionless
(IP) environment
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What is MPLS? (cont.)
• Hop-by-hop or source routing
to establish labels - non-shortest paths
• Uses label native to the media
• Multi level label substitution transport
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Why MPLS ?
• Performance and scalability
• Explicit routing and traffic engineering
– Constraint-based Routing / QoS
• Separation of control (routing) and
forwarding
• Virtual Private Networks
– Controllable tunneling mechanism
• Unified approach to routing functionality
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Best of both Worlds
Packet Circuit
HYBRID Switching
Forwarding
IP MPLS ATM
+IP
• Flexibility and predictability
• Performance - complexity trade-off
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Forwarding Equivalence Classes (FEC)
LER LSR LSR LER
(ingress) (egress)
IP1 IP1
IP1 #L1 IP1 #L2 IP1 #L3
IP2 #L1 IP2 #L2 IP2 #L3
IP2 IP2
LSP
Flow of IP packets
• over the same path
• treated in the same manner
• mapped to the same label
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FEC / label binding mechanism
• Binding is done once at the ingress LER / OXC
• Currently based on destination IP address prefix
• Future mappings based on SP-defined policy
• In electronic MPLS domain
Label FEC (packet associated)
• In photonic MPLS domain
Label Wavelength ( channel associated)
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MPLS Signaling Protocols
• Hop-by-hop & Explicit
• Label Distribution Protocol (LDP)
• Constraint-based Routing LDP (CR-LDP)
• Extensions to RSVP
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Packet Forwarding over LSP-
(Label swapping)
Edge Core Core Edge
Ingress label switch Egress Label Switch
IP addr Out label IP label Next hop
Core
192.4/16 5 Label Switch Label Switch
2 21.9.1.1
In label Out label In label Out label
Layer 2
Assign 5 9 9 2 Transport
192.4.2.1 Layer 2 Initial 5 9 2 Remove 192.4.2.1
transport Label label
Label Label
Swapping Swapping
Label-Switched Path
Label swapping is „simple‟, but is it simple enough?
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Matching the Speeds?
IP/MPLS-over-WDM
IP/MPLS
Electronic Frame
Speed Monitoring
Optical
Speed
Optical (Physical) Layer
For increased speed, the mechanism must be simpler!
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Graceful Numbering of Trees
• It is a well-known labeling 9 7
10
problem in graphs and trees. 6
7 4
• Number the nodes of a graph G 3 14 8
6
with 1, 2,…, e so that induce 2
13
edge labels computed by 1
12
absolute node number
13 1
differences are all distinct. 5 14 2
8
• Notorious conjecture of Ringel- 9
15 11
Kotzig [1963] asserts that “all 11
10
4
trees are graceful” 3
5
12
Graceful numbering of a tree
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MPLS unicast with graceful numbering
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MPLS+Graceful Numbering
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MPLS multicast caterpillar using
graceful numbering
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Graceful numbering of paths and caterpillars (*)
are not complex and resembles label assignment in
PATH MPLS
1 N 2 N-1 3 N-2
N-1 N-2 N-3 N-4 N-5 etc.
CATERPILLAR
backbone path
N-3 N-5 N-6 N-10 N-13 N-14
1 N-2 3 N-3 7 N-6
etc.
N-1 N-2 N-4 N-7 N-9 N-11 N-12
N-8
N N-1 2 4 5 6 N-4 N-5
(*)I. Cahit and R. Cahit, “On Graceful Numbering of Spanning Trees”,
Info. Proc. Lett., 3(4), March 1975,
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MPLS Roles
IP/MPLS:Service and addressing,
MPLS
Quality of service, TE, Protection
SONET
Efficient
Sonet: Multiplexing, Protection logical
Optical overlay over
Optical: Bandwidth
Sonet
Present
IP/MPLS: Service and addressing
MPLS Quality of service, TE, Protection,
Adaptation Multiplexing,
Optical Efficient Peer
Optical: Protection, Multiplexing and
model
Bandwidth transport
Future
topology aware
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One Control (MPLS) - End to End
VPI/VCI
MPLS Control Plane VPI/VCI
/DLCI/ /DLCI/
Label Label Lambda Lambda Label Label
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Lambda-Labeling with Graceful Numbering
(IP-Over-WDM)
• Graceful Lambda
(Gl) Labeling in
Optical Core IP/MPLS network
(electronic)
Network
”Gl - labeling"
I1 Optical MPLS Core I6
M12
M8
Large bandwidth lambda
LSP's explicit routing
I2 M11 I5
M9
M10
I3
I4
Lambda-labeling approach: multiple MPLS network node types
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Graceful Numbering of Two Light-paths
(without lambda conversion)
• IF the light-paths from
C to B and from A to
D arrive to node X
with the same label
but different
wavelengths
• THEN no need to
convert any
wavelength at node X
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Graceful Numbering of Two Light-paths with
wavelength conversion
• IF the light-path from
C to B and from A to
D arrive to node X
with the same labels
and wavelengths
• THEN one of the
wavelength is to be
converted at node X
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Summary
• Topology associated labeling
• Distinct labels per LSP or MC Caterpillar
• Label conflict resolution by central control
• Source controlled Graceful Number assignments
• Labels generation automatic and simple
• Efficient O(n) algorithms
• Minimum label-process time
• Distributed algorithm to assign Gl-labels
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