MultiProtocol Label Switching

1
Multi-Protocol Label Switching
2
Outline

• Virtualisation
• Overview
• Label Encapsulations
• Label Distribution Protocols
• Constraint Based Routing with CR-LDP
• Summary

3
Virtualization of networks

• Virtualization of resources a powerful
  abstraction in systems engineering
• computing examples virtual memory, virtual
  devices
• Virtual machines e.g., java
• IBM VM os from 1960s/70s
• layering of abstractions dont sweat the details
  of the lower layer, only deal with lower layers
  abstractly

4
The Internet virtualizing networks

• 1974 multiple unconnected nets
• ARPAnet
• data-over-cable networks
• packet satellite network (Aloha)
• packet radio network

• differing in
• addressing conventions
• packet formats
• error recovery
• routing

satellite net
ARPAnet
"A Protocol for Packet Network Intercommunication"
, V. Cerf, R. Kahn, IEEE Transactions on
Communications, May, 1974, pp. 637-648.
5
The Internet virtualizing networks

• Gateway
• embed internetwork packets in local packet
  format or extract them
• route (at internetwork level) to next gateway

gateway
satellite net
ARPAnet
6
Cerf Kahns Internetwork Architecture

• What is virtualized?
• two layers of addressing internetwork and local
  network
• new layer (IP) makes everything homogeneous at
  internetwork layer
• underlying local network technology
• cable
• satellite
• 56K telephone modem
• today ATM, MPLS
• invisible at internetwork layer. Looks
  like a link layer technology to IP!

7
ATM and MPLS

• ATM, MPLS separate networks in their own right
• different service models, addressing, routing
  from Internet
• viewed by Internet as logical link connecting IP
  routers
• just like dialup link is really part of separate
  network (telephone network)
• ATM, MPSL of technical interest in their own
  right

8
Asynchronous Transfer Mode ATM

• 1990s/00 standard for high-speed (155Mbps to 622
  Mbps and higher) Broadband Integrated Service
  Digital Network architecture
• Goal integrated, end-end transport of carry
  voice, video, data
• meeting timing/QoS requirements of voice, video
  (versus Internet best-effort model)
• next generation telephony technical roots in
  telephone world
• packet-switching (fixed length packets, called
  cells) using virtual circuits

9
ATM architecture

• adaptation layer only at edge of ATM network
• data segmentation/reassembly
• roughly analogous to Internet transport layer
• ATM layer network layer
• cell switching, routing
• physical layer

10
ATM network or link layer?

• Vision end-to-end transport ATM from desktop
  to desktop
• ATM is a network technology
• Reality used to connect IP backbone routers
• IP over ATM
• ATM as switched link layer, connecting IP routers

IP network
ATM network
11
ATM Layer Virtual Circuits

• VC transport cells carried on VC from source to
  dest
• call setup, teardown for each call before data
  can flow
• each packet carries VC identifier (not
  destination ID)
• every switch on source-dest path maintain state
  for each passing connection
• link,switch resources (bandwidth, buffers) may be
  allocated to VC to get circuit-like perf.
• Permanent VCs (PVCs)
• long lasting connections
• typically permanent route between two IP
  routers
• Switched VCs (SVC)
• dynamically set up on per-call basis

12
ATM VCs

• Advantages of ATM VC approach
• QoS performance guarantee for connection mapped
  to VC (bandwidth, delay, delay jitter)
• Drawbacks of ATM VC approach
• Inefficient support of datagram traffic
• one PVC between each source/dest pair) does not
  scale (N2 connections needed)
• SVC introduces call setup latency, processing
  overhead for short lived connections

13
Label Substitution what is it?

• BROADCAST Go everywhere, stop when you get to B,
  never ask for directions.
• HOP BY HOP ROUTING Continually ask whos closer
  to B go there, repeat stop when you get to B.
  Going to B? Youd better go to X, its on the
  way.
• SOURCE ROUTING Ask for a list (that you carry
  with you) of places to go that eventually lead
  you to B. Going to B? Go straight 5 blocks,
  take the next left, 6 more blocks and take a
  right at the lights.

14
Label Substitution
Have a friend go to B ahead of you using one of
the previous two techniques. At every road they
reserve a lane just for you. At ever intersection
they post a big sign that says for a given lane
which way to turn and what new lane to take.
LANE1
LANE2
15
A label by any other name ...
There are many examples of label substitution
protocols already in existence.

• ATM - label is called VPI/VCI and travels with
  cell.
• Frame Relay - label is called a DLCI and travels
  with frame.
• TDM - label is called a timeslot its implied,
  like a lane.
• X25 - a label is an LCN
• Proprietary PORS, TAG etc..
• In Optical Networks Frequency substitution
  where label is a light frequency

16
ROUTE AT EDGE, SWITCH IN CORE
IP
IP
IP Forwarding
IP Forwarding
LABEL SWITCHING
17
MPLS HOW DOES IT WORK ?
TIME
18
Goals of Multiprotocol Label Switching

• MPLS extends traditional IP in the following
  areas
• Simplified Forwarding
• Based on labels instead of longest prefix-match
• Efficient Explicit Routing
• Route is specified once by source at path setup
  time
• Traffic Engineering
• Split traffic load over multiple parallel or
  alternate routes
• QoS Routing
• Select routes based upon QoS requirements
• Non-trivial Mappings of IP Datagrams onto Paths
• Performed only at network edges/borders

19
What Is MPLS?

• A switched fowarding technique based on IP
• Delivers explicit, switched forwarding to
  IP-based internetworks

• IETF Goals
• Higher performance
• Routing table efficiency
• Frame/Cell integration
• DiffServ

• "New" Goals
• Traffic engineering
• DiffServ

20
BEST OF BOTH WORLDS
CIRCUITSWITCHING
PACKETForwarding
HYBRID

• MPLS IP form a middle ground that combines the
  best of IP and the best of circuit switching
  technologies.
• ATM and Frame Relay cannot easily come to the
  middle so IP has!!

21
MPLS Terminology

• The Easy Stuff
• Label Switch Router
• Label Switch Path
• Label Information Base
• Forwarding Equivalence Class
• The Harder Stuff
• Label Distribution Protocol
• Constraint-Based LDP (CR-LDP)
• RSVP for Traffic Engineering (RSVP-TE)

22
Label Encapsulation
ATM
FR
Ethernet
PPP
L2
VPI
VCI
DLCI
Shim Label
Label
Shim Label .
IP PAYLOAD
MPLS Encapsulation is specified over various
media types. Top labels may use existing format,
lower label(s) use a new shim label format.
23
MPLS Link Layers

• MPLS is intended to run over multiple link layers
• Specifications for the following link layers
  currently exist
• ATM label contained in VCI/VPI field of ATM
  header
• Frame Relay label contained in DLCI field in FR
  header
• PPP/LAN uses shim header inserted between L2
  and L3 headers
• Translation between link layers types must be
  supported

MPLS intended to be multi-protocol below as
well as above.
24
Label Structure
MPLS "shim" headers
...
Layer 2 Header
IP Packet
Label
TTL
Exp.
S
4 Octets
Label 20-bit value, (0-16 reserved) Exp. 3-bits
Experimental (former ToS) S 1-bit Bottom of
stack TTL 8-bits Time To Live
25
Label Switch Router Architecture
Smart Connections Pre-computation
PNNI routing PNNI signaling OSPF(TE), IS-IS(TE),
BGP4 RSVP-TE, CR-LDP
Per Port Per Priority Per Flow Queuing Flow Mergin
g
Policing Marking IP Forwarding Labeling Classifica
tion
Buffer Allocation Packet Drop
Hierarchical Scheduler Shaper
26
Label Edge Routers

• Label Edge Router (LER)
• A tunnel (LSP) endpoint
• Ingress
• Egress
• Push and Pop

LER
10 MB
LER
40 MB
27
Label Switch Router

• Label Switch Router (LSR)
• A tunnel transit point
• active LSR

LSR
LSR
LSR
28
Label Switch Path

• The path followed by packets that have the same
  label!

IP Source Network
IP Destination Network
The Internet
29
Label Information Base (LIB)

• The LSR routing table where a label ID is
  associated with an outbound port

IP Source Network
IP Destination Network
Label (In)
Label (Out)
O/P Port
12
766
Ser_1
The Internet
308
5
Ser_2
30
Forwarding Equivalence Classes
LSR
LSR
LER
LER
LSP
Packets are destined for different address
prefixes, but can be mapped to common path

• FEC A subset of packets that are all treated
  the same way by a router
• The concept of FECs provides for a great deal of
  flexibility and scalability
• In conventional routing, a packet is assigned to
  a FEC at each hop (i.e. L3 look-up), in MPLS it
  is only done once at the network ingress.

31
LABEL SWITCHED PATH (simple)
- An LSP is actually part of a tree from every
source to that destination (unidirectional). -
LDP builds that tree using existing IP forwarding
tables to route the control messages.
32
MPLS BUILT ON STANDARD IP
47.1
1
2
1
3
2
1
47.2
3
47.3
2

• Destination based forwarding tables as built by
  OSPF, IS-IS, RIP, etc.

33
MPLS Routing Protocols
By jove! These look familiar!

• OSPF
• BGP
• ISIS

34
Routing Protocols

• Required for topology determination
• Existing Routing Protocols Can Be Used With MPLS
• But they do not support ER/TE
• Modifications To OSPF, ISIS and BGP Are In Draft

35
MPLS Partitioning Routing and Forwarding
Routing
Based on Classful Addr. Prefix? Classless Addr.
Prefix? Multicast Addr.? Port No.? ToS Field?
OSPF, IS-IS, BGP, RIP
Forwarding Table
Forwarding
Based on Exact Match on Fixed Length Label
MPLS

• Current network has multiple forwarding paradigms
• - class-ful longest prefix match (Class A,B,C
  boundaries)
• - classless longest prefix match (variable
  boundaries)
• - multicast (exact match on source and
  destination)
• - type-of-service (longest prefix. match on
  addr. exact match on ToS)
• As new routing methods change, new route look-up
  algorithms are required
• - introduction of CIDR
• Next generation routers will be based on hardware
  for route look-up
• - changes will require new hardware with new
  algorithm
• MPLS has a consistent algorithm for all types of
  forwarding partitions routing/fwding
• - minimizes impact of the introduction of new
  forwarding methods

MPLS introduces flexibility through consistent
forwarding paradigm
36
Routing Label Distribution

• Label Assignment
• Control-Driven
• Topology-Driven
• Request-Driven
• Traffic Driven

37
Label Distribution Options

• Manual LIB Entries
• Analogous To Static Routes
• Will Not Scale
• May Be Used In Early Interoperability Tests and
  Trade Show Demos
• Label Distribution Protocols
• "A set of procedures by which one Label Switched
  Router (LSR) informs another of the label/FEC
  bindings it has made"

38
Label Distribution Protocols

• LDP, RSVP
• Maps unicast IP destinations into labels
• RSVP-TE, CR-LDP
• Used for Traffic Engineering and Resource
  Reservation
• PIM
• For multicast group-to-label mapping
• BGP
• For "extra" external label mapping

39
Upstream vs Downstream
LSR1
Downstream
LSR6
Router
Router
Upstream
LSR2
LSR3
Request
LSR4
LSR1
LSR5
LSR6
MPLS Domain
40
Label Distribution Protocol (LDP)
Label distribution ensures that adjacent routers
have a common view of FEC lt-gt label bindings
Routing Table Addr-prefix Next
Hop 47.0.0.0/8 LSR3
Routing Table Addr-prefix Next
Hop 47.0.0.0/8 LSR2
LSR1
LSR3
LSR2
IP Packet
47.80.55.3
Label Information Base Label-In FEC
Label-Out XX 47.0.0.0/8 17
For 47.0.0.0/8 use label 17
Label Information Base Label-In FEC
Label-Out 17 47.0.0.0/8 XX
Step 2 LSR communicates binding to adjacent LSR
Step 3 LSR inserts label value into forwarding
base
Step 1 LSR creates binding between FEC and
label value
Common understanding of which FEC the label is
referring to!
Label distribution can either piggyback on top of
an existing routing protocol, or a dedicated
label distribution protocol (LDP) can be created.
41
Label Distribution - Methods
Label Distribution can take place using one of
two possible methods
UPstream Unsolicited Label Distribution
Downstream-on-Demand Label Distribution
LSR2
LSR1
LSR2
LSR1
Label-FEC Binding
Request for Binding

• LSR2 and LSR1 are said to have an LDP adjacency
  (LSR2 being the downstream LSR)
• LSR2 discovers a next hop for a particular FEC
• LSR2 generates a label for the FEC and
  communicates the binding to LSR1
• LSR1 inserts the binding into its forwarding
  tables
• If LSR2 is the next hop for the FEC, LSR1 can use
  that label knowing that its meaning is understood

Label-FEC Binding

• LSR1 recognizes LSR2 as its next-hop for an FEC
• A request is made to LSR2 for a binding between
  the FEC and a label
• If LSR2 recognizes the FEC and has a next hop for
  it, it creates a binding and replies to LSR1
• Both LSRs then have a common understanding

Both methods are supported, even in the same
network at the same time For any single
adjacency, LDP negotiation must agree on a common
method
42
Downstream On Demand ordered

• Ingress requests label from egress

Egress
Ingress
Label Request
LSR 6
LSR 1
Label Assign
Downstream
Upstream
Data Flow
43
Distribution Control Ordered v. Independent
Next Hop (for FEC)
MPLS path forms as associations are made between
FEC next-hops and incoming and outgoing labels
Incoming Label
Outgoing Label
Independent LSP Control
Ordered LSP Control

• Label-FEC binding is communicated to peers if
• - LSR is the egress LSR to particular FEC
• - label binding has been received from
  upstream LSR
• LSP formation flows from egress to ingress

• Each LSR makes independent decision on when to
  generate labels and communicate them to upstream
  peers
• Communicate label-FEC binding to peers once
  next-hop has been recognized
• LSP is formed as incoming and outgoing labels are
  spliced together

Definition

• Labels can be exchanged with less delay
• Does not depend on availability of egress node
• Granularity may not be consistent across the
  nodes at the start
• May require separate loop detection/mitigation
  method

• Requires more delay before packets can be
  forwarded along the LSP
• Depends on availability of egress node
• Mechanism for consistent granularity and freedom
  from loops
• Used for explicit routing and multicast

Comparison
Both methods are supported in the standard and
can be fully interoperable
44
INDEPENDENT MODE
45
Label Retention Methods
Binding for LSR5
LSR2
An LSR may receive label bindings from multiple
LSRs Some bindings may come from LSRs that are
not the valid next-hop for that FEC
LSR1
LSR5
Binding for LSR5
LSR3
Binding for LSR5
LSR4
Conservative Label Retention
Liberal Label Retention
LSR2
LSR2
Label Bindings for LSR5
Label Bindings for LSR5
LSR1
LSR1
LSR3
LSR3
LSR4s Label LSR3s Label LSR2s Label
LSR4s Label LSR3s Label LSR2s Label
LSR4
LSR4
Valid Next Hop
Valid Next Hop

• LSR maintains bindings received from LSRs other
  than the valid next hop
• If the next-hop changes, it may begin using these
  bindings immediately
• May allow more rapid adaptation to routing
  changes
• Requires an LSR to maintain many more labels

• LSR only maintains bindings received from valid
  next hop
• If the next-hop changes, binding must be
  requested from new next hop
• Restricts adaptation to changes in routing
• Fewer labels must be maintained by LSR

Label Retention method trades off between label
capacity and speed of adaptation to routing
changes
46
LIBERAL RETENTION MODE
These labels are kept in case they are needed
after a failure.
47
CONSERVATIVE RETENTION MODE
These labels are released the moment they are
received.
48
IP FOLLOWS A TREE TO DESTINATION

Desta.b.c.d
Desta.b.c.d
Desta.b.c.d
- IP will over-utilize best paths and
under-utilize less good paths.
49
HOP-BY-HOP(A.K.A Vanilla) LDP
216
963
14
612
462
311
99
5
- Ultra fast, simple forwarding a.k.a switching -
Follows same route as normal IP datapath - So
like IP, LDP will over-utilize best paths and
under-utilize less good paths.
50
IP FORWARDING USED BY HOP-BY-HOP CONTROL
47.1
1
IP 47.1.1.1
2
IP 47.1.1.1
1
3
2
IP 47.1.1.1
1
47.2
3
47.3
2
51
MPLS Label Distribution
1
47.1
3
2
3
1
1
2
47.3
3
47.2
2
52
Label Switched Path (LSP)
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
53
Traffic Engineering
B
C
Demand
A
D
Traffic engineering is the process of mapping
traffic demand onto a network
Network Topology
Purpose of traffic engineering

• Maximize utilization of links and nodes
  throughout the network
• Engineer links to achieve required delay,
  grade-of-service
• Spread the network traffic across network links,
  minimize impact of single failure
• Ensure available spare link capacity for
  re-routing traffic on failure
• Meet policy requirements imposed by the network
  operator

Traffic engineering key to optimizing
cost/performance
54
Traffic EngineeringUsing Explicit Routing

• Based On ATM PNNI Experience
• Explicit Routing allows Traffic Flows to be
  mapped onto specific paths

LDP
CR-LDP
Label Distribution
ER / TE
RSVP
RSVP-TE
55
CR-LDP

• CR Constraint based Routing
• eg USE (links with sufficient resources AND
  (links of type someColor) AND
  (links that have delay less than
  200 ms)

56
Hop-by-Hop vs. Explicit Routing
Hop-by-Hop Routing
Explicit Routing

• Source routing of control traffic
• Builds a path from source to dest
• Requires manual provisioning, or automated
  creation mechanisms.
• LSPs can be ranked so some reroute very quickly
  and/or backup paths may be pre-provisioned for
  rapid restoration
• Operator has routing flexibility (policy-based,
  QoS-based,
• Adapts well to traffic engineering

• Distributes routing of control traffic
• Builds a set of trees either fragment by fragment
  like a random fill, or backwards, or forwards in
  organized manner.
• Reroute on failure impacted by convergence time
  of routing protocol
• Existing routing protocols are destination prefix
  based
• Difficult to perform traffic engineering,
  QoS-based routing

Explicit routing shows great promise for traffic
engineering
57
EXPLICITLY ROUTED OR ER-LSP
B
C
A
- ER-LSP follows route that source chooses. In
other words, the control message to establish the
LSP (label request) is source routed.
58
Explicit Routing - MPLS vs. IP Source Routing

• Connectionless nature of IP implies that routing
  is based on information in each packet header.
• Source routing is possible, but path must be
  contained in each IP header.
• Lengthy paths increase size of IP header, make it
  variable size, increase overhead.
• Some gigabit routers require slow path
  option-based routing of IP packets.
• Source routing has not been widely adopted in IP
  and is seen as impractical.
• Some network operators may filter source routed
  packets for security reasons.
• MPLS enables the use of source routing by its
  connection-oriented capabilities.
• - paths can be explicitly set up through the
  network
• - the label can now represent the explicitly
  routed path
• Loose and strict source routing can be supported.

59
EXPLICITLY ROUTED LSP ER-LSP
1
47.1
3
3
2
1
1
2
47.3
3
47.2
2
60
ER LSP - advantages

• Operator has routing flexibility (policy-based,
  QoS-based)
• Can use routes other than shortest path
• Can compute routes based on constraints in
  exactly the same manner as ATM based on
  distributed topology database. (traffic
  engineering)

61
ER LSP - discord!

• Two signaling options proposed in the standards
  CR-LDP, RSVP extensions
• CR-LDP LDP Explicit Route
• RSVP ext Traditional RSVP Explicit Route
  Scalability Extension
• ITU has decided on LDP/CR-LDP for public
  networks.
• Survival of the fittest not such a bad thing
  although RSVP has lots of work in scalability to
  do.

62
Constraint-based LSP Setup using LDP

• Uses LDP Messages (request, map, notify)
• Shares TCP/IP connection with LDP
• Can coexist with vanilla LDP and inter-work with
  it, or can exist as an entity on its own
• Introduces additional data to the vanilla LDP
  messages to signal ER, and other Constraints

63
ER-LSP Setup using CR-LDP
LSR B
LSR C
LER D
LER A
ER Label Switched Path
Ingress
Egress
64
LDP/CR-LDP INTERWORKING
A
B
C
LDP
CR-LDP
- It is possible to take a vanilla LDP label
request let it flow vanilla to the edge of the
core, insert an ER hop list at the core boundary
at which point it is CR-LDP to the far side of
the core.
65
Basic LDP Message additions

• LSPID A unique tunnel identifier within an MPLS
  network.
• ER An explicit route, normally a list of IPV4
  addresses to follow (source route) the label
  request message.
• Resource Class (Color) to constrain the route to
  only links of this Color. Basically a 32 bit mask
  used for constraint based computations.
• Traffic Parameters similar to ATM call setup,
  which specify treatment and reserve resources.

66
CR-LDP Traffic Parameters
67
CRLSP characteristics

• The approach is like diff-servs separation of
  PHB from Edge
• The parameters describe the path behavior of
  the CRLSP, i.e. the CRLSPs characteristics
• Dropping behavior is not signaled
• Dropping may be controlled by DS packet markings
• CRLSP characteristics may be combined with edge
  functions (which are undefined in CRLDP) to
  create services
• Edge functions can perform packet marking
• Example services are in an appendix

68
Peak rate

• The maximum rate at which traffic should be sent
  to the CRLSP
• Defined by a token bucket with parameters
• Peak data rate (PDR)
• Peak burst size (PBS)
• Useful for resource allocation
• If a network uses the peak rate for resource
  allocation then its edge function should regulate
  the peak rate
• May be unused by setting PDR or PBS or both to
  positive infinity

69
Committed rate

• The rate that the MPLS domain commits to be
  available to the CRLSP
• Defined by a token bucket with parameters
• Committed data rate (CDR)
• Committed burst size (CBS)
• Committed rate is the bandwidth that should be
  reserved for the CRLSP
• CDR 0 makes sense CDR ? less so
• CBS describes the burstiness with which traffic
  may be sent to the CRLSP

70
Excess burst size

• Measure the extent by which the traffic sent on a
  CRLSP exceeds the committed rate
• Defined as an additional limit on the committed
  rates token bucket
• Can be useful for resource reservation
• If a network uses the excess burst size for
  resource allocation then its edge function should
  regulate the parameter and perhaps mark or drop
  packets
• EBS 0 and EBS ? both make sense

71
Frequency

• Specifies how frequently the committed rate
  should be given to CRLSP
• Defined in terms of granularity of allocation
  of rate
• Constrains the variable delay that the network
  may introduce
• Constrains the amount of buffering that a LSR may
  use
• Values
• Very frequently no more than one packet may be
  buffered
• Frequently only a few packets may be buffered
• Unspecified any amount of buffering is acceptable

72
Weight

• Specifies the CRLSPs weight in the relative
  share algorithm
• Implied but not stated
• CRLSPs with a larger weight get a bigger relative
  share of the excess bandwidth
• Values
• 0 the weight is not specified
• 1-255 weights larger numbers are larger
  weights
• The definition of relative share is network
  specific

73
Negotiation flags
If a parameter is flagged as negotiable
then LSRs may replace the parameter
value with a smaller value in the label
request mess
age. LSRs discover the
F1

F2

F3

F4

F5

F6

Res

negotiated values in the label mapping

message.






Label
request
-
possible
downward negotiation

Weight Negotiation Flag
CDR Negotiation Flag
PDR Negotiation Flag
CBS Negotiation Flag
PBS Negotiation Flag
EBS Negotiation Flag
Label
mapping

-

no
negotiation

74
CR-LDP PREEMPTION
A CR-LSP carries an LSP priority. This priority
can be used to allow new LSPs to bump existing
LSPs of lower priority in order to steal their
resources. This is especially useful during
times of failure and allows you to rank the LSPs
such that the most important obtain resources
before less important LSPs. These are called the
setupPriority and a holdingPriority and 8 levels
are provided.
75
CR-LDP PREEMPTION
When an LSP is established its setupPriority is
compared with the holdingPriority of existing
LSPs, any with lower holdingPriority may be
bumped to obtain their resources. This process
may continue in a domino fashion until the lowest
holdingPriority LSPs either clear or are on the
worst routes.
76
PREEMPTION A.K.A. BUMPING
B
C
A
77
ER-LSP setup using RSVP
LSR B
LSR C
LER D
LER A
78
THE BASIC DIFFERENCE RSVPREFRESHES CONTINUALLY!!
RSVP
LDP/CR-LDP
THATS ALL!!
FOREVER!!
TIME
79
Summary of Motivations for MPLS

• Simplified forwarding based on exact match of
  fixed length label
• - initial drive for MPLS was based on existence
  of cheap, fast ATM switches
• Separation of routing and forwarding in IP
  networks
• - facilitates evolution of routing techniques by
  fixing the forwarding method
• - new routing functionality can be deployed
  without changing the forwarding techniques of
  every router in the Internet
• Facilitates the integration of ATM and IP
• - allows carriers to leverage their large
  investment of ATM equipment
• - eliminates the adjacency problem of VC-mesh
  over ATM
• Enables the use of explicit routing/source
  routing in IP networks
• - can be easily used for such things as traffic
  management, QoS routing
• Promotes the partitioning of functionality within
  the network
• - move granular processing of packets to edge
  restrict core to packet forwarding
• - assists in maintaining scalability of IP
  protocols in large networks
• Improved routing scalability through stacking of
  labels
• - removes the need for full routing tables from
  interior routers in transit domain only routes
  to border routers are required
• Applicability to both cell and packet link-layers
• - can be deployed on both cell (eg. ATM) and
  packet (eg. FR, Ethernet) media
• - common management and techniques simplifies
  engineering

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PROBABLY THE ONLY OPTION FOR ROUTING AT LIGHT
SPEEDS
Optical Label Switch
l Routing Control
l1 l2 ln
l1 l2 ln
Fabric
l1 l2 ln
l1 l2 ln
When we get to true frequency to frequency
switching there is no way to route and LDP will
be required to setup OSPF routes. CR-LDP will be
required to engineer. l is just another label to
distribute. No new protocols required.
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Where Would We Deploy MPLS?

• In The Core of the Internet
• Alternative to S-PVC mesh over ATM
• Enables DiffServ implementation
• In Metropolitan Networks
• Mechanism for VPN deployment
• In Large Enterprises
• Not totally clear about value/complexity trade-off