Rcom.lecture10.Label Switching

7/29/2019 Rcom.lecture10.Label Switching

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Computer Networks

Label switching

Lecture note 10

MIEEC


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Label switching


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Switching: circuit, virtual

circuit, and datagram


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Virtual circuits

Built on top of datagram network

Each packet follows the same path Can do per circuit:

Admission control

Resource reservation

Can do traffic engineering Specify capacity per VC

Choose paths for VCs based on VC capacity andavailable network resources

Can understand the network usage


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VC vs. Datagram Networks


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Forwarding:

Longest prefix match


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Forwarding:

Virtual circuits


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Production network


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Production network

Whats the underlying topology?

Point to point?

Ethernet switches?

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter Layer 3 IP


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Production network

Layer 1 DWDMDWDM

DWDM

DWDM

DWDM DWDM

DWDM

SONETSONET

SONET

SONETSONET

SONET

SONET

SONET

SONET

SONET

Layer 2 SDH/SONETDWDM

ATM

MPLS

ATM

MPLS

ATMMPLS

ATMMPLS

ATMMPLS

ATM

MPLS

ATMMPLS

Layer 2 ATM/MPLS

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter Layer 3 IP


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Production network

Layer 1 DWDMDWDM

DWDM

DWDM

DWDM DWDM

DWDM

SONETSONET

SONET

SONETSONET

SONET

SONET

SONET

SONET

SONET

Layer 2 SDH/SONETDWDM

ATM

MPLS

ATM

MPLS

ATMMPLS

ATMMPLS

ATMMPLS

ATM

MPLS

ATMMPLS

Layer 2 ATM/MPLS

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter

IProuter Layer 3 IP

Packet in Packet out


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DWDM network


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SDH/SONET


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SDH/SONET


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MPLS

Label switching coexists

with IP longest-prefix match


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OSPF, etc.


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Circuit switching:Digital synchronous

multiplexing(SDH, Sonet),

DWDM

Datagramswitching:CIDR lookup

OSPF, BGP

Virtual circuit switching:ATM, MPLS


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Label switching: ATM evolution to MPLSAsynchronous Transfer Mode

Multiprotocol Label Switching


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ATM

Designed to become the next step after ISDN,

BISDN, etc. Designed to offer integrated networkservices, meaning:

Constant bitrate, variable bitrate Audio, video, etc.

Single network infrastructure, multipleapplications

Based on fixed-size packets (cells) With adaptation protocols for each application


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Applications => cells =>

single transfer mode

N

etwork


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Applications => cells =>

single transfer mode

Cells


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ATM packet switching


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ATM virtual paths and channels


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ATM

Vision 1

Replace IP Applications/hosts all become ATM-speakers

Vision 2

Provide services at the core network ATM overlay network

Traffic engineering, QoS

Overall interesting ideas, wrong approach

L b l it hi


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Label switching:

Overlay vs. peering

Overlay of virtual circuits

Direct peering of routers

Two networks to

manage!


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MPLS

Take the label switching concept

Good for: Traffic engineering

Network control and planning

Apply it to the IP network Not as an overlay network


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MPLS encapsulation format

Shim layer

2.5 layer

MPLS data encapsulatedbetween Layer 2 and

Layer 3 Ethernet and IP

Labels may be

pushed/popped at

intermediate routers


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MPLS scalability via aggregation

One labelswitched

path (LSP) Can

aggregatemultiple IPflows

Aggregationon Edge

Label SwitchRouter (LSR)border


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Aggregation in core


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MPLS tunneling


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MPLS Control Plane

Label Distribution Protocol

Destination-based / control-driven Computed according to IP route

MPLS


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MPLS

LDP control-driven example


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MPLS Explicitly-routed LSP

LSP specified by operator or network

management system Route specified in LDP setup message

Message sent to all LSR in the route

Each LSR sends label request to next-hop LSR

Path independent of IP routes

Opens the door to traffic engineering

Constrained-based Routed LDP


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Constrained-based Routed LDP

CR-LDPLSR A requires route/resources to LSR C

1. LSRA computes path to LSR C

2. LSRA reserves resources, sends label request andtraffic parameters to LSRB/C

3.

4. LSRC checks for resources. If available send mappingmessage to LSRB

5. LSRB does the same, mapping original LSP id


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MPLS with RSVP

Resource Reservation Protocol

Similar to CR-LDP except resources arechecked on the return path


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RSVP vs. CR-LDP

State-full vs. state-less

CR-LDP uses TCP

Hard state

needs explicit label unbinding message RSVP

Uses UDP

Soft state, needs to periodically refresh state Detects changes automatically


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Generalized Multiprotocol Label switching


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TO THINKTO THINKTO THINKTO THINK

MPLS applies to packet switching

Can we apply the same label switchingconcept to the rest of the network?

Time slots (TDM)

Wavelengths (DWDM) Physical fibers

G l


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Goal

Fast and automated way to create

On-demand circuits

N t k hi h


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Network hierarchy

FiberWDM

TDM

Packets

S it hi Hi hi


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Switching Hierarchies

Fiber WDM TDM PacketsPackets WDMTDM

Fiber switching

switching

Timeslot switching

Packet switching

S it hi biliti


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Switching capabilities

Timeslot, TDM(SONET/SDH) Wavelength (lambda) Waveband (sets of lambdas) Port (fiber) switching

G li d l b l


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Generalized label

Fiber id in a fiber bundle,

Waveband in a fiber Wavelength within waveband/fiber

Timeslot within a wavelength MPLS/ATM packet switching label

Hierarchical LSP set p


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Hierarchical LSP setup

Un-established connectionsBi-directional connections



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MPLS vs GMPLS issues


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MPLS vs. GMPLS issues

Control and data could be delivered ondifferent paths

Labels must have meaning (map toresources)

Stacking: tunnels in packet networks,physical hierarchies for others

Set/Delete paths can be more complex

than removing labels from forwardingtable

MPLS vs GMPLS issues


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MPLS vs. GMPLS issues

Label set

No wavelength conversion Same wavelength pool across the optical

network

Contention on wavelengths


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How are virtual circuits implemented over datagramnetworks?

What are the advantages and disadvantages of virtualcircuits?

What are the technologies typically used in aproduction network?

Why is MPLS called a 2.5 layer protocol? How does MPLS scale?

What are the advantages and disadvantages of a hard-state vs. soft-state protocol?

What are the network technologies that are managedby the GMPLS protocol?

What does label stacking mean in GMPLS?

HOMEWORKHOMEWORKHOMEWORKHOMEWORK


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HOMEWORKHOMEWORKHOMEWORKHOMEWORK

Review slides

Read from Kurose

Section 5.8 Link virtualization

Do your Moodle homework

Rcom.lecture10.Label Switching

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