GMPLS Switching

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Grotto Networking 2004Page - 1

Fundamental Switching Types

Circuit Switching

Virtual Circuit Switching Datagram Switching

Implications for Signaling, Routing, PathComputation, and Restoration

MPLS and GMPLS control planes


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Differences in Switching Types

Is connection set up required?

Is statistical multiplexing possible? What are the QoS measures? How is

bandwidth allocated?

How much work is needed to provide QoS

guarantees?

How can reliability/protection/restoration be

provided and what are the trade offs?


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Forwarding at each switch

Datagram (e.g., IP)

Based on complete destination address within the packet.

Any valid destination must be forwarded correctly. Virtual Circuits (e.g., MPLS, ATM, Frame Relay)

Based only on a label with the packet header. Only

packets whose virtual circuit has been set up ahead oftime must be forwarded correctly.

Circuits (not packets)

Based implicitly on either time slot or wavelength. Noforwarding information needed in data. Only thosecircuits whose path has been set up ahead of time must be

forwarded correctly.


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Example Network

Datagram, Virtual Circuits, or Circuits

Switches 1-5, Hosts A-J



Datagram Forwarding Example

Switch #1

Dest Port

A 1

B 2

C 3

D 3

E 4

F 4

G 4

H 4

I 3

J 3

Switch #2

Dest Port

A 2

B 2

C 1

D 3

E 2

F 2

G 4

H 4

I 4

J 4

Switch #3

Dest Port

A 1

B 1

C 1

D 1

E 2

F 4

G 3

H 3

I 3

J 3

Switch #4

Dest Port

A 1

B 1

C 3

D 3

E 1

F 1

G 2

H 4

I 3

J 3

Switch #5

Dest Port

A 1

B 1

C 1

D 1

E 2

F 2

G 2

H 2

I 3

J 4

Graph of our

example networ

with switch port

and hosts show

I

I I I I

I



Virtual Circuit forwarding Example

Connections Host A to Host J, Host B to Host C, Host E to Host I,

Host D to Host H, and Host A to Host G



Virtual Circuit Forwarding

Packets are forwarded based on a label in the header

Labels are not destination addresses, usually much

shorter Labels need to be unique on a link but not in a network,

i.e., we can reuse labels on each link.

Switch forwarding tables consist of a map between(input port, packet label) to (output port, new packet

label)

Table entry for each virtual circuit rather than for eachdestination (the datagram case)

Technologies: MPLS, Frame Relay, ATM, X.25



VC Forwarding Table Example

Switch #2

In Port In Label Out Port Out Label

2 5 4 1

2 1 1 1

3 6 4 3

Switch #3

In Port In Label Out Port Out La

1 1 3 3

2 1 3 1

Switch #5

In Port In Label Out Port Out La

1 1 4 2

1 3 2 1

2 1 3 1

Switch #1

Port In Label Out Port Out Label

2 3 5

1 3 1

1 4 1

Switch #4

Port In Label Out Port Out Label

3 2 5

1 3 1

1 4 1 6

33

1

1

1



Real Circuit Forwarding

No more packets

Bit streams are distinguished by port and

Time slots in the TDM case

Wavelength in the WDM case

Frequency in the FDM case Switching independent of bit stream contents

TDM example (same connections as VC case)

Host A to Host J, Host B to Host C, Host E to Host I,

Host D to Host H, and Host A to Host G



Real Circuit Tables Example

Switch #2

In Port In Slot Out Port Out Slot

2 5 4 1

2 1 1 1

3 6 4 3

Switch #3

In Port In Slot Out Port Out Slo

1 1 3 3

2 1 3 1

Switch #5In Port In Slot Out Port Out Slo

1 1 4 2

1 3 2 1

2 1 3 1

Switch #1

Port In Slot Out Port Out Slot

2 3 5

1 3 1

1 4 1

Switch #4

Port In Slot Out Port Out Slot

3 2 5

1 3 1

1 4 1



Time Division Multiplexing

Regenerator(3R) #1

Regenerator(3R) #2

TDM de-multiplexor

TDMMultiplexor

= Optical Fiber

= Regenerator section overhead

= Multiplex section (line) overhead

= User traffic (path layer)= Unused time slots

Path

MS

RS RS RS

Path

MS

RS

TDM Path

Multiplex Section

RegeneratorSection



Real Circuits and Virtual Circuits

Virtual Circuits

Packet based, label (not destination address) in packet

header Doesnt always consume bandwidth, i.e., traffic can be

bursty

Real Circuits

No packets raw bit stream, implicit label with either

time slot or wavelength

Is always consuming a fixed bandwidth, easy to keep

track of bandwidth but not necessarily the most

efficient utilization of link capacity.



QoS with Real Circuits

Bandwidth

Hard bandwidth guarantees are given by default

(even if you dont want them).

Delay

Very little delay variation. Most delay

attributable to propagation. Switching delays in

most circuit switches is minimal. Bit Error Rate

Is the primary signal quality measure


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QoS with Virtual Circuits

Bandwidth

Is by default shared with other users. Effort required to

make guarantees. Very good statistical multiplexinggain can be obtained.

Delay

In addition to propagation and switch processing delaywe now have queueing induced delays

Queueing delays: can be quite large, can be quite

variable By default no guarantees made

Dropped/Errored Packets

Packets can be errored (bits errors), or dropped due tobuffer overflows.


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Protection/Restoration

Failure detection Most circuit technologies have very fast built-in failure

detection.

For packet technologies this hasnt been the case butnew work, e.g., BFD at IETF is underway.

Alternative Routes

Alternate routes for circuit consume bandwidth or mustbe set up on the fly costing time.

Alternate routes for virtual circuits do not consumebandwidth until they are used, hence can be set upahead of time.

Alternate routes can not be preconfigured for datagram

networks and all switches (routers) must recalculaterouting tables based on link failure info.


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Forwarding Tables

All switching types use them

Datagram Forwarding Tables

Need to account for all destinations no matter whos

communicating at any given time.

Circuit and Virtual Circuit Forwarding Tables Entry for each circuit or VC that traverses a particular

switch.

Note that if there areNhost and they all want to talkto each other at exactly the same time then the network

will need to supportN(N-1) circuits or VCs.


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Scaling Forwarding Tables

Modern networks like the Internet and Telephonenetworks consists of 100 of Millions or more hosts howcan we keep our routing tables under control?

Datagram Tables

We route based on networks and groups of networks.Addresses are given out accordingly. This allows theaggregation of destination addresses.

Circuit Tables

We multiplex circuits onto larger and larger trunks in ahierarchy. Switches generally only work at a couplelevels of the hierarchy. Example a switch working withSONET OC48 links (2.5Gbps) will switch with

50Mbps granularity but not 64kbps granularity!


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Setting up the Routing Tables

Finding Paths from Source to Destination

How do we choose our route?

Algorithms

Protocols

Datagram Routing Must make sure that the tables are consistent so

we dont get datagram loops.

Real Circuit Routing

Need to have enough bandwidth available on

the links to support the circuits.

Differences Between Optical Network


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Differences Between Optical NetworkRouting and IP Routing

IP routing

Per hop forwarding of datagrams based on destinationIP address

Every router must have exactly the same networktopology information (links, nodes, and link wts.)

Every router must run exactly the same pathcomputation algorithm

Failure to insure these last two requirements can resultin routing loops and black holes

Differences Between Optical Network


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Differences Between Optical NetworkRouting and IP Routing...

Optical routing

Circuits are source routed; no loops possible

No standardization of path computation required Okay for information to be slightly out of date, e.g.,

available capacity information; worst case crank-backof connection

Unless restoration action is taken based on link stateupdates, routing is not service impacting in transportdomain


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What is GMPLS?

GMPLS = Generalized MPLS

Refers to adaptation ofMPLS control plane for

the control of other technologies

Includes signaling and routing mechanisms

developed for MPLS traffic engineering GMPLS protocols developed under IETF

Previously called MP

S

Wh i MPLS?


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What is MPLS?

MPLS = Multi-Protocol Label Switching

A virtual circuit form of packet switching

such as frame relay or ATM but with a

more IP centric control plane and built in IP

adaptation.

MPLS and IP


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MPLS and IP

A combine IP router / MPLS switch assigns IP

packets to MPLS flows (virtual circuits)

This process is known as classification and can bevery simple or very complex depending upon the

context.

This box is known as a Label Edge Router (LER)

The IP packet header is not touched or looked at

while in the MPLS network The LSR (label switched routers) only switch based onMPLS labels.

An example


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An example

UnlabeledPacket arrives

IP

Egress routerremoves label

IP

IP20

Label switching &packet forwarding

Ingressrouter addslabel to packet

IP10

Autonomoussystem boundary

Label Switched Path (LSP)


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Label Switched Path (LSP)

A Label Switched Path is like a pipe or tunnel to IP packets.However its just another term for a virtual circuit. While travelingon a label switched path, forwarding is based on the label only,not on destination IP address in packet.

Label switched path

Controlling LSP Set-Up: Explicit


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10.1.1.2

10.1.1.6

10.1.1.3

10.1.1.710.1.1.4

10.1.1.5

10.1.1.1

12.0.0.1

Controlling LSP Set Up: ExplicitRouting

POP

Explicit route10.1.1.7 strict10.1.1.6 strict10.1.1.5 strict

10.1.1.2 strict

10.1.1.1 strict

Strict hop

LSP takes direct route to 10.1.1.7

10.1.1.2

10.1.1.6

10.1.1.7

10.1.1.5

Similar procedure can be used for optical connection set-up.

G li d MPLS


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Generalized MPLS

Virtual Circuits! Real Circuits

From real labels in MPLS to virtual labels in GMPLS

Labels in GMPLS TDM where time slots are the implicit labels (e.g.,

SONET)

FDM where frequencies (or s) are the implicit labels(e.g., WDM)

Space-division multiplexing where port numbers are

the implicit labels (e.g., OXCs) Generalized labels used in MPLS messaging =

Generalized MPLS

Documents

GMPLS Switching