Optical transport networks Introduction Dr. Jnos Tapolcai - - PowerPoint PPT Presentation

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Optical transport networks Introduction

• Dr. János Tapolcai

tapolcai@tmit.bme.hu http://opti.tmit.bme.hu/~tapolcai/

The final goal

• We prefer not to see:

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Telecommunicaiton Networks

http://www.icn.co

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High Speed Backbone

Service providers

PSTN PSTN Internet Internet Video Video Backbone Mobile access Metro Metro Business Business

Telecommunicaiton Networks

Network faults

• We deal with two type of failures

– Physical failts (has a specific location) – Logical faults (Murphy’s law)

Renesys analysis of the

• perating

routers during Sandy hurricane

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Traditional network architecture in backbone networks

IP (Internet Protocol) ATM (Asynchronous Transfer Mode) SDH (Synchronous Digital Hierarchy) WDM (Wavelength Division Multiplexing) Routing, forwarding Traffic engineering Transport and protection High bandwidth

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Evolution of network layers

Thin SONET

Optics

MPLS

SONET IP Optics ATM

Layer 3 2 1

Packet Optical Inter- working Smart Optical Smart Optical Packet IP/Ethernet Packet IP/Ethernet

Layer 2/3 0/1

1999 201x 2003 BGP-4: 15 – 30 minutes OSPF: 10 seconds to minutes SONET: 50 milliseconds

IP

GMPLS

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IP - Internet Protocol

• Packet switched

– Statistical multiplexing – Packets are forwarded based on forwarding tables

• Routing is performed via link-state protocols

– OSPF (Open Shortest Path First), IS-IS (Intermediate System To Intermediate System) – Link states (delays) are spread into the network

• Packets are forwarded on the shortest path tree
• Widespread, its role is straightforward

– From a technical point of view not very popular

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Overlapping prefixes

128.9.16.0/21 128.9.172.0/21 128.9.176.0/24

Forwarding decisions: find the longest prefix match for the destination address

232-1 128.9.0.0/16 142.12.0.0/19 65.0.0.0/8 128.9.16.14

Longest matching prefix 8 32 24

Prefix Length

Default router entry

0.0.0.0/

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IP/MPLS - Multiprotocol Label Switching

• MPLS instead of ATM
• Switching tables

– Link state protocols

• Distribute topology information
• OSPF-TE, IS-IS-TE (Traffic Eng.)

– Control plane and label distribution

• LSPs (Label Switched Path)
• LDP, RSVP-TE, CR-LDP

Forwarding:

Label Swapping

Control:

IP Router Software

Control:

IP Router Software

Forwarding:

Longest-match Lookup

Control:

ATM Forum Software

Forwarding:

Label Swapping

IP Router MPLS ATM Switch

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MPLS overview

• 1a. Routing protocols (e.g. OSPF-TE, IS-IS-TE)

distribute topology information

• 1b. Label Distribution Protocol (LDP)

Configures the packet forwarding tables

• 2. Ingress LER (Label Edge

Router) recieves a packet and attach a label to it

IP

• 3. LSR (Label

Switching Router) forwarding and “label swapping”

• 4. egress LER

removes the MPLS label from the packet

IP

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Traffic Engineering

• A survivable network provides

– The user have to perceive sufficient service between the endpoints of the connection (e.g. congestion) – Efficient bandwidth usage (avoid heavily loaded links) – Even after a failure the network should operate in a reliable manner

• Supervise and optimize routing decisions with

applying traffic engineering (TE). In TE, connection flows are routed on longer paths in

• rder to optimize overall bandwidth usage along

all links in the network.

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What about Traffic Engineering at IP layer?

• TE controls and (optimizes) the traffic in the

network

– The traffic is rerouted for better load balancing and utilization

• The answer is yes in certain sense:

– In case of conjectures TCP sends less packets – IP can deal with topology changes

• There is still a lot of room to improve

– Why using overloaded links if there are spare capacity along other routes?

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TE - The classic example

1 2 3 4 5 6 7 8 9 1 5 6 9 Interference

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Challenges of TE

• Problems with long routes

– Long routes need more network resources

• Eventually every route may become longer than it should be.

– We may limit the length of the routes

• Shortest widest path

– widest = with most free capacity along the path

• Widest shortest path
• Stalled routing information

– Every route avoids the overloaded link – It may lead to oscillation of the traffic

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SONET/SDH

• Time-division multiplexing technology
• Pros

– Fast recovery with 50ms guaranteed recovery time – As a widely deployed and working technology it is cheap

• Cons

– Coarse granularity, provisioned (no control plane) – Framing overhead (an additional layer) – Good for voice traffic, but IP/MPLS/SDH for data…

• New solutions in order to make it more flexible

– Next generation SDH/SONET (ngSDH/SONET)

• GFP: general framing procedure => enables statistical multiplexing
• VCat: Virtual concatenation => allows finer granularity
• LCAS: Link capacity adjustment scheme=> meet application bw need

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WDM

• Frequency-division multiplexing technology

(frequency = wavelength)

• Without any changes in the optical fiber topology

(digging is expensive) the transport capacity of the network is extended

• Typical wavelengthe values are 8 (Coarse WDM)
• r 32 (Dense WDM), or even 155
• With the state-of-the-art modulation technologies

each wavelength can carry 10-40Gbps data

If a fiber is cut 155x40 Gbps = 6.2 Tb loss per second!

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Evolution of transport technologies

Transport

Copper (Analog)

copper (Digital)

Fiber cable Point-point Optical (circuit) switching Opticla packet switching (OPS)

1970 1995

Signalling system

Centralized Network Management System Optical Transport Network (OTN) SDH

Today

Distributed Signalling System (CP)

Transport technology

20xx 20xx

??

Increase in the transmission capacity

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Basic IP-over WDM architecture

• Permanent point-to-point connections, statically

configured via the management system

• Optical circuits are terminated at each node
• O/E and E/O conversions at each node

grooming/degrooming of all requests

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Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures, Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012

IP-over-SDH-over-WDM architecture

• Digital Cross Connects (DXCs) are used
• Low bit-rate requests can be grouped into the same Virtual Container, which

is transmitted over a wavelength channel together with the other VCs.

• At each node OE and EO conversions are performed in order to perform

electronic switching of VCs (through the DXC).

• VCs are terminated whenever a connection needs to be added (or dropped)

to (from) them.

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Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures, Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012

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All-Optical view

• A lightpath is an optical path established between two

nodes of the network, carrying only optical signals. Two lightpaths can use the same links if and only if they use different wavelengths.

• Lightpaths are dynamically built and released connections

using GMPLS via user initiated signals

• Conversion to the electrical domain is needed only at the

endpoints

– Fast

• no need to wait for O/E/O conversion at intermediate nodes

– Wavelength converting transponders

• 3R function Re-time, re-transmit, re-shape in the optical domain
• But: topology mapping is a hard problem

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Optical Cross-connects (OXC)

• Generalized MPLS functions

– Fiber-Switch Capable (FSC) – Lambda Switch Capable (LSC)

• All Optical ADM or Optical Cross-connects (OXC)

– Time Division Multiplexing Capable (TDMC)

• SONET/SDH ADM/Digital Cross-connects

– Packet Switch Capable (PSC)

• Router/ATM Switch/Frame Relay Switch

FSC LSC LSC TDMC TDMC PSC

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Lambda 1 Lambda N

FSC Cloud LSC Cloud TDM Cloud PSC Cloud

Fiber 1 Fiber N

Fiber Bundle

TDM Slot 1 TDM Slot N Packet LSP 1 Packet LSP N Fiber LSP’s Lambda LSP’s TDM LSP’s Packet LSP’s

Combining Low-Order LSP’s Splitting High-Order LSP’s

Distributed signalling - Generalized MPLS

Transparent IP-over-WDM architecture

• Optical Cross Connects (OXCs), Reconfigurable Optical Add-Drop

Multiplexers (ROADMs)

• The requests are groomed and traffic flows bypass IP routers when neither

signal regeneration nor traffic grooming/degrooming is needed.

• In these cases, optical signals are converted into the electronic domain and

electronically processed at the IP layer.

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Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures, Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012

Translucent IP-over-WDM architecture

• The requests are groomed similarly to the TP-IPoWDM case, but

when only signal regeneration is needed, 3R-regenerators are used; thus IP routers are bypassed.

• Tunable Lambda converters and AWG based OXCs
• All-optical wavelength conversion

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Francesco Musumeci, Massimo Tornatore, and Achille Pattavina, A Power Consumption Analysis for IP-Over-WDM Core Network Architectures, Journal of Optical Communication Networks, VOL. 4, NO. 2/FEBRUARY 2012

IP-over-WDM topology mapping

Dependency = Shared risks

Krishnaiyan Thulasiraman and Muhammad S. Javed, Guoliang (Larry) Xue, Circuits/Cutsets Duality and a Unified Algorithmic Framework for Survivable Logical Topology Design in IP-over-WDM Optical Networks, Infocom 2009, pp. 1026-1034

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Shared Risk Link Group

• SRLG expresses statistical dependencies

between a group of network elements (links, nodes, physical devices, software/protocol identities) possibly subject to the same risk of single failure

• Links belong to the same SRLG because

– they are in the same physical hierarchy, which is related to the geographical topology of the network (share the same conduit), – or logical hierarchy, which is related to the lightpaths built on top of this physical topology.

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Recovery in multi-layer networks

Interaction between layers

• Rapid reaction in the upper layer cause redundant

recovery action

Link failure The link is protected by the optical layer Refresh the routing table (link is failed) Refresh the routing table (link is operating) Detect, that the link is

• perational again

100 ms 10 sec 10 sec ALARM Traffic

Source: RHK

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Interworking between layers (1)

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Interworking between layers (2)

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Interworking between layers (3)

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Interworking between layers (4)

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References

• Andrea Bobbio “Dependability & Maintainability Theory and

Methods”

• Jim Gray “Dependability in the Internet Era”
• J.-P. Vasseur, M. Pickavet, P. Demeester, “Network
• Recovery. Protection and Restoration of Optical, SONET-

SDH, IP, and MPLS”, Morgan Kaufmann Publishers, San Francisco 2004.

• Li Yin, „MPLS and GMPLS”
• Kefei Wang, „Protection & Restoration for Optical Ethernet”
• Dimitri Papadimitriou, „Generalized MPLS”
• Ling Huang, „Protection and Restoration in Optical Network”
• Jesús F. Lobo, „Impact of GMPLS on an integrated operator”
• Andrew G. Malis, „Using Multi-Layer Routing to Provision

Services across MPLS/GMPLS Domain Boundaries”