Carrier IP Networks:

MPLS
PBX PBX

1 3 5 2 3

Raj Jain
Washington University in Saint Louis
Saint Louis, MO 63130
Jain@cse.wustl.edu
These slides and audio/video recordings of this class lecture are at:
http://www.cse.wustl.edu/~jain/cse570-15/
Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse570-15/ ©2015 Raj Jain
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 Overview

1. Multiprotocol Label Switching (MPLS)

2. GMPLS, T-MPLS, MPLS-TP
3. Pseudo Wire: L2 Circuits over IP
4. Differentiated Services

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Options to Connect Two Data Centers?

Danforth Campus Medical Campus

1. Dedicated Optical fiber (leased from the phone company)
2. Ethernet over Optical Transport Network (all-Optical Switches)
3. Ethernet over Wavelength Division Multiplexing (DWDM)
4. Ethernet over Synchronous Digital Hierarchy (SDH)
5. Ethernet over Plesiochronous Hierarchy (PDH)
6. Ethernet over Pseudo-wire over MPLS
7. Ethernet over Micro-wave
8. Single Pair High-Speed Digital Subscriber Line (SHDSL)
9. Ethernet with enhancements
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Plesiochronous Digital Hierarchy (PDH)
 Plesios + Synchronous = Near synchronous
 Phone Line = 64 kbps = 1 User channel
 North America
 T1 = 1.544 Mbps = 24 User channels T1
 T2 = 6.312 Mbps = 96 Channels

 T3 = 44.736 Mbps = 480 Channels

 Europe:
 E1 = 2.048 Mbps = 32 Channels

 E2 = 8.448 Mbps = 128 Channels

 E3 = 139.264 Mbps = 2048 Channels

Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse570-15/ ©2015 Raj Jain

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 SONET/SDH
E S S E
Ethernet
S S SDH
 SONET=Synchronous optical network
 Standard for digital optical transmission
 Standardized by ANSI and then by ITU
 Synchronous Digital Hierarchy (SDH)
 Protection: Allows redundant Line or paths
 Fast Restoration: 50ms using rings
 Sophisticated management
 Ideal for Voice: No queues. Guaranteed delay
 Fixed Payload Rates: OC1=51.84 Mbps, OC3=155M,
OC12=622M, OC48=2.4G, OC192=9.5G
Rates do not match data rates of 10M, 100M, 1G, 10G
 Static rates not suitable for bursty traffic
  High Cost
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Washington University in St. Louis ©2015 Raj Jain
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Multiprotocol Label Switching
(MPLS)
PBX PBX

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 Allows virtual circuits in IP Networks (May 1996)

 Each packet has a virtual circuit number called ‘label’
 Label determines the packet’s queuing and forwarding
 Circuits are called Label Switched Paths (LSPs)
 LSP’s have to be set up before use
 Allows traffic engineering

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 Label Switching Example
Ethernet Header IP Header Payload

Ethernet Header Label IP Header Payload

64 3 5
<64>
A R1 <3>
<5>
R3 C
B R2 <2>
<5> <3>

5 3 2
Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse570-15/ ©2015 Raj Jain
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 MPLS Concepts
 Forwarding Equivalence Class (FEC): All packets with the
same top label
 Label Switched Path (LSP): End-to-end path from label push
to label pop
 Label Edge Router (LER): Routers that push labels
at the beginning of LSP and pop at the end LER LER

 Label Switch Router (LSR): Core routers LSR LSR

that forward using the label LER MPLS Network LER

 Label Forwarding Information Base (LFIB): Forwarding

table created using routing protocols, e.g., OSPF, BGP
 Label Distribution Protocol (LDP): Protocol to discover
other MPLS routers and set up LSPs.
 Resource ReSerVation Protocol with Traffic Engineering
(RSVP-TE): Alternative to LDP. BGP is also an alternative.
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 Label Stacks
Label
 Labels are pushed/popped
as they enter/leave MPLS domain
 Routers in the interior will use Interior Gateway Protocol (IGP)
labels. Border gateway protocol (BGP) labels outside.
 Bottom label may indicate protocol (0=IPv4, 2=IPv6)

L2 Header LSE 1 LSE 2 ... LSE n

A A
C C
B A B B
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 MPLS Label Stacking
 Label stacking allows:
 Multiple levels of carriers. VPN1
MPLS
 Multiple VPNs in a single LSP VPN2
LSP
 Multiple types of traffic in a single LSP VPN3

Service Backbone Service

Subscriber Subscriber
Provider Provider Provider

Backbone LSP
Service Provider LSP
Subscriber LSP

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 MPLS Traffic Engineering
 MPLS paths can be provisioned to follow a specific path (no
need to use shortest path)
 Resources on the path can be reserved
 Multiple parallel LSPs can be established between the same
pair of nodes
 Fault recovery via shifting traffic to standby LSPs

Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse570-15/ ©2015 Raj Jain

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 Label Assignment
 Unsolicited: Topology driven  Routing protocols exchange
labels with routing information.
Many existing routing protocols are being extended: BGP,
OSPF
 On-Demand: Label assigned when requested,
e.g., when a packet arrives  latency
 Common MPLS Control Protocols:
 Label Distribution Protocol called LDP
 RSVP has been extended to allow label request and
response (RSVP-TE)
 Border Gateway Protocol (BGP): For signaling and
discovery

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IP over MPLS over Ethernet
PE= Provider Edge
CE PE Carrier Network PE CE
CE = Customer Edge

Dest. Adr Src. Type MPLS Customer Customer Rest of IP Ethernet

Next Hop Adr /Len Tag Dest. IP Adr Src. IP Adr Datagram CRC
48b 48b 16b 32b 32b 32b 32b
Label Experimental Stack Position Time
CoS/Drop-Preced. 1  Bottom to Live
20b 3b 1b 8b
 Allows 220 Label switched paths (LSP)
 Each path can have reserved capacity  Guaranteed QoS
 Explicit paths can be designed for specific traffic going to the
same destination  Traffic Engineering
 Alternate paths can be set up for use if anything on the primary
path fails  Fast Reroute  MPLS became a very popular
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 GMPLS
 Data Plane = Wavelengths, Fibers, SONET Frames, Packets
(October 2000)
 Two separate routes: Data route and control route
 Allows data plane connections between SONET ADMs, PXCs.
FSCs, in addition to routers

IP
IP IP IP
IP
Control Plane

Data Plane
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 Martini Draft
 1995-1999: IP over ATM, IP over Ethernet
L3 IP
L2 Ethernet ATM PPP

 2000+: ATM over IP, Ethernet over IP

SONET over IP
L2 Ethernet ATM PPP
L3 IP

 Idea proposed by Luca Martini of

Level 3 Communications and then
Cisco
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Pseudo Wire: L2 Circuits over IP
CE1 PE1 PE2 CE2
Emulated Service
ATM IP ATM
Network Network Network
A B
Frame Relay Frame Relay
Network Network

Pseudo
Ethernet Tunnel Wires Ethernet

Tunnel Hdr Demux Field [Control] ATM ATM ATM ATM

Payload Type How to de-assemble payload
MPLS/GRE/L2TP - How to get to egress
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Ethernet over PWE3 over MPLS
MPLS Label PW Label [Control] Ethernet Frame w/o FCS

PID Flags FRG Length Sequence # PW1

4b 4b 2b 6b 16b MPLS PW2
 Pseudo-Wire Emulation Edge-to-Edge (PWE3) LSP
PW3
 Multiple pseudo-wires per MPLS LSP
Core routers use outer “path” label and not inner “VC” label
 PW (VC) label format is same as MPLS label with End-of-
Stack=1 and TTL=1. PW label is inserted/removed at the edge.
 Payload ID (PID): 5=Untagged Ethernet, 4=VLAN tagged, …
 4VLAN tag put by carrier and customers may or may not be
relevant for forwarding. Determined administratively by PE.
 Flags: Payload specific. FRG: Used for fragmentation
 Pause frames are obeyedhttp://www.cse.wustl.edu/~jain/cse570-15/
locally. Not transported.
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 T-MPLS
 A new profile for MPLS designed by ITU for carriers.
 No connectionless mode. No IP forwarding.
 Minimum IP-based control plane  Reduce cost
 All LSPs are bidirectional
 No penultimate hop option (PHP): PHP  Last LSR pops the
stack before giving it to LER
 No equal cost multiple path (ECMP)
 Primary LSP and Backup LSP. Switching within 50 ms.
 Protection can be linear or ring

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 MPLS-TP
 Joint IETF and ITU effort to harmonize T-MPLS and MPLS-
TE.
 Network provisioning via centralized network management
system or distributed.
 Generalized Multiprotocol Label Switching (GMPLS), which
is used for other transports, can be used for MPLS also.
 Comprehensive OAM for
 fast detection, localization, troubleshooting, and
 end-to-end SLA verification
 Linear and ring protection with sub-50 ms recovery
 Separation of control and data plane
 Fully automated operation using NMS without control plane
No Label distribution protocol (LDP) or Resource
Reservation Protocol with Traffic Engineering (RSVP-TE)
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 Differentiated Services
 A way for IP routers to provide QoS
 Expedited Forwarding (EF): Also known as Premium Service
 Virtual leased line  Guaranteed minimum service rate

 Policed: Arrival rate < Minimum Service Rate

 Not affected by other forwarding classes

 Assured Forwarding (AF):

 Four Classes: No particular ordering

 Three drop preference per class:

Low, Medium, High
 Best Effort Service
 Differentiated Service Code Point (6 bits) encode the service,
E.g., 101110 = EF
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 Summary

1. SONET, SDH, and PDH networks were designed for voice

traffic
2. MPLS is used carriers to provide reliability and throughput
guarantees similar to their previous networks
3. GMPLS extends MPLS to optical wavelengths
4. MPLS-TP is designed with OAM required for carriers
5. Differentiated services provide relative QoS guarantees using
DSCP byte in the IP header

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 Reading List
 Bruce S. Davie, Adrian Farrel, "MPLS: Next Steps," Morgan
Kaufmann, June 2008, ISBN: 978-0-12-374400-5, 432pp.
(Safari Book)

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 Wikipedia Links
 http://en.wikipedia.org/wiki/Differentiated_services
 http://en.wikipedia.org/wiki/Label-switched_path
 http://en.wikipedia.org/wiki/Label_Distribution_Protocol
 http://en.wikipedia.org/wiki/Link_protection
 http://en.wikipedia.org/wiki/MPLS-TP
 http://en.wikipedia.org/wiki/MPLS_local_protection
 http://en.wikipedia.org/wiki/MPLS_VPN
 http://en.wikipedia.org/wiki/Multiprotocol_Label_Switching
 http://en.wikipedia.org/wiki/Operations,_administration_and_
management
 http://en.wikipedia.org/wiki/Optical_Carrier_transmission_rate
s
Washington University in St. Louis http://www.cse.wustl.edu/~jain/cse570-15/ ©2015 Raj Jain
 http://en.wikipedia.org/wiki/Optical_Transport_Network
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 Wikipedia Links (Cont)
 http://en.wikipedia.org/wiki/Pseudo-wire
 http://en.wikipedia.org/wiki/Resilient_Packet_Ring
 http://en.wikipedia.org/wiki/Synchronous_optical_networking
 http://en.wikipedia.org/wiki/Traffic_policing
 http://en.wikipedia.org/wiki/Traffic_shaping
 http://en.wikipedia.org/wiki/Virtual_Private_LAN_Service
 http://en.wikipedia.org/wiki/Wavelength-division_multiplexing

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 Acronyms
 ADM Add-Drop Multiplexer
 AF Assured Forwarding
 ANSI American National Standards Institute
 ATM Asynchronous Transfer Mode
 BGP Border Gateway Protocol
 CoS Class of Service
 CRC Cyclic Redundancy Check
 DSCP Differentiated Services Code Points
 DWDM Dense Wavelength Division Multiplexing
 ECMP Equal-cost Multipathing
 EF Expedited Forwarding
 FCS Frame Check Sequence
 FEC Frame Equivalence Class
 FRG Fragment Bit
 FSC Fiber Switch Capable
 GMPLS Generalized Multi-Protocol Label Switching
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 Acronyms (Cont)
 GRE Generic Routing Encapsulation
 ID Identifier
 IETF Internet Engineering Task Force
 IGP Interior Gateway Protocol
 IP Internet Protocols
 ITU International Telecommunications Union
 LDP Label Distribution Protocol
 LER Label Edge Router
 LFIB Label Forwarding Information Base
 LSE Label Stack Entry
 LSP Label Switched Paths
 LSR Label Switching Router
 MPLS Multi-Protocol Label Switching
 NMS Network Management System
 OAM Operation, Administration and Maintenance
 OC Optical Carrier
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 Acronyms (Cont)
 OSPF Open Shortest Path First
 PBX Private Branch Exchange
 PDH Plesiochronous Digital Hierarchy
 PE Provider Edge
 PHP Penultimate Hop Option
 PW Pseudo-Wire
 PWE3 Pseudo-Wire Emulation Edge-to-Edge
 PXC Photonic Cross-Connect
 QoS Quality of Service
 RSVP Resource Reservation Protocol
 SDH Synchronous Digital Hierarchy
 SHDSL Single Pair High-Speed Digital Subscriber Line
 SLA Service Level Agreement
 SONET Synchronous optical network
 TE Traffic Engineering
 TP Transport Profile
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 Acronyms (Cont)
 TTL Time to Live
 VC Virtual Circuit
 VLAN Virtual Local Area Network
 VPN Virtual Private Network

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