MPLS .

• MPLS

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Metro Ethernet - MPLS-based Ethernet MANs

1 An MPLS based Metro Ethernet network uses MPLS in the service provider's

network. The subscriber will get an Ethernet interface on copper (for example, 100BASE-

TX) or fiber (such as 100BASE-FX). The customer's Ethernet packet is transported

over MPLS and the service provider network uses Ethernet again as the underlying technology to transport MPLS. So, it is

Ethernet over MPLS over Ethernet.



1 One restoration mechanism used in an MPLS based Metro Ethernet Networks is Fast ReRoute

(FRR) to achieve sub-50ms convergence of MPLS local protection. For each deployment

situation the benefit versus cost of MPLS must be weighed carefully, so if not implemented on a carrier's distribution network there might be

more benefit for MPLS the core network. In some situations the cost may not warrant the benefits, particularly if sub 50ms convergence

time is already being achieved with pure Ethernet.



1 A comparison of MPLS-based Metro Ethernet against a pure

Ethernet MAN:



1 When using MPLS, Ethernet VLANs have local meaning only (like Frame Relay PVC)



1 Resiliency: pure Ethernet network resiliency relies on Spanning Tree

Protocols STP, IEEE 802.1w RSTP or IEEE 802.1s MSTP (30 to sub 50 ms convergence depending on network design) while MPLS-based MANs use

mechanisms such as MPLS Fast Reroute to achieve SDH-like (50 ms)

convergence times



1 Multiprotocol convergence: with the maturity on pseudowires standards (ATM Virtual Leased Line VLL, FR VLL, etc.) an

MPLS-based Metro Ethernet can backhaul IP/Ethernet traffic together with virtually any type of traffic coming from customer

or other access networks (i.e. ATM aggregation for UMTS or TDM aggregation

for GSM), while this could be more challenging in a pure Ethernet scenario.



1 End to End OAM: MPLS-based MAN offers a wide set of troubleshooting and OAM MPLS-based tools which enrich Service Providers ability to

effectively troubleshoot and diagnose network problems


Multiprotocol Label Switching - MPLS operation

1 MPLS works by prefixing packets with an MPLS header, containing one or more labels. This is called a label

stack. Each label stack entry contains four fields:



1 These MPLS-labeled packets are switched after a label lookup/switch instead of a lookup into the IP table.

As mentioned above, when MPLS was conceived, label lookup and label

switching were faster than a routing table or RIB (Routing Information Base) lookup because they could

take place directly within the switched fabric and not the CPU.



1 Routers that perform routing based only on the label are called label switch routers

(LSRs). The entry and exit points of an MPLS network are called label edge routers

(LERs), which, respectively, push an MPLS label onto an incoming packet[note 1] and

pop it off the outgoing packet. Alternatively, under penultimate hop popping this

function may instead be performed by the LSR directly connected to the LER.



1 LSRs in an MPLS network regularly exchange label and reachability

information with each other using standardized procedures in order to

build a complete picture of the network they can then use to forward

packets



1 In the specific context of an MPLS-based virtual private network (VPN), LERs that function as ingress and/or egress routers to the VPN are often called PE (Provider

Edge) routers. Devices that function only as transit routers are similarly called P

(Provider) routers. The job of a P router is significantly easier than that of a PE

router, so they can be less complex and may be more dependable because of this.



1 When an unlabeled packet enters the ingress router and needs to be

passed on to an MPLS tunnel, the router first determines the

forwarding equivalence class (FEC) the packet should be in, and then inserts one or more labels in the

packet's newly created MPLS header. The packet is then passed on to the

next hop router for this tunnel.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html


1 When a labeled packet is received by an MPLS router, the topmost label is examined. Based on the contents of the label a swap, push (impose) or

pop (dispose) operation can be performed on the packet's label stack. Routers can have prebuilt

lookup tables that tell them which kind of operation to do based on the topmost label of the incoming packet so they can process the packet very

quickly.



1 In a push operation a new label is pushed on top of the existing label,

effectively "encapsulating" the packet in another layer of MPLS. This allows hierarchical routing of MPLS packets. Notably, this is used by

MPLS VPNs.



1 In a pop operation the label is removed from the packet, which may

reveal an inner label below. This process is called "decapsulation". If the popped label was the last on the label stack, the packet "leaves" the MPLS tunnel. This is usually done by

the egress router, but see Penultimate Hop Popping (PHP)

below.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html


1 During these operations, the contents of the packet below the MPLS Label stack are not examined. Indeed transit routers typically need only to examine the topmost label on the stack. The forwarding of the packet is done based on the contents of the labels,

which allows "protocol-independent packet forwarding" that does not need to look at a

protocol-dependent routing table and avoids the expensive IP longest prefix match at

each hop.



1 At the egress router, when the last label has been popped, only the

payload remains. This can be an IP packet, or any of a number of other kinds of payload packet. The egress router must therefore have routing

information for the packet's payload, since it must forward it without the help of label lookup tables. An MPLS

transit router has no such requirement.



1 In some special cases, the last label can also be popped off at the penultimate hop (the

hop before the egress router). This is called penultimate hop popping (PHP). This may be interesting in cases where the egress router

has lots of packets leaving MPLS tunnels, and thus spends inordinate amounts of CPU time on this. By using PHP, transit routers connected directly to this egress router effectively offload it, by popping the last

label themselves.



1 MPLS can make use of existing ATM network or Frame Relay

infrastructure, as its labeled flows can be mapped to ATM or Frame

Relay virtual-circuit identifiers, and vice versa.


Multiprotocol Label Switching - MPLS and IP

1 MPLS-capable devices are referred

to as LSRs



1 MPLS Traffic Engineering relies upon the use of TE extensions to Open

Shortest Path First (OSPF) or Intermediate System To Intermediate

System (IS-IS) and RSVP



1 For end-users the use of MPLS is not visible directly, but can be assumed when doing a traceroute: only nodes that do full ip routing are shown as hops in the path, thus not the MPLS nodes used in between, therefore when you see that a packet hops

between two very distant nodes and hardly any other 'hop' is seen in that providers network (or AS) it is very

likely that network uses MPLS.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

Multiprotocol Label Switching - MPLS local protection (fast reroute)

1 In the event of a network element failure when recovery mechanisms

are employed at the IP layer, restoration may take several seconds which may be unacceptable for real-

time applications such as VoIP. In contrast, MPLS local protection meets

the requirements of real-time applications with recovery times

comparable to those of SONET rings of less than 50 ms.


T-MPLS

1 It was intended specifically as a connection-oriented packet-switched (co-ps) application offering a simpler implementation by removing MPLS features that are not relevant to co-

ps applications and adding mechanisms that provide support of

critical transport functionality


T-MPLS

1 ITU-T ceased work on 'T-MPLS' in December 2008, in favour of MPLS-TP

standardization.[ http://www.itu.int/ITU-T/newslog/Clarifications+On+MPLS+For+Transport+Network.aspx Clarifications on MPLS

for transport network] - ITU-T newslog, 10 March 2009


T-MPLS

1 T-MPLS uses the same architectural principles of layered networking that are used in other technologies like Synchronous Digital Hierarchy|SDH and Optical Transport Network|OTN.

Service providers have already developed management processes

and work procedures based on these principles for use in networks that

use those other technologies.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

T-MPLS

1 In this way 'T-MPLS' was intended to provide a reliable packet-based

technology that is familiar and also aligned with circuit-based transport

networking; it supports current organizational processes and large-

scale work procedures.


T-MPLS

1 'T-MPLS' is a low cost Layer 2 technology that provides Quality of service|QoS, end-to-end OAM and

protection switching.


T-MPLS

1 The following ITU-T Recommendations exist for 'T-MPLS'.

These Recommendations will be superseded (i.e., replaced) by new revisions that apply to MPLS-TP and

reference the joint work being understaken by the ITU-T and IETF.


T-MPLS

1 A further set of ITU-T Recommendations were at a draft stage when work on 'T-MPLS' was

halted. These may be resumed at a later stage to reference the material

developed as part of the MPLS-TP effort.


T-MPLS

1 After IETF raised concerns over 'T-MPLS' technology, mainly about incompatibility with the already

established IP/MPLS, the ITU-T and the IETF started a joint activity to

solve potential issues. The decision was to transfer control to IETF to

develop a new 'MPLS' profile specialized for transport (MPLS-TP)

with input from ITU recommendations


T-MPLS

1 A new activity was added to the charter of the MPLS working group of IETF.


MPLS-TP

1 It will offer a dedicated MPLS implementation by removing

features that are not relevant to CO-PS applications and adding

mechanisms that provide support of critical transport functionality.


MPLS-TP

1 'MPLS-TP' is to be based on the same architectural principles of layered

networking that are used in longstanding transport network

technologies like Synchronous Digital Hierarchy|SDH, Synchronous Optical

NETwork|SONET and Optical Transport Network|OTN. Service

providers have already developed management processes and work

procedures based on these principles.


MPLS-TP

1 'MPLS-TP' will provide service providers with a reliable packet-

based technology that is based upon circuit-based transport networking, and thus is expected to align with

current organizational processes and large-scale work procedures similar

to other packet transport technologies.


MPLS-TP

1 'MPLS-TP' is expected to be a low cost L2 technology (if the limited

profile to be specified is implemented in isolation) that will provide Quality of service|QoS, end-to-end OAM and

protection switching.


MPLS-TP

1 on the design of 'MPLS-TP'. Based on this agreement IETF and ITU-T

experts will jointly work out the requirements and solutions. ITU-T in turn will update the existing T-MPLS

standards http://www.itu.int/oth/T0906000001/e

n based on the 'MPLS-TP' related 'RFC's listed below.


MPLS-TP - Solutions

1 The solutions for the above requirements and framework are as

mentioned below and is under development:

http://wiki.tools.ietf.org/misc/mpls-tp/


MPLS-TP - Solutions

1 * RFC 5718 An In-Band Data Communication Network For the MPLS Transport Profile


MPLS-TP - Solutions

1 * [ http://tools.ietf.org/html/draft-boutros-mpls-tp-loopback Loopback] (Individual Draft)


MPLS-TP - Solutions

1 * [ http://tools.ietf.org/html/draft-fhbs-mpls-tp-cv-proactive Proactive

continuity and connectivity verification] (Individual Draft)


MPLS-TP - Solutions

1 * [ http://tools.ietf.org/html/draft-bhh-mpls-tp-oam-y1731 MPLS-TP OAM based on Y.1731] (Individual Draft)


MPLS-TP - Solutions

1 * MPLS-TP Performance monitoring (Individual

Draft)


MPLS-TP - Solutions

1 * [ http://tools.ietf.org/html/draft-zulr-mpls-tp-linear-protection-switching

Linear Protection Switching in MPLS-TP] (Individual Draft)


MPLS-TP - Solutions

1 * MPLS-TP P2MP traffic protection (Individual Draft)


MPLS-TP - Solutions

1 * MPLS-TP OAM Alarm suppression (Individual Draft)


MPLS-TP - Solutions

1 * MPLS-TP IP/MPLS Interworking (Individual

Draft)


MPLS-TP - Solutions

1 * [ http://tools.ietf.org/html/draft-umansky-mpls-tp-ring-protection-

switching MPLS-TP Ring Protection] (Individual Draft)


Carrier Ethernet - Ethernet over MPLS

1 Ethernet links are transported as “pseudowires” using MPLS label

switched paths (LSPs) inside an outer MPLS “tunnel”


GMPLS

1 The 'Generalized Multi-Protocol Label Switching (GMPLS)'E. Mannie,

Generalized Multi-Protocol Label Switching (GMPLS) architecture, RFC 3945, Oct. 2004, IETF. is a protocol suite extending MPLS to manage further classes of interfaces and

switching technologies


GMPLS - Differences between MPLS and GMPLS

1 http://www.macrothink.org/journal/index.php/npa/article/view/819/704 The support for the additional types

of switching has driven GMPLS to extend certain base functions of

traditional MPLS and, in some cases, to add functionality.


GMPLS - How GMPLS works

1 GMPLS is based on Generalized Labels. The Generalized Label is a

label that can represent either (a) a single fiber in a bundle, (b) a single waveband within fiber, (c) a single wavelength within a waveband (or

fiber), or (d) a set of time-slots within a wavelength (or fiber). The

Generalized Label can also carry a label that represents a generic MPLS label, a Frame Relay label, or an ATM

label.



1 * Resource Reservation Protocol with Traffic Engineering extensions (RSVP-TE) signaling protocol.D. Awduche, L. Berger, D. Gan, T. Li, V. Srinivasan,

and G. Swallow, RSVP-TE: Extensions to RSVP for LSP tunnels, RFC 3209,

Dic. 2001, IETF.L. Berger, Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource Reservation Protocol-Traffic

Engineering (RSVP-TE) Extensions, RFC 3473, Jan. 2003, IETF.



1 * Open Shortest Path First with Traffic Engineering extensions (OSPF-TE)

routing protocol.D. Katz, K. Kompella, and D. Yeung, Traffic Engineering (TE)

Extensions to OSPF Version 2 Architecture, RFC 3630, Sep. 2003,

IETF.K. Kompella and Y. Rekhter, OSPF Extensions in Support of Generalized

Multi-Protocol Label Switching (GMPLS), RFC 4203, Oct. 2005, IETF.


MPLS

1 MPLS supports a range of access technologies, including Digital Signal

1|T1/E-carrier|E1, Asynchronous Transfer Mode|ATM, Frame Relay, and

Digital subscriber line|DSL.


MPLS - Label switch router

1 A MPLS router that performs routing based only on the label is called a

'label switch router' ('LSR') or 'transit router'. This is a type of router located in the middle of a MPLS

network. It is responsible for switching the labels used to route

packets.


MPLS - Label edge router

1 LERs respectively, push an MPLS label onto an incoming packetIn some applications, the packet

presented to the LER already may have a label, so that the new LER pushes a second label onto the

packet


MPLS - Label edge router

1 When forwarding Internet Protocol|IP datagrams into the MPLS domain, an LER

uses routing information to determine appropriate labels to be affixed, labels the packet accordingly, and then forwards the

labelled packets into the MPLS domain. Likewise, upon receiving a labelled packet which is destined to exit the MPLS domain, the LER strips off the label and forwards the

resulting IP packet using normal IP forwarding rules.


MPLS - Routing

1 When a labeled packet is received by an MPLS router, the topmost label is examined. Based on the contents of the label a swap, push (impose) or

pop (dispose) operation is performed on the packet's label stack. Routers can have prebuilt lookup tables that tell them which kind of operation to

do based on the topmost label of the incoming packet so they can process

the packet very quickly.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

MPLS - Routing

1 *In a push operation a new label is pushed on top of the existing label, effectively encapsulating the packet in another layer of MPLS. This allows hierarchical routing of MPLS packets. Notably, this is used by MPLS VPNs.


MPLS - Routing

1 *In a pop operation the label is removed from the packet, which may

reveal an inner label below. This process is called decapsulation. If the

popped label was the last on the label stack, the packet leaves the

MPLS tunnel. This is usually done by the egress router, but see

Penultimate Hop Popping (PHP) below.https://store.theartofservice.com/itil-2011-foundation-complete-certification-kit-fourth-edition-study-guide-ebook-and-online-course.html

MPLS - Evolution

1 MPLS has been originally proposed to allow high performance traffic forwarding and

Traffic engineering (telecommunications)|traffic engineering in IP networks. However

it evolved in Generalized Multi-Protocol Label Switching|Generalized MPLS (GMPLS)

to allow the creation of label-switched paths (LSPs) also in not native IP networks, such as SONET|SONET/SDH networks and

wavelength switched optical networks.


MPLS local protection

1 In MPLS local protection each label switched path (LSP) passing through a facilityThe term facility is usually

referred to a link or node


MPLS local protection

1 In contrast, MPLS local protection meets the requirements of real-time

applications with recovery times comparable to those of Synchronous optical networking|SONET rings ( 50

ms).


MPLS VPN

1 'MPLS VPN' is a family of methods for harnessing the power of

multiprotocol label switching (MPLS) to create virtual private networks (VPNs). MPLS VPN gives network

engineers the flexibility to transport and route several types of network traffic using the technologies of a

MPLS backbone.


MPLS VPN - Point-to-point (pseudowire)

1 Point-to-point MPLS VPNs employ VLLs (virtual leased lines) for

providing Layer2 point-to-point connectivity between two sites.

Ethernet, Time-division multiplexing|TDM, and Asynchronous Transfer

Mode|ATM frames can be encapsulated within these VLLs.


MPLS VPN - Layer 2 VPN (VPLS)

1 Layer 2 MPLS VPNs, or VPLS (virtual private LAN service), offers a “switch

in the cloud” style VPLS service. VPLS provides the ability to span

VLANs between sites. L2 VPNs are typically used to route voice, video, and AMI traffic between substation

and data center locations.


Measuring network throughput - MPLS

1 This generates more overhead that has to be taken into account that a

single MPLS label attached to a packet which is then sent 'natively',

with no underlying protocol to a receiving system.


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