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Class XI MPLS (Multiprotocol Label

Switching)

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Outlines

MotivationMPLS OverviewMPLS Operation and Components

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Motivation

• IPThe first defined and used protocol De facto the only protocol for global internet working

… but there are disadvantages

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Motivation

• IP Routing disadvantages:– Connectionless

e.g. no QoS– Each router has to make independent

forwarding decisions based on the IP-address

– Large IP Header At least 20 byte outing in Network Layer

– Slower than Switching

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Motivation

• ATM– connection oriented– Supports QoS– fast packet switching with fixed length

packets(cells)– integration of different traffic types

(voice, data,video)

…but there are also disadvantages

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Motivation

• ATM disadvantages– Complex– Expensive– Not widely adopted

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Motivation

• Traditional Routing and packet switching– A simple-software-based router platform– L2 switching (Hardware) for local

network

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Motivation

Combine the forwarding algorithm usedin ATM with IP.

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Outlines


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MPLS Overview

IP

ATM, FR, Ethernet, PPP

SDH, ODH,WDM,CSMA

MPLS

Layer 3

Layer 2

Layer 1

MPLS is arranged between Layer 2 and Layer 3

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MPLS Functions

• Specified mechanisms to manage traffic flows of various granularities, such as flows between different hardware, machines, or even flow between different applications

• Remains independent of the Layer-2 and Layer-3 Protocols

• Provides a means to map IP addresses to simple, fixed-length labels used by different packet-forwarding and packet-switching technologies

• Interfaces to existing routing protocols such as resource reservation protocol (RSPV) and open shortest path first (OSPF)

• Supports the IP, ATM, and Frame-relay Layer 2 protocols

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MPLS Example

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Outlines


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MPLS Operation

• Label Creation and Distribution• Table Creation at each router• Label-switched path creation• Label insertion/table lookup• Packet forwarding

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MPLS components

• LSRs (Label Switching Router) & LERs (Label Edge Routers)

• FEC (Forward Equivalence Class)• Label &Label Blinding

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MPLS components

• LER (Label Edge Router)– Resides at the edge of an MPLS network

and assigns and removes the labels from the packets.

• LSR (Label Switching Router)– Is a high speed router in the core on an

MPLS network.– ATM switches can be used as LSRs without

changing their hardware. Label switching is equivalent to VP/VC switching.

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Label

• The labels are used to forward the packets on their way ( switching).

• The labels change during transmission.

• Hardware can be used to switch packets quickly between links.

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Label Format

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Label Details

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Label Creation

• Topology-based method – Uses normal processing of routing

protocol (such as OSPF and BGP)

• Request-based method – Uses processing of request-based control

traffic (such as RSVP)

• Traffic-based method – Uses The reception of a packet to trigger

the assignment and distribution of a lable

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Label Distribution

• LDP (Label Distribution Protocol)– Maps unicast destination into labels

• RSVP, CR-LDP– Used for traffic engineering and resource

• PIM (Protocol-Independent multicast (PIM))– Used for multicast states label mapping

• BGP– External Label (VPN)

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Label-Switched Path (LSPs)

• Hop-by-hop routing– Each LSR independent selects the next hop for a

given FEC. This methodology is similar to that currently used in IP networks. The LSR uses any a viable routing protocols, such as OSPF, ATM private network-to-network interface (PNNI), etc.

• Explicit routing– Explicit Routing is similar to source routing. The

ingress LSR specifies the list of nodes through which the ER-LSP traverses. The path specified could be nonoptimal, as well.

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LSP Details• MPLS provides two options to set up an

LSP– hop-by-hop routing:– Each LSR independently selects the next hop

for a given FEC. LSRs support any available routing protocols ( OSPF, ATM …).

– explicit routing: Is similar to source routing. The ingress LSR specifies the list of nodes through which the packet traverses.

– The LSP setup for an FEC is unidirectional.– The return traffic must take another LSP!

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LSP

A path is established before the data transmission starts.

A path is a representation of a FEC. FEC The Forward Equivalence Class is a

representation of a group of packets that share the same requirements for their transport.

The assignment of a particular packet to a particular FEC is done just once (when the packet enters the network).

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Label Space

• Per Platform– The label values are unique across the whole

LSR. The Label are allocated from a common pool. No two labels distributed on different have the same value.

• Per Interface– The label ranges are associated with interfaces.

Multiple label polls are defined for interface, and the labels provided on those interfaces are allocated from the separate polls. The label values provided on different interfaces could be the same.

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Label Merging

• The incoming Streams of traffic from different interface can be merged together and switched using a common label if they are traversing the network toward the same final destination. This is known as strem merging or aggregation of flows

• If the underlying transport network is an ATM networks, LSRs could employ virtual path (VP) or virtual channel (VC) merging

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Label Retention

• Conservative– The binding between a label and an FEC received

from LSRs that are not the next hop for a given FEC are discarded. This mode requires an LSR to maintain fewer Lables.

• Liberal– The binding between a label and an FEC received

from LSRs that are not the next hop for a given FEC are retained. This Mode allows for quicker adaptation to topology changes and allows for the switching of traffic to other LSPs in case of changes

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Label Control

• Independent– An LSR recognizes a particular FEC and makes

the decision to bind a label to the FEC independently to distribute the binding to its peers. The new FECs are recognized whenever new routes become visible to the router

• Ordered– An LSR binds a label to a prticular FEC if and

only if it is the egress router or it has received a label binding fro the FEC from its next hop LSR.

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Signaling Mechanisms

• Label Request– An LSR requests a label from its

downstream neighbor so that it can bind to a specific FEC

• Label Mapping– In response to a label request, a

downstream LSR will send a label to the upstream initiator using the label mapping mechanism

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Label Distribution Protocol

• Discovery Messages– Announce and maintain the presence of an LSR in a

network

• Session Messages– Establish, maintain and terminate sessions between

LDP peers

• Advertisement Messages– Create, change and delete label mapping for FECs

• Notification Messages– Provide advisory information and signal error

information

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Label Stack

• The label stack mechanism allows for hierarchical operation in the MPLS domain. It basically allows MPLS to be used simultaneously for routing at the fine-grain level

• Each level in a label stack pertains to some hierarchical level. This facilitates a tunneling mode of operation in MPLS

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CR (Constraint-based routing)

• CR takes into account parameters such as link characterisitcs (bandwidth, delay, etc. ), hop count and QoS

• The LSP that are established could be CR-LSPs, where the constraints could be explicit hops or QSOS requirements

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Advantages of MPLS

Routing takes place only in the LERs (Label Edge Router)

Label switching increases speedProvides Quality of Service It hides the link layer and the differences between different Layer 2 protocols

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Disadvantages of MPLS

An additional layer is addedThe router has to understand MPLS

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แบบสอบถามเพ��อการร%างหัล�กส�ต่ร ปร�ญญาโทร สาขา Network

engineering• เร#ย์น้วิ�ชุาอะไรบ�างต่ลอด 2 ป* • อย์ากเร#ย์น้วิ�ชุาหัร�อเน้�+อหัาอะไรเพ��ม• อย์ากใหั�ต่�ดเน้�+อหัาอะไรออก• ล�าด�บวิ�ชุาท#�เร#ย์น้ควิรเปล#�ย์น้หัร�อไม%• ควิรม# Lab อะไรเพ��มหัร�อเปล%า• ควิรป�พ�+น้วิ�ชุาอะไรหัร�อเน้�+อหัาอะไร

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โครงสร�างหัล�กส�ต่รใหัม%

Transmission system+Data

Communication (L1->L2)

Computer Network (L3->L7)

Operating System

CCNA1-2

C, C+, Script( perl, bash, etc.)

Network Switching and Routing

Network Management

Project IWireless Networks Network security

Project II

CCNA3-4

Information Technology for

Organization Management

Wireless Network Lab

11

8

10

8

11+8+10+8=37

Telecommunication Networks

Term 1

Term 2

Term 3

Term 4

itec4610 network switching and routing

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