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Spring 2006

EE 5304/EETS 7304 Internet Protocols

Tom OhDept of Electrical Engineering

taehwan@engr.smu.edu

Lecture 10

Multiprotocol Label Switching (MPLS)

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Administrative Issues

We will have test 2 on April 4.

Test will consists of Lecture 6-10

Multiple choice, true/false, short answers

We will have review for test 2 today.

You can use one 3 ½ x 5 card.

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Outline (Comer, pg. 232)

Motivations (IP vs ATM)

Idea of label switching

MPLS standards

MPLS traffic engineering

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Early 1990s “IP vs ATM”

IP ATM

Computer scientists Public carriers

DoD, IETF ITU

Since 1978 Since 1988

Variable Fixed, short

Data All services

Connectionless Connection-oriented

Complex prefix match Simple VPI/VCI lookup

Best effort Guaranteed QoS

Developed by:

Standardized by:

Prevalence:

Packet lengths:

Designed for:

Packet forwarding:

Routing tables:

QoS:

Simple ComplexTraffic control:

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Strengths of ATM

High speed, high throughput switches

VPI/VCI lookup is an exact match algorithm (compared to longest prefix match for IP addresses)

More control over traffic (virtual circuits compared to hop-by-hop routing in IP)

Bandwidth can be reserved on virtual circuits Traffic flows can be “pinned” to specific routes, allowing

more uniform traffic distribution in network

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Why MPLS (1/4)

Internet is getting bigger in any dimension Traffic volume Number of user Number of nodes Bandwidth Required

ISPs need higher performance switching & routing equipment

Scalability

Many solutions being proposed to address those problems: IP V6 IP over ATM Gigabit Ethernet IP Switching

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IP over ATM

Overlay model

IP over ATM described in RFC 1483

“Classical IP over ATM” in RFC 1577

Problem of mapping IP onto ATM was taken up by a number

of standard bodies.

IP over ATM

IP over Large Public Data Networks

LAN emulation

Multiprotocol over ATM

Why MPLS (2/4)

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WHY MPLS (3/4)

Leverage existing ATM hardware

Ultra fast-forwarding

IP traffic engineering Constraint-based routing

Virtual Private Networks Controllable tunneling mechanism

Voice/Video on IP Delay variation + QoS constraints Diversity routing for load-balancing and reliability

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Idea of Label Switching

How to take advantage of ATM strengths without adopting ATM entirely or changing IP control plane (routing protocols)?

Generalize idea of VPI/VCI lookup to “label”

Label is an extra field attached to IP packet header that serves as an index pointing to an entry in routing table

Label

Routing table

Packet

Exact matchEntry contains next hop (or output port) and new outgoing label value

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Label Switching (cont)

LSR (label switching router) is router capable of forwarding packets based on label

Where is the label attached?

Assume LSR are deployed gradually in “islands” in Internet

Edge LSR will attach label which is used throughout island

Island of LSRs

IP packets from other routers

Attach label

Detach label

IP packets

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BEST OF BOTH WORLDS

• MPLS + IP forms a middle ground that combines the best of IP and the best of circuit switching technologies.

• ATM and Frame Relay cannot easily come to the middle so IP has!!

CIRCUITSWITCHING

PACKETForwarding

MPLS+IP

IP ATM

HYBRID

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AT&T Next Generation Network Architecture: The

Concept of One [Eslambolchi, 2002]

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Next Generation Network Architecture

(Dec 2002, J. Jaffee: Lucent President)

M. El-Sayed and J. Jaffee, “A View of Telecommunications Network Evolution”, IEEE Communication Magazine, Dec. 2002.

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Multiprotocol Label Switching (MPLS)

Various companies experimented with proprietary label switching

1997 IETF MPLS working group began to standardize technology integrating ATM-like "label swapping" for packet forwarding with IP layer routing

Use existing IP routing protocols MPLS-enabled routers = LSRs

Ingress edge LSR examines packets and classifies to a flow called forwarding equivalence class (FEC)

FEC = class of packets that should be handled same way along same routes

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MPLS (cont)

FEC granularity is arbitrary - one or more IP "flows" can be mapped to one FEC

Packets are assigned label to identify FEC

Label value is arbitrary, only serves to identify packets of same FEC

Label might be VPI/VCI field in ATM header, DLCI field in frame relay header, or added "shim" label inserted between data link layer header and network layer header → "multiprotocol”

Shim label IP packetLayer 2 headerLayer 2 frame

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MPLS Shim Header (Label) (1/2)

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MPLS (cont)

Core LSRs forward packets based only on MPLS labels, no need to inspect IP header

Incoming label is looked up in forwarding table called label forwarding information base (LFIB)

LFIB contains next hop, forwarding instructions, and new label value

Contiguous LSRs constitute an MPLS domain (maybe an island within IP network)

Concatenated labels constitute a label switched path (LSP) through MPLS domain

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MPLS (cont)

MPLS domain

Ingress edge LSR1

Egress edge LSR3

LSP

Dest. address Next hop Out-label

172.12.3 LSR2 6

In-label Next hop Out-label

6 LSR3 4

In-label Next hop

4 R4

LSR2

LSR1 table

LSR2 table

LSR3 table

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MPLS (cont)

Egress LSR removes label

LSPs are established by a label distribution protocol (LDP) and a routing protocol

LSRs learn topology of network using existing routing protocols, eg, OSPF

A label distribution protocol coordinates assignment of labels among routers, can be standardized LDP [RFC 3031] or extension of RSVP (RSVP-TE)

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IP+ATM

ATM switches already use label switching for packet forwarding (label = VPI/VCI fields) → ATM switches do not need changes in forwarding hardware to support MPLS

IP+ATM refers to combination of ATM, MPLS, and IP technologies in ATM switches

ATM switches do need changes in control plane (software)

Need to operate IP routing protocols to exchange routing info with regular IP routers

Need to support LDP

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MPLS Traffic Engineering

Traffic engineering tries to ensure sufficient resources are available in network to meet traffic demands

Includes uniform distribution of traffic as much as possible

Hop-by-hop IP routing is not designed for traffic engineering

MPLS allows explicit routing - labels “pin” traffic flows to specific routes

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MPLS Traffic Engineering (cont)

Hop-by-hop IP routing

Dest.

Router chooses

least-cost route to

dest.

All traffic goes one way

MPLS explicit routing

Dest.

Router forwards by

label

Label2

Label1

Label2

Label1

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Spring 2006

EE 5304/EETS 7304 Internet Protocols

Tom OhDept of Electrical Engineering

taehwan@engr.smu.edu

Lecture 10

Quality of Service (QoS) in IP

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Outline

Intserv (Integrated services)

Diffserv (Differentiated services)

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Support of QoS in IP

TCP/IP protocol architecture designed in late 1970s to enable a scalable, decentralized internet

IP allows different types of networks to interconnect but only best-effort service (although ToS field in IP header recognizes need for QoS)

TCP adds reliability above IP – the only QoS parameter provided

Success of Internet attests to correctness of TCP/IP design philosophy but mid-1990s Internet was opened to commercial traffic and ISPs

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QoS Support in IP (cont)

New applications are regularly being tried, not imagined in 1970s

Examples: streaming audio/video, voice over IP, desktop videoconferencing, distance learning,…

Many applications require QoS better than best-effort

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IETF Integrated Services (Intserv)

Early 1990s IETF Intserv working group began specifications of architecture based on:

Guaranteed service: hard QoS per packet flow• Bandwidth, packet delay, delay jitter• Flow can be identified by <source IP address, destination IP

address, protocol field, source port, destination port> Resource reservations

• Applications request QoS through standardized Resource Reservation Protocol (RSVP) [RFC 2205]

Or controlled-load service: better than best-effort

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Intserv (cont)

Sender generates RSVP Path message with service specification RSpec and traffic description TSpec

TSpec = peak (max.) rate, average rate, min/max packet size, etc.

RSpec = required bandwidth, slack (tolerable node delay), etc.

Path message finds a route to receiver (remembered by every router) and assigns a unique identifier to session

Receiver returns RSVP Resv message in backward direction to request bandwidth

Resv message carries RSpec and TSpec

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Intserv (cont)

Admission control: every router has chance to admit/reject new sessions and reserve enough resources to ensure the requested QoS

Calculates necessary resources to meet requested QoS based on TSpec

Decides to accept or reject new session Reserves resources (if accepted) Forwards Resv message to next router

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Problems with Intserv

Not scalable to very large networks: routers process requests for each flow and store state info (bandwdith reservation), which increases with number of flows

Reservation overhead is costly for short-lived sessions

RSVP must be deployed to all routers

Not flexible: small number of predefined service classes

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IETF Differentiated Services (diffserv)

Late 1990s IETF Diffserv working group objectives:

Deployable in gradual stages Scalable and flexible service architecture, eg, no per-flow

state info. Minimal overhead on backbone routers Service differentiation with coarse granularity (different

classes of service) instead of absolute guaranteed services with fine granularity (per flow)

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Stateless Core for Scalability

Edge: -assign DSCP -packet classification -traffic conditioning

Stateless core: -forward by PHB

Complex edge routers

Simple core routers

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Diffserv (cont)

To keep core stateless, packets are classified to service class at network edge

Packets carry their service class designation in diffserv code point (DSCP)

DSCP = first 6 bits re-interpreted from ToS field in IP packet header

26 = 64 possible codepoints

Network core uses DSCP in packet header

Core routers forward packets according to their DSCP

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Diffserv (cont)

Diffserv idea: define per-node functional components that can be put together to make different end-to-end services, instead of predefining end-to-end services

Example: intserv guarantees packet delay < D, but not clear what each router should do

DSCP identifies a specific predefined per-hop behavior (PHB)

PHB = instructions for treating packet described in terms of "external behavior"

Eg, queue packet at head of line or back of line No state info. needed in each core router

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Diffserv (cont)

2 PHBs defined: EF and AF

Expedited forwarding (EF) PHB

Forward packets with minimal delay and loss (ie, guaranteed minimum bandwidth)

Only way to guarantee is limiting rate of incoming traffic at network edges => bandwidth brokers keep network-wide view of used/available resources and make decisions for admitting traffic

Other mechanisms: traffic priorities, weighted fair queueing, traffic shaping,...?

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Diffserv (cont)

Assured forwarding (AF) PHB

Statistical service with lower assurance than guaranteed service

4 relative classes can be defined (standard, bronze, silver, gold)

3 packet discarding priorities in each class

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TEST 2 Review

ATM

Cell format, QoS, ATM Services, CAC

IPv4 and ICMP

Role of IP Interworking, IPv4 header, Fragmentation, IP address, ICMP

More about IP Addresses

IP addresses, ARP Dynamic Host Configuration Protocol Subnetting Classless inter-domain routing (CIDR)

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TEST 2 Review-cont

Network Address translation (NAT) Virtual Private Networking (VPN) Mobile IP

IPv6

Motivation and highlights IPv6 Header, flow label, Next Header IPv6 extensions IPv6 addresses Transitioning from IPv4 to IPv6

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TEST 2 Review-Cont

Router, Type of Routers

Generic router and generation routers.

ATM Switching Origins, ATM switching

ATM Fabrics (Space Division Switch, Shared Medium Switch Shared Memory Switch, and Fully Interconnected Switch).

MPLS

Idea of Label Switching MPLS Standards MPLS traffic engineering