Transcript Lecture 10 - Lyle School of Engineering

Spring 2006
EE 5304/EETS 7304 Internet Protocols
Lecture 10
Multiprotocol Label Switching (MPLS)
Tom Oh
Dept of Electrical Engineering
[email protected]
TO 3-7-06 p.
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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
Standardized by:
DoD, IETF
ITU
Prevalence:
Since 1978
Since 1988
Variable
Fixed, short
Data
All services
Connectionless
Connection-oriented
Complex prefix match
Simple VPI/VCI lookup
Best effort
Guaranteed QoS
Simple
Complex
Developed by:
Packet lengths:
Designed for:
Packet forwarding:
Routing tables:
QoS:
Traffic 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)


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Bandwidth can be reserved on virtual circuits
Traffic flows can be “pinned” to specific routes, allowing
more uniform traffic distribution in network
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:




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IP V6
IP over ATM
Gigabit Ethernet
IP Switching
Why MPLS (2/4)
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.
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
IP over ATM

IP over Large Public Data Networks

LAN emulation

Multiprotocol over ATM
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



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Delay variation + QoS constraints
Diversity routing for load-balancing and reliability
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
Routing table
Exact match
Label Packet
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Entry contains next hop
(or output port) and new
outgoing label value
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
IP packets from
other routers
Attach
label
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Detach
label
BEST OF BOTH WORLDS
PACKET
Forwarding
IP
HYBRID
MPLS
+IP
CIRCUIT
SWITCHING
ATM
• 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!!
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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)

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FEC = class of packets that should be handled same way
along same routes
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”
Layer 2 frame
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Layer 2 header
Shim label
IP packet
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
LSR2
LSP
LSR3 table
LSR1 table
Dest. address
172.12.3
Next hop
LSR2
In-label
4
Out-label
6
LSR2 table
In-label
6
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Next hop
LSR3
Out-label
4
Next hop
R4
MPLS (cont)
 Egress LSR removes label
 LSPs are established by a label distribution
protocol (LDP) and a routing protocol


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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)
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)


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Need to operate IP routing protocols to exchange routing
info with regular IP routers
Need to support LDP
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)
All traffic goes one way
Hop-byhop IP
routing
Dest.
Router
chooses
least-cost
route to
dest.
Label2
Label2
MPLS
explicit
routing
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Dest.
Label1
Router
forwards by
label
Label1
Spring 2006
EE 5304/EETS 7304 Internet Protocols
Lecture 10
Quality of Service (QoS) in IP
Tom Oh
Dept of Electrical Engineering
[email protected]
TO 3-7-06 p.
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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,…

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Many applications require QoS better than best-effort
IETF Integrated Services (Intserv)
 Early 1990s IETF Intserv working group began
specifications of architecture based on:

Guaranteed service: hard QoS per packet flow
•
•

Resource reservations
•

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Bandwidth, packet delay, delay jitter
Flow can be identified by <source IP address, destination IP
address, protocol field, source port, destination port>
Applications request QoS through standardized Resource
Reservation Protocol (RSVP) [RFC 2205]
Or controlled-load service: better than best-effort
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

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Resv message carries RSpec and TSpec
Intserv (cont)
 Admission control: every router has chance to
admit/reject new sessions and reserve enough
resources to ensure the requested QoS

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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
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:




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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)
Stateless Core for Scalability
Edge:
-ass ign DSCP
-packet class ification
-traffic conditioning
Stateles s core:
-forward by PHB
Simple core routers
Complex edge 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

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Core routers forward packets according to their DSCP
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)

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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
Diffserv (cont)
 2 PHBs defined: EF and AF
 Expedited forwarding (EF) PHB



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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,...?
Diffserv (cont)
 Assured forwarding (AF) PHB



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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
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
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
IP addresses, ARP

Dynamic Host Configuration Protocol

Subnetting

Classless inter-domain routing (CIDR)
TEST 2 Review-cont

Network Address translation (NAT)

Virtual Private Networking (VPN)

Mobile IP
 IPv6
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
Motivation and highlights

IPv6 Header, flow label, Next Header

IPv6 extensions

IPv6 addresses

Transitioning from IPv4 to IPv6
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
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
Idea of Label Switching

MPLS Standards

MPLS traffic engineering