Spring 2006 EE 5304/EETS 7304 Internet Protocols
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Transcript of Spring 2006 EE 5304/EETS 7304 Internet Protocols
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Spring 2006
EE 5304/EETS 7304 Internet Protocols
Tom OhDept of Electrical Engineering
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
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