large scale ip networks
TRANSCRIPT
Agenda! Background! What is the problem! Solutions - (G)MPLS! Issues with the solutions above! An alternative proposal! Questions
Acronyms! PPS: Packets Per Second! ER/TE: Explicit Routing/Traffic Engineering! FEC: Forwarding Equivalence Class! CSPF: Constrained Shortest Path First! GMPLS: Generalized Multi-Protocol Label Switching ! IGP: Interior Gateway Protocol (OSPF/IS-IS/RIP)! LDP: Label Distribution Protocol! SPF: Shortest Path First
Guide For Talk! Optimize On
! Getting 95% of the problem with 15% effort! Flexibility
! Operations And Engineering Guy! Expertise in building systems, networks, and
organizations that run IP networks! Seen the results of the meeting between
“Networks Powered by PowerPoint ™” and the Real World ™
! Hint: The Real World ™ wins every time
“I dislike rigidity. Rigidity means a dead hand and flexibility means a living hand. One must understand this fully.”
- Miyamoto Musashi
Ordinal Vs. Cardinal Optimization*
! More important to quickly narrow the search for an optimal solution to a “good enough” subset than to calculate the “perfect solution”
! Ordinal (which is better) before Cardinal (value of optimum)
! Ballpark estimate! Historical Internet Vs the Telco approach
*Based on work done by Yu-Chi Ho
we don't need to boil the ocean - all we want is a poached fish
Soften Requirements! Softening strict requirement of
optimality can make problems tractable
Cost = $1m
Cost = $1m/x
Getting the best decision for certain
Getting a decision within the top 5%With probability = 0.99
In real life, we often settle for such a tradeoff with x=100 to 10,000
MPLS! M is for Multiprotocol (inside and out)
! But despite being able to carry “anything” inside, IP is the single most common payload
! IP routers are the most common “outside”
! Nameable aggregates of traffic have value! Explicit Routing! Comes with a price! Hype! QoS! Sings, dances, julienne fries!! One potato, to go.
What Is The Problem! Dense Network! Protect Paths! Routers out of PPS! Solved by
! Constrained Meshed Routing
! Mindset Changed
Problems Solved! MPLS solved ER/TE problems! RSVP-TE is extensible to ask for particular
qualities of service etc. rather than just raw BW! Got perverted by the vendor marketing
folks! Try to do everything under the sun
! QoS!
The Myth of QoS! FECs can be described which ask for particular queuing
disciplines inside switches and routers (via the RSVP-TE mechanism) is very popular with some people
! Fancy queuing and careful resource management can in theory approach the lack of jitter that TDM provides! Never overbook the jitter-free traffic! Jitter-free traffic squeezes out the more elastic traffic
! Belief is that the combination of the control plane and the label-packet format can fully replace traditional TDM! At the cost of some complexity and deploying "new
stuff"
QoS! Tough thing to define
! Tougher to sell! Better make sure Best Effort Internet services work! All Gold, All the Time.
! Differentiation must be palpable to the end user! Cost must not be prohibitive! Should not be hard to manage! Integrated with the best effort network! Also keep up with best effort deployment
! QoS == Quantity of Service! What Are We Optimizing For?
These exhibits were originally published in Peter Ewens, Simon Landless, and Stagg Newman, "Showing some backbone," The McKinsey Quarterly, 2001 Number 1, and can be found on the publication's Web site, www.mckinseyquarterly.com. Used by permission.
Best Effort Is Good Enough! Statistical multiplexing saves money! Mixing various queuing disciplines into a statistically
multiplexed network is! Complicated! Costly! Full of side effects
! Overprovision for now! Less "full" at peak traffic point: less efficient ! But, no queue means no need for queuing disciplines! Small risk of jitter/delay for the sake of less complexity
vs. much more complexity
Cheaper Faster Better! Internet enabled applications will squeeze out
(eventually) applications that aren’t.! The number of mobile phone subscribers
worldwide is expected to reach 560 million by year-end and to exceed the number of households with televisions by 2003.
-Will Daugherty (McKinsey & Company)
GMPLS! The RSVP-TE label mechanism is
generalized in GMPLS to request resources of any nature, notably lambdas, SDH MUXes and "patch-panel" mappings
! GMPLS is a CONTROL PLANE not a packet system: there is no requirement that MPLS "frames" be used in an GMPLS network
GMPLS! No centralized provisioning database! Available resources are consumed where the
CSPF reservation is allowed! IGP does topology discovery (OSPF) detects
faults and allows restart of reservations! OSPF LSP database is also consulted to find
the the CSPF, which will be requested (by RSVP or LDP to all the elements along the path) first.
Unified Control! The GMPLS argument is that one
control and packet system can be used to knit together tremendously different network components! IP Routers! Switching gear
! Including ATM, SDH and WDM "switches"
GMPLS Flexibility Points
! UNI
! RSVP-TE or LDP based
! Routers request concatenation of resources through the network
DWDMDWDM DWDMDWDM
MPλλλλS Control Plane
DWDM Signalling
Control Control Control Control
RouterRouter
ATMATMswitchswitchSONETSONET
ADMADM
RouterRouter
ATMATMswitchswitchSONETSONET
ADMADMXCXC
∼∼∼XCXC
∼∼∼
Benefits Of GMPLS! Meshy Restoral! Clients of all kinds (routers, TDM boxes)! Saves on router ports
! Routers make expensive OEO! Mitigation: cost is amortized over lifetime of
box
! Flattened topology
Benefits of GMPLS! Signaling between routers and optical
switches! Self provisioning! Faster Provisioning
Issues! Best Abstraction Of A Topology Is The
Topology! Spend money on packet-handling rather than
managing lots of meshed mid-sized boxes
! “We have too many boxes now. We’re not going to have a million more boxes in the network. That scenario is utterly unthinkable”
-Mike O’Dell
Reexamining Optical Network Assumptions! Replacing patch cords with OXCs doesn’t
affect the network much! OXCs et al. allow you to redeploy the topology
! Real world topology doesn’t change very fast! Extend planning horizon! City-pair macroflows are long lived and tractable! Cost and complexity of running an IGP over the
optical boxes to gain speed of restoral over a centralized system needs to be examined carefully
Thoughts! Our Control Theory-Fu is weak
! Get provisioning from 18 months to a day or two
! We don't know anything we could do with 50ms provisioning without making a disaster
! Centralize view of topology and lay out paths using expert systems vs. SPF in the network
Self Provisioning Issues! Internet is an intentionally overdamped
system! The consequences of being underdamped
are catastrophic! Got the T-shirt
! Frame Relay wars
! Improving the frequency response of the implementation implies lots more T-shirts
Optimize For The Biggest Consumer! Design Goals Are To Replace
! Back-to-back OEO in middle of nowhere! Unnecessary OEO for passthrough! Slow Humans
TypicallyPacketPacket
CrossCrossConnectConnect
SONETSONETMuxesMuxes
DWDMDWDM CrossCrossConnectConnect
SONETSONETMuxesMuxes
DWDMDWDM
SONETSONET PhotonsPhotons SONETSONET PacketPacket
RoutersRouters RoutersRouters
Multiple levels in Layer 1
Typical Hut
ODF
Flexibility Points: Add or drop traffic to the network
ADM
How To! Use strong enough lasers
! Avoid turning “pass-through” frequencies into electrons
! Attenuation hit (that’s what OEO is for)! Divert frequency bands onto dark or
transponders which do frequency conversion
How To! Integrate the MUX within the control plane of
a large router! Tell router not to use a certain frequency
band for p2p traffic with its neighbor any more because it has to be dropped out an optical port.
! That port is dark fiber terminating! A small WDM MUX (8 colors) ! End piece of equipment @ 2.5GHz, 10GHz, etc.
Proposal
! Optical ADM emits light as necessary by intercepting one frequency & converting it electrically
! The ADM becomes the source of the bits
OEO+OADM
ADM
How To! The router doesn't look at the signal! Doesn’t do
! Regeneration! Look for SONET/SDH signaling
! Passes through the frequency! Unfortunate attenuation hit, but that's
what OEO deals with).
How To! Any space not "reserved" is used in whatever way
seems optimal for big-router-to-big-router connectivity, for moving packets.
! Use some of the spectrum to build a “sub-ring” or smaller p2p circuits for talking to smaller routers in flexibility points along the way, if any
! Or use separate fiber, if fiber-rich or for retaining a historical system in parallel
! Building a “virtual dark fiber” across this is possible, but you need to do your own regen (OEO), cross-connection, etc.
This Solves For! Optimizing the transmission resources
for the largest consumer of optical bitstream – IP
! Saves money on 1310/1550 lasers! Power! SG&A
Save The Hype“You cannot combat glossy magazines with
logic”
-Jeff Aitken
“Somehow “best effort” has become a pejorative.”
-Mike O’Dell
Conclusions! Even the very wise cannot see all ends
! Lets not paint ourselves into corners! Stupid is flexible! Modularity
! Theory of Real Options! End2end arguments in system design
! Trade upfront CAPEX for long term OPEX! Rise of the Stupid Network! Assumptions still undergoing work
References! GMPLS: http://search.ietf.org/internet-drafts/draft-ietf-ccamp-gmpls-architecture-00.txt! MPLS: http://www.rfc-editor.org/rfc/rfc3031.txt
Questions
Thanks to Mike O’Dell, Sean Doran, and
Bill Barns