unswsubjects.ee.unsw.edu.au/tele9751/lec/1.pdffrom full transcript of the discover magazine...

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School of Electrical Engineering and Telecommunications

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TELE 9751 Switching Systems Architecture

TELE 9751 Internet Equipment Architectures Session 1 2017

Lecturer: Tim Moors

97516H 10 March 2017 Tim Moors Copyright ©

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2 10 March 2017 Tim Moors Copyright ©

Cisco Nexus 5548P Switch

Cisco Nexus 5548P Switch Architecture white paper

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http://www.cisco.com/en/US/prod/collateral/switches/ps9441/ps9670/ps11215/white_paper_c11-622479.html

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Cisco Catalyst 3550

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Cisco Nexus concepts in TELE9751

Bigger @ http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/misc/1nexus.pdf 9751E9

http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/misc/1nexus.pdf

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What’s important Approach: First cover important topics, then secondary topics

Tertiary topics hidden from lecture but appear in PDF.

RK Why learn about what goes on inside?

36 Essential administrivia

EM Switched networks

FH Functional definition of “Switch”

55 Lower Layer Switching

FN Higher-layer (4+) switching

D1 Switch classification … By location in … network

KH Switch trends as location in hierarchy changes

YM Switch trends as location in hierarchy changes

!!! Risks with ranking importance

10 March 2017 Tim Moors

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Risks with ranking importance

Evaluation of importance is noisy/subjective

Importance isn’t a step function; n+1th only slightly

(negligibly?) less important than nth of top-n

Top slides may be incomprehensible without context of less

important slides (e.g. EM “advantages”: relative to what?) e.g. tempting to include summary slides

Often r slides represent set of S; importance of slide r << set

S e.g. FN represents set of slides (FN, PR, TR) about higher layer

switching

10 March 2017 Tim Moors 9751!!!

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Who cares?

“Several years ago, I asked my wife: “Does it bother you that

you don’t know how the television works?” I mean, she

just uses it,. . .

She said, “I know how it works; you turn the switch and the

thing comes on.”

I thought, “You know, she's right.” There’s these whole

layers of understanding. There’s a layer where you know

how to turn a switch and make the TV come on.”

-- Robert W. Lucky

From full transcript of the Discover magazine Roundtable "Will Computers Replace

Engineers?“ held as part of IEEE’s INFOCOM Conference, 9751NQ 🚪

http://web.archive.org/web/20041031041432/http:/www.comsoc.org/headlines/EngineerRTFINAL.pdf

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Why learn about what goes on inside? Of a network

Retail customers, businesses

ISPs

Network administrators

Of network equipment

ISPs, businesses, homes

Vendors, e.g. Cisco

Development engineers

Users

Service providers

Designers

Learning about a lower layer helps:

• Select

• Troubleshoot

• Curiosity

• Move closer to the source

• Technophobes

• Geek users

• Operators – Cisco certified

• Network designers

• Equipment designers

• Electronics/software/business design

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Data centre switching

Popular sites (e.g. Google, Facebook, Apple) run their own, others

may buy “cloud” service from a provider (e.g. Amazon,

Akamai, NextDC)

Multiple servers share infrastructure for power, cooling, network

access 100 to 100k physical servers host arbitrary # of virtual machines;

load balancers spread load.

Racks (about 6ft high) hold equipment (typically 19” wide) e.g.

20-40 servers in a rack (larger DCs may use shipping containers)

“Top of Rack” switches interconnect servers within rack + this rack to

others in DC & to Internet access.

ToR switches often interconnect using a Clos fabric [JX>

10 March 2017 Tim Moors

https://www.google.com.au/about/datacenters/inside/streetview/

9751!!!

https://www.google.com.au/about/datacenters/inside/streetview/

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Essential administrivia

1&2

3&4

5

7-9

10&11

12

6 Mid-session exam Final exam Project

975136 Assignment

Read the TELE9751 course outline at

http://www.engineering.unsw.edu.au/electrical-engineering/course-profiles

Tim encourages participation (cards) and constructive suggestions






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Outline (for today) Administrivia: Course outline

Introduction Non-switched networks Defining “switch” Switch examples Switching in other fields External perspective of switches Switch classification 1: External perspective of switches History of switching technologies Terminology Historical perspective Routers vs switches Switching at various layers Hierarchical networks Why have them? How switches vary by location

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https://www.engineering.unsw.edu.au/electrical-engineering/sites/elec/files/u12/CourseOutlines/S12017/TELE9751_S12017.pdf

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TELE9751 compared to TELE9752

9751 is more technical:

• design choices & evaluation

• draws from physics, electronics, computer science

• more (& more interesting?) concepts

More information?

• Information on slides rather than textbook

• Distil in your own notes, see sample for week 8

• View and make mind maps – see course web page

10 March 2017 Tim Moors 9751LK

http://subjects.ee.unsw.edu.au/tele9751/lec/8notes.pdf

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Call for participation Tim welcomes participation during

classes, and encourages it by offering

bonus marks

Hard to remember who made that great

comment during lecture

=> Issue cards to people who participate

well in lecture.

Blue = good, Green = better

See Tim during breaks in lecture to

record last 3 digits of your student ID,

e.g. z1234567 (some exceptions need 4)

Copyright © 2017 Tim Moors

Image from http://eyad-arqoub.com/red-card-lifting-in-my-face/ tele975110

http://eyad-arqoub.com/red-card-lifting-in-my-face/













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Lecture shorthand

Some abbreviations that you may see in lectures: standard mathematics: implies, ≈≊∝

↑↓ increases/decreases √× advantages/disadvantages c.f. compare with s.t. such that wrt with respect to aka: also known as a la: in the manner of b bits, B bytes, k 1000, M 1 000 000, G 1 000 000 000 Ki = kibi = 210=1024, Mi = mebi = 220, Gi = gibi = 230

Slide IDs (click here for more info), e.g. [T9] = http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/T9 Underlined text is usually a link that is clickable in the PDF

∃∃

∃ there exists ∀ for all

9751T9 IEEE 1541 defines prefixes of binary multiples, e.g. kibi 🚪

Slide #s jump

because of slides

hidden from lecture

but appearing in PDF

Stars mark

important slides

(except for this one)

http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/

http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/T9.html

http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/T9

http://en.wikipedia.org/wiki/IEEE_1541

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Ad break

Want to do a thesis/project on networking, e.g. as part of

MEngSc(Ext), ME or BE degree?

Several in the broad areas of “network infrastructure” “video

communication” and “smartphone apps” on offer

See http://www2.eet.unsw.edu.au/~timm/thesis.html

You must have done well in networking course(s), possibly

have industrial experience, confident programming

Email resume, academic records & topics of interest to

[email protected] by noon tomorrow.

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http://www2.eet.unsw.edu.au/~timm/thesis.html

http://www.eet.unsw.edu.au/~timm/thesis.html

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Outline

Motivation for (& definition of) switching

Non-switched networks

Full mesh

Broadcast and select

Switched networks

“Switch” defined

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Network traffic

2 dimensions (More details next week):

Space: Directed [0M>:

• Most is unicast (1-1)

• Some is multicast (1-multiple)

• Broadcast (1-all) doesn’t scale

Time: Bursty [CN>: Sources don’t always have information

to send.

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Full mesh networks

• Each terminal directly connects to every other terminal (that it communicates with)

× Uneconomical: Many (N(N-1)/2, e.g. 15) connections that are poorly utilized (burstiness)

× Unreliable: Single path between endpoints (unless nodes are willing to forward for others)

× Insecure: Endpoints control who can access them. Can’t partition or centrally manage policy.

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Broadcast and select networks

• Each terminal connects to a common shared medium. • Information is broadcast from sources. • Destinations select appropriate information. × Poor scalability: Shared medium is a bottleneck.

• As # of nodes ↑, transmission time spent arbitrating access (e.g. WiFi collisions) also ↑.

× Poor security: Information is visible to all nodes. Endpoint control as per mesh.

× Poor reliability: Single failure point. × Difficult upgrade: Backward compatibility baggage, unless

upgrade is universal.

or

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Switched networks Most traffic is directed (broadcast=bad) and bursty

(mesh=bad)

Switches • Forward traffic only towards its destination(s)

• Multiplex traffic from multiple sources

Advantages:

√ Economical for large scale, e.g. 9 connections

√ Smaller collision domains; less time spent arbitrating access

√ Relatively secure

√ Reliable, e.g. choice of path

√ Simple to upgrade supports heterogeneity

Caveats:

× Switches cost

× Switches may get congested or “block”

× Switches introduce delay

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Functional definition of “Switch” “Switch”: Any device with multiple ports that aims to direct

unicast traffic only to one output port that leads to the destination.

Notes:

“functional definition” – not a marketing “definition” – see later [88>

“multiple ports” – multiple input ports alone would be a multiplexer; multiple output ports alone a demultiplexer. Ports aka interfaces.

Multiple is best thought-of as 3 or more, in which case the switch must decide which output port to send traffic to. A 2 port switch (the routing part of many home “routers” is just that) is effectively a filter. See later [X2>

“unicast traffic” – multicast traffic may be sent to multiple output ports leading to multiple destinations.

“aims to” – “Ethernet switches” may be unable when they are yet to learn the destination’s location

“one output port” rather than “the output port” – there might be choices; which port is the best is a routing decision.

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http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/88.html

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Relatives of “switches”

A multi-port device that directs input traffic to all ports isn’t a switch.

Call it a hub [HE>, combiner [ZF>, etc. (covered in later lectures)

A router is a type of switch that deals with network layer headers.

“a type of switch” => switch functions (fabrics, packet classification,

scheduling, buffer management etc) are used in routers.

We’ll consider detailed definitions of types of switches (routers, Ethernet

switches, etc) shortly.

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Tiny switches

How few ports can a switch have? (recall “multiple” ports <FH])

2 ports: traditional “bridge” [0W>, WiFi Access Point,

“gateway” e.g. home “router” = Ethernet switch + 2-port GW,

Firewall, address translator, cache [9W>

3 ports: VOIP phone: Placed inline between existing PC

(port 2) and Ethernet outlet (port 3) (Also in Windows “network bridge” [UM>)

10 March 2017 Tim Moors Front photo from http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps10998/data_sheet_c78-601648.html

Rear photo from http://www.cisco.com/en/US/docs/voice_ip_comm/unified_communications/csbuc300/installation_an/UC320W_SPA300-500_Install_AN_78-20414.html

9751X2

☎

☒ RJ45

PC symbol

http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps10998/data_sheet_c78-601648.html



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Multidisciplinary switching

Switching information

Switching stuff

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Switching information

• Data communications, integrated services networks

• Telephone network

• Gave rise to Clos networks, SS7 signalling, etc

• Interconnection networks for parallel processors

• Strong parallels with structured

space-division networks (e.g. Banyan)

• Grid computing

Figure 1-8 from A. Tanenbaum and M. v. Steen: 'Distributed Systems: Principles and Paradigms'

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Switching “stuff”

Useful sources of accessible analogies to help

understand networking:

• Vehicular traffic – railway switching yards,

automotive traffic (→ congestion control)

• Irrigation systems → fluid flow models

& Hurst parameter

• Utility networks (water, sewerage,

electricity, gas ...) → reliability assessments

• Merchandise distribution networks

Photo from http://www.flickr.com/photos/dustpuppy/78871005/ licensed under Creative Commons Attribution 2.0

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Outline

External perspective of switches

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Switch classification 1:

By modularity of implementation Bounded systems: fixed,

pre-determined configuration.

Stackable switches: intra-stack connection:

high-speed port (e.g. 10 Gig Ethernet “fabric interconnect”)

Low Voltage Differential Signaling (LVDS)

Chassis switches:

Increasing

• cost

• performance

• flexibility

Image sources unknown 9751MV

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Dominant manufacturers

Computing

background (common in

access

networks)

Consumer devices: D-Link, Netgear, Belkin/Linksys Brocade HP Cisco Juniper, Avici

Telephony

background (common in

core networks)

Alcatel-Lucent

Nokia Solutions & Networks

Ericsson

NEC

Marconi

Newer Chinese manufacturers: Huawei Technologies, ZTE

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Cisco

One of the pioneers

Established Internet Operating System (IOS) that provides consistent interface to their systems

Preaches IOS and products through certification programs, e.g. CCNA, CCNP, CCIE

Good support “networks”

Expensive

Top-of-the-line products:

Cisco Carrier Routing System (CRS)-1 (3D model)

CRS-3 http://www.cisco.com/en/US/prod/routers/ps5763/cisco_crs-3_demo_video.html

9751H7

http://cseweb.ucsd.edu/~varghese/crs1.ppt



http://www.cisco.com/assets/cdc_content_elements/3d_models/router/crs1/?NO_NAV

http://www.cisco.com/en/US/prod/routers/ps5763/cisco_crs-3_demo_video.html




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Outline

Evolution of networks

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History of switching technologies

1876 Bell is first to patent the telephone; manual switchboards

1892 Strowger automated telephone switch

1937 Reeves invents Pulse Coded Modulation (digital transmission)

1950s Research into switching networks (Clos, Batcher, etc)

1965 Bell System introduces the 1ESS (Electronic Switching System)

early- Packet switching invented by Baran, Davies & Kleinrock 1960s

1969 ARPAnet contract awarded to BBN

1973 Metcalfe invents Ethernet

1970s Optical fibre transmission systems

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History of switching (continued)

1976 X.25 recommendation for public data networks

1978 OSI Reference Model

1982 Bell System introduces 5ESS switch

1984 Cisco (dominant router vendor) founded

1988+ ATM

1993 WWW boom

Late MPLS, diffserv, photonic networks, “active networks”,

1990s caching, Content Distribution Networks

21st C software switching between virtualised machines

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Trends in history

Switching techniques: circuit (originally), packet (1960s), more

circuits

What happens in core: switching only (to 1990s), active

networks, caches, CDNs (later)

Content that is switched: Telephone, then data, then integrated

(TV traditionally broadcast, not switched)

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Outline

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Historical perspective of terms

Switching (and hence switches) preceded routing.

=> separation between “switch” (e.g. phone switch) and packet

networks (using gateways, routers, etc)

In the 1990s, the “need for speed” led to new “switching” techniques =>

association between “switch” and “fast”.

1950s 1960s 1970s 1980s 1990s 2000+

telephone

switching

packet

switching

Internet

gateways

LAN bridges (Ethernet switches)

routers‡

brouters

ATM

fast packet switching

photonic

switching

layer 4+

switching

‡ The first RFCs to mention routers were RFC 898 (1984) and RFC 1009 (1987) 9751XF

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Marketing terms/classification

The most widespread, and eventually you have to use it to purchase products

Designed/evolved to earn revenue for manufacturers: It’s easy to upsell to a bewildered customer

Router: A multiport device that uses network layer (e.g. IP) headers to decide which port to forward packets on

e.g. Cisco 7000 series router

“Switch”: A multiport device that uses link layer (e.g. Ethernet) headers to decide which port to forward packets on

e.g. Cisco Catalyst 2900 Series “switch”

This course deals with the design of both routers and “switches”, in the marketing sense.

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Concerns about marketing terms

Classification according to layer (switch=link, router=network) doesn’t say anything about different functionality; just examining different header bits

Doesn’t this just shift the question to one of numbering layers? e.g. Q: Was ATM a link layer or a network layer technology?

A1: ATM was a link layer: You can send IP packets over it => ATM switches A2: ATM was a network layer: It concatenates links to form a path between systems

connected to the ATM network. => ATM routers (term wasn’t used despite definitions justifying it)

What is a “layer 3 switch”?, e.g. Cisco Catalyst 4840G or for that matter, a “switch router”, e.g. Cisco Catalyst 8500 Answer: A fast router.

And questions arising in other layers: Layer 4: What is layer 4 switching? (A: switching affected by transport headers)

e.g. Cisco Catalyst 6500 Series Content Switching Module Layer 2: Why specify “Ethernet switches” unless “switch” is more general? Layer 1: What do we call a device that operates only at the physical layer (e.g. MEMS

photonic switch using mirrors)? Why are some such devices called “lambda routers”?

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https://web.archive.org/web/20060419051925/http:/www.bell-labs.com/news/1999/november/10/1.html

https://web.archive.org/web/20060419051925/http:/www.bell-labs.com/news/1999/november/10/1.html

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The issue of speed

A “router” may require more processing than a “switch”, so may operate slower† (packets/sec) for a given technology

Ethernet switch: 1. Use frame addresses to index a database, indicating

which outgoing port to use. 2. Start forwarding to outgoing port (needn’t wait to

check CRC [V0>)

Router: 1,2: Ethernet processing (check destination address, check CRC, frame validity checks), and only once that is complete, pass the packet up to the network layer

+ 3. IP processing (check destination address, decrement TTL, packet validity checks, IPv4 fragmentation)

perception that routers are slower than (Ethernet) switches

Heaven forbid us marketing a device whose name has “slow” connotations! → “switch router” “layer 3 switch” = fast router (e.g. lots of hardware,

start IP processing before receive Ethernet CRC). † A router may process fewer data units per second than a switch, but can make more informed forwarding decisions, finding better paths etc => network performance may be better

Check CRC

SAR

Check header

Check DA MAC

Link

layer X

Check DA MAC

Link

layer

Net

layer

X

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Classification by implementation

Packet switches traditionally operated on datagrams: self-contained data units.

Routing/switching/forwarding decisions (eg which port or queue) can be made:

• Each time a datagram arrives. This causes appreciable load: • processing to make these decisions • transmission capacity to convey information used for decision making

• At the beginning of a flow of packets. Store the state, and refer back to those decisions whenever subsequent packets arrive. Couldn’t this reduce the processing load?

=> “Fast Packet Switching” (e.g. ATM): 1. Set up state info in switches 2. Transfer data 3. Release state info in switches

e.g. “switches” contain more state information than “routers” & this state info is explicitly established and released for each flow/connection.

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Functional classification of verbs

Functional sense of the verbs (ending in –ing): Routing: Determining how to get there: Which output port should be used to

get to the destination?

Switching†: The process of going there: Moving information from input ports to appropriate output ports.

Automotive analogy: Routing = Navigating, Switching (lanes) = driving the vehicle

The 2 functions can be physically separated

e.g. ATM & MPLS: device that determines routes may be separate (e.g. it could be centralised & omniscient) from the devices that actually do the switching

This course deals with switching in the general sense. We care about achieving functionality, not with naming products.

It does not deal with routing, neither algorithms (e.g. Bellman-Ford) nor protocols (e.g. BGP). (It does deal with routers.)

† Sometimes called “forwarding” to avoid confusion about switching being only part of the role of a switch.

e.g. a router may maintain a Routing Information Base (RIB) and a Forwarding Information Base (FIB)

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Final definitions

“Switch”: Any device with multiple ports that aims to direct

unicast traffic only to one output port that leads to the

destination.

Router: A switch that deals with network layer headers.

“a type of switch” => switch functions (fabrics, packet classification,

scheduling, buffer management etc) are used in routers.

Bridge: A switch that deals with link layer headers.

Ethernet switch: A type of bridge that deals with Ethernet.

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Pronunciation of “routing”

““Rōō’·ting” is what fans do at a football game, what

pigs do for truffles under oak trees in the Vaucluse,

and what nursery workers intent on propagation do to

cuttings from plants.

“Rou’·ting” is how one creates a beveled edge on a tabletop or sends a corps of infantrymen into full-scale, disorganized retreat.

Either pronunciation is correct for routing, which

refers to the process of discovering, selecting, and

employing paths from one place to another (or to

many others) in a network.” – D. Piscitello and A. Chapin: Open Systems Networking: TCP/IP and OSI

cited in Cheswick, W. and S. Bellovin: Firewalls and Internet security: Repelling the wily hacker, Addison-Wesley, p. 26, 1994

+ Australian slang!

Truffle hunting photo from

www.paristempo.com/art/06truf-pig.jpg

Or more succinctly: “there are two different ways to pronounce the word router, either as

“rootor” or as “rowter,” and people waste a lot of time arguing over the proper pronunciation

[Perlman 1999].” [Kurose and Ross, p. 475]

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A variety of textbook definitions

Sources:

• Keshav

• Peterson and Davie

• Kurose and Ross

• Tanenbaum

• CCNA materials

• Goralski

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Keshav’s definitions

Switch: “A switch allows data arriving at any of its inputs to be transferred to any of its outputs.” p. 6 & details in Chapter 8

Routing: “How can we determine the shortest path from a source to a destination, or the best tree along which to distribute data from a source to a set of destinations? This is the problem of routing” p. 7 & details in Chapter 11

See also Keshav’s Infocom panel presentation on “Routing vs. Switching”

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http://wayback.archive.org/web/*/http:/www.cs.cornell.edu/skeshav/talks/infocom97panel/infocom97panel.PPT

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Peterson & Davie’s definitions

“the core job of a switch is to take packets that arrive on an input and

forward (or switch) them to the right output so that they will reach

their appropriate destination. Knowing which output is the right one

requires the switch to know something about the possible routes to the

destination. The process of accumulating and sharing this knowledge,

the second problem for a packet switch, is called routing.”

– L. Peterson and B. Davie: Computer Networks: A Systems Approach,

Morgan Kaufmann, p. 150

and they go into depth about the distinction between bridges, switches,

and routers on pp. 234-237

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Kurose and Ross

3rd edition, Section 5.6 pp. 475-6

“routers are store-and-forward packet switches that forward packets

using network-layer addresses. Although a switch is also a store-and-

forward packet switch, it is fundamentally different from a router in

that it forwards packets using MAC addresses. Whereas a router is a

layer-3 packet switch, a switch is a layer-2 packet switch.”

Problems:

× Tying definitions to layers (see earlier slide)

× Recursive definitions:

switch → packet switch → layer 3 packet switch → router

→ layer 2 packet switch

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Tanenbaum’s definitions

4th edition, p. 415:

“As an aside, some people make a distinction between routing and switching. Routing is the process of looking up a destination address in a table to find where to send it. In contrast, switching uses a label taken from the packet as an index into a forwarding table. These definitions are far from universal, however.”

5th edition, p. 472

“As an aside, some people make a distinction between forwarding and switching. Forwarding is the process of finding the best match for a destination address in a table to find where to send packets. ... In contrast, switching uses a label taken from the packet as an index into a forwarding table. It is simpler and faster. These definitions are far from universal, however.”

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CCNA course materials (v3.0) Semester 1 module 10: "10.2.2 Routing versus switching

Routing is often contrasted with switching. ... The primary difference is that switching occurs at Layer 2, the data link layer, of the OSI model and routing occurs at Layer 3. This distinction means routing and switching use different information in the process of moving data from source to destination.

... Another difference between switched and routed networks is switched networks do

not block broadcasts.”

Semester 3, module 4.2.7 “The features and functionality of Layer 3 switches and routers have numerous similarities. The only major difference between the packet switching operation of a router and a Layer 3 switch is the physical implementation. In general-purpose routers, packet switching takes place in software, using microprocessor-based engines, whereas a Layer 3 switch performs packet forwarding using application specific integrated circuit (ASIC) hardware.”

module 4.3.4: “Today, switches are also able to filter according to the network-layer protocol. This blurs the demarcation between switches and routers. A router operates on the network layer using a routing protocol to direct traffic around the network. A switch that implements advanced filtering techniques is usually called a brouter. Brouters filter by looking at network layer information but they do not use a routing protocol.”

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W. Goralski: The Illustrated Network

p. 37: “On the Internet, the intermediate systems that act at the packet level (Layer

3) are called routers. Devices that act on frames (Layer 2) are called switches,

and some older telephony-based WAN architectures use switches as

intermediate network nodes. Whether a node is called a switch or a router

depends on how they function internally.”

What exactly are Layer 2 & 3? e.g. why is “telephony-based WAN” Layer 2?

Shouldn’t it be the external behaviour that differentiates devices?

p. 324: “A switch in modern networking is a network node that forwards packets

toward a destination depending on a locally significant connection identifier

over a fixed path. The fixed path is called a virtual circuit …

a router is a network node that independently forwards packets toward a

destination based on a globally unique address (in IP, the IP address) over a

dynamic path that can change from packet to packet, but usually is fairly stable

over time.”

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Switching at various layers

Lower layer switching

Higher layer switching

Transport layer switching

Application layer switching

Outline

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Lower Layer Switching Physical: all-optical networks: Wavelength Division

Multiplexing, MicroElectroMechanical Systems (MEMS)

Link: Ethernet switches

Network: routing Most common layers for switching

T. Sridhar: "Layer 2 and Layer 3 Switch Evolution", Internet Protocol Journal,

1(2):38-43

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http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_1-2/switch_evolution.html

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Higher-layer (4+) switching

The switches that we’ve considered so far implement all functions of the layers that they use for switching:

• Layer 2 (link): MAC & framing • Layer 3 (network): routing

Another type of switch (common at higher layers) only implements a subset (possibly null) of the functions of a layer, but is influenced by the information sent by that layer.

i.e. it depends on what protocol is used at that layer, but it doesn’t implement all of the functions of that protocol. congestion

control

error

control

flow

control

multiplexing /

demultiplexing

DNS

port 53

HTTP

web

port 80

TCP

access

control

framing

error check MAC

TCP ports identify software processes, and are different from switch ports

which are hardware entities. 9751FN

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Transport layer switching

Strict interpretation†: Transport layer fields affect direction of propagation (i.e. which output port).

Switching above network layer processing. Switching between processes, e.g. for load balancing on a web server: might construct what clients perceive as a singular “server” by placing a switch between the Internet & a server farm.

might use the source port number to determine which machine receives the request: odd → machine 1, even → machine 2

(Strictly, you could argue that end-systems implement a form of layer 4 switching because they forward segments to the appropriate process, as indicated by their port numbers.)

Loose interpretation: Transport layer fields only affect type of service, i.e. treatment within the switch. Lower layer fields alone may determine direction. e.g. Network layer switch (IP address => direction) that gives VOIP (UDP port 5004) priority over web browsing (TCP port 80)

† Of a switch being something that moves info between ports

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1

2

3

1

2 3

3

1

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Application layer switching

e.g. consider a web service, handling HTTP GET requests

• Switch users → machines: Could use cookies (identifiers included in requests) that identify users to direct them to a specific machine (helps to provide consistent state between consecutive requests)

• Switch objects/services → machines: Could direct GET requests for different information to specialised machines (less content each => higher cache hit rates etc): • image requests (file with .JPG extension) to one machine • HTTPS to machine with crypto hardware • cgi-bin/ to another • ...

Figure from W. Mangione-Smith and G. Memik: “Network Processor Technologies Tutorial”

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Hierarchical networks

a. A flat view of a network/internetwork is of links that interconnect nodes.

b. We can also consider nodes as being interconnected by networks, which

in turn consist of interconnected nodes or even networks.

c. Hierarchical view shows networks with varying distances from terminals.

a. b. c. 975139

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Benefits of hierarchical switching (1)

√ Heterogeneous access networks

Elements of hierarchy may differ by virtue of who

runs/owns them, what technology they use, physical

location, etc

√ Localise problems

√ Localised traffic needn’t burden core

Spatial locality [DT> – how much usually leaves a

workgroup switch to the next level of the hierarchy?

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http://uluru.ee.unsw.edu.au/~tim/courses/tele9751/id/DT.html

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Benefits of hierarchical switching (2)

√ Distribute management/administration of network

√ Different operators for different levels of the hierarchy:

Local area: private institutional network

Metropolitan area: public network providers

Few provide physical infrastructure: Telstra, Optus, VHA, NBNco, TPG, iiNet

Multiple provide service: infrastructure providers+ISPs

Wide area: many provide physical infrastructure and service

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Hierarchy within an organisation

Levels often referred to as

1. Access

2. Distribution / Aggregation

3. Core / backbone

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Examples of network hierarchy

1. The Bell Telephone system (before divestiture

in 1984, after which

it lost its

regular structure)

Regional offices (Class 1)

Sectional offices (Class 2)

Primary offices (Class 3)

Toll offices (Class 4)

End offices (Class 5)

… … … …

Local switch

Transit switch

Local loops

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Examples of network hierarchy

2. The Internet

UNSW (ISP 1)

Virgin (ISP 2)

AARnet (NSP 1)

Optus (NSP 2)

Telstra (NSP 3)

NSP = Network Service Provider

ISP = Internet Service Provider

iiNet (NSP 4)

BigPond (ISP 4)

Reach Internet2 +“Dot bombs”:

Global Crossing, UUnet, ...

(nswrno)

ISPs

NSPs

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DoDo (ISP 2)

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Exercise: Use traceroute to view which networks packets

traverse to reach their destination.

Many servers available through www.traceroute.org

Hierarchical switching in the Internet

unsw.edu.au ↓

aarnet.net.au ↓

pnw-gigapop.net ↓

ucaid.edu ↓

nox.org ↓

mit.edu

www.telstra.net ↓

reach.com ↓

bbnplanet.net ↓

mit.edu

unsw.edu.au ↑

aarnet ↑

pnw-gigapop ↑

jp.apan.net ↑

kreonet.re.kr ↑

ucaid.edu ↑

nox.org ↑

mit.edu

e.g.:

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http://www.traceroute.org/

http://www.traceroute.org/

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Path from UNSW to www.irtf.org

$ traceroute www.irtf.org traceroute to www.irtf.org (192.150.187.18), 30 hops max, 38 byte packets 1 eebu4s1.uwn.unsw.EDU.AU.92.171.149.in-addr.arpa (149.171.92.2) 14.624ms 0.775ms 1.040ms 2 129.94.255.181 (129.94.255.181) 0.436ms 0.409ms 0.384ms 3 gig2-2.nswrnosbb.nswrno.net.au (138.44.1.37) 0.582ms 0.563ms 0.527ms 4 vlan948.gbe3-0.sccn1.broadway.aarnet.net.au(192.231.212.49) 1.450ms 0.805ms 0.758ms 5 pos1-0.sccn1.seattle.aarnet.net.au (192.231.212.34) 157ms 156ms 157ms 6 Abilene-PWAVE-1.peer.pnw-gigapop.net (198.32.170.43) 166ms 165ms 166ms 7 snvang-sttlng.abilene.ucaid.edu (198.32.8.10) 174ms 173ms 173ms 8 losang-snvang.abilene.ucaid.edu (198.32.8.94) 180ms 180ms 180ms 9 hpr-lax-gsr1--abilene-LA-10ge.cenic.net (137.164.25.2) 190ms 190ms 190ms 10 dc-lax-dc1--lax-hpr1-ge.cenic.net (137.164.22.12) 181ms 181ms 181ms 11 dc-sac-dc1--lax-dc1-pos.cenic.net (137.164.22.127) 190ms 190ms 189ms 12 dc-oak-dc2--csac-dc1-ge.cenic.net (137.164.22.110) 201ms 201ms 201ms 13 dc-oak-dc1--oak-dc2-ge.cenic.net (137.164.22.124) 192ms 193ms 192ms 14 dc-svl-dc1--oak-dc1-10ge.cenic.net (137.164.22.30) 192ms 193ms 193ms 15 ucb--svl-dc1-egm.cenic.net (137.164.23.66) 194ms 194ms 193ms 16 fast4-0-0.inr-667-eva.Berkeley.EDU (128.32.0.99) 203ms 203ms 204ms 17 router2-fast0-0-0.ICSI.Berkeley.EDU (169.229.0.30) 195ms 195ms 195ms 18 www.irtf.org (192.150.187.18) 195ms 195ms 194ms

common phrases: gig, ge: Gigabit Ethernet pos: Packet Over SONET

3 delay measurements for each hop Delays vary with link congestion

Large increase in delay as packets pass over the Pacific Ocean

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Switch classification 2:

By location in hierarchical network

moving towards network core

Desktop switch (may merely be a

shared-media LAN)

Workgroup /

LAN switches

Campus

switch

Enterprise

switches

Access

networks

Distribution /

“transport” networks

Private networks Public networks

DLink

DES-1250G

Cisco

Catalyst

4006

Cisco

12000

router

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1. Availability becomes increasingly important High-reliability components

Redundancy in power supplies, even redundant fabrics

Hot swapping of line interfaces & power supplies

May employ “protection switches” to bypass severed links (low switching rate, high throughput)

2. Throughput becomes increasingly important (though load may vary less)

3. Reduced functionality, e.g. NAT, DHCP servers, firewalls, QOS tend to be implemented in workgroup switches but not core switches.

How do switches change as you move into the network core?:

Switch trends as location in hierarchy changes

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4. Fewer, but faster, interfaces (& more expensive) e.g. fiber (not twisted pair), single mode (not multi-mode) fibre

May also offer public-network interfaces, e.g. ISDN – low-speed,

pay-per-use

5. More varied interfaces (although workgroup switch often has

fast interface to connect to backbone/servers)

6. More symmetrical data flow

7. “Transit switching” rather than “line switching” (see next

slide)

Switch trends as location in hierarchy changes (continued)

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Transit and line switching Line switches: specific input to specific output Transit switches: specific input to one of several outputs, e.g. several lines connecting this switch to another.

Transit

switching

S

Line

switching

D Often discussed in the context of hierarchical networks, where a low-level network may connect to multiple higher-level networks for fault tolerance.

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Things to think about Critical thinking:

• What inconsistencies can you see between the definitions of

routers and switches from various sources? What definition

do you think is best?

Engineering methods: • This course is about design trade-offs: different designs suit

different applications. e.g. different switches for different

parts of a hierarchical network.

Links to other areas: • The X symbol for a switch comes from railway signs where

the tracks cross at a switching point.

Independent learning: • Read through the “hidden” slides

Copyright © 2017 Tim Moors

Tele9751!!!

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The end

... for week 1

If you received a participation card, bring it to Tim now & tell

me the last 3 digits of your student ID.

975151

unswsubjects.ee.unsw.edu.au/tele9751/lec/1.pdffrom full transcript of the discover magazine...

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