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CSE524: Lecture 3

Internet history (Part 2), Internet challenges, Physical layer

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Administrative

• Homework #1 due Wednesday, Oct. 3rd

• CSE524 e-mail list created– E-mail TA if you have not received the

introductory message

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Last episode

• Started on brief run-down of Internet history– TCP/IP deployment

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LAN

• Metcalfe– Invents Ethernet (Xerox PARC) 1973

• Proteon, IBM– Token Ring 1970s

• Proliferation of LANs leads to redefining IP space– Split space into 3 classes A, B, and C

– C=LANs (large number of networks with small number of hosts

– B=Regional scale networks

– A=Large scale national networks

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Application protocols

• SMTP – Simple Mail Tranfer Protocol (Aug. 1982) Postel

• http://www.rfc-editor.org/rfc/rfc821.txt

• DNS– Hostnames server, SRI (Mar. 1982) Harrenstien

• http://www.rfc-editor.org/rfc/rfc811.txt

– Current hierarchical architecture (Aug. 1982) Su, Postel• http://www.rfc-editor.org/rfc/rfc819.txt

– Domain Name System standard (Nov. 1983) Mockapetris

• http://www.rfc-editor.org/rfc/rfc882.txt• http://www.rfc-editor.org/rfc/rfc882.txt

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Application protocols

• Telnet– Telnet protocol (May 1983) Postel, Reynolds

• http://www.rfc-editor.org/rfc/rfc854.txt

• FTP– File transfer protocol (Oct. 1985) Postel,

Reynolds• http://www.rfc-editor.org/rfc/rfc959.txt

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Meanwhile, in a parallel universe

• Competing mostly inoperable networks from jealous government agencies and companies

• DOE: MFENet (Magnetic Fusion Energy scientists)• DOE: HEPNet (High Energy Physicists)• NASA: SPAN (Space physicists)• NSF: CSNET (CS community)• NSF: NSFNet (Academic community) 1985• AT&T: USENET with Unix, UUCP protocols• Academic networks: BITNET (Mainframe connectivity)• Xerox: XNS (Xerox Network System)• IBM: SNA (System Network Architecture)• Digital: DECNet• UK: JANET (Academic community in UK) 1984

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NSFNet

• NSF program led by Jennings, Wolff (1986-1995)– Network for academic/research community

– Selects TCP/IP as mandatory for NSFNet

– Structures with DARPA “Requirements for Internet Gateways” to ensure interoperability

• http://www.rfc-editor.org/rfc/rfc985.txt

– Builds out wide area networking infrastructure

– Develops strategy for developing and handing it over eventually to commercial interests

– Historical note: Al Gore helps win funding for NSFNet program

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NSFNet

• Structure– 6 nodes with 56kbs links– Jointly managed exchange points

• Statistical, non-metered peering agreements– CSNET (Farber)– Kahn (ARPANET)

• Cost-sharing of infrastructure

– Seek out commercial, non-academic customers• Help pay for and expand regional academic facilities• Economies of scale• Prohibit commercial use of NSFNet to encourage commercial

backbones• Leads to PSINet, UUNET, ANS, CO+RE backbone

development

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TCP/IP software

• Berkeley– Unix TCP/IP available at no cost (DoD)– Incorporates BBN TCP/IP implementation– Later re-implements– Large dispersal to community– Critical mass (like the fax machine)

• PCs– Low cost PC access (Wintel)– Economies of scale

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Privatization

• Commercial interconnection– US Federal Networking Council (1988-1989)– MCI Mail allowed

• ARPANET decommissioned (1990)• NSFNet decommissioned (1995)

– 21 nodes with multiple T3 (45Mbs) links– Regional academic networks forced to buy national

connectivity from private long haul networks– TCP/IP supplants and marginalizes all others to become

THE bearer service for the Internet– Total cost of NSF program?

$200 million from 1986-1995

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Growing pains

• Explosion of networks– Routing initially flat, each node runs the same

distributed routing algorithm– Moved to hierarchical model

• IGP (interior gateway protocol) within a region• EGP (exterior gateway protocol) to tie regions together• Individual regions use their own IGP• Saves on cost (CPU+bandwidth)• Allows rapid reconfiguration, robustness, scalability• Distributes control (a bit)

– Evolves into AS=Autonomous System• IGP ->Intra-AS routing (RIP/OSPF)• EGP -> Inter-AS routing (BGP)

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Growing pains

• Each backbone router keeps global table of exponentially increasing network routes

• CIDR– Classless Inter-Domain Routing– Aggregate numerically adjacent routes going to

the same AS– Variable-length subnetting– Saves space, but makes lookups harder– Longest prefix match lookup

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IETF

• Origins– DARPA

• Cerf forms coordination bodies (late 1970s)– ICB (International Cooperation Board)– ICCB (Internet Configuration Control Board)

• Leiner takes over Internet research program (1983)– ICCB disbanded– Forms structure of task forces– Forms umbrella IAB (Internet Activities Board) to manage TFs– IETF (Internet Engineering) is one task force

• Internet research program discontinued (1985)– IAB becomes default leadership organization for the Internet– IESG created (Internet Engineering Steering Group)– IRTF created (Internet Research Task Force)

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IETF

• CNRI (Corporation for National Research Initiatives)– Headed by Kahn (1991)– Creates Internet Society to make process open

and fair across research and commercial interests

– IAB reorganized to Internet Architecture Board under Internet society

• IAB, IESG, and IETF in place as they are now• Process for arbitration and operation established

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WWW

• CERN (European Organization for Nuclear Research)– Berners-Lee, Caillau work on WWW (1989)

– First WWW client (browser-editor running under NeXTStep)

– Defines URLs, HTTP, and HTML

– Berners-Lee goes to MIT and LCS to start W3C• Responsible for evolving protocols and standards for the web

– http://www.w3.org/People

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WWW

• NCSA (National Center for Supercomputing Applications)– Federally funded research center at University

of Illinois at Urbana-Champaign– Andreessen: Mosaic and eventually Netscape

(1994)– http://www.dnai.com/~thomst/marca.html

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Internet challenges

• Not a complete list– Address depletion (IPv4, IPv6)– NAT and the loss of transparency– Routing infrastructure– Quality of service– Security– DNS scaling– Dealing with privatization– Interplanetary Internet

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Address depletion

• IPv4: 32-bit address (4.3 billion identifiers)– 25% in use 960 million addresses (advertised in BGP

tables)

– http://www.caida.org/outreach/resources/learn/ipv4space/

– Inactive IP addresses advertised as well

– Estimated 86 million active (July 2000)

– http://www.netsizer.com/

– Do we need more addresses?

• IPv6: 128-bit address

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Current IP address allocation

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NAT

• Network address translation• Source and destination IP addresses and

(sometimes) ports rewritten by device• Rewritten without knowledge of end-hosts• Translation typically performed only on IP address

portion of packet not on addresses within data• Envelope analogy

– Return address on outside changed– Return address on inside unchanged– Application data must be rewritten to maintain

consistency

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NAT

• What’s bad about NAT?– Breaks transparency of IP

– Breaks hourglass and end-to-end principles (network must be changed for new applications to be deployed)

– FTP, servers, P2P services and NAT

– SIP, conferencing applications

– Breaks IPsec

– Man-in-the-middle attacks

• What’s good about NAT?– Renumbering easy

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NAT

• Application writing before NAT– New applications require no changes to be

deployed on the Internet– New applications require no changes in the

Internet to be deployed

• Application writing after NAT– All new applications must be written with

explicit knowledge of intermediate devices which rewrite network and application information

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Routing infrastructure

• http://www.telstra.net/ops/bgptable.html• Backbone routers must keep table of all routes

(75000 entries)• Growth of table size

– Alleviated with CIDR aggregation and NAT– Potentially exacerbated if portable addressing used

• Routing instability– Frequency of updates increases with size– Update damping occuring already

• Potential for breakdown in connectivity

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Routing infrastructure

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Routing infrastructure

• Reducing state in the network– Global state at every backbone router– Other non-global approaches?

• Ambulance routing

• Airplane routing

• Landmark routing

• Chess games

• Limited-distance look-ahead

• Better scaling properties

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Routing infrastructure

• Non-adaptive routing on backbone– Opt-out early routing

• Tier 1 ISPs route traffic solely on whether destination is within network

• Limited alternative paths

• Limited robustness and poor performance

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Routing Infrastructure

• Increasing routing performance– Lambda switching, MPLS

• DWDM requires extremely fast forwarding

• At edges, map traffic based on IP address to wavelength or other non-IP label

• Wavelength or label switch across multiple hops to other edge

• Eliminate intermediate IP route lookups

– Faster IP lookups• Data structures and algorithms for fast lookups

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Routing Infrastructure

• Other challenges– Policy-based routing, packet classification– Non-destination-based routing– Route-pinning for QoS

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Quality of service

• Predictable performance• “Weak-link” phenomenon• Requires

– ISP agreements– Global support for QoS

• Applications• OS• All devices in the network (routing failures, updates,

queuing)

– Packet sizes and unpredictable media

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Security

• Anonymity of IP– Sender fills in its address– Connectivity over security

• Spoofing and DDoS• IP traceback

– http://www.acm.org/sigs/sigcomm/sigcomm2001/p1.html

• Ingress filtering– http://www.ietf.org/rfc/rfc2827.txt

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Security

• DNS centralized– 13 root name servers– Limited due to packet size constraints

• Routing decentralized– Rogue source sending updates– Convergence problems

• L0pht– May 1998: 30min to shut down Internet

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DNS scaling

• Relatively flat structure

• 13 centralized TLD name servers

• .com servers overloaded

• DNS used as a directory service

• Internet directory service?– RealNames– AOL Keywords

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Dealing with Privatization

• Improving routing instability, traffic characterization, security, etc. difficult

• Finding sources of disruption (software, hardware, users) difficult

• Problems are hidden not shared• Open standards in the face of commercial interests

– Patents on protocols– Closed protocols

• ICQ, AIM, Hotmail

– Potential for closed networks• Cable network consolidation, ISP consolidation

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Interplanetary Internet

• Extremely long round-trip times

• Protocols designed with terrestrial timeout parameters

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The rest of the course

• From birds-eye view, we will now focus on specific components

• Review Lectures 1, 2, and 3 for perspective when looking at the parts

• Mostly classical material with some references to newer technologies

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Physical Layer

• Plethora of physical media– Fiber, copper, air

– Specifies the characteristics of transmission media

– Too many to cover in detail, not the focus of the course

– Many data-link layer protocols (i.e. Ethernet, Token-Ring, FDDI. ATM run across multiple physical layers)

– Physical characteristics dictate suitability of data-link layer protocol and bandwidth limits

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PL: Good URLs

• Get ‘em while they last….– ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/comp/answers/LANs/

cabling-faq

– http://fcit.coedu.usf.edu/network/

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PL: Common Cabling

• Copper– Twisted Pair

• Unshielded (UTP)– CAT-1, CAT-2, CAT-3, CAT-4, CAT-5, CAT-5e

• Shielded (STP)

– Coaxial Cable

• Fiber– Single-mode– Multi-mode

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PL: Twisted Pair

• Most common LAN interconnection

• Multiple pairs of twisted wires

• Twisting to eliminate interference More twisting = Higher bandwidth, cost

• Standards specify twisting, resistance, and maximum cable length for use with particular data-link layer

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PL: Twisted pair

• 5 categories– Category 1

• Voice only (telephone wire)

– Category 2• Data to 4Mbs (LocalTalk)

– Category 3• Data to 10Mbs (Ethernet)

– Category 4• Data to 20Mbs (16Mbs Token Ring)

– Category 5 (100 MHz)• Data to 100Mbs (Fast Ethernet)

– Category 5e (350 MHz)• Data to 1000Mbs (Gigabit Ethernet)

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PL: Twisted Pair

• Common connectors for Twisted Pair– RJ11 (6 pairs)– RJ45 (8 pairs)

• Allows both data and phone connections

• (1,2) and (3,6) for data, (4,5) for voice

• Crossover cables for NIC-NIC, Hub-Hub connection (Data pairs swapped)

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PL: UTP

• Unshielded Twisted Pair– Limited amount of protection from interference– Commonly used for voice and ethernet

• Voice: multipair 100-ohm UTP

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PL: STP

• Shielded Twisted Pair– Not as common at UTP– UTP susceptible to radio and electrical

interference– Extra shielding material added– Cables heavier, bulkier, and more costly– Often used in token ring topologies

• 150 ohm STP two pair (IEEE 802.5 Token Ring)

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PL: Coaxial cable

• Single copper conductor at center

• Plastic insulation layer

• Highly resistant to interference– Braided metal shield – Support longer connectivity distances over UTP

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PL: Coaxial cable

• Thick (10Base5) – Large diameter 50-ohm cable

– N connectors

• Thin (10Base2) cables– Small diameter 50-ohm cable

– BNC, RJ-58 connector

• Video cable– 75-ohm cable

– BNC, RJ-59 connector

– Not compatible with RJ-58

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PL: Fiber

• Center core made of glass or plastic fiber

• Transmit light versus electronic signals– Protects from electronic interference, moisture

• Plastic coating to cushion core

• Kevlar fiber for strength

• Teflon or PVC outer insulating jacket

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PL: Fiber• Single-mode fiber

– Smaller diameter (12.5 microns)– One mode only– Preserves signal better over longer distances– Typically used for SONET or SDH– Lasers used to signal– More expensive

• Multi-mode fiber– Larger diameter (62.5 microns)– Multiple modes– LEDs used to signal– WDM and DWDM

• Photodiodes at receivers

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PL: Fiber connectors

• ESCON

• Duplex SC

• ST

• MT-RJ (multimode)

• Duplex LC

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PL: Wireless

• Entire spectrum of transmission frequency ranges– Radio

– Infrared

– Lasers

– Cellular telephone

– Microwave

– Satellite

– Acoustic (see ESE sensors)

– Ultra-wide band

• http://www.ntia.doc.gov/osmhome/allochrt.html

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PL: What runs on them?Protocol Summary

Protocol Cable Speed Topology

Ethernet Twisted Pair, Coaxial, Fiber 10 Mbps Linear Bus, Star, Tree

Fast Ethernet Twisted Pair, Fiber 100 Mbps Star

LocalTalk Twisted Pair .23 Mbps Linear Bus or Star

Token Ring Twisted Pair 4 Mbps - 16 Mbps Star-Wired Ring

FDDI Fiber 100 Mbps Dual ring

ATM Twisted Pair, Fiber 155-2488 Mbps Linear Bus, Star, Tree

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PL: Bandwidth lingo

• Specifies capacities over physical media• Electronic

– T1/DS1=1.54 Mbps – T3/DS3=45Mbps

• Optical (OC=optical carrier)– OC1=52 Mbps– OC3/STM1=156 Mbps– OC12=622 Mbps– OC48=2488 Mbps– OC192=10 Gbps – OC768=40 Gbps

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Next class

• Data-link layer (Chapter 5)