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EECS 228a – Lecture 1Overview: Networks*
Pravin VaraiyaShyam Parekh
www.eecs.berkeley.edu/~varaiya
Fall 2003* These notes were created by Prof. Walrand, F’02
EECS228a - Walrand 2
Course Information
Instructors: � Pravin Varaiya, OH:Tu,Th 4:00-5:00, 271M Cory� Shyam Parekh, OH: Tu,Th 4:00-5:00, 463 Cory
Time/Place:Tu,Th 2:00-3:30 in 299 CoryHome Page:� http://www-inst.eecs.berkeley.edu/~ee228a
EECS228a - Walrand 3
Topics
Overview [1 week]Economics of Networks [4]802.11 and Sensor Networks [4]Congestion Control [2.5]Traffic Models [2.5]Review [1]
Theoretical backgroundState of the art
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Details
Grading:� Class participation & presentations: 65%� Project: 35% - Original research on
selected topic
Material:� Lecture Slides and Notes� Research Papers
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OverviewNetwork ExamplesNetwork ComponentsInternetworkingInternetOther NetworksPacketsTransportWeb BrowsingTelephone CallResource Sharing – MultiplexingProtocolsIETF
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Network ExamplesTeleglobe Communications Corporation – Fiber + Satellite
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Network ExamplesGlobal Crossing Corporation
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Network ExamplesKPNQWEST
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Network ExamplesWilliams Communications
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Network ExamplesPalo Alto Network
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Network Components
Link: carry bits from one place to another (or maybe to many other places)Switch/router: move bits between links, forming internetworkHost: communication endpoint (workstation, PDA, cell phone, toaster, tank)
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Network Components
Fibers
Cat5 UnshieldedTwisted Pairs
Coaxial Cable
Links
Wireless
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Network ComponentsEthernet Network Interface Card
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Network ComponentsEthernet
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Network Components
Ethernet is a broadcast-capable, multi-access LAN
Link: Ethernet
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Network Components
IEEE 802.11 WLAN is adaptation of Ethernet like protocol for wireless medium
Link: IEEE 802.11 WLAN
Laptop
Laptop Laptop
Independent Basic Service Set (IBSS)
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IEEE 802.11 WLAN Products
Access Points
PC Cards
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3G UMTS Cellular NetworkConvergence of Voice and Data
“Mobile Network Evolution: A Revolution on the Move,” J. De Vriendt, et al.,IEEE Comm. Magazine, April 2002.
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Network ComponentsTelephone Switch Large Router
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Network with RoutersLANs interconnected by routers
LAN1
LAN2
LAN3 Internet
R1R2
R3 R4
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InternetworkingProvides message delivery between multiple networks:
Subnet 1Subnet 2
ISP 2ISP 1
Example: Subnet 1 = network of LANs of previous slideISP 1 = Sprint, ISP 2 = MCISubnet 2 = UCB network
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The InternetA global network of networks all using a common protocol (IP, the Internet Protocol)One focus of this classA challenge to understand:� large scale (10’s of millions of users, 10’s
of thousands of networks)� heterogeneity, irregular topology,
decentralized management
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Scale of Internet
• Data from www.nw.com
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Other Networks
The Telephone NetworkProcessor Interconnection NetworksATM NetworksCable-TV Networks
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Packets
A
B
A | B | ...
B → port 2
12
3
A | B | ...
A | B | ...
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Packets: Main Ideas
The switches (routers) have no memory of packets: scalabilityThe network is independent of the applications: flexibilityThe packet formats and addresses are independent of the technology: extensibility
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Transport
Packets
ACKs
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Web Browsing:top-down view
ExampleLocating Resource: DNSConnectionEnd-to-endPacketsBitsPoints to remember
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Click Link or URL� get content from localor remote computerURL:
http://www.google.com/stringSpecifies- Protocol: http- Computer: www.google.com- String: computer (server)
selects contents based on string
Web: Example
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Web: Locating Resourcewww.google.com is the name of a computerNetwork uses IP addressesTo find the IP address, the application uses a hierarchical directory service called theDomain Name System
local
com
host
www.google.com?IP = a.b.c.d
IP = a.b.c.d
www.google.com?
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Web: ConnectionThe protocol (http) sets up a connection between the host and www.google.com to transfer the pageThe connection transfers the page as a byte stream, without errors: pacing + error control
Host www.google.com
connect
OK
get page
page; close
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Web: End-to-endThe byte stream flows from end to end across many links and switches: routing (+ addressing)That stream is regulated and controlled by both ends: retransmission of erroneous or missing bytes; flow control
End-to-end pacing andflow control
Routing
www.google.com
host
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Web: PacketsThe network transports bytes grouped into packetsThe packets are “self-contained” and routers handle them one by oneThe end hosts worry about errors and flow control:� Destination checks packet
for errors (using error detection code CKS) and sends ACKs with sequence number #
� Source retransmits packets that were not ACKed and adjusts rate of transmissions
C
A | B | # , CKS | bytes
B C
www.google.comIP address: A
HostIP address: B
Destination
Next Hop
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Web: Bits
Equipment in each node sends the packets as a string of bitsThat equipment is not aware of the meaning of the bits
01011...011...110
Transmitter Physical Medium Receiver
01011...011...110
OpticalCopperWireless
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Web: Points to remember
Separation of tasks� send bits on a link: transmitter/receiver [clock, modulation,…]
� send packet on each hop [framing, error detection,…]
� send packet end to end [addressing, routing]
� pace transmissions [detect congestion]
� retransmit erroneous or missing packets [acks, timeout]
� find destination address from name [DNS]
Scalability� routers don’t know about connections� names and addresses are hierarchical
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Telephone Call
Telephone NetworkDialing a NumberSetting up a CircuitPhone ConversationReleasing the Circuit
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Telephone Network
5ESS (Lucent)
DMS100 (Nortel)
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Telephone Network
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Telephone NetworkLogic Diagram:
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Dialing a Number
A Off-HookS1 ListensA dialsS1 Registers
A
BS1
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Setting Up a Circuit
A
Bring
Circuit = capacity to carry one phone call (shown by thin lines)Circuit is allocated to the call between A and BCircuits are not shared; they are dedicated.
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Phone Conversation
A
B
Voice signals use the reserved circuits
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Release Circuits
A
B
A or B goes Off-HookCircuits get released
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Resource Sharing - Multiplexing
Networks are shared resourcesSharing via multiplexingFundamental Question:how to achieve controlled sharing
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Multiplexing
Methods for sharing a communication channelTradeoff between utilization and predictabilityCommon Approaches:� TDM (time-division multiplexing)� Statistical Multiplexing
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Time Division Multiplexing(also called STDM --Synchronous Time Division Multiplexing)
Multiplexern linksrate r bpseach 1 link, rate nr bps
Frame:
Time “slots” are reservedbps = bits per second
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Statistical Multiplexing
Multiplexern linksany rate 1 link, any rate
TraceExcerpt:
Variable-sized “packets” of data are interleavedbased on the statistics of the senders
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Analysis of STDM/FDMTDM, FDM (frequency division multiplexing), and WDM (wavelength) may under-utilize channel with idle sendersApplicable only to fixed numbers of flowsRequires precise timer (or oscillator and guard bands for FDM)Resources are guaranteed
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Analysis of Statistical Mux’ing
Traffic is sent on demand, so channel is fully utilized if there is enough demandAny number of flowsNeed to control sharing:� packets are limited in size� prevents domination of single sender
Resources are not guaranteed
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Protocols
Agreement dictating the form and function of data exchanged between two (or more) parties to effect a communicationTwo parts: syntax and semantics� syntax: where bits go� semantics: what they mean and what to do
with them
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Protocol Example
Internet Protocol (IP)� if you can generate and understand IP,
you can be on the Internet� media, OS, data rate independent
TCP and HTTP� if you can do these, you are on the web
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Protocol Standards
New functions require new protocolsThus there are many (e.g. IP, TCP, UDP, HTTP, RIP, OSPF, IS-IS, SMTP, SNMP, Telnet, FTP, DNS, NNTP, NTP, BGP, PIM, DVMRP, ARP, NFS, ICMP, IGMP; IEEE802.x)Specifications do not change frequentlyOrganizations: IETF, IEEE, ITU
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The IETF
Specifies Internet-related protocolsProduces “RFCs” (www.rfc-editor.org)Quotation from IETF T-shirt:
We reject kings, presidents and voting.We believe in rough consensus and running code.
--- David Clark