Networks

1
Networks

• Goal Communication between computers
• Eventual Goal treat collection of computers as
  if one big computer, distributed resource sharing
• Theme Different computers must agree on many
  things
• Overriding importance of standards and protocols
• Error tolerance critical as well

2
Networking

• Issues
• direct (point-to-point) vs. indirect (multi-hop)
• topology (e.g., bus, ring, DAG)
• routing algorithms
• switching (aka multiplexing)
• wiring (e.g., choice of media, copper, coax,
  fiber)
• What really matters
• latency
• bandwidth
• cost
• reliability

3
Interconnections (Networks)

• Examples (see Figure 7.19, page 633)
• Wide Area Network (ATM) 100-1000s nodes 5,000
  kilometers
• Local Area Networks (Ethernet) 10-1000 nodes
  1-2 kilometers
• System/Storage Area Networks (FC-AL) 10-100s
  nodes 0.025 to 0.1 kilometers per link

a.k.a. end systems, hosts
a.k.a. network, communication subnet
Interconnection Network
4
SAN Storage vs. System

• Storage Area Network (SAN) A block I/O oriented
  network between application servers and storage
• Fibre Channel is an example
• Usually high bandwidth requirements, and less
  concerned about latency
• in 2001 1 Gbit bandwidth and millisecond latency
  OK
• Commonly a dedicated network (that is, not
  connected to another network)
• May need to work gracefully when saturated
• Given larger block size, may have higher bit
  error rate (BER) requirement than LAN

5
SAN vs. NAS

• Storage area network
• Network-attached storage
• Storage virtualization
• Continuous data protection

6
SAN Storage vs. System

• System Area Network (SAN) A network aimed at
  connecting computers
• Myrinet is an example
• Aimed at High Bandwidth AND Low Latency.
• in 2001 gt 1 Gbit bandwidth and 10 microsecond
• May offer in order delivery of packets
• Given larger block size, may have higher bit
  error rate (BER) requirement than LAN

7
More Network Background

• Connection of 2 or more networks Internetworking
• 3 cultures for 3 classes of networks
• WAN telecommunications, Internet
• LAN PC, workstations, servers cost
• SAN Clusters, RAID boxes latency (System A.N.)
  or bandwidth (Storage A.N.)
• Motivate the interconnection complexity
  incrementally

8
ABCs of Networks

• Starting Point Send bits between 2 computers
• Queue (FIFO) on each end
• Information sent called a message
• Can send both ways (Full Duplex)
• Rules for communication? protocol
• Inside a computer
• Loads/Stores Request (Address) Response (Data)
• Need Request Response signaling

9
A Simple Example

• What is the format of mesage?
• Fixed? Number bytes?

Request/ Response
Address/Data
1 bit
32 bits
0 Please send data from Address 1 Packet
contains data corresponding to request

• Header/Trailer information to deliver a message
• Payload data in message (1 word above)

10
Questions About Simple Example

• What if more than 2 computers want to
  communicate?
• Need computer address field (destination) in
  packet
• What if packet is garbled in transit?
• Add error detection field in packet (e.g.,
  Cyclic Redundancy Chk)
• What if packet is lost?
• More elaborate protocols to detect loss
  (e.g., NAK, ARQ, time outs)
• What if multiple processes/machine?
• Queue per process to provide protection
• Simple questions such as these lead to more
  complex protocols and packet formats gt complexity

11
A Simple Example Revisted

• What is the format of packet?
• Fixed? Number bytes?

Request/ Response
Address/Data
CRC
2 bits
32 bits
4 bits
00 RequestPlease send data from Address 01
ReplyPacket contains data corresponding to
request 10 Acknowledge request 11 Acknowledge
reply
12
Software to Send and Receive

• SW Send steps
• 1 Application copies data to OS buffer
• 2 OS calculates checksum, starts timer
• 3 OS sends data to network interface HW and says
  start
• SW Receive steps
• 3 OS copies data from network interface HW to OS
  buffer
• 2 OS calculates checksum, if matches send ACK
  if not, deletes message (sender resends when
  timer expires)
• 1 If OK, OS copies data to user address space
  and signals application to continue
• Sequence of steps for SW protocol
• Example similar to UDP/IP protocol in UNIX

13
Low-Latency Message Passing

• Reducing data copying
• Interrupt coalescing
• Decreasing context switch
• More efficient DMA transactions
• Wither TCP offload engine?

14
Network Performance Measures

• Overhead latency of interface vs. Latency
  network

15
Universal Performance Metrics
Sender
(processor busy)
Transmission time (size bandwidth)
Time of Flight
Receiver Overhead
Receiver
(processor busy)
Transport Latency
Total Latency
Total Latency Sender Overhead Time of Flight
Message Size BW
Receiver Overhead
Includes header/trailer in BW calculation?
16
Total Latency Example

• 1000 Mbit/sec., sending overhead of 80 µsec
  receiving overhead of 100 µsec.
• a 10000 byte message (including the header),
  allows 10000 bytes in a single message
• 2 situations distance 100 m vs. 1000 km
• Speed of light 300,000 km/sec
• Latency0.01km 80 0.01km / (50 x 300,000)
  10000 x 8 / 1000 100 260 µsec
• Latency0.5km 80 0.5km / (50 x 300,000)
  10000 x 8 / 1000 100 263 µsec
• Latency1000km 80 1000 km / (50 x 300,000)
  10000 x 8 / 1000 100 6931
• Long time of flight gt complex WAN protocol

17
Universal Metrics

• Apply recursively to all levels of system
• inside a chip, between chips on a board, between
  computers in a cluster,
• Look at WAN v. LAN v. SAN

18
Simplified Latency Model

• Total Latency Overhead Message Size / BW
• Overhead Sender Overhead Time of Flight
• Receiver Overhead
• Example show what happens as vary
• Overhead 1, 25, 500 µsec
• BW 10,100, 1000 Mbit/sec (factors of 10)
• Message Size 16 Bytes to 4 MB (factors of 4)
• If overhead 500 µsec, how big a message gt 10
  Mb/s?

19
Overhead, BW, Size
Delivered BW
Msg Size

• How big are real messages?

20
Measurement Sizes of Message for NFS
Why?

• 95 Msgs, 30 bytes for packets 200 bytes
• gt 50 data transfered in packets 8KB

21
Impact of Overhead on Delivered BW

• BW model Time overhead msg size/peak BW

22
Interconnect Issues

• Performance Measures
• Network Media

23
Network Media
Twisted Pair
Copper, 1mm think, twisted to avoid attenna
effect (telephone) "Cat 5" is 4 twisted pairs in
bundle
Coaxial Cable
Plastic Covering
Used by cable companies high BW, good noise
immunity
Insulator
Copper core
Braided outer conductor
Buffer
Light 3 parts are cable, light source, light
detector. Note fiber is unidirectional need 2
for full duplex
Cladding
Total internal
Fiber Optics
reflection
Transmitter
Receiver
L.E.D
Photodiode
Laser Diode
light
source
Silica core
Cladding
Buffer
24
Fiber

• Multimode fiber 62.5 micron diameter vs. the
  1.3 micron wavelength of infrared light. Since
  wider it has more dispersion problems, limiting
  its length at 1000 Mbits/s for 0.1 km, and 1-3 km
  at 100 Mbits/s. Uses LED as light
• Single mode fiber "single wavelength" fiber (8-9
  microns) uses laser diodes, 1-5 Gbits/s for 100s
  kms
• Less reliable and more expensive, and
  restrictions on bending
• Cost, bandwidth, and distance of single-mode
  fiber affected by power of the light source, the
  sensitivity of the light detector, and the
  attenuation rate (loss of optical signal strength
  as light passes through the fiber) per kilometer
  of the fiber cable.
• Typically glass fiber, since has better
  characteristics than the less expensive plastic
  fiber

25
Wave Division Multiplexing Fiber

• Send N independent streams on single fiber!
• Just use different wavelengths to send and
  demultiplex at receiver
• WDM in 2000 40 Gbit/s using 8 wavelengths
• Plan to go to 80 wavelengths gt 400 Gbit/s!
• A figure of merit BW max distance
  (Gbit-km/sec)
• 10X/4 years, or 1.8X per year

26
Compare Media

• Assume 40 2.5" disks, each 25 GB, Move 1 km
• Compare Cat 5 (100 Mbit/s), Multimode fiber (1000
  Mbit/s), single mode (2500 Mbit/s), and car
• Cat 5 1000 x 1024 x 8 Mb / 100 Mb/s 23 hrs
• MM 1000 x 1024 x 8 Mb / 1000 Mb/s 2.3 hrs
• SM 1000 x 1024 x 8 Mb / 2500 Mb/s 0.9 hrs
• Car 5 min 1 km / 50 kph 10 min 0.25 hrs
• Car of disks high BW media

27
Interconnect Issues

• Performance Measures
• Network Media
• Connecting Multiple Computers

28
Connecting Multiple Computers

• Shared Media vs. Switched pairs communicate at
  same time point-to-point connections
• Aggregate BW in switched network is many times
  shared
• point-to-point faster since no arbitration,
  simpler interface
• Arbitration in Shared network?
• Central arbiter for LAN?
• Listen to check if being used (Carrier Sensing)
• Listen to check if collision (Collision
  Detection)
• Random resend to avoid repeated collisions not
  fair arbitration
• OK if low utilization

(A. K. A. data switching interchanges,
multistage interconnection networks, interface
message processors)
29
Main Issues

• Addressing
• Routing
• Congestion control
• Flow control

30
Connection-Based vs. Connectionless

• Telephone operator sets up connection between
  the caller and the receiver
• Once the connection is established, conversation
  can continue for hours
• Share transmission lines over long distances by
  using switches to multiplex several conversations
  on the same lines
• Time division multiplexing divide B/W
  transmission line into a fixed number of slots,
  with each slot assigned to a conversation
• Problem lines busy based on number of
  conversations, not amount of information sent
• Advantage reserved bandwidth

31
Connection-Based vs. Connectionless

• Connectionless every package of information must
  have an address gt packets
• Each package is routed to its destination by
  looking at its address
• Analogy, the postal system (sending a letter)
• also called Statistical multiplexing
• Note Split phase buses are sending packets

32
Routing Messages

• Shared Media
• Broadcast to everyone
• Switched Media needs real routing. Options
• Source-based routing message specifies path to
  the destination (changes of direction)
• Virtual Circuit circuit established from source
  to destination, message picks the circuit to
  follow
• Destination-based routing message specifies
  destination, switch must pick the path
• deterministic always follow same path
• adaptive pick different paths to avoid
  congestion, failures
• Randomized routing pick between several good
  paths to balance network load

33
Deterministic Routing Examples

• mesh dimension-order routing
• (x1, y1) -gt (x2, y2)
• first ?x x2 - x1,
• then ?y y2 - y1,
• hypercube edge-cube routing
• X xox1x2 . . .xn -gt Y yoy1y2 . . .yn
• R X xor Y
• Traverse dimensions of differing address in order
• tree common ancestor
• Deadlock free?

34
Store and Forward vs. Cut-Through

• Store-and-forward policy each switch waits for
  the full packet to arrive in switch before
  sending to the next switch (good for WAN)
• Cut-through routing or worm hole routing switch
  examines the header, decides where to send the
  message, and then starts forwarding it
  immediately
• In worm hole routing, when head of message is
  blocked, message stays strung out over the
  network, potentially blocking other messages
  (needs only buffer the piece of the packet that
  is sent between switches).
• Cut through routing lets the tail continue when
  head is blocked, and putting the whole message
  into a single switch. (Requires a buffer large
  enough to hold the largest packet).

35
Cut-Through vs. Store and Forward

• Advantage
• Latency reduces from function ofnumber of
  intermediate switches X by the size of the packet
  to time for 1st part of the packet to
  negotiate the switches the packet size
  interconnect BW

36
Congestion Control

• Packet switched networks do not reserve
  bandwidth this leads to contention (connection
  based limits input)
• Solution prevent packets from entering until
  contention is reduced (e.g., freeway on-ramp
  metering lights)
• Options
• Packet discarding If packet arrives at switch
  and no room in buffer, packet is discarded (e.g.,
  UDP)
• Flow control between pairs of receivers and
  senders use feedback to tell sender when
  allowed to send next packet
• Back-pressure separate wires to tell to stop
• Window give original sender right to send N
  packets before getting permission to send more
  overlaps latency of interconnection with
  overhead to send receive packet (e.g., TCP),
  adjustable window
• Choke packets aka rate-based Each packet
  received by busy switch in warning state sent
  back to the source via choke packet. Source
  reduces traffic to that destination by a fixed
  (e.g., ATM)

37
Protocols HW/SW Interface

• Internetworking allows computers on independent
  and incompatible networks to communicate reliably
  and efficiently
• Enabling technologies SW standards that allow
  reliable communications without reliable networks
• Hierarchy of SW layers, giving each layer
  responsibility for portion of overall
  communications task, called protocol families or
  protocol suites
• Transmission Control Protocol/Internet Protocol
  (TCP/IP)
• This protocol family is the basis of the Internet
• IP makes best effort to deliver TCP guarantees
  delivery
• TCP/IP used even when communicating locally NFS
  uses IP even though communicating across
  homogeneous LAN

38
Connecting Networks

• Bridges connect LANs together, passing traffic
  from one side to another depending on the
  addresses in the packet.
• operate at the Ethernet protocol level
• usually simpler and cheaper than routers
• Routers or Gateways these devices connect LANs
  to WANs or WANs to WANs and resolve incompatible
  addressing.
• Generally slower than bridges, they operate at
  the internetworking protocol (IP) level
• Routers divide the interconnect into separate
  smaller subnets, which simplifies manageability
  and improves security
• Cisco is major supplier basically special
  purpose computers

39
Virtual LAN

• Layer2 technology that tries to achieve what
  Layer3 routers can do limit broadcast traffic
• Distributed spanning tree protocol (802.1D)
• Per-tree spanning tree
• VLAN to emulate ATM
• Transparent reliable multicast
• IGMP snooping

40
Wireless Networks

• Media can be air as well as glass or copper
• Radio wave is electromagnetic wave propagated by
  an antenna
• Radio waves are modulated sound signal
  superimposed on stronger radio wave which carries
  sound signal, called carrier signal
• Radio waves have a wavelength or frequency
  measure either length of wave or number of waves
  per second (MHz) long waves gt low frequencies,
  short waves gt high frequencies
• Tuning to different frequencies gt radio receiver
  pick up a signal.
• FM radio stations transmit on band of 88 MHz to
  108 MHz using frequency modulations (FM) to
  record the sound signal

41
Issues in Wireless

• Wireless often gt mobile gt network must
  rearrange itself dynamically
• Subject to jamming and eavesdropping
• No physical tape
• Cannot detect interception
• Power
• devices tend to be battery powered
• antennas radiate power to communicate and little
  of it reaches the receiver
• As a result, raw bit error rates are typically a
  thousand to a million times higher than copper
  wire

42
Reliability of Wires Transmission

• bit error rate (BER) of wireless link determined
  by received signal power, noise due to
  interference caused by the receiver hardware,
  interference from other sources, and
  characteristics of the channel
• Path loss power to overcome interference
• Shadow fading blocked by objects (walls,
  buildings)
• Multipath fading interference between multiple
  version of signals arriving different times
• Interference reuse of frequency or from adjacent
  channels

43
2 Wireless Architectures

• Base-station architectures
• Connected by land lines for longer distance
  communication, and the mobile units communicate
  only with a single local base station
• More reliable since 1-hop from land lines
• Example cell phones
• Peer-to-peer architectures
• Allow mobile units to communicate with each
  other, and messages hop from one unit to the next
  until delivered to the desired unit
• More reconfigurable

44
Unified P2P Architecture

• Completely distributed system dont even know
  who to talk to ?
• Advantages scalability, fault tolerance, and
  anonymity
• Examples
• KaZaA
• Routing protocol for wired networks
• Routing protocol for wireless networks

45
Cellular Telephony

• Exploit exponential path loss to reuse same
  frequency at spatially separated locations,
  thereby greatly increasing customers served
• Divide region into nonoverlaping hexagonal cells
  (2-10 mi. diameter) which use different
  frequencies if nearby, reusing a frequency when
  cells far apart so that mutual interference OK
• Intersection of three hexagonal cells is a base
  station with transmitters and antennas
• Handset selects a cell based on signal strength
  and then picks an unused radio channel
• To properly bill for cellular calls, each
  cellular phone handset has an electronic serial
  number

46
Cellular Telephony II

• Orginal analog design frequencies set for each
  direction pair called a channel
• 869.04 to 893.97 MHz, called the forward path
• 824.04 MHz to 848.97 MHz, called the reverse path
• Cells might have had between 4 and 80 channels
• Several digital successors
• Code division multiple access (CDMA) uses a wider
  radio frequency band
• time division multiple access (TDMA)
• global system for mobile communication (GSM)
• International Mobile Telephony 2000 (IMT-2000)
  which is based primarily on two competing
  versions of CDMA and one TDMA, called Third
  Generation (3G)

47
Wireless Networking vs. Communications

• The name of the game is wireless communications
  modulation, MIMO, diversity
• Networking part routing, transport protocol,
  handoff, security

48
Practical Issues for Inteconnection Networks

• Connectivity max number of machines affects
  complexity of network and protocols since
  protocols must target largest size
• Connection Network Interface to computer
• Where in bus hierarchy? Memory bus? Fast I/O bus?
  Slow I/O bus? (Ethernet to Fast I/O bus,
  Inifiband to Memory bus since it is the Fast I/O
  bus)
• SW Interface does software need to flush caches
  for consistency of sends or receives?
• Programmed I/O vs. DMA? Is NIC in uncachable
  address space?

49
Practical Issues for Inteconnection Networks

• Standardization advantages
• low cost (components used repeatedly)
• stability (many suppliers to chose from)
• Standardization disadvantages
• Time for committees to agree
• When to standardize?
• Before anything built? gt Committee does design?
• Too early suppresses innovation
• Reliability (vs. availability) of interconnect

50
Practical Issues

• Interconnection SAN LAN WAN
• Example Inifiband Ethernet ATM
• Standard Yes Yes Yes
• Fault Tolerance? Yes Yes Yes
• Hot Insert? Yes Yes Yes
• Standards required for WAN, LAN, and likely SAN!
• Fault Tolerance Can nodes fail and still deliver
  messages to other nodes?
• Hot Insert If the interconnection can survive a
  failure, can it also continue operation while a
  new node is added to the interconnection?

51
Cross-Cutting Issues for Networking

• Efficient Interface to Memory Hierarchy vs. to
  Network
• SPEC ratings gt fast to memory hierarchy
• Writes go via write buffer, reads via L1 and L2
  caches
• Example 40 MHz SPARCStation(SS)-2 vs 50 MHz
  SS-20, no L2 vs 50 MHz SS-20 with L2 I/O bus
  latency different generations
• SS-2 combined memory, I/O bus gt 200 ns
• SS-20, no L2 2 busses 300ns gt 500ns
• SS-20, w L2 cache miss500ns gt 1000ns

52
Crosscutting Smart Switch vs. Smart Network
Interface Card

• Inexpensive NIC gt Ethernet standard in all
  computers
• Inexpensive switch gt Ethernet used in home
  networks

53
Cluster

• LAN switches gt high network bandwidth and
  scaling was available from off the shelf
  components
• 2001 Cluster collection of independent
  computers using switched network to provide a
  common service
• Many mainframe applications run more "loosely
  coupled" machines than shared memory machines
  (next chapter/week)
• databases, file servers, Web servers,
  simulations, and multiprogramming/batch
  processing
• Often need to be highly available, requiring
  error tolerance and reparability
• Often need to scale

54
Cluster Drawbacks

• Cost of administering a cluster of N machines
  administering N independent machines vs. cost of
  administering a shared address space N processors
  multiprocessor administering 1 big machine
• Clusters usually connected using I/O bus, whereas
  multiprocessors usually connected on memory bus
• Cluster of N machines has N independent memories
  and N copies of OS, but a shared address
  multi-processor allows 1 program to use almost
  all memory
• DRAM prices has made memory costs so low that
  this multiprocessor advantage is much less
  important in 2001

55
Cluster Advantages

• Error isolation separate address space limits
  contamination of error
• Repair Easier to replace a machine without
  bringing down the system than in an shared memory
  multiprocessor
• Scale easier to expand the system without
  bringing down the application that runs on top of
  the cluster
• Cost Large scale machine has low volume gt fewer
  machines to spread development costs vs. leverage
  high volume off-the-shelf switches and computers
• Amazon, AOL, Google, Hotmail, Inktomi, WebTV, and
  Yahoo rely on clusters of PCs to provide services
  used by millions of people every day

56
Addressing Cluster Weaknesses

• Network performance SAN, especially Inifiband,
  may tie cluster closer to memory
• Maintenance separate of long term storage and
  computation
• Computation maintenance
• Clones of identical PCs
• 3 steps reboot, reinstall OS, recycle
• At 1000/PC, cheaper to discard than to figure
  out what is wrong and repair it?
• Storage maintenance
• If separate storage servers or file servers,
  cluster is no worse?

57
Clusters and TPC Benchmarks

• Shared Nothing database (not memory, not disks)
  is a match to cluster
• 2/2001 Top 10 TPC performance 6/10 are clusters
  (4 / top 5)

58
Putting it all together Google

• Google search engine that scales at growth
  Internet growth rates
• Search engines 24x7 availability
• Google 12/2000 70M queries per day, or AVERAGE
  of 800 queries/sec all day
• Response time goal lt 1/2 sec for search
• Google crawls WWW and puts up new index every 4
  weeks
• Stores local copy of text of pages of WWW
  (snippet as well as cached copy of page)
• 3 collocation sites (2 CA 1 Virginia)
• 6000 PCs, 12000 disks almost 1 petabyte!

59
Hardware Infrastructure

• VME rack 19 in. wide, 6 feet tall, 30 inches
  deep
• Per side 40 1 Rack Unit (RU) PCs 1 HP Ethernet
  switch (4 RU) Each blade can contain 8
  100-Mbit/s EN or a single 1-Gbit Ethernet
  interface
• Frontback gt 80 PCs 2 EN switches/rack
• Each rack connects to 2 128 1-Gbit/s EN switches
• Dec 2000 40 racks at most recent site

60
Google PCs

• 2 IDE drives, 256 MB of SDRAM, modest Intel
  microprocessor, a PC mother-board, 1 power supply
  and a few fans.
• Each PC runs the Linix operating system
• Buy over time, so upgrade componentspopulated
  between March and November 2000
• microprocessors 533 MHz Celeron to an 800 MHz
  Pentium III,
• disks capacity between 40 and 80 GB, speed 5400
  to 7200 RPM
• bus speed is either 100 or 133 MH
• Cost 1300 to 1700 per PC
• PC operates at about 55 Watts
• Rack gt 4500 Watts , 60 amps

61
Reliability

• For 6000 PCs, 12000s, 200 EN switches
• 20 PCs will need to be rebooted/day
• 2 PCs/day hardware failure, or 2-3 / year
• 5 due to problems with motherboard, power
  supply, and connectors
• 30 DRAM bits change errors in transmission
  (100 MHz)
• 30 Disks fail
• 30 Disks go very slow (10-3 expected BW)
• 200 EN switches, 2-3 fail in 2 years
• 6 Foundry switches none failed, but 2-3 of 96
  blades of switches have failed (16 blades/switch)
• Collocation site reliability
• 1 power failure,1 network outage per year per
  site
• Bathtub for occupancy

62
Google Performance Serving

• How big is a page returned by Google? 16KB
• Average bandwidth to serve searches
• 70,000,000/day x 16,750 B x 8 bits/B
• 24 x 60 x 60
• 9,378,880 Mbits/86,400 secs
• 108 Mbit/s

63
Google Performance Crawling

• How big is a text of a WWW page? 4000B
• 1 Billion pages searched
• Assume 7 days to crawl
• Average bandwidth to crawl
• 1,000,000,000/pages x 4000 B x 8 bits/B
• 24 x 60 x 60 x 7
• 32,000,000 Mbits/604,800 secs
• 59 Mbit/s

64
Google Performance Replicating Index

• How big is Google index? 5 TB
• Assume 7 days to replicate to 2 sites, implies BW
  to send BW to receive
• Average bandwidth to replicate new index
• 2 x 2 x 5,000,000 MB x 8 bits/B
• 24 x 60 x 60 x 7
• 160,000,000 Mbits/604,800 secs
• 260 Mbit/s

65
Co-location Sites

• Allow scalable space, power, cooling and network
  bandwidth plus provide physical security
• charge about 500 to 750 per Mbit/sec/month
• if your continuous use measures 1- 2 Gbits/second
• to 1500 to 2000 per Mbit/sec/month
• if your continuous use measures 1-10 Mbits/second
• Rack space costs 800 -1200/month, and drops by
  20 if gt 75 to 100 racks (1 20 amp circuit)
• Each additional 20 amp circuit per rack costs
  another 200 to 400 per month
• PGE 12 megawatts of power, 100,000 sq.
  ft./building, 10 sq. ft./rack gt 1000 watts/rack

66
Google Performance Total

• Serving pages 108 Mbit/sec/month
• Crawling 59 Mbit/sec/week, 15 Mbit/s/month
• Replicating 260 Mbit/sec/week, 65 Mb/s/month
• Total roughly 200 Mbit/sec/month
• Googles Collocation sites have OC48
• (2488 Mbit/sec) link to Internet
• Bandwidth cost per month? 150,000 to 200,000
• 1/2 BW grows at 20/month

67
Google Costs

• Collocation costs 40 racks _at_ 1000 per month
  500 per month for extra circuits
• 60,000 per site, 3 sites
• 180,000 for space
• Machine costs
• Rack 2k 80 1500/pc 2 1500/EN
• 125k
• 40 racks 2 Foundry switches _at_100,000
• 5M
• 3 sites 15M
• Cost today is 10,000 to 15,000 per TB

68
Comparing Storage Costs 1/2001

• Google site, including 3200 processors and 0.8 TB
  of DRAM, 500 TB (40 racks) 10k - 15k/ TB
• Compaq Cluster with 192 processors, 0.2 TB of
  DRAM, 45 TB of SCSI Disks (17 racks) 115k/TB
  (TPC-C)
• HP 9000 Superdome 48 processors, 0.25 TB DRAM,
  19 TB of SCSI disk (23 racks) 360k/TB (TPC-C)

69
Putting It All Together Cell Phones

• 1999 280M handsets sold 2001 500M
• Radio steps/components Receive/transmit
• Antenna
• Amplifier
• Mixer
• Filter
• Demodulator
• Decoder

70
Putting It All Together Cell Phones

• about 10 chips in 2000, which should shrink, but
  likely separate MPU and DSP
• Emphasis on energy efficiency

From How Stuff Works on cell phones
www.howstuffworks.com
71
Cell phone steps (protocol)

• Find a cell
• Scans full BW to find stronger signal every 7
  secs
• Local switching office registers call
• records phone number, cell phone serial number,
  assigns channel
• sends special tone to phone, which cell acks if
  correct
• Cell times out after 5 sec if doesn't get
  supervisory tone
• Communicate at 9600 b/s digitally (modem)
• Old style message repeated 5 times
• AMPS had 2 power levels depending on distance
  (0.6W and 3W)

72
Frequency Division Multiple Access (FDMA)

• FDMA separates the spectrum into distinct voice
  channels by splitting it into uniform chunks of
  bandwidth
• !st generation analog

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Time Division Multiple Access (TDMA)

• a narrow band that is 30 kHz wide and 6.7 ms long
  is split time-wise into 3 time slots.
• Each conversation gets the radio for 1/3 of time.
  
• Possible because voice data converted to digital
  information is compressed so
• Therefore, TDMA has 3 times capacity of analog
• GSM implements TDMA in a somewhat different and
  incompatible way from US (IS-136) also encrypts
  the call

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74
Code Division Multiple Access (CDMA)

• CDMA, after digitizing data, spreads it out over
  the entire bandwidth it has available.
• Multiple calls are overlaid over each other on
  the channel, with each assigned a unique sequence
  code.
• CDMA is a form of spread spectrum All the users
  transmit in the same wide-band chunk of spectrum.
  
• Each user's signal is spread over the entire
  bandwidth by a unique spreading code. same unique
  code is used to recover the signal.

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75
Single-Chip PC

• What constitutes a PC?
• Can they all be packaged into one chip?
• 100 million transistors
• 100 Notebook computer