Lecture 21: Networking

1
Lecture 21Networking

• Prof. Kenneth M. Mackenzie
• Computer Systems and Networks
• CS2200, Spring 2003

Includes slides from Bill Leahy
2
Review Example Thread Package
3
Review how to wait

• (4. blocking) Proper Implementation
• scheduler data structures protected by a
  spin-lock
• blocking mutex implementation bootstraps on
  that spin-lock

void blocking_mutex_lock(mutex_t mutex)
spin_mutex_lock(theschedulermutex) if
(mutex-gtstate 1) enqueue(running,
mutex-gtblocklist) scheduler() /
unlocks theschedulermutex / else
mutex-gtstate 1 spin_mutex_unlock(the
schedulermutex)
4
Review when to waitCondition Variable
This is your lock on your data structure
pthread_mutex_t mutex pthread_cond_t cond
pthread_mutex_lock(mutex) while
(my_elaborate_condition()) pthread_cond_wait(
cond, mutex) / do stuff that depended on
condition / pthread_mutex_unlock(mutex)
This is the pcblist
block this thread call the scheduler
5
Review example usagedequeue code with
cond_wait()
static void queue_dequeue(queue_t queue)
queueitem_t queueitem void item
pthread_mutex_lock(queue-gtmutex) while
(queue-gthead NULL) pthread_cond_wait(queue
-gtempty, queue-gtmutex) queueitem
queue-gthead queue-gthead queueitem-gtlink
if (queue-gthead NULL) queue-gttail NULL
pthread_mutex_unlock(queue-gtmutex) item
queueitem-gtitem queueitem_free(queueitem)
return(item)
6
Overview

• Today
• A Brief History
• Basic Concepts
• Network Hardware
• Ethernet
• Demo simple protocol wires
• Network Basics
• Basic problem move bits from point a to point b
• Performance metrics
• Extended Example Ethernet

7
A Brief History

• 1876 Telephone Invented
• (Analog technology)
• 1942 Mainframes Developed
• Use continues today
• Initially batch oriented environment
• Evolution to Timesharing
• i.e. Data terminals connected to mainframes
• Early 60's Voice telephony switches to digital

8
A Brief History

• 1960 ATT Introduced Dataphone
• First commercial modem
• Modem Modulator/Demodulator
• Convert between digital and analog signals
• (Essentially same technology used today)

9
A Brief History

• 1965 DoD Advanced Research Projects Agency (ARPA)
  begins work on ARPANET
• 1968/9 Carterphone decision allowed devices which
  were beneficial and not harmful to the network to
  be connected to the Public Switched Telephone
  Network (PSTN).
• Paved the way for computers to communicate using
  the telephone switching infrastructure.

10
A Brief History

• 1969 ARPANET connects 4 computers
• Stanford Research Institute, UCLA, UC Santa
  Barbara, and the University of Utah
• 1971 The ARPANET grows to 23 hosts connecting
  universities and government research centers
  around the country.
• 1971 Intel introduces the first microprocessor -
  the Intel 4004.

11
A Brief History

• 1971 The Kenbak-1, the first microcomputer, is
  introduced in Scientific American, selling a
  total of 40 units in 2 years.
• Used 130 IC's with a 256 byte memory and 8-bit
  words, processed 1000 instructions per second,
  and cost 750.

12
A Brief History

• 1972 Intel launches the 8-bit 8008 - the first
  microprocessor which could handle both upper and
  lowercase characters.
• 1972 Xerox develops the Xerox Alto - the first
  computer to use a Graphic User Interface.

The Alto consists of four major parts the
graphics display, the keyboard, the graphics
mouse, and the disk storage/processor box. Each
Alto is housed in a beautifully formed, textured
beige metal cabinet that hints at its 32,000
price tag (1979US money). With the exception of
the disk storage/processor box, everything is
designed to sit on a desk or tabletop
13
A Brief History

• 1973 Robert Metcalfe invents the Ethernet
  networking system at the Xerox Palo Alto Research
  Center.

14
A Brief History

• 1973 The ARPANET goes international
• 1974 Intel introduces the 8080 microprocessor
• 5 times faster than the 8008.
• And the heart of the future Altair 8800.

15
A Brief History

• 1975 MITS markets the Altair 8800 - the first
  mass-market microcomputer, launching the Personal
  Computer Revolution.
• 1975 Internet operations transferred to the
  Defense Communications Agency
• 1975 Bill Gates and Paul Allen form the Microsoft
  company to create software for the new Altair
  8800.

16
A Brief History

• 1976 Apple Computer is formed by Steve Jobs,
  Steve Wozniak, and Ron Wayne, and launches the
  Apple Computer.
• 1977 Tandy Radio Shack ships its first personal
  computer - the TRS-80. It sells over 10,000
  units, tripling expectations.
• 1977 Apple Computer launches the Apple II, which
  sets new standards for sophisticated personal
  computer systems.

17
A Brief History

• 1978 The C programming language is completed at
  ATT Bell Laboratories, offering a new level of
  programming.
• 1978 Apple and Tandy ship PCs with 5.25" floppy
  disks, replacing cassette tape as the standard
  storage medium for PCs.
• 1978 Hayes Microcomputer Products releases the
  first mass-market modem, transmitting at 300 bps
  (0.3K).

18
A Brief History

• 1978 Intel ships the Intel 8086 microprocessor,
  with 29,000 transistors, and running at 4.77
  megahertz.
• 1979 Personal Software creates VisiCalc for the
  Apple II, the first electronic spreadsheet
  program, selling over 100,000 copies.
• 1979 Intel develops the 8088 microprocessor,
  which would later become the heart of the IBM PC.

19
A Brief History

• 1979 Motorola develops the Motorola 68000
  microprocessor, offering a new level of
  processing power.
• 1980 Seagate Technology introduces the first
  microcomputer hard disk, capable of holding 5
  megabytes of data.
• 1980 Philips introduces the first optical laser
  disk, with many times the storage capacity of
  floppy or hard disks.

20
A Brief History

• 1980 Xerox creates Smalltalk - the first
  object-oriented programming language.
• 1980 John Shoch at Xerox creates the first worm
  program, with the capacity to travel through
  networks.
• 1981 Ungermann-Bass ships the first commercial
  Ethernet network interface card.

21
A Brief History

• 1981 Xerox introduces the Xerox Star 8010, the
  first commercial Graphic User Interface computer,
  for 16,000-17,000.
• 1981 Microsoft supplies IBM with PC-DOS (which it
  would also sell as MS-DOS), the OS that would
  power the IBM PC.
• 1981 IBM brings to market the IBM PC, immediately
  establishing a new standard for the world of
  personal computers.

22
A Brief History

• 1981 ARPANET has 213 hosts. A new host is added
  approximately once every 20 days.
• 1982 The term 'Internet' is used for the first
  time.
• 1983 TCP/IP becomes the universal language of the
  Internet

23
http//research.lumeta.com/ches/map/
24
Networking Basics
25
Network Culture(s)

• 3 cultures for 3 classes of networks
• SAN performance, latency and bandwidth
• LAN workstations, cost
• WAN telecommunications, phone call revenue
• Connection of 2 or more networks Internetworking
• Will attempt a single terminology

26
Interconnections (Networks)

• Examples
• System Area Networks (SP2) 100s nodes 25
  meters per link
• Local Area Networks (Ethernet) 100s nodes
  1000 meters
• Wide Area Network (ATM) 1000s nodes 5,000,000
  meters

a.k.a. end systems, hosts
a.k.a. network, communication subnet
Interconnection Network
27
Example 1 (of 2)FTP over WAN
bus
NI
M
P
D
mountains
swamp

• Disk-to-disk transfer
• 1. universality
• 2. reliability
• 3. performance (bandwidth)
• Distance may be great
• multiple trips through memory, processor may be
  fine
• performance issue is pipelining packets through
  the system

28
Example 2 (of 2)Parallel Program on a SAN
bus
switch
0.5 meter
0.5 meter
NI
M
P
D

• Distance small and known
• mem-to-mem or even reg-to-reg
• switch may use ECC reliability
• Application may be limited by network latency as
  well as bandwidth

Jacobi method Aij ave. of neighbors
from previous iter. (HW8)
29
Example Major Networks

• Ethernet and Ethernet
• 10/100/1000... (10000Mb)
• 1500B packets, 100m
• originally shared bus, now switched star
• ATM
• 155/620Mb... (10000Mb)
• OC-3/-12... (-192)
• 53B cells, arbitrary dist.
• circuit-switched

• Myrinet
• cluster interconnect
• 1200Mb
• Fibre Channel
• I/O interconnect
• 1000/2000Mb
• Infiniband
• I/O and cluster interconnect
• 2.5/10Gb

30
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

31
Trivial Examplesupport read of remote memory

• 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)

32
Extensions

• 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., CRC)
• 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 elaborate
  protocols and packet formats gt complexity
• note complexity often gt slow

33
A Simple Example Revisted

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

Address/Data
CRC
Code
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
34
Simple Example SoftwareHW kernel-controlled,
memory-mapped

• Send steps
• 1 Application copies data to OS buffer, then
  does a system call
• 2 OS computes checksum, copies data/checksum to
  NI hardware
• 3 OS sets timeout timer, tells NI to start
• SW Receive steps
• 1 OS copies data from hardware to OS buffer,
  performs checksum
• 2 If checksum matches send ACK if not, OS
  deletes message (sender resends when timer
  expires)
• 3 If OK, notify application application copies
  data from OS buffer
• Sequence of steps protocol
• Example similar to UDP/IP protocol in UNIX

35
Protocols

• Sequence of steps performed by software to send
  and receive messages.
• Issues
• Lost messages
• Duplicate messages
• Queue full
• Endianess
• etc.
• More next time...

36
Performancevocabulary fun

• Bandwidth
• Time of Flight
• Transmission Time
• Transport Latency
• Sender Overhead
• Receiver Overhead

37
Network Performance Measures

• Overhead latency of interface vs.
• Latency latency of network

38
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?
39
Example Performance Measures

• Interconnect MPP LAN WAN
• Example CM-5 Ethernet ATM
• Bisection BW N x 5 MB/s 1.125 MB/s N x 10 MB/s
  
• Int./Link BW 20 MB/s 1.125 MB/s 10 MB/s
• Transport Latency 5 µsec 15 µsec 50 to 10,000 µs
• HW Overhead to/from 0.5/0.5 µs 6/6 µs 6/6 µs
• SW Overhead to/from 1.6/12.4 µs 200/241
  µs 207/360 µs (TCP/IP on LAN/WAN)

Software overhead dominates in LAN, WAN
40
There is an old network saying Bandwidth
problems can be cured with money. Latency
problems are harder because the speed of light is
fixed--you cant bribe God.

• David Clark, MIT

41
Connecting Computers
42
Connecting Computers

• 1. Network Interface
• 2. Media
• 3. Connecting more than two computers
• Routing
• Network topologies
• 4. Internetworking connecting across multiple
  protocols

43
Where to place NI card
CPU
Network
Network

ideal high bandwidth, low latency, standard
interface
L2
Memory Bus
I/O bus
Memory
Bus Adaptor

• Where to connect network to computer?
• Cache consistent to avoid flushes? (gt memory
  bus)
• Latency and bandwidth? (gt memory bus)
• Standard interface card? (gt I/O bus)
• MPP gt memory bus LAN, WAN gt I/O bus
• Future?

44
Hierarchy of Media

• Twisted Pair
• Coaxial Cable
• Fiber Optics

45
Media

• Twisted Pair
• 10 Mb/Sec 2 km 0.23/m 15
• 1000 Mb/sec 0.2 km 0.23/m 500
• Coaxial Cable
• 10 Mb/sec 1 km 1.64 25
• Multimode Fiber
• 1000 Mb/sec 2 km 1.03 500
• Single-Mode Fiber
• 10000 Mb/sec 100 km 1.64 10000

46
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)
47
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

48
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

49
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

50
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?

51
Routing Policies

• Store and Forward
• Wormhole
• http//www.johnlockhart.com/research/janet/

52
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, accordioning the whole message
  into a single switch. (Requires a buffer large
  enough to hold the largest packet).

53
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

54
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
  overlapslatency 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)

55
Protocol Family Concept
Message
Message
Message
56
Protocol Family Concept

• Key to protocol families is that communication
  occurs logically at the same level of the
  protocol, called peer-to-peer,
• but is implemented via services at the next lower
  level
• Encapsulation carry higher level information
  within lower level envelope
• Fragmentation break packet into multiple smaller
  packets and reassemble
• Danger is each level increases latency if
  implemented as hierarchy (e.g., multiple check
  sums)

57
TCP/IP packet, Ethernet packet, protocols

• Application sends message

• TCP breaks into 64KB segments, adds 20B header

• IP adds 20B header, sends to network

• If Ethernet, broken into 1500B packets with
  headers, trailers (24B)

• All Headers, trailers have length field,
  destination, ...

58
The Ethernet
A drawing of the first Ethernet system by Bob
Metcalfe.
59
Ethernet Evolution

• X_Base_Y
• X stands for the available media bandwidth
• Base stands for base band signaling on the medium
• Y stands for the maximum distance a station can
  be from the vampire tap (i.e. Length of Attach
  Unit Interface)

60
Ethernet Evolution

• 10_base_5 (1979-1985)
• 10 Mbits/Sec with base band signaling with a
  maximum station distance of 500 meters
• Thick shielded copper conductor used as the medium

MAU-Medium Access Unit
61

• 10_base_2 (1985-1993)
• Thin net, cheaper net
• Distance to the station shrinks to 200 meters
• No more vampire taps
• BNC connector to connect the stations to the
  Attach Unit Interface (AUI) cables, the AUI
  cables to the medium
• The medium is daisy-chained via the stations
  using the BNC connectors

Bayonet Neil-Concelman, or sometimes British
Naval Connector
62

• 10_base_T (1993-1995)
• Attach Unit Interface (AUI) is a twisted pair of
  copper wires
• AUIs from the stations come to a hub which is a
  multiplexor/transceiver
• Did away with the BNC connectors which were a
  source of connector problems
• Use phone jack technology (RJ45 connectors) to
  connect AUI cables to the hub
• Hubs are connected to other hubs using the same
  connectors (RJ45)

63

• 10_base_T (1993-1995) continued
• All the hubs together form the entire medium
• All the stations in the same collision domain
• Hub is also usually called a repeater

64
More Ethernet

• 10BROAD36 - 10BROAD36 is a seldom used Ethernet
  specification which uses a physical medium
  similar to cable television, with CATV-type
  cables, taps, connectors, and amplifiers.
• 1BASE5 - 1BASE5 is a specification of Ethernet
  that runs at 1 Mb/s over twisted pair wiring.
  This physical topology uses centralized hubs to
  connect the network devices.
• FOIRL - Fiber Optic Inter-Repeater Link - This
  specification of the 802.3 standard defines a
  standard means of connecting Ethernet repeaters
  via optical fiber.

65
More Ethernet

• 10BASE-F - 10BASE-F is a set of optical fiber
  medium specifications which define connectivity
  between devices.
• 100BASE-T - 100BASE-T is a series of
  specifications that provides 100 megabit speeds
  over copper or fiber. These topologies are often
  referred to as Fast Ethernet.
• Gigabit Ethernet - Gigabit Ethernet provides
  speeds of 1000 Mb/s over copper and fiber.

66
Where will it end???
67
Broadband vs. Baseband

• A baseband network has a single channel that is
  used for communication between stations. Ethernet
  specifications which use BASE in the name refer
  to baseband networks.
• A broadband network is much like cable
  television, where different services communicate
  across different frequencies on the same cable.
• Broadband communications would allow a Ethernet
  network to share the same physical cable as voice
  or video services. 10BROAD36 is an example of
  broadband networking.

68
Current Technology

• Most modern Ethernet networks use twisted pair
  copper cabling or fiber to attach devices to the
  network. The 10BASE-T, 100BASE-T, and Gigabit
  Ethernet topologies are well suited for the
  modern cabling and fiber infrastructures.

69
Still Hungry?

• http//www.faqs.org/faqs/LANs/ethernet-faq/

70
Ethernet

• The various Ethernet specifications include a
  maximum distance
• What do we do if we want to go further?
• Repeater
• Hardware device used to extend a LAN
• Amplifies all signals on one segment of a LAN and
  transmits them to another
• Passes on whatever it receives (GIGO)
• Knows nothing of packets, addresses
• Any limit?

71
Repeaters
R1
R2
R3
72
Repeaters
R1
R2
R3
73
Bridges

• We want to improve performance over that provided
  by a simple repeater
• Add functionality (i.e. more hardware)
• Bridge can detect if a frame is valid and then
  (and only then) pass it to next segment
• Bridge does not forward interference or other
  problems
• Computers connected over a bridged LAN don't know
  that they are communicating over a bridge

74
Bridges

• Typical bridge consists of conventional CPU,
  memory and two NIC's.
• Does more than just pass information from one
  segment to another
• A bridge can be constructed to
• Only pass valid frame if necessary
• Learn what is connected to network "on the fly"

75
Bridges

• Event Segment 1 List Segment 2 List
• Bridge boots - -
• U send to V U -
• V sends to U U, V -
• Z broadcasts U, V Z
• Y sends to V U, V Z, Y
• Y sends to X U, V Z, Y
• X sends to W U, V Z, Y, X
• W sends to Z U, V, W Z, Y, X

76
Bridges

• A bridge will connect to distinct segments
  (usually referring to a physical length of wire)
  and transmit traffic between them.
• This allows you to extend the maximum size of the
  network while still not breaking the maximum wire
  length, attached device count, or number of
  repeaters for a network segment.

77
Switch
A
B
C
D
78
Virtual LANs

• VLANs may span bridges
• Nodes 1 and 5 same VLAN 2, 6, 7 same VLAN
• All nodes on the same VLAN hear broadcasts from
  any node on that VLAN
• VLAN limits the traffic flow among bridges
• A hierarchical network with only bridges results
  in a switched ethernet with no collisions!

79
http//www.cisco.com/univercd/cc/td/doc/product/so
ftware/ios113ed/113ed_cr/switch_c/xcvlan.htm
80
Network Interface Card

• NIC
• Sits on the host station
• Allows a host to connect to a hub or a bridge
• If connected to a hub, then NIC has to use
  half-duplex mode of communication (i.e. it can
  only send or receive at a time)
• If connected to a bridge, then NIC (if it is
  smart) can use either half/full duplex mode
• Bridges learn Media Access Control (MAC) address
  and the speed of the NIC it is talking to.

81
Routers

• Work much like bridges
• Pay attention to the upper network layer
  protocols
• (OSI layer 3) rather than physical layer (OSI
  layer 1) protocols.
• Will decide whether to forward a packet by
  looking at the protocol level addresses (for
  instance, TCP/IP addresses) rather than the MAC
  address.

82
Routers

• Because routers work at layer 3 of the OSI stack,
  it is possible for them to transfer packets
  between different media types (i.e., leased
  lines, Ethernet, token ring, X.25, Frame Relay
  and FDDI). Many routers can also function as
  bridges.

83
Routers

• Repeaters and Bridges understand only Media
  Access Control (MAC) addresses
• Traffic flow between nodes entirely based on MAC
  addresses
• Packet from a host station ltmac-addr, payloadgt
• Routers understand IP addresses
• Special board that sits inside a bridge
• IP layer on all nodes send packets destined
  outside the LAN to the router
• Router sees a packet as ltip-hdr, payloadgt
• uses the ip-hdr to route the packet on to internet