case studies - csperkins.org€¦ · case studies networked systems 3 lecture 3. lecture outline...
TRANSCRIPT
The Telephone System
• Public switched telephone network (PSTN) • Voice phones
• Fax machines
• Dial-up modems
• Ignoring (for now): • Mobile phones, VoIP
���3
History and Development
• 1876: Alexander Graham Bell
• Bell Telephone Company → AT&T
• National telephone monopolies • Strong governmental regulation
• Slow pace of innovation and service change
• Liberalisation, competition, and opening of the local loop
Alexander Graham Bell
Sou
rce:
Pub
lic d
omai
n
���4
Basic Concepts
• Multi-level circuit switched network • Analogue circuits transport speech to exchange
• Sampled at exchange, digital circuits in the core
• Optimised for speech traffic • Only a single service provided: convey speech
data
• Circuit capacity based on speech characteristics
• Network dimensioned using typical call duration
���5
Physical and Link Layers
• Single twisted pair cable forms the local loop
• Analogue circuit, band limited to 300 – 3,400Hz • Acceptable quality speech; not suitable for music
0.0001
0.001
0.01
0.1
1
1 100.1Frequency (kHz)
Rel
ativ
e E
nerg
y
300-3400Hz pass band
Speech
Time
Am
plitu
de
���6
Network Layer
• Local loop terminates at exchange
• Structured hierarchical circuit switching and addressing to route call to destination
• Calls block if no capacity at intermediate circuit
• Structured addressing: +44 141 330 4256Country
ExchangeCustomer
���7
Transport Layer
Analogue speech signal is digitised at the exchange: 7 bits × 8000 samples/second = 56kbps channel (US & Japan) 8 bits × 8000 samples/second = 64kbps channel (Elsewhere)
Channel 1 Channel 2 Channel 3 Channel 24
Frame 1 (193 bits)
Each frame comprises: 1 framing bit, 24 channels (7 data bits, 1 control bit)
24 voice channels
Outside US & Japan: 32 voice channels,E1 line (2.048 Mbps)
T1 line (1.544 Mbps)
Multiplexing continues at higher rates Synchronous Digital Hierarchy (SDH)
All digital circuits in the phone system are defined as synchronous multiples of the voice channel rate
���8
Encoded as audio tones sent over the voice path
Digital path extended to edge
Primary service• Voice telephony
• Fax
• Video conferencing
• Data circuits
Applications
���9
Telephony Standards
• International Telecommunications Union • http://www.itu.int/
• Governmental-level body: part of The United Nations
• Formal representation and voting process • Companies send representatives to national standards bodies (e.g.
BSI, ANSI, DIN); national standards bodies cast their country’s vote at the ITU plenary meeting
• Cycle of formal comments on technical protocols between plenary and national standards bodies
• Liaisons with other standards bodies (e.g. IETF, W3C)
���10
Design Choices
• Circuit switched network • Potential blocking; high quality guaranteed if accepted
• Traditionally strong reliability guarantees
• Highly optimised for voice telephony
• Inflexible architecture, bureaucratic standards • Stability and reliability preferred over flexibility
���11
The Internet
• Interconnected set of global networks, running a common network layer • The Internet Protocol (IP)
• Supporting technology for application protocols • World Wide Web (HTTP)
• Email (SMTP)
• Instant Messaging (Jabber, etc.)
���12
History and Development
• 1965: Packet switching • Paul Baran (RAND),
Donald Davies (NPL)
• 1969: ARPA funding • First link: UCLA – SRI
• 1973: First non-US sites
• 1983: Switch to IPv4
• 1990: World Wide Web • Tim Berners-Lee
ARPA network map December 1972
Sou
rce:
RFC
432
���13
2457
2149
1842
1535
1228
921
614
307
0
Peering:OutDegree
157
58
50
41
33
25
16
8
0
010W
20W
30W
40W
50W
60W
70W
80W90W
100W
110W
120W
130W
140W
150W
160W
170W
180E/W
170E
160E
150E
140E
130E
120E
110E
100E90E
80E
70E
60E
50E
40E
30E
20E
10E
O
C
E
A
N
I
A
A
FR
IC
A
S
O
U
T
H
AM
ER
IC
A
A
S
IA
EU
RO
PE
NO
RTH AME
RI
CA
Brussels, BE
Oslo, NO
RK,lu
oeS
SU,ululonoH
SU,revne
D
Toronto, C
A
SU,ogei
DnaS
SU,esoJnaS
SU,xineohP
SU,notsuo
H
Chicago, U
S
Ottaw
a, CA
Washington, U
SBoston, U
S
Buenos Aires, AR
Rio de Janeiro, BR
London, UKParis, FR
Berlin, DE
Vienna, ATStockholm
, SESofi
a, BGHel
sinki, FIPre
toria, ZA
Kiev, UA
Warsaw,
PL
Ankara, TR
Tel Aviv, IL
Moscow,RU
AbuDhabi,AEBombay,IN
Delhi, IN
HT,
kokg
naB
GS,e
ropa
gniS
DI,a
trak
aJ
NC,
gniji
eBWT
,iepia
T
PJ,oyk
oT
UA,yen
dyS
Frankfurt, DE
UR,k
otsovi
dalV
Alges, PT
Dublin, IE
Bombay,IN
Delhi, IN
HT,
kokg
naB
GS,e
ropa
gniS
DI,a
trak
aJ
NC,
gniji
eBWT
,iepia
T
PJ,oyk
oT
UA,yen
dyS
Frankfurt, DE
UR,k
otsovi
dalV
Alges, PT
Dublin, IE
Toronto, C
A
SU,ogei
DnaS
SU,esoJnaS
SU,xineohP
SU,notsuo
H
Chicago, U
S
Ottaw
a, CA
Washington, U
SBoston, U
S
Buenos Aires, AR
Rio de Janeiro, BR
London, UKParis, FR
Berlin, DE
Vienna, ATStockholm
, SESofi
a, BGHel
sinki, FIPre
toria, ZA
Kiev, UA
Warsaw,
PL
Ankara, TR
Tel Aviv, IL
Moscow,RU
AbuDhabi,AE
0 1
0W
20W
30W 40W
50W 60W 70W 80W 90W
100W
110W
1
20W
1
30W
140W
15
0W
160W
1
70
W
18
0E/
W 1
70
E
1
60E
15
0E
140
E
130E
1
20E
110E
100E 90E 80E 70E 60E 50E 40E 30E 20E 1
0E
O
C
E
A
N
I
A
A
FR
IC
A
S
O
U
T
H
AM
ER
IC
A
Brussels, BE
Oslo, NO
RK,lu
oeS
SU,ululonoH
SU,revne
D
3257(Tinet)3257(Tinet)
2516(KDDI)2516(KDDI)
6939(Hurricane)6939(Hurricane)
3356(LEVEL3)3356(LEVEL3)12008(Centertgate)12008(Centergate)
2697(ERX)2697(ERX)
1200(ANSIX)1200(AMSIX)
2914(NTT)2914(NTT)11537(Internet2)11537(Internet2)6453(GLOBEINTERNET)6453(GLOBEINTERNET)
2500(WIDE)2500(WIDE)
6695(DECIX)6695(DECIX)
5459(LINX)5459(LINX)
LavaNet (6435)6435(LavaNet)
3549(GBKX)3549(GBLX)
2914(NTT)2914(NTT)
2697(ERX)2697(ERX)
8359(COMSTAR)8359(COMSTAR)
1299(TeliaNet)1299(TeliaNet) 702(MCI)702(MCI)
10026(Asia Netcom)10026(Asia Netcom)
4755(TATACOMM)4755(TATACOMM)
8395(COMSTAR)8395(COMSTAR)
2516(KDDI)2516(KDDI)
7575(AARNET)7575(AARNET)
38809(NXGNET)38809(NXGNET) 3904 (Hutchison)9304 (Hutchison)
7714(TelstraClear)7714(TelstraClear)
20485(JSC)20485(JSC)
1273(CW)1273(CW)5459(London IX)5459(London IX)
1239(Sprint)1239(Sprint) 12989(HWNG)12989(HWNG)3549(Global Crossing)3549(Global Crossing)
4320(Embratel)4320(Embratel)
577(Bell Canada)577(Bell Canada)7843(Road Runner)7843(Road Runner)
2828(XOXO)2828(XOXO)3561(Savvis)3561(Savvis)
701(UUNET)701(UUNET)3356(Level 3)3356(Level 3)
6677(ICENET)6677(ICENET)
3320(Deutsche Telekom)3320(Deutsche Telekom) 8928(Interoute)8928(Interoute)
2914(NTT)2914(NTT)
A S - l e v e l I N T E R N E T G R A P H
I P v 4 & I P v 6 I N T E R N E T T O P O L O G Y M A P J A N U A RY 2 0 0 9
Source: CAIDA
Basic Concepts
• Global inter-networking protocol
• Hour glass protocol stack • Single standard network layer protocol (IP)
• Packet switched network, best effort packet delivery
• Uniform network and host addressing
• Uniform end-to-end connectivity (subject to firewall policy)
• Range of transport & application layer protocols
• Range of link-layer technologies supported
IP
TCPSMTP
HTTP RTPSIP
HTMLMIMESDP Codecs
Wi-Fi
EthernetADSL
SONET
UDP
WirelessTwisted Pair
Optical FibrePhysical
Data Link
Network
Transport
Session
Application Presentation
���15
Lower Layers
• IP runs on any data link/physical layer • Ethernet, ADSL, Wi-Fi, optical fibre, carrier pigeon…
• Anything that can deliver packets, can support IP
• No requirement for synchronous circuits
���16
The Internet Protocol (IP)
• Gives each host a globally unique address
• Delivers packets from one host to another • Best effort delivery – discards packets on failure
• No performance guarantees
• Agnostic of packet contents – except firewalls
• Provides uniform network connectivity
���17
The Internet Transport Layer
• Hide vagaries of IP layer • UDP: unreliable packet (“datagram”) delivery service, with no guarantee
of reception
• TCP: reliable, in-order, byte stream service
���18
Applications
• End-to-end argument
• Flexible, supports wide range of applications
• Intelligence at edge of the network; dumb core • Innovation happens at end hosts
• Core network doesn’t know or care what application data is being transported
• Allows rapid change, deployment of new protocols
���19
Internet Standards (1)
• Internet Engineering Task Force • Volunteer standards body; open membership
• Mailing lists; 3 physical meetings per year
• Standards and work-in-progress drafts freely available to all: • http://www.ietf.org/
• http://www.rfc-editor.org/
• Primary focus: network and transport layers (IP, UDP, TCP), session and presentation layer protocols to support applications (e.g. HTTP, SMTP, SIP), and routing
Data Link
Network
Transport
Session
Presentation
Application
Physical
���20
Design Choices
• Packets rather than circuits
• Single generic best-effort network layer • Generic packet delivery service
• Easy to implement on any link-layer
• The end-to-end argument • Transparent network: not optimal for any application
• Application flexibility at the expense of performance
���22