Transcript COMP680E by M. Hamdi - Hong Kong University of Science and

High-Speed Internet
Switches and Routers
COMP 680E
Mounir Hamdi
Professor, Computer Science
Director, MSc-IT
Hong Kong University of Science and Technology
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Goals of the Course
• Understand the architecture, operation, and evolution of the
Internet
– IP, ATM, Optical
• Understand how to design, implement and evaluate Internet
routers and switches (Telecom Equipment)
– Both hardware and software solutions
• Get familiar with current Internet switches/routers research and
development efforts
• Appreciate what is a good project
– Task selection and aim
– Survey & solution & research methodology
– Presentation
• Apply what you learned in a small class project
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Outline of the Course
• The focus of the course is on the design and analysis
of high-performance electronic/optical
switches/routers needed to support the development
and delivery of advanced network services over highspeed Internet.
• The switches and routers are the KEY building blocks
of the Internet, and as a result, the capability of the
Internet in all its aspects depends on the capability of
its switches and routers.
• The goal of the course is to provide a basis for
understanding, appreciating, and performing research
and development in networking with a special
emphasis on switches and routers.
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Outline of the Course
• Introduction
– Definition and History of Networking/Internet
– Evolution and Trends in the Internet
– Architecture of The Internet
– Classification and Evolution of Internet Equipment
– Review and Evolution of Internet Protocols
– Different technologies of the Internet
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Outline of the Course
• Network Processors: Table Lookup and
Packet Classification
– Internet addressing and CIDR
– Table Lookup: Exact matches, longest prefix matches,
performance metrics, hardware and software solutions.
– Packet classifiers for firewalls, QoS, and policy-based
routing; graphical description and examples of 2-D
classification, examples of classifiers, theoretical and
practical considerations
– State-of-the-art commercial products
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Outline of the Course
• High-Performance Packet Switches/Routers
– Architectures of packet switches/routers (IQ, OQ,
VOQ, CIOQ, SM, Buffered Crossbars)
– Design and analysis of switch fabrics (Crossbar,
Clos, shared memory, etc.)
– Design and analysis of scheduling algorithms
(arbitration, Maximum/maximal matching, shared
memory contention, etc.)
– Emulation of output-queueing switches by more
practical switches
– State-of-the-art commercial products
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Outline of the Course
• Quality-of-Service Provision in the Internet
– QoS paradigms (IntServ, DiffServ, Controlled load,
etc.)
– MPLS/GMPLS
– Flow-based QoS frameworks: Hardware and
software solutions
– Stateless QoS frameworks: RED, WRED,
congestion control, and Active queue management
– State-of-the-art commercial products
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Outline of the Course
• Optical Networks
– Optical technology used for the design of
switches/routers as well as transmission links
– Dense Wavelength Division Multiplexing
– Optical Circuit Switches: Architectural alternatives and
performance evaluation
– Optical Burst switches
– Optical Packet Switches
– Design, management, and operation of DWDM
networks
– State-of-the-art commercial products
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Grading
•
Homework
20%
•
Midterm
30%
•
Project
50%
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Course project
• Investigate existing advances and/or new ideas
and solutions – related to Internet Switches and
Routers - in a small scale project (To be given
or chosen on your own)
– define the problem
– execute the survey and/or research
– work with your partner
– write up and present your finding
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Course Project
• I’ll post on the class web page a list of projects
– you can either choose one of these projects or come up with
your own
• Choose your project, partner (s), and submit a
one page proposal describing:
– the problem you are investigating
– your plan of project with milestones and dates
– any special resources you may need
• Final project presentation (~ 30 minutes)
• Submit project papers
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Homework
•
Goals:
1.
Synthesize main ideas and concepts from very important research or
development work
•
I will post in the class web page a list of “well-known” papers
to choose from
•
Report contains:
1.
Description of the papers
2.
Goals and problems solved in the papers
3.
What did you like/dislike about the paper
4.
Recommendations for improvements or extension of the work
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How to Contact Me
• Instructor: Mounir Hamdi [email protected]
• Office Hours
– You can come any time – just email me ahead of
time
– I would like to work closely with each student
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Overview and History of
the Internet
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What is a Communication Network?
(from an end system point of view)
• A network offers a service: move information
– Messenger, telegraph, telephone, Internet …
– another example, transportation service: move objects
• horse, train, truck, airplane ...
• What distinguishes different types of networks?
– The services they provide
• What distinguish the services?
–
–
–
–
–
latency
bandwidth
loss rate
number of end systems
Reliability, unicast vs. multicast, real-time, message vs. byte ...
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What is a Communication Network?
Infrastructure Centric View
• Hardware
– Electrons and photons as communication data
– Links: fiber, copper, satellite, …
– Switches: mechanical/electronic/optical,
• Software
– Protocols: TCP/IP, ATM, MPLS, SONET, Ethernet, PPP,
X.25, Frame Relay, AppleTalk, IPX, SNA
– Functionalities: routing, error control, congestion control,
Quality of Service (QoS), …
– Applications: FTP, WEB, X windows, VOIP, IPTV...
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Types of Networks
• Geographical distance
– Personal Areas Networks (PAN)
– Local Area Networks (LAN): Ethernet, Token ring, FDDI
– Metropolitan Area Networks (MAN): DQDB, SMDS (Switched Multi-gigabit
Data Service)
– Wide Area Networks (WAN): IP, ATM, Frame relay
• Information type
– data networks vs. telecommunication networks
• Application type
– special purpose networks: airline reservation network, banking network, credit
card network, telephony
– general purpose network: Internet
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Types of Networks
• Right to use
– private: enterprise networks
– public: telephony network, Internet
• Ownership of protocols
– proprietary: SNA
– open: IP
• Technologies
– terrestrial vs. satellite
– wired vs. wireless
• Protocols
– IP, AppleTalk, SNA
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The Internet
• Global scale, general purpose, heterogeneoustechnologies, public, computer network
• Internet Protocol
– Open standard: Internet Engineering Task Force
(IETF) as standard body
– Technical basis for other types of networks
• Intranet: enterprise IP network
• Developed by the research community
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Internet History
1961-1972: Early packet-switching principles
• 1961: Kleinrock - queueing
theory shows effectiveness of
packet-switching
• 1964: Baran – Introduced first
Distributed packet-switching
Communication networks
• 1967: ARPAnet conceived and
sponsored by Advanced Research
Projects Agency – Larry Roberts
• 1969: first ARPAnet node
operational at UCLA. Then
Stanford, Utah, and UCSB
• 1972:
– ARPAnet demonstrated
publicly
– NCP (Network Control
Protocol) first host-host
protocol (equivalent to
TCP/IP)
– First e-mail program to
operate across networks
– ARPAnet has 15 nodes and
connected 26 hosts
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Internet History
1972-1980: Internetworking, new and proprietary nets
• 1970: ALOHAnet satellite network
in Hawaii
• 1973: Metcalfe’s PhD thesis
proposes Ethernet
• 1974: Cerf and Kahn - architecture
for interconnecting networks (TCP)
• late70’s: proprietary architectures:
DECnet, SNA, XNA
• late 70’s: switching fixed length
packets (ATM precursor)
• 1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking
principles:
– minimalism, autonomy - no
internal changes is required to
interconnect networks
– best effort service model
– stateless routers
– decentralized control
define today’s Internet architecture
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1971-1973: Arpanet Growing
• 1970 - First 2 cross-country link, UCLA-BBN and MITUtah, installed by AT&T at 56kbps
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Internet History
1980-1990: new protocols, a proliferation of networks
• 1983: deployment of
TCP/IP
• 1982: SMTP e-mail
protocol defined
• 1983: DNS defined for
name-to-IP-address
translation
• 1985: ftp protocol defined
(first version: 1972)
• 1988: TCP congestion
control
• New national networks:
CSnet, BITnet, NSFnet,
Minitel
• 100,000 hosts connected to
confederation of networks
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Internet History
1990’s: commercialization, the WWW
• Early 1990’s: ARPAnet
decomissioned
• 1991: NSF lifts restrictions on
commercial use of NSFnet
(decommissioned, 1995)
• early 1990s: WWW
– hypertext [Bush 1945, Nelson
1960’s]
– HTML, http: Berners-Lee
– 1994: Mosaic, later Netscape
– late 1990’s: commercialization of
the WWW
Late 1990’s:
• est. 50 million computers on
Internet
• est. 100 million+ users in 160
countries
• backbone links running at 1
Gbps+
2000’s
• VoIP, Video on demand,
Internet business
• RSS, Web 2.0
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Growth of the Internet
• Number of Hosts on the
Internet:
Aug. 1981
213
Oct. 1984
1,024
Dec. 1987
28,174
Oct. 1990
313,000
Oct. 1993
2,056,000
Apr. 1995
5,706,000
Jan. 1997 16,146,000
Jan. 1999 56,218,000
Jan. 2001 109,374,000
Jan. 2003 171,638,297
Jul 2004 285,139,107
Jul 2005 353,284,187
Today ~ 440,000,000
Source:
http://www.isc.org/index.pl?/ops/ds/host-counthistory.php
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Internet - Global Statistics
2005
1997
• 22.5 Million Hosts
• 350 Million Hosts
• 50 Million Users
• 1,018 Million Users
(approx. 2.4 Billion Telephone Terminations, 660 Million PCs and
1.6B mobile phones)
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Internet Penetration December 2006
(Source www.internetstats.com)
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Top 10: % Internet Use (Dec 2006)
Country or
Region
Penetration
(% Population)
% Internet
Users
1
Iceland
86.3 %
2
New Zealand
74.9 %
3
Sweden
74.7 %
4
Portugal
73.8 %
5
Australia
70.2 %
6
United States
69.6 %
7
Falkland Islands
69.4 %
8
Denmark
69.2 %
9
Hong Kong (China)
68.2 %
10
Luxembourgh
68.0 %
www.internetworldstats.com
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Languages of Internet Users
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Who is Who on the Internet ?
• Internet Engineering Task Force (IETF): The IETF
is the protocol engineering and development arm of the
Internet. Subdivided into many working groups, which specify
Request For Comments or RFCs.
• IRTF (Internet Research Task Force): The Internet
Research Task Force is composed of a number of focused,
long-term and small Research Groups.
• Internet Architecture Board (IAB): The IAB is
responsible for defining the overall architecture of the Internet,
providing guidance and broad direction to the IETF.
• The Internet Engineering Steering Group (IESG):
The IESG is responsible for technical management of IETF
activities and the Internet standards process. Composed of the
Area Directors of the IETF working groups.
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Internet Standardization Process
• All standards of the Internet are published as RFC
(Request for Comments). But not all RFCs are Internet
Standards !
– available: http://www.ietf.org
• A typical (but not only) way of standardization is:
– Internet Drafts
– RFC
– Proposed Standard
– Draft Standard (requires 2 working implementation)
– Internet Standard (declared by IAB)
• David Clark, MIT, 1992: "We reject: kings, presidents,
and voting. We believe in: rough consensus and running
code.”
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Services Provided by the Internet
• Shared access to computing resources
– telnet (1970’s)
• Shared access to data/files
– FTP, NFS, AFS (1980’s)
• Communication medium over which people interact
– email (1980’s), on-line chat rooms, instant messaging (1990’s)
– audio, video (1990’s)
• replacing telephone network?
• A medium for information dissemination
– USENET (1980’s)
– WWW (1990’s)
• replacing newspaper, magazine?
– audio, video (1990’s)
• replacing radio, CD, TV?
– 2000s: peer-to-peer systems – triple play bundles
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Today’s Vision
• Everything is digital: voice, video, music,
pictures, live events, …
• Everything is on-line: bank statement, medical
record, books, airline schedule, weather,
highway traffic, …
• Everyone is connected: doctor, teacher, broker,
mother, son, friends, enemies
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What is Next? – many of it already here
• Electronic commerce
– virtual enterprise
• Internet entertainment
– interactive sitcom
• World as a small village
– community organized according to interests
– enhanced understanding among diverse groups
• Electronic democracy
– little people can voice their opinions to the whole world
– little people can coordinate their actions
– bridge the gap between information haves and have no’s
• Electronic Crimes
– hacker can bring the whole world to its knee
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Industrial Players
• Telephone companies
– own long-haul and access communication links, customers
• Cable companies
– own access links
• Wireless/Satellite companies
– alternative communication links
• Utility companies: power, water, railway
– own right of way to lay down more wires
• Medium companies
– own content
• Internet Service Providers
• Equipment companies
– switches/routers, chips, optics, computers
• Software companies
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What is the Internet?
• The collection of hosts and routers that are
mutually reachable at any given instant
• All run the Internet Protocol (IP)
– Version 4 (IPv4) is the dominant protocol
– Version 6 (IPv6) is the future protocol
• Lots of protocols below and above IP, but only
one IP
– Common layer
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Commercial Internet after 1994
• Roughly hierarchical
• National/international
backbone providers
(NBPs)
– e.g., Sprint, AT&T, UUNet
– interconnect (peer) with
each other privately, or at
public Network Access
Point (NAPs)
• regional ISPs
regional ISP
NBP B
NAP
NAP
NBP A
regional ISP
– connect into NBPs
• local ISP, company
local
ISP
– connect into regional ISPs
local
ISP
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Internet Organization
CN
NAP
POP
ISP
CN
CN
ISP
CN
BSP
POP
POP
NAP
POP
POP
CN
BSP
NAP
POP
BSP
CN
POP
CN
ISP
CN
COMP680E by M.
ISP = Internet Service Provider
BSP = Backbone Service Provider
NAP = Network Access Point
POP = Point of Presence
CN = Customer Network 38
Hamdi
Commercial Internet after 1994
Joe's Company
Campus Network
Berkeley
Stanford
Regional ISP
Bartnet
Xerox Parc
SprintNet
America On Line
UUnet
NSF Network
IBM
NSF Network
Modem
Internet MCI
IBM
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Internet Architecture
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Basic Architecture: NAPs and National ISPs
• The Internet has a hierarchical structure.
• At the highest level are large national
Internet Service Providers that interconnect
through Network Access Points (NAPs).
• There are about a dozen NAPs in the U.S., run
by common carriers such as Sprint and
Ameritech, and many more around the world
(Many of these are traditional telephone
companies, others are pure data network
companies).
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The real story…
• Regional ISPs interconnect with
national ISPs and provide services to
their customers and sell access to
local ISPs who, in turn, sell access to
individuals and companies.
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pop
pop
pop
pop
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The Hierarchical Nature of the Internet
Central
Office
Central
Office
San Francisco
Node
Central
Office
Major
City
Regional
Center
Node
Long Distance Network
New York
Major
City
Regional
Center
Central
Office
Central
Office
Central
Office
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Node
Node
Metro Network
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Points of Presence (POPs)
POP2
A
POP1
POP4
B
C
POP3
D
E
POP5
POP6
POP7
POP8
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A Bird’s View of the Internet
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A Bird’s View of the Internet
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Hop-by-Hop Behavior
From traceroute.pacific.net.hk to cs.stanford.edu
Within HK
Los Angeles
Qwest
(Backbone)
Stanford
traceroute to cs.stanford.edu (171.64.64.64) from lamtin.pacific.net.hk (202.14.67.228),
rsm-vl1.pacific.net.hk (202.14.67.5)
gw2.hk.super.net (202.14.67.2)
3 wtcr7002.pacific.net.hk (202.64.22.254)
4 atm3-0-33.hsipaccess2.hkg1.net.reach.com (210.57.26.1)
5 ge-0-3-0.mpls1.hkg1.net.reach.com (210.57.2.129)
6 so-4-2-0.tap2.LosAngeles1.net.reach.com (210.57.0.249)
7 unknown.Level3.net (209.0.227.42)
8 lax-core-01.inet.qwest.net (205.171.19.37)
9 sjo-core-03.inet.qwest.net (205.171.5.155)
10 sjo-core-01.inet.qwest.net (205.171.22.10)
11 svl-core-01.inet.qwest.net (205.171.5.97)
12 svl-edge-09.inet.qwest.net (205.171.14.94)
13 65.113.32.210 (65.113.32.210)
14 sunet-gateway.Stanford.EDU (171.66.1.13)
15 CS.Stanford.EDU (171.64.64.64)
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NAP-Based Architecture
CHI
NAP
SF
NAP
Sprint Net
MAE
West
NY
NAP
QWest
MCI
UUNET
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WDC
NAP
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Basic Architecture: MAEs and local ISPs
• As the number of ISPs has grown, a new type of
network access point, called a metropolitan area
exchange (MAE) has arisen.
• There are about 50 such MAEs around the U.S.
today.
• Sometimes large regional and local ISPs (AOL) also
have access directly to NAPs.
• It has to be approved by the other networks already
connected to the NAPs – generally it is a business
decision.
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Internet Packet Exchange Charges
Peering
• ISPs at the same level usually do not
charge each other for exchanging
messages.
• They update their routing tables with
each other customers or pop.
• This is called peering.
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Charges: Non-Peering
• Higher level ISPs, however, charge lower level
ones (national ISPs charge regional ISPs which
in turn charge local ISPs) for carrying Internet
traffic.
• Local ISPs, of course, charge individuals and
corporate users for access.
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Connecting to an ISP
• ISPs provide access to the Internet through a
Point of Presence (POP).
• Individual users access the POP through a
dial-up line using the PPP protocol.
• The call connects the user to the ISP’s modem
pool, after which a remote access server
(RAS) checks the userid and password.
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More on connecting
• Once logged in, the user can send
TCP/IP/[PPP] packets over the telephone
line which are then sent out over the
Internet through the ISP’s POP (point of
presence)
• Corporate users might access the POP using
a T-1, T-3 or ATM OC-3 connections, for
example, provided by a common carrier.
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DS (telephone carrier) Data Rates
Designation
DS0
Number of
Voice Circuits
1
Bandwidth
64 kb/s
DS1 (T1)
24
1.544 Mb/s
DS2 (T2)
96
6.312 Mb/s
DS3 (T3)
672
44.736 Mb/s
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SONET Data Rates
A small set of fixed data transmission rates is defined for SONET. All of these rates
are multiples of 51.84 Mb/s, which is referred to as Optical Carrier Level 1 (on the
fiber) or Synchronous Transport Signal Level 1 (when converted to electrical signals)
Optical Level
Line Rate, Mb/s
OC-1
51.840
OC-3
155.520
OC-9
466.560
OC-12
622.080
OC-18
933.120
OC-24
1244.160
OC-36
1866.240
OC-48
2488.320
OC-96
4976.640
OC-192
9953.280
OC-768
39813.120
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ISPs and Backbones
POP: Connection with
customers
T1 Lines to
Customers
POP: connection with POP of the
same ISP or different ISPs
T3 Lines to
Other POPs
Line
Server
Dialup Lines
to Customers
T3 Line
Router
Ethernet
Point of Presence (POP)
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OC-3
Line
ATM
Switch
Core
Router
OC-3
Lines
to Other
ATM Switches
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Individual
Dial-up Customers
ISP Point-of-Presence
ISP POP
Modem Pool
ISP POP
Corporate
T1 Customer
T1 CSU/DSU
ATM
Switch
ATM
Switch
Corporate
T3 Customer
ISP POP
T3 CSU/DSU
Remote
Access
Server
Corporate
OC-3 Customer
ATM Switch
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NAP/MAE
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HK Major Internet Exchange (HK –NAP/
MAE)
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From the ISP to the NAP/MAE
• Each ISP acts as an autonomous system,
with is own interior and exterior routing
protocols.
• Messages destined for locations within the
same ISP are routed through the ISP’s own
network.
• Since most messages are destined for other
networks, they are sent to the nearest MAE
or NAP where they get routed to the
appropriate “next hop” network.
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From the ISP to the NAP/MAE
• Next is the connection from the local ISP to
the NAP. From there packets are routed to
the next higher level of ISP.
• Actual connections can be complex and
packets sometimes travel long distances.
Each local ISP might connect a different
regional ISP, causing packets to flow
between cities, even though their
destination is to another local ISP within the
same city.
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ISP A
Inside an Internet Network Access Point
Router
ISP D
Router
ATM
Switch
ISP B
ISP E
Router
ISP C
ATM Switch
Route
Server
Router
ISP F
ATM Switch
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Inside an Internet Network Access Point
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Network Access Point
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ISPs and Backbones
POP
POP
POP
POP
POP
POP
ATM/SONET
Core
POP
POP
POP
Router Core
POP
POP
POP
Access Network
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POP
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Three national ISPs in North America
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Backbone Map of UUNET - USA
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UUNET
• Mixed OC-12 –
OC-48 – OC 192
backbone
• 1000s miles of
fiber
• 3000 POPs
• 2,000,000 dial-in
ports
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Backbone Map of UUNET - World
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Qwest
•
•
•
•
OC-192 backbone
25,000 miles of fiber
635 POPs
85,000 dial-in ports
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AT&T
• OC-192 backbone
• 53,000 miles of
fiber
• 2000 POPs
• 0 dial-in ports
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Internet Backbones in 2006
• As of mid-2001, most backbone circuits for national
ISPs in the US are 622 Mbps ATM OC-12 lines.
• The largest national ISPs are planning to convert to
OC-192 (10 Gbps) by the end of 2003.
• A few are now experimenting with OC-768 (40 Gbps)
and some are planning to use OC-3072 (160 Gbps).
• Aggregate Internet traffic reached 2.5 Terabits per
second (Tbps) by mid-2001. It is expected to reach 35
Tbps by 2007.
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Links for Long Haul Transmission
• Possibilities
–
–
–
–
IP over SONET
IP over ATM
IP over Frame Relay
IP over WDM
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User Services & Core Transport
EDGE
Frame Relay
IP
IP
Router
CORE
Frame
Relay
ATM
ATM
Switch
Lease Lines
Sonet
ADM
Users
Services
TDM
Switch
OC-3
OC-3
OC-12
STS-1
STS-1
STS-1
Service Provider
Networks
Transport Provider
Networks
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Typical (BUT NOT ALL) IP Backbone (Late
1990’s)
Core
Router
Core
Router
ATM
Switch
ATM
Switch
MUX
SONET/SDH
ADM
MUX
SONET/SDH
ADM
SONET/SDH
DCS
SONET/SDH
DCS
SONET/SDH
ADM
SONET/SDH
ADM
MUX
MUX
ATM
Switch
ATM
Switch
Core
Router
Core
Router
• Data piggybacked over traditional voice/TDM transport
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IP Backbone Evolution (One version)
Core
Router
(IP/MPLS)
• Removal of ATM Layer
FR/ATM
Switch
MUX
SONET/SDH
– Next generation routers
provide trunk speeds and
SONET interfaces
– Multi-protocol Label
Switching (MPLS) on
routers provides traffic
engineering
Core
Router
(IP/MPLS)
SONET/
SDH
DWDM
DWDM
(Maybe)
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Hierarchy of Routers and Switches
Core
IP Router
FR/ATM
Switch
SONET/SDH
•IP Router (datagram packet switching)
• Deals directly with IP addresses;
• Slow – typically no interface to SONET equipment
• Expensive
• Efficient (No header overhead and alternative routing)
•ATM Switch (VC packet switching)
• Label based switching
• Fast (Hardware forwarding)
• Header Tax
•SONET OXC (Circuit switching)
• Extremely fast – Optical technology
• Inexpensive
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Customer Network
• All hosts owned by a single enterprise or
business
• Common case
–
–
–
–
–
Lots of PCs
Some servers
Routers
Ethernet 10/100/1000-Mb/s LAN
T1/T3 1.54/45-Mb/s wide area network (WAN)
connection
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Customer Network
Clients
LAN
Ethernet
10 Mb/s
Servers
Router
WAN
T1 Link
1.54 Mb/s
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Internet Access
Technologies
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Internet Access Technologies
• Previously, most people use 56K dial-up lines
to access the Internet, but a number of new
access technologies are now being offered.
• The main new access technologies are:
–
–
–
–
Digital Subscriber Line/ADSL
Cable Modems
Fixed Wireless (including satellite access)
Mobile Wireless (WAP)
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Digital Subscriber Line
• Digital Subscriber Line (DSL) is one of the most used
technologies now being implemented to significantly
increase the data rates over traditional telephone
lines.
• Historically, voice telephone circuits have had only a
limited capacity for data communications because
they were constrained by the 4 kHz bandwidth voice
channel.
• Most local loop telephone lines actually have a much
higher bandwidth and can therefore carry data at
much higher rates.
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Digital Subscriber Line
• DSL services are relatively new and not all
common carriers offer them.
• Two general categories of DSL services have
emerged in the marketplace.
– Symmetric DSL (SDSL) provides the same
transmission rates (up to 128 Kbps) in both
directions on the circuits.
– Asymmetric DSL (ADSL) provides different data
rates to (up to 640 Kbps) and from (up to 6.144
Mbps) the carrier’s end office. It also includes an
analog channel for voice transmissions.
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Customer Premises
DSL Modem
Local Carrier End Office
Main
Distribution
Frame
Line Splitter
DSL Architecture
Voice
Telephone
Network
Local Loop
Hub
Telephone
ATM Switch
Computer
Computer
Customer
Premises
ISP POP
DSL Access
Multiplexer
ISP POP
ISP POP
ISP POP
Customer
Premises
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Cable Modems
• One potential competitor to DSL is the “cable
modem” a digital service offered by cable
television companies which offers an upstream
rate of 1.5-10 Mbps and a downstream rate of
2-30 Mbps.
• A few cable companies offer downstream
services only, with upstream communications
using regular telephone lines.
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Cable Company
Fiber Node
Customer Premises
Cable Modem
Cable Company Distribution Hub
TV Video
Network
Cable Splitter
Downstream
Optical/Electrical
Converter
Combiner
Upstream
Hub
TV
Router
Computer
Computer
Shared
Coax
Cable
System
Cable
Company
Fiber Node
Customer
Premises
Customer
Premises
Cable Modem
Termination
System
ISP POP
Cable Modem Architecture
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Fixed Wireless
• Fixed Wireless is another “dish-based”
microwave transmission technology.
• It requires “line of sight” access between
transmitters.
• Data access speeds range from 1.5 to 11
Mbps depending on the vendor.
• Transmissions travel between transceivers at
the customer premises and ISP’s wireless
access office.
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Customer Premises
Individual Premise
DSL Modem
Fixed Wireless Architecture
Main
Distribution
Frame
Line Splitter
Voice
Telephone
Network
Hub
Telephone
Individual
Premise
Wireless
Transceiver
Individual
Premise
DSL Access
Multiplexer
Computer Computer
Wireless Access Office
Customer
Premises
Wireless
Transceiver
Customer
Premises
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Router
ISP POP
88
Classifying Computer
Networks
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A Taxonomy of Communication Networks
• Communication networks can be classified based on the way
in which the nodes exchange information:
Communication
Network
Switched
Communication
Network
Circuit-Switched
Communication
Network
Broadcast
Communication
Network
Packet-Switched
Communication
Network
Datagram
Network
Virtual Circuit Network
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Broadcast vs. Switched Communication
Networks
• Broadcast communication networks
– information transmitted by any node is received by every
other node in the network
• examples: usually in LANs (Ethernet, Wavelan)
– Problem: coordinate the access of all nodes to the shared
communication medium (Multiple Access Problem)
• Switched communication networks
– information is transmitted to a sub-set of designated nodes
• examples: WANs (Telephony Network, Internet)
– Problem: how to forward information to intended node(s)
• this is done by special nodes (e.g., routers, switches) running routing
protocols
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Circuit Switching
• Three phases
1. circuit establishment
2. data transfer
3. circuit termination
• If circuit is not available: “Busy signal”
• Examples
 Telephone networks
 ISDN (Integrated Services Digital Networks)
 Optical Backbone Internet (going in this direction)
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Timing in Circuit Switching
Host 1
Node 1
Node 2
Host 2
processing delay at Node 1
propagation delay
between Host 1
and Node 1
Circuit
Establishment
propagation delay
between Host 2
and Node 1
Data
Transmission
DATA
Circuit
Termination
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Circuit Switching
• A node (switch) in a circuit switching network
incoming links
Node
outgoing links
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Circuit Switching:
Multiplexing/Demultiplexing
• Time divided in frames and frames divided in slots
• Relative slot position inside a frame determines which
conversation the data belongs to
• If a slot is not used, it is wasted
• There is no statistical gain
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Packet Switching
• Data are sent as formatted bit-sequences, so-called packets.
• Packets have the following structure:
Header
Data
Trailer
• Header and Trailer carry control information (e.g., destination address, check
sum)
• Each packet is passed through the network from node to node along some
path (Routing)
• At each node the entire packet is received, stored briefly, and then forwarded
to the next node (Store-and-Forward Networks)
• Typically no capacity is allocated for packets
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Packet Switching
• A node in a packet switching network
incoming links
Node
outgoing links
Memory
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Packet Switching:
Multiplexing/Demultiplexing
• Data from any conversation can be transmitted
at any given time
• How to tell them apart?
– use meta-data (header) to describe data
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Datagram Packet Switching
• Each packet is independently switched
– each packet header contains destination address
• No resources are pre-allocated (reserved) in
advance
• Example: IP networks
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Timing of Datagram Packet Switching
Host 1
transmission
time of Packet 1
at Host 1
Node 1
Packet 1
Host 2
Node 2
propagation
delay between
Host 1 and
Node 2
Packet 2
Packet 1
Packet 3
processing
delay of
Packet 1 at
Node 2
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
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Datagram Packet Switching
Host C
Host D
Host A
Node 1
Node 2
Node 3
Node 5
Host B
Node 6
Node 7
Host E
Node 4
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Virtual-Circuit Packet Switching
• Hybrid of circuit switching and packet
switching
– data is transmitted as packets
– all packets from one packet stream are sent along a
pre-established path (=virtual circuit)
• Guarantees in-sequence delivery of packets
• However: Packets from different virtual
circuits may be interleaved
• Example: ATM networks
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Virtual-Circuit Packet Switching
• Communication using virtual circuits takes
place in three phases
1. VC establishment
2. data transfer
3. VC disconnect
• Note: packet headers don’t need to contain the
full destination address of the packet (One key
to this idea)
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Timing of VC Packet Switching
Host 1
Node 1
Host 2
Node 2
propagation delay
between Host 1
and Node 1
VC
establishment
Packet 1
Packet 2
Packet 1
Data
transfer
Packet 3
Packet 2
Packet 3
Packet 1
Packet 2
Packet 3
VC
termination
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VC Packet Switching
Host C
Host D
Host A
Node 1
Node 2
Node 3
Node 5
Host B
Node 6
Node 7
Host E
Node 4
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Packet-Switching vs. Circuit-Switching
• Most important advantage of packet-switching over circuit
switching: Ability to exploit statistical multiplexing:
– efficient bandwidth usage; ratio between peek and average rate is 3:1 for
audio, and 15:1 for data traffic
• However, packet-switching needs to deal with congestion:
– more complex routers
– harder to provide good network services (e.g., delay and bandwidth
guarantees)
• In practice they are combined
– IP over SONET, IP over Frame Relay
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Fixed-Rate versus Bursty Data
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Packet Switches
Destination
Address
Routing
Table
Connectionless
Packet Switch
A
A
Possibly different paths through switch
A
Connection
Identifier
B
B
Always same path through switch
B
Connection-Oriented
Connection
Packet Switch
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Store-and-Forward Operation
• Packet entering switch or router is stored in a queue
until it can be forwarded
–
–
–
–
Queueing
Header processing
Routing-table lookup of destination address
Forwarding to next hop
• Queueing time variation can result in nondeterministic delay behavior (maximum delay and
delay jitter)
• Packets might overflow finite buffers (Network
congestion)
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Link Diversity
• Internet meant to accommodate many different
link technologies
–
–
–
–
–
Ethernet
ATM
SONET
ISDN
Modem
• The list continues to grow
• “IP on Everything”
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Internet Protocols
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Internet Protocols
Application
Application
Transport
Transport
Network
Link
Host
Network
Link
Link
Router
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Network
Link
Host
112
IP Protocol Stack
Ping
Telnet
FTP
H.323
SIP
RTSP
TCP
RSVP
S/MGCP/
NCS
User
application
UDP
OSPF
ARP
ICMP
IP
IGMP
RARP
Link Layer
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Demultiplexing
Application
Application
Transport
ICMP
Application
Application
TCP
Application
UDP
IGMP
Network
IP
ARP
Link
RARP
Ethernet
Driver
incoming frame
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Link Protocols
• Numerous link protocols
– Ethernet + LLC (Logical Link Control)
– T1/DS1 + HDLC (High-level Data Link Control)
– T3/DS3 + HDLC
– Dialup + PPP (Point-to-Point Protocol)
– ATM/SONET + AAL (ATM Adaptation Layer)
– ISDN + LAPD (Link Access Protocol) + PPP
– FDDI + LLC
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Additional Link Protocols
• ARP (Address Resolution Protocol) is a
protocol for mapping an IP address to a
physical machine address that is
recognized in the local network. Most
commonly, this is used to associate IP
addresses (32-bits long) with Ethernet MAC
addresses (48-bits long).
• RARP is the reverse of ARP
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ARP Protocol
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Sending an IP Packet over a LAN
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Transport Protocols
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
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Application Protocols
•
•
•
•
•
•
•
File Transfer Protocol (FTP)
Simple Mail Transfer Protocol (SMTP)
Telnet
Hypertext Transfer Protocol (HTTP)
Simple Network Management Protocol (SNMP)
Remote Procedure Call (RPC)
DNS: The Domain Name System service provides
TCP/IP host name to IP address resolution.
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The Internet Network layer: The Glue of all
Networks
Transport layer: TCP, UDP
Network
layer
IP protocol
•addressing conventions
•datagram format
•packet handling conventions
Routing protocols
•path selection
•RIP, OSPF, BGP
routing
table
ICMP protocol
•error reporting
•router “signaling”
Link layer
physical layer
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Demultiplexing Details
echo
server
1024-5000
FTP
server
User process
User process
User process
User process
21
9
TCP src port
UDP
ICMP
IGMP
TCP dest port

header

data


17
1
2

IP header
x0806
discard
server
TCP
TCP
ARP
23
7
telnet
server
6
protocol type

hdr
cksum
dest
addr
source
addr

data

Others
RARP
x8035
IP
Novell
IP
x0800
AppleTalk
dest
addr
source
addr
Ethernet frame type

data
CRC

(Ethernet frame types in hex, others in decimal)
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IP Features
•
•
•
•
•
•
Connectionless service
Addressing
Data forwarding
Fragmentation and reassembly
Supports variable size datagrams
Best-effort delivery: Delay, out-of-order, corruption,
and loss possible. Higher layers should handle these.
• Provides only “Send” and “Delivery” services
Error and control messages generated by
Internet Control Message Protocol (ICMP)
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What IP does NOT provide
• End-to-end data reliability & flow control (done by TCP or
application layer protocols)
• Sequencing of packets (like TCP)
• Error detection in payload (TCP, UDP or other transport layers)
• Error reporting (ICMP)
• Setting up route tables (RIP, OSPF, BGP etc)
• Connection setup (it is connectionless)
• Address/Name resolution (ARP, RARP, DNS)
• Configuration (BOOTP, DHCP)
• Multicast (IGMP, MBONE)
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Internet Protocol (IP)
• Two versions
– IPv4
– IPv6
• IPv4 dominates today’s Internet
• IPv6 is used sporadically
– 6Bone, Internet 2
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IPv4 Header
0
15
Ver
HLen
TOS
Length
Ident
TTL
31
Flags
Protocol
Offset
Checksum
SrcAddr
DestAddr
Options
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IPv4 Header Fields (1)
• Ver: version of protocol
– First thing to be determined
– IPv4  4, IPv6  6
• Hlen: header length (in 32-bit words)
– Usually has a value of 5
– When options are present, the value is > 5
• TOS: type of service
– Packet precedence (3 bits)
– Delay/throughput/reliability specification
– Rarely used
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IPv4 Header Fields (2)
• Length: length of the datagram in bytes
– Maximum datagram size of 65,535 bytes
• Ident: identifies fragments of the datagram
(Ethernet 1500 Bytes max., FDDI: 4900 Bytes
Max., etc.)
• Flag: indicates whether more fragments follow
• Offset: number of bytes payload is from start of
original user data
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Fragmentation Example
20-byte optionless
IP headers
Id = x
0 0 1
0
492 data bytes
Id = x
0 0 0
1400 data bytes
0
Id = x
0 0 1
492
492 data bytes
Id = x
0 0 0
984
416 data bytes
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IPv4 Header Fields (3)
• TTL: time to live gives the maximum number
of hops for the datagram
• Protocol: protocol used above IP in the
datagram
– TCP  6, UDP  17,
• Checksum: covers IP header
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IPv4 Header Fields (4)
• SrcAddr: 32-bit source address
• DestAddr: 32-bit destination address
• Options: variable list of options
– Security: government-style markings
– Loose source routing: combination of source and
table routing
– Strict source routing: specified by source
– Record route: where the datagram has been
– Options rarely used
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IPv6
• Initial motivation: 32-bit address space completely
allocated by 2008.
• Additional motivation:
– header format helps speed processing/forwarding
– header changes to facilitate QoS
– new “anycast” address: route to “best” of several replicated
servers
• IPv6 datagram format:
– fixed-length 40 byte header
– no fragmentation allowed (done only by source host)
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IPv6: Differences from IPv4
Flow label
– Intended to support quality of service (QoS)
•
•
•
•
128-bit network addresses
No header checksum – reduce processing time
Fragmentation only by source host
Extension headers
– Handles options (but outside the header, indicated by “Next
Header” field
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IPv6 Headers
0
15
Ver
Pri
31
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Destination Address
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IPv6 Header Fields (1)
• Ver: version of protocol
• Pri: priority of datagram
– 0 = none, 1 = background traffic, 2 = unattended data
transfer
– 4 = attended bulk transfer, 6 = interactive traffic, 7 =
control traffic
• Flow Label
– Identifies an end-to-end flow
– IP “label switching”
– Experimental
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IPv6 Header Fields (2)
• Payload Length: total length of the datagram
less that of the basic IP header
• Next Header
– Identifies the protocol header that follows the basic
IP header
– TCP => 6, UDP => 17, ICMP => 58, IP = 4, none
=> 59
• Hop Limit: time to live
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IPv6 Header Fields (3)
• Source/Destination Address
– 128-bit address space
– Embed world-unique link address in the lower 64
bits
– Address “colon” format with hexadecimal
– FEDC:BA98:7654:3210:FEDC:BA98:7654:3210
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Addressing Modes in IPv6
• Unicast
– Send a datagram to a single host
• Multicast
– Send copies a datagram to a group of hosts
• Anycast
– Send a datagram to the nearest in a group of hosts
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Migration from IPv4 to IPv6
• Interoperability with IPv4 is necessary for gradual
deployment.
• Two mechanisms:
– dual stack operation: IPv6 nodes support both address types
– tunneling: tunnel IPv6 packets through IPv4 clouds
• Unfortunately there is little motivation for any one
organization to move to IPv6.
– the challenge is the existing hosts (using IPv4 addresses)
– little benefit unless one can consistently use IPv6
• can no longer talk to IPv4 nodes
– stretching address space through address translation seems to
work reasonably well
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