COMP680E by M. Hamdi 1 High-Speed Internet Switches and Routers COMP 680E Mounir Hamdi Professor, Computer Science Director, MSc-IT Hong Kong University

1COMP680E by M. Hamdi

High-Speed Internet High-Speed Internet Switches and RoutersSwitches and Routers

COMP 680ECOMP 680E

Mounir HamdiMounir HamdiProfessor, Computer ScienceProfessor, Computer Science

Director, MSc-ITDirector, MSc-IT

Hong Kong University of Science and TechnologyHong Kong University of Science and Technology


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


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 high-speed 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.


Outline of the Course

• IntroductionIntroduction

– 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



• 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



• High-Performance Packet Switches/RoutersHigh-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




• 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



• Optical NetworksOptical 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



Grading

• Homework 20%

• Midterm 30%

• Project 50%


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


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


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


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


Overview and History of the Internet


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 ...


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...


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


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


The Internet

• Global scale, general purpose, heterogeneous-technologies, 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


Internet History

• 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

1961-1972: Early packet-switching principles


Internet History

• 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

1972-1980: Internetworking, new and proprietary nets


1971-1973: Arpanet Growing• 1970 - First 2 cross-country link, UCLA-BBN and MIT-

Utah, installed by AT&T at 56kbps


Internet History

• 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

1980-1990: new protocols, a proliferation of networks


Internet History

• 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

1990’s: commercialization, the WWW


Growth of the Internet

• Number of Hosts on the Internet:

Aug. 1981 213Oct. 1984 1,024Dec. 1987 28,174 Oct. 1990 313,000 Oct. 1993 2,056,000Apr. 1995 5,706,000Jan. 1997 16,146,000Jan. 1999 56,218,000Jan. 2001 109,374,000Jan. 2003 171,638,297Jul 2004 285,139,107Jul 2005 353,284,187 Today ~ 440,000,000

Source: http://www.isc.org/index.pl?/ops/ds/host-count-history.php

COMP680E by M. Hamdi

Internet - Global Statistics

1997

• 22.5 Million Hosts

• 50 Million Users

2005

• 350 Million Hosts

• 1,018 Million Users

(approx. 2.4 Billion Telephone Terminations, 660 Million PCs and 1.6B mobile phones)


Internet Penetration December 2006

(Source www.internetstats.com)(Source www.internetstats.com)


Top 10: % Internet Use (Dec 2006)

www.internetworldstats.com

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 %


Languages of Internet Users


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.


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.”


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


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


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


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


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


Commercial Internet after 1994

NBP A

NBP B

NAP NAP

regional ISP

regional ISP

localISP

localISP

• 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– connect into NBPs

• local ISP, company– connect into regional

ISPs


Internet Organization

ISP = Internet Service ProviderBSP = Backbone Service ProviderNAP = Network Access PointPOP = Point of PresenceCN = Customer Network

NAP

NAP

NAP

BSP

ISP

ISP

POP

POP

POP

ISPPOP

BSP

BSPPOP

POP

CN

CN

CN

CNCN

CN

CN

CN

POP


Commercial Internet after 1994

NSF Network

Regional ISP

America On Line

IBM

BartnetCampus Network

Joe's CompanyStanford

Xerox Parc

Berkeley

NSF Network

Internet MCI

UUnet

SprintNet

Modem

IBM


Internet Architecture


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).


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.


pop

pop

pop po

p


Long Distance Network

Central

Office

Central

Office

The Hierarchical Nature of the InternetThe Hierarchical Nature of the Internet

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Central

Office

Major

City

-

Regional

Center

Major

City

-

Regional

Center

Major

City

-

Regional

Center

Major

City

-

Regional

Center

Node

Node

Node

Node

San FranciscoSan Francisco New YorkNew York

Metro Network


Points of Presence (POPs)

A

B

C

POP1

POP3POP2

POP4 D

E

F

POP5

POP6 POP7POP8


A Bird’s View of the Internet


A Bird’s View of the Internet


Hop-by-Hop Behavior

From traceroute.pacific.net.hk to cs.stanford.edutraceroute 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)

Within HK

Qwest(Backbone)

Stanford

Los Angeles


NAP-Based Architecture

UUNET

NYNAP

CHINAP

WDCNAP

SFNAP

MCI

QWest

Sprint Net

MAEWest


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.


Internet Packet Exchange ChargesPeering

• 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.


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.


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.


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.


DS (telephone carrier) Data Rates

DesignationNumber of

Voice CircuitsBandwidth

DS0 1 64 kb/s

DS1 (T1) 24 1.544 Mb/s

DS2 (T2) 96 6.312 Mb/s

DS3 (T3) 672 44.736 Mb/s


SONET Data RatesA 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)

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/sOptical Level Line Rate, Mb/s

OC-1

OC-3

OC-9

OC-12

OC-18

OC-24

OC-36

OC-48

OC-96

OC-192

OC-768

51.840

155.520

466.560

622.080

933.120

1244.160

1866.240

2488.320

4976.640

9953.280

39813.120


ISPs and Backbones

LineServer

Dialup Linesto Customers

Ethernet

Router

T1 Lines toCustomers

CoreRouter

Point of Presence (POP)

T3 Line

T3 Lines toOther POPs

ATMSwitch

OC-3Line

OC-3Lines

to OtherATM Switches

POP: Connection with customers

POP: connection with POP of the same ISP or different

ISPs


ISP Point-of-Presence

Modem Pool

Individual Dial-up Customers

Corporate T1 Customer

T1 CSU/DSU

Corporate T3 Customer

T3 CSU/DSU

Corporate OC-3 Customer

ATM Switch

ATM Switch

ISP POP

ISP POP

ISP POP

NAP/MAE

RemoteAccess Server

ATM Switch


HK Major Internet Exchange (HK –NAP/ MAE)


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.


• 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.

From the ISP to the NAP/MAE


ATM Switch

RouteServer

Router

ISP A

Router

ISP B

Router

ISP C

Router

ISP D

ISP E

ATM Switch

ISP F

ATM Switch

Inside an Internet Network Access Point


Inside an Internet Network Access Point


Network Access Point


ISPs and Backbones

ATM/SONETCore

Router Core

Access Network

POP

POP

POP

POPPOP

POP

POP

POP

POP

POPPOPPOP

POP


Three national ISPs in North America


Backbone Map of UUNET - USA


UUNET

• Mixed OC-12 – OC-48 – OC 192 backbone

• 1000s miles of fiber

• 3000 POPs• 2,000,000 dial-in

ports


Backbone Map of UUNET - World


Qwest

• OC-192 backbone• 25,000 miles of fiber• 635 POPs• 85,000 dial-in ports


AT&T

• OC-192 backbone• 53,000 miles of

fiber• 2000 POPs• 0 dial-in ports


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.


Links for Long Haul Transmission

• Possibilities– IP over SONET – IP over ATM– IP over Frame Relay– IP over WDM


User Services & Core Transport

ATMSwitch

SonetADM

IPRouter

TDMSwitch

Transport ProviderNetworks

Service ProviderNetworks

OC-3

OC-3

OC-12

STS-1STS-1STS-1

FrameRelay

UsersServices

Frame Relay

IP

ATM

Lease Lines

COREEDGE


Typical (BUT NOT ALL) IP Backbone (Late 1990’s)

• Data piggybacked over traditional voice/TDM transport

SONET/SDHDCS

SONET/SDHDCS

CoreRouter

ATMSwitch

MUX

SONET/SDHADM

CoreRouter

ATMSwitch

MUX

CoreRouter

ATMSwitch

MUX

CoreRouter

ATMSwitch

MUX

SONET/SDHADM

SONET/SDHADM

SONET/SDHADM


SONET/SDH

DWDM

CoreRouter(IP/MPLS)

IP Backbone Evolution (One version)

• Removal of ATM Layer– Next generation routers

provide trunk speeds and SONET interfaces

– Multi-protocol Label Switching (MPLS) on routers provides traffic engineering

CoreRouter(IP/MPLS)

MUX

SONET/SDH

DWDM(Maybe)

FR/ATM Switch


Hierarchy of Routers and Switches

SONET/SDHCoreIP Router

FR/ATM Switch

•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


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


Customer Network

Clients

Servers

LAN

WAN

Ethernet10 Mb/s

T1 Link1.54 Mb/s

Router


Internet Access Technologies


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)


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.


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.


DSL ArchitectureLocal Carrier End Office

Line Splitter

Customer Premises

Telephone

DSL Modem

Hub

Computer Computer

Local Loop

MainDistribution

Frame

CustomerPremises

CustomerPremises

VoiceTelephoneNetwork

DSL AccessMultiplexer

ATM Switch

ISP POP

ISP POP

ISP POP

ISP POP


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.


Cable Modem Architecture

Cable Company Distribution Hub

Cable Splitter

Customer Premises

TV

Cable Modem

Hub

Computer Computer

SharedCoaxCable

System

Combiner

CustomerPremises

CustomerPremises

TV VideoNetwork

Cable ModemTermination

System

ISP POP

Cable CompanyFiber Node

Optical/ElectricalConverter

Downstream

Upstream

Router

Cable Company

Fiber Node


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.


Fixed Wireless Architecture

Wireless Access Office

WirelessTransceiver

Customer Premises

Telephone

DSL Modem

Hub

Computer Computer

CustomerPremises

CustomerPremises

MainDistribution

Frame

VoiceTelephoneNetwork

DSL AccessMultiplexer

WirelessTransceiver

Router

Line Splitter

Individual Premise

IndividualPremise

IndividualPremise

ISP POP


Classifying Computer Networks


• Communication networks can be classified based on the way in which the nodes exchange information:

A Taxonomy of Communication Networks

Communication Network

SwitchedCommunication

Network

BroadcastCommunication

Network

Circuit-Switched


Packet-Switched


Datagram Network

Virtual Circuit Network


• 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

Broadcast vs. Switched Communication Networks


Circuit Switching

• Three phases1. 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)


Timing in Circuit Switching

DATA

Circuit Establishment

Data Transmission

Circuit Termination

Host 1 Host 2Node 1 Node 2

propagation delay between Host 1 and Node 1

propagation delay between Host 2 and Node 1

processing delay at Node 1


Circuit Switching

• A node (switch) in a circuit switching network

incoming links outgoing linksNode


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


Packet Switching

• Data are sent as formatted bit-sequences, so-called packets.

• Packets have the following structure:

• 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

Header Data Trailer


Packet Switching

• A node in a packet switching network

incoming links outgoing linksNode

Memory


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


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


Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Timing of Datagram Packet Switching

Packet 1

Packet 2

Packet 3

processing delay of Packet 1 at Node 2

Host 1 Host 2Node

1Node

2

propagationdelay betweenHost 1 and Node 2

transmission time of Packet 1at Host 1


Datagram Packet Switching

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7


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


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)


Packet 1

Packet 2

Packet 3

Packet 1

Packet 2

Packet 3

Timing of VC Packet Switching

Packet 1

Packet 2

Packet 3

Host 1 Host 2Node

1Node

2

propagation delay between Host 1 and Node 1VC

establishment

VCtermination

Datatransfer


VC Packet Switching

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7


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


Fixed-Rate versus Bursty Data


Connec-tion

Table

RoutingTable

Packet Switches

DestinationAddress

ConnectionIdentifier

A

B

A

A

B B

Possibly different paths through switch

Always same path through switch

ConnectionlessPacket Switch

Connection-OrientedPacket Switch


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 non-deterministic delay behavior (maximum delay and delay jitter)

• Packets might overflow finite buffers (Network congestion)


Link Diversity

• Internet meant to accommodate many different link technologies– Ethernet

– ATM

– SONET

– ISDN

– Modem

• The list continues to grow

• “IP on Everything”


Internet Protocols


Internet Protocols

Network

Link

Transport

Application

Network

Link

Transport

Application

Network

Link Link

Host HostRouter


IP Protocol Stack

Link Layer

RARP

Telnet FTP

OSPF

SIP RTSP RSVPS/MGCP/

NCSUser

application

UDP

H.323

IGMPIP

TCP

ICMP

Ping

ARP


Demultiplexing

incoming frame

RARPARP

UDP

Application Application

TCP

Application Application

IGMPICMP

EthernetDriver

IP

Application

Transport

Network

Link


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


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


ARP Protocol


Sending an IP Packet over a LAN


Transport Protocols

• Transmission Control Protocol (TCP)

• User Datagram Protocol (UDP)


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.


The Internet Network layer: The Glue of all Networks

routingtable

Routing protocols•path selection•RIP, OSPF, BGP

IP protocol•addressing conventions•datagram format•packet handling conventions

ICMP protocol•error reporting•router “signaling”

Transport layer: TCP, UDP

Link layer

physical layer

Networklayer


Demultiplexing Details

(Ethernet frame types in hex, others in decimal)

destaddr

sourceaddr

Ethernet frame type data CRC

destaddr

sourceaddr

dataprotocol type

IP header

hdrcksum

ARP

RARPNovell

IP

Others

AppleTalk

dataTCP src port

headerTCP dest port

FTPserver

telnetserver

echoserver

discardserver

23

7

9

21User process

User processUser process

User process

1024-5000

UDP 17

6

IGMP

ICMP 1

2

TCP

IPIP

TCPTCP

x0800

x8035

x0806


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)


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)


Internet Protocol (IP)

• Two versions – IPv4– IPv6

• IPv4 dominates today’s Internet

• IPv6 is used sporadically– 6Bone, Internet 2


IPv4 Header

Length

Ident

Checksum

SrcAddr

DestAddr

Options

0 3115

TOS

TTL

HLenVer

Flags Offset

Protocol

Pad


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



• 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


Fragmentation Example

Id = x

1400 data bytes

00 0 0

Id = x

492 data bytes

00 0 1

Id = x

492 data bytes

4920 0 1

Id = x

416 data bytes

9840 0 0

20-byte optionlessIP headers



• 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



• 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


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)


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


IPv6 Headers

Flow Label

Payload Length

Source Address

PriVer

Hop LimitNext Header

Destination Address

0 3115



• 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



• 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



• 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


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


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

Documents

COMP680E by M. Hamdi 1 High-Speed Internet Switches and Routers COMP 680E Mounir Hamdi Professor, Computer Science Director, MSc-IT Hong Kong University