advanced networking technologies · internet interface for non-techies. cern web browser, 1993...

Advanced Networking (SS 16): 11 – Introduction to Content Networking 1

Advanced Networking Technologies

Chapter 11Introduction to

Content Networking

(Acknowledgement: These slides have been compiled from a set of slides prepared by Dr.-Ing. Markus Hofmann)


A Big Thank You And Book Recommendation

The slides in this and the following lectures on Content Networking have been compiled from Dr.-Ing. Markus Hofmann’s set of slides

He is co-author of the following book that is recommended as accompanying reading:

M. Hofmann, L. R. Beaumont. Content Networking. Morgan Kaufmann 2005.


Motivation: Today’s Internet Surfer

Today’s “Internet Surfer” ispermanently looking out for newexciting information.

Information made available forretrieval from the Internet isalso referred to as content, e.g.

Textual documents,

Web pages,

Images and photos,

Software, etc.

A communication infrastructure supporting the retrieval and delivery of content is referred to as content network.

Content networks operate on protocol layers 4 through 7.

Keep in mind - “surfing for content” has not always been the main application on the Internet…


How Internet Usage Changed

Initially, the Internet was used largely

by the scientific community,

for sharing resources on computers,

for interacting with colleagues in the respective research fields.

Today, the Internet is

one of the most relevant information access and retrieval systems,

used worldwide by private users and users from academia/industry,

used to a large extend for commercial purposes.

The Internet has evolved with the changes in usage- and the evolution needs to go on!

The Internet has evolved with the changes in usage- and the evolution needs to go on!


A Timeline of Early “Content Networking”

Late 1960s: Prevailing applications on the ARPANET are access to remote machines, e-mail and copying files between computers.

Early 1970s: Electronic distribution of documents gains importance; the File Transfer Protocol (FTP) is developed and evolves to the primary means for document retrieval and software distribution over the Internet.

At the end of the 1980s, almost half of the Internet traffic is caused by FTP.

Early 1990s: New developments support the user in locating and navigating content on the Internet…

1990/91: archie

1991/92: Wide Area Information Server (WAIS)

1991/92: Gopher

… and were subsumed into the the World Wide Web (WWW).


Archie: Locating Files on the Internet

The archie system helped users to find and locate specific files based on their name.

How archie worked:

Archie servers periodically searched FTP servers on the Internetusing the “anonymous” FTP account.

The filenames found on the various FTP servers was recorded and organized into a global file catalog.

Users could utilize this catalog to search for file names that match certain patterns.

When matches were found, the archie server returned the specificFTP servers from which the files were available.

Limitations:

Archie was restricted to pattern matching on filenames rather than the actual content of files.


WAIS: Locating Content on the Internet

The Wide Area Information Server (WAIS) helped users to find and locate files not only based on their name, but also based on their content.

Databases were created by searching through the document text, rather than the name and title only.

WAIS also introduced provisioning of a scored response based on

the quantity of keyword appearances in the text, and

on how close to the document’s beginning they turned up.

Limitations:

User interface was relative difficult to handle.

Initially limited to text documents.

Ranking system favored long documents (quantity vs. frequency ofkeywords).

Limited to keyword searches, no support for database navigation.


Gopher: Navigating Content on the Internet

Gopher allows users to navigate through content databases and to retrieve data over the Internet without using complicated commands and addresses.

How it works:

Gopher servers search the Internet using WAIS and arrange the results in hierarchical menus.

As users select menu items, they are lead to other menus, files, or images, which might not even reside on the local Gopher server.

References could move users to remote servers or fetch files from distant locations.

Menu based navigation does not require the user to know how and from where to retrieve relevant resources.

Gopher significantly simplified information retrieval on the Internet.


The World Wide Web (WWW, Web)

The Web provides easy access to distributed information by linking objects across a network via hyperlinks.

Hyperlinks are embedded in Web pages.

Users follow hyperlinks to access referenced resources.

Referenced resources can be local or remote.

Users do not have to worry about the location or the format of a resource.

Graphical browser provides an Internet interface for non-techies.

CERN Web browser, 1993


A History of the Web (1)

1989-1992: Tim Berners-Lee invents the Web at CERN.

Aimed to help communication within the particle physics community at CERN.

HTML, HTTP, first simple browser finished Christmas 1990.

Released by CERN in 1991.

1993

First alpha release of “Mosaic for X”.

About 50 Web servers in operation.

TCP/IP is integrated in Microsoft and Apple operating systems.

1994

Marc Andreesen and Eric Bina commercialize the Mosaic browser and establish Netscape Communications Corporation.

1st WWW conference and 1st W3C meeting.

About 500 Web Servers in operation.


A History of the Web (2)

1995:

Web traffic becomes dominant Internet traffic, nearly 10,000 WebServers in operation.

Compuserve and AOL provide Internet/Web service.

Netscape goes public

About 75% of Web users use the Netscape browser.

1996:

Microsoft enters the Web browser market.

Beginning of the “Browser War”.

1998: Over two million web servers in less than ten years.

2000: Web has more than one billion unique pages.

2001: About 80% of Web users use the Microsoft browser.

End of the browser war


The Growth of the Web – Web Servers

The number of Web servers is doubling almost every year.

*Source: Netcraft


The Growth of the Web – Web Sites

The first Netcraft survey in August 1995 found 18,957 hosts.

*Source: Netcraft


Web Trends – The Mobile Web

Ubiquitous Data Access -Anywhere, any time!

But in privacy!


Web Trends - Convergence

In the Future…

… you will be able to communicate with the world…

… with a richness making it just about as good as being there!

You can use whatever media best suites your needs – voice,

data, video, messaging,…

Different types of convergence:

Voice/data, wireline/wireless, packet/circuit.


Web Trends – Aspects of Convergence

NetworkProvider

ApplicationProvider

User

EquipmentManufacturer


Basic Concepts of the Web

The Web follows a client/server model

Information is represented in form of Web objects.

Web clients request Web objects from Web servers.

The Web is modeled around three fundamental concepts:

Representation of Web objects (i.e. HTML)

Identification of Web objects (i.e. URI, URL, URN)

Transport of Web objects (i.e. HTTP)

Request

ResponseInternet

Web Client Web Server


HTML: Representation of Web Objects (1)

Hypertext documents on the Web are typically represented in the Hypertext Markup Language (HTML).

Simple document syntax that is used to describe the structure ofweb documents (not primarily the formatting).

Originally developed by Tim Berners-Lee in 1990.

HTML is specified in Internet Drafts, but is is constantly evolving.

HTML provides:

Text formatting commands,

Embedded objects (e.g. images),

Hyperlinks to other objects.



HTML is ASCII based and can easily be written by hand

Meta-Tags can be used to imitate HTTP header fields

Web servers do not need to understand or interpret HTML.

HTML pages are rendered at the client’s Web browser.

Not all Web objects have to be authored in HTML

Images, unstructured text documents, audio, video, etc.

<html><head><meta http-equiv="Content-Type" content="text/html><meta http-equiv="Pragma" content="no-cache">

...</head><body>




Identification of Web Objects

Users need some kind of handle to uniquely identify Web objects.

Two fundamental ways to identify Web objects:

A name distinguishes objects from each other,

A location tells where an object can be found.

The two concepts are reflected in two identification schemes:

A Uniform Resource Name (URN) provides a persistent, globally unique name for a Web object.

A Uniform Resource Locator (URL) provides a non-persistent means to identify an object based on its current location, e.g. http://www.content-networking.com/lecture/intro.html

The Uniform Resource Identifier (URI) is an abstraction that includes both, URNs and URLs.


Transport of Web Objects

The Hypertext Transport Protocol (HTTP) is the primary means to transport objects on the Web.

Application-level protocol that mostly runs over TCP/IP.

Follows the request/response paradigm.

Text-based protocol (as opposed to binary) .

Stateless protocol

HTTP evolved in two major phases:

From the initial proposal HTTP/0.9 in early 1990s to the official HTTP/1.0 specification in 1996.

Second phase moved HTTP from version 1.0 to version 1.1 in 1999.

(for more info on HTTP see slides of course “Telematics 2”)


Web Applications

The growth and evolution of the Web are driven by applications that individuals and businesses use.

The Web is no longer only about sharing (static) documents.

New types of Web applications had (and still have) significant impact on the evolution of Web technology.

Retrieval of static content,

Retrieval of dynamic content,

Retrieval of streaming content,

Interactive collaboration.

New applications expose shortcomings of existing network and Webtechnology, and will continue to drive their future evolution.

What applications to expect next?What applications to expect next?


The Next Generation Couch Potato…

… will not only expect fast web access, but also:

high quality audio and video, on demand and live,

personalized and dynamic content provisioning,

content that adapts to user and device needs.

Can today’s Internet and the Web live up to these expectations?Can today’s Internet and the Web live up to these expectations?


Today’s Internet

Today’s Internet technology is suited to support the currently prevailing applications:

Web access and E-Mail are still the most popular Internet applications.

Web traffic is the dominant Internet traffic.

But… ISPs and service providers are struggling to cope with the explosion in Internet usage while worrying about what new applications will come next.

The Web is often referred to as “WWW = World Wide Wait””:

High access delays,

Servers overloaded or not available,

Limited service quality.


The Reality - Today’s Internet Experience

Source*: Keynote Consumer 40 Index, January 9-15, 2005.

Graph shows the seven fastest web pages in the Index.

Worst average (anonymous) was 79.95 seconds.

Ave

rage

Dia

l-Up

Dow

nloa

d T

ime

[sec

]

*See http://www.keynote.com/

4.61 6.01 9.52 11.2 13.8 15.23 14.410

4

8

12

16

Google FedEx Ask Jeeves

Infospace Fidelity Yahoo! UPS

15.35


Impact of Web Performance

Yes, found new site for that session only:

13%

Yes, found new site I use regularly:

24%

Yes, permanentlystopped using site:

9%

No answer:1%

No:53%

Source: Jupiter Communications Survey of 2,369 users, pub. 6/99

Has Web site performance affected your usage of a Web site?Has Web site performance affected your usage of a Web site?


The Growth of the Internet

Growth of the Internet is exponential.

Growth in Internet traffic is driven by:

Growing number of Internet users - 400 million by 2002/03.

More time spent on the Internet.

Richer, broadband content.

In 2000, the Web had more than one billion unique pages (source:Inktomi Cooperation).

ISPs are concerned whether their infrastructure can growth as fast as user demand.

There is an explosive need for scalableand reliable Content Networking technology.


Enabling Technologies

High-speed access links

Fast/Gigabit Ethernet from office

Cable modem and xDSL from home and home office

More powerful end-user equipment

Multimedia PCs

Digital vide cameras and digital photography

Costs are dropping for:

Disk storage

Bandwidth

Processing power

More efficient coding and compression techniques


Possible Solutions to the Web Slowdown

Improving the backbone infrastructure by adding more bandwidth and QoS capabilities:

costly and difficult to deploy

will take a long time

does not address the fundamental problem of overloaded servers

improves performance only, but it does not enable new content services for additional revenue.

Alternative (but not exclusive) solutions involve:

Multicast technology, either at the network level or above

Moving and storing content closer to the user, at the edge of the network

Caching and Web Switching

Content Delivery and Distribution (CDD)


Central Content and Services

Client

OriginServer

Internet


Distributed Content, Central Services

Client

OriginServer

InternetRequestRouting

CooperativeCaching


Distributed Content and Services

Client

OriginServer


CooperativeCaching Content

Services


Content Distribution Internetworking

Client

OriginServer


CachingCooperativeCaching

ContentServices

CachingCooperative

CachingContentServices

CDN A

CDN B

Content PeeringContent Peering


Content Networking Defined

The terminology as used throughout this lecture is defined as follows:

The term content network refers to a communication networkthat deploys infrastructure components operating at protocol layers 4-7. These components interconnect with each other, creating a virtual network layered on top of an existing packet network infrastructure.

The term content network refers to a communication networkthat deploys infrastructure components operating at protocol layers 4-7. These components interconnect with each other, creating a virtual network layered on top of an existing packet network infrastructure.

The term content refers to any information that is made available to other users on the Internet. This includes, but is not limited to Web pages, images, textual documents, audio and video as well assoftware downloads, broadcasts, instant messages and forms data

The term content refers to any information that is made available to other users on the Internet. This includes, but is not limited to Web pages, images, textual documents, audio and video as well assoftware downloads, broadcasts, instant messages and forms data


Functional Components of Content Networks

Content Distribution:

Services for moving content from its source to the users.

Request-Routing:

Services for navigating user requests to a location best suited for retrieving the requested content.

Content Processing:

Services for creating or adapting content to suit user preferences and device capabilities.

Authorization, Authentication, Accounting:

Services that enable monitoring, logging, accounting, and billing of content usage.


The Diversity of Interests

Understanding the diversity of interests and the role of each party is important for designing and deploying efficient content networks.

ContentHost

Content Creator

Content ProviderContent Consumer Content Network Provider

Different parties havedifferent interests and goals

Different parties havedifferent interests and goals


Some Basics: Internet Design Paradigms

Content networks depend on the capability to interact and to transport messages between servers and clients.

The Internet typically serves as the “transport vehicle” for content networks and for the Web.

The design of content networks requires an understanding of the fundamental design paradigms of the Internet.

Two important characteristics of the Internet design are given by:

The hourglass protocol architecture,

The end-to-end principle.

Both principles are at the hard core of the Internet, but they increasingly become topics of controversial discussions – especially in the context of content networking.


Watching the Waist of the Protocol Hourglass (S. Deering)

Original Hourglass Putting on Weight Midlife Crisis

An Accident (NAT) IP Tunneling Evolution to Wineglass?

(Taken from a talk of S. Deering at 51. IETF: http://www.ietf.org/proceedings/01aug/slides/plenary-1/ )


More Fattening Temptations

Reliable multicast assists,

Packet-intercepting caches,

Content-based routing,

Active networking,

And more…

email WWW phone...

SMTP HTTP RTP...

TCP UDP…

IP + ? + ?...ethernet PPP…

CSMA async sonet...

copper fiber radio...

email WWW phone...

SMTP HTTP RTP...

TCP UDP…

IP + ? + ?...ethernet PPP…

CSMA async sonet...

copper fiber radio...

Keep the hourglass model in mindwhen we talk about content networking

techniques later on!

Keep the hourglass model in mindwhen we talk about content networking

techniques later on!


The End-to-End Principle

Describes a design principle that organizes and guides the placement of functions within a system.

Postulates the sharing of responsibilities between the network and its connected end hosts.

Attributed to Dave Clark and colleagues from MIT (1984).

Key messages of the end-to-end principle:

Keep the core network simple and move necessary intelligence as much as possible outside the network into the end hosts.

A function or a service should be provided within the network only if it is needed by all end hosts connected to that network.

As such, the core Internet provides only for simple forwarding of individual data packets, while the end hosts do the control and provide for more sophisticated communication services.


The End-to-End Principle Illustrated

Ether.

HTTP

TCP

IP

Web Server

HTTP

TCP

IP

Web Client

802.11

Router

802.11 ATM

IPRouter

ATM Ether.

IP

End Host Network End Host


Discussion of the End-to-End Principle

The end-to-end argument is in sharp contrast to the legacy telephone network.

Smart network, dumb end devices (i.e. phones).

Legacy telephone network is highly optimized for a very specificapplication (i.e. real-time voice transmission).

The end-to-end argument does not preclude the idea of building programmable networks.

It is more about who should provide and control the code for specific functions rather than about where the code should be executed.

A related principle is network transparency.

Packets flow from source to destination essentially unaltered.

Network addresses are unique and durable.


An Analogy to the Postal System

Customer Postal System Customer


The Vanishing of Network Transparency

The uniqueness/durability of IP addresses is often taken for granted and is required for higher-level mechanisms to work properly, e.g.

TCP includes IP address in checksum calculation,

Web applications use IP addresses for identification.

But: The threat of IPv4 address exhaustion and new business models drive technologies that break this assumption, e.g.

Network Address Translators (NATs),

Interception proxies.

Result: Many applications will fail unless they are adapted to overcome the assumption of address transparency, e.g.

Application-Level Gateways (ALGs).

Designers of content networks must be aware of the Internet’sdesign principles and of the dependencies they create.


Improving Content Transport with Multicast: Unicast

Unicast transmits data between a single sender and a single receiver.

Most applications on the Internet are based on unicast (e.g. telnet, ftp, etc.).

Unicast allows provisioning of individual services.

Problems:

Server load increases linearly with the number of receivers.

Network load increases with the number of receivers.

Sender needs to know the identity of all receivers (complicated addressing).

Internet

Sender

Receiver


IP Multicast

IP multicast supports data delivery to multiple receivers by replicating data packets at branching points in the network.

Sends a message to multiple receivers using a single local „transmit“ operation.

Benefits:

Reduced server load,

Reduced network load,

Simplified addressing.

IP multicast was defined by Steve Deering in 1989.

Even today, IP multicast service is not yet widely available.

Internet

Sender

Receiver


A Spectrum of Paradigms

UnicastUnicast BroadcastBroadcast

MulticastMulticast

Send toone

Send toall

Send tosome

Improved Efficiency

Improved “Individuality”


Multicast Applications

Data transfer to multiple receivers:

Video conferencing,

Distance learning,

Push applications,

File distribution (software, databases, etc.),

Large scale content distribution (e.g. TV, Internet radio, etc.).

Resource discovery:

Discovery of network equipment (e.g. printers)

Discovery of services (e.g. print services)

Discovery of software (e,g, mobile agents)

And Content Networking ?!?And Content Networking ?!?


The Layering of Multicast

Multicast byUnicast

Multicast byUnicast

ProtocolLayer n+1

ProtocolLayer n

Multicast byMulticast

Multicast byMulticast

ProtocolLayer n+1

ProtocolLayer n

Multicast byBroadcast

Multicast byBroadcast

ProtocolLayer n+1

ProtocolLayer n


MC-NetMC-Net

The Early Days of Internet Multicast - MBone

Sender

Receiver

UnicastRouter

MC-PacketMC-Packet MC-PacketMC-Packet

Tunnel

UC-NetUC-Net MC-NetMC-Net

MC-PacketMC-PacketUC-Head

MulticastRouter

ReceiverMulticastRouter


Inefficiencies on the MBone

UC-Router

ReceiverReceiver

UC-Router

Unicast-Network

Sender

MC-Routeron Workstation



Data Stream

Efficient multicasting requires “native” multicast support.


Why is native IP Multicast not available?

Multicast technology already widely deployed, but multicast service not yet turned on – why?

Multicast is hard to debug and hard to manage.

There is not yet a real “killer” application.

Receivers prefer using unicast instead of the low-quality and unstable MBone service (user perception: “Multicast = MBone”).

IP multicast service model not inline with requirements for commercial deployment.

No group membership control,

Open to denial of service attacks,

Domain dependency.

Lack of a business model for multicast pricing.


The IP Multicast Service Model

(Original) IP multicast offers many-to-many communication.

New approaches propose a single source multicast model.

Open service model, i.e. everybody can:

create a multicast group,

receive data from a group,

send data to a group.

No multicast address reservation.

Problems:

Router state,

Inter-domain multicast,

Denial-of-service attacks.


Multicast Problems: Unauthorized Receivers

Internet

Possible Solution:Data Encryption?


Multicast Problems: Denial-of-Service Attacks

Internet


Requirements for Commercial Deployment

At least same level of availability and maintainability as unicast.

Easy and transparent installation:

ISP must be able to install, manage, and maintain multicast service.

Setup and configuration of multicast session must have low latency and be straightforward.

Group membership should be controlled.

Only authorized sources send to a group,

Senders want to control the receiver set.

Globally unique multicast addresses.

Bandwidth fairness,

Network maintenance and debugging.

Appropriate business model and mechanisms for charging and billing


Alternative Service Models

Single-source service model:

Multicast groups are source-specific, i.e. only a single source can send to a multicast group.

Multicast groups are identified by a (S, G) pair => simple multicast address allocation.

Explicit join signaling to the source.

Single source allows efficient shortest path routing.

Pricing and charging is simpler.

Authorization of the source can be provided by border/edge routers.

Example: Express (by Holbrook and Cheriton, Sigcomm 1999).


“Early” Commercial Multicast Services (2000)

Multicast by Uunet:

Multicast service is called Uucast,

Not a native IP multicast solution,

Uucast sources unicast data to a proxy, which multicasts the data over the Internet,

Flat rate pricing: $2200 (5kbps), $4300 (10 kbps), $10,900 (25 kbps), $15,200 (35 kbps), $27,000 (64 kbps), $54,000 (128 kbps),streams up to 1.5 Mbps will be available in the future

Multicast by Sprint:

Native IP multicast service,

Provided to customers at no charge.


Charging for Multicast Services

Several possible business models:

Flat rate charged to source,

Free service paid for by ISP,

Cost splitting charged to receivers,

Who benefits from multicast?

Sender?

ISP?

Receiver?

Motivation for multicast usage?

ISP A

ISP DISP C

ISP B


Recapture: Key concerns with IP Multicast

Scalability with number of groups.

Routers need to maintain per-group state,

Management of multicast addresses is complicated.

Supporting higher level functionality is difficult:

IP Multicast: best-effort multi-point delivery service,

Reliability and congestion control for IP Multicast complicated.

Need to deal with heterogeneous receiver => negotiation hard.

Deployment is difficult and slow.

ISP’s reluctant to turn on IP Multicast.

Approach: Provide Multicast functionality above the IP layer- Application Level Multicast (ALM)

Approach: Provide Multicast functionality above the IP layer- Application Level Multicast (ALM)


What is Application Level Multicast?

Uses unicast at transport level and below to transmit data to multiple receivers.

Relay Points (RP) receive data, replicate it, send it out to other RPs/receivers.

Most interesting in case of reliable, congestion controlled datatransfer:

Data between sender, relay points, receivers sent via TCP.

Reliability, congestion control provided by TCP.S

RP

R R

RP

RR


The General Question

Application Level Multicast vs. native IP Multicast:

What is better, when to choose one over the other?

The answer strongly depends on:

Network environment,

Application type,

Goals of optimization (which performance metric to optimize?).

It is important to provide some general guidelines in finding the right decision.


Aspects to be Considered

Network Bandwidth: In most cases, ALM requires more network bandwidth due to multiple unicast connections.

Throughput: ALM provides better throughput in heterogeneous groups (assuming that native IP multicast uses some sort of “worst receiver path” congestion control).

Buffer Requirements: ALM requires additional buffer at RPs; buffer size depends on rate mismatch of incoming, outgoing TCP connections, transmission duration.

Group Membership State: Native IP multicast requires group state in core routers, while ALM requires group state only in RPs.

Configuration Overhead: Native multicast routing protocols vs. overlay tree construction in ALM.

Congestion Control: ALM congestion control “comes for free”, but requires RPs at both ends of bottleneck link.

advanced networking technologies · internet interface for non-techies. cern web browser, 1993...

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