© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1Version 4.1

ISP Services

Working at a Small-to-Medium Business or ISP – Chapter 7

2© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Objectives

Network services provided by an ISP

Protocols that support the network services

Purpose, function, and hierarchical nature of the Domain Name System (DNS)

Common services and their protocols

3© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP Services

Critical services for small-to-medium businesses:

Email

Web hosting

Media streaming

IP telephony

File transfer

4© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP ServicesMožné vztahy mezi zákazníkem a ISP

1.

Zákazník má veškeré zařízení u sebe. Všechno vlastní a provozuje sám. Od ISP žádá jen rychlé připojení k internetu.

5© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP ServicesMožné vztahy mezi zákazníkem a ISP

2.

Zařízení je umístěno u zákazníka, ale patří ISP, který se o všechno stará.

6© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP ServicesMožné vztahy mezi zákazníkem a ISP

3.

Zařízení patří zákazníkovi. Důležité servery jsou umístěny u ISP. Ten se o ně stará a provozuje na nich zákazníkovy aplikace.

Zákazník kromě toho žádá od ISP rychlé připojení k internetu.

7© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP Services

Meeting customer requirements:

Reliability

Availability

Co chtějí zákazníci:

• Spolehlivost

• Dostupnost

Zdvojování, zálohování zařízení a cest

Spolehlivé technologie

Náhradní díly stále po ruce

8© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP Services

Meeting customer requirements:

ReliabilityMTBF = Mean Time Between Failure

MTTR = Mean Time To Repair

Fault tolerance = measure of equipment robustness

The longer the MTBF, the greater the fault tolerance.

MTTR is established by warranty or service agreements.

MTBF = střední doba mezi poruchami

MTTR = střední doba do opravy

Fault tolerance = míra odolnosti proti poruchám

Čím delší MTBF, tím větší odolnost proti poruchám.

MTTR je zaručován záručními podmínkami nebo smlouvami o servisu.

9© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Introducing ISP Services

Meeting customer requirements: Availability

Availability is the percentage of time that a resource is accessible. Ideal availability percentage is 100%, that is the system is never down. Telephone services are expected to be available 99.999% of the time. ISPs must meet even higher conditions.

Availability is ensured by • doubling up on network devices • using reliable technologies

Dostupnost je procento času, kdy je zařízení použitelné.Ideální dostupnost je 100%, tj. systém není nikdy mimo provoz.U telefonních služeb se očekává dostupnost po 99.999% času.ISP musí splňovat ještě náročnější podmínky.Dostupnost se zajišťuje• zdvojováním, zálohováním síťových zařízení• použitím spolehlivých technologií

10© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP ServicesTeď budeme chvíli používat čtyřvrstvý TCP/IP model místo sedmivrstvého.

Prostřední vrstvy si odpovídají, jen Network se jmenuje Internet.

Co je nad tím, shrne se do Aplication, ....

... co je pod tím, shrne se do Network Access.

11© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services The TCP/IP suite of protocols supports reliability Sada protokolů TCP/IP podporuje spolehlivostVíme, že v aplikační vrstvě jsou věci blízké člověku. Proč tam tedy jsou např. DNS, DHCP, které s člověkem nijak nepřicházejí do styku?

Protože využívají služeb protokolu TCP, aby si zajistily spolehlivost. Proto jsou ve vrstvě nad ním, tj. ve vrstvě aplikační.

Celý systém je totiž vystavěn tak, že ti nahoře využívají služeb těch dole.

12© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

Transport needs determine the choice of Transport Layer Protocol

13© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

The TCP three-way handshake:

Synchronization

Synchronization acknowledgement

Acknowledgement

14© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

How TCP supports reliability:

Acknowledgement

Retransmission

Sequencing

Flow control

15© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

UDP: not connection-oriented, simple protocol

Used by online games, DHCP, DNS

16© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

TCP and UDP use ports to support multiple services

17© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Protocols That Support ISP Services

Socket: combination of Transport Layer port number and Network Layer IP address of host

Socket pair: source and destination IPs and port numbers identify each conversation

18© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Domain Name System (DNS)

Networking naming systems translate human-readable names into machine-readable addresses

srv2

19© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Domain Name System (DNS)

Advantages of DNS:

Hierarchical structure

Small, manageable zones

Scalable

20© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Domain Name System (DNS)

Components of DNS:

Resource records and domain namespace

Domain name system servers

Resolvers

21© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Domain Name System (DNS)

DNS name resolution:

Dynamic updates

Forward lookup zones

Reverse lookup zones

Primary zones

Secondary zones

22© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Domain Name System (DNS)

Implementing DNS solutions:

ISP DNS servers

Local DNS servers

23© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Services and Protocols

ISPs provide many business-oriented services

Secure versions of Application Layer protocols support customer security requirements

24© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Services and Protocols

HTTP is a request-response protocol

HTTPS adds authentication and encryption

25© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Services and Protocols

FTP uses a protocol interpreter (PI) and data transfer process (DTP)

Two connections: one to send commands, one for actual file data transfer

26© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Services and Protocols

SMTP: specific message format and processes running on both client and server

POP3: mail is downloaded from server to client and then deleted

IMAP4: keeps messages on server

27© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public

Summary

TCP and UDP use port numbers to provide multiple services to hosts.

DNS uses a hierarchical system of databases to resolve names and IP addresses of known hosts within networks and across the Internet.

The most common services used on the Internet include FTP, FTPS, HTTP, HTTPS and SMTP.

ISPs use high-performance servers to support these services.

28© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public