© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Version 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:   Web hosting  Media streaming  IP telephony  File transfer

4 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introducing ISP Services Možné 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 Services Možné 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 Services Možné 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:  Reliability MTBF = 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 % 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 % 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 Services Teď 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 spolehlivost Víme, 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