ISP Services
Working at a Small-to-Medium Business or ISP –
Chapter 7
Version 4.1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 1

Objectives
 Describe the network services provided by an ISP.
 Describe the protocols that support the network
services provided by an ISP.
 Describe the purpose, function, and hierarchical nature
of the Domain Name System (DNS).
 Describe and enable common services and their
protocols.
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 2

Introducing ISP Services
Critical services for small-to-medium businesses:
 Email
 Web hosting
 Media streaming
 IP telephony
 File transfer
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 3

Introducing ISP Services
Meeting customer requirements:
 Reliability
 Availability
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 4

Protocols That Support ISP Services
 The TCP/IP suite of protocols supports
reliability
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 5

Protocols That Support ISP Services
 Transport needs determine the choice of
Transport Layer Protocol
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 6

Protocols That Support ISP Services
The TCP three-way handshake:
 Synchronization
 Synchronization acknowledgement
 Acknowledgement
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 7

Protocols That Support ISP Services
How TCP supports reliability:
 Acknowledgement
 Retransmission
 Sequencing
 Flow control
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 8

Protocols That Support ISP Services
 UDP: not connection-oriented, simple protocol
 Used by online games, DHCP, DNS
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 9

Protocols That Support ISP Services
 TCP and UDP use ports to support multiple
services
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 10

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

Domain Name System (DNS)
 Networking naming systems translate human-
readable names into machine-readable
addresses
srv2
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 12

Domain Name System (DNS)
Advantages of DNS:
 Hierarchical structure
 Small, manageable zones
 Scalable
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 13

Domain Name System (DNS)
Components of DNS:
 Resource records and domain namespace
 Domain name system servers
 Resolvers
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 14

Domain Name System (DNS)
DNS name resolution:
 Dynamic updates
 Forward lookup zones
 Reverse lookup zones
 Primary zones
 Secondary zones
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 15

Domain Name System (DNS)
Implementing DNS solutions:
 ISP DNS servers
 Local DNS servers
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 16

Services and Protocols
 ISPs provide many business-oriented services
 Secure versions of Application Layer protocols
support customer security requirements
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 17

Services and Protocols
 HTTP is a request-response protocol
 HTTPS adds authentication and encryption
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public 18

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

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

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

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