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

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.

Introducing ISP Services Critical services for small-to-medium businesses: Email Web hosting Media streaming IP telephony File transfer

Introducing ISP Services Meeting customer requirements: Reliability Availability

Protocols That Support ISP Services The TCP/IP suite of protocols supports reliability

Protocols That Support ISP Services Transport needs determine the choice of Transport Layer Protocol

Protocols That Support ISP Services The TCP three-way handshake: Synchronization Synchronization acknowledgement Acknowledgement

Protocols That Support ISP Services How TCP supports reliability: Acknowledgement Retransmission Sequencing Flow control

Protocols That Support ISP Services UDP: not connection-oriented, simple protocol Used by online games, DHCP, DNS

Protocols That Support ISP Services TCP and UDP use ports to support multiple services

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

Domain Name System (DNS) Networking naming systems translate human-readable names into machine-readable addresses srv2

Domain Name System (DNS) Advantages of DNS: Hierarchical structure Small, manageable zones Scalable

Domain Name System (DNS) Components of DNS: Resource records and domain namespace Domain name system servers Resolvers

Domain Name System (DNS) DNS name resolution: Dynamic updates Forward lookup zones Reverse lookup zones Primary zones Secondary zones

Domain Name System (DNS) Implementing DNS solutions: ISP DNS servers Local DNS servers

Services and Protocols ISPs provide many business-oriented services Secure versions of Application Layer protocols support customer security requirements

Services and Protocols HTTP is a request-response protocol HTTPS adds authentication and encryption

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

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

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.