Computer and Communication Networks (paperback)

9.8. Summary

The top layer of the networking stack is known as the application layer. Services in this category allow users and programs to interact with services on remote machines and with remote users. The application layer offers network services and applications to users and runs certain applications. The Domain Name System (DNS) is a distributed hierarchical and global directory that translates machine or domain names to numerical IP addresses. An IP address can be assigned a domain name . Unique domain names assigned to hosts must be selected from a name space and are generally organized in a hierarchical fashion.

The TELNET remote login protocol uses a negotiation method to allow clients and servers to reconfigure the parameters controlling their interaction. The Secure Shell (SSH) remote login protocol is implemented on TCP for communications. SSH is more powerful and flexible than TELNET and allows the user to more easily execute a single command on a remote client.

The Simple Mail Transfer Protocol (SMTP) can transfer e-mail from the mail server of a source to mail servers of destinations. A user mailbox is a certain space the mail server allocates to the user to keep its e-mail. SMTP is designed to connect only the two mail servers of the associated parties, regardless of the distance between the two users. Consequently, this protocol involves only the two mail servers of the communicating users.

File transfer allows geographically distributed files and information to be shared among the members of a working group and for information sharing. A user can use a file transfer protocol to access a server and transfer the desired file. Two such protocols are FTP and SCP. The World Wide Web (WWW), or simply the Web , is a global network of servers linked together by a common protocol allowing access to all connected hypertext resources. HTTP requests are first directed to the network proxy server called Web cache . Once configured by the network, a browser's request for an object is directed to the Web cache.

The chapter ended with network management aspects of computer networks. Managed devices, such as routers and hosts, are managed objects, and each object has a formal ASN.1 definition. Another tool through which a database of information and characteristics for objects can be accommodated is MIB. With SNMP, a network manager can find the location of a fault. SNMP runs on top of UDP and uses client/server configurations. SNMP commands define how to query information from a server and forward information to a server or a client.

The next chapter discusses the security aspects of computer networking. Types of network attacks, message encryption protocols, and message authentication techniques are covered.