* Domain Name System (DNS) is a client-server application that identifies each host on the Internet with a unique user-friendly name.
* DNS organizes the name space in a hierarchical structure to decentralize the responsibilities involved in naming.
* DNS can be pictured as an inverted hierarchial tree structure with one root node at the top and a maximum of 128 levels.
* Each node in the tree has a domain name.
* A domain is defined as any subtree of te domain name space.
* The name space information is distributed among DNS servers. Each server has jurisdiction over its zone.
* A root server's zone is the entire DNS tree.
* A primary server creates, maintains, and updates information about its zone.
* A secondary server gets its information from a primary server.
* The domain name space in the Internet is divided into three sections: generic domains, country domains, and inverse domains.
* There are seven traditional generic labels, each specifying an organization type. Recently some new labels have been added.
* Each country domain specifies a country.
* The inverse domain finds a domain name for a given IP address. This is called address-to-name resolution.
* Name servers, computers that run the DNS server program, are organized in a hierarchy.
* The DNS client, called a resolver, maps a name to an address or an address to a name.
* In recursive resolution, the client may send its request to multiple servers before getting an answer.
* In iterative resolution, the client may send its request to multiple servers before getting an answer.
* A fully qualified doman name (FQDN) is a domain name consisting of labels beginning with the host and going back through each level to the root node.
* A partially qualified domain name (PQDN) is a domain name that does not include all the levels between the host and the root node.
* There are two types of DNS messages: queries and responses.
* There are two types of DNS records: question records and resource records.
* Dynamic DNS (DDNS) automatically updates the DNS master file.
* DNS uses the services of UDP for messages of less than 512 bytes; otherwise, TCP is used.
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Wednesday, May 14, 2008
Client-Server Model: Socket Interface
* In the client-server model, the client runs a program to request a service and the server runs a program to provide the service. These two programs communicate with each other.
* One server program can provide services for many client programs.
* Clients can be run either iteratively (one at a time) or concurrently (many at a time).
* Servers can handle clients either iteratively (one at a time) or concurrently (many at a time).
* A connectionless iterative server uses UDP as its transport layer protocol and can serve one client at a time.
* A connection-oriented concurrent server uses TCP as its transport layer protocol and can serve many clients at the same time.
* When the operating system executes a program, an instance of the program, called a process, is created.
* If two application programs, one running on a local system and the other running on the remote system, need to communicate with each other, a network program is required.
* The socket interface is a set of declarations, definitions, and procedures for writing cleint-server programs.
* The communication structure needed for socket programming is called a socket.
* A stream socket is used with a connection-oriented protocol such as TCP.
* A datagram socket is used with a connectionless protocolsuch as UDP.
* A raw socket is sued by protocols such as ICMP or OSPF that directly use the services of IP.
* One server program can provide services for many client programs.
* Clients can be run either iteratively (one at a time) or concurrently (many at a time).
* Servers can handle clients either iteratively (one at a time) or concurrently (many at a time).
* A connectionless iterative server uses UDP as its transport layer protocol and can serve one client at a time.
* A connection-oriented concurrent server uses TCP as its transport layer protocol and can serve many clients at the same time.
* When the operating system executes a program, an instance of the program, called a process, is created.
* If two application programs, one running on a local system and the other running on the remote system, need to communicate with each other, a network program is required.
* The socket interface is a set of declarations, definitions, and procedures for writing cleint-server programs.
* The communication structure needed for socket programming is called a socket.
* A stream socket is used with a connection-oriented protocol such as TCP.
* A datagram socket is used with a connectionless protocolsuch as UDP.
* A raw socket is sued by protocols such as ICMP or OSPF that directly use the services of IP.
Congestion Control and Quality of Service
* The average data rate, peak data rate, maximum burst size, and effective band-width are qualitative values that describe a data flow.
* A data flow can have a constant bit rate, a variable bit rate, or traffic that is bursty.
* Congestion control refers to the mechanisms and techniques to control congestion and keep the load below capacity.
* Delay and throughput measure the performance of a network.
* Open-loop congestion control prevents congestion; closed-loop congestion control removes congestion.
* TCP avoids congestion through the use of two strategies: the combination of slow start and additive increase, and multiplicative decrease.
* Frame relay avoids congestion through the use of two strategies: backward explicit congestion notification (BECN) and the forward explicit congestion notification (FECN).
* A flow can be characterized by its reliability, delay, jitter, and bandwidth.
* Scheduling, traffic shaping, resource reservation, and admission control are techniques to improve quality of service (QoS).
* FIFO queuing, priority queuing, and weighted fair queuing are scheduling techniques.
* Leaky bucket and token bucket are traffic shaping techniques.
* Integrated Services is a flow-based QoS model designed for IP.
* The Resource Reservation Protocol (RSVP) is a signaling protocol that helps IP create a flow and makes a resource reservation.
* Differential Services is a class-based QoS model designed for IP.
* Access rate, committed burst size, committed information rate, and excess burst size are attributes to control traffic in Frame Relay. * Quality of service in ATM is based on service classes, user-related attributes, and network-related attributes.
* A data flow can have a constant bit rate, a variable bit rate, or traffic that is bursty.
* Congestion control refers to the mechanisms and techniques to control congestion and keep the load below capacity.
* Delay and throughput measure the performance of a network.
* Open-loop congestion control prevents congestion; closed-loop congestion control removes congestion.
* TCP avoids congestion through the use of two strategies: the combination of slow start and additive increase, and multiplicative decrease.
* Frame relay avoids congestion through the use of two strategies: backward explicit congestion notification (BECN) and the forward explicit congestion notification (FECN).
* A flow can be characterized by its reliability, delay, jitter, and bandwidth.
* Scheduling, traffic shaping, resource reservation, and admission control are techniques to improve quality of service (QoS).
* FIFO queuing, priority queuing, and weighted fair queuing are scheduling techniques.
* Leaky bucket and token bucket are traffic shaping techniques.
* Integrated Services is a flow-based QoS model designed for IP.
* The Resource Reservation Protocol (RSVP) is a signaling protocol that helps IP create a flow and makes a resource reservation.
* Differential Services is a class-based QoS model designed for IP.
* Access rate, committed burst size, committed information rate, and excess burst size are attributes to control traffic in Frame Relay. * Quality of service in ATM is based on service classes, user-related attributes, and network-related attributes.
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