Skip to main content

UDP operation

UDP operation
10.1.7 This page will explain the similarities and differences between TCP and UDP.
The TCP/IP protocol stack contains many different protocols, each designed to perform a certain task. IP provides Layer 3 connectionless transport through an internetwork. TCP enables connection-oriented, reliable transmission of packets at Layer 4 of the OSI model. UDP provides connectionless, unreliable transmission of packets at Layer 4 of the OSI model.
Both TCP and UDP use IP as their Layer 3 protocol. In addition, TCP and UDP are used by various application layer protocols. TCP provides services for applications such as FTP, HTTP, SMTP, and DNS. UDP is the transport layer protocol used by DNS, TFTP, SNMP, and DHCP. 
TCP must be used when applications need to guarantee that a packet arrives intact, in sequence, and unduplicated. The overhead necessary to ensure delivery of a packet is sometimes a problem with TCP. Not all applications need to guarantee delivery of the data packet, so they use the faster, connectionless delivery mechanism afforded by UDP. The UDP protocol standard is described in RFC 768.
UDP does not use windowing or ACKs so application layer protocols must provide error detection. 
The Source Port field is an optional field used only if information needs to return to the sending host. When a destination router receives a routing update, the source router is not requesting anything so nothing needs to return to the source. There is no exchange of information or data. The Destination Port field specifies the application to which UDP needs to pass the protocol. A DNS request from a host to a DNS server would have a Destination Port field of 53, the UDP port number for DNS. The Length field identifies the number of octets in the UDP segment. The UDP checksum is optional but should be used to ensure that the data has not been damaged during transmission. For transport across the network, UDP is encapsulated within the IP packet.
Once a UDP segment arrives at the destination IP address, a mechanism must exist which allows the receiving host to determine the exact destination application. Destination ports are used for this purpose. If a host is running both TFTP and DNS services, it must be able to determine what service the arriving UDP segments need. The Destination Port field in the UDP header determines the application to which a UDP segment will be delivered.
This page concludes this lesson. The next lesson will provide an overview of transport layer ports. The first page describes multiple conversations between hosts

Comments

Post a Comment

Popular posts from this blog

OSI layers / Peer-to-peer communications / TCP/IP model

OSI layers 2.3.4 This page discusses the seven layers of the OSI model. The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. - Dividing the network into seven layers provides the following advantages: • It breaks network communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand. In the foll...
Post a Comment
Read more

Advantages and disadvantages of link-state routing

Advantages and disadvantages of link-state routing 2.1.5  This page lists the advantages and disadvantages of link-state routing protocols. The following are advantages of link-state routing protocols:  Link-state protocols use cost metrics to choose paths through the network. The cost metric reflects the capacity of the links on those paths. Link-state protocols use triggered updates and LSA floods to immediately report changes in the network topology to all routers in the network. This leads to fast convergence times. Each router has a complete and synchronized picture of the network. Therefore, it is very difficult for routing loops to occur. Routers use the latest information to make the best routing decisions. The link-state database sizes can be minimized with careful network design. This leads to smaller Dijkstra calculations and faster convergence. Every router, at the very least, maps the topology of it...
Post a Comment
Read more

Ports for services

Ports for services 10.2.2  Services running on hosts must have a port number assigned to them so communication can occur. A remote host attempting to connect to a service expects that service to use specific transport layer protocols and ports. Some ports, which are defined in RFC 1700, are known as the well-known ports. These ports are reserved in both TCP and UDP.  These well-known ports define applications that run above the transport layer protocols. For example, a server that runs FTP will use ports 20 and 21 to forward TCP connections from clients to its FTP application. This allows the server to determine which service a client requests. TCP and UDP use port numbers to determine the correct service to which requests are forwarded. The next page will discuss ports in greater detail.
Post a Comment
Read more