It is equally acceptable for the protocol to be deduced in this manner or specified explicitly. Assuming you previously used getaddrinfo to construct the remote address then the required values can be obtained from the addrinfo structure:. As noted previously, the server socket must be bound to a local address before it can listen for inbound datagrams. This should be done using the bind function:.
The first argument is the socket descriptor. The second and third arguments are the local address and its length. If the local address was constructed using getaddrinfo then the memory occupied by the address list can now be released:. If the address list has been searched or filtered then take care that it is the head of the list that is released, not the address that you have chosen to use.
Datagrams can be received using any function that is capable of reading from a file descriptor, however if you are listening for unsolicited datagrams as in this example then you will normally want to know where each datagram originated from so that it can be replied to.
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This information is provided by the functions recvfrom and recvmsg. Of these recvmsg is the more flexible option, but at the cost of a significantly more complex interface. Details for each function are given below. Regardless of which function you choose you will need to supply a buffer to receive the data.
If this is too small to accommodate a complete datagram then any excess is discarded. That means you need not be concerned about tracking datagram boundaries, because the first byte returned by a read operation will always be the start of a datagram. However it does raise two issues: how the buffer size should be chosen, and how any overflow can be detected. UDP-based application-layer protocols often limit the size of datagram that can be sent in order to provide an solution to the first issue.
For DHCP the limit defaults to bytes, but a larger value can be negotiated if both parties are willing to support it. In the absence of such guidance it is necessary to consider what the transport, network and link layer protocols are likely to support. However, the largest payload that an implementation is required to support is bytes for IPv4 and bytes for IPv6. On an Ethernet with the standard MTU of bytes, the largest payload that can be sent without fragmentation is bytes.
On this basis, bytes would be a reasonable choice if you have no reason to believe that a larger buffer is needed or that a smaller buffer would suffice. Alternatively, truncation can be detected when using any of the available functions by providing a buffer that is one byte longer than the largest payload that you actually wish to receive, then interpreting a full buffer as a truncated datagram.
To call recvfrom you need a buffer for the datagram and a buffer for the remote address:. The fourth argument is for specifying flags which modify the behaviour of recvfrom , none of which are needed in this example. The value returned by recvfrom is the number of bytes received, or -1 if there was an error. Truncation is detected in this example using the technique described above of providing a slightly over-sized datagram buffer. To call recvmsg , in addition to buffers for the datagram and remote address you must also construct an iovec array and a msghdr structure:.
In this example the entire payload is stored in a single buffer, therefore only one array element is needed.
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The msghdr structure exists to bring the number of arguments to recvmsg and sendmsg down to a managable number. On entry to recvmsg it specifies where the source address, the datagram payload and any ancillary data should be stored. In this example no ancillary data has been requested, therefore no provision has been made for receiving any. Instead you must pass them using the third argument to recvmsg which is zero in this example. When listening for a reply to a datagram that you have sent then three of the four steps listed above may be omitted:.
When we understand something, we are able to attach meaning by connecting information to previous experiences. Through the process of comparing new information with old information, we may also update or revise particular schemata if we find the new information relevant and credible. After all, we can move something to our long-term memory by repetition and then later recall it without ever having understood it. I remember earning perfect scores on exams in my anatomy class in college because I was able to memorize and recall, for example, all the organs in the digestive system.
In fact, I might still be able to do that now over a decade later. Our ability to recall information is dependent on some of the physiological limits of how memory works.
Overall, our memories are known to be fallible. We forget about half of what we hear immediately after hearing it, recall 35 percent after eight hours, and recall 20 percent after a day. Our sensory storage is very large in terms of capacity but limited in terms of length of storage. We can hold large amounts of unsorted visual information but only for about a tenth of a second.
By comparison, we can hold large amounts of unsorted auditory information for longer—up to four seconds. As stimuli are organized and interpreted, they make their way to short-term memory where they either expire and are forgotten or are transferred to long-term memory. Short-term memory A mental storage capability that can retain stimuli for twenty seconds to one minute. Long-term memory A mental storage capability to which stimuli in short-term memory can be transferred if they are connected to existing schema.
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Once there, they can be stored indefinitely. Working memory is a temporarily accessed memory storage space that is activated during times of high cognitive demand.
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When using working memory, we can temporarily store information and process and use it at the same time. This is different from our typical memory function in that information usually has to make it to long-term memory before we can call it back up to apply to a current situation.
People with good working memories are able to keep recent information in mind and process it and apply it to other incoming information. This can be very useful during high-stress situations. A person in control of a command center like the White House Situation Room should have a good working memory in order to take in, organize, evaluate, and then immediately use new information instead of having to wait for that information to make it to long-term memory and then be retrieved and used.
Some people have excellent memories and recall abilities and can tell you a very accurate story from many years earlier during a situation in which they should actually be listening and not showing off their recall abilities. Recall is an important part of the listening process because it is most often used to assess listening abilities and effectiveness. Many quizzes and tests in school are based on recall and are often used to assess how well students comprehended information presented in class, which is seen as an indication of how well they listened.
When recall is our only goal, we excel at it. Experiments have found that people can memorize and later recall a set of faces and names with near percent recall when sitting in a quiet lab and asked to do so. Even in interpersonal encounters, we rely on recall to test whether or not someone was listening.
Imagine that Azam is talking to his friend Belle, who is sitting across from him in a restaurant booth. When we evaluate something, we make judgments about its credibility, completeness, and worth. Studying communication is a great way to build your critical thinking skills, because you learn much more about the taken-for-granted aspects of how communication works, which gives you tools to analyze and critique messages, senders, and contexts.
Critical thinking and listening skills also help you take a more proactive role in the communication process rather than being a passive receiver of messages that may not be credible, complete, or worthwhile. One danger within the evaluation stage of listening is to focus your evaluative lenses more on the speaker than the message. This can quickly become a barrier to effective listening if we begin to prejudge a speaker based on his or her identity or characteristics rather than on the content of his or her message.
We will learn more about how to avoid slipping into a person-centered rather than message-centered evaluative stance later in the chapter. Responding entails sending verbal and nonverbal messages that indicate attentiveness and understanding or a lack thereof. From our earlier discussion of the communication model, you may be able to connect this part of the listening process to feedback. Later, we will learn more specifics about how to encode and decode the verbal and nonverbal cues sent during the responding stage, but we all know from experience some signs that indicate whether a person is paying attention and understanding a message or not.
We send verbal and nonverbal feedback while another person is talking and after they are done. Back-channel cues are generally a form of positive feedback that indicates others are actively listening. If another person is looking away, fidgeting, texting, or turned away, we will likely interpret those responses negatively. Listeners respond to speakers nonverbally during a message using back-channel cues and verbally after a message using paraphrasing and clarifying questions.
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Paraphrasing is a responding behavior that can also show that you understand what was communicated. When you paraphrase A message that is rephrased in your own words. It is often a good idea to pair a paraphrase with a question to keep a conversation flowing. Is that right? Paraphrasing is also a good tool to use in computer-mediated communication, especially since miscommunication can occur due to a lack of nonverbal and other contextual cues.
Understanding how listening works provides the foundation we need to explore why we listen, including various types and styles of listening. In general, listening helps us achieve all the communication goals physical, instrumental, relational, and identity that we learned about in Chapter 1 "Introduction to Communication Studies". Listening is also important in academic, professional, and personal contexts. Wendy S. Zabava and Andrew D. In general, students with high scores for listening ability have greater academic achievement.