Table of Contents Link to heading
- Communication Fundamentals
- Rule Establishment
- Message Encoding
- Message Formatting and Encapsulation
- Message Segmentation
- Message Timing
- Message Delivery Options
Communication Fundamentals Link to heading
A network can be as complex as devices connected across the Internet, or as simple as two computers directly connected to one another with a single cable, and anything in-between. Networks can vary in size, shape, and function. However, simply having a wired or wireless physical connection between end devices is not enough to enable communication. For communication to occur, devices must know “how” to communicate.
People exchange ideas using many different communication methods. However, regardless of the method chosen, all communication methods have three elements in common.
- The message source, or sender. The source are people, or electronic devices, that need to send a message to other individuals or devices.
- The message destination, or receiver, of the message. The destination receives the message and interprets it.
- A channel, consists of the media that provides the pathway over which the message travels from source to destination.
Communication begins with a message, or information, that must be sent from a source to a destination. The sending of this message, whether by face-to-face communication or over a network, is governed by rules called protocols. These protocols are specific to the type of communication method occurring.
Rule Establishment Link to heading
Before communicating with one another, individuals must use established rules or agreements to govern the conversation. These rules, or protocols, must be followed in order for the message to be successfully delivered and understood.
Protocols must account for the following requirements:
- An identified sender and receiver
- Common language and grammar
- Speed and timing of delivery
- Confirmation or acknowledgement requirements
The protocols used in network communications share many of these fundamental traits. In addition to identifying the source and destination, computer and network protocols define the details of how a message is transmitted across a network.
Common computer protocols include the following requirements:
- Message Encoding
- Message Formatting and Encapsulation
- Message Segmentation
- Message Timing
- Message Delivery Options
Message Encoding Link to heading
Encoding is the process of converting information into another acceptable form, for transmission
Encoding between hosts must be in an appropriate format for the medium. Messages sent across the network are first converted into bits by the sending host. Each bit is converted to patterns of electrical, light, or electromagnetic energy and carried on the medium.
Decoding reverses this process in order to interpret the information.
The destination host receives and decodes the signals in order to interpret the message.
Message Formatting and Encapsulation Link to heading
The format (structure) of a message depends on the type of message and the channel used to deliver the message.
A message sent over a computer network follows specific format rules for it to be delivered and processed. Just as a letter is encapsulated in an envelope for delivery, so too are computer messages. Each computer message is encapsulated in a specific format, called a frame, before it is sent over the network. A frame, acting like an envelope, provides the address of the destination and the address of the source host.
The format and contents of a frame are determined by the type of message being sent and the channel over which it is communicated. Messages that are not correctly formatted are not successfully delivered to or processed by the destination host.
Message Segmentation Link to heading
In theory, a single communication, such as a music video or an email message, could be sent across a network from a source to a destination as one massive, uninterrupted stream of bits. If messages were actually transmitted in this manner, it would mean that no other device would be able to send or receive messages on the same network while this data transfer was in progress. These large streams of data would result in significant delays. Further, if a link in the interconnected network infrastructure failed during the transmission, the complete message would be lost and have to be retransmitted in full.
A better approach is to divide the data into smaller, more manageable pieces to send over the network. This division of the data stream into smaller pieces is called segmentation.
Advantages Link to heading
- By sending smaller individual pieces from source to destination, many
different conversations can be interleaved on the network, called
multiplexing.
- Multiplexing: the segment of more than two messages shuffle into each other and share the medium.
- Segmentation can increase the efficiency of network communications. If a part of the message fails to make it to the destination, due to failure in the network or network congestion, only the missing parts need to be retransmitted.
Disadvantages Link to heading
The challenge to using segmentation and multiplexing to transmit messages across a network is the level of complexity that is added to the process. Imagine if you had to send a 100-page letter, but each envelope would only hold one page. The process of addressing, labeling, sending, receiving, and opening the entire 100 envelopes would be time-consuming for both the sender and the recipient.
In network communications, each segment of the message must go through a similar process to ensure that it gets to the correct destination and can be reassembled into the content of the original message.
Message Timing Link to heading
affects how well a message is received and understood.
Access Method Link to heading
determines when someone is able to send a message.
If two people talk at the same time, a collision of information occurs and it is necessary for the two to back off and start again. Likewise, it is necessary for computers to define an access method for hosts on a network to know when to begin sending messages and how to respond when collisions occur.
For example, when a device wants to transmit on a wireless LAN, it is necessary for the WLAN network interface card to determine whether the wireless medium is available.
Flow Control Link to heading
prevents packets from being dropped because too much data is being sent too quickly.
Timing affects how much information can be sent and the speed that it can be delivered. If one person speaks too quickly, it is difficult for the other person to hear and understand the message. In network communication, source and destination hosts use flow control methods to negotiate correct timing for successful communication.
Response Timeout Link to heading
specifies how long to wait for responses and what action to take if a response timeout occurs.
If a person asks a question and does not hear a response within an acceptable amount of time, the person assumes that no answer is coming and reacts accordingly. The person may repeat the question, or may go on with the conversation. Hosts on the network also have rules that specify how long to wait for responses and what action to take if a response timeout occurs.
Message Delivery Options Link to heading
A message can be sent to a single individual, to a group at the same time, or even to all people in the same area.
There are also times when the sender of a message needs to be sure that the message is delivered successfully to the destination. In these cases, it is necessary for the recipient to return an acknowledgment to the sender. If no acknowledgement is required, the delivery option is referred to as unacknowledged.
Unicast (one-to-one) Link to heading
Information is being transmitted to a single host or destination.
Multicast (one-to-many) Link to heading
Information is being transmitted to a group of hosts or destinations simultaneously.
Broadcast (one-to-all) Link to heading
Information is being transmitted to all hosts simultaneously.
Some protocols use a special multicast message that is sent to all devices, making it essentially the same as a broadcast.
Hosts may be required to acknowledge the receipt of some messages while not needing to acknowledge others.