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The term used by Cisco to refer to a variety of security tools that help prevent various attacks, including antivirus, anti-phishing, and anti-spam.
connection establishment
The process by which a connection-oriented protocol creates a connection. With TCP, a connection is established by a three-way transmission of TCP segments.
error detection
The process of discovering whether or not a data-link level frame was changed during transmission. This process typically uses a Frame Check Sequence (FCS) field in the data-link trailer.
error recovery
The process of noticing when some transmitted data was not successfully received and resending the data until it is successfully received.
A device that forwards packets between the less secure and more secure parts fo the network, applying rules that determine which packets are allowed to pass, and which are not.
flow control
The process of regulating the amount of data sent by a sending computer toward a receiving computer. Several flow control mechanisms exist, including TCP flow control, which uses windowing.
forward acknowledgment
A process used by protocols that do error recovery in which the number that acknowledges data lists the next data that should be sent, not the last data that was successfully received.
Hypertext Transfer Protocol. The protocol used by web browsers and web servers to transfer files, such as text and graphic files.
Intusion Detection System (IDS)
A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reporting the threats.
Intrusion Prevention System (IPS)
A security function that examines more complex traffic patterns against a list of both known attack signatures and general characteristics of how attacks may be carried out, rating each perceived threat and reacting to prevent the more sinificant threats.
ordered data transfer
A networking function, included in TCP, in which the protocol defines how the sending host should number the data transmitted, defines how the receiving device should attempt to reorder the data if it arrrives out of order, and specifies to discard the data if it cannot be delivered in order.
In TCP and UDP, a number that is used to uniquelyidentify the application process that either sent (source port) or should receive (destination port) data. In LAN switching, another term for switch interface.
Positive Acknowledgment and Retransmission (PAR)
A generic reference to how the error recovery feature works in many protocols, including TCP, in which the receiver must send an acknowlegment that either implies that the data was (positively) received, or send an acknowledgement that implies that some data was lost, so the sender can then resend the lost data.
In TCP, a term used to describe a TCP header and its encapsulated data (also called an L4PDU). ALso in TCP, the process of accepting a large chunk of data from the application layer and breaking it into smaller pieces that fit into TCP segments. In Ethernet, a segment is either a single Ethernet cable or a single collision domain (no matter how many cables are used).
sliding windows
For protocols such as TCP that allow the receiving device to dictate the amount of data the sender can send before receiving an acknowledgment - a concept called a window - a reference to the fact that the mechanism to grant future windows is typically just a number that grows upwards slowly after each acknowledgment, sliding upward.
Universal Resource Locator. A standard for how to refer to any piece of information retrievable via a TCP/IP network, most notably used to identify web pages. For example, is a URL that identifies the protocol (HTTP), hostname (, and web page (/univerce).
virtual private network (VPN)
The process of securing communication between two devices whose packets pass over some public and unsecured network, typically the Internet. VPNs encrypt packets so that the communication is private and authenticate the identity of the endpoints.
Voice over IP. The transport of voice traffice inside IP packets over an IP network.
web server
Software, running on some computer, that stores web pages and sends those web pages to web clients (web browsers) that request the web pages.
User Datagram Protocol. Connectionless transport layer protocol n the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without acknowledgments or guaranteed delivery.
Transmission Control Protocol. A connection-oriented transport layer TCP/IP protocol that provides reliable data transmission.
Transmission COntrol Protocol/Internet Protocol. A common name for the suite of protocols developed by the U.S. Department of Defense in the 1970s to support the construction of worldwide internetworks. TCP and IP are the two best-known protocols in the suite.
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