Frame relay is a telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame relay puts data in a variable-size unit called a frame. It checks for lesser errors as compared to other traditional forms of packet switching and hence speeds up data transmission. When an error is detected in a frame, it is simply dropped. The end points are responsible for detecting and retransmitting dropped frames. Answer option C is incorrect. Integrated Services Digital Network (ISDN) is a digital telephone/telecommunication network that carries voice, data, and video over an existing telephone network infrastructure. It requires an ISDN modem at both the ends of a transmission. ISDN is designed to provide a single interface for hooking up a telephone, fax machine, computer, etc.ISDN has two levels of service, i.e., Basic Rate Interface (BRI) and Primary Rate Interface (PRI). Answer option A is incorrect. The Point-to-Point Protocol, or PPP, is a data link protocol commonly used to establish a direct connection between two networking nodes. It can provide connection authentication, transmission encryption privacy, and compression. PPP is commonly used as a data link layer protocol for connection over synchronous and asynchronous circuits, where it has largely superseded the older, non-standard Serial Line Internet Protocol (SLIP) and telephone company mandated standards (such as Link Access Protocol, Balanced (LAPB) in the X.25 protocol suite). PPP was designed to work with numerous network layer protocols, including Internet Protocol (IP), Novell's Internetwork Packet Exchange (IPX), NBF, and AppleTalk. Answer option D is incorrect. The X.25 protocol, adopted as a standard by the Consultative Committee for International Telegraph and Telephone (CCITT), is a commonly-used network protocol. The X.25 protocol allows computers on different public networks (such as CompuServe, Tymnet, or a TCP/IP network) to communicate through an intermediary computer at the network layer level. X.25's protocols correspond closely to the data-link and physical-layer protocols defined in the Open Systems Interconnection (OSI) communication model.

In information security, security risks are considered an indicator of threats coupled with vulnerability. In other
words, security risk is a probabilistic function of a given threat agent exercising a particular vulnerability and the
impact of that risk on the organization. Security risks can be mitigated by reviewing and taking responsible
actions based on possible risks. These risks can be analyzed and measured by the risk analysis process.
Answer option B is incorrect. Security risks can never be removed completely but can be mitigated by taking
proper actions.

A dynamic packet-filtering firewall is a fourth generation firewall technology. It is also known as a stateful firewall. It tracks the state of active connections and determines which network packets are allowed to enter through the firewall. It records session information, such as IP addresses and port numbers to implement a more secure network. The dynamic packet-filtering firewall operates at Layer3, Layer4, and Layer5.
Answer option A is incorrect. A circuit-level gateway is a type of firewall that works at the session layer of the OSI model between the application layer and the transport layer of the TCP/IP stack. They monitor TCP handshaking between packets to determine whether a requested session is legitimate. Information passed to a remote computer through a circuit level gateway appears to have originated from the gateway. This is useful for hiding information about protected networks. Circuit-level gateways are relatively inexpensive and have the advantage of hiding information about the private network they protect.
Answer option C is incorrect. A proxy server firewall intercepts all messages entering and leaving the network.
The proxy server effectively hides the true network addresses.