Wireless Communication Interview Preparation Guide

The following are the disadvantages of Symmetric Cryptosystems:

- Key transportation is one disadvantage of Symmetric Cryptosystems. From the sending system to the receiving system the secret key is to be transmitted before the actual message transmission. Electronic communication, in every means is insecure as it is not guarantee that no tapping communication channels can be tapped. Personal exchanging of key exchange is the only source.

- repudiate digital signatures can not be provided

A digital certificate is a credential which validates the certificate owner’s identity. The information provided by the digital certificate is known as ‘the subject distinguished name’. Certificate Authority issues the digital certificates to the users or the organizations. The trust in the certificate as a valid credential is provided as the foundation by the Certificate Authority.

Public Key Infrastructure: A set of hardware, software, people, policies and procedures comprises the Public Key Infrastructure (PKI) and digital certificates are revoked. The arrangement of public key binding with respective of identification of users by means of a Certificate Authority , is done in PKI. Every certificate authority should have a unique user identity. The registration and issuance process that is depending on the level of assurance is involved in binding, which may be carried out be software at a CA. The binding assurance portrayed by PKI is known as Registration Authority. The public key certificates issued by the CA are comprised unforgettable user identity, public key and their binding, validity conditions and other attributes.

Challenge-Handshake Authentication Protocol authenticates to an authenticating entity of a user or network. The entity can be an Internet access provider. CHAP is used by Point-to-Point Protocol that servers for the validation of identifying of remote clients. The identity of the client is verified by CHAP periodically with the use of a three-way handshake. This situation occurs when an initial link is established and maybe repeated after at any time. The shared secret is the base for verification. CHAP protection to play back attack by the peer. This is done by using an incrementally changing identifier and of a variable challenge-value. Both client and server need to know about the plain text of secret which uses CHAP.

PPTP is one of the methods to implement Virtual Private Networks. Confidentiality or encryption does not provided by PPTP. The reliability of PPTP is being tunneled for the purpose of providing privacy. PPTP works by sending Point-to-Point Protocol to the peer with the Generic Encapsulation protocol. Because of its easy way of configuration, it is most popular protocol used in VPNs. It was the first protocol for VPNs and was supported by Dial-up network of Microsoft.

The user creates a voluntary tunnel model. This model is typically uses a L2TP enabled client. An L2TP packet is sent by user to the Internet Service Provider which will in turn forward them on to LNS. The support of L2TP support is not needed by ISP. The L2TP tunnel initiator resides on the same system effectively playing as a remote client.

The tunnel creation in compulsory tunnel, no action from the user and without allowing the user any choice is performed. Internet service provider access concentrator receives a point-to-point protocol packets from the user. The encapsulation of packets in L2TP and sending them through a tunnel to the L2TP network server is performed by the ISP. It is mandatory that the ISP is L2TP-capable.

The following is the process for Tcp connection:

1. As connection is made by synchronizing sender and receiver and the OS is informed about the connection establishment.

2. Sender starts sending information and gets acknowledged. Soon after the sender sends the data, a timer is started.

3. When the sender is not received any acknowledgement ever after exceeding the timer’s limit, the data is transmitted.

4. If windowing occurs, buffer on the receiver is full, then a stop signal is sent by the sender and stops sending information

5. Soon after processing all data, a go signal is sent by the sender, followed by transmitting data again.

Internet Control Message Protocol: This protocol is used for while checking the connectivity using ping command

Address Resolution Protocol: This protocol is used to know about the properties of TCP/IP. For example, to know other system MAC addresses.

Multicast: Communication between single sender and a list of select recipients in a network.

Broadcast: To send messages to all the recipients simultaneously in a network.

For Voice transfer, SCO (Synchronous Connection Oriented) links are used for good synchronization and reliability.