The medium access control (MAC) is a sublayer of the data link layer of the open system interconnections (OSI) reference model for data transmission. It is responsible for flow control and multiplexing for transmission medium. It controls the transmission of data packets via remotely shared channels. It sends data over the network interface card.MAC Layer in the OSI ModelThe Open System Interconnections (OSI) model is a layered networking framework that conceptualizes how communications should be done between heterogeneous systems. The data link layer is the second lowest layer. It is divided into two sublayers −The logical link control (LLC) sublayerThe ... Read More

PPP over ATM (PPPoA) is a data link layer protocol to transmit PPP data over ATM networks, by encapsulating PPP frames in ATM Adaptation Layer 5 (AAL 5) frames.Point − to − Point Protocol (PPP) is a data link layer protocol that is used to transmit data between two directly connected (point-to-point) computers. It is a byte – oriented protocol that is widely used in broadband communications having heavy loads and high speeds. It is also known as RFC 1661.In Asynchronous Transfer Mode (ATM) networks, the ATM Adaptation Layer (AAL) provides facilities for non-ATM based networks to connect to ATM ... Read More

In Asynchronous Transfer Mode (ATM) networks, the ATM Adaptation Layer (AAL) provides facilities for non-ATM based networks to connect to ATM network and use its services. International Telecommunication Union Telecommunication Standardization Sector (ITU-T) have defined several AALs for a range of services. The most widely deployed is ATM Adaptation Layer 5 (AAL 5).AAL 5 was originally named as Simple and Efficient Adaptation Layer (SEAL).The main functions of AAL 5 are segmentation and reassembly. It accepts higher layer packets and segment them into 48-byte ATM cells before transmission via ATM network. At the receiving end it reassembles the cells to the ... Read More

In Asynchronous Transfer Mode (ATM) networks, the ATM Adaptation Layer (AAL) provides facilities for non-ATM based networks to connect to ATM network and use its services.AAL is basically a software layer that accepts user data, which may be digitized voice, video or computer data, and makes them suitable for transmission over an ATM network. The transmissions can be of fixed or variable data rate. AAL accepts higher layer packets and segments them into fixed sized ATM cells before transmission via ATM. It also reassembles the received segments to the higher layer packets.The following diagram illustrates the function of AAL −This ... Read More

Virtual Circuit Identifier (VCID or VCI) is an identifier or label on any virtual circuit in a computer network that indicates where a data unit has to travel over the network.A virtual circuit (VC) is a technique by which data is transmitted over a packet switched network such that it seems as though there is a dedicated physical link between the source and destination systems.VCID allows the same channel to be used for simultaneous connections. The same VCID may be reused by connections having disjoint paths, allowing the network to support concurrent connections.Establishment of VC and use of VCIDThe following ... Read More

Asynchronous Transfer Mode (ATM) is a switching technique that uses time division multiplexing (TDM) for data communications. It is a network technology that supports voice, video and data communications. ATM encodes data into small fixed − sized cells so that they are suitable for TDM and transmits them over physical medium.The functional reference model of ATM is illustrated as below −FeaturesATM technology provides dynamic bandwidth that is particularly suited for bursty traffic.All data are encoded into identical cells. Hence, data transmission is simple, uniform and predictable. Uniform packet size ensures that mixed traffic is handled efficiently.The size of an ATM ... Read More

Asymmetric Digital Subscriber Line (ADSL) is a type of broadband communications technology that transmits digital data at a high bandwidth over existing phone lines to homes and businesses.ADSL protocol stack depicts the set of protocols and devices that are used along with ADSL.In order to access ADSL, a Digital Subscriber Line modem (DSL modem) is installed at the customer site. The DSL modem sends data bits over the local loop of the telephone network. The local loop is a two − wire connection between the subscriber’s house and the end office of the telephone company. The data bits are accepted ... Read More

Asymmetric Digital Subscriber Line (ADSL) is a type of broadband communications technology that transmits digital data at a high bandwidth over existing phone lines to homes and businesses.In order to access ADSL, a Digital Subscriber Line modem (DSL modem) is installed at the client side. The DSL modem sends data bits over the local loop of the telephone network. The local loop is a two – wire connection between the subscriber’s house and the end office of the telephone company. The data bits are accepted at the end office by a device called Digital Subscriber Line Access Multiplexer (DSLAM).Features of ... Read More

In computer networking and telecommunications, when a transmission unit is sent from the source to the destination, it contains both a header and the actual data to be transmitted. This actual data is called the payload. The header contains the protocol information as well as the source and destination addresses, which are required for delivery of the payload. The payload is required by the destination client.The following diagram depicts encapsulation of payload field in a data link layer frame. The data packet from the upper layer is framed by adding a header that contains the control information for data transmission, ... Read More

Network Control Protocol (NCP) is a set of protocols forming a part of Point − to − Point Protocol (PPP). PPP is a data link layer protocol that is used to transmit multiprotocol data between two directly connected (point-to-point) computers. PPP is composed of link control protocol (LCP), authentication protocol (AP) and network control protocol (NCP). NCPs are used for negotiating the parameters and facilities for the network layer. For every higher-layer protocol supported by PPP, one NCP is there.The following diagram illustrates the layer in which NCPs operate:List of NCPsSome of the NCPs are −Internet Protocol Control Protocol (IPCP) ... Read More