Synchronous optical networking (SONET) is a physical layer protocol for transmitting multiple digital bit streams over optical fiber links that form the backbone of the communication networks. Packet-over-SONET (POS) is a standard that maps IP packets into SONET frames. To implement this mechanism, Point – to – Point Protocol (PPP) runs on IP routers. 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.The following diagram shows ... Read More

The data link protocols operate in the data link layer of the Open System Interconnections (OSI) model, just above the physical layer.The services provided by the data link protocols may be any of the following −Framing − The stream of bits from the physical layer are divided into data frames whose size ranges from a few hundred to a few thousand bytes. These frames are distributed to different systems, by adding a header to the frame containing the address of the sender and the receiver.Flow Control − Through flow control techniques, data is transmitted in such a way so that ... Read More

Selective repeat protocol, also called Selective Repeat ARQ (Automatic Repeat reQuest), is a data link layer protocol that uses sliding window method for reliable delivery of data frames. Here, only the erroneous or lost frames are retransmitted, while the good frames are received and buffered.It uses two windows of equal size: a sending window that stores the frames to be sent and a receiving window that stores the frames receive by the receiver. The size is half the maximum sequence number of the frame. For example, if the sequence number is from 0 – 15, the window size will be ... Read More

In data communications, when a receiver receives a message, it sends an acknowledgement back to the sender to notify it about correct receipt of the message. Cumulative acknowledgement is a process in which the receiver sends a single acknowledgement in response to a finite number of frames received. Through this, the receiver acknowledges that it has correctly received all previous frames or packets. When the sender receives an acknowledgement for frame n, it understands correct delivery of frames n – 1, n – 2 and so on.Cumulative acknowledgement is used along with sliding window protocols. It reduces the time and ... Read More

Dynamic channel allocation are schemes for allotting shared network channels to competing users in a dynamic manner as per their requirements. The users may be base stations, access points or terminal equipment which are allotted channels from a central pool. There are a number of methods for dynamic channel allocation. The key assumptions of these methods are −Independent Traffic − It is assumed that the users are independent of each other, i.e. each user has to send or receive data which is independent of the data transmission of the other users in the network system. Each user has a program ... Read More

When there are more than one user who desire to access a shared network channel, an algorithm is deployed for channel allocation among the competing users. Dynamic channel allocation encompasses the channel allocation schemes where channels are allotted to users dynamically as per their requirements, from a central pool.Working PrincipleIn dynamic channel allocation schemes, frequency channels are not permanently allotted to any user. Channels are assigned to the user as needed depending upon the network environment. The available channels are kept in a queue or a spool. The allocation of the channels is temporary. Distribution of the channels to the ... Read More

When there is more than one user who desires to access a shared network channel, an algorithm is deployed for channel allocation among the competing users. Static channel allocation is a traditional method of channel allocation in which a fixed portion of the frequency channel is allotted to each user, who may be base stations, access points or terminal equipment. This scheme is also referred to as fixed channel allocation or fixed channel assignment.Working PrincipleSuppose that there are N competing users. Here, the total bandwidth is divided into N discrete channels using frequency division multiplexing (FDM). In most cases, the ... Read More

When there are more than one user who desire to access a shared network channel, an algorithm is deployed for channel allocation among the competing users. The network channel may be a single cable or optical fiber connecting multiple nodes, or a portion of the wireless spectrum. Channel allocation algorithms allocate the wired channels and bandwidths to the users, who may be base stations, access points or terminal equipment.Channel Allocation SchemesChannel Allocation may be done using two schemes −Static Channel AllocationDynamic Channel AllocationStatic Channel AllocationIn static channel allocation scheme, a fixed portion of the frequency channel is allotted to each ... Read More

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