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Showing posts from May, 2007

LLC (Logical Link Control) IEEE 802.2

In IEEE's version of Ethernet, the top sublayer of Data link layer is Logical Link Control(LLC). LLC's function is performed in software. LLC defines how to multiplex multiple network layer protocols in the data link layer frames. Logical Link Control sublayer performs its multiplexing by using Service Access Point (SAP) identifiers. Logical Link Control sublayer is defined under IEEE 802.2. There are two types of IEEE 802.2 frames. They are: Service Access Point(SAP) Subnetwork Access Protocol(SNAP) Major Duties of Logical Link Control(LLC) Multiplex multiple network layer protocols into frames Sequencing and flow control IEEE 802.2 uses SAP(Service Access Point) or SNAP(Subnetwork Access Protocol) field to differentiate between encapsulated layer 3 payloads. IEEE 802.2 (LLC) concerns Ethernet, Token Ring, and FDDI. To read more about MAC sublayer, visit the link below. MAC Sublayer IEEE 802.3 Though sequencing and flow control can be done in Logical Lin

Data Link Layer Provide Physical Addresses

The second layer in the OSI Reference model is the Data Link Layer. The data link layer is responsible for providing physical addresses for the devices connected to the network. The physical address is also called hardware address because it is built-in address (not a logical address like IP address). The data link layer is responsible for taking bits from the Physical layer and convert them to frames. All communications done in Data link layer is in the form of frames. Sub division in Data-link Layer In IEEE version of Ethernet, Data link layer is subdivided in to: 1. Logical Link Control ( LLC ) 2. Media Access Control ( MAC ) Data-link Layer devices Networking devices functioning at Data link layer are: Switch NIC Bridge Responsibilities of Data Link Layer Define Physical Addresses Communication in the same network in form of Frames Define hardware topology of the network Major Data Link layer Protocols CIF : Cells in Frames Ethernet FDDI : Fiber D

Physical layer

The physical layer is the first layer in the OSI model which deals with the physical transmission medium. The data transferred via the physical layer is in the form of electrical signals. In a real life, we can treat the physical layer as the road where the vehicles are passing. Because the road is the one which is carrying the vehicles and linking the cities. Like that the physical layer is transmitting the data signal in the form of electrical signal and connecting nodes. The major cables using in physical layer are: 1. Coaxial cable 2. Twisted pair cable 3. Optical fiber cable Devices working in physical layer: 1. Internet gateway 2. Hub 3. Repeater The major functions and services performed by the Physical Layer are: 1. Bit-by-bit delivery 2. Modulation 3. Encoding and Signaling: 4. Bit synchronization 5. Physical network Topology In Physical Layer data is transmitting in the form of an electric pulse and the cables are responsible for the safe deli

OSI Reference Model

The International Organization for Standardization (ISO) developed a seven-layer model called Open Systems Interconnection (OSI)Reference Model to help vendors and network experts to learn how data is transferred between networking devices. OSI Reference Model helps networking device manufacturers to implement new network standards and policies. OSI Reference Model helps network administrators to reduce the complexity of networks and makes it easy to troubleshoot networking issues. Seven Layers of OSI Reference Model There are seven layers in the OSI Reference Model and each layer has a specific role in data communication. Seven layers of the OSI reference model are listed below. Physical layer Data link layer Network layer Transport layer Session layer Presentation layer Application layer What is The Need of OSI Reference Model Prior to the introduction of Open System Interconnection (OSI) Reference Model, each vendor has their own manufacturing sta

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Alex George
Alex George has Engineering graduation in Computer Science and an MBA in Finance. He had been working as a senior Network Engineer for ten years. His specialization is in Cisco products. Traveling is one of his hobbies and visited various places as part of his onsite work. He visited different places as part of his onsite work like New York, Dubai, London, etc. Right now Alex is a director of one of the leading career development firms in India, which trains students for UPSC, SSC, and PSC examinations. He guides a lot of students to get selection for various prestigious institutions like CBI, Income Tax Department, etc. Alex George is a stock market investor and a very active intraday trader. Engineering Background: He has a B.Tech in Computer Science and Engineering and passed different network and security courses like CCNA, CCNP (Security), CEH, and various Microsoft certifications. Finance Background: Alex has an MBA in Finance. He is an active intraday trader and a Share Market Investor. Webmaster Skills: Alex is a blogger since 2004. He has a working knowledge of HTML, CSS, PHP, and JavaScrip.