Saturday, February 8, 2020

DCN - Application Layer Introduction

The application layer is the highest layer in the OSI and TCP / IP layer model. This layer is found in both models in layers due to its importance, for interacting with the user and user applications. This layer is intended for applications participating in the communication system.

The user may or may not interact directly with the applications. The application layer is where real communication begins and is reflected. Because this layer is at the top of the layer stack, it does not serve any other layer. The application layer takes Transport instructions and all the layers below to connect your data or transfer it to the remote host.

When the application layer protocol wants to communicate with its peer application layer protocol on a remote host, it delivers data or information to the transport layer. The transport layer does the rest with all the layers beneath it.

There is ambiguity in understanding the application layer and its protocol. Not all user apps can be placed in the application layer. Except for those applications that interact with the communication system. For example, program design or text editor cannot be considered application layer programs.

On the other hand, when we use a web browser, we actually use Hypertext Transfer Protocol (HTTP) to interact with the network. HTTP is the application layer protocol.

Another example is File Transfer Protocol, which helps the user to transfer text or binary files over the network. User can use this protocol in graphical user interface-based programs like FileZilla or CuteFTP and the same user can use FTP in command line mode.

Therefore, no matter which program you use, it is the protocol that is considered in the application layer used by this program. DNS is a protocol that helps a user’s application protocols, such as HTTP, to function.

Friday, December 6, 2019


The fiber distributed data interface (FDDI), which is a standard for optical data communication used in long distance networks, provides connection to fiber optic lines up to 200 kilometers at a speed of 100 megabits per second (Mbps) .

The fiber distributed data interface is standard for transferring data on a local network. The optical fibers are used as the standard primary physical medium, although it is then determined that they use copper cables, in which case they can be called CDDI, standardized as TP-PMD and also called TP-DDI.

FDDI is used as the main pillar to connect copper LAN as shown in the figure. The FDDI cable consists of two fibrous rings, one of them clockwise and the other counterclockwise. A set of ANSI protocols to send digital data through a fiber optic cable. FDDI networks are token pass networks and support data rates of 100 Mbps (100 million bits) per second. FDDI networks are generally used as the basis for broadband networks.

Although the FDDI logical structure is a ring-based token network, it did not use the IEEE 802.5 token loop protocol as the basis for it; instead, its protocol was derived from the IEEE 802.4 token bus protocol.


WiMAX (global microwave interoperability) is a set of wireless broadband standards based on the IEEE 802.16 set of standards, which provides multiple physical layer (PHY) and media access control (MAC) options.

According to some estimates, the cost of existing subscriber equipment is around $ 300, almost double the price of WiFi devices, cables and DSL customer service. On the platform, it is estimated that it will take a total of $ 3 billion to establish a national WiMAX network in the United States.

Wi-Fi generally provides access to the local network for a few hundred feet at speeds of up to 54 Mbps, and a single WiMAX antenna range is expected to reach 40 miles at speeds of 70 Mbps or more. As such, WiMAX can provide the basic Internet connection necessary to service local Wi-Fi networks.

The WiMAX architecture developed by the WiMAX model support is a unified network architecture to support fixed, nomadic and mobile operations. Communication service network, CSN: This part of the WiMAX network provides IP connectivity and all the main functions of the IP network.

Static WiMAX works in the 2.5 GHz and 3.5 GHz frequency bands, which require a license, in addition to the 5.8 GHz frequency band without a license. WiMAX Portable, also called IEEE 802.16e, allows the client's mobile devices to connect to the Internet.


The Layer Two Tunnel Protocol (L2TP) is a tunnel protocol that is used to support virtual private networks (VPNs) or as part of the provision of services by Internet service providers. It does not provide any encryption or confidentiality in itself.

The Layer Two Tunnel Protocol (L2TP) protocol is designed on all modern operating systems and devices that support VPN. ... alone, L2TP does not provide any encryption or confidentiality for the traffic it is going through, so it is generally applied using an IPsec Authentication Kit (L2TP / IPsec).

L2TP generally uses the authentication protocol, IPSec (Internet Protocol Security). Use strong encryption and documentation. IPSec gives you a final advantage over some of the most commonly used protocols such as PPTP. The protocol uses UDP ports 1701. L2TP is the VPN protocol that does not provide encryption or protection against traffic passing through the connection. For this reason, it is usually combined with IPSec, which is an encryption protocol.

Layer Two Tunneling Protocol (L2TP) is a computer network protocol that the ISP uses to enable virtual private network (VPN) operations. L2TP is similar to the data link layer protocol in the OSI reference model, but in reality it is a session layer protocol.

Star LAN

A star topology is a local area network (LAN) topology in which all nodes are individually connected to a central connection point, such as a hub or switch. The star takes more than one cable as a bus, but the benefit is that if a cable fails, only one node will fall.

A local network can operate as a few or two users (for example, in a small office network) or several hundred users in a larger office. LANs consist of cables, switches, routers and other components that allow users to connect to internal servers, websites and other local networks through broadband networks.

Asterisk is an application of the hub distribution model in computer networks. In the stellar network, each host is connected to a central hub. In its simplest form, a central hub acts as a channel for transmitting messages. The stellar network is one of the most common computer network topologies.

A stellar network is a local area network (LAN) where all nodes (workstations or other devices) are connected directly to a shared central computer. Each workstation is indirectly connected to each other through the mainframe. In some star networks, the central computer can also act as a workstation.


Link Layer Discovery Protocol (LLDP) is a neutral link layer protocol for the provider that network devices use to advertise their identity, capabilities and neighbors in a local IEEE 802 based network, essentially wired Ethernet.

To support non-Cisco devices and allow interworking between other devices, the adapter supports the IEEE 802.1AB link layer discovery (LLDP) protocol. LLDPis is a neighbor discovery protocol that is used for network devices to advertise information to other devices on the network.

LLDP is enabled by default on all supported interfaces to send and receive LLDP packets. The frame contains the MAC address of the device as the multicast address that is not forwarded outside the network, assuming compliance with 802.1D. LLDP supports a set of features that it uses to know information about neighboring devices. These attributes have a specific format known as Type-Length-Value (TLV). Devices that support LLDP can use TLV to receive and send information to their neighbors.

LLDP for media endpoint devices (LLDP-MED) is an LLDP enhancement that works between endpoint devices such as IP phones and network devices as adapters. It specifically provides support for Voice over Internet Protocol (VoIP) applications and provides additional TLVs. LLDP-MED below is compatible with TLV: LLDP-MED TLV capabilities.


LocalTalk is a specific application for the physical layer of Apple Computer's AppleTalk network system. LocalTalk assigns a system of shielded twisted pair cables, connected to future automatic cord transmitters, operating at 230.4 kbit / s. CSMA / CA was implemented as a multiple random access method.

Apple's previous LAN access method uses twisted pair cables at 230,400 bps. It runs under AppleTalk and uses a Daisy Chain topology that can connect up to 32 devices at a distance of 1,000 feet. Third-party products allowed you to connect to the bus, the passive star and the active star topology. Apple's Apple PC Card Card allows the computer to access the AppleTalk network.

LocalTalk consists of an integrated console, with cables and expansion cards that are sometimes required. You have enabled the chrysanthemum sequence, which connects a series of devices to each other using LocalTalk cables.

Farallon Computing introduced a cheaper localTalk difference called PhoneNet. Install PhoneNet on standard telephone cables and existing connectors with unprotected twisted cables. LocalTalk uses expensive twisted wire pairs. PhoneNet allowed users to divide their residential telephone connections into two parts, one going to the telephone jack and the other to an Apple or Macintosh computer.


The complete form of DCAP is Link Switching Client Access Protocol. It is the data link layer protocol used between workstations and routers to transfer SNA / NetBIOS traffic through TCP sessions.

DLSw data link switching is a means of the System Network Engineering (SNA) tunnel and NetBIOS traffic through an IP network. Before developing DLSw, SNA and NetBIOS traffic was transferred through Source-Route Bridging (SRB), which is a transport protocol in token loop environments.

In a large network, DCAP addresses the problem of scalability by significantly reducing the number of peers that connect to the central site router. Workstations (DCAP clients) and the router (DCAP server) work in client / server relationships. Workstations are connected to a DCAP server. The DCAP server has a peer connection to the central site router.

DLSw uses the switching protocol to switch instead of SRB between routers to create DLSw peer connections, locate resources, redirect data, manage flow control and error recovery. Routers are called data link switches.

The Clien tAccess Protocol data hierarchy provides a hierarchical structure to solve scalability problems. All workstations are clients of the router and not their counterparts of the router. This creates the client / server model. It also provides a more efficient protocol between the workstation and the router.