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Non-Real Time Variable Bit Rate - nrt-VBR
Non-Real Time Variable Bit Rate is an ATM service category that is similar to rt-VBR but is used for applications with bursty transmission characteristics that tolerate high cell delay, but require low cell loss.
Registered Ports are software ports in the range 1024 to 49151 and the Internet Assigned Numbers Authority also manages and registers these ports. Less common TCP IP applications use these port numbers.
A repeater is a physical layer device used to connect two or more separate physical cable segments together, making it act like one long cable. A repeater is a simple hardware device that regenerates electrical signals, sending all frames from one physical cable segment to another.
The RFC 4291 standard specifies rules regarding prefix notation for IPv6.
The RFC 5952 standard specifies key requirements for the representation of IPv6 addresses. The format should be followed by people and systems when representing IPv6 addresses as text, but systems should be able to accept and handle any legitimate IPv6 format.
Routing Information Protocol (RIP)
Routing Information Protocol (RIP) is a routing protocol by which routers in one network learn how to communicate with routers in another network.
Regional Internet Registries (RIRs)
Regional Internet Registries (RIRs) are regional organizations overseeing IP address assignment within a particular region of the world. Currently, five RIRs exist.
Route summarization is also known as route aggregation. It combines a group of network numbers into a single route and makes routing traffic across the network and the Internet much more efficient because it involves fewer routes in the routing table and fewer routes to advertise.
A router is a Layer 3 device that allows communication between separate broadcast domains or networks. In order to forward data from one network to another, routers must know how to reach other networks. A router stores network location information in a routing table. Each entry in the routing table includes the destination network number and indicates how the destination network may be reached by specifying which port or interface on the router should be used and what 'Next Hop' address should be used. When a router receives a packet, the router uses the data's Layer 3 destination address and the routing table to make intelligent decisions on where to send the packet next. Routers can read, but cannot modify, Layer 3 addresses. Routers change Layer 2 addresses in data whenever they route data.
The routing table is where a router stores network location information including all possible destination network numbers and how to reach them. Each entry in the routing table includes the destination network number, the next hop along the way to the destination network, and which port or interface on the router should be used to reach the next hop.
A segment is one unit of data encapsulated at Layer 4, or the Transport Layer. Each segment is divided into two parts, a header followed by data. The segment header contains the data's destination port number, which indicates which application layer protocol should be used to process the data on the receiving computer. It also specifies a source port number, which uniquely identifies the connection on the sending side, allowing the receiving computer to carry on multiple sessions with the sending computer without intermixing the data.
A service provider is a business such as a telephone company that provides WAN carrier network services to other businesses. Also called WAN service providers, telcos, WAN carriers, carriers.
Session Layer/Layer 5
In the OSI Reference Model, Layer 5 is the Session Layer. The Session Layer establishes, manages, and ends the connections or sessions between the applications on the communicating computers. For example, a Web conferencing application has to maintain separate sessions for each user participating in the conference. The server runs one conference application, but tracks each session individually.
A shared bus is a physical network topology or layout in which multiple devices are connected to the same physical wire or cable. When one device transmits data, all other devices on the shared bus receive it.
The Simple Mail Transfer Protocol (SMTP) is the most popular protocol for sending electronic mail on the Internet.
Software ports are specific to the Transport Layer, and are used to route data to the appropriate Application Layer protocol and ultimately the correct application program.
Sustainable Cell Rate (SCR)
Sustainable Cell Rate (SCR) is the ATM traffic descriptor for the maximum average cell transfer rate over an extended period of time.
Synchronous Digital Hierarchy (SDH)
Synchronous Digital Hierarchy (SDH) is a standard that defines a basic frame format and a hierarchy of signaling speeds for use on a fiber optic line. SDH operates at Layer 1 or the Physical Layer and is available outside of North America and Japan.
Synchronous Optical Network (SONET)
Synchronous Optical Network (SONET) is a standard that defines a basic frame format and a hierarchy of signaling speeds for use on a fiber optic line. SONET operates at Layer 1 or the Physical Layer and is available in North America and Japan.
Synchronous Transport Module (STM)
Synchronous Transport Module (STM) is the frame format used by SDH. In the SDH hierarchy, the lowest or base-level signal is the STM-1 which operates at 155.52 Mbps. The STM Level indicates the speed of an STM-n line where the n is multiplied by 155.52 Mbps. For example, an STM-4 signal has the bit rate of (4 * 155.52 Mbps) or 622 Mbps.
Synchronous Transport Signal (STS)
Synchronous Transport Signal (STS) is the frame format used by SONET. In the SONET standard, the lowest or base-level signal is the Synchronous Transport Signal level 1 (STS-1). An STS-1 operates at 51.84 Mbps, which is enough to carry an entire DS3 link.
Spanning Tree Protocol
The Spanning Tree Protocol (STP) selectively disables forwarding on individual ports of a bridge or switch to ensure that the network topology is loop free. This prevents forwarding storms.
Subnet is short for sub-network and is the splitting of a single network number into smaller networks by changing the mask assigned to each broadcast domain.
Summary route is the address range allocated to a specific location.
Supernet is the aggregation of many classful network numbers into a single address or routing table entry.
A switch is a Layer 2 network device that enables full-duplex data transmission. Because switches dedicate a single port to each end-user device, collision domains have only two devices-the end-user device and the switch. When connected to a switch, an end-user device can send and receive data simultaneously. A switch builds a MAC address table that it uses to manage traffic flow. Switches operate based on reading Layer 2 frame information only. They cannot change Layer 2 addresses, and they do not have any access to Layer 3 data. In addition to basic Ethernet connectivity, switches make possible virtual LANs.
Switched Virtual Circuits (SVCs)
Switched virtual circuits (SVCs) are connections that dynamically establish only when data needs sending and terminates when the transmission is complete. Frame Relay and ATM networks use SVCs.
A T1 line is a dedicated copper telephone line that supports data rates of 1.54 Mbps. A T1 line operates at Layer 1 or the Physical layer and is commonly available in North American and Japan. A T1 line consists of 24 individual channels or DS0s, each of which supports 64 Kbps. Each channel or DS0 can transport voice or data. A customer can lease an entire T1 line or only a few channels, which is known as fractional T1 service. The equivalent line outside of North America and Japan is an E1 line.
A T3 line is a dedicated copper telephone line that supports data rates of 44.74 Mbps and like a T1, is also built on the base DS0 signal. A T3 is 28 DS1s-or 672 DS0s-bundled together.
Transmission Control Protocol (TCP) is a protocol for sending data that provides delivery notification, error checking, and recovery procedures. With TCP, the receiving computer tells the sending computer when the data was received.
TCP/IP Reference Model
The TCP/IP Reference Model is a simple four-layer model developed by the Department of Defense and the Internet Engineering Task Force. This model defines specific protocols at each of the four layers, such as TCP and IP, two of the Internet's core protocols. The four layers of the TCP/IP Model are as follows: Application Layer, Transport Layer, Internet Layer, Network Access Layer
Time Division Multiplexing (TDM)
Time Division Multiplexing (TDM) is the combining or multiplexing of voice and data signals from different devices into a single link.
Transit LSRs are routers that only examine the MPLS label on a packet.
In the TCP/IP Reference Model, the Transport Layer takes data from the Application Layer, converts it to a format that can be transmitted over the network, and manages the flow of data between the two hosts that are communicating. This is the same functionality as the Transport Layer in the OSI Reference Model and the Five-Layer Model. In those models, the Transport Layer is Layer 4.
Transport Layer/Layer 4
In the OSI Reference Model and the Five-Layer Model, Layer 4 is the Transport Layer. The Transport Layer takes data from the upper layers, converts it to a format that can be transmitted over the network, and manages the flow of data between the two hosts that are communicating. This is the same functionality as the Transport Layer in the TCP/IP Reference Model, but in that model it is the third layer.
The Trivial File Transfer Protocol (TFTP) is a network protocol used to transfer data from one computer to another through a network, such as over the Internet.
Trunking is the switching of a single ATM virtual path rather than many individual virtual circuits, so that switches do not need to examine each and every virtual circuit to make a switching decision.
Twisted Pair Cabling
Twisted pair cabling consists of twisted pairs of unshielded, but insulated wires. It is also known as UTP, or unshielded twisted pair, cabling. The first 10Base-T networks used ordinary telephone cabling, which is a type of twisted pair cabling. In this type of cable, there are four twisted pairs of wires: two for transmitting data and another two for receiving data. In other applications, such as outdoor telephone cables, twisted pair cabling may have many more twisted pairs of wires.
Unspecified Bit Rate (UBR)
Unspecified Bit Rate (UBR) is the ATM service category that is used for the lowest priority traffic and provides absolutely no guarantees.
User Datagram Protocol (UDP) is a very simple and fast protocol for sending data. UDP is a best effort delivery service, providing no delivery notification, error checking, or recovery procedures.
A unicast MAC address uniquely identifies one device. Other types of MAC addresses include multicast addresses and the broadcast address.
A Uniform Resource Locator (URL) is the address where a file can be accessed on the Internet, for example http://www.sony.com/training/index.html. In this example, the protocol is HTTP, the domain is sony.com, and the path to the file is training/index.html.
Unshielded twisted pair (UTP) cabling is another name for twisted pair cabling.
Virtual Circuits are the logical connections running over a single physical communications line and are used to connect two devices or locations. A virtual circuit, also known as a virtual connection, acts like a dedicated connection through the provider's network even though the physical lines might be shared by multiple customers. Frame Relay and ATM networks make use of virtual circuits. Virtual circuits come in two types. A permanent virtual circuit is like a leased line in that the service provider defines a path to each customer location. Permanent virtual circuits are always on and ready to use. A switched virtual circuit is dynamically establishes only when data needs sending and terminates when the transmission is complete.
Virtual Channel Connection (VCC)
A Virtual Channel Connection (VCC) is a logical connection between two devices or end points in an ATM network, and is sometimes referred to as a virtual circuit. A VCC is identified by a Virtual Channel Identifier. A collection of VCCs can be bundled together into a Virtual Path Connection, which is identified by a Virtual Path Identifier. The combination of VPI and VCI identify the circuit.
Virtual Channel Identifier (VCI)
A Virtual Channel Identifier (VCI) identifies an ATM VCC.
Virtual Collision Detection
Virtual Collision Detection is a system that can be used by wireless networks to handle and avoid collisions. Virtual Collision Detection uses Request to Send (RTS) and Clear to Send (CTS) control frames to control which client may send data at a given time.
Virtual Connections are logical connections running over a single physical communications line and are used to connect two devices or locations. A virtual connection, also known as a virtual circuit, acts like a dedicated connection through the provider's network even though the physical lines might be shared by multiple customers. Frame Relay and ATM networks make use of virtual connections or circuits. ATM uses two-level virtual connections: Virtual Channel Connections and Virtual Path Connections, which contain a group or bundle of VCCs.
Virtual Path Connection (VPC)
A Virtual Path Connection (VPC) is a collection of VCCs bundled together. A VPC is identified by a Virtual Path Identifier.
Virtual Routing and Forwarding (VRF)
A Virtual Routing and Forwarding (VRF) table or VRF instance is a repository on an MPLS Provider Edge router where customer routing information is stored. VRFs are specific to a customer or VPN and are not shared.