Routing GLOSSARY
AGS (Advanced Gateway Server)
Invented in 1984 by two Stanford University researchers and introduced in 1986 by Cisco Systems, it was the first multi-protocol router. Early features included 1 MB of memory and connection support for Ethernet and ARPAnet - the predecessor of the Internet.
ASIC (Application-Specific Integrated Circuit)
A chip with custom-built hardware circuits for a particular set of functions. ASICs are commonly used in networking devices to maximize performance and provide integration of multiple functions into a single chip.
ATM (Asynchronous Transfer Mode)
A dedicated connection switching technology that organizes and transmits voice, video, or data in fixed 53-byte cells. ATM creates a fixed route between two network points. This differs from IP, where packets can each take a different route to the destination, but ATM, like IP, supports multiple types of traffic service (data, voice, video).
Availability
Ability of a system or service to work continuously without interruption. It is usually expressed as a percentage, representing the ratio of available network time to total time. Carrier-class is typically 99.999% -- about five minutes of downtime for failures or repairs per year.
Backbone
Major arterial networks carrying high volumes of traffic. A backbone network typically interconnects multiple lower-speed networks together. This usually involves very high-speed connections and geographically long links. Also referred to as the core.
Bandwidth
The amount of data (in bits) that can be transmitted per second over a particular network connection, or through a system.
Broadband
Generally refers to a user access network connection with bandwidth approximately 1 Mbps or more. It is essential for graphic-intensive websites, music services and video applications. Common forms of broadband include DSL (Digital Subscriber Line), cable modem, WiFi (wireless access), and Metro Ethernet (Ethernet access over optical fiber).
Carrier-Class
A networking system is considered 'carrier class' if it meets certain availability and operational standards to make it qualified for use in a telecom carrier's facility. Examples of such characteristics are 99.999% availability, system packaging, access and usability aspects.
Circuit Switching (Circuit-Switched)
A network communications technology that preceded packet switching. Originally designed for the analog-based phone networks but modified to use a digital circuit switching technology called TDM. Circuit-switching creates a dedicated connection between originator and receiver, and data is sent in one continuous stream. Circuit-switched networks lack flexibility, convergence capabilities, and the advanced services available in packet-switched networks.
Control plane
The software which manages all operational aspects of a router except the per-packet analysis and delivery. This can include updating routing tables, managing user interfaces, and monitoring system status/health.
Convergence
The consolidation of all communications - voice, data (Internet, ATM, Frame Relay, etc), and video (broadcast TV and video on demand) - onto a single network infrastructure. By placing all communications into digitized packets, convergence makes it easier to combine communications into new or more cost-effective applications, while helping telecommunications companies reduce capital and operational expenses.
Core
See Backbone.
Edge
The edge of a network is where users are directly connected and their data aggregated into the network backbone. This is where user-specific services and policies are enabled such as security, DSL broadband, accounting and quality of service.
Fault-tolerance
Ability of a system or component to continue normal operation despite equipment failures, power outages or other catastrophic events. Usually, fault-tolerance is achieved through redundant elements that quickly and automatically replicate activities of failed elements.
Frame Relay
A widely used connection-oriented networking service typically used to transport packet data from one local area network (LAN) across a wide-area network (WAN) to another LAN.
Gbps (gigabits per second)
One billion bits per second. Measure of bandwidth and performance.
IP (Internet protocol)
IP is the communication protocol used throughout the Internet for directing data. All traffic needs to have IP address information for the routers to steer it to the correct destination.
Jitter
Jitter is a measure of the variability over time of the latency across a network. A very low amount of jitter is important for real-time applications using voice and video.
Kernel
Manages all basic operations within an operating system of a computer device.
Latency
Time information takes to move across a network. For voice networks, latency is the delay from when a word is spoken to the time it is heard by the listener. Low latency is usually highly desirable for real-time applications such as voice and video.
Line Card
A card or assembly that contains data interfaces (e.g. optical fibers) which can be inserted into a communications system such as a router.
MPLS (Multi-Protocol Label Switching)
MPLS is a scheme typically used to enhance an IP network. Routers on the incoming edge of the MPLS network add an 'MPLS label' to the top of each packet. This label is based on some criteria (e.g. destination IP address) and is then used to steer it through the subsequent routers. The routers on the outgoing edge strip it off before final delivery of the original packet. MPLS can be used for various benefits such as multiple types of traffic coexisting on the same network, ease of traffic management, faster restoration after a failure, and, potentially, higher performance.
Optical Fiber
A very thin strand of transparent glass-like material that can be used to carry light pulses very long distances and at extremely high speeds.
Packet
A block of data that can move autonomously across a packet-switched network. Packet information is digitally encoded information that can vary in length (measured in bytes). Each packet contains a header of information to help routers and other network devices direct the packet to its proper destination.
Packet Switching (Packet-Switched)
Communications system that uses digital packets to transmit all forms of communication signals. A single packet may represent a small fraction of a second of a phone conversation or a small piece of a much larger file or image. Each packet contains the instructions, such as destination address and order in a message, that coordinate its arrival with other associated packets. Packets are reassembled into the proper sequence at the destination. Packet switching is the primary method of communications for the Internet and other digital communications.
PoP (Point-of-Presence)
A facility where telecommunications companies house servers, routers, switches and other communications equipment. Core and edge network functions are implemented on systems within a PoP. Telcos commonly operate hundreds of PoPs within major metropolitan areas.
Port
Connection point for a communications line, such as Ethernet or fiber optics, into a network router or switch.
Protocol
Set of rules or procedures that enable two or more systems to exchange information.
QoS (Quality-of-Service)
QoS is a general term that incorporates bandwidth, latency, and jitter to describe a network's ability to customize the treatment of specific classes of data. For example, QoS can be used to prioritize video transmissions over Web-browsing traffic. Advanced networks can offer greater control over how data traffic is classified into classes and greater flexibility as to how the treatment of that traffic is differentiated from other traffic.
Route Processor
A router module or card that creates routing tables and other information to tell the system where to transmit each received packet. It communicates to the route processors within neighboring routers via a special Routing Protocol in order to do this.
Router
A packet-switching communications device that interconnects multiple computer networks together. It uses the information in the header of each packet to access a 'routing table' to decide where to send each packet. It can translate between different interface types (e.g. optical fiber and Ethernet), and between different network protocol types (e.g. IP and MPLS). A typical router will include a route processor and a number of line cards.
Scalability
The ability to increase workloads or the number of users, ports or capabilities without making major changes to systems or software and without affecting network performance. Scalability is especially important for rapidly growing enterprises and networks.
Service Provider
A telecommunications company.
SONET (Synchronous Optical Network)
The North American standard widely used for high-speed transmission of data over optical fiber.
Switch Fabric
The foundation of a router, interconnecting incoming data from ingress (input) ports to egress (output) ports. There are multiple switch fabric architectures with differing strengths in terms of bandwidth, throughput and delay.
Tbps (terabits per second)
A trillion bits per second.
Throughput
Amount of useful data bandwidth transported through a system. Usually measured in Kbps, Mbps, or Gbps.
VoIP (Voice over IP)
Describes the ability to convert voice or fax calls into data packets for transmission over the Internet or other IP-based networks.
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