CCNAe4 Chapter 1

Central Office (CO)

A local service provider facility or building where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipment.

WAN switch

A multiport internetworking device used in carrier networks. These devices typically switch traffic such as Frame Relay, ATM, or X.25, and operate at the Data Link layer of the OSI reference model. Public switched telephone network (PSTN) switches may also be used within the cloud for circuit-switched connections like Integrated Services Digital Network (ISDN) or analog dialup.

Permanent Virtual Circuit (PVC)

A permanently established virtual circuit that consists of one mode: data transfer. PVCs are used in situations in which data transfer between devices is constant. PVCs decrease the bandwidth use associated with establishing and terminating VCs, but they increase costs because of constant virtual circuit availability. PVCs are generally configured by the service provider when an order is placed for service.

Scalability

Because VPNs use the Internet infrastructure within ISPs and devices, it is easy to add new users. Corporations are able to add large amounts of capacity without adding significant infrastructure.

Broadband Services

Broadband connection options are typically used to connect telecommuting employees to a corporate site over the Internet. These options include cable, DSL, and wireless.

Enhanced business productivity

Metro Ethernet enables businesses to take advantage of productivity-enhancing IP applications that are difficult to implement on TDM or Frame Relay networks, such as hosted IP communications, VoIP, and streaming and broadcast video.

Metro Ethernet

Metro Ethernet is a rapidly maturing networking technology that broadens Ethernet to the public networks run by telecommunications companies. IP-aware Ethernet switches enable service providers to offer enterprises converged voice, data, and video services such as IP telephony, video streaming, imaging, and data storage. By extending Ethernet to the metropolitan area, companies can provide their remote offices with reliable access to applications and data on the corporate headquarters LAN.

Enterprise Teleworker Architecture

Many businesses today offer a flexible work environment to their employees, allowing them to telecommute from home offices. To telecommute is to leverage the network resources of the enterprise from home. The teleworker module recommends that connections from home using broadband services such as cable modem or DSL connect to the Internet and from there to the corporate network. Because the Internet introduces significant security risks to businesses, special measures need to be taken to ensure that teleworker communications are secure and private.

Municipal WiFi

Many cities have begun setting up municipal wireless networks. Some of these networks provide high-speed Internet access for free or for substantially less than the price of other broadband services. Others are for city use only, allowing police and fire departments and other city employees to do certain aspects of their jobs remotely. To connect to a municipal WiFi, a subscriber typically needs a wireless modem, which provides a stronger radio and directional antenna than conventional wireless adapters. Most service providers provide the necessary equipment for free or for a fee, much like they do with DSL or cable modems.

Easy integration with existing networks

Metro Ethernet connects easily to existing Ethernet LANs, reducing installation costs and time.

Time-division multiplexing (TDM)

gives each conversation a share of the connection in turn. TDM assures that a fixed capacity connection is made available to the subscriber.

The most common WAN data-link protocols are:

- HDLC - PPP - Frame Relay - ATM

The three major characteristics of WANs:

- WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN. - WANs use the services of carriers, such as telephone companies, cable companies, satellite systems, and network providers. - WANs use serial connections of various types to provide access to bandwidth over large geographic areas.

Core router

-A router that resides within the middle or backbone of the WAN rather than at its periphery. To fulfill this role, a router must be able to support multiple telecommunications interfaces of the highest speed in use in the WAN core, and it must be able to forward IP packets at full speed on all of those interfaces. The router must also support the routing protocols being used in the core.

Switched Virtual Circuit (SVC)

A VC that is dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination. The establishment phase involves creating the VC between the source and destination devices. Data transfer involves transmitting data between the devices over the VC, and the circuit termination phase involves tearing down the VC between the source and destination devices. SVCs are used in situations in which data transmission between devices is intermittent, largely to save costs. SVCs release the circuit when transmission is complete, which results in less expensive connection charges than those incurred by PVCs, which maintain constant virtual circuit availability. Connecting to a Packet-Switched Network

VPN Technology

A VPN is an encrypted connection between private networks over a public network such as the Internet. Instead of using a dedicated Layer 2 connection such as a leased line, a VPN uses virtual connections called VPN tunnels, which are routed through the Internet from the private network of the company to the remote site or employee host.

What is a WAN?

A WAN is a data communications network that operates beyond the geographic scope of a LAN. In addition, an enterprise must subscribe to a WAN service provider to use WAN carrier network services. LANs are typically owned by the company or organization that uses them.

Enterprise Campus Architecture

A campus network is a building or group of buildings connected into one enterprise network that consists of many LANs. A campus is generally limited to a fixed geographic area, but it can span several neighboring buildings, for example, an industrial complex or business park environment. In the Span Engineering example, the campus spanned multiple floors of the same building. The Enterprise Campus Architecture describes the recommended methods to create a scalable network, while addressing the needs of campus-style business operations. The architecture is modular and can easily expand to include additional campus buildings or floors as the enterprise grows.

Circuit Switching

A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate.

Core layer (also referred to as the backbone)

A high-speed backbone that is designed to switch packets as fast as possible. Because the core is critical for connectivity, it must provide a high level of availability and adapt to changes very quickly. It also provides scalability and fast convergence.

Demarcation Point

A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to the service provider. This is very important because when problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair.

Distribution layer

Aggregates the wiring closets, using switches to segment workgroups and isolate network problems in a campus environment. Similarly, the distribution layer aggregates WAN connections at the edge of the campus and provides policy-based connectivity.

Data Communications Equipment (DCE)

Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.

Cable Modem

Coaxial cable is widely used in urban areas to distribute television signals. Network access is available from some cable television networks. This allows for greater bandwidth than the conventional telephone local loop. Cable modems provide an always-on connection and a simple installation. A subscriber connects a computer or LAN router to the cable modem, which translates the digital signals into the broadband frequencies used for transmitting on a cable television network. The local cable TV office, which is called the cable headend, contains the computer system and databases needed to provide Internet access. The most important component located at the headend is the cable modem termination system (CMTS), which sends and receives digital cable modem signals on a cable network and is necessary for providing Internet services to cable subscribers. Cable modem subscribers must use the ISP associated with the service provider. All the local subscribers share the same cable bandwidth. As more users join the service, available bandwidth may be below the expected rate.

Access server

Concentrates dial-in and dial-out user communications. An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users.

Connection-oriented systems

Connection-oriented systems predetermine the route for a packet, and each packet only has to carry an identifier. In the case of Frame Relay, these are called Data Link Connection Identifiers (DLCIs). The switch determines the onward route by looking up the identifier in tables held in memory. The set of entries in the tables identifies a particular route or circuit through the system. If this circuit is only physically in existence while a packet is traveling through it, it is called a virtual circuit (VC).

Connectionless systems

Connectionless systems, such as the Internet, carry full addressing information in each packet. Each switch must evaluate the address to determine where to send the packet.

DSL

DSL technology is an always-on connection technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, and provides IP services to subscribers. A DSL modem converts an Ethernet signal from the user device to a DSL signal, which is transmitted to the central office. Multiple DSL subscriber lines are multiplexed into a single, high-capacity link using a DSL access multiplexer (DSLAM) at the provider location. DSLAMs incorporate TDM technology to aggregate many subscriber lines into a single medium, generally a T3 (DS3) connection. Current DSL technologies use sophisticated coding and modulation techniques to achieve data rates of up to 8.192 Mb/s. There is a wide variety of DSL types, standards, and emerging standards. DSL is now a popular choice for enterprise IT departments to support home workers. Generally, a subscriber cannot choose to connect to an enterprise network directly, but must first connect to an ISP, and then an IP connection is made through the Internet to the enterprise. Security risks are incurred in this process, but can be mediated with security measures.

Enterprise Data Center Architecture

Data centers are responsible for managing and maintaining the many data systems that are vital to modern business operations. Employees, partners, and customers rely on data and resources in the data center to effectively create, collaborate, and interact. Over the last decade, the rise of Internet and web-based technologies has made the data center more important than ever, improving productivity, enhancing business processes, and accelerating change.

WAN Encapsulation

Data from the Network layer is passed to the Data Link layer for delivery on a physical link, which is normally point-to-point on a WAN connection. The Data Link layer builds a frame around the Network layer data so that the necessary checks and controls can be applied. Each WAN connection type uses a Layer 2 protocol to encapsulate a packet while it is crossing the WAN link. To ensure that the correct encapsulation protocol is used, the Layer 2 encapsulation type used for each router serial interface must be configured. The choice of encapsulation protocols depends on the WAN technology and the equipment. HDLC was first proposed in 1979 and for this reason, most framing protocols which were developed afterwards are based on it.

CSU/DSU

Digital lines, such as T1 or T3 carrier lines, require a channel service unit (CSU) and a data service unit (DSU). The two are often combined into a single piece of equipment, called the CSU/DSU. The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. The DSU converts the T-carrier line frames into frames that the LAN can interpret and vice versa.

Access layer

Grants user access to network devices. In a network campus, the access layer generally incorporates switched LAN devices with ports that provide connectivity to workstations and servers. In the WAN environment, it may provide teleworkers or remote sites access to the corporate network across WAN technology.

Packet Switching

In contrast to circuit switching, packet switching splits traffic data into packets that are routed over a shared network. Packet-switching networks do not require a circuit to be established, and they allow many pairs of nodes to communicate over the same channel.

Reduced expenses and administration

Metro Ethernet provides a switched, high-bandwidth Layer 2 network capable of managing data, voice, and video all on the same infrastructure. This characteristic increases bandwidth and eliminates expensive conversions to ATM and Frame Relay. The technology enables businesses to inexpensively connect numerous sites in a metropolitan area to each other and to the Internet.

Modem

Modulates an analog carrier signal to encode digital information, and also demodulates the carrier signal to decode the transmitted information. A voiceband modem converts the digital signals produced by a computer into voice frequencies that can be transmitted over the analog lines of the public telephone network. On the other side of the connection, another modem converts the sounds back into a digital signal for input to a computer or network connection. Faster modems, such as cable modems and DSL modems, transmit using higher broadband frequencies.

Virtual Circuits

Packet-switched networks may establish routes through the switches for particular end-to-end connections. These routes are called virtual circuits. A VC is a logical circuit created within a shared network between two network devices

Router

Provides internetworking and WAN access interface ports that are used to connect to the service provider network. These interfaces may be serial connections or other WAN interfaces. With some types of WAN interfaces, an external device such as a DSU/CSU or modem (analog, cable, or DSL) is required to connect the router to the local point of presence (POP) of the service provider.

Remote-access VPNs

Remote-access VPNs enable individual hosts, such as telecommuters, mobile users, and extranet consumers, to access a company network securely over the Internet. Each host typically has VPN client software loaded or uses a web-based client.

Site-to-site VPNs

Site-to-site VPNs connect entire networks to each other, for example, they can connect a branch office network to a company headquarters network, as shown in the figure. Each site is equipped with a VPN gateway, such as a router, firewall, VPN concentrator, or security appliance. In the figure, a remote branch office uses a site-to-site-VPN to connect with the corporate head office.

Local Loop

The copper or fiber telephone cable that connects the CPE at the subscriber site to the CO of the service provider. The local loop is also sometimes called the "last-mile."

Data Terminal Equipment (DTE)

The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The DTE connects to the local loop through the DCE.

Customer Premises Equipment (CPE)

The devices and inside wiring located at the premises of the subscriber and connected with a telecommunication channel of a carrier. The subscriber either owns the CPE or leases the CPE from the service provider. A subscriber, in this context, is a company that arranges for WAN services from a service provider or carrier.

The Hierarchical Design Model

The hierarchical network model is a useful high-level tool for designing a reliable network infrastructure. It provides a modular view of a network, making it easier to design and build a scalable network.

V.35

This is the ITU-T standard for synchronous communications between a network access device and a packet network. Originally specified to support data rates of 48 kb/s, it now supports speeds of up to 2.048 Mb/s using a 34-pin rectangular connector.

Enterprise Branch Architecture

This module allows businesses to extend the applications and services found at the campus to thousands of remote locations and users or to a small group of branches. Much of this course focuses on the technologies that are often implemented in this module.

Enterprise Edge Architecture

This module offers connectivity to voice, video, and data services outside the enterprise. This module enables the enterprise to use Internet and partner resources, and provide resources for its customers. This module often functions as a liaison between the campus module and the other modules in the Enterprise Architecture. The Enterprise WAN and Metropolitan-Area Network (MAN) Architecture, which the technologies covered later in this course are relevant to, are considered part of this module.

EIA/TIA-232

This protocol allows signal speeds of up to 64 kb/s on a 25-pin D-connector over short distances. It was formerly known as RS-232. The ITU-T V.24 specification is effectively the same.

EIA/TIA-449/530

This protocol is a faster (up to 2 Mb/s) version of EIA/TIA-232. It uses a 36-pin D-connector and is capable of longer cable runs. There are several versions. This standard is also known as RS422 and RS-423.

X.21

This protocol is an ITU-T standard for synchronous digital communications. It uses a 15-pin D-connector.

EIA/TIA-612/613

This standard describes the High-Speed Serial Interface (HSSI) protocol, which provides access to services up to 52 Mb/s on a 60-pin D-connector.

Satellite Internet

Typically used by rural users where cable and DSL are not available. A satellite dish provides two-way (upload and download) data communications. The upload speed is about one-tenth of the 500 kb/s download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than an analog modem. To access satellite Internet services, subscribers need a satellite dish, two modems (uplink and downlink), and coaxial cables between the dish and the modem.

Compatibility with broadband technology

VPN technology is supported by broadband service providers such as DSL and cable, so mobile workers and telecommuters can take advantage of their home high-speed Internet service to access their corporate networks. Business-grade, high-speed broadband connections can also provide a cost-effective solution for connecting remote offices.

Cost savings

VPNs enable organizations to use the global Internet to connect remote offices and remote users to the main corporate site, thus eliminating expensive dedicated WAN links and modem banks. Security-VPNs provide the highest level of security by using advanced encryption and authentication protocols that protect data from unauthorized access.

Security

VPNs provide the highest level of security by using advanced encryption and authentication protocols that protect data from unauthorized access.

Broadband Wireless

Wireless technology uses the unlicensed radio spectrum to send and receive data. The unlicensed spectrum is accessible to anyone who has a wireless router and wireless technology in the device they are using. Until recently, one limitation of wireless access has been the need to be within the local transmission range (typically less than 100 feet) of a wireless router or a wireless modem that has a wired connection to the Internet. The following new developments in broadband wireless technology are changing this situation:

WiMAX

Worldwide Interoperability for Microwave Access (WiMAX) is a new technology that is just beginning to come into use. It is described in the IEEE standard 802.16. WiMAX provides high-speed broadband service with wireless access and provides broad coverage like a cell phone network rather than through small WiFi hotspots. WiMAX operates in a similar way to WiFi, but at higher speeds, over greater distances, and for a greater number of users. It uses a network of WiMAX towers that are similar to cell phone towers. To access a WiMAX network, subscribers must subscribe to an ISP with a WiMAX tower within 10 miles of their location. They also need a WiMAX-enabled computer and a special encryption code to get access to the base station.

Examples of packet- or cell-switched connections include:

X.25 Frame Relay ATM

Data Link layer (OSI Layer 2)

define how data is encapsulated for transmission toward a remote location and the mechanisms for transferring the resulting frames. A variety of different technologies are used, such as Frame Relay and ATM.

Physical layer (OSI Layer 1)

describe how to provide electrical, mechanical, operational, and functional connections to the services of a communications service provider.