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Services In a Converged Network

What is a WAN

A WAN is a network beyond the geographic scope of a LAN.

Lan’s connect devices in a small area, but WAN’s allow data transmission across a greater distance.

Lans are typically self owned whereas WANs are usually leased from a service provider or carrier.

Wans generally carry a variety of traffic (voice data video).

Wans generally use serial connections of various types.

Why WANS are necessary

Regonal/branch offices need to be able to communicate with a central site Office.

Organizations often share info with other organizations.

Employees who travel frequently need to access info that resides on their corporate network.

In addition home computer users need to send a receive data across increasingly larger distances.

Wans used by themselves or in concert with the internet allow organizations & individuals to

meet their WAN needs.

Businesses & their network

Company networks change to accommodate changing business requirements.

Establishing & managing networks can be expensive & time consuming.

To justify this networks must perform optimally to increase productivity & profitability.

Hierarchial design model

Provides a modular view of a network, making it easier to design & build scalable networks

ACCESS LAYER : grants remote access to the network across WAN technology

DISTRIBUTION LAYER : aggregates WAN connections at the edge of campus & provides policy based

connectivity

CORE LAYER : high speed backbone designed to switch packets as fast as possible

Network infrastructure is only the foundation to a comprehensive architecture.

Currently network elements are more aware.

The enterprise Architecture

Networks often grow haphazardly and become complex & expensive to manage

with a mix of new and older parts.Cisco recommends the CISCO enterprise architecture.

Its designed to provide a roadmap for network growth as the business moves through stages.

Modules in the Enterprise architecture

Enterprise Branch - Extends service to remote locations

Enterprise DATA center architecture - responsible for managing & maintaining data.

Enterprise teleworkers architecture - Connections from home using broadband (cable/dsl).

Special measures needed to ensure security and privacy.

Enterprise Campus architecture - Consists of many lans limited to fixed geographic location.

Can span several buildings or floors of same building.

Modular architecture is easily expanded.

Enterprise Edge architecture - Offers connectivity outside the enterprise.

Enables access to the internet & partner resources & provides resources for its customers.

Often functions as a liason between the campus module & other modules.

The WAN & MAN are considered part of this module.

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 the CCNA course focuses on the technologies that are often implemented in the WAN.

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.

WANS & OSI model

Wans focus primarily on L1 & L2.

Includes physical addressing, flow control, & encapsulation.

Wan standards are defined by ISO, TIA/EIA among others.

Wans use a much wider variety of technologies than LANs

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.

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.

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.

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.

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."

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 Devices

WANs use numerous types of devices that are specific to WAN environments, including:

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.

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 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.

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.

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.

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.

WAN physical -layer protocols describe how to provide electrical, mechanical, operational, and functional connections for WAN services. The WAN physical layer also describes the interface between the DTE and the DCE. The DTE/DCE interface uses various physical layer protocols, including:

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.

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.

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.

X.21 -This protocol is an ITU-T standard for synchronous digital communications. It uses a 15-pin D-connector.

DATA LINK PROTOCOLS

ISDN -frame relay & ATM all used the same basic framing mechanism, HDLC or one of its variants.

ATM - different because it uses small fixed cells of 53 bytes (48 bytes for data).

The most common WAN data link protocols are:

HDLC,PPP,FRAME RELAY,ATM

ISDN is still used in VOiP networks using PRI links.

x.25 is a forerunner of frame relay & still is used in developing countries for credit & debit transactions

MPLS - layer 2.5 protocol that is increasingly being used, especially by service providers

WAN ENCAPSULATION

Each wan connection type uses a L2 frame to encapsulate an IP packet while it crosses a WAN link.

The choice of encapsulation protocols depends on the WAN technology & the network equipment.

HLDC was developed in 1979 & most protocols are based off it.

HDLC FRAME

Starts & ends with a flag field

The address is not needed - almost always point to point but is always present & may be 1 or 2 bytes long

The control field (1 byte) is a protocol dependent and usually indicates wether data is control info on a network layer data

The FCS uses CRC to establish a 2 or 4 byte field.

Both PPP & cisco HDLC have an extra field in the header to identify the encapsulated network layer

WAN connections can be either over a private infrastructure or over a public infrastructure, such as the Internet.

Private WAN Connection Options

Private WAN connections include both dedicated and switched communication link options.

Dedicated communication links

When permanent dedicated connections are required, point-to-point lines are used with various capacities that are limited only by the underlying physical facilities and the willingness of users to pay for these dedicated lines. A point-to-point link provides a pre-established WAN communications path from the customer premises through the provider network to a remote destination. Point-to-point lines are usually leased from a carrier and are also called leased lines.

Switched communication links

Switched communication links can be either circuit switched or packet switched.

Circuit-switched communication links -Circuit switching dynamically establishes a dedicated virtual connection for voice or data between a sender and a receiver.

Before communication can start, it is necessary to establish the connection through the network of the service provider.

Examples of circuit-switched communication links are analog dialup (PSTN) and ISDN.

Time Division Multiplexing TDM

Gives each conversation a share to the connection in turn..

TDM assures that a fixed capacity connection is made available to the subscriber.

It is not always efficient especially for pc data.

Switched circuits are generally expensive at moving data.

PSTN & ISDN are circuit switched technology used to implement a WAN in an enterprise setting.

Packet-switched communication links - Many WAN users do not make efficient use of the fixed bandwidth that is available with dedicated, switched, or permanent circuits because the data flow fluctuates.

Communications providers have data networks available to more appropriately service these users. In packet-switched networks, the data is transmitted in labeled frames, cells, or packets.

Packet-switched communication links include Frame Relay, ATM, X.25, and Metro Ethernet.

Splits data into packets that are routed over a shared network

There are 2 approaches: Connectionless & connection-oriented

Connectionless systems(internet) carry full addressing info in each packet

Connection-oriented systems predetermine the route & each packet carries the identifier

The switch determines the route by looking up the DLCI in tables held in memory.

The set of table entries identifies a particular route or circuit.

If this circuit only exists while the packet is traveling through it, it is called a virtual circuit.

Packet switching

Delays(latency) & variability of delay (jitter) are greater in packet switched networks

Despite latency & jitter they still transport voice & data

A VC is a permanently established VC consisting of one mode: data transfer

Used where data transfer between devices is constant

PVCs decrease the bandwidth use for establishing & terminating VCs but increase cost > constant availability

PVCs are configured by the provider.

Switched virtual circuit

Used where data is intermittent, largely to save cost.

Releases the circuit when transmitting is complete.

Dynamically establish on demand & terminated when transmission is complete.

Connecting to a packet switched network

A subscriber needs a local loop to the nearest location where the provider makes the service available

This is called the Point-of-presence (POP).

Normally this is a dedicated leased line.

This line is much shorter than a line directly connected to all subscriber locations, & often carries several VCs

Because not all VCs require full bandwidth simultaneously, the capacity of a leased line can be smaller than the sum of the individual VCs

Leased lines

Leased lines are available in different capacity & are priced on bandwidth & distance

More expensive than shared media.

Dedicated capacity reduces jitter & latency.

A CSU DSU & circuit from the provider are also required.

Provide permanent dedicated capacity & are used extensively for building WANs.

Analog Dialup

When intermittent, low-volume data transfers are needed, modems and analog dialed telephone lines provide low capacity and dedicated switched connections. This topic describes the pros and cons of using analog dialup connection options, and identifies the types of business scenarios that benefit most from this type of option.

Traditional local loops can transport binary computer data through the voice telephone network using a modem. The modem modulates the binary data into an analog signal at the source and demodulates the analog signal to binary data at the destination. The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal to less than 56 kb/s.

The advantages of modem and analog lines are simplicity, availability, and low implementation cost. The disadvantages are the low data rates and a relatively long connection time. The dedicated circuit has little delay or jitter for point-to-point traffic, but voice or video traffic does not operate adequately at these low bit rates.

Integrated Services Digital Network

Integrated Services Digital Network (ISDN) is a circuit-switching technology that enables the local loop of a PSTN to carry digital signals, resulting in higher capacity switched connections. ISDN changes the internal connections of the PSTN from carrying analog signals to time-division multiplexed (TDM) digital signals. TDM allows two or more signals or bit streams to be transferred as subchannels in one communication channel. The signals appear to transfer simultaneously, but physically are taking turns on the channel. A data block of subchannel 1 is transmitted during timeslot 1, subchannel 2 during timeslot 2, and so on. One TDM frame consists of one timeslot per subchannel.

ISDN turns the local loop into a TDM digital connection. This change enables the local loop to carry digital signals that result in higher capacity switched connections. The connection uses 64 kb/s bearer channels (B) for carrying voice or data and a signaling, delta channel (D) for call setup and other purposes.

There are two types of ISDN interfaces:

Basic Rate Interface (BRI) -ISDN is intended for the home and small enterprise and provides two 64 kb/s B channels and a 16 kb/s D channel. The BRI D channel is designed for control and often underused, because it has only two B channels to control. Therefore, some providers allow the D channel to carry data at low bit rates, such as X.25 connections at 9.6 kb/s.

Primary Rate Interface (PRI) -ISDN is also available for larger installations. PRI delivers 23 B channels with 64 kb/s and one D channel with 64 kb/s in North America, for a total bit rate of up to 1.544 Mb/s. This includes some additional overhead for synchronization. In Europe, Australia, and other parts of the world, ISDN PRI provides 30 B channels and one D channel, for a total bit rate of up to 2.048 Mb/s, including synchronization overhead. In North America, PRI corresponds to a T1 connection. The rate of international PRI corresponds to an E1 or J1 connection.

X.25 L3 protocol

X.25 is a legacy network-layer protocol that provides subscribers with a network address. Virtual circuits can be established through the network with call request packets to the target address. The resulting SVC is identified by a channel number. Data packets labeled with the channel number are delivered to the corresponding address. Multiple channels can be active on a single connection.

Typical X.25 applications are point-of-sale card readers. These readers use X.25 in dialup mode to validate transactions on a central computer. For these applications, the low bandwidth and high latency are not a concern, and the low cost makes X.25 affordable.

X.25 link speeds vary from 2400 b/s up to 2 Mb/s. However, public networks are usually low capacity with speeds rarely exceeding above 64 kb/s.

Frame Relay L2 protocol

Although the network layout appears similar to X.25, Frame Relay differs from X.25 in several ways. Most importantly, it is a much simpler protocol that works at the data link layer rather than the network layer. Frame Relay implements no error or flow control. The simplified handling of frames leads to reduced latency, and measures taken to avoid frame build-up at intermediate switches help reduce jitter. Frame Relay offers data rates up to 4 Mb/s, with some providers offering even higher rates.

Frame Relay VCs are uniquely identified by a DLCI, which ensures bidirectional communication from one DTE device to another. Most Frame Relay connections are PVCs rather than SVCs.

Frame Relay provides permanent, shared, medium-bandwidth connectivity that carries both voice and data traffic. Frame Relay is ideal for connecting enterprise LANs. The router on the LAN needs only a single interface, even when multiple VCs are used. The short-leased line to the Frame Relay network edge allows cost-effective connections between widely scattered LANs.

ATM

Asynchronous Transfer Mode (ATM) technology is capable of transferring voice, video, and data through private and public networks. It is built on a cell-based architecture rather than on a frame-based architecture. ATM cells are always a fixed length of 53 bytes. The ATM cell contains a 5 byte ATM header followed by 48 bytes of ATM payload. Small, fixed-length cells are well suited for carrying voice and video traffic because this traffic is intolerant of delay. Video and voice traffic do not have to wait for a larger data packet to be transmitted.

The 53 byte ATM cell is less efficient than the bigger frames and packets of Frame Relay and X.25. Furthermore, the ATM cell has at least 5 bytes of overhead for each 48-byte payload. When the cell is carrying segmented network layer packets, the overhead is higher because the ATM switch must be able to reassemble the packets at the destination. A typical ATM line needs almost 20 percent greater bandwidth than Frame Relay to carry the same volume of network layer data.

ATM was designed to be extremely scalable and can support link speeds of T1/E1 to OC-12 (622 Mb/s) and higher.

ATM offers both PVCs and SVCs, although PVCs are more common with WANs. And as with other shared technologies, ATM allows multiple VCs on a single leased-line connection to the network edge.

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.

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.

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.

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.

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.

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.

VPN Benefits

Benefits of VPN include the following:

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.

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.

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.

Types of VPN Access

There are two types of VPN access:

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.

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.

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.

Benefits of Metro Ethernet include:

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.

Easy integration with existing networks - Metro Ethernet connects easily to existing Ethernet LANs, reducing installation costs and time.

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.

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