(These notes are to be used in conjunction with the slides on QOS - Lecture 1)

Transcription

1 (These notes are to be used in conjunction with the slides on QOS - Lecture 1) A telephone system consists of four elements: Each subscriber uses a telephone set that converts sound into electrical signals and then back again to sound. Most telephone sets have a handset with a transmitter and receiver and a base. The base has a dial to initiate a call and a bell or other signaling device to notify the user that a call from another user is being received. One or more central switching facilities or telephone exchanges interconnect groups of local subscribers. Modern telephone exchanges use time-division multiplexing (TDM) to digitize analog signals from subscribers. Exchanges assign these digitized signals to the appropriate time slots. Exchanges interconnect both digital data and voice circuits. Inter-exchange transport facilities connect multiple exchanges across telephone networks. Wiring and cables connect subscribers to the exchange. There are three ways for a subscriber to connect to the telephone exchange: By using dedicated physical wire connections run in overhead or underground cables By radio (cellular, satellite or radiotelephone) By using VoIP Long distance in telecommunications refers to telephone calls made outside a certain area, usually characterized by an area code outside of a local call area. International Calls are made between different countries. The calls are processed by gateway exchanges (switches). The rates for these calls were expensive but are now cheaper due to advances in technology. Originally they were placed via operator. The calls were transmitted by cable, satellite, radio, and more recently, fiber optics and VOIP. IDD or ISD (International Direct Dialing) was introduced in the 1970's, so calls can be dialed without an operator. A central office is the physical building used to house inside plant equipment including telephone switches, which make phone calls "work" in the sense of making connections and relaying the speech information. In telephony, the local loop (also referred to as a subscriber line) is the physical link or circuit, that connects from the demarcation point of the customer premises to the edge of the carrier, or telecommunications service provider, network. Plain old telephone service, or POTS, is the standard telephone service that remains the basic form of residential and small business telephone service nearly everywhere in the world, and was the only basic telephone service known to most people until the introduction of mobile phones. 1

2 Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. It does this by utilizing frequencies that are normally not used by a voice telephone call, in particular, frequencies higher than normal human hearing. Home office connectivity can be achieved over POTS and ADSL and can include VPN and VoIP technologies. Mobile phones and the cellular phone system they operate under vary significantly from provider to provider, and nation to nation. However, all of them communicate through electromagnetic microwaves with a cell site base station, the antennas of which are usually mounted on a tower, pole, or building. The Public Switched Telephone Network (PSTN) in North America and the Postal, and the Telephone and Telegraph (PTT) services in much of the rest of the world, carry analog voice over copper wires. This basic telephone service is often called POTS. In some places, POTS means the Post Office Telephone Service or Post Office Telephone System. However, as legislation removed telephone services from the control of national post offices, the term became more widely known as meaning plain old telephone service. POTS remains the basic form of residential and small business telephone service nearly everywhere in the world. Until the introduction of mobile telephones, POTS was the only telephone service that most people knew. POTS has been available almost since the introduction of the telephone system in the late 19th century. Telephone service remained mostly unchanged to the average user since the middle of the 20th century, despite the introduction of electronic telephone exchanges into the PSTN and PTT. While POTS provides a relatively limited feature set, low bandwidth and no mobile capabilities, it does provide (in most geographic areas) much greater reliability than any of the more modern telephone systems (wireless, cellular, VoIP, etc). Listed here are some of the POTS services that are available. Recently, telcos began moving their digital networks closer to the customer premises. Generally, telcos offer digital transport services in one of two forms. Integrated Services Digital Network (ISDN) or T1/E1. ISDN provides a digital loop from the exchange (or central office) to the customer premises. ISDN provides digital transmission over ordinary telephone copper wire as well as over other media. Conceptually, ISDN integrates both analog or voice traffic with digital data over the same network. Home and business users receive data at rates up to twice the rate of a modem connection. There are two levels of ISDN service. Both rates include a number of B- channels and a D-channel. Each B-channel carries data, voice, and other services at a rate of 64 kbps. Each D-channel carries control and signaling information: Basic Rate Interface (BRI) is for home and small business use. BRI contains two B-channels and one D-channel. 2

3 Primary Rate Interface (PRI) is for larger users. PRI includes 23 B- channels in North America and Japan (30 in Europe) and one D- channel. Service providers usually transmit PRI service through a T1 line in North America and an E1 line in Europe. From a consumer point of view, and as a data connection service, DSL replaces ISDN. In North America and Japan, transmission 1 (T1) carrier technology provides trunk lines between exchanges. Europe 1 (E1), is used in Europe. T1 and E1 lines are dedicated telephone connections supporting high data rates. Companies often use T1 for Internet traffic. A Private Branch exchange (also called PBX, Private Business exchange or PABX for Private Automatic Branch exchange) is a telephone exchange that serves a particular business or office. Medium-sized and larger companies use a PBX because it is much less expensive than connecting an external telephone line to every telephone in the organization. In addition, it is easier to make internal calls within a PBX using only three or four digits. Many telephones can be attached to a PBX, but users can only share a certain number of outside lines for external calling. Usually to secure an outside line, the caller dials the digit 9 before the full outside telephone number. For companies that are not willing or able to invest in PBX technology, many telephone companies offer central office exchange service (Centrex). Centrex is a virtual PBX with all the switching occurring at the telephone office instead of at the company's premises. Typically, the telephone company owns and manages all the communications equipment that is needed to implement the PBX and then sells various services to the company. The Centrex customer is not restricted to using the features available to POTS (Plain Old Telephone Service) customers, but can choose from a wide variety of special services and features. In fact, telecommunications companies generally offer numerous types of Centrex service, including "Packaged Centrex", "Centrex Data", and "Customized Centrex".Enterprises increasingly rely on their ability to communicate directly with customers, suppliers, partners, branches, and teleworkers. Long-distance services represent a significant expense. When long-distance costs were relatively high, companies kept control over long-distance access. This graphic shows a historical example of how operator intervention was required for a caller inside the PBX to access long-distance service. Long-distance trunk lines connecting exchanges usually use TDM technologies and T1 or E1 transport. The most common long-distance service that is offered in North America is Wide Area Telephone Service (WATS). Other parts of the world have similar services. 3

4 WATS-type plans provide access to long-distance telephone lines for commercial use at reduced rates. WATS is outward (OUT-WATS), inward (IN-WATS), or both: With outward WATS, the calling party can make an unlimited number of long-distance calls (toll calls) for a fixed price within pre-determined time and distance constraints. Most telephone companies now market OUT- WATS as something called a flat-rate plan. Initially, operator assistance was necessary to control access to OUT-WATS from within a PBX. Following company policy, callers asked the company operator at their PBX to connect them to the tie-line, or the OUT-WATS line that tied into the long distance system. However, as long distance calling rates fell, operator intervention has almost disappeared. Callers making a call from inside a PBX usually only need to add a prefix to gain access to outside long-distance numbers. With IN-WATS, subscribers have a toll-free telephone number. IN-WATS service reduces the time that operators spend processing toll-collect calls for businesses. The IN-WATS area codes in North America are 800, 888, 877, and 866. More 800 numbers are reserved for the future (855, 844, 833 and 822). Telephone users within a designated area can call the IN-WATS telephone number of an organization without having to pay a toll charge. Many businesses have toll-free 800 numbers that can ring at multiple callcenters. Before advanced networking technologies allowed convergence, enterprises provisioned separate networks for voice, video, and data applications. In most cases, enterprises deployed voice, video, and data networks autonomously and operated them in isolation. Enterprises managed and implemented these networks with separate teams. The separate networks encompass the enterprise local and wide-area networks. In simple terms, voice traffic used PBXs and data used routers. PBXs connected to dedicated leased lines. Data used a combination of leased lines, Frame Relay, and ATM. The figure shows a typical deployment of these disparate networks. Video relied on special and very expensive leased line connections. It is widely accepted and acknowledged by the communications industry and industry analysts as a whole that IP will become the universal transport of the future. The rapid adoption and migration of vendors to the use of IP as a transport for data, voice, and video applications further endorses the transition to a converged networking paradigm. This graphic shows an enterprise network converging over common IP transport. Using IP as the form of transport offers the enterprise significant statistical gains in bandwidth efficiency, lower overall bandwidth requirements, ease of management, and the ability to deploy new applications rapidly. There are fewer WAN facilities and fewer devices required to terminate those facilities. Enterprises add bandwidth incrementally as required and statistically share bandwidth between applications, adding efficiency and reducing complexity. 4

5 The traditional model uses a three-layer hierarchical model. Initially, the model provided a modular framework that allowed flexibility and made implementation and troubleshooting easy. The hierarchical model divides networks or their modular blocks into the access, distribution, and core layers. Each layer has specific features: Access layer: The access layer grants user access to network devices. In a campus network, the access layer most often uses switched LAN devices with ports that provide connectivity to workstations and servers. The access layer of the corporate network topology is the site where WAN links associated with remote sites and teleworkers are aggregated. Distribution layer: The distribution layer aggregates the wiring closets by 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. Core layer: The core layer, or backbone design, switches packets as fast as possible. Because the core layer is critical for connectivity, this layer must provide a high level of availability and adapt to changes very quickly. Cisco provides the enterprise-wide systems architecture that helps companies to protect, optimize, and grow the infrastructure that supports business processes. The architecture provides for integration of the entire network campus, data center, WAN, branches, and teleworkers offering staff secure access to tools, processes, and services. From an Information Technology staff point of view, the Cisco Enterprise Architecture facilitates planning, designing, implementing, operating, and troubleshooting (PDIOT) networks by focusing on network elements and on the relationships between those elements Cisco Enterprise Campus Architecture combines a core infrastructure of intelligent switching and routing with tightly integrated productivity-enhancing technologies, including IP communications, mobility, and advanced security. The campus architecture provides many features: High availability with a resilient multilayer design and redundant hardware and software features. Automatic procedures for reconfiguring network paths when failures occur. Multicast to provide optimized bandwidth consumption. Quality of service (QoS) that prevents oversubscription to ensure the network does not drop or delay real-time traffic, such as voice and video or critical data. Integrated security to protect against and mitigate the impact of worms, viruses, and other attacks on the network, even at the switch port level. Cisco enterprise-wide 5

6 architecture extends authentication support using standards such as 802.1x and Extensible Authentication Protocol (EAP). Cisco Enterprise Campus Architecture provides the flexibility to add IPsec and Multiprotocol Label Switching virtual private networks (MPLS VPNs), identity and access management, and VLANs to compartmentalize access. These features help improve performance and security and decrease cost. Cisco Enterprise Data Center Architecture is a cohesive and adaptive network architecture. The Cisco Enterprise Data Center supports business and IT requirements for consolidation, business continuity, and security. At the same time, this architecture enables emerging service-oriented architectures, virtualization, and on-demand computing. IT staff can easily provide departmental staff, suppliers, or customers with secure access to applications and resources. This structure simplifies and streamlines management, significantly reducing overhead. Redundant data centers provide backup using synchronous and asynchronous data and application replication. The network and devices offer server and application load balancing to maximize performance. This solution allows the enterprise to scale without major changes to the infrastructure. Cisco Enterprise Branch Architecture allows enterprises to extend head-office applications and services, such as security, Cisco IP Communications, and advanced application performance, to thousands of remote locations and users or to a small group of branches. Cisco integrates security, switching, network analysis, caching, and converged voice and video services into a series of integrated services routers in the branch. With this integration, enterprises can deploy new services when they are ready to do so without having to buy new equipment. This solution provides secure access to voice, mission-critical data, and video applications anywhere and anytime. Advanced network routing, VPNs, redundant WAN links, application content caching, and local IP telephony call processing provide a robust architecture with high levels of resilience for all the branch offices. An optimized network leverages the WAN and LAN to reduce traffic and save bandwidth and operational expenses. Enterprises can easily support branch offices with the ability to centrally configure, monitor, and manage devices that are located at remote sites, including tools, such as AutoQoS or the Security Device Manager (SDM) QoS wizard, that proactively resolve congestion and bandwidth issues before they affect network performance. Slide 19; This graphic shows a network structured on the Cisco hierarchical model design and using the Cisco Enterprise Architectures described above. Various architectures and sub-modules form an integrated converged network that supports business processes. In this example, the enterprise campus network comprises five submodules: Building access with access switches and end devices (PCs and IP phones) Building distribution with distribution multilayer switches Backbone 6

7 Edge distribution that concentrates all branches and teleworkers accessing the campus via WAN or the Internet Server farm that represents the data center Additional submodules represent remote access and VPN, Internet, and traditional WAN (Frame Relay, ATM, and leased lines with Point-to-Point Protocol [PPP]). Converged networks with integrated voice, video, and data contain a mix of traffic patterns and requirements. The diversity of the traffic mix imposes stringent performance and security requirements on the network. The requirements differ significantly, depending on the traffic type. For example, voice and video require constant bandwidth with low delay and jitter, while transactional traffic requires high reliability and security with relatively low bandwidth. In addition, voice applications, such as IP telephony, require high reliability and availability, because users expect the dial tone in the IP network to be the same as in a traditional telephone network. To meet the traffic requirements in the network, voice and video traffic must be treated differently from other traffic, such as web-based (HTTP) traffic. Quality of Service mechanisms are mandatory in converged networks. Security is a key issue in fixed networks but is even more important in wireless mobility, where access to the network is possible from virtually anywhere. Several security strategies, such as device hardening with strict access control and authentication, intrusion protection, intrusion detection, and traffic protection with encryption, can mitigate network security threats. Slide 21; This graphic shows a sample converged network with integrated secured services. The network deploys advanced technologies including IP communications (IP telephony and unified messaging), wireless mobility, and security. The clouds in the figure represent the Cisco Enterprise WAN Architecture. The links in this area can easily become blocked and affect the performance of IP telephony. One of the solutions to this issue, Cisco AutoQoS, is shown on the voice-enabled router in a simple branch consisting of one user. To increase IP telephony reliability and availability, Cisco Survivable Remote Site Telephony (SRST) has been deployed at one of the branches. There are many reasons to increase security, including, in this example, wireless mobility. Encryption and identity-based networking (including authentication and access control) and device hardening provide increased security in the sample network with integrated router security. The AutoSecure feature is used to provide simple and straightforward one touch device lockdown. The Cisco Intelligent Information Network (IIN) vision is a strategy that meets the evolving role of the network within businesses and directly meets the need to align IT resources with business priorities. The Cisco IIN vision has three key features: Integration of networked resources and information assets: Modern networks with integrated voice, video, and data allow IT departments to link the IT infrastructure more closely with the information network. 7

8 Intelligence across multiple products and infrastructure layers: The intelligence that is built into each network component extends networkwide and applies end-to-end. Active participation of the network in the delivery of services and applications: With added intelligence within network devices, the IIN makes it possible for the network to actively manage, monitor, and optimize service and application delivery across the entire enterprise environment. With these features, the IIN offers much more than basic connectivity, bandwidth for users, and access to applications. The IIN offers end-to-end functionality and a centralized, unified control that promotes true business transparency and agility. The Cisco Intelligent Information Network helps organizations meet new IT challenges including deploying service-oriented architectures, web services, and virtualization. Cisco SONA is an architectural framework that details the set of common services that are deployed in the network to close gaps between the resources and applications. Cisco SONA describes how to build an IIN. The Cisco SONA framework provides these advantages to enterprises: Outlines the path toward the IIN Illustrates how to build integrated systems across a fully converged IIN Improves flexibility and increases efficiency resulting in optimized applications, processes, and resources Cisco SONA uses the extensive product line, services, proven architectures, and experience of Cisco and its partners to help the enterprises achieve their business goals. The Cisco SONA framework shows how integrated systems allow a dynamic, flexible architecture and provide for operational efficiency through standardization and virtualization. The premise that the network is the common element that connects and enables all components of the IT infrastructure, is the basis of Cisco SONA. Cisco SONA outlines three layers of the IIN: networked infrastructure layer, interactive services layer, and application layer. The infrastructure layer interconnects all IT resources across a converged network foundation. IT resources include servers, storage, and clients. The networked infrastructure layer represents how these resources exist in different places in the network, including campus, branch, data center, WAN, metropolitan-area network (MAN), and teleworker locations. The infrastructure layer provides customers with connectivity anywhere and anytime. The interactive services layer delivers efficient allocation of resources to applications and business processes through the networked infrastructure. This layer includes these services: Voice and collaboration services Mobility services 8

9 Security and identity services Storage services Computer services Application networking services Network infrastructure virtualization Services management Adaptive management servicesthe application layer includes business applications and collaboration applications. The objective for customers in this layer is to meet business requirements and achieve efficiencies by leveraging the interactive services layer. 9