cisco avvid ip telephony phần 9 pptx

Designing and Implementing Multisite Solutions Solutions in this chapter: ■ IP Telephony Multisite Centralized Call Processing Solutions ■ IP Telephony Multisite Distributed Call Processing Solutions ■ Multisite AVVID Solutions ; Summary ; Solutions Fast Track ; Frequently Asked Questions Chapter 11 391 109_AVVID_DI_11 10/9/01 2:53 PM Page 391 392 Chapter 11 • Designing and Implementing Multisite Solutions Introduction In this chapter, you’ll extend your knowledge of Chapter 10’s single site VoIP solutions into a multisite corporate environment.We’ll be performing specialized network designs geared to the AVVID functionality.These solution designs will evaluate the benefits and detriments of a centralized design versus a distributed environment for large environments, and will tackle the following design and operational issues: ■ Providing cost-effective small site connectivity while providing required CallManager redundancy. ■ Assuring a seamless growth path when a small site grows to consume more network resources. ■ Ensuring that CallManager solutions are flexible in their coverage of the corporate users. ■ Providing the network engineers and managers with adequate docu- mentation of the design, and showing how the various AVVID solutions fit within each part of the design. The solutions will first review what you’ve learned in the Chapter 10 single site solutions, then expand each of those topics out to a full corporate system. We’ll show you how to build redundancy and resiliency into each design, how to build out clustered CallManager solutions. Lastly, you’ll learn how to deploy other AVVID solutions in this same corporate environment.When you finish this chapter, you’ll have at least a solid view of the minimum requirements of a Cisco AVVID enterprise network. IP Telephony Multisite Centralized Call Processing Solutions In centralized solutions, CallManager and all of the related VoIP resources are located on the main corporate backbone networks, or at some other primary location.These VoIP resources are any device or function that provide core VoIP functions for everyone else, and which usually have the highest capital cost.This is usually a data center or some other highly protected location that uses condi- tioned power, redundant WAN connections, and physical security such as per- sonnel badges and magnetic entry cards. Because of this seemingly precarious www.syngress.com 109_AVVID_DI_11 10/9/01 2:53 PM Page 392 www.syngress.com position, all infrastructure supporting this configuration must be of the highest quality, and utilize the most redundant design possible. A centralized call processing solution is arguably the configuration most often found in enterprise VoIP solutions.This section will show you how to design such a solution, plan for WAN changes to support branch offices from a centralized solution, and how to provide backup and disaster recovery solutions that will help recover failed installations. Wide Area Network Considerations In centralized network designs, all CallManagers reside on the head office network (as do associated solutions like Unity messaging) in a central location such as the main head office backbone, not at field locations. Figure 11.1 illustrates a typical centralized design. (Figure 11.1 will be used as the main reference point in this section, and will be adjusted to reflect the amended designs explored throughout the chapter.) This is a balanced design, meaning that the capacity of the WAN circuits to the branch offices equals the maximum capacity of the head office.This means that if you add up the speed of the WAN links to all branch offices, the total does not exceed the head office WAN connection to the frame cloud. Referring to Figure 11.1, the three branch offices each use a 512 Kbps connection, which totals 1536 Kbps. Since this is equal to the head office WAN connection speed, the head office WAN connection cannot be over-subscribed.This is a very important factor to consider when designing the VoIP solution. The total VoIP seats in the branch offices cannot exceed the capacity of the circuits, nor the centralized CallManager. Off-net calls are routed to, and placed through, the Primary Rate Interface (PRI) to the telecommunications office that is local to the head office network. In this manner, head office management can negotiate the best rates for local and long distance calls, and also get the maximum utilization out of the Frame Relay circuits by using the voice and data paths together. However, notice that the branch offices use a FXO connection to their local telecommunications office to off-net their local calls instead of routing them across the Frame Relay circuit to off-net them.The FXO ports use a standard analog telephone line instead of a specialized PRI circuit, and the cost is dramati- cally different.Also, standard analog lines are available in nearly every town in the country. If you can get an analog line, this is the first step towards centralized design.We’ll get into this more in the section about creating the off-net solution. Designing and Implementing Multisite Solutions • Chapter 11 393 109_AVVID_DI_11 10/9/01 2:53 PM Page 393 394 Chapter 11 • Designing and Implementing Multisite Solutions The Gatekeeper Function The gatekeeper is a Cisco router that runs the H.323 MCM feature set, and pro- vides the H.323 centralized call admissions control for the enterprise, call setup, and related management issues.Among these functions is the decision regarding whether the destination path can support the required bandwidth requirement of the device placing the call.To illustrate this concept, let’s go through a call, referring to Figure 11.1 as a common reference point. A user on Site A wants to call a user on Site C.When the Site A user picks up the phone and gets a dial tone, this person types in the digits of the destination phone.This request is sent to the CallManager on the head office backbone, which determines that the destination device is on Site C, and then contacts the gatekeeper.The gatekeeper looks at the request in regards to the amount of bandwidth requested, the type of services requested, and then makes the determination as to whether the total amount of bandwidth is available to the site. www.syngress.com Figure 11.1 A Typical Centralized VoIP Design Backbone Router (R1) 3524 Switch CallManager Unity Site A Router (R4) 3524 Switch T-1 512K Frame Relay Cloud Site B Router (R5) 3524 Switch 512K Site C Router (R6) 3524 Switch 512K Network Exchange MGCP (R3) Gateway PRI Telco FXO Telco FXO Telco FXO Telco H.323 (R2) Gatekeeper Head Office 109_AVVID_DI_11 10/9/01 2:53 PM Page 394 Designing and Implementing Multisite Solutions • Chapter 11 395 The gatekeeper knows these things because it keeps track of the amount of calls currently placed to Site C, and the amount of bandwidth dedicated to that site.With the WAN link currently set at 512 Kbps, the average g.711 call uses 64 Kbps of bandwidth, which means that 8 simultaneous calls are possible to Site C from any other site, provided that none of the 512 Kbps is used for data streams. If other compression techniques are used, the voice streams can be compressed to as low as 5.3 Kbps with the high-complexity digital signal processor (DSP) CODECs in the voice-capable gateways. However, Cisco design rules state that no more than 75 percent of the circuit capacity should be used for voice traffic. Furthermore, overhead in the IP packets can raise the total per-call bandwidth requirement for a G.711 call to 80 Kbps per call. Using these parameters on the same 512 Kbps connection now yields the primary reason many VoIP designs fail to meet expectations: 75 percent of 512 Kbps is 384 Kbps. Divided by 80 Kbps per G.711 call, we now have a maximum of four possible calls at the same time.This is quite a difference from the previous para- graph, and illustrates how and why these designs sometimes go wrong. NOTE The gatekeeper does not handle the actual voice stream between the two endpoints, but rather assures that the proper bandwidth is available between the two endpoints. Voice-Capable Gateways As explained in Chapter 10, a voice-capable gateway is a Cisco router that runs the MGCP IOS firmware that performs processing for voice calls on the local network to local or external destinations.These routers are installed with PRI, FXO, or FXS ports that form the external connectivity to a local telecommunications carrier office.The voice-capable gateways for branch offices are: ■ Model 175x for small site gateways, for up to 10 users ■ Model 26xx for small sites, for up to 50 users ■ Mixed variations of these two devices These two models are frequently used units; the Model 175x is the more cost-effective unit, but has less flexibility than the 26xx series and VG200 gateways. www.syngress.com 109_AVVID_DI_11 10/9/01 2:53 PM Page 395 396 Chapter 11 • Designing and Implementing Multisite Solutions The field gateway router used for data only might also be an older 2500 or 3600 class router that has been at the branch office for quite some time.Also, newer Model 1600 series routers may be positioned as small branch office gateways to handle the data portion of the site. It is important not to not mix up these gateways, and equally important to not try and use one gateway for both data and voice combined.While such a combination has worked at times, it usually is not a good idea to have all your eggs in one basket. The important thing to understand is that voice-capable gateways exist to provide external telecommunications connections at that site.The nonvoice- capable gateways can still be used in a centralized environment where all calls are passed through the central site, and there are no off-net local calls.While the central site would then bear all telecommunications costs for the branch office, this isn’t necessarily a bad thing. If the pre-VoIP design assessment found that 95 percent of all calls were to the head office, then the cost of the remaining 5 percent of calls could be routed through the head office backbone, resulting in that 5 percent being all long distance calls back to that branch office, but now coming from head office and not the branch office. However, you must be aware that the 5 percent of rerouted calls could substantially increase your long distance toll call costs, and thus should be a factor when deciding how to reroute calls like these. This is just one example of how VoIP solutions must be approached in any part of the design.The cost savings realized by not purchasing the voice-capable gateways might be realized in that 5 percent of long distance calls.With long distance calls now costing as little as four cents per minute from major carriers, this might just be a negligible expense. Look at Figure 11.2, and you’ll see the changes in removed external telecommunications costs. This is possible if VoIP MGCP firmware is used, but the site will not have any options to create external connectivity without replacing the router and adding the new telco cards, causing site downtime. Notice that routers R4 through R6 have no external connectivity, nor do they have a gatekeeper at each site.This is because the WAN circuit is powerful enough to centralize those functions and still carry the data load as well. Choosing Frame Relay or Leased Lines for Site-to-Site Connectivity The arguments for choosing Frame Relay or leased lines has caused some of the most spirited debates possible, but it must still be discussed no matter what. Frame Relay is less costly than using leased lines, yet it’s usually stable enough to carry the load that leased lines do. So what’s the difference that causes the cost delta? www.syngress.com 109_AVVID_DI_11 10/9/01 2:53 PM Page 396 Designing and Implementing Multisite Solutions • Chapter 11 397 Frame Relay uses a shared medium “cloud” provided by the telecommunications carrier.While your circuit goes from your premises to the provider, the circuit ends and hits the “cloud,” so called because no one really knows (except for the provider) where the data passes through the network devices.All you know is that the data arrives at the destination safely. Figure 11.3 shows an example of a Frame Relay cloud used by many subscribers. This cloud spans the United States and is typically joined by several telecommunications carriers.This cloud is really a series of clouds that serve specific areas of the country, and specific portions of each state as well.These connections are joined by what is called a Permanent Virtual Circuit (PVC).A PVC is nothing more than an increment of 64 Kbps channels bonded together to form the desired capacity of circuit, up to the limit of the carrier. Figure 11.4 shows an expanded view of the state of Florida to show the frame clouds at each of the major cities displayed. www.syngress.com Figure 11.2 Nonvoice-Capable Gateways Remove Extra Costs Backbone Router (R1) 3524 Switch CallManager Unity Site A Router (R4) 3524 Switch T-1 512K Frame Relay Cloud Site B Router (R5) 3524 Switch 512K Site C Router (R6) 3524 Switch 512K Network Exchange MGCP (R3) Gateway PRI Telco H.323 (R2) Gatekeeper Head Office 109_AVVID_DI_11 10/9/01 2:53 PM Page 397 398 Chapter 11 • Designing and Implementing Multisite Solutions www.syngress.com Figure 11.3 A Frame Relay Cloud California Colorado Florida Maine Frame Relay Cloud Frame Relay Cloud Frame Relay Cloud Figure 11.4 The Florida Frame Relay Cloud Florida Frame Cloud Frame Cloud Frame Cloud Frame Cloud Frame Cloud Frame Cloud Pensacola Panama City Jacksonville Daytona Beach Tampa Bay Miami 109_AVVID_DI_11 10/9/01 2:53 PM Page 398 Designing and Implementing Multisite Solutions • Chapter 11 399 This illustrates why connectivity is available in some areas, but not others. Panama City is situated on the coastline of the Florida Panhandle, whereas Pensacola sits on a major junction of highways and cities. Between Panama City and Tampa, all along the southern coastline, little in the way of major commerce exists to warrant the high cost of running the fiber optics cables required to carry Frame Relay communications. Notice how the cities are interconnected in what is called a “full mesh” that assures each city has two or more paths to take between cities.All of these circuits are the responsibility of the carrier, or carriers in some cases, to maintain and grow as demand warrants. However, cities often expand beyond the coverage of their particular commu- nication form (like in Figure 11.5, where Frame Relay spreads out of the central office to the businesses). From these series of figures, it should be clear the bulk of the risk, expenses, and maintenance sits squarely on the shoulders of the carriers.The users only need be concerned with the local connections between the central office and their location. But, when the Frame Relay cloud gets cloudier, increased traffic can impede your traffic, and cause all manner of problems.This is why frame carriers use two functions of Frame Relay to control traffic: www.syngress.com Figure 11.5 A Typical City Frame Cloud Panama City Frame Cloud 4th Street Central Office Bank 23rd Street Offices Court House College 15th Street Hwy 231 Hwy 77 To Pensacola To Tampa To Jacksonville 109_AVVID_DI_11 10/9/01 2:53 PM Page 399 400 Chapter 11 • Designing and Implementing Multisite Solutions ■ Port speed This is the speed of the port on the router where the connection initiates from the central office, and can be as high as a T-1 of 1.536 Mbps.This is sometimes called the burst rate of the connection. ■ Committed Information Rate (CIR) This is the circuit speed the provider guarantees you’ll get all the time, regardless of how many subscribers are on the frame cloud. ■ Committed Burst Size (Bc) This is the maximum volume of data the network agrees to move through the frame cloud under normal working conditions. ■ Excess Burst Size (Be) Under normal working conditions, this is the amount of data above and beyond the Bc mentioned in the preceding bullet. ■ Discard Eligible (DE) This is the Be data marked as lower priority than Bc data; if the frame cloud gets congested, Be data marked with its DE bit set can be discarded to help reduce frame cloud congestion. For most customers, the CIR is one half of the port speed, so a 256 Kbps circuit would have a CIR of 128 Kbps.You pay for the CIR, and a marginal amount higher for the port speed. But, if your traffic flow exceeds the CIR, and the frame cloud is congested, then the carrier can discard your packets at its own judgment to reduce the traffic in the cloud.This means your traffic flows must slow down to account for the congestion. For the most part, Frame Relay works fairly efficiently. But if your connection must remain reliable and not experience discarding of packets, then your only option is to use a leased line circuit (shown in Figure 11.6). Leased lines can easily exceed three times the cost of a Frame Relay pipe, because the connection is 100 percent dedicated from the carrier to your connection. Figure 11.6 shows two sites connected via a leased line, which is directly connected to the central office. In some leased lines, the router in the central office is a massive unit that can host hundreds of connections.This figure has been broken out slightly to show that in a leased line connection, there are patch panels between devices, but only to create the physical circuit directly between devices. The benefit is that at whatever speed you subscribe, you get it on a constant basis regardless of the number of people subscribed to the carrier.Your connection is truly independent, but you’ll most certainly pay for that privilege. In VoIP systems, if the sites are within a few miles of one another, leased lines are usually www.syngress.com 109_AVVID_DI_11 10/9/01 2:53 PM Page 400 [...]... on the Cisco www.syngress.com 407 1 09 _AVVID_ DI_11 408 10 /9/ 01 2:53 PM Page 408 Chapter 11 • Designing and Implementing Multisite Solutions IP SoftPhone, conferencing, and features such as call park and call pickup So, let’s assign a group of numbers: s Head Office 6000 through 699 9 s Site A 7000 through 7 099 s Site B 7100 through 7 199 s Site C 7200 through 7 299 s Conference Calls 799 0 through 799 9 s Call... unmanageable level of expense, one which has virtually no return on investment Multisite AVVID Solutions This last major section of the chapter will be devoted to the remaining major functions of the AVVID family: IP Television (Cisco s IP/ TV), IP Video Conferencing (Cisco IP/ VC), and the associated family of tools for the AVVID family In order to properly implement these solutions, the underlying network... mobile users But currently, site-to-site calling is a function of invoking the IP WAN infrastructure and using up more of the IP WAN bandwidth Since there will soon be more setup information streaming across the IP WAN, the IP WAN must be able to handle an increased level of traffic www.syngress.com 413 1 09 _AVVID_ DI_11 414 10 /9/ 01 2:53 PM Page 414 Chapter 11 • Designing and Implementing Multisite Solutions... cost of providing the partially meshed WAN connections Table 11.2 Approximate Cost of a Partially Meshed WAN Design Item Unit Cost Quantity Subtotal 3640 router $90 00 1 $9, 000 Continued www.syngress.com 1 09 _AVVID_ DI_11 10 /9/ 01 2:53 PM Page 4 19 Designing and Implementing Multisite Solutions • Chapter 11 Table 11.2 Continued Item Unit Cost Quantity Subtotal NM-4T serial card T-1 CSU/DSU 2621 router 2621... all, another benefit of the AVVID platform www.syngress.com 411 1 09 _AVVID_ DI_11 412 10 /9/ 01 2:53 PM Page 412 Chapter 11 • Designing and Implementing Multisite Solutions In the next section, you’ll learn how and why you should either take an existing centralized CallManager and distribute it, or design a brand new distributed solution No matter which direction you take, the principles are the same as that... prevention is one main reason for not configuring your network like the one in Figure 11 .9 Just because a Frame Relay cloud exists in one major metropolis doesn’t mean that there aren’t multiple Frame Relay clouds extending all over the city In Atlanta, Georgia, there are www.syngress.com 405 1 09 _AVVID_ DI_11 406 10 /9/ 01 2:53 PM Page 406 Chapter 11 • Designing and Implementing Multisite Solutions 14 major... that each site now has www.syngress.com 1 09 _AVVID_ DI_11 10 /9/ 01 2:53 PM Page 417 Designing and Implementing Multisite Solutions • Chapter 11 five connections to the Frame Relay cloud.This consists of one of two possible connection types: s One serial port on each router, dividing the T-1 capacity into chunks of equal capacity s Multiple serial ports on multiple routers to provide T-1 capacity to each... 3524 Switch FXO 1 09 _AVVID_ DI_11 3524 Switch PRI Site C Router (R6) VLAN Routing 3524 Switch CallManager Unity Exchange The VLANs between Site C and the head office backbone are just an example, because the real network would have the same VLANs extending to all sites, through all switches, and across the head office backbone to extend through www.syngress.com 403 1 09 _AVVID_ DI_11 404 10 /9/ 01 2:53 PM Page... Services 798 0 through 798 9 These numbers provide for sufficient growth for all sites in question, at least for the foreseeable future Each of the four sites has their own local calling access, so calling overhead has been reduced but not quite eliminated.With these numbers, creating the initial route plans simply point to Site A if the dialed number has the last four digits of 7000 through 7 099 , while... does—reducing network overhead while reaching out to multiple users In the Figure 11.17 example, you saw that using multicast controls effectively used only two streams of data to reach the simple network configuration.This is www.syngress.com 1 09 _AVVID_ DI_11 10 /9/ 01 2:53 PM Page 425 Designing and Implementing Multisite Solutions • Chapter 11 due to the usage of what Cisco calls a rendezvous point (RP) of distribution.This . Office 6000 through 699 9 ■ Site A 7000 through 7 099 ■ Site B 7100 through 7 199 ■ Site C 7200 through 7 299 ■ Conference Calls 799 0 through 799 9 ■ Call Services 798 0 through 798 9 These numbers provide. Solutions • Chapter 11 393 1 09 _AVVID_ DI_11 10 /9/ 01 2:53 PM Page 393 394 Chapter 11 • Designing and Implementing Multisite Solutions The Gatekeeper Function The gatekeeper is a Cisco router that runs. City Jacksonville Daytona Beach Tampa Bay Miami 1 09 _AVVID_ DI_11 10 /9/ 01 2:53 PM Page 398 Designing and Implementing Multisite Solutions • Chapter 11 399 This illustrates why connectivity is available

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