All Packet

Web ProForum Tutorials http://www.iec.org

Copyright The International Engineering Consortium

1/17

Advancing the All-Packet Network

Overview The Internet is producing an exceptionally challenging traffic environment for the circuit-switched public switched telephone network (PSTN). This tutorial proposes an economical and effective solution: preswitch offload of dial-up Internet traffic from the PSTN by advancing the all-packet network closer to the customer than ever before.

Topics 1. Introduction

2. PSTN Congestion: The Internet Brings the Network to Its Knees

3. Implications of Congestion to the PSTN

4. Evolution of Narrowband Off-Load: Moving the Problem Upstream

5. Preswitch Off-Load: Complete Relief to the Network

6. Preswitch Packetization: Relief, Economy, and the Foundation for Convergence

7. Off-Load Economics

8. Summary

Self-Test

Correct Answers

Glossary

1. Introduction Were sorry. All circuits are currently busy. Please try your call again later.

Remember when the busy-out message was pretty much limited to holidays? Seasonable and predictable, that message was not so much bothersome as a simple reminder that an unusually high number of families were using the PSTN to eliminate distances at an important time. Wait a few minutes, dial again, and a connection was likely.



2/17

The success of the Internet and the World Wide Web has changed all that, producing a challenging traffic environment for the PSTN and making the busy-out message a common occurrence. Dial-up Internet calls have dramatically increased both the number of connections and average call hold times, and network load is skyrocketing. Carriers, unable to economically scale their networks to meet exploding demand, have attempted to mitigate the problem with a variety of stopgap measures. These measures, typically trunk-side or post-switch solutions, have met with limited success because they only move the problem upstream rather than eliminate it. Consumer demand for circuits continues to pose a significant threat to the PSTN.

As mentioned, this tutorial will explore an economical and effective solution: preswitch offload. This approach expands off-load to the line-side of overloaded switches, leverages the economies of the public data network for transport on the trunk side, and coexists with current infrastructure. Very important, implementation of this solution represents a tremendous cost savings for carriers. Equally important, preswitch offload is a strategic investment in the next-generation network, providing a scalable infrastructure solution that is an important step toward truly converged data and voice.

2. PSTN Congestion: The Internet Brings the Network to Its Knees Certainly, broadband solutionsprimarily DSL and cableare making an impression on customer choice for Internet access, and their impact will only grow over time. However, growth in new subscribers utilizing PSTN dial-up as their Internet access technology of choice is continuing as well and is not forecast to peak until 2005 (see Figure 1). It will take years for broadband to begin supplying relief to the PSTN from Internet access.

Figure 1. Access Technology Evolution



3/17

Equally concerning for the PSTN, call hold times for Internet access are increasing along with the number of dial-up users. Actual usage data indicates that average Internet session length increased 16 percent (55 to 64 minutes) in the first quarter of 2000 versus the same period in 1999. In terms of PSTN load in centum call seconds (CCS), forecasted subscriber growth multiplied by the increase in hold time nets an increase above 30 percent in data traffic over just the past year. Extrapolating an even more conservative 8 percent CAGR through 2005 predicts PSTN load increasing to more than 300 percent of what it was in 1999 (see Figure 2).

Figure 2. PSTN Impact of Increasing Hold Times

Under the weight of Internet traffic passing through the conventional Class-5 switch and tandem architecture, the PSTN collapses, leaving us with increasing busy-outs as bandwidth is consumed and the network overloaded. The dreaded Were sorry, all circuits are busy message is becoming increasingly common.

3. Implications of Congestion to the PSTN The PSTN as it exists today presents a number of scaling points that provide obstacles to rapid growth. Unplanned network loading, as with the increases in dial-up Internet call hold times, does not follow the more predictable population migration or growth formula that traditionally allowed carriers to upgrade and expand their networks over time. Hot spots emerge as these scaling points are stressed under load.



4/17

Figure 3. Public Switched Telephone Network (PSTN)

Class-5 Switch

An integral part of the PSTN, the Class-5 switch is an extremely complex and expensive piece of equipment that resides within the local exchange or central office (CO). Although all Class-5 switches perform the same tasks within the network, there are two types of Class-5 switches from a connection standpoint. The Class-5 switch at the CO to which the dial-up Internet call is madethe point at which the traffic makes ingress to the PSTNis an ingress switch. The Class-5 switch at the CO to which an Internet service provider (ISP) is connectedwhere the Internet traffic egresses the PSTNis an egress switch. Anything on the network before a switch is considered to be line-side or preswitch, whereas anything after the ingress Class-5 switch is considered trunk-side. Hot spots can occur as a result of unplanned network loading on both the line side and trunk side of the PSTN.

Class-4 Switch

Another major component within the PSTN is the Class-4 tandem switch, which is responsible for intermediate connection of trunk lines between the station originating the call and the destination. Like the Class-5 switch, the Class-4 tandem switch has capacity limitations of its own. Certainly one of the primary scaling points in the PSTN, any necessity to rapidly increase the amount of traffic or number of trunks a tandem facility must manage may cause congestion, creating an additional hot spot.

From a network management perspective, not only is each component complex and expensive, it is also proprietary equipment with very few suppliers and long procurement lead-times. This scenario does not lend itself to economical, rapid scaling to meet new demand for subscribers or for additional network load due to increasing dial-up Internet call hold times. Implied within these major PSTN facility descriptions is that, regardless of where on the network the particular



5/17

component resides, increased load stresses each element's capability and capacitythe more unplanned the load or stress, the more problematic for the carrier and the more likely that facility will become a network hot spot. Moreover, any investment the carrier makes to mitigate the problem reaps no increased revenue due to flat-rate access.

To date, the majority of efforts devoted to easing congestion have targeted the trunk side of the PSTN, attempting to off-load the network and alleviate the need for additional Class-4 tandem switches and Class-5 egress switches.

4. Evolution of Narrowband Off-Load: Moving the Problem Upstream In the beginning, the ISP connection to the PSTN was a dedicated high-speed line from the egress switch to ISPowned modem banks utilizing remote access server (RAS) technology. These huge modem banks proved to be very expensive for the ISP because the more successful the Internet became, the more dial-up modems needed to be purchased and operated in order to meet demand. Meanwhile, in terms of traffic management, because the egress Class-5 switch now had to handle local voice traffic and 100 percent of the ISPs traffic, the egress switch became the network hot spot as dial-up Internet traffic grew.

Figure 4. Remote Access Server (RAS) and Egress Switch Congestion

Carriers were motivated to respond to ISPs with the concept of CObased RAS (COBRAS) service. In this scenario, the modem pool evolves from strategic technology that the ISP must own, to a service purchased from the lowest-cost provider. From a carrier perspective, as RAS is housed within the egress central office, COBRAS provides much greater control over modem traffic engineering and eliminates mandated reciprocal compensation. But despite the advantages to



6/17

this approach, the network hot spot remains the egress Class-5 switch as Internet usage heats up.

Figure 5. COBRAS and Continued Egress Switch Congestion

Egress switch congestion has driven carriers to look at alternative RAS connection architectures, including direct RAS connection to tandem switches. This tandem-based approach effectively off-loaded the egress Class-5 switch, but the burden just moved upstream to the tandem switch. Juggling the demands of its normal voice-oriented trunk switching and handling direct RAS connections, the Class-4 tandem switch now experienced capacity problemsit had become the network facility being overrun by dial-up Internet traffic instead of the Class-5 switch. In the end, direct RAS connections to tandem switches merely served to aggravate tandem exhaust problemsa new hotspot but a hot spot just the same.

Figure 6. Tandem-Based Off-Load Moves Hot Spot to Class-4 Facilities



7/17

The tandem exhaust issues have driven carriers to directly connect RAS to ingress Class-5 switches, which offload both egress Class-5 switches and Class-4 tandem switches. As major ISPs have begun demanding their own direct trunks to COBRAS, capacity issues arise again at the ingress Class-5 switch. The tandem exhaust problem is solved but not the overall problemthe hot spot is simply being moved around.

Figure 7. Direct Trunk Offload and Resulting Ingress Switch Congestion

More recently, a fresh offload approach has emerged with the advent of the trunking gateway (TGW). Deploying a TGW within a tandem application allows trunks to be shared across multiple RASs/ISPs and provides a secondary benefit of simplifying trunk management. Furthermore, the gateway can parse voice and data traffic, totally off-loading the egress Class-5 switch of ISP traffic.

Figure 8. Trunk Consolidation/Off-Load via Trunking Gateway (TGW) and Continued Ingress Switch Congestion



8/17

However, the TGW does nothing to mitigate the traffic problems at the ingress Class-5 switchesthey remain hot spots. In other words, no matter what solution is employed on the trunk side, the hot spot inevitably moves upstream to a Class-5 switch or Class-4 tandem switch.

5. Preswitch Off-Load: Complete Relief to the Network Having exhausted trunk-side solutions in attempts to relieve the entire network, exploration of line-side solutions is in order. Line-side off-loading serves to relieve the PSTN by keeping data traffic away from Class-5 and tandem switches entirely.

The key component in line-side off-loading is the access gateway (AGW), which separates data calls from voice calls before they hit the ingress switch. The AGW dynamically determines call type using dialed number via intelligent network (IN)/local number portability (LNP) or local database, and routes the traffic accordingly.

Figure 9. Access Gateway Preswitch Off-Load in Detail

In this approach, baseband voice calls are sent to the ingress PSTN Class-5 switch as always, while dial-up ISP calls are routed around it. Fully compatible with trunk-side off-load, COBRAS, and RAS, Internet off-load prior to the ingress switch provides for parsed time division multiplexing (TDM) modem data transport to the egress central office TGW via DS1 or IMT/PRI, affording total network off-load.



9/17

Figure 10. Preswitch Off-Load: Hot Spot Elimination through Redirecting Dial-Up Internet Calls before the Class-5 Switch

Ultimately, preswitch off-load solutions allow carriers to save tremendous switch resources by redirecting various access technologies to the Internet or other data networks without involving any Class-5 switch. By utilizing a preswitch off-load solution, carriers can lessen their investment in costly, inefficient circuit-switched technology and invest in the future.

6. Preswitch Packetization: Relief, Economy, and the Foundation for Convergence Clearly, implementing preswitch off-load via AGW is a major step in the right direction. Preswitch packetization provides even further improvement in off-load and economics, as well as positioning the infrastructure for next-generation converged voice and data.

In terms of economy, packetization at the ingress CO reduces modem transport bandwidth required by a ratio of greater than 6 to 1. This allows the use of this bandwidth for other purposes and extends the life of existing equipment as PSTN tandem trunk and switching capacity is reclaimed through the absence of Internet traffic.

Moreover, preswitch packetization provides the platform for strategic investment in voice off-load. Advancing the all-packet network deep into the line side, new access gateways can be devised to packetize all voice and data preswitch for ultimate off-load, as well as form the foundation for next-generation convergence platforms.

In the carrier-grade convergence solution, voice, modem, and DSL traffic will terminate right on the platform, obviating the need for external DSLAMs and



10/17

other stand-alone access equipment. GR303/TR08 support will make the platform totally transparent to the DLC and the Class-5 switch, while voice will be directly and reliably packetized to VoIP, VoATM (VToA), or VoFR and transported accordingly. Scalability will be improved by eliminating the need to purchase extremely expensive, long lead-time Class-5 and tandem switching equipment.

Figure 11. Preswitch Packetization Off-Loads PSTN and Provides Foundation for Converged Network

In the end, next-generation convergence solutions will allow carriers to save tremendous switch resources by redirecting data access technologies as well as terminating services on a platform that resides before the traditional circuit-switched network. By accomplishing this directly upon a next-generation convergence platform, carriers can lessen their investment in circuit-switching equipment as well as service-specific narrowband and broadband platforms.

7. Off-Load Economics Rapid5 Networks performed a case study to test and analyze the economics of the various approaches within a representative carrier environment. This environment consisted of a LATA with over 1M lines and 23 central offices.

Figure 12. Offload Economics Case Study



11/17

The data in Figure 12 represents the costs of increasing PSTN capacity over a five-year period (20002005) and off-load savings from reduction in growth of PSTN equipment (Class-5 and tandem switches) and interoffice trunks but not including operational savings.

Referring to Figure 12, this data shows that continuing to support increasing data traffic without any type of off-load technology would require expenditures in excess of $12 million over the period for a single LATA. Simply implementing trunk-side off-load gains a reduction of over one-third. However, preswitch off-load and preswitch packetization have far greater impact, reducing costs by almost 80 percent. Furthermore, with the preswitch packetization approach, the fundamental infrastructure is already in place for next-generation convergence.

8. Summary This tutorial has identified the problem and the source of PSTN overloading, the various methods employed by carriers to mitigate that congestion, and the preswitch solutions that work in concert with trunk-side methods to provide total PSTN off-load of problematic, long hold-time Internet and data traffic.

Among all off-load options, preswitch packetization takes off-load to the next level by providing relief to the entire PSTN: ingress switches, tandem switches, egress switches, and interoffice facilities. Furthermore, this technique provides a key infrastructure component for the next-generation converged network, in which all voice traffic will be packetized and routed along with data traffic over the public data network (PDN).

The convergence platform will initially off-load and extend the life of PSTN investments. It will follow on to augment the network and its equipment with increased capability, enabling the carrier to be more transport-agnostic while becoming more service-centric. Finally, the converged network will arise from the very platform the carriers used to off-load and extend the life of their PSTN gear. Enabling a graceful migration to the next-generation networkwithout a forklift changeoverthe convergence platform will ultimately replace legacy infrastructure with the capability to packetize all traffic on the line side and best-way routing on the trunk side.

Advancing the all-packet network nearer to the customer, to modernize, extend, evolve, and ultimately revolutionize the network, is the future of telecommunications.



12/17

Self-Test 1. The ______________ is an extremely complex and expensive piece of

equipment that resides within the local exchange or central office (CO).

a. PSTN

b. ISP

c. Class-5 switch

d. Class-4 switch

2. The _______________ tandem switch is responsible for intermediate connection of trunk lines between the station originating the call and the destination.

a. PSTN

b. ISP

c. Class-5

d. Class-4

3. To date, the majority of efforts devoted to easing congestion have targeted the trunk side of the PSTN, attempting to off-load the network and alleviate the need for additional Class-4 tandem switches and Class-5 egress switches.

a. true

b. false

4. Egress switch congestion has driven carriers to look at alternative RAS connection architectures, including direct RAS connection to tandem switches.

a. true

b. false



13/17

5. The key component in line-side off-loading is the ________________, which separates data calls from voice calls before they hit the ingress switch.

a. softswitch

b. access gateway

c. trunking gateway

d. none of the above

6. Preswitch off-load solutions are typically more costly to carriers because they redirecting various access technologies to the Internet or other data networks without involving any Class-5 switch.

a. true

b. false

7. In the carrier-grade convergence solution, voice, modem, and DSL traffic will terminate right on the platform, obviating the need for external DSLAMs and other stand-alone access equipment.

a. true

b. false

8. By accomplishing convergence solutions directly upon a next-generation convergence platform, carriers can lessen their investment in circuit-switching equipment as well as service-specific narrowband and broadband platforms.

a. true

b. false

9. Actual usage data indicates that average Internet session length increased _______ percent (55 to 64 minutes) in the first quarter of 2000 versus the same period in 1999.

a. 25

b. 66

c. 10

d. 16



14/17

10. Advancing the all-packet network nearer to the customer, to modernize, extend, evolve, and ultimately revolutionize the network, is the future of telecommunications.

a. true

b. false

Correct Answers

1. The ______________ is an extremely complex and expensive piece of equipment that resides within the local exchange or central office (CO).

a. PSTN

b. ISP

c. Class-5 switch

d. Class-4 switch

See Topic 3.

2. The _______________ tandem switch is responsible for intermediate connection of trunk lines between the station originating the call and the destination.

a. PSTN

b. ISP

c. Class-5

d. Class-4

See Topic 3.

3. To date, the majority of efforts devoted to easing congestion have targeted the trunk side of the PSTN, attempting to off-load the network and alleviate the need for additional Class-4 tandem switches and Class-5 egress switches.

a. true

b. false

See Topic 3.



15/17

4. Egress switch congestion has driven carriers to look at alternative RAS connection architectures, including direct RAS connection to tandem switches.

a. true

b. false

See Topic 4.

5. The key component in line-side off-loading is the ________________, which separates data calls from voice calls before they hit the ingress switch.

a. softswitch

b. access gateway

c. trunking gateway

d. none of the above

See Topic 5.

6. Preswitch off-load solutions are typically more costly to carriers because they redirecting various access technologies to the Internet or other data networks without involving any Class-5 switch.

a. true

b. false

See Topic 5.

7. In the carrier-grade convergence solution, voice, modem, and DSL traffic will terminate right on the platform, obviating the need for external DSLAMs and other stand-alone access equipment.

a. true

b. false

See Topic 6.



16/17

8. By accomplishing convergence solutions directly upon a next-generation convergence platform, carriers can lessen their investment in circuit-switching equipment as well as service-specific narrowband and broadband platforms.

a. true

b. false

See Topic 6.

9. Actual usage data indicates that average Internet session length increased _______ percent (55 to 64 minutes) in the first quarter of 2000 versus the same period in 1999.

a. 25

b. 66

c. 10

d. 16

See Topic 2.

10. Advancing the all-packet network nearer to the customer, to modernize, extend, evolve, and ultimately revolutionize the network, is the future of telecommunications.

a. true

b. false

See Topic 8.

Glossary AGW access gateway

CAGR cumulative annual growth rate

CCS centum call seconds



17/17

CO central office

COBRAS CObased RAS

DSL digital subscriber line

DSLAM digital subscriber line access multiplexer

IN intelligent network

ISP Internet service provider

LATA local access transport area

LNP local number portability

PDN public data network

PSTN public switched telephone network

RAS remote access server

TDM time division multiplexing

TGW trunking gateway

VoATM voice over asynchronous transfer mode

VoFR voice over frame relay

VoIP voice over Internet protocol

Overview1. Introduction2. PSTN Congestion: The Internet Brings the Network to Its Knees3. Implications of Congestion to the PSTN4. Evolution of Narrowband Off-Load: Moving the Problem Upstream5. Preswitch Off-Load: Complete Relief to the Network6. Preswitch Packetization: Relief, Economy, and the Foundation for Convergence7. Off-Load Economics8. SummarySelf-TestCorrect AnswersGlossary

Documents

All Packet