VoIP and E911 by Cory M Langston


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VoIP and E911 by Cory M Langston

  1. 1. VoIP and E911 1 Running head: VoIP and E911 Modern problems: VoIP and E911 Cory M Langston University of Central Florida
  2. 2. VoIP and E911 2 Abstract This paper discusses some of the issues facing VoIP as it continues to mature. After a brief introduction to the technology, it focuses on Quality of Service and compliance with the FCC’s E911 initiative.
  3. 3. VoIP and E911 3 Modern problems: VoIP and E911 Introduction For years, technologists have spoken about digital convergence. The goal, too integrate voice service with our existing packet switched data networks. The ability to use one network to carry voice, data, and video lowers infrastructure costs and give us more benefits than maintaining two separate networks for voice and data. Voice over the Internet Protocol (VoIP) is one of the technologies making this goal a reality. Essentially, VoIP lets us digitize a voice stream and then we chop that data into little slices called packets and then we send them over the internet (Hardy & NetLibrary Inc., 2003). Since the dawn of the broadband era, internet service providers have increased the bandwidth available to consumers so even residential customers have the spare bandwidth to consider migrating their voice service from the public switched telephone network (PSTN) to VoIP. Service providers like Vonage are already boasting more than 2 million subscribers and they off a slew of features like free long distance, caller ID, and much more. However, VoIP service providers still have several issues to overcome before they can match the PSTN. One issue is maintaining an acceptable level of Quality of Service, availability, and reliability (Khasnabish & NetLibrary Inc., 2003). Another issue is integrating with the Emergency Public Safety Answering Point (PSAP) so users can call 911 directly and trust that their location will automatically be conveyed to the operator. Quality of Service A major issue facing VoIP is Quality of Service (QoS). To improve the quality of service of VoIP sessions the IETF has defined Differentiated Services (a.k.a. DiffServ) which helps provide priority based handling for packets that need real time service. DiffServ helps
  4. 4. VoIP and E911 4 administrators prioritize voice packets on their network (Nichols, 1998). Prioritization is necessary to help prevent packet loss and excess delay. Packet Loss Packet switch networks were originally designed for transmitting data. Data communications are not as disrupted by packet loss as voice communication. If someone sends an email and the network gets congested then routers will start dropping the extra packets they can’t process. If one or two packets of your email gets dropped, the packet is simply resent after a watchdog timer expires on the transmitter. However, VoIP expects all of its packets to arrive within a certain period. If a VoIP call misses a few packets, the packets are not resent and the recipient does not get the whole message. This can lead to a choppy phone conversation as the speakers voice cuts in and out. Unfortunately, packet loss usually tends to occur in bursts during brief periods of congestion at network peering points, which can completely ruin a conversation. A priority based handling lets routers differentiate between packets that need real-time priority. Differentiated service lets applications use the type of service (TOS) field in the IP header to indicate when a packet needs increased priority. If routers are configured to use this service, they will give them preferential treatment when they get congested they will drop excess packets that do not need real-time service first (Nichols, 1998). One of the issues with differentiated service is it must be enabled by each network to maintain a quality connection between networks. Your ISP may use it for their network, however, there is no guarantee the intermediary networks handling your call support differentiated service.
  5. 5. VoIP and E911 5 Jitter Latency is another issue that must be overcome by VoIP services. Since packet switching networks dynamically route information VoIP packets can traverse any path. The service can not depend upon a virtual circuit with a fixed amount of latency. Instead, it has to be prepared to handle a stream of packets with a variable amount of latency. The difference in the amount of latency experienced is called jitter. When latency exceeds 150 milliseconds in one direction the natural flow of conversation is strained[…] (Phil & Cary, 2004). To compensate VoIP applications utilize a jitter buffer, which essentially introduces a fixed amount of delay prior to playback in order to give packets enough time to arrive. To help reduce latency VoIP uses the connectionless user datagram protocol (UDP) to send information. The real-time protocol (RTP), which rides on top of UDP, is used to handle packet sequence information and timestamps so endpoints can manage jitter. RTP helps the service dynamically adjust the jitter buffer based on changing network conditions (Phil & Cary, 2004). Availability One of the biggest challenges facing VoIP is availability. VoIP service may be lost in the event of a power outage (FCC, 2006). In this regard, VoIP service is not as reliable as the PSTN. The PSTN provides central power. In the event of a power outage, the PSTN is still able to provide dial tone. Local exchange carriers have invested in generators to power the central office and battery backups in their SLECs to provide power in the event of a power failure so your service will always be available. Major VoIP service providers use the Internet to route calls. The Internet is a distributed network that depends on edge equipment and access units to provide their own power. In order for your VoIP service to work properly, your broadband modem must have power as well as
  6. 6. VoIP and E911 6 your network service provider. Currently, some modem manufacturers provide a built-in lithium ion battery to provide power in the event of a power failure (WikiPedia, 2006). Businesses that implement a VoIP infrastructure with an IP enabled PBX have the option of providing central power to their VoIP phones by using Power over Ethernet (PoE). Power over Ethernet lets a switch use one of the unused pairs in a CAT5 cable to provide DC to power a phone. Central power is a critical component for availability. A system is only as robust as its weakest component. Since power cables are not always buried underground, the power grid is vulnerable to failure. Consider what happens to the power grid in the event of some common Florida emergencies. A car crashes into a power pole outside of your business resulting in injuries and a local power outage. Central power lets you call for help. A squirrel running across a power line shorts a circuit, is electrocuted, and trips the inline breakers on the power pole. Central power lets you call the power company for help. A cell phone could also work in these situations. Due to availability issues, companies like Vonage recommend keeping a landline if you have an alarm system that needs to be able to dial out in an emergency. VoIP providers offer a network availability feature to address incoming calls during a disruption. When enabled, network availability lets a person designate a phone number to forward their calls to during service outage. The FCC’s E911 mandate In June 2005, the FCC mandated that interconnected VoIP services provide access to Enhanced 911 (E911) for every customer. E911 is a mechanism that automatically transmits your location and phone number to an emergency operator when you dial 911. The 911 calls from VoIP system may work differently than calls from a landline.
  7. 7. VoIP and E911 7 Currently, local exchange carriers provide access to the local public safety answering point (PSAP). When you dial 911 from a landline, your phone number is transmitted to the local PSAP operator via an automatic number identification (ANI) message. The incumbent local exchange carrier maintains an automatic location identification (ALI) database that matches each phone number with a location. The operator uses the phone number lookup the location of the caller in the ALI database (WikiPedia, 2006). Under the FCC mandate, interconnected VoIP services must; deliver all 911 calls to the local emergency call center; deliver the customer’s call back number and location information where the emergency call center is capable of receiving it; and inform their customers of the capabilities and limitations of their VoIP 911 service (FCC, 2006). Today, when you dial 911 from a VoIP connection, it may not go directly to the PSAP. Instead you may be routed to the VoIP’s emergency call center so they can verify your location information and route you to the appropriate local PSAP (FCC, 2006). Alternatively you may be routed to the wrong PSAP or your call may not transmit your location or call back number correctly. Implementing these features is a challenge that VoIP providers are trying to address. AT&T has come up with a solution to address their “nomadic” users. Nomadic users are those who are mobile and travel from one area to the next. When a nomadic user powers down their phone, CallVantage will disconnect their service. The next time they power up they will be asked if their location has changed. If it has not then service is restored. If it has changed then they’re directed to update their location information by calling an 800 number or visiting a web page (Cauley, 2005). The drawback of this method of maintaining location information is that it completely depends upon the user to enter address updates accurately and on demand whenever they change. An automatic solution would make it much more reliable and user friendly.
  8. 8. VoIP and E911 8 Conclusion VoIP may promise to offer more features with less cost, but it has several issues to solve as it matures. Although VoIP can provide free long distance for those wishing to place international calls, it is struggling to deal with new regulations that require service providers to integrate with local public safety access points. Will VoIP continue to be affordable as the government imposes new regulations? The Quality of service (QoS) of VoIP calls is threatened by jitter and congestion. Peer networks that carry VoIP without properly implementing differentiated service also threaten QoS. The distributed nature of the Internet makes it difficult to control quality. The lack of central power means service is lost during a power outage. VoIP has a long way to go, if it is going to offer the same reliability and quality as circuit switched phone networks.
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