[ Pobierz całość w formacie PDF ]
.These evolving technologies include one or moreof the following:a.Routing the packets for real-time voice sessions using an overprovisionedor overcapacity-based voice-grade transport network (e.g., one-way ETEdelay of less than 100 msec, delay variation of less than 20 msec, andpacket loss of less than 3%; for G.711, a coded voice signal withoutsilence suppression with 20 msec of voice sample or packet);b.Administration of voice call admission on the basis of ETE monitoring ofmultiplexing, storage, and bandwidth or transmission resources;c.Categorization of real-time voice and loss-sensitive data into separatestreams so that they can be multiplexed over di¤erent sets of RTP andUDP ports and, if required, can even be routed over di¤erent sets of IPaddresses to guarantee the required quality of service; andd.Deployment of IP version 6 (IPv6, IETF s RFC 2460/1883) or IP version4 (IPv4, IETF s RFC 791) with IPSec infrastructure in the network. VoIP IN THE ACCESS OR LOCAL LOOP 99Many next-generation network element manufacturers and service providersare exploring the e¤ectiveness of these technologies for VoIP service in the pilotnetworks.These are discussed further later in this chapter and in Chapter 9.It is well known [1 4] that PSTN networks are inherently more secure andreliable than VoIP networks and are capable of providing high-quality oftransmission.However, they are neither open nor flexible enough to accom-modate new value-added services as rapidly as VoIP-based networks.Using the architecture shown in Figure 7-1, VoIP-based LD and otherCLASS-4 services can be deployed as per the service capacity and capabilityrequirements.For example, one can start with one VoIP call server, two IP-PSTN MGWs, a firewall and network address translator (NAT) device, and aVPN with a few call-originating and -terminating sites at the beginning.Then,as the demand increases, a network of VoIP call servers can be created, witheach server controlling a cluster of IP-PSTN MGWs, and so on.For large-scale deployment, service providers may consider using the archi-tecture framework shown in Figure 1-9, as recommended by the MultiserviceSwitching Forum (MSF) in their recently published implementation agree-ments (available at www.msforum.org/techinfo/approved.shtml, 2001).Thebeauty of this architecture is that the functional elements used here are su0 -ciently modular or granular, and the interactions among these elements canoccur over, IP links using various open or standard VoIP protocols such asSIP, MGCP, Megaco/H.248, and SCTP.These make the network architecturemore scalable, growable, and proof of any emerging technologies.In addition,these characteristics can help the service providers launch new and emergingservices such as Internet call waiting, customized criteria-based call forward-ing, instant messaging and conferencing, and so on very quickly and eco-nomically.VoIP IN THE ACCESS OR LOCAL LOOPIn residential access networks, IP-based real-time voice or telephony servicecan be o¤ered using a variety of access networking technologies.Recent devel-opments in the technologies for access networking and physical transmissionhave significantly contributed to delivering broadband services to the home(BTTH, [5]).These include digital subscriber line (DSL, www.dslforum.org,www.dsllife.com, 2001) technologies, Ethernet in the first mile (EFM, www.efmalliance.org, 2001) technology, packet-cable and data over cable serviceinterface specifications (DOCSIS, www.packetcable.com, 2001) technologies,and various WLL technologies.These are discussed in details in References 4to 6.In PSTNs, traditionally CLASS-5 switches along with twisted-pair copperwire based local loops, are used to o¤er telephony service using channel asso-ciated signaling (CAS) [1,4,6].Table 7-2 presents a list of the most widely usedCLASS-5 features and services.A detailed list of all of the CLASS-5 features 100 VoIP IN THE PUBLIC NETWORKSTABLE 7-2 Widely Used CLASS-5 Features and ServicesAutomatic callback: automatic redialing of the last number dialedAutomatic recall: automatic dialing of the last incoming caller s phone numberCall blocking: blocking of certain outgoing calls by the subscriberCall pickup: answering a call to one line from another line location by using an accesscodeCall transfer: transferring calls from one line to anotherCall waiting: flashing of a text message (in the display of the phone set) or a back-ground audio message/tone to announce a second incoming callCall forwarding busy line: forwarding incoming calls to another number when thedialed telephone is busyCall forwarding don t answer: forwarding incoming calls to another number whenthe call is not answeredCall forwarding universal: unconditional forwarding of incoming calls to anothernumberCall forwarding call-waiting calls: forwarding incoming call-waiting calls to anothernumberCall forward remote activation: activation of call forwarding remotely from anyother phoneCall hold: putting an active call on hold in order to pick it up from another lineCall intercept or anonymous caller rejection: intercepting or rejecting all incoming callsthat block delivery of the caller s telephone number, name, or bothCaller s name and number (caller ID) delivery: displaying the calling party s telephonenumber and name after one ringCalled ID blocking: to blocking the calling party s identification (name, number, orboth)Cancel call waiting: special prefix code (e.g
[ Pobierz całość w formacie PDF ]