Telcordia
`Notes on the Networks
`
`
`
`Telcordia Technologies Special Report
`SR-2275
`Issue 4
`October 2000
`
`An SAIC Company
`
`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 1
`
`

`

`Telcordia Notes on the Networks
`Copyright Page
`
`SR-2275
`Issue 4
`October 2000
`
`Telcordia Notes on the Networks
`
`SR-2275 replaces SR-2275, Bellcore Notes on the Networks, Issue 3, December 1997.
`
`Related documents:
`
`SR-NOTES-SERIES-01, Telcordia Notes on the Synchronous Optical Network
`(SONET)
`SR-NOTES-SERIES-02, Telcordia Notes on Dense Wavelength-Division
`Multiplexing (DWDM) and Optical Networking
`SR-NOTES-SERIES-03, Telcordia Notes on Number Portability and
`Number Pooling
`SR-NOTES-SERIES-04, Telcordia Notes on the Evolution of Enhanced
`Emergency Services.
`
`To obtain copies of this document, contact your company’s document coordinator
`or your Telcordia account manager, or call +1 800.521.2673 (from the USA and
`Canada) or +1 732.699.5800 (all others), or visit our Web site at www.telcordia.com.
`Telcordia employees should call +1 732.699.5802.
`
`Copyright © 2000 Telcordia Technologies, Inc. All rights reserved. This document
`may not be reproduced without the express written permission of Telcordia
`Technologies, and any reproduction without written authorization is an
`infringement of copyright.
`
`Trademark Acknowledgments
`Telcordia is a trademark of Telcordia Technologies, Inc.
`CLCI, CLEI, CLFI, CLLI, ISCP, NMA, and SEAS are trademarks of Telcordia Technologies, Inc.
`COMMON LANGUAGE, SPACE, TELEGATE, AIRBOSS, and TIRKS are registered trademarks of
`Telcordia Technologies, Inc.
`CLASS is a service mark of Telcordia Technologies, Inc.
`Appletalk is a registered trademark of Apple Computer, Inc.
`DECNet is a trademark of Digital Equipment Corporation.
`1/1AESS, 4ESS, 5ESS, Dataphone, and SLC are registered trademarks of Lucent Technologies, Inc.
`DMS-10, DMS-100F, DATAPATH, and TOPS are trademarks of Nortel.
`DMS-100 is a registered trademark of Nortel.
`NEAX-61E is a trademark of NEC America, Inc.
`EWSD is a registered trademark of Siemens AG.
`
`Any other companies and products not specifically mentioned herein are trademarks or service marks
`of their respective trademark and service mark owners.
`
`ii
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`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 2
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`

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`SR-2275
`Issue 4
`October 2000
`
`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`18. IP Networking and Next Generation Networks
`
`18.1 Introduction to Next Generation Networks
`
`Telecommunications networks have traditionally focused on the support of voice
`traffic and voice services. As a result, the Public Switched Telephone Network
`(PSTN) has been optimized for voice traffic and services through a combination of
`circuit-switching, Time-Division Multiplexing (TDM), and Signaling System Number
`7 (SS7). This voice infrastructure, developed and refined over the past century, has
`matured into a high-quality, reliable network. The network is ubiquitous and highly
`secure. Over the past decades, numerous voice services have been introduced in the
`PSTN.
`
`With the growth of computing and networking, there has been a significant
`development of a data communications infrastructure. The data communications
`infrastructure was primarily developed to help corporations and other private
`networks (such as Universities) send information within a defined and closely
`managed group. The role of the public network infrastructure was to connect
`numerous private networks, using two distinct approaches:
`
`1. Using either dedicated digital switched circuits or dedicated T1/E1 lines
`
`2. Building and operating separate parallel networks to carry high-capacity data
`traffic.
`
`The explosive growth of the Internet, with its accessibility to businesses and
`residences, has led to a new way of looking at the data communications
`infrastructure. The growth in the Internet has popularized the deployment of packet
`switching, and more and more public carriers have had to start considering using
`packet switching for the parallel data infrastructure. The Internet (and, in
`particular, use of the Internet Protocol) is providing a framework for sending and
`receiving voice, data, video, and multimedia over a common infrastructure. The
`Internet also provides a model for an infrastructure that can support a wide variety
`of applications, that could be rapidly introduced, often relying on intelligence being
`distributed at the “edges” of the network.
`
`As technology has evolved, it is clear that Next Generation Networks (NGNs) are
`emerging. The goal of NGNs is to use the best from both the voice and data
`communications infrastructures. Thus, the vision of NGN is to provide a common
`infrastructure that supports a wide range of applications, including voice, data,
`video, and multimedia, while maintaining the high reliability, security, ubiquity, and
`controlled Quality of Service (QoS) offered by today's voice infrastructure. The
`NGN is intended to be able to support users with a wide range of Customer
`Premises Equipment (CPE), from the telephony phones in the PSTN to Internet
`appliances including PCs and PDAs, using a variety of wireline and wireless access
`technologies. NGN is intended to provide an infrastructure to rapidly offer new
`innovative applications and services and offer service providers the option of time
`or usage-sensitive billing.
`
`18–1
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`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
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`SR-2275
`Issue 4
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`18.1.1 Motivation for Next Generation Networks
`
`Various industry experts have published numerous forecasts about the amount of
`voice and data traffic that will be transmitted over worldwide networks. Their
`published forecasts seem to support just about every point of view, from the wildly
`optimistic, to the rather conservative, with a variance of over 100 percent for the
`years 2002 and 2003. A composite of forecasts by these industry experts suggests
`that, while voice traffic is growing at 6 to 9 percent a year, data traffic is expected
`to grow at rates between 45 and 100 percent, leading to a dominance of data traffic
`over voice.
`
`NGN would allow carriers to take advantage of savings as a result of the
`consolidation of voice and data networks. Today, many large carriers have
`independent networks for transporting voice and data. While the existing circuit-
`switched network is mainly used for voice calls, newer packet-based networks are
`being deployed to handle data transport. However, maintaining two independent
`networks is inherently expensive. One important component of NGN is Voice Over
`Packet (VOP). VOP transports voice calls on packet-based data networks. The
`NGN/VOP thus presents carriers with an opportunity to migrate all information
`transport, i.e., voice, data, fax, image, and video, onto a single medium. This would
`likely create significant cost reductions on transport, switching, on-site cabling and
`equipment, and administration and management, with the single network for both
`voice and data communications.
`
`Given the much higher growth in data traffic, carriers are being forced to make
`investments to upgrade their packet networks. VOP would allow the carrier to use
`the same packet network to handle the growth in its voice traffic. For newer
`carriers who do not have their own infrastructure, the economics are even more
`compelling. Given the faster growth in data traffic, the carrier is likely to deploy a
`packet network to handle its data traffic. NGN/VOP would allow the carrier to use
`the same network for voice. Another motivation is that NGN/VOP provides the
`opportunity for additional revenues for service providers that have data network
`with spare capacity, which can be used for voice calls. Many service providers, such
`as ICs, CLECs, and alternate access providers, have already deployed high-capacity
`digital networks to key enterprise sites. The same scenario is true in many other
`countries, where INCs have bypassed the incumbent’s PSTN to selected large
`business sites. These same high-speed networks, which were originally used for
`data, can be utilized using VOP for long-distance and international voice calls.
`
`Another key motivation for service providers is that NGN can provide the necessary
`infrastructure for offering bundled services to its key customers. There are industry
`studies that indicate that a residential customer is much more likely to change
`service providers if the customer obtains only a single service from a provider. An
`example, is the high “churn” among long-distance customers of major ICs. However,
`if a customer is offered multiple services such as wireless, local phone, long-
`distance phone, and Internet access bundled together as a single offering by a
`service provider, then the customer is much less likely to switch to another carrier.
`
`18–2
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`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 4
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`SR-2275
`Issue 4
`October 2000
`
`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`Over the longer term, arguably the most significant motivation is that NGN provides
`carriers with the potential for new service offerings. Such newer services, most of
`which are still in the conceptual stage, could take advantage of both voice and data
`offerings. In addition, packet networks offer a more “open” environment with
`greater flexibility for service creation and customization than the relatively “closed”
`telephony environment. NGN could allow the option of supporting Application
`Programming Interfaces (APIs) that are open and available to any developer or in-
`house development group, to create custom services for each enterprise. Large
`businesses, such as banks, government, transportation companies, hi-tech, and
`health care concerns, who are likely to be a carrier's key customers, would be able
`to create and deploy custom telecommunications services to meet their unique
`requirements. This is in contrast to traditional telephony networks where there are
`few open APIs. For example, a traveling employee can connect a notebook
`computer to the public Internet or a corporate Intranet to obtain information,
`access databases, and send/receive e-mail. However, on the same call, the user can
`also use the speaker and microphone built into the notebook PC to check voice
`mail, and make voice calls through an office PBX.
`
`In addition, there are studies that suggest cost advantages of NGN. Analyses show
`that NGN offers cost advantages for both switching and transport. Some studies
`have suggested that the combined infrastructure and operations cost savings could
`be as much as 30 to 50 percent. However, such analyses depend on the specific
`assumptions used, and are often based on market forecasts and assumptions that
`may or may not be applicable to a particular situation. The cost-savings potential of
`NGN is realistic, but needs to be quantified on a case-by-case basis to develop a
`sound business case for migration to NGN.
`
`Another consideration for NGN is that, despite the much faster growth of data
`traffic, most revenues and profits for service providers today are obtained by
`supporting voice and voice services. As a result, support for voice and voice
`services over a packet infrastructure can be considered a critical component of
`NGN deployment. As such, VOP, which provides a carrier class solution for
`supporting voice, should be viewed as the first step toward NGN.
`
`The technology that enables VOP is not new. Technologies such as voice
`packetization, data detection, and silence suppression have been used for many
`years as a means of improving the trunking efficiencies for international submarine
`cable systems and other transport systems, with a relatively high cost of bandwidth
`and low flexibility in system bandwidth upgrade. What is new is this:
`
`1. Signal processing technology has advanced enough to allow these systems to be
`implemented on single chip digital signal processors and personal computers
`
`2. Protocols have been developed which standardize the means for packetized
`voice to be transmitted and controlled over ordinary data networks, based on
`the Internet Protocol stack.
`
`Many of the initial NGN/VOP solutions are based on the H.323 family of standards,
`which is published by the ITU-T. However, existing standards do not address all the
`needs of a carrier wanting to deploy VOP. For example, H.323 does not address
`
`18–3
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`IP Networking and Next Generation Networks
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`SR-2275
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`guaranteed QoS, and it is generally acknowledged that, in order to have acceptable
`voice quality using VOP over wide area networks, some control over such
`parameters as packet latency and packet loss is required. NGN/VOP solutions that
`are considered for wide deployment in public networks may have to demonstrate
`suitability from several different perspectives. The NGN/VOP solution would have
`to provide necessary reliability and security that is expected in public networks. It
`would also be critical for the NGN/VOP solution to be scalable (lack of scalability is
`one of the inadequacies of initial NGN/VOP solutions). In addition, the following
`issues are important:
`(cid:127) Interoperability
`The NGN/VOP deployed in the network would have to interwork not only with
`other VOP networks, but also with the legacy PSTN for support of end-to-end
`voice calls and other narrowband services.
`(cid:127) Voice Quality
`The NGN/VOP would have to offer voice quality comparable to that offered by
`the PSTN.
`(cid:127) Telephony Features and Services
`The NGN/VOP would have to be able to support the suite of telephony features
`and services offered by the typical PSTN. This would, in many cases, imply that
`the NGN/VOP would be able to interact with the Common Channel Signaling
`(CCS) network and Service Control Points (SCPs) in the PSTN. In addition, the
`NGN/VOP would need a framework to support new services.
`(cid:127) Accounting and Settlements
`The NGN/VOP would have to provide necessary capabilities for billing and
`accounting management. In many cases, this implies the ability to interact with
`legacy billing systems.
`(cid:127) Network Management
`The NGN/VOP would need to support the necessary operations and network
`management capabilities expected in public networks. This implies that the
`elements of the NGN/VOP architecture would need to have built-in capabilities
`to support operations and network management. These capabilities would have
`to be integrated into an overall operations architecture.
`
`18.1.2 Next Generation Network Framework Architecture
`
`Figure 18-1 illustrates the functional elements in a typical NGN framework
`architecture. The key functional elements shown in the figure are described below.
`In addition, the architecture relies on a Core Network and an Access Network for
`providing the necessary connectivity and transport. The Core Network is the packet
`transport network (typically based on IP-networking) that provides connectivity to
`the functional elements in the NGN. The Access Network represents the local loop
`
`18–4
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`SR-2275
`Issue 4
`October 2000
`
`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`network of the NGN. There are various ways of offering access to the NGN. The
`Access Network could be based on the existing copper plant of LECs or could use
`other technical options such as Hybrid Fiber-Coax (HFC), Digital Subscriber Loop
`(xDSL), wireless access, etc.
`
`However, the descriptions of the Functional Elements (FEs) and the interfaces do
`not imply any specific physical implementation. Various suppliers have developed
`products with functional elements within a single node that communicate with the
`relevant elements in other nodes. This architecture framework does not endorse
`any particular physical architecture.
`
`Service Agent
`
`Call Connection
`Agent
`
`SCP
`
`STPs
`
`Signaling
`Gateway
`
`IP Networking
`Core Network
`
`Access
`Network
`
`Customer
`Gateway
`
`Access
`Gateway
`
`Trunk
`Gateway
`
`PSTN
`
`Figure 18-1. NGN Basic Framework Architecture
`
`The FEs in this architecture include:
`(cid:127) Access Gateway (AG)
`An AG supports the line side interface to an NGN. Traditional phones and PBXs
`currently used for the PSTN can access the network through this FE. As such,
`this FE provides functions such as packetization, echo control, etc. It is
`associated with a specific Call Connection Agent (CCA) that provides the
`
`18–5
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`IP Networking and Next Generation Networks
`
`SR-2275
`Issue 4
`October 2000
`
`necessary call control instructions. On receiving the appropriate commands
`from the CCA, the AG also provides functions such as audible ringing, power
`ringing, miscellaneous tones, etc. It is assumed that the AG has the functionality
`to set up a transport connection through the core network when instructed by
`the CCA. An AG is also commonly referred to as a “Media Gateway.”
`(cid:127) Customer Gateway (CG)
`A CG provides access to the network to some of the non-traditional CPEs that
`could have an associated IP address, such as IP-phones, personal computers,
`etc. Although a CG provides many of the functions associated with the AG, this
`FE is associated with a particular customer (business or residence). The CG is
`associated with a specific CCA that provides the necessary call control
`instructions. Calls originating in the CG would by-pass the AG and go directly
`into the core network.
`(cid:127) Trunk Gateway (TG)
`A TG supports a trunk side interface to the PSTN. The TG terminates circuit-
`switched trunks in the PSTN and virtual circuits in the packet network (the core
`network) and, as such, provides functions such as packetization. Even though a
`TG terminates trunks in the PSTN, this FE does not provide the resource
`management functions for trunks it terminates. However, the TG has the
`capability to set up and manage transport connections through the core
`network when instructed by the CCA. It is associated with a specific CCA that
`provides it with the necessary call control instructions.
`(cid:127) Signaling Gateway (SG)
`An SG interconnects an NGN to the PSTN signaling network. An SG terminates
`SS7 links from the PSTN CCS networks and thus provides the MTP Level 1 and
`Level 2 functionality. An SG communicates with the CCA to support the end-to-
`end signaling for calls with the PSTN. Each SG is associated with a specific
`CCA.
`(cid:127) Call Connection Agent (CCA)
`A CCA provides much of the necessary call processing functionality to support
`voice on the packet network. A CCA processes messages received from various
`other FEs to manage call states. A CCA communicates with other CCAs to set
`up and manage an end-to-end call. Although each gateway (AG, CG, SG, and TG)
`is associated with a specific CCA, a CCA would typically interact with several
`gateways. A CCA instructs gateways with call control commands. A CCA
`interacts with the Billing Agent to generate usage measurements and billing data
`such as Call Data Records (CDRs). A CCA is also commonly referred to as a
`“Call Agent,” “Media Gateway Controller,” or “Soft Switch.”
`(cid:127) Service Agent (SA)
`An SA supports supplementary services and generates TCAP messages to
`interact with SCPs for vertical services (Intelligent Network [IN] services) such
`as 800 and Local Number Portability (LNP). An SA interacts with multiple CCAs.
`
`18–6
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`SR-2275
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`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`The preceding list provides a high-level view of the key FEs involved in the typical
`service in an NGN. A more comprehensive view of an NGN framework architecture
`is shown in Figure 18-2. In addition to the FEs described above and shown in Figure
`18-1, Figure 18-2 shows the various user devices (e.g., IP-phones, traditional phones,
`etc.) that could be used to initiate a voice call on an NGN, and some other FEs that
`are also important in the network. The additional FEs include the following:
`(cid:127) Domain Name Server (DNS)
`A DNS is used to translate IP names to routable addresses.
`(cid:127) Routing and Translation Server (RTS)
`An RTS is used by the CCAs during a call setup to determine the CCA and
`gateways (CG, TG, SG or AG) associated with a particular called number.
`(cid:127) Billing Agent (BA)
`A BA supports much of the billing functionality needed in the VOP network. It
`collects the necessary usage measurements from the CCAs and processes them
`for use by downstream billing systems.
`(cid:127) Voice Feature Servers
`Voice Feature Servers are special purpose servers that support various voice
`features and services. Examples include Announcement Servers, Interactive
`Voice Response Units, etc. In addition, the Announcement Server would also be
`used as part of call processing to generate necessary tones and announcements.
`
`18–7
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`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 9
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`

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`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`SR-2275
`Issue 4
`October 2000
`
`Service Agent
`
`Call Connection
`Agent
`
`RTS
`
`SCP
`
`DNS
`
`Billing
`Agent
`
`Voice
`Feature
`Server
`
`STPs
`
`IP Networking
`Core Network
`
`Signaling
`Gateway
`
`Access
`Network
`
`Customer
`Gateway
`
`Access
`Gateway
`
`Trunk
`Gateway
`
`PSTN
`
`IP Phones, IP PBXs,
`PCs, H.323 devices
`
`PSTN/ISDN phones,
`PBXs, Mobile phones
`
`Figure 18-2. NGN Extended Framework Architecture with CPE Examples
`
`18.2 Survey of IP Networking
`
`18.2.1
`
`Introduction
`
`18.2.1.1 Circuit versus Packet Switching
`
`This section introduces IP networking to readers who are interested in
`understanding the transition of communications technologies from circuit
`switching to IP-based packet switching. IP networking is a specific instance of
`
`18–8
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`October 2000
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`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`packet switching, so understanding packet switching in general is a first step in
`understanding IP networking.
`
`In circuit switching, data transfer has three phases:
`
`1. A circuit is established
`
`2. Information is transferred
`
`3. The circuit is disconnected.
`
`Because the two end-points are connected by a dedicated link for the duration of a
`circuit-switched connection, there is no contention for the resources of that link
`once the circuit is established. For example, once a telephone call is set up across
`the PSTN, the two end points have full use of that circuit until the call is ended.
`
`A packet switching environment is different. In some cases, a packet containing
`data is simply dispatched to its destination. The sending entity may not necessarily
`determine that the receiving entity is available, and the recipient is not necessarily
`required to acknowledge receipt. In other cases, the two entities may follow a
`higher layer protocol to establish a relationship, transmit data, and close off the
`relationship, but this session does not guarantee them resources on their
`communications channel. This synchronization is for the end-to-end relationship,
`not for the end-to-end circuit. A variety of issues arise because a packet-switched
`connection does not generally offer full use of the intervening physical media.
`These issues include unpredictable delay, lost or corrupted packets, and the
`overhead needed to overcome these problems and route packets correctly. In spite
`of these shortcomings, however, one type of packet switching-IP networking is
`moving toward dominance in the communications industry.
`
`Packet-based IP networks rely on deterministic routing protocols and intelligence
`within each network element to deliver data, rather than an end-to-end call setup
`common within a circuit-switched network. Each IP aware hop, or router, within
`the network needs to know only what the next hop is to best deliver a packet
`through the network, rather than require full knowledge about the end-to-end path
`as in a circuit-switched network. This reduction in overhead leads to efficiencies
`within the packet-switched network as compared to a circuit-switched network.
`
`In the IP packet-switched network, higher layer protocols and handshakes are used
`to guarantee delivery of data and recover from delivery errors within the “best
`effort” network model. As more time-sensitive and delivery-critical data are moved
`onto IP-based networks (due to their inherently lower cost models), additional
`protocols are being developed and deployed to manage intra-layer performance
`characteristics better ensuring data delivery across the network. Protocols such as
`Multi Protocol Label Switching (MPLS) and Differentiated Services (DiffServ) are
`used to create guaranteed QoS channels within a packet-based IP network.
`
`18–9
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`18.2.1.2 History of the Internet and Success of IP
`
`In packet switching, equipment and software can provide multiple virtual
`connections over single network connections. The economic value of this approach
`has been proven in the market. The shortcomings of this approach, however,
`represent areas that must be addressed for IP to complete its migration to being the
`common technology that underlies all business-critical applications and voice/
`telephony services.
`
`The Internet is the most visible example of IP networking, and some of its key
`characteristics can be traced to the underlying technology of IP networking.
`
`Table 18-1. Internet Characteristics
`
`Internet
`
`Affordable
`Changing rapidly
`Robust
`
`Does not guarantee reliable service
`
`IP Technology
`Cost-effective
`Rapidly evolving
`Designed to survive component
`failures
`A “best-effort” technology
`
`18.2.1.3 Recent Developments
`
`The success of the Internet has fueled the expansion of IP networking into new
`areas. These expansions are motivating changes in IP networking technologies.
`
`18.2.1.3.1
`
`Intranets
`
`IP networking has moved into corporate networks and begun replacing older
`network protocols. IP networking offers several important advantages in this
`environment. First, IP is not a proprietary protocol; therefore, it does not tie an
`enterprise to a particular vendor. Second, IP is often more cost effective, thanks to
`vendor competition and IP’s widespread deployment. Third, IP expertise is
`relatively easy to find, compared to expertise in niche or proprietary protocols.
`Fourth, key IP-based applications such as web browsers and email fit well into the
`corporate environment.
`
`18.2.1.3.2 E-commerce
`
`As the Internet has reached critical mass and become commercialized, IP
`technologies have faced challenges related to security and reliability. The first
`generation of commercially viable solutions to these challenges has matured.
`Concerns about the security of transactions conducted over the Internet have not
`
`18–10
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`
`become a roadblock to the explosive “dot-com” marketplace. Technologies such as
`Secure Sockets Layer (SSL) are well-accepted, and more extensive capabilities for
`further encryption and certification are reaching the broader commercial market.
`Behind the scenes, technical support personnel have become more aware of
`security tools such as intrusion detection systems, firewalls, and router filters. The
`general issue of reliability is being addressed on a number of fronts, ranging from
`server mirroring, load balancing, and managed web hosting.
`
`18.2.1.3.3 Multimedia and Voice
`
`IP and voice networks are beginning to converge. However, multimedia and voice
`calls are sensitive to delay. If a person is browsing the Internet, a slight delay in the
`midst of downloading a web page does not present an unacceptable barrier to
`communication. However, a user engaged in a voice call may find performance to
`be unacceptable when resource contention causes delays or lost information.
`Creating solutions to these challenges includes some of the most interesting and
`dynamic areas of work in communications technology today.
`
`18.2.1.4 Architecture of Internetworks
`
`18.2.1.4.1 Conceptual Overview
`
`The term “IP Networking” is actually shorthand for a whole group of technologies,
`many of which are introduced in this chapter. These technologies range from lower
`layer protocols such as Ethernet, to applications, to network architectures. They
`are grouped under the title of “IP” because the Internet Protocol is the single
`technology that is common among these technologies.
`
`The fundamental role of IP is to ensure that information (e.g., packets) gets from its
`source network to its destination network. IP provides the addressing to
`accomplish this task. All other technologies and protocols exist to “take care of the
`details.”
`
`Network A
`
`Network B
`
`Network C
`
`Router
`
`Router
`
`Client
`
`Server
`
`Figure 18-3. A Simple Internetwork
`
`18–11
`
`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 13
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`

`

`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`SR-2275
`Issue 4
`October 2000
`
`Consider the simple internetwork depicted in Figure 18-3, which comprises three
`networks. If Network A represents a LAN at home, Network B could represent a
`nationwide ISP, and Network C could be a corporation’s intranet. The essential
`point is that IP is the common basis for communicating from one endpoint (the
`client PC) across multiple networks to the other endpoint (the enterprise’s server).
`This communication link may include a variety of physical media (e.g., twisted pair
`wire, coaxial cable, fiber), a variety of transmission protocols (e.g., Ethernet, ATM,
`FDDI), and a variety of applications (e.g., file transfer, electronic mail, web
`browsing). What is common, however, is the IP. The relations and roles of these
`various media, protocols, and applications is described in further detail in Section
`18.2.2.
`
`18.2.2
`
`IP Protocol Suite
`
`Before examining the many aspects of IP networking, one must first understand IP
`as a communications protocol, some of its related protocols, and their relationship.
`
`18.2.2.1 OSI Model
`
`Before IP became ascendant, a good deal of standards work under the sponsorship
`of ISO was completed under the Open Systems Interconnect (OSI) umbrella. One
`of the benefits of this effort is the OSI seven-layer model, which is represented in
`Figure 18-4.
`
`Layer 7
`
`Layer 6
`
`Layer 5
`
`Layer 4
`
`Layer 3
`
`Layer 2
`
`Layer 1
`
`Application
`
`Presentation
`
`Session
`
`Transport
`
`Network
`
`Data Link
`
`Physical
`
`Application
`
`Presentation
`
`Session
`
`Transport
`
`Network
`
`Data Link
`
`Physical
`
`Layer 7
`
`Layer 6
`
`Layer 5
`
`Layer 4
`
`Layer 3
`
`Layer 2
`
`Layer 1
`
`Figure 18-4. OSI Conceptual Model
`
`The chief value of this model is that it provides a common framework for
`understanding end-to-end communications between computers. Upper layers are
`typically implemented as protocols in software; lower layers are typically
`implemented as protocols in hardware. Each layer is generally self-contained and
`
`18–12
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`AT&T Exhibit 1017
`AT&T v. VoIP, IPR 2017-01382, Page 14
`
`

`

`SR-2275
`Issue 4
`October 2000
`
`Telcordia Notes on the Networks
`IP Networking and Next Generation Networks
`
`provides services to the layer above it. Note that these layers represent network
`communications functionality. So, the application layer does not represent
`computer applications (e.g., an email application), but instead refers to network
`applications (e.g., the Simple Mail Transfer Protocol [SMTP]) that provide network
`services. Information originates at the top of one stack, and is processed by each
`layer until it reaches the physical media that connect the two stacks at the bottom.
`As it emerges at its destination, the information moves back up to the top of the
`stack until it reaches the peer application.
`
`A key concept for understanding this model is that lower-layer protocols
`encapsulate adjacent higher-layer protocols. Figure 18-5 depicts the basic concept
`of encapsulation.
`
`Layer N Header
`
`Layer N Data
`
`Layer N-1 Header
`
`Layer N-1 Data
`
`Figure 18-5. Encapsulation
`In Figure 18-5, the Layer N header and data are encapsulated by a lower layer,
`thereby becoming its data payload. A typical metapho