Home > Articles > Cisco Network Technology > IP Communications/VoIP > Offering Bundled Voice and Data Services

Offering Bundled Voice and Data Services

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Oct 11, 2002.

Chapter Description

This sample chapter focuses on offering managed services to SMBs. Three areas are discussed to help provide an overview of bundled voice and data service architectures: Overview of Managed Voice and Data Services, Managed Voice and Data Services Using AAL2, Fundamentals of AAL2.

Fundamentals of AAL2

The AAL2 protocol has two layers:

  • Service specific convergence sublayer (SSCS)

  • Common part sublayer (CPS)

The SSCS encodes different information streams for the transport by AAL2 over a single ATM connection. The information streams might be active voice encodings, silence insertion descriptors, dialed digits, or fax. SSCS can provide error control on critical information (CAS signaling and dialed digits) by using a 10-bit CRC. This is called an AAL2 Type 3 cell. The SSCS segments the information that is being passed from a higher layer application, such as samples of voice from a digital phone into a number of units of data, and submits these units of data to the CPS for transmission. The length of the segmented data can be between one and the maximum length supported by the CPS connection, which is either 45 or 64 bytes. At the SSCS receiver, the units of data are reassembled back into the information before being passed to the higher layer application.

The second layer, the CPS, is specifically responsible for transporting end-to-end connections across the network. The format of AAL2 protocol structure is shown in Figure 4-2.

Figure 4-2Figure 4-2 AAL2 Protocol Structure

Figure 4-2 shows that AAL2 uses an additional byte of overhead for each ATM cell and an additional three bytes of overhead for each voice packet (e.g., compressed 8 kbps voice). The benefits of the AAL2 scheme are that there is no padding overhead except when there is insufficient data to complete a packet in a prespecified time interval, and the voice channels can be multiplexed over a single ATM virtual circuit.

The content of the Start field and the CPS packet are shown in Figure 4-3.

Figure 4-3Figure 4-3 Start Field and CPS Packet Formats

The CPS layer enables the multiplexing of variable length voice packets of end users onto a single ATM virtual channel that is an AAL2 channel. This is accomplished through the different information fields shown in Figure 4-2. Although AAL2 with its three-byte packet header introduces some inefficiency for small packets, the improvement that is reached by having no padding more than offsets this minor inefficiency. Each of the CPS fields and the Start field are described here:

  • Start field—Enables efficient packing of the voice packets over a single ATM virtual circuit. The Offset field is a six-bit pointer within the Start field that points to the position of the first CPS packet that follows the OSF. A sequence number protects the order of the Offset field. If a Start field parity error exists, all the CPS packets that are associated with the Start field are discarded.

  • CID (Channel ID)—Identifies the end user, which is referred to as the SSCS entity in the International Telecommunication Union (ITU) AAL2 specifications. The CID allocates the value 1 to exchange layer management peer-to-peer procedures, such as set-up negotiations. CID enables the multiplexing of up to 248 user channels, whereas some CID values are reserved for other uses, such as peer-to-peer layer management. For example, if 8 E1s terminated on an MGX, 240 CID values would be used.

  • LI (Length Indicator)—Identifies the length of the CPS packet. The default payload length is 45 bytes, and an optional maximum length of 64 bytes can be selected. The maximum length is channel specific.

  • UUI (User-to-User Indication)—Provides two functions: It conveys specific information transparently between two end points (e.g., CPS or SSCS entity) and distinguishes between the different users, such as SSCS entities and layer management users.

  • HEC (Header Error Control)—Discards the rest of the CPS packets until the next Start field. As a result, not all voice users residing on the single ATM virtual channel are affected by other end-user errors, which results in a higher end-to-end efficiency.

The CID is an important concept in AAL2. CIDs provide a binding between an endpoint and an AAL2 connection. This is the mechanism that binds the TDM traffic to the ATM traffic. For example, if a service provider needs to provision 100 DS0s between two sites for one of its enterprise customers, 100 CIDs are created across the ATM network. Furthermore, a unique coder-decoder (codec) type is assigned to each individual DS0 because the codec type is assigned to each CID through an AAL2. For example, individual customers in a multitenant building can each support multiple compression schemes over a single T1 access link. Each CID is configured and includes the following parameters: codec type, profile type, voice activity detection (VAD), DTFM Tones, and packet period for G.729. For example, to transmit DTMF tones transparently across the ATM PVC, DTMF must be enabled in the CID.

An AAL2 profile is a mechanism that the MGX 8850 uses to assign the compression and encoding scheme of the AAL2 trunking service. A profile is defined by a profile type, which is either an ITU standard or a custom type and a number. These profiles need to match on both ends of the network for the two end devices, such as PBXs, to interoperate. A profile is configured for each CID. For example, if the profile type is ITU and the profile number is 1, you must use G.711. In other words, the profile type and the profile number identify the compression type.

CID enables the use of subcell multiplexing, which provides many of the benefits of AAL2. If you use G.711, subcell multiplexing does not provide any value because G.711 already uses an 80-byte packet. The real advantage of subcell multiplexing is the G.729 encoding scheme. If you use G.729 with a packetization period of 30 milliseconds, three 10-byte packets of payload from one DS0 are packed into one ATM cell. Therefore, the efficiency of packing the voice sample into the ATM cell is increased threefold, and instead of 34 bytes of padding, only 14 bytes exist in the ATM cell. Assuming that VAD provides an additional 50 percent of bandwidth savings, G.729 subcell multiplexing uses approximately 6 kbps of bandwidth per DS0 channel of voice traffic. This is a significant amount of bandwidth savings.

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020