Chapter 2, "VoIP Network Architectures: H.323, SIP, and MGCP," describes a managed voice and data service architecture that uses a call agent. A call agent solution is commonly used for the small and medium-sized business (SMB) market. This solution uses an integrated access device (IAD) at the customer premises that supports voice and data using IP or Asynchronous Transfer Mode adaptation layer 2 (AAL2) transport over a T1 access link to the service provider.
This chapter continues the focus on offering managed services to SMBs. Service providers that traditionally use time-division multiplexing (TDM) access and that need to add other service offerings can bundle voice and data services over a single access link to the customer. For example, traditional T1 circuits that are offered to customers to interconnect their private branch exchange (PBX) to interexchange carriers (IXCs) can now be used instead for integrated voice and data traffic, thereby eliminating the need for multiple access links between the customer and the service provider.
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
Overview of Managed Voice and Data Services
Integrated voice and data is a new service that is offered by service providers. The architecture design to deploy managed voice and data services is based on many factors. One of these factors is the required customer premises equipment (CPE), which is based on the type of business customer.
Two general types of business customers exist. One is a business customer with fewer than 100 users, such as a doctor's office, an insurance agent's office, or a small home office. These businesses are normally single-site locations that require telephony services, Internet access, firewall, and Virtual Private Network (VPN) services. Typically, these businesses do not have older networking protocols, such as AppleTalk or IPX, and they do not have a full-time support staff to maintain their own private network. A service provider can support these services with an IAD on the customer premises, such as a Cisco 2400.
The second type of business customer is an enterprise customer. An enterprise customer has a large installed base of devices that supports many flavors of protocols, sophisticated routing designs, multiple T1s, and back-hauling needs. An enterprise customer needs a multiservice platform, such as the Cisco 2600 and 3600. Many of these enterprise businesses have their own large private networks and their own full-time staff to maintain their multiservice network. However, because of various reasons, such as fast growth and economics, many of these large customers are outsourcing some or all of their services to service providers.
Integrated Access Architectures
Traditionally, service providers offer TDM services that connect a customer's PBX to an IXC Class 4 switch, which provides long distance voice services. Many of these service providers are currently switching from using a TDM-based infrastructure to using a packet-based infrastructure, either IP or ATM. This approach allows for a more efficient method to provide voice transport and also helps to integrate voice and data services over one access link to the customer premises.
NOTE
Many incumbent carriers are adding IP to their core ATM network by inserting Multiprotocol Label Switching (MPLS) technology. This change enables service providers to shift from transport service offerings to IP-based service offerings.
ADSL and T1 ATM are two types of access technologies that can be supported between the SMB and the service provider.
Other Cisco IADs
Other IADs available for SMBs are the Cisco 827-4V and the 1750. Both of these IADs support four Foreign Exchange Station (FXS) interfaces, and the 1750 also supports FX0 and E&M interfaces. The 827-4V supports a fixed configuration that includes Ethernet and DSL WAN-access only, and the 1750 supports a modular configuration that includes Fast Ethernet and multiple WAN options, such as DSL and T1 access. To help further differentiate these two IADs, the 1750 supports dual WAN interfaces for WAN backup or load sharing, hardware Triple Data Encryption Standard (3DES) encryption, and Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP) routing—these capabilities are not present in the 827-4V. The 827-4V is well suited for small offices that do not require the extra capabilities of the 1750 and are not concerned with expandability, but do require core services such as basic voice (FXS), VPN, and a firewall from their service provider.