VoDSL Network Infrastructure
Today’s PSTN Voice Networks
Today’s voicenetworks rely on analog lines and trunks as well as digital T1 circuits toconnect to SMB subscribers. Delivering voice and data to SMB customers requires multiple multiple voice lines and end-user data services.
Class 4 and 5 Switch Functions
The centralized voice networks in use today are highly reliant on expensive and complex legacy Class 5 TDM circuit switches. Located at every subscriber end office, these switches supply local and long-distance phone service to subscribers. Class 5 switches provide the following features and functionality:
Lines
Lines connect subscribers to network resources and are typically analog copper loops or POTS lines.For POTS service, lines provide power to the user telephony equipment and deliver call progres sinformation from the switch, such as dial tone, ringing, and ringback.
Trunks
Trunks are used to interconnect network resources such as Class 4 and 5switches. Class 5 switches ina regional area may have trunks between them for local calling, and Class 5switches may be connectedto ILEC and IXC Class 4 tandems to offer long-distance and toll calling.
Signaling
On the side of the Class 5 switch that faces subscribers, the switch providesline-side signaling andfeatures such as callback (*69), call waiting, caller ID, and others. On thetrunk side of the switch,network signaling for toll call routing and PSTN database access is obtainedby accessing the SS7network over dedicated digital links, sometimes referred to as ‘A’- or‘F’-links. The trunk side Class 4tandem features, like feature group D (1+ dialing for long-distance carrieraccess), local numberportability (LNP), 800 number dialing, and directory services, are accessedover the A-link using SS7protocols, such as ISDN User Part (ISUP) and Transaction CapabilitiesApplication Part (TCAP).
Switching
The Class 5 switching matrix switches local calls from line to line, andnon-local and toll calls fromline to trunk and from trunk to trunk.
VoDSL replaces edge access and core transport components of the legacy voicenetwork with elementsthat offer lower capital and recurring costs. There are several deliverymethods for VoDSL, differentiatedby the network elements that transport voice and by the various interactionsand dependencies on thePSTN and data backbone. The initial VoDSL solutions are GR-303 gateways usingInternet Protocol (IP)packet or AAL2 Asynchronous Transfer Mode (ATM) cell encapsulations for voicebearer traffic. Thesesolutions are still dependent on the traditional centralized Class 5switches. However, emerging are thenext generation packet-based MGCP voice networks. Using a distributedarchitecture that partitions thenetwork functions with lower-cost and optimally-sited broadband voicedevices, this solution allows carriersto deliver voice services without deploying expensive Class 5 switches.
| Yesterday | Today | Tomorrow | |
| Products &Services | POTS Analog Modems Leased Lines T1/E1's DLCs |
GR-303/V5.2 Gateways PBX Extension ADSL Baseband Voice |
MGCP/SIP Packet Voice Networks Softswitches Trunk Gateways |
| Benefits |
|
|
|
Because of the risk involved with migrating to new equipment capabilities,picking the right equipmentto deploy is probably one of the most challenging decisions that carrierswill face. Two of the keycomponents that carriers must decide on for VoDSL deployment are:
- Integrated access devices (IADs)
- Voice gateway technologies
This introduction is meant to teach you about the functions and technology of DSL.