The base signaling for VoIP is an ITU H.323 standard. This standard defines both the signaling and transport for a VoIP network. To support this signaling standard, H.323 will be imple-mented in the Common Routing Software used across the product family. This will allow SELG’s routers to inter-operate with compliant H.323 implementations. Implementing the H.323 on the router CPU also allows the router to make multiple voice adapters appear as a single H.323 gateway.

It is important to note that H.323 only specifies the signaling and encapsulation of voice data over an IP network. The integration of voice and data over shared links is not specified by the H.323 standard. Therefore, it is once again time to look at how to control the delay and jitter for high quality voice in the VoIP environment.

The requirement to segment user data sharing the low speed access link with voice remains the same. When the access link is Frame Relay, we will use FRF.12 to segment the data before it is transmitted over the FR link. VoIP also allows other access connectivity. Point to Point Proto-col (PPP) is a common layer protocol used for low speed access in IP networks, especially for backup scenarios. To support the segmentation required on PPP links, we will utilize the standard Multi-Link PPP (MLPPP) support already included with our router products, allow-ing the user to configure MLPPP over a single PPP interface. Secondly, this will allow the large data frame to be segmented with minimal overhead, so the voice packets can be interleaved efficiently w/the data. Lastly, this allows interoperabilty with other standard compliant MLPPP implementations.

The last requirement in the access router, as in the case of VoFR, is prioritization. Since VoIP is DLC-independent, there are multiple options for accomplishing the necessary prioritization on the access link. The first option is BRS, which can still be used to classify and prioritize traffic. Additionally, IP Differentiated Service will support the prioritization of voice traffic. The use of RSVP will also be supported.

For VoIP, the HQ site is mainly a larger image of the branch. Since the H.323 protocol already allows any to any connectivity, no call switching is required in the HQ. Additionally, the H.323 gatekeeper is responsible for coordinating the dialing plans for the network. Because of the additional capacity requirements, only the 2212 multiprotocol router and the 2216 multi-access connector are targeted to have integrated digital (T1/E1) connectivity.

With SELG routers, VoFR can migrate to an IP-based with minimal changes to the branch infra-structure. There are issues associated with migration and inter operability as people migrate. In figure 3, the two independent networks are connected via a router that contains a H.323 proxy function. This proxy converts between the H.323 signaling used in the VoIP network to the signaling used in the VoFR network. The H.323 proxy is then connected to the VFRAD via a Frame Relay connection. Since the VFRAD has the call switching functionality, it can complete the call to the locally attached PBX or switch the call to one on the branches that are connected to it. This allows a branch connected via VoIP to complete a call to the HQ PBX or Branch office connected via VoFR.


 Summary Ease into eBusiness economically with SELG solutions! Let SELG merge voice onto your IP or FR network either in steps or full transformation. With worldwide experience in designing small to large networks, SELG delivers superior integrated solutions that includes component software and hardware. Each solution is bundled with high quality support and service.

 Acronyms   ATM - Asynchronous Transfer Mode
BRS - Bandwidth Reservation System
CELP - Code Excited Linear Prediction
CS-CELP - Conjugate-Structure Algebraic-Code-Excited Linear Prediction
CIR - Committed Information Rate
CPE - Customer Premise Equipment
CPU - Computer Processing Unit
DLCI - Data Link Connection Identifier
DSP - Digital Signal Processor
E&M - Ear and Mouth
FR - Frame Relay
FRF - Frame Relay Forum
FXO - Foreign Exchange Office
FXS - Foreign Exchange Subscriber or Station
HQ - HeadQuarters
IP - Internet Protocol
ISDN BRI - Integrated Services Digital Network Basic Rate Interface
ISP - Internet Service Provider
ITU/IETF - International Telecommunications Union/Internet EngineeringTask Force
MLPPP - Multi-Link Point to Point Protocol
MTU - Maximum Transmission Unit
PBX - Private Branch eXchange
PCM - Pulse Code Modulation
PPP - Point to Point Protocol
PSTN - Public Switched Telephone Network
PVM - Pass-through Virtual Machine protocol
QoS - Quality of Service
RSVP - Reservation
UNI - User Network Interface
VAD - Voice Activity Detection
VFRAD - Voice enabled Frame Relay Access Device
VoFR - Voice over Frame Relay
VoIP - Voice over Frame Relay
VPN - Virtual Private Network