About Gateway Call Bandwidth Overhead

Chapter 1 Functionality

About Cisco Unified Videoconferencing 3500 Gateway Functionality

According to the H.320 standard, the available bandwidth allocated to a call at any given bit rate will always be slightly less than the stated maximum for the following reasons:

•All stated maximum call bandwidths include provision for control, audio, video, and data traffic.

•Video traffic on the ISDN side contains additional bits for error correction purposes which also consume bandwidth. Video traffic on the IP side does not include this additional load.

•Opening an audio channel further reduces the bandwidth available to the video traffic.

For example, a call at 384 Kbps actually has only 363 Kbps available to it. Control and error correction account for the remaining 21 Kbps.

Resource Allocation across E1/T1 Lines

The gateway can allocate bandwidth resources to calls across separate E1 or T1 connections to maximize bandwidth capacity in cases where there is not enough capacity for a call on a single E1 or T1 connection, but where sufficient capacity does exist when remaining capacity on both E1/T1 lines is combined.

For example, a gateway using two T1 lines can support three 6B calls on each T1 line, with 320 Kbps spare capacity per line:

•Each T1 line provides 23 B channels.

•Each B channel supports 64 Kbps

•Each T1 line supports 23 x 64 = 1472 Kbps

•Each 6B call requires 6 x 64 = 384 Kbps

•Each T1 line supports 1472/384 = 3 6B calls + 320 Kbps spare

The gateway processes an additional 6B call requiring a further 384 Kbps by taking bandwidth resources from each of the two T1 lines, both of which have 320 Kbps available. In this way, the gateway spreads the call over both T1 lines.

About Peer-to-Peer Connectivity

The gateway supports the following types of connectivity to the IP network

•Through a gatekeeper

•Directly to a peer device such as Cisco Unified Communications Manager without the need for a gatekeeper.

	Installation and Upgrade Guide for Cisco Unified Videoconferencing 3522 BRI Gateway and 3527 PRI Gateway Release 5.6
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3522 BRI specifications

Cisco Systems has long been a leader in networking and telecommunications equipment, and its BRI (Basic Rate Interface) and PRI (Primary Rate Interface) products are essential components in enabling businesses to manage voice and data communications efficiently. Notable models such as the Cisco 3522 BRI and 3527 PRI have earned recognition for their robust performance and versatile features.

The Cisco 3522 BRI is designed to deliver high-quality voice and data services over ISDN (Integrated Services Digital Network) connections. With two B channels for voice or data transmission, each supporting up to 64 Kbps, this device is ideal for small to medium-sized businesses that require reliable communication solutions while maintaining cost-effectiveness. The Cisco 3522 BRI supports multiple protocols, making it a flexible choice to adapt to various network environments.

On the other hand, the Cisco 3527 PRI supports up to 30 B channels, thereby significantly increasing the capacity for voice calls and data transfer. This scalability makes the 3527 PRI suitable for larger organizations that demand higher throughput and call handling capability. It operates over T1 and E1 lines, allowing businesses to leverage existing infrastructure while improving operational efficiencies. Additionally, the 3527's advanced features, such as call processing and load balancing, contribute to a seamless communication experience.

Both devices support a range of technologies that enhance functionality and performance. They are equipped with Call Admission Control (CAC) to optimize bandwidth use and reduce congestion during peak traffic. Cisco's VoIP technology, including features such as voice provisioning, fax over IP, and QoS (Quality of Service) mechanisms, ensures voice clarity and reliability.

Security is paramount, and both the 3522 and 3527 incorporate various protocols such as SRTP (Secure Real-Time Transport Protocol) to protect voice communications against unauthorized access. Furthermore, integration with Cisco's unified communications offerings allows for a more cohesive communication strategy, ensuring that users can take advantage of collaboration tools and data services.

In conclusion, the Cisco 3522 BRI and 3527 PRI models stand out with their impressive feature sets and technologies, making them an excellent investment for businesses needing reliable, scalable, and secure voice and data communication solutions. Choosing Cisco means embracing a future-proof solution that can grow with your organization's communication needs.