Vendor Network Architectures�Part VIII: Juniper Networks

Juniper Networks, Inc. of Sunnyvale, California, approaches the multivendor, converged networks with products that are called Session Border Controllers, or SBCs, not softswitches. The SBC provides some of the functions of the softswitch, but also adds some of its own. So as you might expect, there is considerable debate within the vendor community as to which of these devices—the softswitch, the SBC, or perhaps some combination of the two—will emerge as the preferred VoIP network building block. So let’s begin by looking at what constitutes the SBC.

Converged networks, by definition, combine in their architectures elements of both circuit switching networks and packet switching networks. The point of interconnection between these subnetworks is called the border. And just as there are rules when humans cross the border between two countries, there are protocols that must be considered when information crosses network borders. The SBC handles those border crossing functions, which may include network security and firewalls, edge routing between the two domains, proxy servers, hiding network topologies, call routing, bandwidth management and quality of service, signaling between the two networks, conversion between two different codec formats, plus accounting and billing functions.

Juniper’s research has identified three distinct border and end-user application configurations, each with unique requirements:

  • Small Office/Home Office (SOHO) and Residential Configurations: where the border interface is through a cable modem, integrated access device (IAD), or a firewall. These access devices may not support VoIP packet formats, and/or real-time traffic exchanges.
  • Enterprise and Virtual Private Network (VPN) Configurations: where the softswitch or server in the carrier’s network must be able to correctly identify private addresses with their virtual local area network (VLAN) tags in order to properly route calls to or from different customer sites.
  • Carrier Interconnection Configurations: where two carriers that are connecting their peer networks must provide protocol translation to/from SIP, H.323, MGCP, H.248/MEGACO, or other protocols in order to successfully terminate each others’ calls.

The Juniper SBC design addresses three different architectures that solve these challenges:

  • Proxy Architecture: A proxy is a device that acts on behalf of something else, to provide for network and feature transparency, such as adding parameters to requests for network service. For example, the SBC could change one addressing format (e.g. private network addresses) into another format (e.g. public network addresses). This architecture would benefit the SOHO/Residential application, as very little, or no, reconfiguration would be required for the devices at the customer site.
  • Distributed MIDCOM Architecture: The Middlebox Communication (MIDCOM) architecture and protocol is defined by the Internet Engineering Task Force in RFC 3303,, which allows complex applications, such as VoIP, music file sharing, or video conferencing to communicate through trusted third parties. Different SBCs would be deployed for separate tasks, such as address translation and media processing, thus balancing the network processing load.
  • Back-to-Back User Agent (B2BUA) Architecture: When one carrier uses SIP, while another uses H.323, the SBC handles the protocol operations between these peer networks, including call state monitoring and signaling message translation, thus the “back-to-back” designation.

Juniper Networks has developed the VF series of SBCs to address the application and architectural requirements discussed above, and resolve critical issues at VoIP network borders. These include: security, quality of service (QoS), address translation, and regulatory compliance. The various models are designed for both enterprise and carrier deployments, and are positioned for consumer, SOHO, enterprise, VPN, and carrier applications. They handle a variety of IP traffic, voice, video, and multimedia, using all common VoIP protocols, including SIP, H.323 and MGCP. Both signaling and media information streams are processed, to classify, measure, and manipulate each packet for management and traffic reporting functions. The Juniper SBC product line includes three models. The VF 1000E is designed for service provider and large enterprise applications, and can handle a minimum of 200 concurrent calls. The VF3000 is designed for service provider and carrier edge or core applications, with a minimum capacity of 1,000 concurrent calls. The VF4000, with an announced general availability later in 2006, is designed for large service provider and carrier edge or core applications, and will be able to handle a minimum of 5,000 concurrent calls.

Further details on the Juniper Networks SBC architecture and products can be found at Our next tutorial will continue our examination of vendors’ VoIP architectures.

Copyright Acknowledgement: © 2006 DigiNet ® Corporation, All Rights Reserved

Author’s Biography
Mark A. Miller, P.E. is President of DigiNet ® Corporation, a Denver-based consulting engineering firm. He is the author of many books on networking technologies, including Voice over IP Technologies, and Internet Technologies Handbook, both published by John Wiley & Sons.

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