Civil Rights
Movements, leaders, victories and the continuing fight for equality.
q2K BHP
Black History Portal
THE BHP WIRE —
HIDDEN TRUTHS
What's New!
Explore the people, places, events, achievements, struggles and stories that shaped our journey.
Movements, leaders, victories and the continuing fight for equality.
Innovation, patents, science, technology and world-changing contributions.
Pioneers, champions, Negro Leagues, records, activism and excellence.
Meet the people whose lives, choices and achievements shaped the journey.
Black towns, communities, institutions and places where history happened.
Moments that changed communities, movements, institutions and the nation.
In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article needs more citations. (January 2018) |
A session border controller (SBC) is a network element deployed to protect SIP-based VoIP networks.[1]
Early deployments of SBCs were focused on the borders between two service provider networks in a peering environment. This role has since expanded to include significant deployments between a service provider's access network and its backbone network, providing service to residential and/or enterprise customers.[2]
The term "session" refers to a communication between two or more parties – in the context of telephony, this would be a call. Each call consists of one or more call signaling message exchanges that control the call, and one or more call media streams which carry the call's audio, video, or other data along with information of call statistics and quality. Together, these streams make up a session. It is the job of a session border controller to exert influence over the data flows of sessions.
The term "border" refers to a point of demarcation between one part of a network and another. As a simple example, at the edge of a corporate network, a firewall demarcates the local network (inside the corporation) from the rest of the Internet (outside the corporation). A more complex example is that of a large corporation where different departments have security needs for each location and perhaps for each kind of data. In this case, filtering routers or other network elements are used to control the flow of data streams. It is the job of a session border controller to assist policy administrators in managing the flow of session data across these borders.
The term "controller" refers to the influence that session border controllers have on the data streams that comprise sessions, as they traverse borders between one part of a network and another. Additionally, session border controllers often provide measurement, access control, and data conversion facilities for the calls they control.
| This section relies on a single source. (August 2026) |
SBCs commonly maintain full session state and offer the following functions:
With the advent of WebRTC some SBCs have also assumed the role of SIP to WebRTC Gateway and translate SIP. While no one signalling protocol is mandated by the WebRTC specifications,[3] SIP over WebSockets (RFC 7118) is often used partially due to the applicability of SIP to most of the envisaged communication scenarios as well as the availability of open source software such as JsSIP. In such a case the SBC acts as a gateway between the WebRTC applications and SIP end points.
SBCs are inserted into the signaling and/or media paths between calling and called parties in a VoIP call, predominantly those using the Session Initiation Protocol (SIP), H.323, and MGCP call-signaling protocols.
In many cases the SBC hides the network topology and protects the service provider or enterprise packet networks. The SBC terminates an inbound call and initiates the second call leg to the destination party. In technical terms, when used with the SIP protocol, this defines a back-to-back user agent (B2BUA). The effect of this behavior is that not only the signaling traffic, but also the media traffic (voice, video) is controlled by the SBC. In cases where the SBC does not have the capability to provide media services, SBCs are also able to redirect media traffic to a different element elsewhere in the network, for recording, generation of music-on-hold, or other media-related purposes. Conversely, without an SBC, the media traffic travels directly between the endpoints, without the in-network call signaling elements having control over their path.
In other cases, the SBC simply modifies the stream of call control (signaling) data involved in each call, perhaps limiting the kinds of calls that can be conducted, changing the codec choices, and so on. Ultimately, SBCs allow the network operators to manage the calls that are made on their networks, fix or change protocols and protocol syntax to achieve interoperability, and also overcome some of the problems that firewalls and network address translators (NATs) present for VoIP calls.
To show the operation of an SBC, one can compare a simple call establishment sequence with a call establishment sequence with an SBC.[4] In the simplest session establishment sequence with only one proxy between the user agents the proxy’s task is to identify the callee’s location and forward the request to it. The proxy also adds a Via header with its own address to indicate the path that the response should traverse. The proxy does not change any dialog identification information present in the message such as the tag in the From header, the Call-Id or the Cseq. Proxies also do not alter any information in the SIP message bodies. Note that during the session initiation phase the user agents exchange SIP messages with the SDP bodies that include addresses at which the agents expect the media traffic. After successfully finishing the session initiation phase the user agents can exchange the media traffic directly between each other without the involvement of the proxy.
SBCs are designed for many applications and are used by operators and enterprises to achieve a variety of goals. Even the same SBC implementation might act differently depending on its configuration and the use case. Hence, it is not easily possible to describe an exact SBC behavior that would apply to all SBC implementations. In general it is possible to identify certain features that are common to SBCs. For example, most SBCs are implemented as back-to-back user agent. A B2BUA is a proxy-like server that splits a SIP transaction in two call legs: on the side facing the user agent client (UAC), it acts as server, on the side facing user agent server (UAS) it acts as a client. While a proxy usually keeps only state information related to active transactions, B2BUAs keep state information about active dialogs, e.g., calls. That is, once a proxy receives a SIP request it will save some state information. Once the transaction is over, e.g., after receiving a response, the state information will soon after be deleted. A B2BUA will maintain state information for active calls and only delete this information once the call is terminated.
When an SBC is included in the call path, the SBC acts as a B2BUA that behaves as a user agent server towards the caller and as user agent client towards the callee. In this sense, the SBC actually terminates that call that was generated by the caller and starts a new call towards the callee. The INVITE message sent by the SBC contains no longer a clear reference to the caller. The INVITE sent by the SBC to the proxy includes Via and Contact headers that point to the SBC itself and not the caller. SBCs often also manipulate the dialog identification information listed in the Call-Id and From tag. Further, in case the SBC is configured to also control the media traffic then the SBC also changes the media addressing information included in the c and m lines of the SDP body. Thereby, not only will all SIP messages traverse the SBC but also all audio and video packets. As the INVITE sent by the SBC establishes a new dialog, the SBC also manipulates the message sequence number (CSeq) as well the Max-Forwards value. Note that the list of header manipulations listed here is only a subset of the possible changes that an SBC might introduce to a SIP message. Furthermore, some SBCs might not do all of the listed manipulations. If the SBC is not expected to control the media traffic then there might be no need to change anything in the SDP body. Some SBCs do not change the dialog identification information and others might even not change the addressing information.
SBCs are often used by corporations along with firewalls and intrusion prevention systems (IPS) to enable VoIP calls to and from a protected enterprise network. VoIP service providers use SBCs to allow the use of VoIP protocols from private networks with Internet connections using NAT, and also to implement strong security measures that are necessary to maintain a high quality of service. SBCs also replace the function of application-level gateways.[5] In larger enterprises, SBCs can also be used in conjunction with SIP trunks to provide call control and make routing/policy decisions on how calls are routed through the LAN/WAN. There are often tremendous cost savings associated with routing traffic through the internal IP networks of an enterprise, rather than routing calls through a traditional circuit-switched phone network.
Additionally, some SBCs can allow VoIP calls to be set up between two phones using different VoIP signaling protocols (e.g., SIP, H.323, Megaco/MGCP) as well as performing transcoding of the media stream when different codecs are in use. Most SBCs also provide firewall features for VoIP traffic (denial of service protection, call filtering, bandwidth management). Protocol normalization and header manipulation is also commonly provided by SBCs, enabling communication between different vendors and networks.
From an IP Multimedia Subsystem (IMS) or 3GPP (3rd Generation Partnership Project) architecture perspective, the SBC is the integration of the P-CSCF and IMS-ALG at the signaling plane and the IMS Access Gateway at the media plane on the access side. On the interconnect side, the SBC maps to the IBCF, IWF at the signaling plane and TrGW (Transition Gateway) at the media plane.
From an IMS/TISPAN architecture perspective, the SBC is the integration of the P-CSCF and C-BGF functions on the access side, and the IBCF, IWF, THIG, and I-BGF functions on the peering side. Some SBCs can be "decomposed", meaning the signaling functions can be located on a separate hardware platform than the media relay functions – in other words the P-CSCF can be separated from the C-BGF, or the IBCF/IWF can be separated from the I-BGF functions physically. Standards-based protocol, such as the H.248 Ia profile, can be used by the signaling platform to control the media one while a few SBCs use proprietary protocols.
|
During its infancy, the concept of SBC was controversial to proponents of end-to-end systems and peer-to-peer networking because:
Most of the controversy surrounding SBCs pertains to whether call control should remain solely with the two endpoints in a call (in service to their owners), or should rather be shared with other network elements owned by the organizations managing various networks involved in connecting the two call endpoints. For example, should call control remain with Alice and Bob (two callers), or should call control be shared with the operators of all the IP networks involved in connecting Alice and Bob's VoIP phones together. The debate of this point was vigorous, almost religious, in nature. Those who wanted unfettered control in the endpoints only, were also greatly frustrated by the various realities of modern networks, such as firewalls and filtering/throttling. On the other side, network operators are typically concerned about overall network performance, interoperability and quality, and want to ensure it is secure.
 | This section has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these messages)
|
Lawful intercept is governed in America by the Communications Assistance for Law Enforcement Act (CALEA).
An SBC may provide session media (usually RTP) and signaling (often SIP) wiretap services, which can be used by providers to enforce requests for the lawful interception of network sessions. Standards for the interception of such services are provided by ATIS, TIA, CableLabs and ETSI, among others.
|
According to Jonathan Rosenberg, the author of RFC 3261 (SIP) and numerous other related RFCs, Dynamicsoft developed the first working SBC in conjunction with Aravox, but the product never truly gained marketshare.[citation needed] Newport Networks was the first to have an IPO on the London Stock Exchange's AIM in May 2004 (NNG), while Cisco has been publicly traded since 1990. Acme Packet followed in October 2006 by floating on the NASDAQ. With the field narrowed by acquisition, NexTone merged with Reefpoint becoming Nextpoint, which was subsequently acquired in 2008 by Genband. At this same time, there emerged the "integrated" SBC where the border control function was integrated into another edge device. In 2009, Ingate Systems' Firewall became the first SBC to earn certification from ICSA Labs, a milestone in certifying the VoIP security capabilities of an SBC.
The continuing growth of VoIP networks pushes SBCs further to the edge, mandating adaptation in capacity and complexity. As the VoIP network grows and traffic volume increases, more and more sessions are passing through SBC. Vendors are addressing these new scale requirements in a variety of ways. Some have developed separate, load balancing systems to sit in front of SBC clusters. Others, have developed new architectures using the latest generation chipsets offering higher performance SBCs and scalability using service cards.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A session border controller (SBC) is a network element deployed to protect SIP-based VoIP networks. Early deployments of SBCs were focused on the borders between two service provider networks in a peering environment. This role has since expanded to include significant deployments between a service provider's access network and its backbone network, providing service to residential and/or enterprise customers. The term "session" refers to a communication between two or more parties – in the context of telephony, this would be a call. Each call consists of one or more call signaling message exchanges that control the call, and one or more call media streams which carry the call's audio, video, or other data along with information of call statistics and quality. Together, these streams make up a session. It is the job of a session border controller to exert influence over the data flows of sessions. The term "border" refers to a point of demarcation between one part of a network and another. As a simple example, at the edge of a corporate network, a firewall demarcates the local network (inside the corporation) from the rest of the Internet (outside the corporation). A more complex example is that of a large corporation where different departments have security needs for each location and perhaps for each kind of data. In this case, filtering routers or other network elements are used to control the flow of data streams. It is the job of a session border controller to assist policy administrators in managing the flow of session data across these borders. The term "controller" refers to the influence that session border controllers have on the data streams that comprise sessions, as they traverse borders between one part of a network and another. Additionally, session border controllers often provide measurement, access control, and data conversion facilities for the calls they control.
Network address translators (NAT) are used to overcome the lack of IPv4 address availability by hiding an enterprise or even an operator's network behind one or few IP addresses. The devices behind the NAT use private IP addresses that are not routable in the public Internet. The Session Initiation Protocol (SIP) has established itself as the de facto standard for voice over IP (VoIP) communication. In order to establish a call, a caller sends a SIP message, which contains its own IP address. The callee is supposed to reply back with a SIP message destined to the IP addresses included in the received SIP message. This will obviously not work if the caller is behind a NAT and is using a private IP address. Probably the single biggest mistake in SIP design was ignoring the existence of NATs. This error came from a belief in IETF leadership that IP address space would be exhausted more rapidly and would necessitate global upgrade to IPv6 and eliminate the need for NATs. The SIP standard has assumed that NATs do not exist, an assumption, which turned out to be a failure. SIP simply didn't work for the majority of Internet users who are behind NATs. At the same time it became apparent that the standardization life-cycle is slower than how the market ticks: Session Border Controllers (SBC) were born, and began to fix what the standards failed to do: NAT traversal. In case a user agent is located behind a NAT then it will use a private IP address as its contact address in the contact and via headers as well as the SDP part. This information would then be useless for anyone trying to contact this user agent from the public Internet. There are different NAT traversal solutions such as STUN, TURN and ICE. Which solution to use depends on the behavior of the NAT and the call scenario. When using an SBC to solve the NAT traversal issues the most common approach for SBC is to act as the public interface of the user agents. This is achieved by replacing the user agent's contact information with those of the SBC.
The office controller was a networking concept of the early to mid-1980s. The concept was used by PABX manufacturers as the basis of families of products in which the PBX would supply data connectivity and applications along with its traditional voice services. The office controller would be a central switch which would link users to applications and provide necessary services such as security. There was much discussion at that time of multimedia voice/data services but the conception of these services was very vague. There was no real understanding of the utility and therefore customer value of these services. As a result, office controller services were usually restricted to various forms of modem pooling. With the development of LANs and PCs, client/server became the dominant distributed application model, along with standalone applications as PCs became more powerful. As a result, the centralised model supported by the office controller fell out of style. Office controller products were withdrawn from the market. Remnants of the idea, with examples such as thin clients and three-layer architectures, did persist with some interest. However the thick client PC model of services was predominant in the 1990s. However the office controller idea is not without merit. With the development of SIP with its session border controllers and service-oriented architectures, the centralized creation and management of user services is again finding widespread interest.
Anti-tromboning (also referred to as anti-hairpinning or media release) is a feature employed in telecommunication networks, such as voice over IP networks, that optimises the use of the access network and reduces excess processing and traffic. Tromboning is a type of situation that occurs when data is transferred through a path that goes to a large exchange node and back, much in the way that the path of the sound waves inside a trombone can be elongated by extending the trombone's slide, despite the air entry and exit points remaining the same. For example, in a poorly optimised network a local telephone call may be routed through an international exchange; or internet traffic between an internet user and a website may be needlessly diverted through a data center, adding to latency and costs. A network border node, such as a session border controller, handling calls as they pass from the access network to the core network can examine the IP address or domains of both the caller and called parties and if they reside in the same part of the network the media path can be released allowing media to flow directly between the two parties without entering the access network. The benefits of this action are twofold: 1) the caller is not paying for any bandwidth usage on the carrier network (but may be arbitrarily paying for the carrier's handoff service) and 2) The carrier's network is less congested. In mobile networks servicing a large number of geographically dense peers, any two peers who wish to communicate between one another may exchange their media data through a separate path that exploits localised and lower-power transmission, as a form of sub-band signalling. This extends into situations where bulk data can be sent over a less reliable but higher-bandwidth (capacity) and cheaper or faster link, whilst parity data for reconstructing bad packets or supporting determinancy in fuzzy-state weakly determined data can be sent over more reliable but lower-bandwidth and more expensive or more latency-incurring link. The session and control data can be completely decentralised, removing the tromboned line altogether, under a suitable multiple-input multiple-output (MIMO) network system. In this case, the aggregate media and session control data may be distributed across the network in a dynamic best-possible solution form that meets the link criteria of both the individual peer and the constraints of the network infrastructure (other peers, basestations, etc.), which may vary between each individual peers. A subscription service may primarily support paying members, but allocate a certain amount of under-utilised bandwidth to provide longhaul access to non-paying members, with the assumption that these members will in turn provide paying members with traversal of bulk media data within a geographical area, or even high-latency propagation across cells. The lowered cost to the service provider that results from resource sharing is the economic rationale for these network provision schemes.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
