Everything You Always Wanted to Know about SS7 But Were Afraid to Ask:
A regular NN follower sent me the nwfusion article by Briere and Heckart and reading about SS7 sent me back to Newbridge's webpages to double check their status and sure enough it's already integrated into their 36170 and 36190 switches.
Does anyone know the status of SS7 development in other companies? Who's their closest competitor?
Thanks in advance.
Pat
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What do you think? Jump into nwfusion.talk and comment on this column.
Briere is president and Heckart is vice president at TeleChoice, Inc., a consultancy in Verona, N.J. They can be reached at dbriere@telechoice.com and checkart@telechoice.com.
The SS7-ization of the Internet
By Daniel Briere and Christine Heckart
Leave it to the little guys to do what's important in the market.
Little-known competitive local exchange carrier XCOM Technologies, Inc., which humorously dubs itself "the data phone company,'' has come up with a way to bypass heavily burdened central office switches when data traffic is involved.
XCOM's first client, Ascend, is probably one of many that is going to start using the smarts of the voice network to figure out what the heck to do with all the data traffic that is blowing through the central office.
The XCOM platform separates data from normal voice traffic using features and intelligence in the public switched telephone network (PSTN), such as Signaling System 7 (SS7) and proprietary software developed by XCOM. Acting like a traffic cop, XCOM's box identifies and directs incoming data straight to a terminal server, bypassing the voice switch entirely.
The result? Data is off-loaded from the congested PSTN, enabling better connectivity and true integration of data and voice traffic.
What will make hot technologies such as virtual private networks hum, and bring IP telephony folk into the mainstream, is the interface of the IP layers with the smarts of existing SS7 databases, to do the things that make sense to all of us.
Recall that it is SS7 and centralized databases that allow you to do geographic and time-based routing of phone calls. If your New York office were closed, then all calls would be routed to your California office, which would still be open. The same would be true of IP-based telephony calls. The need for similar routing is clearly there.
When MCI launched its Vault capability last year, if you squinted at the architecture schematics, you could see dotted lines from the IP switching layer to the SS7 data access points in the MCI architecture.
This was really the first public play for serious integration of data networking with voice networking because it was being done on more than just a transport layer.
As you see telcos such as GTE preparing to do battle with extensive nationwide IP networks, a critical piece has to be SS7 integration.
Still, achieving SS7 and data network integration won't be a trivial task. For example, data networks, and the Internet in particular, handle calls in fundamentally different ways. There are a lot of neat features that carriers have developed over time, such as routing by area code, that will be tough to carry over to the data environment.
But then there are features that reside in the data network that should work easily in an SS7-data network environment. For example, look-ahead routing, which scouts forward in the network for congestion and busy signals, should work well. After all, SS7 is a packet network that talks to all the switches and other network adjunct devices.
The following are all from NN's website:
newbridge.com
Signaling Standards
Generally, a distinction is made between two different types of signaling. One type is subscriber signaling, the signaling between terminal and network, meaning the user network interface (UNI). The other type is interexchange signaling -- the signals passed between exchanges or switches -- referred to as network to network interface (NNI).
Inevitably a carrier's customers need to communicate with the customers of another carrier. To enable this, it is necessary for the networks of the various providers to be interoperable according to some agreed-upon standard interface. To provide manufacturer independence and make existing hardware more future proof, internationally standardized UNI and NNI signaling is also needed within the networks.
The most important standardization bodies for ATM networks are the International Telecommunications Union (ITU) and the ATM Forum. Both organizations issue new or expanded recommendations for UNI and NNI standards, with the recommendations of the ATM Forum being based mostly on those of the ITU. The diagram below shows the current UNI and NNI signaling standards of the two organizations for ATM (these will be discussed in more detail below).
ATM ForumITU-T
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User Network
Interface (UNI)Latest version: UNI 4.0
(based on ITU-T UNI)DSS2: Q.2931 + capability
Sets (CS1 & CS2.1 approved)
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Network to Network
Interface (NN1)PNN1 V1.0SS7 (B-ISUP + MTP)InterCarrier
Interface (ICI)BICI V2.0
(based on ITU-T)
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Figure 1: Current UNI and NNI signaling standards
User Network Interface (UNI)
The function of the UNI is to control the connection sections (e.g., set up and release of connections, and activation of features) between the customer premise equipment (CPE) and the ATM switch. To do this, it uses the layer below it, the signaling ATM adaptation layer (SAAL). The SAAL in its turn accesses the ATM layer and the physical layer. The UNI for its part receives requests from the terminal equipment. Figure 2 contains the complete UNI protocol stack for a connection.
Figure 2: The complete UNI protocol stack
UNI was specified by the ITU-T in Recommendation Q.2931. It is described in this document under the name DSS2 (digital subscriber signaling system number 2) and is a further development of the approved DSS1 protocol for narrowband ISDN. For the basic connection, specified in Q.2931, the ITU is constantly standardizing new features, grouping them in capability sets (CS). There are currently CS1 and CS2.1.
In contrast to the ITU, the ATM Forum brings out completely new UNI versions. The most recent version is UNI 4.0. It is based on ITU and also largely contains the features of the ITU CS, but Version 4.0 does have a few features that the ITU has not yet specified.
The UNI protocol has proven its worth over the last few years in broadband applications. The specifications of the ITU and the ATM Forum are largely identical since they have the same basis, and existing and new features are included from both sides.
Private Network to Network Interface (PNNI)
PNNI is the protocol defined by the ATM Forum for interexchange signaling and routing in ATM networks. PNNI Version 1.0 was approved in 1996. It uses the SAAL in exactly the same way as the UNI protocol, and the SAAL in its turn accesses the ATM layer and the physical layer. Figure 3 shows the protocol stack for PNNI.
Figure 3: The PNNI protocol stack
Many of the advantages of PNNI come from the world of internetworking. PNNI consists of a signaling protocol and a routing protocol. The signaling protocol is based upon UNI 4.0 with extensions for crankback and alternate routing. The routing protocol borrows and extends many of the concepts from internetworking protocols such as OSPF and IDRP.
The routing protocol is what sets PNNI apart from other networking protocols. It uses what are known as hello packets to identify and verify neighboring switches, and to determine the state of the individual links between nodes. By propagating this routing information, each node gathers enough informa-tion to understand and maintain the network's topology. Any topology changes to the network, such as link failures or newly provisioned links, are automatically propagated throughout the network. Link state information is not limited to being just up or down. Detailed quality of service (QoS) information, such as available bandwidth, cell transfer delay, cell delay variation and cell loss ratio can also be advertised to allow an even more detailed view of the network to be obtained by each node.
PNNI is based upon a source routing concept. This implies that path selection is done at the source, typically the first switch with an NNI interface and/or the first entry switch (or border node) of a peer group. The source signals a designated transit list (DTL) that specifies which nodes (or peer groups) to traverse through the network. In the event of a call failing along a specified source route, a call can be 'cranked back' (or cleared back) to the source of the DTL and an alternate path can be selected.
Note PNNI does not standardize the method of path selection. This offers the service provider community the advantages of equipment vendor differentiation while ensuring interoperability. To assist in path selection, a source may run a generic call admission control (GCAC) algorithm. The GCAC mimics the actual call admission control (CAC) algorithms running at each individual switch through the network by using the advertised QoS information previously mentioned. By running a GCAC, the number of calls that are blocked or cranked back due to switch CAC rejections, are significantly reduced. As it does away with the need to manually create and maintain routing tables, lower operations, administration, maintenance and provisioning (OAM&P) costs are a great advantage of PNNI. PNNI is also a hierarchical network protocol, which gives it the ability to scale to extremely large networks. Hierarchy limits the amount of information exchanged between nodes throughout the network. Nodes are grouped into peer groups which are interconnected through higher level logical peer groups. Figure 4 shows an example PNNI network with 3 levels of hierarchy. In the example, detailed topology information about peer group B is not exchanged with peer group A -- only the interconnection between the peer groups and a generalized understanding of the state of each peer group. This limited information exchange allows PNNI to scale to large networks without worrying about the routing storms experienced with non-hierarchical routing protocols.
Figure 4: A possible design structure for a PNNI network
While the "P" in PNNI stands for private, many carriers who are looking to reduce their OAM&P costs are applying PNNI to their public networks. It is less expensive to implement and administer, and with its hierarchical routing protocol, it scales to very large networks. For these reasons, PNNI will be very important for many service provider organizations, such as those delivering data overlay services, who are looking to leverage the advantages of internetworking within their own multiservice networks.
Signaling System No. 7 (SS7)
The SS7 protocol specified by the ITU, like PNNI, is also a protocol for interexchange signaling. It came originally from the world of public telephone switching where it proved very successful. Since then it has been implemented in all the world's telephone networks. Its great flexibility makes it suited to ATM networks as well. Although a routing mechanism is not specified, static routing is normally used.
Figure 5: The SS7 protocol stack
SS7 comprises various user parts, all of which work together in accordance with the OSI model. The diagram above shows the user parts in the protocol stack which can currently be used in broadband applications (their functions will be discussed in brief below).
The message transfer part (MTP 3b) has two functions: signaling network management and signaling message handling. Signaling network management, manages the SS7 network. It is responsible for executing measures during changes to network availability, such as putting into or removing from service signaling links, paths and points, and during overload in the signaling network. Thus, the transfer facilities in the signaling network are maintained without affecting signaling traffic. Message handling is used to implement the actual message switching function for signaling messages within the network.
The B-ISUP (broadband ISDN user part) includes the signaling function for controlling connections, handling services, and managing connections within the B-ISDN. Connectionless services can also be supported in the broadband network using the signaling connection control part (SCCP) and the transaction capabilities application part (TCAP). TCAP/SCCP can be used to exchange information independently of connections. Applications using TCAP/SSCP include the Intelligent Network (IN) or the Q3 interface for network management.
The diagram below shows an ATM network using SS7 signaling to interwork with other networks currently supported by SS7. There are numerous advantages to using SS7. It is covered by international standards, tried and tested in all the countries of the world and suitable for all communication services (data, video and voice). It can be used for national and international networks, even for gateways. SS7 in ATM networks allows interworking to narrowband networks and to IN, enabling IN functionality to be extended to the broadband network. Connectionless services are also supported (for IN and features, for example). The signaling network is automatically controlled and monitored. Mechanisms for controlling overload are provided automatically. In summary, SS7 offers great availability, it is flexible, and it fulfills the most exacting security requirements. The high level of acceptance and widespread use of SS7 in today's global telecommunication systems makes it highly future-proof. Any ATM core node that is unable to accommodate SS7 will be limited in the role it can play in carriers' networks.
Figure 6: An ATM network design using SS7 to interwork with other networks
And another, this time in layman's language:
newbridge.com
If We Build It, They Will Come
MainStreetXpress 36190 in a Field of its Own
The Internet, along with ATM, took center field at ComNet '97, making it difficult to imagine that life existed before the advent of this global network.
Said one observer, whose own booth boasted the largest Internet network in the United States: "If they're not selling Internet services, they're using the Internet to sell their services."
ATM shared the limelight and proved a big attraction with attendees who recognized that it could speed up their Internet connection and thus bring long-anticipated multimedia services from around the world to their home computers. That made the launch of the MainStreetXpress 36190 Core Services Switch something of an anomaly for this crowd. Few could confirm just how many bits are in a Terabit, let alone imagine the 1 Terabit and beyond scaling performance of the MainStreetXpress 36190.
The world's most powerful switch won Best of Show in its category, laying low the competition delivered by Nortel and IBM. Faster and stronger, the MainStreetXpress 36190 caught the eye of some of the industry's keenest scouts. It is the prodigy of two companies that have led their respective industries -- voice and data -- and, as a result, has the blended strengths of both parents.
What They Said
"I'm very impressed with the product," said James Stone, Managing Director of Preferred Technology, Inc. of San Francisco. "I have a background that includes the voice side and the data side, and I keep wondering when the two sides are going to talk to each other. And it looks to me like a real breakthrough product in terms of integrating the voice and the data and making it happen."
"To produce this large a product in this short a time frame shows that the two groups are really working well together," added Stone.
"Embedding SS7 in an ATM backbone is very interesting," said Michael Khalilian, Director of Applications Development Technology at Time-Warner Communications. "It's the best of both worlds."
"I came here to get educated about how Siemens and Newbridge are merging these two technologies," added Khalilian, who was attending the Siemens/Newbridge Customer Breakfast. "Siemens understands carrier telephone requirements and Newbridge understands data. How they mergethe two -- how we get those killer applications from ATM being integrated in the Central Office -- this is interesting for providing value-added services."
"There are strong ATM backbone switches from other companies," Khalilian explained, "but SS7 is really what is attracting us."
SS7 on ATM Core Switch Delivers Competitive Advantage
"When ATM was first proposed," explained Pierre-Yves Sibille, Director, Advanced Broadband Planning at Siemens Stromberg-Carlson, "it was proposed by PSTN (Public Switched Telephone Network, or, major carriers)people as a successor to TDM technology. ATM was thought to be the next-generation technology, precipitated by experimentation with voice packetization."
They wanted to move away from the enforced Nx64 rigidity of the TDM networks and ATM evolved as the surefire technology to deliver the extensive array of new services: video, imaging, and data. Voice was still part of the ATM picture, but the intricacies of SS7 signaling needed to also be molded to fit with the intricacies of the ATM Forum's PNNI signaling. The MainStreetXpress 36190 delivers the two on the same platform.
"The 36190 is the critical link in this concept," he added. "The voice concepts are actually very old, very established and proven. However, the ability to bridge the legacy voice network to ATM lies in SS7signaling."
<Picture: MainStreetXpress>
Data Plays Catch-Up To Voice
Voice specialists have devoted years to the refinement of network signaling. For example, based on Advanced Intelligence in the Network(AIN), a superior selection of advanced services is available (800numbers, calling cards, virtual private networks, automated attendants), call routing is lightning fast due to sophisticated databases, and dial tones are natural and expected by end users. Providers need a reliable network such as AIN to deliver these services, but they need SS7 to access AIN.
The data world is following a similar evolutionary path to the one voice has already traveled, and those in the data world (or, most often, in both worlds) want to eliminate many of the problems the voice world has already conquered. For example, in the data world, if a file has not transferred, the sender doesn't know until it's returned. In the voice world, the lack of a dial tone or congestion tones on the phone line indicates immediately that there is a problem with the network.
The bottleneck issues with the Internet are well-known. That's because the computers need to map out points along the way to get to the endpoint, which takes a painfully long time in comparison to the voice world. We wait less than three seconds for a connection in the voice world. In the data world, users can wait minutes for a response when they download Internet pages or send electronic mail.
"ATM is an ideal environment for distributing 'intelligence'. In such an environment," said Sibille, "intelligence (features and services, for example) is not tied anymore to the switch, but can be positioned anywhere in the network, depending on where it is most appropriate."
What is most interesting about SS7 on an ATM core switch is that the two technologies complement and enhance each other. While SS7 addresses the signaling issues, ATM addresses the bandwidth issues.
"Our original goal is to provide all means of communication -- voice, video, data -- to everybody via a single pipe, and all on-demand, "Sibille explained. "The pipe is fiber, the technology is ATM, and the on-demand switched virtual circuits utilize the proven voice network signaling system -- SS7. This is how we can deliver our goal."
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This page was last updated on Monday, May 12, 1997.
c 1995, 1996, 1997 Newbridge Networks Corporation.
For comments on our Web pages contact the webmaster.
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MainStreetXpress Solution
The MainStreetXpress 36190 Core Services Switch and the MainStreetXpress 36170 Multiservices Switch, both from the Siemens / Newbridge Alliance, support the UNI protocols of the ITU and ATM Forum. Allowing easy connection of customer premise equipment, the UNI protocol provides subscriber signaling which is already largely in line with the requirements of service providers.
With interexchange signaling, it is no longer possible to talk of almost identical standards between ATM Forum and ITU, since the ways in which PNNI and SS7 function are based on fundamentally different approaches. Despite this, both signaling variants will be legitimate in the ATM networks of the future.
SS7 is a proven interexchange signaling system. It will be used particularly in public ATM carrier networks where high availability and security are required. Its widespread use in the narrowband world ensures interworking with the narrowband networks and intelligent networks. The MainStreetXpress 36190 Core Services Switch is ideally suited to such networks. It incorporates the competence and experience that Siemens has accumulated in recent years as the world market leader of narrowband switches.
PNNI will find its main area of application in networks whose focus is not narrowband traffic based on SS7. PNNI is attractive to many carriers because the administrative overhead is low and it has the ability to scale to very large networks.
The MainStreetXpress 36190 and 36170 both have full PNNI capabilities. The MainStreetXpress 36190 is particularily suited to the core. Reflecting the world leadership of Newbridge in building data networks, the MainStreetXpress 36170 Multiservices Switch is especially suited to deploying services on the edge segment of public ATM networks.
newbridge.com
SS7 and ATM In Action
One of the services SS7 makes possible is Local Number Portability (LNP). This is a particularly timely service in the United States, as all US telecommunications providers are moving rapidly to meet an FCC enforced deadline of January 1998 to deliver LNP. In the UK, LNP was introduced more than 18 months ago.
Local Number Portability
LNP allows users to keep the same telephone and/or facsimile number, even if they change carriers and/or location. This clearly has the potential to solve some of the industry's more urgent issues:
With the advent of increased competition and the emergence of so many new services, consumers have tremendous choice. Not only do we have telephone and fax numbers now, we also have mobile and voice mail numbers, and perhaps soon, a satellite number. As a result, some carriers are actually running out of available combinations of numbers. For example, Canada and the US recently had to add new area codes in reaction to the shortage.
Changing numbers is a great deal of trouble for businesses who move. They have invested significant dollars in advertising, which frequently includes a contact telephone/fax number, and they don't want to re-invest in a new number.
The telephone book is an expensive database to update as diligently as customers require.
LNP is just one of the applications made possible by the sophisticated database and routing functions of SS7. The available bandwidth in an ATM core switch the size of the MainStreetXpress 36190 will make it possible to deliver not only services like LNP, but also a full range of interactive applications. That includes services like video-on-demand, teleshopping, tele-banking, and -- not the least -- telephony.
"If we want a movie, we place a call for a movie, and the signaling system is what allows, for instance, 4,000 calls requesting the service at the same time," said Pierre-Yves Sibille, Director, Advanced Broadband Planning at Siemens Stromberg-Carlson. "The SS7 signaling system was designed to bring flexibility to a complex call process in an environment where there is a high call rate, such as the public telephone network."
Trials to date on delivering these bandwidth-intensive services have hit serious capacity roadblocks which a superior signaling system -- coupled with the appropriate amount of bandwidth that ATM delivers -- can resolve.
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This page was last updated on Monday, May 12, 1997.
c 1995, 1996, 1997 Newbridge Networks Corporation.
For comments on our Web pages contact the webmaster. |
