The Integrated Service Digital Network (ISDN)

The Integrated Service Digital Network (ISDN) was first offered to the public in the 1980s,as telephone provider began deploying their SS7 networks.With ISN, many new services could be extended to the customer premises.By using ISDN subscribers and consolidate all their trunks to one DS1 facility.The ISDN protocols provide circuit allocation within the ISDN

When additonal badwidth is needed for high speed data communication, the protocol is capable of allocating additional channel within the DS1 to carry the others calls.This is often reffered to as dynamic bandwidth allocation and is one of the principle feature of ISDN.Beside transmitting voice,ISDN is also capable of transmitting data using the same facilities as the voice

ISDN signaling uses a separates channel and is compatibel with SS7.The signaling information is handled off to the SS7 network and tranfered to the distance end using the SS7 ISDN User Part (ISUP).The ISUP was developed for all call setup adn teardown, and replaced the SS7 Telephone User Part (TUP) protocol in ANSI network

The term of ISDN was originally used to refer to the entire of IN, including SS7.This later evolved to reference only the subscriber interface.Oroginally the creator of SS7 thought of extending the SS7 network all the way to the subscribers.This was abondoned, however, over concern of security and network fraud.The solution was to create an intelligent interface, compatoble with SS7, which could offer the same services and intelligeces as the SS7 network. It was this that spuured the creation of the ISDN protocol

Perhaps the most important application for ISDN is the concept of connecting PBXs within a private network

ISDN offers many services to the subscribers.The basic lavels of service are defined as:

1.Transport elements.Allow information to be transported through the telephone service provider network and its switches, routers, multiplexer and other network equipment tranparently without alteration to the original data

2.Control elements.Support real time operations of transport capabilities (connection establishment and database queries)

3.Network managemenet elements.Provide procedures and capabilities ad administer,maintain and operate the communication infrastructure.Include provisioning of transmission facilities, fault mangement,cogestion control and administration of database and routing table

4.Communication applications environment.Provide a development for programmers from which application can be developed, using other three elements

5.Tranport.Provide the lower thredd layers of OSI, providing allocation of badwidth,routing,ralaying and error detection/correction

TO understand how ISDN can be of significant benefit to PBX networks, consider this example.Many large corporation will own several PBXs at different location.The line are often used to tie the PBXs together.This allows users to access extension in any other company location by dialling adn access number (to access teh tie line) and dialing the extension.Many digital PBXs allow callers to dial extension numbers of remote extensions without dialing an access code.Automatic routing features provide software to determine which trunk the call must be routed to

There are two classes of ISDN service: Basic Rate (BRI) and Primary Rate (PRI).BRI service provides two 64kbps bearer channel (B channels) and one 16 kbps signaling channel.This service is designed for residential and small business usage.PRI offer 23 64 kbps bearer channels (B channel) and one 64 kbps siganling channel (D channel).PRI is designed for larger businnesses with large call volume.Many PBX manufacturers already provide ISDN compatible trunking interfaces for their equimpment, making ISDN a good choice for companies who need end to end voice and data communications

ISDN cannot be succesful by itself.As we have already seen, without SS7, ISDN remains a local digital service providing a limited numbers of features and applications.With the addtion of SS7, ISDN can become an extension of the telephone network to the customer premise, offering true end to end voice and data communication woth no boundaries

The ISDN standards can be founf in the ITU-TS"I" series. The siganling standards are defined in publication Q.921 (defines the Link Access Procedure -D Channel) and Q.931 publication (defined the ISDN call control procedures at layer three) Read More..

The SS7 protocol stack

The SS7 protocol differs somewhat from the OSI model.While the OSI moden consists of seven different layers, the SS7 standar uses only four level.The functions carried out by these four levels correspond with the OSI model's seven layer.Some of the functions called for in the OSI model have no purpose in the SS7 network and are therefore undifined

It should also be noted that the functions in the SS7 protocol have been refined over the years and tailored for the specific requirments of the SS7 network.For this reason,there are many discrepancies betwen the two protocol and their corresponding functions

Regardless of the differences, the SS7 protocol has proven to be a highly reliable packet switching protocol,providing all of the services and function required bt the telephone service providers.THis protocol continues to evolve as the network grows and the services provided by the telephone companies change

1.Level one -Physical level

it is virtually the same as that of the OSI model.THe OSI model does not specify any specific interface to be used, as that will always differ from network to network.In SS7,we can specify which interface will be used, since the Bellcore standard and the ANSI standard all call for one or two types or interface - the DS0A or V.35
THe DS0A interface is the most forward for the application with the V.35 acceptable as the second choice

2.Level two - data link level

it provides the SS7 network with error detection/correction and sequenced delivery of all SS7 message packets.A with OSI model,this level is concerned only with the transmission of data from one node to the next node in the network.It does not concerned it self with the final destination of the message.As the message travels from one node to node, each node examine the dialied digits (contained in level four) and use that information to determine the next route of the message
Level two is provided the inforamation by level three which determines message routing

3.Level three-network level

it rpovides three functions;routing,message discrimination and distributin.All three functions depend on the servicee of the level two.When a mesaage is received, it is passed by level two to level three for message discrimination
Message discrimination determines who the message is addressed to.If the mesage contains the local addess (of the receiving node), then the message is passed to message distribution.If the message isnot addressed to the local node,then it is passed to the message routing function.The message routing function reads the called and dialling party address int the message to determine which physical address to route to.The called and the calling party addresses can be considered logical addresses and the physical address the node address

4.Level four-user parts

it consists of several different protocols, all called user parts and applicaiton parts.For basic telephone call connection and disconnect, the Telephone User part (TUP) or ISDN user part protocol (ISUP) are used.TUP is used in Europe and other countries following ITU-TS standards, while ISUP is used primarily in Nort America Read More..

UMA vs IMS

Inmoving beyond superficial services bundling in pursuit of truly integrated FMC services,carriers are proceesing down two distinct main technology paths:unlicensed mobile access (UMA) and IP multimedia system (IMS)

UMA is preferred primarily by mobile carriers,as it operates effectively as an extention of the mobile network,keeping all control in the hands of the mobile carrier.When a mobile subscriber with a UMA-enabled,dual mode handset moves within range of a WLAN access point, it can attemp to roam onto WLAN.The handset contacts a UMA network controller via the IP access network, and if authenticated and authorized,has it current location information registered by the mobile network,which routes further calls via the WLAN

Most industry analysts view UMA as tactical,intermediary step on the part of mobile carriers who are not yet ready to convert their extensive global system for mobile communication (GSM) and general packet radio service (GPRS) core networks to IP, an IMS prerequisite

The UMA functional architecture are:

1. mobile station
2. WLAN access point
3. Broadband IP network
4. UMA network controller (UNA)
5. UNC security gateway
6. Public land mobile network (PLMN) : mobile switching center, serving GPRS support node, AAA proxy server, HLR
7. Home PLMN (roaming case) : AAA server, HLR

IMS is prefered primarily by carriers (typically fixed) that already have extensive IP backbones in place, as it keeps call control in their hands and runs VOIP and SIP without major impact on their networks.

Its primary advantages over UMA are its scalability and applicability to a much broader range of underlying access technologies.Its basis in IP yields an ability to leverage the much wider range of applications that already exploit IP based services and interfaces.Its reliance on SIP based signalling simplifies the introduction of multiservice combinations,e.g, instant messaging plus voice

Perhaps most important,it provides a basis for more sophisticated billing of new services,allowing carriers to more quickly monetize the considerable investments they will have to make in network infrastucture, OSS upgrades and system integration services to migrate to IMS

The three layer architecture of IMS are:

1. Transport layer : core network
2. Control layer : home subscriber service and call session control function
3. Service layer : application servers

What FMC means to enterprises today

Many enterprises may look at the timeline for the arrival of true FMC services and conclude that it can be safetly ignored for now. To the extent that FMC is in the hands of carriers, this is largely true.But enterprises do have one critical element of FMC in their control today: their WLANs. Furthure, most market researchers are forecasting rapid growth over the next few years in enterprise spending on WLAN equipment.

A majority of network managers expect to voice enable their WLANs in that timeframe.Even if enterprises discount the possible arrival of FMC service, they should be scrutinizing how well ther WLAN build outs can accomodate high quality mobile voice service

As it happens,the key WLAN capabilities required to deliver mobile voice over WLAN services - granular control of QoS and security,fast voice call handoffs when raoming,zero configuration access from a wide range of devices,graceful capacity scaling,tighter integration with wired LAN infrastructure and improved WLAN security - are perfectly congruent with those needed to facilitate FMC services.Thus investments in voice grade WLAN infrastructure today can yield a second payoff if enterprise eventually migrates to FMC services Read More..

Traditional SS7 Protocol

1. Message transfer part 2 (MTP2)

MTP2 corresponds to OSI Layer 3 (the data link layer) and such is the lowest protocol in the stack.Sitting on the phisical layer, its provide a realiable means of transfer for siganling information between two direcly connected singaling point (SPs),ensuring that the signaling information is delivered in the sequence and error free

MTP2 performs the following functions:

1.Delimination of signal units
2.Alignment of signal units
3.Siganling link error detection
4.Siganling link error correction by retransmission
5.Signaling link initial alignment
6.Error monitoring and reporting
7.Link flow control

Message transfer part 3 (MTP3)

The primary purpose of this protocol is to route message between SS7 network node in the reliable manner.This responsibility is devided into two categories:

1.Signaling message handling (SMH)

2.Siganling network management (SNM)

SMH is concerned with the routing message to the appropriate network destination.Each node analyzes the incoming message based on its destination point code (DPC) to detemine whether the message is destined for that node.If the receiveing node is the destination, the incoming message is delivered to the appropriate MTP3 user.If the receiving node is not the destination and the message has routing capability, i.e, is an STP, an attempt us made to route the message
SNM is set of message and procedures whose purporse is to handle network failure in a manner that allows message continue to reach their destiantion whenever possible.These procedures work together to coordinates SS7 resource that are becoming available or unavaiable with the demand of user traffic

ISDN user part (ISUP)

ISUP is responsible for setting up and releasing trunk used for inter exchange calls.As its name implies, ISUP was created to provide core network signaling that is compatible with ISDN access siganling.The combination of ISDN access signaling and ISUP network signaling provides end to end transport mechanism for signaling data between subscribers.ISUP provides siganling for both non ISDN and ISDN traffic, in fact the majority of ISUP signaled traffic currently originates from analog acccess signaling like that used by telephone service phone

The primay benefits of ISUP are its speed,increased signaling badwidth and standardization of message exchange.Providing faster call setup times than Channel Associated Signaling (CAS), it ultimately uses trunk resource more effectively.The difference in post dial delay for calls using ISUP trunk is quite noticeable to the subscriber who make a call that traverses several switches
ISUP consists of call processing, suplementary service and maintenance functions.

Signaling Connection Control Part (SCCP)

SCCP sits on top of MTP3 in the SS7 protocol stack.The SCCP provides additional network layer function to provide trandfer of noncircuit-related (NCR) signaling information,appliation management and alternative and more flexible methods of routing
SCCP was developed after the MTP and together with the MTP3 it provides the capabilities corresponding to layer 3 of the OSI references model

SCCP provides the folowing additional capabilities over the MTP:

1.Enhance MTP to meet OSI layer 3

2.Powerfull and flexible routing mechanism

3.Enhance transfer capability, including segmentation/reassembly when message is too large to fit into one Message Signal Unit (MSU

4.Connectionless and connection-oriented data transfer services

5.Management adn addressing of subsystem (primarly database-driven applicaiton)

Transction capabilities applicaiton (TCAP)

TCAP allows service at network to communicate with each other using an agrees upon of data elements.Prior to SS7, one of the problem with implementing swtiching service beyond the boundary of the lcoal switch was the propreitary nature of the switches.TCAP provides a generic interface between service that is based on the concept of componnents.Componnects comprise the instructure that service applications exchange at different nodes Read More..

FMC solution

Telecom convergence on IP networks has been underway for at least a decade, as both carriers and entrprise have sought to replace separate,single purpose infrastructures with integrated,multi service ones.This is evolution is reflected in the convergence of voice and data in enterprise campus IP telephony,consumer VoIP services and local carroer Digital SUbscriber Line (DSL) services.FMC merges service in the fixed line and mobile telecom worlds,as exemplified by voice roaming between a cellular network and a campus voice enable WLAN.
In its ultimate form,FMC reflects a true integration of underlying network and aasociated management infrastructures.But there are several interim steps in the way to the most seamless form of FMC

Broadly speaking,carriers rollouts of converged services begin with simple service bundling,followed by real integration of underlaying network infrastructure,followed by integration in operations support system (OSS). The baby step of carrier servies bundling can be taken without any techincal integration between the fixed and the mobile network, and only a consolidation of previously separate customer interface, e.g, single sales contact instead of two; an integrated support and help desk function and single bill for both mobile and fixed services.

The customers get some modest benefits in terms of consolidated purchasing and discounting leverage as well as fewer carriers to deal with.The carriers get some modest uptick in customer retention and can market its entry into FMC. Such service bundling is already taking place today,but that barely scratches the surface of FMC's potential

The benefits of FMC appear much more compelling to both the enterprise customer and the carrier once the underlying fixed and mobile telecom infrastructures - plus OSS functions for management, provisioning and billing - begin to converge.

The evolution toward true FMC service is projected to proceed through five major phases:

1. Phase 1: Basic network infrastructure convergence

already well underway.The carrier consolidates voice traffic onto its IP WAN using VoIP and the enterprise begins moving its campus voice service to some form of IP telephony, often using a hybrid approach than combines Time Divission Multuplexing (TDM) and VoIP.The main benefits are cost savings through reduction in capital expenditures for network infrastructure for network infrastructure and in operating expenses to maintain it

2. Phase 2: Addition of enterprise wireless LANs, followed by voice over WLANs

Party to well underway at most large enterprise. Enterprise WLANs move from limited deployments serving nomadic users in conference room and lobbies to ubiquitous campu wide coverage, serving as the primay means of network acccess for all users.Greater integration of wire and wireless LAN infrastructure begins , e.g the use of common authentication mechanisms and endpoint security plociy is enforced for both wired and wirelss LAN users,thus deploying voice over the WLAN

3. Phase 3: Early managed FMC services

were underway as of 2006. Carriers and carrier partnership begin to roll out the first managed FMC services, providing mobile users with the ability to roam seamlessly between cellular netwrok and enterprise voice enable WLANs, using dual mode handsets or PDAs equipmed with both Wi-Fi and 3G radios

4. Phase 4: Tighter integration of fixed and mobile network infrastructure and back office system

Begin in late 2007, with broader adoption expected in the beginning of 2009. FMC carriers and their partners began to functionally converge their network signaling and back office system. Consolidation of formely separate control paths for service setup and feature delivery enable new services beyond cellular to voice - over - WLAN roaming - e.g, push to talk voice and application like instant message that exploit a user's presence and availability profile

5. Phase 5: High value FMC application delivery

As the undustry matures and accelerates through 2011. With a truly integrated, multimedia infrastructure in place that supports any combination of information types, end device and access technologies, FMC providers begin to focus their efforts to developing new application services. They take further advantage of converged network' presence awareness, effectively delivering services to specific persons rather than device or via specific access networks.

Providers begin creatively mixing and matching once disparate services - voice, audio conferencing, video, video conferencing, text based instant messaging, email, games, SIP enabled conferencing and collaboration, broadcast video and audio - to serve an array of new applications and end user needs Read More..

DPI (Deep Packet Inspection)

The rapid growth and popularity of broadband service presents both opportunities and challenge for carriers. On the other hand, the popularization of such service as, P2P,online games,WebTV and VoIP means that many people are now using and enjoying these service and telling their friends abotu them, so the number of usrs is growing larger everyday. On the other hand,carriers now have to resolve a series of problems in relation to bandwidth management,content billing and information security

The most obvious problem has to do with P2P application.P2P technology in effect clears a path through the C/S traffic model.By adopting a non concentrated server mode, it is able to penetrate and break up server bottleneck and so it is now being widely used in many domains including downloading,streaming and VoIP.According to the statistic data, at present, P2P traffic accounts for over 50% of all online traffic and the percentage is growing higher all the time.Many people are even saying that P2P is a killer application or revolutionary technology.However most carriers' network planning and construction mode are not suitable for the P2P applications traffic model

In addition most network equipment is lacking int terms of efficient technical monitoring, so P2P application would not recognized if used. As a result,carriers are unable to properly identify or manage network applications.Hence their networks are always congested and operations are in a state of confusion pr facing some technical dilemma

Another barrier reratding carriers' development is that they are unable to implement content billing.Content billing means that a carrier is able to perform in depth analysis in data packets,differentiate type of user service and set reasonable rates according to service features
At present, as data services and content services have been developing, the lack of complete content billing modes make it virtually impossible to convert service increase into equivalent benefits.

What makes things worse is that the benefits derived from some services have even decreased. In providing voice, IM (instant messageing) and game applications, ISP and ICPs utilize cheap network resource to attract and develop users and recieve a huge portion of the profits. leaving carriers helpless, receiving an insubstantial portion of the profits.

Thus far content billing become an important threshold feature upon which are wireless carriers have started to deploy content billing and fixed netwrok carreirs are also investigating useful steps in this direction

Content security presents another headache for carriers.Over the past few years, intrussions and attacks from online hackers have resulted in huge loss for carriers.Although a firewall can repel some of these attacks, it offers little if any protection againts viruses that are hiden in IP packet net loads.Currently, network attacks have been gradually shifted toward high level application.According to recent statistics released by Gartner, the application layer has been the target of over 70% of network attacks, and the percentage is still increasing steadily.Therefore,content security has become a key focus in information security

While carriers are failing to identify services, implement content billing and not meeting information security demands, they are on the one hand being forced to pay more in terms of operation costs and are recieving lower customer satisfaction in return. Therefore, a major concern for carriers is acquiring the ability to perceive network applications and provide network service control and management measures, so that their networks are both operable and manageable

A positive step in this direction is the recent development of DPI.Deep Packet Inspection is a new technology is comparasion to ordinary message analysis.Ordinary message inspection only analyze contents under layer 4 of each IP packet, which includes the source address, destination address, source port, destination port and protocol type.So on this basis DPI is capable of implementing analysis on the application layer that can identify applications and their contents

In fact, DPI technology has already been applied in the security protection system of intranets.Since its application scope is relatively samll, it has thus far not attracted much attention,However the forces that are currently driving it to center stage are P2P application and content billing Read More..

Metro Transport network

MSTP is based on SDH,can enjoy existing SDH network resource and provides various interface to support data service such as ethernet and ATM.Through the analysis of SDH network operational,maintenance and management experience,MSTP is fully compatible with existing TDM service and can integrate multiple service transport and access to meet upward spiraling data service commands.

Fro traditional carriers with mature SDH network offering a huge quantity of TDM service,MSTP is the most direct and efficient metro transport network solution.

MSTP has been widely applied and most new metro SDH networks are MSTP.To efficienly process and transmit data service,it utilize some key technologies including GFP,VC (virtual connection) and LCAS (Link capacity adjustment scheme).As MSTP is TDM based,the service mode it suits is the provision of traditional TDM service while partially supporting IP and ATM service.

MSTP can be located on the convergence adn access layers of a metro transport network and can integrate service networks into both

The existing network environment bears traditional TDM services, whereas MSTP can reliably bear new,high capaity services such as ethernet leased line,point to multipoint and ring services.Integrated access with convergence from DSLAM to BRAS can be offered to large scale customers and it can also transmit NGN and 3G services

MSTP mainly exist as a layer 1 network and is not suitable for large scale layer 2 and layer 2 services.Ehen introducing MSTP,carriers should ensure that existing networks can coordinate and coorporate.MSTP can mainly offer existing metro network and ATM networks access and convergence functions, and it can be used to expand the ethernet and ATM service coverage.Its data processing function effeciently handles data services but it can not wholly replace data service networks

MSTP related rechnologies have been constantly developed adn optimized.To further improve its perfomance in transmitting ethernet services and balance nodes, some MSTPs adopt embedded RPR (Resilence packet ring),which enables highly efficent data service transport.Given RPR only supports ring network topologies,some MSTPs adopt built in MPLS (multi protocol lable switching) to process inter ring services

As MAN bandwidth demands have been soaring,it is increasingly difficult for SDH based MSTP to cater to MAN developments. A trend for solving the MAN bandwidth bottleneck is to gradually introduce WDM into MAN.WDM represents a mainstream technology in terms of long haul transport, but it has only been recently applied to MAN.Metro WDM embodies another type of driving force and characteristic that are different to those of long haul WDM.When used in long haul transport,WDM can save on expensive long haul optical fiber resources.

In the MAN network with its mostly short transport distance, costs on optical fibers will be much lower than in long haul backbones.Node equipment normally incurs high costs in each metro transport network and while it is beneficial to save optical fibers in some MAN,however service flexibility,manageability and cost effetiveness are more important for MAN applications.

The metro WDM network must support multiple services on the same platform and should be transparent to rates and protocols.Equipment ought to be low in price and the network should feature good expandibility in order to adapt to various metro service demands.Wavelength management capabilities must be strong to facilitate rapid wavelength service deployment.

A solid network self healing capacity that matches SDH network is necessary to offer different levels of protection according to services demands.As transmisiion distances in the MAN are alwasys short, there is no unreasonable demand on network capacity, and some cheaper components can be employed to reduce DWDM equipment cost.Alternatively,the network can adopt CWDM,which enable large inter channel distance.Point to point WDM cannot meet the demands of MAN applications so, as ROADM (reconfigurable optical add drop multiplexer) matures, ROADM can enable optical layer networking and introduce the control plane so that WDM plays greater role in MAN networks

Metro optical networks can provide strong bandwidth support for metro IP networks and ethernet.Compared with pure,direct optical fiber connections,this is network is more flexible,secure and resource efficient.The WDM networkcan deploy some new service such as BoD (bandwidth od demand),wavelength wholesale,wavelength lending,OVPN (optical VPN) and optical multicast.As the SDH network on the electronic layer is gradually replaced by IP/ethernet,future metro transport network will adopt the optocal layer metro WDM network Read More..