Cell Relay Archive[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index][Thread Index][Author Index][Subject Index] RE: Interworking PSTN and ATM
------ =_NextPart_000_01BE3382.67F199A0 Content-Type: text/plain Hi Debayan, I am attaching a paper on our view of some of the issues and trends of the Broadband/Narrowband interworking. The document is a simple ascii text document. Trillium provides for some of these solutions and is in process of developing more. You may be interested in visiting the Trillium Web page at: http://www.trillium.com/products/interworking/1078134.html I hope it helps -Ashish -----Original Message----- From: owner-cell-relay@newstone.ucs.indiana.edu [mailto:owner-cell-relay@newstone.ucs.indiana.edu]On Behalf Of Debayan Chaudhuri Sent: Tuesday, December 29, 1998 2:30 PM To: cell-relay@cell.ucs.indiana.edu Subject: CR: Interworking PSTN and ATM Distribution: world Hello all, I would really appreciate some pointers on the issue of interworking between PSTN and ATM networks. If a PSTN call needs to be routed through an ATM network ( eg. offloading of data traffic from the congested PSTN ), I understand that there needs to be interworking between SS7 ( N-ISUP ) and B-ICI ( B-ISUP ) in order to establish the call. But what if if the ATM network does not support B-ICI ? Should we try to interwork between SS7 and Q.2931 ( the local PSTN switch is treated as an ATM end-point )? Or between SS7 and P-NNI ( the local switch is treated as an ATM network node ) ? Interworking between N-ISUP and B-ISUP is specified in ITU-T Q.2660. But while interworking between SS7 and P-NNI ( say ), how do we map physical circuit identifiers ( N-ISUP ) with virtual circuit identifiers ( ATM ) ? There must be T1/T3 links connecting the PSTN switch with the ATM network node. Thanks in advance, Debayan Chaudhuri. _________________________________________________________ DO YOU YAHOO!? Get your free @yahoo.com address at http://mail.yahoo.com ------ =_NextPart_000_01BE3382.67F199A0 Content-Type: application/msword; name="aal2.doc" Content-Transfer-Encoding: quoted-printable Content-Disposition: attachment; filename="aal2.doc" This document tries to cover the existing trends in the industries to = provide=0A= the Narrowband services over the Broadband N/W. It also tries to cover = some =0A= technical Jargons which are being used in the industry at this = stage.=0A= =0A= There is a demand for being able to use the Broadband technology in the = backbone=0A= N/W to provide both Broadband service and the Existing Narrowband = services. =0A= =0A= The salient point for having the Broadband backbone N/W will be:=0A= =0A= i) Operators would prefer to upgrade to a common N/W which would = support both =0A= Broadband services as well as the Narrowband Services. They would = not like=0A= maintain seperate N/W's if possible, for Narrowbad Services.=0A= =0A= ii) The Broadband N/W is increasing becoming capable of providing = higher =0A= utilization and better Cost to Maintenance Ratio, than the Existing = =0A= narrowband trunk n/w.=0A= =0A= iii) However moving to the Broadband N/W should not result into loss of = services=0A= offered by the existing SS7/IN networks.=0A= =0A= iv) Migration should be fast, and thus should require minimal and = simple =0A= extensions to the existing narrowband and broadband signallings.=0A= =0A= The Broadband N/W will use the AAL1 and AAL2 adaptation layers to = transport the=0A= Voice Traffic and the Voice band Data traffic which was being carried = in the=0A= Narrowband N/W's.=0A= =0A= AAL1, Adaptation layer which is used to transport the CBR traffic, does = not =0A= currently provides for the best utilization of the ATM resources, as in = such a=0A= case the speech processing techniques are not used and the voice is = code into =0A= the ATM cells which corresponds to a constant bit rate traffic at the = rate of =0A= 64 Kbps, and does not deals with the silence Detection/ Removal and = Insertion =0A= and nor does it considers compression and the low bit rate encoding of = Voice.=0A= =0A= The usage of AAL1 technology for Voice over ATM may not be the best = utilization=0A= of the resources however, it definitately proivdes for a fast migration = path=0A= from the Narrowband backbone N/W to the Broadband backbone N/W.=0A= =0A= The Approaches which are being viewed to work using the AAL1 adaptation = for =0A= voice encoding are:=0A= =0A= i) Signalling Interworking Using ISDN or ISUP Signalling in the = Narrowband=0A= Network and the B-ISUP in the Broadband N/W.=0A= This approach is a used in public N/W's which uses the ISUP protocol = in the=0A= Narrowband public N/W and the B-ISUP in the broadband public N/W.=0A= In this apporach each narrowband call, requires a dedicated VCC = across the =0A= boadband N/W. The Interworking Nodes will switch the narrowband = Channel(CIC)=0A= to the broadband VCC.=0A= =0A= Advantange of this approach:=0A= =0A= a) Both the ISUP and B-ISUP are well defined standards from ITU-T = for the=0A= public N/W's. Also ITU-T specifies the standards for providing = the =0A= interworking between the ISUP and the B-ISUP signalling.=0A= =0A= Disadvantages:=0A= a) This approach is not capable of using the AAL2 Adaptation layer = for coding=0A= the voice, voice band data and other traffic in the narrowband = N/W.=0A= b) The interworking is not capable of completly mapping the ISUP = services =0A= (Supplementary services) to the B-ISUP signalling, thus sometimes = =0A= lead to loss of information and thus degraded quality of = service.=0A= c) In the event of modification of ISUP signalling to support = additional =0A= services, it may take a long time before the ISUP-B-ISUP = interworking will=0A= also be upgraded to support this enhanced services provided by = (ISUP) SS7=0A= N/W.=0A= d) The B-ISUP technology for ATM is used much less popular as = compared to the =0A= PNNI (Private NNI) in the ATM world. And thus there are fewer = implemenation=0A= of the Public Broadband N/W's using the B-ISUP (SS7) = technology.=0A= =0A= =0A= ii) Signalling Interworking using ISUP and PNNI signalling.=0A= =0A= This apporach is used when the islands of Narrowband public N/W = running ISUP=0A= (SS7) stack are connected using the Private ATM n/w with PNNI = signalling.=0A= Also as in previous case, each narrowband call requries a VCC to be = =0A= established across the ATM n/w. There are no standards available to = do =0A= interworking, however there are some contributions in the ATM forum = to =0A= include an addtional parameter to the PNNI signalling, which may = enable the=0A= interworking between ISUP and PNNI, atleast for the application = where the=0A= Broadband could be used in the Backbone n/w to carry narrowband = traffic.=0A= =0A= Advantages of this approach:=0A= =0A= a) The availability of the private broadband n/w's using the PNNI = n/w.=0A= These pre-existing N/W's could carry the narrowband traffic.=0A= Also as PNNI is a matured technology, it should be available=0A= at compatitive cost and quality.=0A= =0A= Disadvantages of this apporach:=0A= =0A= a) Since the ISUP (Narrowband signalling) standards are primarily = governed =0A= by ITU-T and the PNNI standards are governed by the ATM Forum, = none of =0A= the bodies have made much progress in developing the = Interworking Specs=0A= between the two signalling systems. Infact it may even be = difficult to =0A= establish a basic call using the Broadband N/W using the PNNI as = a=0A= backbone N/W in its existing form. =0A= =0A= b) Only properitory mappings available to support this interworking = using=0A= (GAT) parameter which is not completely agreed upon by the = forum. =0A= However the acceptance of this parameter is in an advance = stage.=0A= =0A= c) Currently the PNNI does not seem to be capable for setting up an = AAL2=0A= Channel and thus this interworking will not be able to benefit = from the=0A= better bandwidth utilization provided by AAL2 adaptation.=0A= =0A= =0A= iii) VTOA LandLine trunking using AAL1.=0A= =0A= This approach has primarily concentrated on the application of =0A= connecting Private PBX's, to form a Private N/W using the ATM = backbone to=0A= provide interconnectivity between the PBX's.=0A= This is targetted for the scenario's where the PBX's where = connected to =0A= each other over the Physical Trunks, in a mesh or hierarchial = architecture,=0A= to form a Private N/W.=0A= The solutions, provides for connecting such PBX's using the ATM = n/w, =0A= instead of the PCM's, making it more cost efficient and = mantainable. Also=0A= this may be required as these organization may have other reasons = to have=0A= broadband N/W's for the organizational needs.=0A= =0A= In this scenario, a new Functional entity, called the IWF is = introduced=0A= between the existing PBX's, and the ATM N/W. The VCC's are = established =0A= between the IWF's, to carry the Narrowband Traffic (i.e. voice, = voiceband=0A= data). Although single VCC may be configured to carry multiple = narrowband=0A= calls, the Adaptation layer still follows the AAL1 functionality = and does=0A= not support for a Real Time Variable Bit Rate Data streams = (rt-VBR), which=0A= is the true nature of a voice call, if the silence periods in the = =0A= conversation is removed, and if the low bit rate coding mechanisms = are used=0A= =0A= The Q.93b or Q.2931 based ATM signalling is used to establish the = VCC's =0A= which are used to carry the narrowband user traffic. Also = signalling VCC's=0A= are established between the IWF's, and the Q.SIG or some variant = of ISDN =0A= protocol is used to map the events on the PBX's interface to the = =0A= destination PBX's, over the signalling VCC.=0A= =0A= In this approach there is practically no signalling interworking = between=0A= narrowband signalling system, which supports numerous services, = =0A= and the non-compliant broadband signalling, which at this stage = are not =0A= sufficiently mature to support the services offered by the SS7 = (ISUP)/IN=0A= signalling systems. The narrowband signalling is used on all the = hops and =0A= signalling interworking specifications between narrowband and = broadband =0A= signalling are NOT needed to provide the service transparency.=0A= =0A= Advantage:=0A= =0A= a) Minimal Changes to the existing narrowband signalling system, = which=0A= is used to communciate between the IWF, over the signalling = VCC.=0A= =0A= b) Minimal changes required in the Broadband signalling, on the = nodes which=0A= behave as IWF. The intermediate ATM nodes would not requrie any = change=0A= to be able to support this solution. Thus the available ATM = switches=0A= and the ATM n/w's can be used.=0A= =0A= c) Time to make such a solution work is minimal.=0A= =0A= d) Due to almost no signalling interworking, minimum chances of = lossing=0A= the services available to the narrowband users. Also this = solution is=0A= capable to support the new services which may develop over a = period of=0A= time as it is transparent to such signalling comlexity.=0A= =0A= e) Solution could be extended to use the AAL2 Adaptation layer and = thus=0A= could be extended to be able optimize the utilization of the = ATM N/w=0A= resources.=0A= =0A= Disadvantage:=0A= =0A= a) This solution is currently targeted towards the requirements of = =0A= connecting the PBX's in a private n/w over the ATM n/w.=0A= =0A= b) It does not answers the requriements for connecting the Public = switches=0A= in the narrowband network, over the ATM n/w.=0A= =0A= c) This solution requires lots of VCC's both data and the = signalling VCC,=0A= to be established between the IWF's, which would be lying at the = edge=0A= of the ATM N/W. Although it is better than establishing a VCC, = per=0A= narrowband call.=0A= =0A= AAL2 Adaptation layer=0A= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0A= =0A= This adaptation layer suits well to the real time VBR traffic. The = motivation=0A= for this layer is the fact that in case of the Sileance Detection & = Removal in=0A= voice traffic and by using a low bit rate coding of voice, means lesser = bits=0A= need to be sent for transmitting voice. In such cases waiting to fill a = 48 bit=0A= cell corresponding to a single call, would lead to high level of = delays and=0A= which will cause speech distortion to unacceptable limits.=0A= =0A= AAL2, allows mixing of VBR streams of different length from different = sources =0A= into same cell. Thus a 48 byte ATM cell is further divided in the AAL2 = scheme=0A= to carry data from multiple sources in AAL2 Channels. There could be = multiple=0A= channels with different amount of data in a single Cell. The number of = channels=0A= which could present in a single cell at any time depends on the amount = of data =0A= needs to coded for each of the data stream. There is no fixed mapping = between=0A= the cell and the AAL2 channels or the data filled in each AAL2 channel = in a=0A= cell. However a maximum of 255 Channels could be associated with a = VCC.=0A= =0A= The solutions of using the Broadband N/W using AAL2 adaptation layer, = to carry=0A= the narrowband traffic are:=0A= =0A= v) VTOA Land Line trunking using AAL2=0A= = =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=0A= =0A= The solution is same as VTOA Land Line trunking solution using AAL1 = =0A= adaptation layer, except that it use the AAL2 adaptation to carry = the=0A= narrowband traffic. Thus the n/w's using this solution perform the = Silence=0A= Detection/Removal and Insertion. And allows for a low bit encoding = on voice.=0A= Thus it can use the ATM n/w in a more efficient manner than if = AAL1=0A= is used to carry the narrowband traffic.=0A= =0A= Advantages:=0A= ----------=0A= =0A= a) All the advantages listed for VTOA Landling trunking using AAL1 = are =0A= applicable.=0A= =0A= b) In addition, the usage of AAL2 allows for better utilization of = the ATM=0A= N/W resources, leading to cheaper call cost.=0A= =0A= =0A= Disadvantage:=0A= -------------=0A= =0A= a) As indicated in the disadvantages for VTOA Landline truncking = using AAL2=0A= this solution has primarily been targetted to interconnect the = PBX's =0A= across ATM N/W's. Currently it does not offer solutions for =0A= interconnecting, the Switches in a public N/W.=0A= =0A= b) As indicated in case of VTOA LLTAAL1, too many VCC needs to be = established=0A= between the IWF's (either SVC's or PVC's). =0A= =0A= AAL2 Signalling and AAL2 Switching=0A= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0A= =0A= The primary shortcoming of VTOA LLTAAL2 is that all the IWF's needs to = be=0A= connected in a mesh architecture. In such case VCC's have to be = preestablished=0A= between the IWF's (or the edge nodes), and each time a new IWF (an = edge node)=0A= needs to be added, AAL2 VCC's will have to be established between the = new node =0A= and all pre-configured IWF nodes. =0A= =0A= It could be better both from maintenance point view as well as = resource =0A= dimensioning to be able to establish AAL2 VCC's between a IWF and = another=0A= Node in the ATM N/W (For the time let us call this an AAL2 Switching = node).=0A= All the IWF's could thus be connected to this AAL2 Switching node in a = Star=0A= Configuration.=0A= =0A= In such a scenario, to establish a voice call between two IWF's, a = signalling=0A= mechanism is required to get a AAL2 CHANNEL between the First IWF and = the=0A= AAL2 Switching Node and the Destination IWF and the AAL2 switching = node, and=0A= the AAL2 Switching node could switch any AAL2 CHANNEL on any AAL2 VCC = from=0A= one IWF to any other AAL2 Channel on a different AAL2 VCC.=0A= =0A= This objective is achieve using the AAL2Signalling. AAL2 signalling is = being=0A= defined by the AAL2 Signalling group in ITU and is used to establish = an AAL2 =0A= CONNECTION. AAL2 Signalling is a signalling system which is at same = level as=0A= Q.2931 based ATM signalling. In case of AAL2 Signalling, some of the = ATM nodes=0A= in the N/W's will be designated as AAL2 Switching nodes. Also the edge = nodes=0A= will have the AAL2 Switching and Signalling capability if they want to = use the=0A= AAL2 switching capability of the N/W. Adjacent AAL2 Switching nodes = will=0A= perform AAL2 signalling to be able establish an AAL2 CONNECTION across = the N/W.=0A= =0A= The AAL2 Switching Nodes, will have AAL2 VCC's terminating between = them. Thus=0A= the AAL2 Switching node will be able to extract a AAL Channel from an = AAL2 VCC=0A= and is capable of switching it to another AAL2 channel on a VCC = towards another=0A= AAL2 Switch.=0A= =0A= The AAL2 Switching/Signalling may not be adjacent ATM nodes, and the = AAL2 VCC's=0A= between the AAL2 Switching nodes may be established using the Q.2931 = based ATM=0A= Signalling. Subsequently when a voice connection needs to be made = between two=0A= edge AAL2 Switching node, the Ingress AAL2 Switching node shall = initiate the=0A= AAL2 Signalling, identifing the AAL2 VCC, AAL2 Channel on that VCC, = and the=0A= Address of the Destination (Egress edge) AAL2 switching node. The = intermediate=0A= AAL2 switching node will perform the Routing based on the Address = received in =0A= the AAL2 Signalling SETUP message. Also it shall allocate a AAL2 = channel on the=0A= AAL2 VCC towards the next AAL2 Switch to which the AAL2 Call is = Routed, and =0A= perform the switching between AAL2 Channel on the incoming side of = this AAL2=0A= call and the outgoing side of AAL2 Call.=0A= =0A= Such a voice path which uses different AAL2 Channels on different AAL2 = VCC's =0A= between different AAL2 Switching node and which are switched at the = AAL2 nodes=0A= is called an AAL Connection.=0A= =0A= The above indicate STAR configuration for AAL2 Switches can than be = extended=0A= to a hierarchical n/w configuration of AAL2 Switches.=0A= =0A= Scope of AAL2 Signalling=0A= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =0A= =0A= Scope of AAL2 Siganlling is be able to establish a AAL2 Connection, = however it=0A= does not provides for any I.E.'s which may be required to support = interworking=0A= with the Narrowband n/w.=0A= =0A= Concept of Connection Control and Call Control=0A= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0A= =0A= It is felt that we so many Broadband Signalling system it may not be = easy to =0A= define interworking between the narrowband signalling and the broadband = =0A= signalling system. Thus it may make sense to use the newer signalling = systems=0A= to establish a User Data path (e.g. AAL2 Channel which could carry = narrowband=0A= data), while use the existing narrowband signalling to complete the = call.=0A= =0A= Thus the seperation of the Call control and connection control would be = able to=0A= take advantage of the development in the technology to carry the = narrowband =0A= traffic and still be able to provide the services which are possible = using the=0A= SS7/IN infrastructure which is available.=0A= =0A= One example to achieve this is specified in a contribution made in the = ATM forum=0A= The example solution is aimed to connect the Public Narrowband N/W = nodes using=0A= the ISUP switches, across the ATM N/W. This contribution which is = currently =0A= focused at using AAL1 technology to do this, is sufficently flexible to = be later=0A= extended to make use of AAL2 technology, when the AAL2 Signalling is in = place.=0A= =0A= In this scenario, the Existing Narrowband N/W could be thought of as = consisting =0A= of ISUP(SS7) nodes. The objective is to replace the network of the = Tandem SS7=0A= nodes, with an ATM N/W, while continuing to use the SS7 signalling = infrastruture=0A= =0A= In this example each of the Tandem SS7 node is to be replaced by a IWF = which =0A= terminates the ISUP trunks, while it replaces the SS7 trunks between = the Tandem=0A= SS7 nodes, by an ATM N/W.=0A= =0A= The Call processing is done as follows. The IAM when reaches the = Ingress Tandem=0A= (IWF), the call is routed and the routing determines the next node as = the SS7=0A= node which is connected over the ATM N/W. The IAM is forwarded to the = Next SS7=0A= Node, over the SS7 signalling N/W, however the ATM address = corresponding to this=0A= IWF is also included in the IAM. =0A= =0A= Also included in the IAM is a "Call Correlation Tag". When the call = reaches=0A= the Next Node, which is an Egress node to the ATM N/W, the ATM Address = of the =0A= Ingress IWF is used and a Broadband call is initiated to the Ingress = IWF. =0A= =0A= The "Call Correlation ID" is transfered in the Broadband SETUP message = to the =0A= Ingress IWF, so that it is able to Correlate this broadband call with = the =0A= previously initiated, Narrowband call.=0A= =0A= The AAL1 VCC so established will be used in the ATM N/W to carry the = narrowband=0A= traffic for this call. The Ingress node returns a CONNECT for the = Broadband =0A= call, and the Egress nodes knows which AAL1 VCC to be used for this = call. The=0A= Narrowband may be processed, in the Egress node as any other SS7 = Call.=0A= =0A= The concept could be extended to use the AAL2 signalling to establish a = AAL2=0A= CONNECTION in the ATM N/W in the backward direction, instead of an = AAL1 VCC.=0A= =0A= Thus the connection control and the call control can be disassociated = to provide=0A= narrowband services over the ATM or even IP N/W.=0A= =0A= =0A= The above proposal is just one solution, however the ATM forum has = requested=0A= ITU to look into such possibility and come up with a generic solution = to =0A= disassoicate the Call Control with Connection Control.=0A= =0A= =0A= =0A= =0A= =0A= =0A= ------ =_NextPart_000_01BE3382.67F199A0-- |
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