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Lecture #10Lecture #10: ISDN : ISDN Architecture and Architecture and

Services.Services.C o n t e n t s C o n t e n t s Narrowband ISDN - Services and Narrowband ISDN - Services and

ArchitectureArchitecture Broadband ISDNBroadband ISDN

Switching technologiesSwitching technologies

ATM SwitchingATM Switching15

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ISDN ServicesISDN Services ISDN - Integrated Services Digital NetworkISDN - Integrated Services Digital Network

- communication technology intended to - communication technology intended to

pack all existing and arising services:pack all existing and arising services:

digitized voice services (caller ID, digitized voice services (caller ID,

messaging, persistent calls, redirected messaging, persistent calls, redirected

calls, multicast calls, waiting calls, in-call calls, multicast calls, waiting calls, in-call

functions)functions)

multimedia quality exchangemultimedia quality exchange

enhanced digital services - computer enhanced digital services - computer

interconnectioninterconnection

entertainment services - TV, VOD (video on entertainment services - TV, VOD (video on

demand) demand)

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N-ISDN ArchitectureN-ISDN Architecture Narrowband ISDN communications are based on Narrowband ISDN communications are based on bi-directional serial digital exchange (“bit pipe”) bi-directional serial digital exchange (“bit pipe”) between end-user devices and the public service between end-user devices and the public service network; network; circuit switching technologycircuit switching technology

Digitized user devices: phone, fax, terminal Digitized user devices: phone, fax, terminal (incl. VOD services)(incl. VOD services)

Network congestion method: time division Network congestion method: time division multiplexing over the bit stream according 2 multiplexing over the bit stream according 2 standards:standards:– low bandwidth: single channel for home uselow bandwidth: single channel for home use

– high bandwidth: multiplied single channels for high bandwidth: multiplied single channels for business use. business use.

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N-ISDN ArchitectureN-ISDN Architecture Basic ISDN configurationBasic ISDN configuration

– Low bandwidth Low bandwidth – NT1 - Network Terminating device by the user’s NT1 - Network Terminating device by the user’s

place place – passive bus connection between NT1 and user passive bus connection between NT1 and user

devices (up to 8 devices per connection) - ITU-T devices (up to 8 devices per connection) - ITU-T standard reference point “T”standard reference point “T”

– twisted pair between NT1 and Carrier’s office (up to twisted pair between NT1 and Carrier’s office (up to few km) - ITU-T standard reference point “T”.few km) - ITU-T standard reference point “T”.

Extended ISDN configurationExtended ISDN configuration– High bandwidthHigh bandwidth– NT1NT1– NT2 - small ISDN switch “PBX” (Private Branch NT2 - small ISDN switch “PBX” (Private Branch

Xchange) by the user’s office Xchange) by the user’s office – passive connections between NT2 and user ISDN passive connections between NT2 and user ISDN

devices - ITU-T standard reference point “S”devices - ITU-T standard reference point “S”– optional terminal adapter TA supporting interface to optional terminal adapter TA supporting interface to

one or more non-ISDN terminals - reference point one or more non-ISDN terminals - reference point “R”.“R”.

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N-ISDN PerformanceN-ISDN Performance ITU-T standard allowsITU-T standard allows

– Basic bit pipeBasic bit pipe: 128kb/S voice/data : 128kb/S voice/data channel + 16kb/S signalingchannel + 16kb/S signaling

– Primary bit pipePrimary bit pipe: combination up to : combination up to 1.92Mb/s + 16-64 kb/S signaling (to fit in 1.92Mb/s + 16-64 kb/S signaling (to fit in the ITU-T E1 PCM carrier of 2.048Mb/S)the ITU-T E1 PCM carrier of 2.048Mb/S)

Obsolete standard regarding audio/video Obsolete standard regarding audio/video communications (because of the low transfer communications (because of the low transfer rate)rate)

Data applications: inapplicable by open Data applications: inapplicable by open system interconnections but still good for non-system interconnections but still good for non-interactive and non-real-time applications interactive and non-real-time applications (Internet, remote access to databases, etc.)(Internet, remote access to databases, etc.)

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Broadband ISDNBroadband ISDN155 Mb/S155 Mb/S digital virtual circuit for fixed size digital virtual circuit for fixed size

data packetsdata packets enough rate for hard transfer applications like enough rate for hard transfer applications like

digital transmission of High Definition Television digital transmission of High Definition Television

(HDTV)(HDTV)

ATM based technologyATM based technology

packet switchingpacket switching

high speed transmission media up to the customer high speed transmission media up to the customer

device - basically fiber optics device - basically fiber optics

New switching principles differing from multistage New switching principles differing from multistage

and time-division switchesand time-division switches

Joint existence of PSTN, N-ISDN and B-ISDN.Joint existence of PSTN, N-ISDN and B-ISDN.

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Switching technologiesSwitching technologies Switching technologiesSwitching technologies have been developed have been developed

for end to end routing of the data flows. The for end to end routing of the data flows. The following switching technologies are available following switching technologies are available today:today:

– Circuit SwitchingCircuit Switching which is based on the division which is based on the division of the transmission capacity into fixed timeslots of the transmission capacity into fixed timeslots called as channels or circuits. Channels are called as channels or circuits. Channels are allocated end to end between users.allocated end to end between users.

– Packet SwitchingPacket Switching where variable length data where variable length data units (from 40 to 4000 octets) are stored and units (from 40 to 4000 octets) are stored and forwarded in each network node.forwarded in each network node.

– Cell SwitchingCell Switching where small fixed length data where small fixed length data units called cells (ATM 53 octets) are stored and units called cells (ATM 53 octets) are stored and forwarded.forwarded.

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Circuit SwitchingCircuit Switching Circuit switchingCircuit switching has been the first approach to has been the first approach to routing communication channels between users. The routing communication channels between users. The originating user request the connection establishment originating user request the connection establishment with the user signaling. If the channel is available, it with the user signaling. If the channel is available, it will be established between the communicating parties will be established between the communicating parties for the complete duration of the connection and for the complete duration of the connection and remains occupied until either communicating end remains occupied until either communicating end signals a disconnect requestsignals a disconnect request

Circuit switching has been used in classical Circuit switching has been used in classical POTSPOTS (Plain Old Telephone Service)(Plain Old Telephone Service) and and ISDN ISDN networks. networks. Since the channel resource is occupied during the Since the channel resource is occupied during the connection even if there is no traffic between the connection even if there is no traffic between the parties, the circuit switching with dedicated resources parties, the circuit switching with dedicated resources is considered more expensive than routing.is considered more expensive than routing.

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Packet SwitchingPacket Switching Burst data traffic does not make efficient use of Burst data traffic does not make efficient use of

circuit switched transmission. Hence in 1960’s circuit switched transmission. Hence in 1960’s there was developed a new data communication there was developed a new data communication approach called approach called packet switchingpacket switching..

In packet switching variable length data units (from In packet switching variable length data units (from 40 to 4000 octets) are stored and forwarded in each 40 to 4000 octets) are stored and forwarded in each network node. network node.

Each packet contains additional information (in the Each packet contains additional information (in the packet header part) for routing, error correction, packet header part) for routing, error correction, flow control etc.flow control etc.

Each packet is transferred to its destination Each packet is transferred to its destination independently.independently.

In packet switching, network resources are In packet switching, network resources are used only when there is real information that used only when there is real information that is transferred.is transferred.

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Cell SwitchingCell Switching The newest switching technology calledThe newest switching technology called

Cell SwitchingCell Switching uses small fixed length data uses small fixed length data units called cells (ATM 53 octets)units called cells (ATM 53 octets) thatthat are stored are stored and forwarded.and forwarded.

Asynchronous transfer mode (ATM)Asynchronous transfer mode (ATM) is an is an example of a cell switched system. Its cell size is example of a cell switched system. Its cell size is 53 bytes (header 5 + data 48 octets).53 bytes (header 5 + data 48 octets).

ATM is a compromise between the synchronous ATM is a compromise between the synchronous circuit-switched and the packet-switched circuit-switched and the packet-switched systems both in delays, resource use and systems both in delays, resource use and complexity.complexity.

Cell switching is a preferred technology for theCell switching is a preferred technology for the Broadband ISDNBroadband ISDN because of the flexible data because of the flexible data transfer rates.transfer rates.

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B-ISDN Virtual Circuit B-ISDN Virtual Circuit

Circuit switching technology of PSTN is Circuit switching technology of PSTN is

replaced by B-ISDN replaced by B-ISDN virtual circuit (VC)virtual circuit (VC). . 2 categories virtual circuit 2 categories virtual circuit

Permanent virtual circuitPermanent virtual circuit - guarantied - guarantied

access and rate between several service access and rate between several service

access points (SAP) of the subscriberaccess points (SAP) of the subscriber

Switched virtual circuitSwitched virtual circuit - non- - non-

guaranteed access and rate, they are guaranteed access and rate, they are

granted after the request and last only granted after the request and last only

during the service periodduring the service period

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B-ISDN Virtual CircuitB-ISDN Virtual Circuit Switching the virtual circuit does not mean Switching the virtual circuit does not mean

commutation like by classical circuit commutation like by classical circuit switching but in fact switching but in fact routingrouting, i.e., i.e.

virtual circuit switches are routersvirtual circuit switches are routers

virtual path (VP) is a collection of records in virtual path (VP) is a collection of records in

the router tablesthe router tables

like IP routing, the control information like IP routing, the control information

resides in the packet’s header but resides in the packet’s header but

unlike IP routing, the header contains virtual unlike IP routing, the header contains virtual

circuit ID instead of “source/destination” circuit ID instead of “source/destination”

recordrecord

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B-ISDN Virtual CircuitB-ISDN Virtual Circuit Permanent VCPermanent VC have (for agreed period): have (for agreed period):

reserved records in the routing tables reserved records in the routing tables

describing the route of the circuitdescribing the route of the circuit

allocated allocated weightedweighted communication capacity communication capacity

(bandwidth and inside-switch buffers/lines) - (bandwidth and inside-switch buffers/lines) -

not as monopoly wasteful allocation of the not as monopoly wasteful allocation of the

leased lines by the circuit switching leased lines by the circuit switching Switched VCSwitched VC have have and and dynamically for the dynamically for the

period of communication i.e. there exists period of communication i.e. there exists setup setup

delaydelay (for specifying records in routing tables and (for specifying records in routing tables and

possibly for waiting free resources or allocating possibly for waiting free resources or allocating

buffers) in the beginning of each communication buffers) in the beginning of each communication

process.process.

Period charge

Trafficcharge

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ATM TransmissionATM Transmission Asynchronous transmission:Asynchronous transmission:

no ordering among the cellsno ordering among the cells no specified period between consecutive cells of a no specified period between consecutive cells of a

transmissiontransmission possibility for blank space between data cells - filling of possibility for blank space between data cells - filling of

service cellsservice cells Transmission media is [chiefly] fiber optic; therefore:Transmission media is [chiefly] fiber optic; therefore:

– point-to-point network topology of 2 parallel unidirectional point-to-point network topology of 2 parallel unidirectional links between any two points in full-duplex transmissionlinks between any two points in full-duplex transmission

– each network point is either user-device or network switcheach network point is either user-device or network switch– multicasting is done by propagation of cells in the multicasting is done by propagation of cells in the

switches: 1 cell to multiple outputsswitches: 1 cell to multiple outputs– standardized basic rate 155,52 Mb/S and extended rate standardized basic rate 155,52 Mb/S and extended rate

622.08 Mb/S (4 times)622.08 Mb/S (4 times) In layered model the ATM physical layer consists ofIn layered model the ATM physical layer consists of

– Physical Media Dependent (PMD) sublayer specifies bit-Physical Media Dependent (PMD) sublayer specifies bit-stream parameters for different media - fiber, twisted pairstream parameters for different media - fiber, twisted pair

– Transmission Convergence (TC) sublayer transfers the PMD Transmission Convergence (TC) sublayer transfers the PMD bit-stream into ATM cells and present them to the ATM bit-stream into ATM cells and present them to the ATM layerlayer

In contrast to the

synchro-nous PCM carrier T1

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ATM switchingATM switching Conceptually, Conceptually, switchingswitching is “the establishing, on is “the establishing, on

demand, of an individual connection from a desired inlet demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information” as long as is required for the transfer of information” (ITU-T).(ITU-T).

In the case of ATM, this means that in an ATM network In the case of ATM, this means that in an ATM network switching node (switch) ATM cells are transported from switching node (switch) ATM cells are transported from an incoming logical channel (VP/VC) to one or more (by an incoming logical channel (VP/VC) to one or more (by multicasting) outgoing logical channels.multicasting) outgoing logical channels.

The establishment of logical channels is controlled by The establishment of logical channels is controlled by network management operations (specify VP network management operations (specify VP interconnection) or directly by user or network signaling interconnection) or directly by user or network signaling (specify VC interconnection).(specify VC interconnection).

A A logical channellogical channel is identified by is identified by– the number of the physical link andthe number of the physical link and– the identity of the channel (VPI/VCI) on the physical linkthe identity of the channel (VPI/VCI) on the physical link

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ATM SwitchATM Switch

Synchronously working in 3 cycles: fetching cells in some/all of the input lines, reorder the cells in cross-connecting switch and transmit the cells on appropriate output lines

For 150Mb/S VC and 53b/cell Ti+1-Ti2.7S i.e. 360000 cells/S.

For 622Mb/S VC and 53b/cell Ti+1-Ti0.7S i.e. 1380000 cells/S.

M, N may vary between 16 and 1K

Inputstage 1

Inputstage 2

Inputstage N

Outputstage 1

Outputstage 2

Outputstage M

Crossconnectingswitch

N Incominglinks carrying cells

M Outgoinglinks carrying cels

cell cell x,x,

TTii

cell cell x,x,TTii+1+1

(! For bi-directional lines M = N)

Because of the equal length of the cells (unlike the variable length of the packets)

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ATM SwitchingATM Switching Rules:Rules:

Reduce cell loss rate (normally Reduce cell loss rate (normally 1010-12-12, but not 0), but not 0)FIFO discipline of cell service for each VC (virtual FIFO discipline of cell service for each VC (virtual

circuit)circuit)Input queuing: 2 and more cells competing for Input queuing: 2 and more cells competing for

the same output are stored in line in their input the same output are stored in line in their input stages; only one of them is transmitted to the stages; only one of them is transmitted to the output (in random/Round-robin or other selection) output (in random/Round-robin or other selection) Head-of-line-blockingHead-of-line-blocking effect: the newly effect: the newly arrived cells in the next cycle[s] wait because of arrived cells in the next cycle[s] wait because of rule rule - although their output is free - although their output is free

[Alternative to [Alternative to ] Output queuing: conflicting ] Output queuing: conflicting cells are stored in the output stage. No possibility cells are stored in the output stage. No possibility for blocking; less delay for queued cell[s]; simpler for blocking; less delay for queued cell[s]; simpler circuit implementationcircuit implementation

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ATM Switches - ATM Switches - Knockout Knockout

Applies crossbar switching and output Applies crossbar switching and output

buffering:buffering:– allows multiple input cells to reach the same allows multiple input cells to reach the same

output stage output stage output buffering is needed output buffering is needed

– allows multi-/broad-casting: an input cell can allows multi-/broad-casting: an input cell can

reach multiple or all of output stagesreach multiple or all of output stages

The number of output buffers per stage is The number of output buffers per stage is n n < <

NN (the incoming lines number); if the number (the incoming lines number); if the number

of collisions for output of collisions for output ii ccii > > nn then ( then (ccii--nn) cells ) cells

are discarded (“knocked out”) by special are discarded (“knocked out”) by special

device - “concentrator”device - “concentrator”

(cost-performance optimization of (cost-performance optimization of nn))

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ATM Switches - BanyanATM Switches - BanyanAn East Indian fig tree (Ficus benghalensis) of the mulberry family which root form secondary trunks (NOT a banana tree!)

Applies multistage synchronous switchingApplies multistage synchronous switchingin order to reduce switching elements numberin order to reduce switching elements number(for crossbars – (for crossbars – N N 22).).

For For 2:22:2 switching elements (typical) switching elements (typical)– the number of stages the number of stages ss = lb = lbNN and and – the number of elements per stage the number of elements per stage ee = = NN/2/2 – the number of switching elements the number of switching elements SS = = sese = 2 = 2-1-1N N lblbNN

(<< (<< N N 22)) Interstage communication pattern is such that:Interstage communication pattern is such that:

– there exists only one path from there exists only one path from iimm to to ookk

– at each stage the switching elements examine the at each stage the switching elements examine the consecutive bits of the destination address (1consecutive bits of the destination address (1st st stage-stage-rightmost bit etc.) rightmost bit etc.) possible collisions on the outputs possible collisions on the outputs of the switching elementsof the switching elements

– Collisions are input-order-dependent; reordering the Collisions are input-order-dependent; reordering the cells regarding to the output pattern solvecells regarding to the output pattern solve the collisionthe collision

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ATM Switches - ATM Switches - Batcher-banyanBatcher-banyan

Collision free extension of Collision free extension of Banyan switchesBanyan switches for the for the

price of additional stages (i.e. hardware and delay) - a price of additional stages (i.e. hardware and delay) - a

preceding switch reorders the cells of the input flow in preceding switch reorders the cells of the input flow in

a sorted order by the output indexes.a sorted order by the output indexes.

Applies multistage Applies multistage synchronous switchingsynchronous switching ; each ; each

switching element compares the whole destination switching element compares the whole destination

field of the two input cells and switches them field of the two input cells and switches them

according to the stage pattern (arrow marks), that according to the stage pattern (arrow marks), that

resembles the bubble sortresembles the bubble sort

kk input cells on input cells on NN inputs are put in the first inputs are put in the first kk outputs in outputs in

sorted ordersorted order

The interface between the Batcher and the Banyan The interface between the Batcher and the Banyan

switches is shuffle netswitches is shuffle net

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