B-ISDN Network Concept - BZU PAGES

greydullNetworking and Communications

Oct 30, 2013 (3 years and 7 months ago)

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atm
-
signaling

1

ATM Signaling


ATM signaling is mainly used for setup/release of virtual
connections.


A phased approach was taken for the introduction of ATM
networks supporting switched services.


This concept comprises three steps which are called
capability sets (CS1, CS2, CS3).


In CS1, simple switched services with constant bit rates are provided
and basic interworking with existing 64 Kb/s ISDN is foreseen.


More sophisticated services with variable bit rates, point
-
to
-
multipoint
connections and multi
-
connections will be supported by CS2.


With CS2, call and connection control will be separated.


Finally, CS3 provides full range of services, including multimedia and
distributive services.


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-
signaling

2

Capability Sets for B
-
ISDN Signaling

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-
signaling

3

ATM Forum UNI Signaling


ATM Forum UNI signaling specifications are based on the
specifications of ITU
-
T.


ATM Forum UNI 3.0


ATM Forum UNI 3.1


ATM Forum UNI 4.0


UNI 4.0 provides features such as

-

anycast
: A user of a specific service need not know which entity in the
network actually performs the service, and instead can use a published
group address assigned to this service. The network can automatically
distribute service requests to the service
-
providing group members.

-

leaf
-
initiated join
: join an already established VCC.

-

proxy
-
signaling
: a user performs signaling for one or more other users.

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-
signaling

4

Protocol Architecture for CS1


Two signaling access configurations at the UNI:


-

Point
-
to
-
point:


Only one signaling endpoint on the user side.


A single permanently established point
-
to
-
point SVC is required.

-

Point
-
to
-
Multipoint:


Several signaling endpoints are located at the user side.


Meta
-
signaling is necessary to manage other signaling relations.

S
-
AAL

Q.2931

ATM

PHY

S
-
AAL

Q.2931

ATM

PHY

MS

Point
-
to
-
point

signaling access

Point
-
to
-
multipoint

signaling access

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-
signaling

5

Protocol Architecture for CS1


At the NNI, either the existing STM
-
based common
channel signaling system no. 7 (SS7) or an ATM based
network can be used to transport the signaling messages.

MTP
-
3

B
-
ISUP

MTP
-
2

MTP
-
1

S
-
AAL

MTP
-
3

ATM

PHY

STM based

signaling network

ATM
-
based

signaling network

B
-
ISUP

atm
-
signaling

6

ATM Adaptation Layer for Signaling


A suitable signaling AAL (S
-
AAL) is required in order to
adapt the signaling application protocols to the services
provided by the underlying ATM layer.








ITU
-
T uses AAL5 for Common part.


SAR

SSCF

SSCOP

CP convergence sublayer

Common Part

Service
-
Specific Part

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-
signaling

7

S
-
AAL Service Specific Part


The service
-
specific connection
-
oriented protocol (SSCOP)
provides mechanisms for the establishment and release of
connections and the reliable exchange of signaling
information between signaling entities.


The service
-
specific coordination functions (SSCFs) map
the requirements of the layer above to the requirements of
the next lower layer.


ITU
-
T uses a common SSCOP for UNI and NNI.


SSCOP could have been designed by using an existing data
link layer protocol, with some modifications.


ITU
-
T decided to specify a new protocol for SSCOP.








ITU
-
T uses AAL5 for Common part.


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-
signaling

8

SSCOP Functions


Sequence Integrity:
preserve SDU order


Error correction by retransmission:
error detected by sequencing
mechanism; corrected by selective retransmission.


Flow control:
receiver controlled; by dynamic window mechanism.


Error reporting to layer management:


Keep alive:


Local data retrieval:
SDUs can be retrieved which have not yet been
delivered


Link management:
establish/release SSCOP connections


Transfer of Data:
assured or unassured


PCI error detection:
errors within PCI are detected


Status reporting







ITU
-
T uses AAL5 for Common part.


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-
signaling

9

atm
-
signaling

10

Signaling Protocols for CS1


Reuse of existing protocols with some modifications.




Q.2931 is the layer 3 signaling protocol for B
-
ISDN.


-

UNI: Q.931, layer 3 protocol for 64 Kb/s ISDN

-

NNI: ISDN User Part (ISUP)


-

Q.2931 includes the specification of the signaling messages,
information elements and communication procedures between
signaling endpoints for the B
-
ISDN UNI.

-

Main modifications from Q.931:

-

a new information element (IE) for users to select between
different AAL classes and the associated protocols.

-

a new connection identifier IE consisting of VPCI and VCI. (The
Virtual Path Connection Identifier identifies a VPC while a VPI
identifies a VP link. VPCI is necessary because a VP cross
-
connect
may exist between the local exchange and the TE.)

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-
signaling

11

Signaling Messages


Call establishment messages




Call clear messages



Status Messages



Global Call Reference Related Messages


Point
-
to
-
Multipoint Connection Control


-

Add Party

-

Add Party Acknowledge

-

Add Party Reject

-

Drop Party

-

Drop Party Acknowledge

-

Status Enquiry

-

Status (Response)

-

Release

-

Release Complete

-

Call Proceeding

-

Connect

-

Connect Acknowledge

-

Setup

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-
signaling

12

UNI Point
-
to
-
Point Signaling Example

Source

Destination

SETUP

SETUP

CONNECT

CONNECT

CONNECT ACK

CONNECT ACK

CALL PROCEEDING

CALL PROCEEDING

Network

UNI

UNI

RELEASE

RELEASE

RELEASE COMPLETE

RELEASE COMPLETE

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-
signaling

13

Point
-
to
-
Multipoint Call Setup Example

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-
signaling

14

Signaling Message



Each message contains several common mandatory
information elements:


protocol discriminator (1)


call reference (4)


variable length info

elements, as required (1)

message length (2)

message type (2)

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-
signaling

15

SETUP message format

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-
signaling

16

ATM Addressing


ATM uses two basic types of addresses: E.164 and AESA
(ATM end system addresses).


Telecom uses the global ISDN numbering plan specified in
ITU
-
T E.164.


AESAs are based on ISO NSAP (network service access
point).


Computer networks mostly employ the OSI NSAP
addressing mechanism.


E.164 addresses comprise 15 digits (8 bytes): country code
+ area or city code + subscriber number.


ATM Forum chose 20
-
octet NSAP address format and
encoding for addressing of ATM systems connected to a
private network; systems connected to an public network
can use either NSAP or E.164 addresses.

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-
signaling

17

ATM Addressing


Current version of the NSAP addressing planes


Three addressing formats


DCC (Data Country Code): the country with an address is
registered


ICD (International Code Designator): an international organization


E.164: ISDN & telephone numbers


Each address is composed of IDP (Initial Domain Part) & DSP
(Domain Specific Part).


AFI (Authority and Format Identifier): Which of the formats


IDI (Initial Domain Identifier): specifies the Authority that allocates the
DSP that follows.

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-
signaling

18


1 3 13


19

20

AFI ICD HO
-
DSP ESI SEL

IDI


IDP DSP


1 3 13


19

20

AFI DCC HO
-
DSP ESI SEL

IDI


IDP DSP

(a) DCC ATM format

(b) ICD ATM format


1 9 13


19

20

AFI E.164 HO
-
DSP ESI SEL

IDI


IDP DSP

(c) E.164 ATM format

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-
signaling

19



The number is coded in Binary Coded Decimal (BCD)



PAD: with zeroes on the left side




15 digits constant length

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-
signaling

20

PNNI


The private network
-
network interface (PNNI) is a
trunking, routing and signaling protocol specified by the
ATM Forum. It is an inter
-
switch protocol which supports
SVC between switches of multiple vendors.

PNNI

Network A

Network B

PNNI

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-
signaling

21

PNNI Signaling Example

Source
Switch

Transit
Switch

Destination
Switch

Source A

Destination B

SETUP

SETUP

SETUP

SETUP

CONNECT

CONNECT

CONNECT

CONNECT

CONNECT ACK

CONNECT ACK

CONNECT ACK

CONNECT ACK

CALL PROCEEDING

CALL PROCEEDING

CALL PROCEEDING

CALL PROCEEDING

RELEASE

RELEASE

RELEASE

RELEASE

RELEASE COMPLETE

RELEASE COMPLETE

RELEASE COMPLETE

RELEASE COMPLETE

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-
signaling

22

Example of PNNI Hierarchy

A

B

PG(A)

PG(B)

A.1

A.2

PG(A.1)

PG(A.2)

A.1.1

A.1.2

A.1.3

A.2.1

A.2.2

A.2.3

A.2.4

B.1

B.2

B.3

B.4

Peer Group Leader

Logical Link

Physical Link

Logical Group Node

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-
signaling

23

Topology seen by Switch A.1.1

B

A.2

A.1.1

A.1.2

A.1.3

DTL: Designated Transit List

DTL: [A.1.1,
A.1.2
]

DTL: [
A.1
, A.2]

DTL: [
A
, B]

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-
signaling

24

Switch A.1.2

B

A.2

A.1.1

A.1.2

A.1.3

When A.1.2 receives the call setup message, it finds that it

is at the end of top DTL, so it removes the top DTL and sends

The message to A.2 (via A.2.1).

DTL: [A.1.1,
A.1.2
]



DTL: [A.1,
A.2
]

DTL: [
A
, B]

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-
signaling

25

Switch A.2.1

B

A.1

A.2.1

A.2.2

A.2.4

When A.2.1 receives the call setup message, it finds that A.2
has been reached. So it builds a route to B (say via A.2.3 and
A.2.4) and pushes a new DTL onto the stack.

DTL: [A.2.1,
A.2.3
, A.2.4]

DTL: [A.1,
A.2
]

DTL: [
A
, B]

A.2.3

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-
signaling

26

Switch A.2.4

B

A.1

A.2.1

A.2.2

A.2.4

When A.2.4 receives the call setup message, it finds that the
targets at the top two DTLs have been reached. So it removes
the top two DTLs and forwards the message with the
following DTL to its neighbor:

DTL: [A.2.1, A.2.3,
A.2.4
]

DTL: [A.1,
A.2
]

DTL: [A,
B
]

A.2.3

atm
-
signaling

27

Switch B.1

A

B.2

B.1

B.3

When B.1 receives the call setup message, it finds that the
current DTL has been reached.

B.1 builds a new DTL, resulting in

DTL: [B.1,
B.3
]

DTL: [A,
B
]

B.4

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-
signaling

28

Switch B.3

A

B.2

B.1

B.3

When B.3 receives the call setup message, it finds that it is the
DTL terminator since all DTLs are at the end.

DTL: [B.1,
B.3
]

DTL: [A,
B
]

B.4