bicc

1 BICC
 Key points:
 Basic concept of BICC.
 Protocol model of BICC.
 Signaling process of BICC
1.1 Overview
1.1.1 Background of BICC
In the past few years, the demand for the integration of the data network and the voice network has become more obvious. The telecom network accesses the WWW through dialup. The IP network is also used to provide low-quality and low-cost voice services. The circuit contention results in the transferring of both voice stream and data stream over the ATM network. The WEB access can be used for managing voice services, though the voice services need be initiated through dialup. The ETSI and the TIPHON define gateways for the H.323 to provide VOIP service for the PSTN/ISDN. In 1999, the ITU-T presented the BICC protocol.
The drive for the development of the BICC is that the voice service has grown rapidly in the past few years due to the wide use of the WWW dialup access. This brings a problem to the network operator. On one hand, it is hard to broaden the application of the PSTN/ISDN, so such growth requires a big investment. On the other hand, the network operator is unwilling to invest much in the old network due to the fact that the packet-based network will bring in the major revenue in the next few years.
In 1998, the major telecom operators in America raised this problem. One of the presented solutions was to separate the call control and the bearer control of the PSTN/ISDN, modify the ISUP protocol, and compile a new call control protocol. The modification brings about the BICC protocol. The BICC protocol provides a full range of PSTN/ISDN services. Various packet-based networks can serve as the bearer network, for example, ATM switching network and IP network. The bearer control protocol is used to set up the bearer necessary to the PSTN/ISDN services, for example, UNI4.0, DSS2 and BISUP used in the ATM switching network.
The BICC protocol enables various packet-based networks to offer a full range of PSTN/ISDN services, including all the supplementary services. The PSTN/ISDN services require the operation-level quality. Because of the system architecture of the BICC, the BICC network has a high scalability.
With the historic development of the BICC, the operators can move their PSTN/ISDN networks to the high-capacity packet-based networks. BICC becomes the first step in the development of the multi-service platform and enables the IP to provide voice and data services.
1.1.2 Definition of BICC
BICC stands for bearer independent call control protocol. As the name implies, the BICC has one fundamental feature, namely, the separation between the call control plane and the bearer control plane, making the call service function (CSF) and the bearer control function (CSF) independent of each other.
In one word, the BICC protocol provides the signaling functions required to support narrowband ISDN services independent of the bearer technology and signaling transport technology used, and it is an evolution of the ISUP. The following first compares the BICC with the ISUP.
1.1.3 Capabilities of BICC
Table 5.1 -1 lists the signaling capabilities of the BICC for supporting basic call. Table 5.1 -2 lists the general signaling procedures, supplementary services, and some additional functions/services supported by the BICC.
Table 5.1‑1 Basic Call Capabilities of BICC
Function/Service
Speech/3.1 kHz audio
64 kbit/s unrestricted
Multirate connection types
N  64 kbit/s connection types
En block address signaling
Overlap address signaling
Transit network selection
Continuity indication
Simple segmentation
Tones and announcements
Access delivery information
Transportation of user teleservice information
Suspend and resume
Signaling procedures for connection type allowing fallback capability
Propagation delay determination procedure
Simplified echo control signaling procedure
Automatic repeat attempt
Blocking and unblocking
CIC group query
Dual seizure
Reset
Receipt of unreasonable signaling information
Compability procedure (BICC and BAT APM user application)
ISDN user part signaling congestion control
Automatic congestion control
Interaction with INAP
Unequipped CIC
ISDN user part availability control
MTP pause and resume
Overlength messages
Temporary Alternative Routing (TAR)
Hop counter procedure
Collect call request procedure
Hard-to-Reach
Calling geodetic location procedure
Carrier selection information
Inter-nodal traffic group identification
Codec negotiation and modification procedures
Joint BIWF support
Global Call Reference procedure
Out of band transport of DTMF tones and information
Table 5.1‑2 Generic Signaling Procedures, Services and Functions
Function/Service
Generic signaling procedures
Generic number transfer
Generic digit transfer
Generic notification procedure
Service activation
Remote Operations Service Element (ROSE) capability
Network specific facilities
Pre-release Information transport
Application Transport Mechanism (APM)
Redirection
Pivot routing
Bearer redirection
Supplementary services
Direct-Dialling-In (DDI)
Multiple Subscriber Number (MSN)
Calling Line Identification Presentation (CLIP)
Calling Line Identification Restriction (CLIR)
Connected Line Identification Presentation (COLP)
Connected Line Identification Restriction (COLR)
Malicious Call Identification (MCID)
Sub-addressing (SUB)
Call Forwarding Busy (CFB)
Call Forwarding No Reply (CFNR)
Call Forwarding Unconditional (CFU)
Call Deflection (CD)
Explicit Call Transfer (ECT)
Call Waiting (CW)
Call Hold (HOLD)
Completion of Calls to Busy Subscriber (CCBS)
Completion of Calls on No Reply (CCNR)
Terminal Portability (TP)
Conference calling (CONF)
Three-Party Service (3PTY)
Closed User Group (CUG)
Multi-Level Precedence and Preemption (MLPP)
Global Virtual Network Service (GVNS)
International Telecommunication Charge Card (ITCC)
Reverse charging (REV)
User-to-User Signaling (UUS)
Additional functions/services
Support of VPN applications with PSS1 Information Flows
Support of GAT protocol
Support of Number Portability (NP)
1.1.4 Capability Set of BICC
The ITU-T has released these BICC versions: CS1, CS2, and CS3.
1.1.4.1 BICC CS1
The application background of the BICC CS1 is the concept of "ATM relay" presented by the ATM Forum. The PSTN/ISDN toll network is replaced with ATM broadband network. In this case, the ATM network involves bearer signaling and call control signaling. The bearer signaling can be the B-ISUP presented by the ITU-T or the signaling standard presented by the ATM Forum; the call control signaling can be the BICC signaling defined in Q.1901. The BICC signaling has two functions. On one hand, it relays the narrowband ISUP signaling messages for use by the subsequent ISDN network. On the other hand, it transfers information related to the association between the call and bearer of the ATM relay network; the association information is contained in the subsequent bearer signaling, and the outgoing and incoming gateway exchanges associate the established bearer connection with the corresponding call.
In BICC CS1, the CSF and BCF of the ISN are integrated in a physical device. Therefore, Q.1901 only defines the call control signaling.
CS1 has the following features:
 Forward and backward setup of backbone network;
 Call control transfer based on the SS7 MTP and the ATM;
 Supporting most of the current narrowband services;
 Supporting the backbone network connection with or without codec;
 Reusing the idle backbone network connections;
 Separating calls and releasing backbone network connection;
 Supporting these bearer types: AAL1 and AAL2.
1.1.4.2 BICC CS2
The application background of the BICC CS2 is the IP relay network used by the IP telephone service. Affected by the idea of physically separating the functions of the network nodes, the CS2 physically separates the CSF and BCF in the serving nodes; the interface between the CSF and the BCF is called vertical interface, and the call control signaling interface is generally called parallel interface.
CS2 has the following features:
 Extending the use of the BICC to the local exchange;
 Supporting IP bearer;
 Defining the call bearer control interface;
 Defining new identifiers, including traffic group and global call reference;
 Supporting the call mediation node;
 Supporting the IP signaling transfer;
 Supporting the structured AAL1.
1.1.4.3 BICC CS3
BICC CS3 adds the following functions based on CS2 Q.1902.4:
 Supporting end-to-end QoS;
 Processing the information elements for national use at the international gateway exchange SN or the CMN; if the network operators have not reached bilateral or multilateral agreements, all the messages, parameters, and parameter values labeled "for national use" will be invalid in the international network;
 Modifying the codec negotiation;
 Adding the auto rerouting signaling procedure;
 Supporting the international routing addresses.
1.2 Basic Concepts Related to BICC
To enable you to better understand the features of the BICC protocol, the following first describes the major terms and concepts related to the BICC.
1. Backbone Network Connection (BNC): Represents the edge to edge transport connection within the backbone network, consisting of one or more Backbone Network Connection Links (BNCL). The Backbone Network Connection represents a segment of the end to end Network Bearer Connection (NBC).
2. Backbone Network Connection Link (BNCL): Represents the transport facility between two adjacent backbone network entities containing a bearer control function.
3. Bearer Control Function (BCF): Five types of BCFs are illustrated in the functional model: BCF-G, BCF-J, BCF-N, BCF-R and BCF-T.
 The Bearer Control Joint Function (BCF-J) provides the control of the bearer switching function, the communication capability with two associated call service functions (CSF), and the signaling capability necessary to establish and release the backbone network connection.
 The Bearer Control Gateway Function (BCF-G) provides the control of the bearer switching function, the communication capability with its associated call service function (CSF-G), and the signaling capability necessary to establish and release of the backbone network connection.
 The Bearer Control Nodal Function (BCF-N) provides the control of the bearer switching function, the communication capability with its associated call service function (CSF), and the signaling capability necessary to establish and release of the backbone network connection to its peer (BCF-N).
 The Bearer Control Relay Function (BCF-R) provides the control of the bearer switching function and relays the bearer control signaling requests to next BCF in order to complete the edge to edge backbone network connection
 The Bearer Control Transit Function (BCF-T) provides the control of the bearer switching function, the communication capability with its associated call service function (CSF-T), and the signaling capability necessary to establish and release of the backbone network connection.
4. Bearer Control Segment (BCS): Represents the signaling relationship between two adjacent Bearer Control Functional entities (BCF)
5. Bearer InterWorking Function (BIWF): A functional entity which provides bearer control functions (BCF) and media mapping/switching functions within the scope of a Serving Node (BCF-N, BCF-T or BCF-G) and one or more MCF and MMSF, and is functionally equivalent to a Media Gateway that incorporates bearer control.
6. Bearer InterWorking Node (BIWN): A physical unit incorporating functionality similar to a BIWF.
7. Call Control Association (CCA): Defines the peer to peer signaling association between Call, and Call & Bearer state machines located in different physical entities.
8. Media Control Function (MCF): A functional entity that interacts with the BCF to provide the control of the bearer and MMSF. The precise functionality is outside the scope of BICC.
9. Media Mapping/Switching Function (MMSF): An entity providing the function of controlled interconnection of two bearers and optionally the conversion of the bearer from one technology and adaptation/encoding technique to another.
10. Call Mediation Node (CMN): A functional entity that provides CSF-C functions without an associated BCF entity.
11. Call Service Function (CSF): Four types of CSF are defined:
 The Call Service Nodal Function (CSF-N) provides the service control nodal actions associated with the narrowband service by interworking with narrowband and Bearer Independent Call Control (BICC) signaling, signaling to its peer (CSF-N), and invoking the Bearer Control Nodal Functions (BCF-N) necessary to transport the narrowband bearer service across the backbone network.
 The Call Service Transit Function (CSF-T) provides the service transit actions necessary to establish and maintain a backbone network call, and its associated bearer by relaying signaling between CSF-N peers and invoking the Bearer Control Transit Functions (BCF-T) necessary to transport the narrowband bearer service across the backbone network.
 The Call Service Gateway Function (CSF-G) provides the service gateway actions necessary to establish and maintain a backbone network call and its associated bearer by relaying signaling between CSF-N peers and invoking the Bearer Control Gateway Functions (BCF-G) necessary to transport the narrowband bearer service between backbone networks.
 The Call Service Co-ordination Function (CSF-C) provides the call co-ordination and mediation actions necessary to establish and maintain a backbone network call by relaying signaling between CSF-N peers. The CSF-C has no association with any BCF. It is only a call control function.
12. Gateway Serving Node (GSN): A functional entity which provides gateway functionality between two network domains. This functional entity contains one or more call service gateway functions (CSF-G), and one or more bearer interworking functions (BIWF).
13. Interface Serving Node (ISN): A functional entity which provides the interface with non-BICC networks and terminal equipment. This functional entity contains one or more call service nodal functions (CSF-N), and one or more bearer inter-working functions (BIWF) which interact with the non-BICC networks and terminal equipment and its peers within the broadband backbone network.
14. Signaling Transport Layers (STL): Any suite of protocol layers currently specified to provide Transport and/or Network Layer services to the BICC.
15. Signaling Transport Converter (STC): A protocol layer between the STL and BICC. This layer enables the BICC protocol to be independent of the STL being used.
16. Transit Serving Node (TSN): A functional entity which provides transit functionality between ISNs and GSNs. This functional entity contains one or more call service transit functions (CSF-T), and one or more bearer interworking functions (BIWF). TSNs interact with other TSNs, GSNs and ISNs within their own backbone network domain.
17. Serving Node (SN): A generic term referring to ISN, GSN or TSN nodes.
1.3 Protocol Model of BICC
1.3.1 Protocol Stack of BICC
Fig. 5.3 -1 shows the MTP3B protocol stack mode of the BICC.

Fig. 5.3‑1 Protocol Stack of STC on MTP
Fig. 5.3 -2 shows the IP protocol stack mode of the BICC.

Fig. 5.3‑2 Protocol Stack of STC on SCTP
1.3.2 Network Function Model
Fig. 5.3 -3 shows the complete functional model of the BICC. The CSFs transfer call control signaling in between; the BCFs transfer bearer control signaling in between. As shown in the figure, the call control and the bearer control are separated in the BICC.

Fig. 5.3‑3 Network Function Model
1.3.3 Protocol Model

Fig. 5.3‑4 Protocol Model
The interaction between the CSF and the BCF is implemented through the mapping function. The mapping function implements mapping between the BICC bearer control primitives and the interfaces provided by different bearer control protocols.
The signaling receiving/sending (BICC) of the CSF is implemented through the signaling transport converter (STC). The STC shields the interface difference of the lower-layer transmission protocol and provides a unified interface for the upper-layer BICC protocol.
The BICC protocol model encapsulates the BICC message in the message of the signaling transport layer (STL) by using the signaling interface point. In this way, the messages are exchanged between the BICC entities. The STC implements conversion between the signaling transport primitives of the BICC and the primitives of the STL (for example, between the BICC and the MTP3/MTP3B/SCTP). In the STL, MTP3 is used in the TDM signaling bearer network; SCTP over IP is used in the IP bearer network; the MTP3B is used in the ATM network. The BICC controls and queries the bearer by using the bearer interface point.
The BICC protocol model shows this solution: To make the BICC completely independent of any other part of the interface (transport signaling or bearer), the BICC standardizes the two interface points. From the perspective of the BICC process, it provides an unique set of external abstracted operation primitives, and then converts the primitives of the specific part (transport signaling or bearer) through the "converting/mapping" component.
1.3.4 Separation Between Bearer and Control
As stated earlier, the fundamental feature of the BICC is the separation between the call control plane and the bearer control plane. In this case, the BICC specification is only responsible for the processing of the CSF and does not involve specific bearer control (including the type of the bearer medium used).
The figures below show the separation between the call control and the bearer control in the BICC. The CSF part represents the main scope of the BICC specification.
In Fig. 5.3 -5, the SN has the BCF function.
In Fig. 5.3 -6, the CMN does not have the BCF function. In an SN, the CSF and BCF can be physically separated. When the two entities are physically separated, the call&bearer control (CBC) signaling is used between them. Both SNs and CMNs are modelled using the “Half Call” modelling technique. Every call processing scenario is thus divided between an incoming and an outgoing signaling procedure.

Fig. 5.3‑5 SN Model

Fig. 5.3‑6 CMN Model
1.3.5 Bearer Control Tunnelling Mechanism
When the media stream is borne over IP, the bearer control protocol is IPBCP. The BCFs cannot directly transfer IPBCP-related messages in between. The BICC transfers the bearer control signaling (currently IPBCP messages) through the BCF and CSF and the channel between the two CSFs by using the tunneling packets of the H.248 and the application transport mechanism (APM) of the BICC. In this way, the channel between the media streams is set up for transferring voice signal in the packet-based network. This mode is called tunneling.
Fig. 5.3 -7 shows the implementation of the tunneling mechanism.

Fig. 5.3‑7 Tunnelling Mechanism
1.4 BICC Messages
The BICC messages are exchanged between two peer protocol entities by using the BICC signaling transport service of the signaling transport conversion function. Each BICC PDU consist of multiple octets, including the following parts (see Fig. 5.4 -8):
1. CIC;
2. Message type code;
3. Mandatory fixed part;
4. Mandatory variable part;
5. Optional part. It may include the fields of fixed length and variable length.
CIC
Message type code
Mandatory fixed part
Mandatory variable part
Optional part
Fig. 5.4‑8 BICC Message (BICC PDU)
In the BICC protocol, the call instance code (CIC) is used to identify the signaling relationship between two peer BICC entities and all the PDUs belonging to the signaling relationship. Fig. 5.4 -9 shows the format of the CIC field in the BICC protocol. 8
7
6
5
4
3
2
1
1 CIC Least significant bit
2
CIC
3
CIC
4
Most significant bit CIC
Fig. 5.4‑9 CIC Field in BICC
The message type code contains an octet. It is mandatory to each message. It uniquely defines the function and format of each BICC PDU.
Table 5.4‑3 Message Types and Codes
Message Type
Code
Address complete
0000 0110
Answer
0000 1001
Application transport
0100 0001
Call progress
0010 1100
CIC group blocking
0001 1000
CIC group blocking acknowledgement
0001 1010
CIC group query
0010 1010
CIC group query response
0010 1011
CIC group reset
0001 0111
CIC group reset acknowledgement
0010 1001
CIC group unblocking
0010 1001
CIC group unblocking acknowledgement
0001 1011
Charging information (for national use)
0011 0001
Confusion
0010 1111
Connect
0000 0111
Continuity
0000 0101
Facility
0011 0011
Facility accepted
0010 0000
Facility rejected
0010 0001
Facility request
0001 1111
Forward transfer
0000 1000
Identification request
0011 0110
Identification response
0011 0111
Information
0000 0100
Information request
0000 0011
Initial address
0000 0001
Loop prevention
0100 0000
Network resource management
0011 0010
Pre-release information
0100 0010
Release
0000 1100
Release complete
0001 0000
CIC reset
0001 0010
Resume
0000 1110
Segmentation
0011 1000
Subsequent address
0000 0010
Subsequent directory number
0100 0011
Suspend
0000 1101
Unequipped CIC
0010 1110
User-to-user information
0010 1101
Reserved
0000 1010
0000 1011
0000 1111
0010 0010
0010 0011
0010 0101
0010 0110
Reserved
0001 1101
0001 1100
0001 1110
0010 0111
Reserved
0011 1001 to 0011 1101
Reserved for future expansion
1000 0000
Note: The message format is defined in China.
For a specified message type, the mandatory parameters of fixed length are included in the mandatory fixed part. The position, length, and sequence of each parameter are specified by the message type. Therefore, the message does not include the name or length indicator of the parameter.
The mandatory parameters of variable length will be included in the mandatory available part. A pointer is used to indicate the start of a parameter. The message does not include the parameter name.
The parameters in the optional part may appear any specified message type. These parameters can be of fixed or variable length. Each optional parameter shall contain parameter name (1 octet), length indicator (1 octet), and parameter content.
If optional parameters are included, after all the optional parameters are sent, the octet of "end of optional parameters" is sent, and the octet is all "0"s.
Fig. 5.4 -10 shows the basic format of the BICC PDU.

Fig. 5.4‑10 Format of the BICC PDU
1.5 BICC Message Flow
1.5.1 BICC Bearer Setup Mode
The tunneling mechanism is used in three cases:
 Fast setup: The bearer control message is carried in the IAM and the subsequent APM. Both the forward setup and backward setup are supported.
 Delayed forward setup: The bearer control message is carried in the APM following the first backward APM message.
 Delayed backward setup: The bearer control message is carried in the first backward APM and the subsequent APM.
The tunneling mechanism is not used in two cases:
 Forward call bearer setup: The bearer control is implemented by using the separate bearer control protocol and is initiated in the forward direction (in relation to the call setup direction).
 Backward call bearer setup: The bearer control is implemented by using the separate bearer control protocol and is initiated in the backward direction (in relation to the call setup direction).
1.5.2 Call Setup Flow
1.5.2.1 Fast Setup (Forward)

Fig. 5.5‑11 Fast Setup (Forward))
1.5.2.2 Delayed Forward Setup

Fig. 5.5‑12 Delayed Forward Setup
1.5.2.3 Delayed Backward Setup

Fig. 5.5‑13 Delayed Backward Setup
1.5.2.4 Forward Bearer Setup (Without Tunnelling)

Fig. 5.5‑14 Forward Bearer Setup (Without Tunnelling)
1.5.2.5 Backward Bearer Setup (Without Tunnelling)

Fig. 5.5‑15 Backward Bearer Setup (Without Tunnelling)
1.5.2.6 Call Release Flow

Fig. 5.5‑16 Call Release Flow
Principle of releasing bearer:
 If the tunneling mechanism is not used, the party initiates the bearer setup releases the bearer.
 If the tunneling mechanism is used, the bearer is released based on the indication of the BICC message (for example, REL for call message and RSC for maintenance message).
1.6 Relationship Between BICC and ISUP
1.6.1 Separation Between Bearer and Control
The protocol stack of the ISUP is based on MTP3, so the STL of the ISUP is MTP3, and the voice channel of the ISUP must be borne over the narrowband TDM trunk circuit. For the BICC, after the call control and bearer control are separated, the BICC signaling can be transferred through various STLs, and the bearer signaling/media stream can be transferred through various bearer networks (while the voice channel bearer of the ISUP must be transferred over the SS7 bearer network, namely, the TDM trunk circuit).
1.6.2 Extension of CIC Concept
In the ISUP, the label in the SIF field includes CIC. Here "CIC" stands for circuit identification code. It is a logical number of an inter-office trunk circuit. It identifies which circuit is related to the message. The CIC in the ISUP contains 12 bits, so there are a maximum of 4,096 (212) trunk circuits between two signaling points.
To correspond to the structure of the ISUP, the BICC also introduces the concept of CIC. Here "CIC" stands for call instance code. It is a logical number of the inter-office call relationship. It identifies which call instance corresponds to the message. The CIC in the BICC contains 32 bits, so the number of the inter-office call instances can be up to 4,294,967,296 (232) theoretically.
1.6.3 Message and Parameter Changes
Based on the ISUP, the BICC deletes bearer-related messages and parameters and adds application transport message (APM) and application transport parameter (APP parameter) to control multiple bearer types.
As for the call flow, the BICC adds the interaction process of the APM messages, and other call flows are similar to those of the ISUP. The APM is used for exchanging the bearer-related control information. Therefore, the BICC inherits the call control flow from the ISUP. In this way, the BICC has and supports many features of the ISUP.