ISDN User Part (ISUP)
This protocol is used as signalling in trunks between telephone exchanges to establish and release calls.
ISUP is standardized by ITU-T in Q.761 to Q.769. There are several national variants as well.
BICC (Bearer Independent Call Control), defined by Q.1901 and annexes, is an extension of ISUP.
History
ISUP supercedes TUP (Telephony User Part) as the standard for call control between telephone exchanges. Its first deployments date back to the early 80's, It is still used by most exchanges. BICC, ISUP's successor and extension should replace this protocol as Telephone Operators migrate from TDM links (E1/T1) to Packet Based systems (mainly IP and ATM).
Protocol dependencies
Example traffic
1 0.000000 10.28.6.42 -> 10.28.6.44 ISUP (ITU) IAM (CIC 213)
2 0.006621 10.28.6.44 -> 10.28.6.42 ISUP (ITU) CFN (CIC 213)
3 0.123844 10.28.6.44 -> 10.28.6.42 ISUP (ITU) ACM (CIC 213)
4 0.124157 10.28.6.44 -> 10.28.6.42 ISUP (ITU) ANM (CIC 213)
5 17.068921 10.28.6.42 -> 10.28.6.44 ISUP (ITU) REL (CIC 213)
6 17.089918 10.28.6.44 -> 10.28.6.42 ISUP (ITU) RLC (CIC 213)
Message Transfer Part Level 3
Service information octet
11.. .... = Network indicator: Reserved for national use (0x03)
..00 .... = Spare: 0x00
.... 0101 = Service indicator: ISUP (0x05)
Routing label
.... .... .... .... ..10 1111 1000 0011 = DPC: 12163
.... 1011 0100 0000 10.. .... .... .... = OPC: 11522
0101 .... .... .... .... .... .... .... = Signalling Link Selector: 5
ISDN User Part
CIC: 213
Message type: Initial address (1)
Nature of Connection Indicators: 0x0
Mandatory Parameter: 6 (Nature of connection indicators)
.... ..00 = Satellite Indicator: No Satellite circuit in connection (0x00)
.... 00.. = Continuity Check Indicator: Continuity check not required (0x00)
...0 .... = Echo Control Device Indicator: Echo control device not included
Forward Call Indicators: 0xa001
Mandatory Parameter: 7 (Forward call indicators)
.... ...0 .... .... = National/international call indicator: Call to be treated as national call
.... .00. .... .... = End-to-end method indicator: No End-to-end method available (only link-by-link method available) (0x0000)
.... 0... .... .... = Interworking indicator: no interworking encountered (No.7 signalling all the way)
...0 .... .... .... = End-to-end information indicator: no end-to-end information available
..1. .... .... .... = ISDN user part indicator: ISDN user part used all the way
10.. .... .... .... = ISDN user part preference indicator: ISDN user part required all the way (0x0002)
.... .... .... ...1 = ISDN access indicator: originating access ISDN
.... .... .... .00. = SCCP method indicator: No indication (0x0000)
Calling Party's category: 0xa (ordinary calling subscriber)
Mandatory Parameter: 9 (Calling party's category)
Calling Party's category: ordinary calling subscriber (0x0a)
Transmission medium requirement: 2 (64 kbit/s unrestricted)
Mandatory Parameter: 2 (Transmission medium requirement)
Transmission medium requirement: 64 kbit/s unrestricted (2)
Called Party Number: 4891F
Mandatory Parameter: 4 (Called party number)
Pointer to Parameter: 2
Parameter length: 5
1... .... = Odd/even indicator: odd number of address signals
.000 0001 = Nature of address indicator: subscriber number (national use) (1)
1... .... = INN indicator: routing to internal network number not allowed
.001 .... = Numbering plan indicator: ISDN (Telephony) numbering plan (1)
Called Party Number: 4891F
.... 0100 = Address signal digit: 4 (4)
1000 .... = Address signal digit: 8 (8)
.... 1001 = Address signal digit: 9 (9)
0001 .... = Address signal digit: 1 (1)
.... 1111 = Address signal digit: Stop sending (15)
E.164 Called party number digits: 4891F
Pointer to start of optional part: 7
Calling Party Number: 3933399708
Optional Parameter: 10 (Calling party number)
Parameter length: 7
0... .... = Odd/even indicator: even number of address signals
.000 0011 = Nature of address indicator: national (significant) number (3)
0... .... = NI indicator: complete
.001 .... = Numbering plan indicator: ISDN (Telephony) numbering plan (1)
.... 01.. = Address presentation restricted indicator: presentation restricted (1)
.... ..11 = Screening indicator: network provided (3)
Calling Party Number: 3933399708
.... 0011 = Address signal digit: 3 (3)
1001 .... = Address signal digit: 9 (9)
.... 0011 = Address signal digit: 3 (3)
0011 .... = Address signal digit: 3 (3)
.... 0011 = Address signal digit: 3 (3)
1001 .... = Address signal digit: 9 (9)
.... 1001 = Address signal digit: 9 (9)
0111 .... = Address signal digit: 7 (7)
.... 0000 = Address signal digit: 0 (0)
1000 .... = Address signal digit: 8 (8)
E.164 Calling party number digits: 3933399708
Optional forward call indicators: non-CUG call (128)
Optional Parameter: 8 (Optional forward call indicators)
Parameter length: 1
.... ..00 = Closed user group call indicator: non-CUG call (0)
.... .0.. = Simple segmentation indicator: no additional information will be sent
1... .... = Connected line identity request indicator: requested
Access transport (5 bytes length)
Optional Parameter: 3 (Access transport)
Parameter length: 5
Access transport parameter field (-> Q.931)
Low-layer compatibility
Information element: Low-layer compatibility
Length: 3
...0 1000 = Information transfer capability: Unrestricted digital information (0x08)
.00. .... = Coding standard: ITU-T standardized coding (0x00)
1... .... = Extension indicator: last octet
...1 0000 = Information transfer rate: 64 kbit/s (0x10)
.00. .... = Transfer mode: Circuit mode (0x00)
1... .... = Extension indicator: last octet
...0 0110 = User information layer 1 protocol: Recommendation H.223 and H.245 (0x06)
1... .... = Extension indicator: last octet
User service information, (3 bytes length)
Optional Parameter: 29 (User service information)
Parameter length: 3
User service information (-> Q.931 Bearer_capability)
...0 1000 = Information transfer capability: Unrestricted digital information (0x08)
.00. .... = Coding standard: ITU-T standardized coding (0x00)
1... .... = Extension indicator: last octet
...1 0000 = Information transfer rate: 64 kbit/s (0x10)
.00. .... = Transfer mode: Circuit mode (0x00)
1... .... = Extension indicator: last octet
...0 0110 = User information layer 1 protocol: Recommendation H.223 and H.245 (0x06)
1... .... = Extension indicator: last octet
Propagation delay counter = 100 ms
Optional Parameter: 49 (Propagation delay counter)
Parameter length: 2
Propagation delay counter = 100 ms
Location number: 00600001
Optional Parameter: 63 (Location number)
Parameter length: 6
0... .... = Odd/even indicator: even number of address signals
.000 0011 = Nature of address indicator: national (significant) number (3)
1... .... = INN indicator: routing to internal network number not allowed
.001 .... = Numbering plan indicator: ISDN (Telephony) numbering plan (1)
.... 00.. = Address presentation restricted indicator: presentation allowed (0)
.... ..11 = Screening indicator: network provided (3)
Location number: 00600001
.... 0000 = Address signal digit: 0 (0)
0000 .... = Address signal digit: 0 (0)
.... 0110 = Address signal digit: 6 (6)
0000 .... = Address signal digit: 0 (0)
.... 0000 = Address signal digit: 0 (0)
0000 .... = Address signal digit: 0 (0)
.... 0000 = Address signal digit: 0 (0)
0001 .... = Address signal digit: 1 (1)
Parameter Type unknown/reserved (5 Bytes)
Optional Parameter: 244 (unknown)
Parameter length: 5
Parameter compatibility information (2 bytes length)
Optional Parameter: 57 (Parameter compatibility information)
Parameter length: 2
Upgraded parameter no: 1 = unknown (244)
Instruction indicators: 0x90
.... ...0 = Transit at intermediate exchange indicator: Transit interpretation
.... ..0. = Release call indicator: do not release call
.... .0.. = Send notification indicator: do not send notification
.... 0... = Discard message indicator: Do not discard message (pass on)
...1 .... = Discard parameter indicator: Discard parameter
.00. .... = Pass on not possible indicator: Release call (0x00)
1... .... = Extension indicator: last octet
End of optional parameters (0)
Wireshark
The ISUP dissector is fully functional
Preference Settings
The only preference is "Show CIC in info column" a Boolean used to show the CIC (channel ID) to which the message is referred.
Example capture file
SampleCaptures/isup.cap a single call's signalling sequence using ISUP/MTP3/M3UA/SCTP/IP ( Note that this trace is a M3UA draft 6 capture. You must set your M3UA preferences to Draft 6 by selecting Edit ->Preferences -> Protocols ->M3UA -> Draft 6 )
Display Filter
A complete list of ISUP display filter fields can be found in the display filter reference
- Show only the ISUP traffic:
isup
Capture Filter
You cannot directly filter ISUP packets while capturing. However, in case ISUP runs over MTP3/M3UA/SCTP/IP you could filter SCTP traffic using
ip proto 0x84
- or, with newer versions of libpcap/WinPcap,
ip proto sctp
.
External links
http://www.itu.int ITU - International Telecommunication Union