Reference #17018
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ISDN protocol, standardi
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Izmjenjeno od Ernad Husremović prije oko 16 godina
There are two basic types of ISDN service: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI consists of two 64 kb/s B channels and one 16 kb/s D channel for a total of 144 kb/s. This basic service is intended to meet the needs of most individual users.
PRI is intended for users with greater capacity requirements. Typically the channel structure is 23 B channels plus one 64 kb/s D channel for a total of 1536 kb/s. In Europe, PRI consists of 30 B channels plus one 64 kb/s D channel for a total of 1984 kb/s. It is also possible to support multiple PRI lines with one 64 kb/s D channel using Non-Facility Associated Signaling (NFAS).
H channels provide a way to aggregate B channels. They are implemented as:- H0=384 kb/s (6 B channels)
- H10=1472 kb/s (23 B channels)
- H11=1536 kb/s (24 B channels)
- H12=1920 kb/s (30 B channels) - International (E1) only
To access BRI service, it is necessary to subscribe to an ISDN phone line. Customer must be within 18000 feet (about 3.4 miles or 5.5 km) of the telephone company central office for BRI service; beyond that, expensive repeater devices are required, or ISDN service may not be available at all. Customers will also need special equipment to communicate with the phone company switch and with other ISDN devices. These devices include ISDN Terminal Adapters (sometimes called, incorrectly, "ISDN Modems") and ISDN Routers.
Izmjenjeno od Ernad Husremović prije oko 16 godina
In the early 1990s, an industry-wide effort began to establish a specific implementation for ISDN in the U.S. Members of the industry agreed to create the National ISDN 1 (NI-1) standard so that end users would not have to know the brand of switch they are connected to in order to buy equipment and software compatible with it. However, there were problems agreeing on this standard. In fact, many western states would not implement NI-1. Both Southwestern Bell and U.S. West (now Qwest) said that they did not plan to deploy NI-1 software in their central office switches due to incompatibilities with their existing ISDN networks.
Ultimately, all the Regional Bell Operating Companies (RBOCs) did support NI-1. A more comprehensive standardization initiative, National ISDN 2 (NI-2), was later adopted. Some manufacturers of ISDN communications equipment, such as Motorola and U S Robotics (now owned by 3Com), worked with the RBOCs to develop configuration standards for their equipment. These kinds of actions, along with more competitive pricing, inexpensive ISDN connection equipment, and the desire for people to have relatively low-cost high-bandwidth Internet access have made ISDN more popular in recent years.
Most recently, ISDN service has largely been displaced by broadband internet service, such as xDSL and Cable Modem service. These services are faster, less expensive, and easier to set up and maintain than ISDN. Still, ISDN has its place, as backup to dedicated lines, and in locations where broadband service is not yet available.
Izmjenjeno od Ernad Husremović prije oko 16 godina
The modem was a big breakthrough in computer communications. It allowed computers to communicate by converting their digital information into an analog signal to travel through the public phone network. There is an upper limit to the amount of information that an analog telephone line can hold. Currently, it is about 56 kb/s bidirectionally. Commonly available modems have a maximum speed of 56 kb/s, but are limited by the quality of the analog connection and routinely go about 45-50 kb/s. Some phone lines do not support 56 kb/s connections at all. There were currently 2 competing, incompatible 56 kb/s standards (X2 from U S Robotics (recently bought by 3Com), and K56flex from Rockwell/Lucent). This standards problem was resolved when the ITU released the V.90, and later V.92, standard for 56 kb/s modem communications.
Izmjenjeno od Ernad Husremović prije oko 16 godina
ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring used for analog lines. The change comes about when the telephone company's switches can support digital connections. Therefore, the same physical wiring can be used, but a digital signal, instead of an analog signal, is transmitted across the line. This scheme permits a much higher data transfer rate than analog lines. BRI ISDN, using a channel aggregation protocol such as BONDING or Multilink-PPP, supports an uncompressed data transfer speed of 128 kb/s, plus bandwidth for overhead and signaling. In addition, the latency, or the amount of time it takes for a communication to begin, on an ISDN line is typically about half that of an analog line. This improves response for interactive applications, such as games.
Izmjenjeno od Ernad Husremović prije oko 16 godina
Multiple Devices¶
Previously, it was necessary to have a separate phone line for each device you wished to use simultaneously. For example, one line each was required for a telephone, fax, computer, bridge/router, and live video conference system. Transferring a file to someone while talking on the phone or seeing their live picture on a video screen would require several potentially expensive phone lines.
ISDN allows multiple devices to share a single line. It is possible to combine many different digital data sources and have the information routed to the proper destination. Since the line is digital, it is easier to keep the noise and interference out while combining these signals. ISDN technically refers to a specific set of digital services provided through a single, standard interface. Without ISDN, distinct interfaces are required instead.
Izmjenjeno od Ernad Husremović prije oko 16 godina
Signaling¶
Instead of the phone company sending a ring voltage signal to ring the bell in your phone ("In-Band signal"), it sends a digital packet on a separate channel ("Out-of-Band signal"). The Out-of-Band signal does not disturb established connections, no bandwidth is taken from the data channels, and call setup time is very fast. For example, a V.90 or V.92 modem typically takes 30-60 seconds to establish a connection; an ISDN call setup usually takes less than 2 seconds.
The signaling also indicates who is calling, what type of call it is (data/voice), and what number was dialed. Available ISDN phone equipment is then capable of making intelligent decisions on how to direct the call.
Izmjenjeno od Ernad Husremović prije oko 16 godina
- Fajl isdn_ifaces2.gif isdn_ifaces2.gif dodano
Interfaces¶
In the U.S., the telephone company provides its BRI customers with a U interface. The U interface is a two-wire (single pair) interface from the phone switch, the same physical interface provided for POTS lines. It supports full-duplex data transfer over a single pair of wires, therefore only a single device can be connected to a U interface. This device is called an Network Termination 1 (NT-1). The situation is different elsewhere in the world, where the phone company is allowed to supply the NT-1, and thereby the customer is given an S/T interface.
The NT-1 is a relatively simple device that converts the 2-wire U interface into the 4-wire S/T interface. The S/T interface supports multiple devices (up to 7 devices can be placed on the S/T bus) because, while it is still a full-duplex interface, there is now a pair of wires for receive data, and another for transmit data. Today, many devices have NT-1s built into their design. This has the advantage of making the devices less expensive and easier to install, but often reduces flexibility by preventing additional devices from being connected.
Technically, ISDN devices must go through an Network Termination 2 (NT-2) device, which converts the T interface into the S interface (Note: the S and T interfaces are electrically equivalent). Virtually all ISDN devices include an NT-2 in their design. The NT-2 communicates with terminal equipment, and handles the Layer 2 and 3 ISDN protocols. Devices most commonly expect either a U interface connection (these have a built-in NT-1), or an S/T interface connection.
Devices that connect to the S/T (or S) interface include ISDN capable telephones and FAX machines, video teleconferencing equipment, bridge/routers, and terminal adapters. All devices that are designed for ISDN are designated Terminal Equipment 1 (TE1). All other communication devices that are not ISDN capable, but have a POTS telephone interface (also called the R interface), including ordinary analog telephones, FAX machines, and modems, are designated Terminal Equipment 2 (TE2). A Terminal Adapters connects a TE2 to an ISDN S/T bus.
Going one step in the opposite direction takes us inside the telephone switch. Remember that the U interface connects the switch to the customer premises equipment. This local loop connection is called Line Termination (LT function). The connection to other switches within the phone network is called Exchange Termination (ET function). The LT function and the ET function communicate via the V interface.
Izmjenjeno od Ernad Husremović prije oko 16 godina
znači mi od telecom-a dobijamo S/T interface, i na njega možemo zakačiti više ISDN terminalne opreme TE1, ili starih uređaja TE2 preko terminalnih adaptera
Izmjenjeno od Ernad Husremović prije oko 16 godina
ono što mi zovemo NT je precizno rečeno NT1 uređaj, uređaj koji U interface prebacuje na S/T ili skraćeno na S interface
Izmjenjeno od Ernad Husremović prije oko 16 godina
Layer 1 - fizički layer¶
The ISDN Physical Layer is specified by the ITU I-series and G-series documents. The U interface provided by the telco for BRI is a 2-wire, 160 kb/s digital connection. Echo cancellation is used to reduce noise, and data encoding schemes (2B1Q in North America, 4B3T in Europe) permit this relatively high data rate over ordinary single-pair local loops.
2B1Q echoding schema - North America¶
2B1Q (2 Binary 1 Quaternary) is the most common signaling method on U interfaces. This protocol is defined in detail in 1988 ANSI spec T1.601.
In summary, 2B1Q provides:- Two bits per baud
- 80 kilobaud (baud = 1 modulation per second)
- Transfer rate of 160 kb/s
Bits Quaternary Symbol Voltage Level 00 -3 -2.5 01 -1 -0.833 10 +3 +2.5 11 +1 +0.833
This means that the input voltage level can be one of 4 distinct levels (note: 0 volts is not a valid voltage under this scheme). These levels are called Quaternaries. Each quaternary represents 2 data bits, since there are 4 possible ways to represent 2 bits, as in the table above.
Frame Format¶
Each U interface frame is 240 bits long. At the prescribed data rate of 160 kb/s, each frame is therefore 1.5 ms long.
Each frame consists of:- Frame overhead - 16 kb/s
- D channel - 16 kb/s
- 2 B channels at 64 kb/s - 128 kb/s
Sync: 18 bits, 12 * (B1 + B2 + D) = 216 bits, Maintenance: 6 bits
irb(main):001:0> 18+216+6 => 240
- The Sync field consists of 9 Quaternaries (2 bits each) in the pattern +3 +3 -3 -3 -3 +3 -3 +3 -3.
- (B1 + B2 + D) is 18 bits of data consisting of 8 bits from the first B channel, 8 bits from the second B channel, and 2 bits of D channel data.
- The Maintenance field contains CRC information, block error detection flags, and "embedded operator commands" used for loopback testing without disrupting user data.
Data is transmitted in a superframe consisting of 8 240-bit frames for a total of 1920 bits (240 octets). The sync field of the first frame in the superframe is inverted (i.e. -3 -3 +3 +3 +3 -3 +3 -3 +3).
Izmjenjeno od Ernad Husremović prije oko 16 godina
Layer 2 - Data Link Layer¶
The ISDN Data Link Layer is specified by the ITU Q-series documents Q.920 through Q.923. All of the signaling on the D channel is defined in the Q.921 spec.
LAP-D - (ovo je protokol koji se koristi u US u euroisdn koristi DSS1, pogledaj dole)¶
Link Access Protocol - D channel (LAP-D) is the Layer 2 protocol used. This is almost identical to the X.25 LAP-B protocol.
Here is the structure of a LAP-D frame:
| a) Flag | b) Address | c) Control | d) Information | e) CRC | f) Flag |
LAP-D/a) Flag (1 octet) - This is always 7E16 (0111 11102)
LAP-D/b) Address (2 octets)
1 2 3 4 5 6 - SAPI (6 bits) ; 7 8 - C/R EA0 ; TEI (7 bits) EA1
SAPI (Service access point identifier), 6-bits (see below)- C/R (Command/Response) bit indicates if the frame is a command or a response
- EA0 (Address Extension) bit indicates whether this is the final octet of the address or not
- TEI (Terminal Endpoint Identifier) 7-bit device identifier (see below)
- EA1 (Address Extension) bit, same as EA0
LAP-D/c) Control (2 octets) - The frame level control field indicates the frame type (Information, Supervisory, or Unnumbered) and sequence numbers (N(r) and N(s)) as required.
LAP-D/d) Information - Layer 3 protocol information and User data
LAP-D/e) * CRC (2 octets) - Cyclic Redundancy Check is a low-level test for bit errors on the user data.
LAP-D/f) * Flag (1 octet) - This is always 7E16 (0111 11102)
SAPIs¶
The Service Access Point Identifier (SAPI) is a 6-bit field that identifies the point where Layer 2 provides a service to Layer 3.
See the following table:
- SAPI Description
- 0 Call control procedures
- 1 Packet Mode using Q.931 call procedures
- 16 Packet Mode communications procedures
- 32-47 Reserved for national use
- 63 Management Procedures
Others Reserved for Future Use
TEIs¶
Terminal Endpoint Identifiers (TEIs) are unique IDs given to each device (TE) on an ISDN S/T bus. This identifier can be dynamic; the value may be assigned statically when the TE is installed, or dynamically when activated.
- TEI Description
- 0-63 Fixed TEI assignments
- 64-126 Dynamic TEI assignment (assigned by the switch)
- 127 Broadcast to all devices
Establishing the Link Layer¶
The Layer 2 establishment process is very similar to the X.25 LAP-B setup, if you are familiar with it.
- The TE (Terminal Endpoint) and the Network initially exchange Receive Ready (RR) frames, listening for someone to initiate a connection
- The TE sends an Unnumbered Information (UI) frame with a SAPI of 63 (management procedure, query network) and TEI of 127 (broadcast)
- The Network assigns an available TEI (in the range 64-126)
- The TE sends a Set Asynchronous Balanced Mode (SABME) frame with a SAPI of 0 (call control, used to initiate a SETUP) and a TEI of the value assigned by the network
- The network responds with an Unnumbered Acknowledgement (UA), SAPI=0, TEI=assigned.
At this point, the connection is ready for a Layer 3 setup.
Izmjenjeno od Ernad Husremović prije oko 16 godina
Layer 3 - Network Layer¶
The ISDN Network Layer is also specified by the ITU Q-series documents Q.930 through Q.939. Layer 3 is used for the establishment, maintenance, and termination of logical network connections between two devices.
SPIDs¶
Service Profile IDs (SPIDs) are used to identify what services and features the telco switch provides to the attached ISDN device. SPIDs are optional; when they are used, they are only accessed at device initialization time, before the call is set up. The format of the SPID is defined in a recommendation document, but it is only rarely followed. It is usually the 10-digit phone number of the ISDN line, plus a prefix and a suffix that are sometimes used to identify features on the line, but in reality it can be whatever the telco decides it should be. If an ISDN line requires a SPID, but it is not correctly supplied, then Layer 2 initialization will take place, but Layer 3 will not, and the device will not be able to place or accept calls. See ITU spec Q.932 for details.
Information Field Structure¶
The Information Field is a variable length field that contains the Q.931 protocol data.
Information Field| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
| Protocol Discriminator | |||||||
| 0 | 0 | 0 | 0 | Length of CRV | |||
| Call Reference Value (1 or 2 octets) | |||||||
| 0 | Message Type | ||||||
| Mandatory & Optional Information Elements (variable) | |||||||
- Protocol Discriminator (1 octet) - identifies the Layer 3 protocol. If this is a Q.931 header, this value is always 0816.
- Length (1 octet) - indicates the length of the next field, the CRV.
- Call Reference Value (CRV) (1 or 2 octets) - used to uniquely identify each call on the user-network interface. This value is assigned at the beginning of a call, and this value becomes available for another call when the call is cleared.
- Message Type (1 octet) - identifies the message type (i.e., SETUP, CONNECT, etc.). This determines what additional information is required and allowed.
- Mandatory and Optional Information Elements (variable length) - are options that are set depending on the Message Type.
Layer 3 Call Setup¶
These are the steps that occurs when an ISDN call is established. In the following example, there are three points where messages are sent and received; 1) the Caller, 2) the ISDN Switch, and 3) the Receiver.
1. Caller sends a SETUP to the Switch.
2. If the SETUP is OK, the switch sends a CALL PROCeeding to the Caller, and then a SETUP to the Receiver.
3. The Receiver gets the SETUP. If it is OK, then it rings the phone and sends an ALERTING message to the Switch.
4. The Switch forwards the ALERTING message to the Caller.
5. When the receiver answers the call, is sends a CONNECT message to the Switch
6. The Switch forwards the CONNECT message to the Caller.
7. The Caller sends a CONNECT ACKnowledge message to the Switch
8. The Switch forwards the CONNECT ACK message to the Receiver.
9. Done. The connection is now up.
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Q.931 Disconnect Reasons
Code Cause
0 Valid cause code not yet received
1 Unallocated (unassigned) number
2 No route to specified transit network (WAN)
3 No route to destination
4 send special information tone
5 misdialled trunk prefix.
6 Channel unacceptable
7 Call awarded and being delivered in an established channel
8 Prefix 0 dialed but not allowed
9 Prefix 1 dialed but not allowed
10 Prefix 1 dialed but not required
11 More digits received than allowed, call is proceeding
16 Normal call clearing
17 User busy
18 No user responding
19 no answer from user
21 Call rejected
22 Number changed
23 Reverse charging rejected
24 Call suspended
25 Call resumed
26 Non-selected user clearing
27 Destination out of order
28 Invalid number format (incomplete number)
29 Facility rejected
30 Response to STATUS ENQUIRY
31 Normal, unspecified
33 Circuit out of order
34 No circuit/channel available
35 Destination unattainable
37 Degraded service
38 Network (WAN) out of order
39 Transit delay range cannot be achieved
40 Throughput range cannot be achieved
41 Temporary failure
42 Switching equipment congestion
43 Access information discarded
44 Requested circuit channel not available
45 Pre-empted
46 Precedence call blocked
47 Resource unavailable - unspecified
49 Quality of service unavailable
50 Requested facility not subscribed
51 Reverse charging not allowed
52 Outgoing calls barred
53 Outgoing calls barred within CUG
54 Incoming calls barred
55 Incoming calls barred within CUG
56 Call waiting not subscribed
57 Bearer capability not authorized
58 Bearer capability not presently available
63 Service or option not available, unspecified
65 Bearer service not implemented
66 Channel type not implemented
67 Transit network selection not implemented
68 Message not implemented
69 Requested facility not implemented
70 Only restricted digital information bearer capability
is available
79 Service or option not implemented, unspecified
81 Invalid call reference value
82 Identified channel does not exist
83 A suspended call exists, but this call identity does not
84 Call identity in use
85 No call suspended
86 Call having the requested call identity has been cleared
87 Called user not member of CUG
88 Incompatible destination
89 Non-existent abbreviated address entry
90 Destination address missing, and direct call not subscribed
91 Invalid transit network selection (national use)
92 Invalid facility parameter
93 Mandatory information element is missing
95 Invalid message, unspecified
96 Mandatory information element is missing
97 Message type non-existent or not implemented
98 Message not compatible with call state or message type
non-existent or not implemented
99 information element nonexistant or not implemented
100 Invalid information element contents
101 Message not compatible with call state
102 Recovery on timer expiry
103 parameter non-existent or not implemented - passed on
111 Protocol error unspecified
127 Internetworking, unspecified
Izmjenjeno od Ernad Husremović prije oko 16 godina
Izmjenjeno od Ernad Husremović prije oko 16 godina
- Fajl binary_vs_quaternaer.gif binary_vs_quaternaer.gif dodano
What does 4B3T stand for? 4 Binary, 3 Ternary (Euro-ISDN)
http://www.rainsbrook.co.uk/networking/fvc/hdb3/hdb3_c.html
4B3T-Code¶
The 4B3T-Code combines in each case 4 Bit(4B) of a binary signal into a block, and codes it in three ternary Signalelemente(3T). The allocation of the 4B-Werte in 3T-Elemente takes place after a code table.
As a 4B-Wort is coded in each case, depends on the coding of the previous 4B-Wortes. In this way the direct current liberty is realized.
By the code conversion from 4 bits to 3 bit, amounts to the modulation rate only 75% in relation to transmission rate.
For the clock recuperation a Scrambler is necessary.
Step duration T S = 1666.67 µs
Modulation rate v S = 6 kBaud
Transmission rate v D = 8 kBit
The 4B3T-Code was used in the national and in the euro ISDN of the German Telekom as cable code.
2B1Q-Code¶
2B1Q-Code
With the 2B1Q- Code 2 binary signals are converted into a Quaternaeres signal. This knows 4 different conditions haben(00, 01, 10, 11).
The modulation rate v S amounts to only 50% of transmission rate v D .
Duch the use of the 2B1Q-Leitungscodes is reduced the frequency spectrum necessary for the transmission. By the use of the lower part of the frequency spectrum the absorption precipitates extremely small. Also the disturbance of neighbouring veins by the transmission is low.
The 2B1Q-Code is used in the euro ISDN as cable code.
Izmjenjeno od Ernad Husremović prije oko 16 godina
još jedan dobar materijal o ISDN-u http://ckp.made-it.com/isdn.html, čini mi se evropljanin je pisao
Izmjenjeno od Ernad Husremović prije oko 16 godina
s0 bus¶
Da razjasnim termin koji sam kod nas često čuo "S0 bus".
The switches are part of the telco network from which the U-interface enters the customer premisis. Most US telcos leave it to that, where the European telcos do supply the NT-1 (Network Termination unit 1) and leave the customer with the S/T interface, also called S-bus or S0-bus.
Znači precizni isdn termin je S/T interface, a kod nas se često koristi S0 bus.
Izmjenjeno od Ernad Husremović prije oko 16 godina
- Fajl isdn-made-it.pdf isdn-made-it.pdf dodano
ovaj gore made-it isdn dokument sam pokupio jer sadrži pored ostalog i raspored pinova
Izmjenjeno od Ernad Husremović prije oko 16 godina
http://en.wikipedia.org/wiki/DSS1
Digital Subscriber Signalling System No. 1 (DSS1), also known as Euro-ISDN or E-DSS1 (European DSS1), is a digital signalling protocol used for the ISDN. The interface is also called NET3 for BRI and NET5 for PRI lines. Can also be called CTR4. It is defined by ITU-T I.411 (ETS 300 102). It supports Bearer Capability, Low Level Compatibility and High Level Compatibility, ANI, DNIS and redirected number signaling in both directions.
DSS1 is a pan-European standard developed by ETSI. In 1989, 26 network operators from 20 European countries decided to develop this standard to replace earlier national protocols (such as FTZ 1 TR 6 or VN3). DSS1 has been one of the keys to the success of the ISDN within European countries (as compared to, for example, the U.S.).
Non-European countries using DSS1 include Australia, Brazil, India, Israel, New Zealand, Pakistan, Peru, Singapore, South Africa, Sri Lanka, Taiwan and the United Arab Emirates.
The DSS1 protocol knows four different codesets for information elements. Codeset 0 regards to Q.931, Codeset 5 to the ETSI standard, Codeset 6 for national applications and Codeset 7 for PBX applications. The most common Codeset is 0/Q.931.
Retrieved from "http://en.wikipedia.org/wiki/Digital_Subscriber_System_No._1"
Izmjenjeno od Ernad Husremović prije oko 16 godina
lista isdn standarda
http://www.zytrax.com/tech/protocols/isdn/isdn_stds.htm
pored ostalog imamo vezano za DSS1:- Q.930 March 1993 Digital Subscriber Signalling System No. 1 (DSS1) - ISDN user-network interface layer 3 - General Aspects
- Q.931 May 1998 Digital Subscriber Signalling System No. 1 (DSS1) - ISDN user-network interface layer 3 - specification for basic call control
- Q.932 June 2000 Digital subscriber Siganlling System No. 1 (DSS1) - Generic Procedures for the control of ISDN Supplementary Services
Izmjenjeno od Ernad Husremović prije oko 16 godina
- Fajl T-REC-Q.932-199805.pdf T-REC-Q.932-199805.pdf dodano
- Fajl T-REC-Q.930-199303.pdf T-REC-Q.930-199303.pdf dodano
- Fajl T-REC-X.31-199511.pdf T-REC-X.31-199511.pdf dodano
- Fajl T-REC-Q.920-199303-PDF-E.pdf T-REC-Q.920-199303-PDF-E.pdf dodano
Izmjenjeno od Ernad Husremović prije oko 16 godina
Q.931 Protocol Overview, lincoln.edu¶
http://www.lincoln.edu/math/rmyrick/ComputerNetworks/InetReference/126.htm
Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates bandwidth in fixed increments of 64 kbps. Q.931 does manage connection setup and breakdown. Like TCP, Q.931 documents both the protocol itself and a protocol state machine.
...
vrlo dobar dokument, ovaj lincoln.edu je baš dobar resurs izgleda za sve protokole
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- Status promijenjeno iz Novo u Zatvoreno
- % završeno promijenjeno iz 0 u 100
Izmjenjeno od Ernad Husremović prije oko 16 godina
- Naslov promijenjeno iz ISDN u ISDN protocol, standardi