1. 7.0 INTEGRATED SERVICES DIGITAL NETWORKS (ISDN)
7.1 Background and Goals of ISDN
7.2 User Access and Interface
7.3 ISDN Protocol Structure
ISDN and OSI
Layer 1 Interface, Basic Rate
Layer 1 Interface, Primary Rate
7.4 Layer Interface: Link Access Procedure for D Channel
7.5 Layer 3 Specification

2. What Is ISDN?

3. ISDN Defined Known as the Integrated Services Digital Network
Data, audio, image and video transmission
It is a switched digital telecommunication line that can be delivered over regular copper wires
Possible to provide end-to-end digital communications

4. ISDN Application Examples
On/off ramp to the information super-highway to communicate at speeds of 128 Kbps for a single ISDN line
Multiple ISDN lines can be combined together to achieve higher communication speeds
Home use
On/Off ramp to the Internet
Business world
Provide remote access to LANs .

5. ISDN Standard
There is a national ISDN standard known as the NI standard
It is being implemented in phases
Current implementation is termed as NI-1 to indicate that it is in phase 1 of the implementation process
Can be obtained from a local telephone company in the same way an analog connection is obtained
Phone companies offer different types of ISDN connections

6. Features of ISDN Uses Digital Signal Uses Existing telephone wiring
Charges are generally based on the duration of call (How long the WAN link was used)
Alternate to using leased lines
Can transport many types of Network traffic (Voice, Data, Video, Text, Graphics etc)
Faster Data transfer rate than modems
Faster Call setup than Modems

7. ISDN Architecture Subscriber premises Digital subscriber Subscriber
Network
Subscriber
premises
>64kbps
non-switched
capabilities
>64kbps
switched
capabilities
Digital
subscriber
loop to
C. O.
Subscriber
interface to
ISDN
64kbps
ckt non-switched
capabilities
Network
Termination
(NT)
Subscriber
site or
service
provider
Terminal
equipment
(TE)
ISDN
switch
>64kbps
ckt switched
capabilities
ISDN
switch
Packet switched
capabilities
User-network
signaling
Frame mode
capabilities
Common-
channel signaling
capabilities
User-network
signaling

8. Fundamentals Service types
Basic Rate Interface (2 B channels + 1 D channel (16 kb/s))
Primary Rate Interface (30 B channels + 1 D channel (64 kb/s))
Primary Rate Interface (23 B channels + 1 D channel (64 kb/s)) for North America

9. ISDN Service BRI (Basic Rate Interface)
Connection from the ISDN office to the user location provides for access to three channels. The channels are two 64Kb B-channels and one 16Kb D-channel
The B-channels and the D-channel provide the user with access to the circuit switched network

10. ISDN Service PRI (Primary Rate Interface)
ISDN Primary Rate Interface service provides digital access via a T1 line. A T1 line provides a bandwidth. This bandwidth is divided into 24 64Kb channels. The ISDN PRI service uses 23 B channel access and uses the 24th (D) channel for signaling purposes

11. Basic Rate Interface (BRI) Primary Rate Interface (PRI)
ISDN Interfaces
Basic Rate Interface (BRI)
144 Kbps 2B D }
64 Kbps
16 Kbps
Primary Rate Interface (PRI)
1.544 Mbps in U.S.
2.048 Mbps in Europe
23B or 30B D
64 Kbps }

12. User Access and Interface

13. GENERAL
ISDN transmission rates were to be accommodated on copper wire pairs. The objectives of any digital interface design and specifically of ISDN access and interface, are as follows:
i. Electrical and mechanical specification
ii. Channel structure and access capabilities
iii. User network protocols
iv. Maintenance and operation
v. Performance
vi. Services

14. ISDN SINGLE ISDN TERMINAL MULTIPLE ISDN TERMINAL INSTALLATION
PBX/CBX/LAN PRIVATE NETWORK
MAINFRAME COMPUTERS; BULK STORAGE
OTHERS

15. ISDN Devices
Terminal Adapter (TA) - Converter device that converts standard electrical signals into the form used by ISDN - allows non-ISDN devices to operate on an ISDN network.
Terminal Equipment Type 1 (TE1) - Compatible with the ISDN network. Example:Telephones, personal computers, fax machine or videoconferencing machine.

16. ISDN Devices
Terminal Equipment Type 2 (TE2) - Not compatible with the ISDN network. Example: Analog phone or modem, requires a TA (TE2 connects to TA).
Network termination type 1 & 2 (NT1 and NT2) - A small connection box that physically connects the customer site to the Telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network (PRI – CSU/DSU).

17. ISDN Components and Reference Points

18. ISDN Reference Points
U - Two wire cable that connects the customer’s equipment to the telecommunications provider
R - Point between non-ISDN equipment (TE2) and the TA
S - Four-wire cable from TE1 or TA to the NT1 or NT2
T - Point between NT1 and NT2

19. Analogies NT-1 (Network Terminator-1)
An NT-1 is an interface box that converts ISDN data into something a PC can understand (and vice versa). It works a little like a cable TV descrambler for ISDN signals, and is often built into ISDN adapters..

20. Analogies TA (Terminal Adapter)
This chunk of hardware converts the data it receives over ISDN to a form your computer can understand.
Sometimes mistakenly called an ISDN modem or a digital modem, a terminal adapter handles data digitally and does not need to modulate or demodulate an analog signal.
Terminal adapters can be an internal board or an external board that connects to the computer through the serial port.

21. ISDN Components and Reference Points #2

22. ISDN Reference Points

23. ISDN and the OSI Reference Model
The ISDN Physical Layer
The ISDN Data Link Layer
The ISDN Network Layer

24. ITU-T Standards of the First Three Layers of ISDN

25. ISDN Protocols
E-series protocols—Telephone network standards for ISDN.
I-series protocols—Specify ISDN concepts and interfaces.
Q-series protocols—Standards for ISDN switching and signaling.
Operate at the physical, data link, and network layers of the OSI reference model
Developed by the ITU-T are organized and grouped into three different series: (Know these – what is on the slide is adequate)
A. E-series protocols – Telephone network standards for ISDN. For example, E.164 specifies international ISDN addressing
B. I-series protocols – Specify ISDN concepts and interfaces. Grouped into four subcategories:
1. I.100 series – Specify ISDN concepts and structures
2. I.200 series – Deals with ISDN service aspects
3. I.300 series – Deals with network layer aspects
4. I.400 series – Deals with the user network interface (UNI)
C. Q-series protocols – Specify standards for ISDN switching and signaling
1. Q.921 describes Link Access Procedure on the D Channel (LAPD).
2. Q.931 defines Layer 3 features
Teaching Tip
A simple way to tell these Q protocols apart is to use the 2nd digit, 2 for Layer 2 and 3 for Layer 3. Cute but effective.
Recognizing the E, I and Q protocols and their general purpose (Q: switching and signaling) is critical for the CCNA exam. The E and I subcategories are not likely but recognizing what you see in C and the Teaching Tip above should be assumed
D. The ISDN protocols operate at the physical, data-link, and network layers of the OSI reference model. Examples:
1. Physical Layer ISDN Protocols – BRI is defined by the ITU-T I.430 protocol (PRI is defined by ITU-T I.431), which describes the physical connections between the ISDN CPE and the ISDN local exchange. I.430 also defines two ISDN physical layer frame formats.
a) Inbound frame formats (frames that travel from the local exchange to the ISDN customer)
b) Outbound frame formats (frames that travel from the ISDN customer to the local exchange)
2. Data Link Layer ISDN protocols – LAPD signaling protocol, defined by ITU-T Q.920 (BRI) and Q.921 (PRI) for transmitting control and signaling information over the D channel between the ISDN CPE and local exchange
a) LAPD frame format is similar to that of the ISO HDLC frame format. Like HDLC and PPP it include a flag, an address, a control, an information (data), and a frame check sequence (FCS) field.
Don’t confuse LAPD with Link Access Procedure, Balanced (LAPB), the data-link layer protocol used in X.25 networks (Chapter 17)
3. Network Layer ISDN protocols - Responsible for specifying the switching and signaling in the end-to-end ISDN communication over the D channel. These protocols include ITU-T I.930) and ITU-T Q.931
There are two useful ISDN debug commands “debug isdn q921” to troubleshoot L2 connectivity to the switch. Also “debug isdn q931” to troubleshoot call processing

26. ISDN Protocol Operating OSI Layers 1 Through 3
Physical layer ISDN protocols
BRI (ITU-T I.430) / PRI (ITU-T I.431)
Defines two ISDN physical layer frame formats
Inbound (local exchange to ISDN customer)
Outbound (ISDN customer to local exchange)
The ISDN protocols operate at the physical, data-link, and network layers of the OSI reference model. Examples:
1. Physical Layer ISDN Protocols – BRI is defined by the ITU-T I.430 protocol (PRI is defined by ITU-T I.431), which describes the physical connections between the ISDN CPE and the ISDN local exchange. I.430 also defines two ISDN physical layer frame formats.
a) Inbound frame formats (frames that travel from the local exchange to the ISDN customer)
b) Outbound frame formats (frames that travel from the ISDN customer to the local exchange)
2. Data Link Layer ISDN protocols – LAPD signaling protocol, defined by ITU-T Q.920 (BRI) and Q.921 (PRI) for transmitting control and signaling information over the D channel between the ISDN CPE and local exchange
a) LAPD frame format is similar to that of the ISO HDLC frame format. Like HDLC and PPP it include a flag, an address, a control, an information (data), and a frame check sequence (FCS) field.
Don’t confuse LAPD with Link Access Procedure, Balanced (LAPB), the data-link layer protocol used in X.25 networks (Chapter 17)
3. Network Layer ISDN protocols - Responsible for specifying the switching and signaling in the end-to-end ISDN communication over the D channel. These protocols include ITU-T I.930 and ITU-T Q.931
Teaching Tip
There are two useful ISDN debug commands “debug isdn q921” to troubleshoot L2 connectivity to the switch. Also “debug isdn q931” to troubleshoot call processing
Note: With Q.921/Q.931 the second digit indicates the OSI layer.

27. ISDN Protocol Operating OSI Layers 1 Through 3
Data link layer ISDN protocols
LAPD signaling protocol (ITU-T Q.920 for BRI and Q.921 for PRI) for transmitting control and signaling information over the D channel
LAPD frame format similar to ISO HDLC frame format
Network layer ISDN protocols
ITU-T I.930 and ITU-T Q.931 defines switching and signaling methods using the D channel.
The ISDN protocols operate at the physical, data-link, and network layers of the OSI reference model. Examples:
1. Physical Layer ISDN Protocols – BRI is defined by the ITU-T I.430 protocol (PRI is defined by ITU-T I.431), which describes the physical connections between the ISDN CPE and the ISDN local exchange. I.430 also defines two ISDN physical layer frame formats.
a) Inbound frame formats (frames that travel from the local exchange to the ISDN customer)
b) Outbound frame formats (frames that travel from the ISDN customer to the local exchange)
2. Data Link Layer ISDN protocols – LAPD signaling protocol, defined by ITU-T Q.920 (BRI) and Q.921 (PRI) for transmitting control and signaling information over the D channel between the ISDN CPE and local exchange
a) LAPD frame format is similar to that of the ISO HDLC frame format. Like HDLC and PPP it include a flag, an address, a control, an information (data), and a frame check sequence (FCS) field.
Don’t confuse LAPD with Link Access Procedure, Balanced (LAPB), the data-link layer protocol used in X.25 networks (Chapter 17)
3. Network Layer ISDN protocols - Responsible for specifying the switching and signaling in the end-to-end ISDN communication over the D channel. These protocols include ITU-T I.930 and ITU-T Q.931
Teaching Tip
There are two useful ISDN debug commands “debug isdn q921” to troubleshoot L2 connectivity to the switch. Also “debug isdn q931” to troubleshoot call processing
Note: With Q.921/Q.931 the second digit indicates the OSI layer.

28. ISDN Physical Layer
ISDN physical-layer frame formats are 48 bits long, of which 36 bits represent data

29. ISDN Data Link Layer
Frame format is very similar to that of HDLC

30. ISDN Network Layer
Two Layer 3 specifications are used for ISDN signaling:
ITU-T I.450 (also known as ITU-T Q.930)
ITU-T I.451 (also known as ITU-T Q.931)
Together, these protocols support:
User-to-user circuit-switched connections
User-to-user packet-switched connections
A variety of standards for:
Call establishment
Call termination

31. 7.4 Layer Interface: Link Access Procedure for D Channel

32. Link access procedure (LAP) for D channel (LAPD) is used to convey information between layer 3 entities across the ISDN used network interface using D channel.
A service access point (SAP) is a point at which the data link layer provides services to its next higher OSI layer or layer 3.
Associated with each data link layer (OSI layer 2) is one or more data link connection endpoints.
Data link connection endpoint is identified by a data link connection endpoint identifier, from layer 3 and by data link connection identifier (DLDI), as from the data link layer

33. . Layer 3 entity Data Link Layer entity
Data link layer service access point .
Data link connection endpoint
Data Link Layer entity
Data link layer
Entities, service access points (SAPs) and endpoints.

34. Between the data link layer and its adjacent layers there are four types of service primitives;
Request – used where a higher layer is requesting service from the next lower layer
Indication – used by a layer providing service to notify the next higher layer of activities related to the REQUEST primitive

35. Response – used by a layer to acknowledge receipt from a lower layer of the INDICATON primitive
Confirm – the confirm primitive is used by the layer providing the requested service to confirm that the requested activity has been complete

36. FRAME STRUCTURE FOR PEER TO PEER COMMUNICATION
LAYER 2
FRAME STRUCTURE FOR PEER TO PEER COMMUNICATION
There are two frame formats used on layer 2 frames:
Format A, for frames where there is no information field
Format B, for frames containing an information field

38. Flag Field The opening and closing flags are used for frame synchronization. These flag are called the opening and closing flag. If sequential frames are transmitted, the closing flag of one frame is opening flag of the next frame.
Address Field
The address consists of two octets and identifies the intended receiver of a command frame and the transmitter of a response frame.

39. Control Field
Consists of one or two octets. It identifies the type of frame, either command or response. It contains sequence numbers where applicable. There are three (3) types of control field formats.
Information Field
The information field of a frame, follows the control field and precedes the frame check sequence (FCS), contains an integer number of octets