ISDN

1
ISDN

• Raj Jain
• Professor of CIS The Ohio State
  UniversityColumbus, OH 43210http//www.cse.ohio-
  state.edu/jain/

2
Overview

• History
• Interfaces and protocol layers
• Reference points
• Addressing

3
Integrated Digital Networks

• Integrated ? Both transmission and Switching
• Access was still analog

AnalogSwitch
FD M
FD M
AnalogSwitch
FD M
FD M
AnalogSwitch
TDM P C M
TDM P C M
(a) Nonintegrated
DigitalSwitch
DigitalSwitch
DigitalSwitch
(b) Integrated
4
Int. Service Digital Network

• Past IDN Integrated Digital Network ?
  Standardized digital techniques for switching and
  transmission (T1 etc)
• 1980 ISDN ? Integrated access to all services ?
  Digital end-to-end (Digital subscriber loop)
• One set of interfaces for all services at
  multiple speeds
• Supports both circuit switching and packet
  switching
• Out-of-band signaling. Sophisticated network
  management and maintenance using Signaling System
  7 (SS7)
• Layered protocol architecture

5
History

• 1968 Study Group D set by CCITT to study digital
  voice
• 1972 G.702 Integrated digital switching and
  transmission (IDN) concept
• 1976 Digital switching and signaling (SS7) spec
• 1980 G.705 - One page recommendation on ISDN
• 1984 First set of standards in 1984.
  Inconsistent and incomplete.
• 1988 Revised set of standards. Implementation
  feasible.
• 1992 Additional revisions

6
ISDN Architecture

• non-switched ? dedicated ? Permanent

Network
gt64 kbps nonswitched
Possibly ATM
gt64 kbps switched
Subscriber Premises
64 kbps ckt nonswitched
Subscriber or Provider
ISDN Switch
ISDN Switch
TE
NT
64 kbps ckt switched
X.25Packetswitching
User-Networksignaling
Frame Mode
User-Networksignaling
CCS
7
ISDN Channels

• B 64 kbps for data or voice
• D 16 or 64 kbps for signaling or packet switched
  data
• H 384 kbps (H0), 1536 kbps (H11), 1920 kbps (H12)

8
ISDN Access Interfaces

• Basic Rate Interface (BRI) 2B D 2 64 16
  144 kbps (192 kbps total)
• Primary Rate Interface (PRI) For LANs or PBX
• 23 B D 23 64 64 1.536 Mbps ? T1
• 30 B D 30 64 64 1.984 Mbps 5H0D
  E1- 64 kbps Framingmgmt

9
Other PRI Interfaces

• PRI H0
• 3H0D or 4H0 1.544 Mbps
• 5H0D 2.048 Mbps
• PRI H1
• One H11 in 1.544 Mbps
• One H12 in 2.048 Mbps
• PRI for Mixture of B and H0
• 0 or 1 D and any combination of B and H0, e.g.,
  3H05BD or 3H06B for 1.544 Mbps

10
Functional Groupings

• Terminal Equipment 1 (TE1) ISDN terminal
• Terminal Equipment 2 (TE2) Non-ISDN terminal,
  e.g., POT
• Terminal Adapter (TA) Allows non-ISDN devices on
  ISDN
• Network Termination 1 (NT1) Physical layer
  device. Separates user premises from phone
  company. Owned by user in USA. Owned by PTT in
  many countries.
• Network Termination 2 (NT2) OSI layers 2-3,
  e.g., PBX, LAN
• Network Termination 1,2 (NT12) NT1 NT2

11
Functional Groupings

• NT1
• Physical and electrical terminal of ISDN at user
• Isolates the user from the transmission
  technology of the subscriber loop
• Line maintenance functions such as loop back
  testing and monitoring
• Bit multiplexes various B and D channels
• Supports multi-drop lines ? Telephone, personal
  computer, and alarm on one NT1
• NT2 Digital PBX, LAN, Terminal
  controllerSwitching and concentration

12
ISDN Reference Points

• Rate (R) Between Non-ISDN and Terminal Adapter.
  Uses X or V series recommendations.
• System (S) Between ISDN equipment and NT2.
  Separates user equipment from switching
  equipment.
• Terminal (T) Between NT2 and NT1. Separates
  network from user.
• User (U) U interface not defined by ITU.
  Defined in North America since NT owned by user.

S
TE1
NT2
NT1
R
TE2
TA
NT2
NT1
T
TE1 or TE2TA
NT12
U
13
Protocol Reference Model

• Similar to OSI 7-layer model
• Separate user, control, and management planes
• Control signaling
• Management network diagnosis, maintenance, and
  operation

14
ISDN Protocols at UNI
End-to-end user signaling
Application
Presentation
Session
Transport
Q.931
Network
X.25packet
X.25packet
I.465/V.120
LAPB
LAPD
Datalink
I.430 basic or I.431 Primary
Physical
ControlSignaling
Cktswitched
Packet
Semi permanent
PacketSwitched
D Channel
B Channel
15
LAPD

• Link Access Protocol for D Channel
• Similar to HDLC and LAPB
• X.25 packets are transmitted in LAPD frames
• LAPD used for signaling messages

16
ISDN Services

• Six types of services
• Circuit switched calls over a B or H channel
• Semi-permanent connections over a B or H channel
• Packet switched calls over a B or H channel
• Packet switched calls over a D channel
• Frame relay calls over a B or H channel
• Frame relay calls over a D channel

17
ISDN Addressing

• E.164 designed for ISDN allows up to 15 digits
  Superset of E.163 for telephony (12 digits)
• Country code 1 to 3 digits
• National Destination Code Provider ID or Area
  code
• ISDN Address ISDN number ISDN subaddress

National ISDN Number
International ISDN Number (max 15 digits)
ISDN Address (max 55 digits)
18
Other Addressing Structures

• X.121 Data Networks

Zone
Network term. number
Country code
PDN code
Data Network Identification Code
Data country code
National number
Country code
National significant number
9
E.163
Telex destination code
National telex number
8

• ISO 7498

Initial domain identifier
Domain specific part
Authority and format identifier
19
Other Addressing (Cont.)

• IDI Initial domain identifier
• DSP Domain specific part
• AFI Authority and format identifier (Six
  authorities)
• Four ITU controlled Packet-switched Data
  Networks (PSDN), Telex, Packet-switched Telephone
  Networks (PSTN), ISDN.
• Two ISO Controlled
• ISO geographic domain Assigned by countries
• International organization domain, e.g., NATO.
• AFI 44 ? ISDN in decimal, 45 ? ISDN in binary

20
Summary

• B, D, and H channels
• BRI and PRI
• NT1, NT2, TE1, TE2, TA
• R, S, T, and U reference points
• Addressing, E.164, ISO

21
Homework

• Read Chapters 4, 5.1-5.5 of Stallings ISDN book
• Submit answers to Exercise 5.1

22
ISDN Books

• P. Bocker, "ISDN - The Integrated Services
  Digital Network Concepts, Methods, Systems,"
  Springer-Verlag, 1987, 250 pp.
• G.C. Kessler, "ISDN Concepts, Facilities, and
  Services," 2nd Edition, McGraw-Hill, 1993, 454
  pp.
• D.Z. Deniz, "ISDN and Its Application to LAN
  Interconnection," McGraw-Hill, 1994, 254 pp.
• F.R. Goldstein, "ISDN in Perspective,"
  Addison-Wesley, 1991, 246 pp.
• J. Laino, "Telephony for Computer Professionals,"
  Flatiron publishing, 1994, 248 pp.

23
RFCs and Internet Drafts

• RFC 2127, ISDN MIB using SMIv2, March 1997.
• RFC1618, PPP over ISDN, 05/13/1994, 7 pp.
• RFC1356, Multiprotocol Interconnect on X.25 and
  ISDN in the Packet Mode, 08/06/1992, 14 pp.

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25
LAPB vs LAPD

• The first bit of the address field is always 1 in
  LAPB and is always 0 in LAPD. This helps
  distinguish the two frame formats.
• LAPD does not provide selective retransmission.
  It provides only go-back n.
• In both LAPB and LAPD, the command/response bit
  is coded differently in network-to-user and
  user-to-network sides. In analog modems, it
  helped to detect accidental remote loopbacks.
  LAPF uses same coding in both directions.

26
LAPB vs LAPD (Cont)

• LAPB does not support multidrop lines and so does
  not use the address bits. LAPD uses the first six
  bits of the address octet for SAPI to indicate
  the higher layer protocol. For example, SAPI 0
  ? DSS1 layer 3 signaling, 16 ? X.25, 63 ? LMI.
• The terminal endpoint identifier (TEI) is used in
  LAPD to indicate the TE in a multipoint
  connection. For point to point connectons, TEI0.
  TEI127 is broadcast.
• Both LAPB and LAPD use only balanced HDLC
  procedures.

27
LAPB vs LAPD (Cont)

• LAPB, LAPD, and SDLC all use CRC-CCITT. CRC-16
  was used in older protocols, e.g., bisync.

28
ISDN Physical Layer

• BRI S or T reference point (I.430)
• Point to Point 1 km max between TE and NT (NT1
  or NT2)
• Point to multipoint
• TEs anywhere 200 m max
• All TEs at one end 1 km max
• All TEs share the D channel. Only one TE owns B
  channel at a time.
• Pseudo-ternary coding 0 V (alternately) 1 0
  V
• Frame 48 bits every 250 ?s ? 192 kbps 16
  bits of B1, 16 bits of B2, 4 bits of D