Emerged Technologies
ISDN
Nirmala Shenoy
Information Technology Dept
Rochester Institute of Technology
ISDN
• Purpose
– Digital interface between user and network
– An all digital network to support the transport
for digitized information
– For the user the type of transport network is
transparent, voice, video, data
– ISDN nodes provides this transparency
• Based on technologies used in T1/E1
ISDN
• Topology
– Similar to X.25
– UNI protocol
– Comprises of
• Functional groupings
– Set of capabilities,
– Multiple pieces of equipment or software
ISDN
• Topology
– Comprises of
• Reference Points
– Interfaces between the functional groupings
– Physical interface between two pieces of
equipment
ISDN
• Topology
TE1
NT1
NT2
S
LT/ET
U
T
Network SS7, packet,
cellular, satellite etc
R
TE2
S
TA
T
NT2
NT1
LT/ET
U
ISDN
• Topology
– Functional Groupings
– TE1
• Terminal equipment type 1 – ISDN
compatible equipment
• Uses twisted pair – 4 wire digital link
ISDN
• Topology
– Functional Groupings
– NT2 -Network Termination type 2
• An intelligent equipment, layer 2 & 3
functions
• Concentration, multiplexing of channels to a
defined rate
• Support multiple terminals
ISDN
• Topology
– Functional Groupings
– NT1 -Network Termination type 1
• Connects 4 wire subscriber to 2 wire local loop
• Physical layer – signaling, synchronization and
timing
• TEs can connect direct to NT1 – can address up to 8
TEs
• NT1 + NT2 = NT12 - combined functions
ISDN
• Topology
– Functional Groupings
– TE2 – non-ISDN compatible TE type 2
• Requires an adapter to connect to ISDN
– TA – Terminal Adapter
• provides adaptive function for non-ISDN
terminals
ISDN
• Topology
–
–
–
–
Reference points
S – logical interface between TE and network
R – between non-ISDN TE and adapter
U – 2 wire side of the NT equipment
• TE – user related , NT – Network related
ISDN
• Topology
– TDM based
– 2B + D channels – Basic Rate InterfaceBRI
– B – user data – 64 Kbps
– D – signaling – 16kbs – out-of band
– 8 TE1s can share a 2B+D channel
ISDN
• Topology
– PRI – Primary Rate interface
– 23B + D channels – NA & Japan
• 1.544 Mbps
– 31B + D channels – Europe
• 2.048 Mbps
ISDN
• Layers
Management Plane
User’s choice
End-to-end
signaling
X.25 & others
Q.931
LAPB & others
BRI (I.430)
User Plane
LAPD
&
PRI (I.431)
Control Plane
ISDN
• Layers
– 3 layers, Network, data link and physical
– Physical –
• Basic Rate Interface & Primary Rate Interface
– Data Link layer
• LAPD – Link Access Procedures for D
channel
ISDN
• Layers
– Network Layer – Q.931
• Establishing and releasing connection
ISDN
• PDUs
– LAPD- subset of HDLC
– Carries Q.931 messages
– SAPI – Service Access point identifier
• Port used between adjacent layers
– TEI – Terminal Equipment Identifier
• Identifies one or several TEs
ISDN
• PDUs
– LAPD– SAPI+TEI = DLCI = Data link connection
identifier
ISDN
• PDUs
– Q.931 – signaling protocol
– Four categories
• Establishment
• Tear Down
• Information phase
• Miscellaneous
ISDN
• Conclusions
– Starting problems – policies
– Later problems – upcoming technologies
– LAPD and Q.931 – very useful
contributions