1. ISDN REFERENCE MODEL

2. BASIC RATE ACCESS (BRI) 2B + D S0 interface B-CHANNEL D-CHANNEL BRI

3. TELEPHONE CALL D-CHANNEL 408-526-1234 CONVERSATION B-CHANNEL END D-CHANNEL

4. E1 PRIMARY RATE INTERFACE (PRI) E1 PRI or S2 interface Used in Europe 30 B + D E1-PRI B-CHANNEL D-CHANNEL

5. REFERENCE POINTS Reference points characterize the different interfaces TE1 NT 2NT1LTET TE 2TA R S T U V TE1 NT1LTET TE 2TA R S T U V

6. POINT TO POINT CONFIGURATION Supported on BRI and PRI Maximum 1 TE Maximum 1 km (BRI) Most straightforward wiring configuaration NT1 Max 1km TE

7. SHORT PASSIVE BUS Only on BRI Maximum 8 TE Each TE can be located anyware along the passive bus Passive bus distance maximum 200 m Distance TE to passive bus maximum 7 - 10 m NT1 Max 7 - 10 m Max 200 m

8. LONG PASSIVE BUS Only on BRI Maximum 8 TE All TE must be concentrated at the last 50 m of the bus Passive bus distance maximum 500 m Distance TE to passive bus maximum 7 - 10 m NT1 Max 7 - 10 m Max 500 m Max 50 m

9. STAR CONFIGURATIONS Only on BRI Maximum 8 TE Passive bus in a box NT1 with multiple S0 ports Distance TE to NT1 maximum 7 - 10 m NT1 Max 7 - 10 m

10. THE DATA LINK LAYER The ISDN network does not impose the use of any data link layer protocol for the B channels On the D channel the use of Q.921 or LAPD is defined LAPD : Link Access Procedure on the D channel Specified in CCITT I.441 and Q.921 Q.921 protocol is used between the TE and the local ISDN switch (not end to end !) TE ET [ NT1LT Q.921 - LAPD

11. Q.931

12. PROGRESS AND ALERTING Optional progress and allerting messages are possible TEET TE SETUP CALL PROCEEDING ALERTING CONNECT ACK PROGRESS CONNECT

13. CALL REFUSED Call can be refused for various reasons TEET TE SETUP RELEASE COMPLETE RELEASE COMPLETE

14. CALL CLEARING Any side can clear the call TEET TE RELEASE COMPLETE RELEASE COMPLETE DISCONNECT