1. UNIT I – FRAME RELAY AND ISDN
NETWORK PROTOCOLS
UNIT I – FRAME RELAY AND ISDN

2. Frame Relay Background - X.25
Call control packets, in band signaling
Multiplexing of virtual circuits at layer 3
Layer 2 and 3 include flow and error control
Considerable overhead
Not appropriate for modern digital systems with high reliability

3. Frame Relay - Differences
Call control carried in separate logical connection
Multiplexing and switching at layer 2
Eliminates one layer of processing
No hop by hop error or flow control
End to end flow and error control (if used) are done by higher layer
Single user data frame sent from source to destination and ACK (from higher layer) sent back

4. Advantages and Disadvantages
Lost link by link error and flow control
Increased reliability makes this less of a problem
Streamlined communications process
Lower delay
Higher throughput
ITU-T recommend frame relay above 2Mbps

5. Protocol Architecture

6. Control Plane Between subscriber and network
Separate logical channel used
Similar to common channel signaling for circuit switching services
Data link layer
LAPD (Q.921)
Reliable data link control
Error and flow control
Between user (TE) and network (NT)
Used for exchange of Q.933 control signal messages

7. User Plane End to end functionality Transfer of info between ends
LAPF (Link Access Procedure for Frame Mode Bearer Services) Q.922
Frame delimiting, alignment and transparency
Frame mux and demux using addressing field
Ensure frame is integral number of octets (zero bit insertion/extraction)
Ensure frame is neither too long nor short
Detection of transmission errors
Congestion control functions

8. LAPF Core Formats

9. User Data Transfer One frame type No inband signaling
No control frame
No inband signaling
No sequence numbers
No flow nor error control

10. Primary ISDN Point to point Typically supporting PBX 1.544Mbps
Based on US DS-1
Used on T1 services
23 B plus one D channel
2.048Mbps
Based on European standards
30 B plus one D channel
Line coding is AMI usingHDB3

11. Primary ISDN Frame Formats

12. Sonet/SDH Synchronous Optical Network (ANSI)
Synchronous Digital Hierarchy (ITU-T)
Compatible
Signal Hierarchy
Synchronous Transport Signal level 1 (STS-1) or Optical Carrier level 1 (OC-1)
51.84Mbps
Carry DS-3 or group of lower rate signals (DS1 DS1C DS2) plus ITU-T rates (e.g Mbps)
Multiple STS-1 combined into STS-N signal
ITU-T lowest rate is Mbps (STM-1)

13. SONET Frame Format

14. SONET STS-1 Overhead Octets

15. Statistical TDM In Synchronous TDM many slots are wasted
Statistical TDM allocates time slots dynamically based on demand
Multiplexer scans input lines and collects data until frame full
Data rate on line lower than aggregate rates of input lines

16. Statistical TDM Frame Formats

17. Performance Output data rate less than aggregate input rates
May cause problems during peak periods
Buffer inputs
Keep buffer size to minimum to reduce delay