Data Link Protocols, ATM, and Routing Optimization

Data Link Protocols

LAPB, LAPF, and LAPD

These are Data Link protocols:

• LAPB (Link Access Procedure, Balanced): A subset of HDLC, providing asynchronous balanced mode (ABM) for point-to-point links between user systems and packet-switching network nodes.
• LAPF (Link Access Procedure for Frame-Mode Bearer Services): Includes a control protocol (similar to HDLC) and a core protocol (subset of the control protocol). LAPF control uses ABM and 7-bit sequence numbers. LAPF core has flag, address, information, and FCS fields, but no control field.
• LAPD (Link Access Procedure, D-Channel): Provides data link control over the ISDN D channel. Uses ABM, 7-bit sequence numbers, a 16-bit CRC FCS, and a two-part address field for device and logical user identification.

Frame Relay

Frame Relay is a streamlined data link control facility for high-speed packet-switched networks, used as a replacement for X.25.

ATM Adaptation Layer (AAL)

AAL provides streamlined data transfer across high-speed networks using a fixed-length cell format (53 octets/424 bits), unlike Frame Relay, which is based on HDLC.

Zone Routing Protocol (ZRP)

ZRP is a hybrid routing protocol that proactively maintains routes within a local routing zone. This knowledge improves the efficiency of a reactive route query/reply mechanism. ZRP configuration is adjusted by the routing zone radius (r), which defines the zone for each node as including nodes within r hops.

Minimum Spanning Tree (MST)

A tree (T) spans G = (V, E) if T = (V, E_) and E_ º E. An MST is a spanning tree of G with the minimum sum of edge weights.