The Data Link Switching Client Access Protocol (DCAP) is an application layer protocol used between workstations and routers to transport SNA/NetBIOS traffic over TCP sessions.
DCAP was introduced to address a few deficiencies by the Data Link Switching Protocol (DLSw). The implementation of Data Link Switching Protocol (DLSw) on a large number of workstations raises the important issues of scalability and efficiency. Since DLSw is a switch-to-switch protocol, it is not efficient when implemented on workstations. DCAP addresses these issues. It introduces a hierarchical structure to resolve the scalability problems. All workstations are clients to the router (server) rather than peers to the router. This creates a client/server model. It also provides a more efficient protocol between the workstation (client) and the router (server).
In a DLSw network, each workstation needs a MAC address to communicate with a FEP attached to a LAN. When DLSw is implemented on a workstation, it does not always have a MAC address defined. For example, when a workstation connects to a router through a modem via PPP, it only consists of an IP address. In this case, the user must define a virtual MAC address. This is administratively intensive since each workstation must have an unique MAC address.
DCAP uses the Dynamic Address Resolution protocol to solve this problem. The Dynamic Address Resolution protocol permits the server to dynamically assign a MAC address to a client without complex configuration.
Protocol Structure
| 4 | 4 | 16 |
| Protocol ID | Version Number | Message Type |
| Packet Length | ||
- Protocol ID - The Protocol ID is set to 1000.
- Version number - The Version number is set to 0001.
- Message type - The message type is the DCAP message type.
- Packet length - The total packet length is the length of the packet including the DCAP header, DCAP data and user data. The minimum size of the packet is 4, which is the length of the header.
Related Terms: TCP, DLSw, NetBIOS
Sponsor Source: DCAP is defined by IETF (http://www.ietf.org) RFC2114.
Reference: http://www.javvin.com/protocol/rfc2114.pdf: Data Link Switching Client Access Protocol (DCAP)