B-channel
In the Integrated Services Digital Network (Integrated Services Digital Network), the B-channel is the channel that carries the main data. (The "B" stands for "bearer" channel.)
In ISDN, there are two levels of service: the Basic Rate, intended for the home and small enterprise, and the Primary Rate, for larger users. Both rates include a number of B (bearer) channels and a D-channel. The B channels carry data, voice, and other services. The D channel carries control and signaling information.
The Basic Rate consists of two 64 Kbps B channels and one 16 Kbps D channel. Thus, a Basic Rate user can have up to 128 Kbps service. The Primary Rate consists of 23 B channels and one 64 Kpbs D channel in the United States or 30 B channels and 1 D channel in Europe.
Pacific Bell, which offers ISDN to users in urban areas of California, provides an introduction to ISDN as part of their Web site.
BRON :
http://whatis.techtarget.com/WhatIs_Definition_Page/0,4152,211646,00.html
X.25
The X.25 protocol, adopted as a standard by the Consultative Committee for International Telegraph and Telephone (CCITT), is a commonly-used network protocol. The X.25 protocol allows computers on different public networks (such as CompuServe, Tymnet, or a TCP/IP network) to communicate through an intermediary computer at the network layer level. X.25's protocols correspond closely to the data-link and physical-layer protocols defined in the Open Systems Interconnection (OSI) communication model.
BRON :
http://whatis.techtarget.com/WhatIs_Search_Results_Exact/1,282033,,00.html?query=x.25
OSI -->
http://whatis.techtarget.com/WhatIs_Definition_Page/0,4152,212725,00.html
:strip_exif()/u/10335/1.gif?f=community)
nee het is lunchtijd. Duh 
