ISDN Planes ISDN Layer Architecture

As with every technology, the ISDN architecture creates a framework for more informed decision making, including appropriate investments in network technologies, products, and services. The CCITT defines the ISDN architecture to consist of four planes:

• T-plane—Transport plane

• M-plane—Management plane

The C-plane primarily deals with UNIs and establishing and tearing down the calls, and, the U-plane deals with User-Network data carried by the B channel. When troubleshooting ISDN, it is important to remember how the ISDN protocol architecture relates to the OSI reference model. Unlike other technologies, ISDN covers the physical, data link, and network layers, which match the first three layers of the OSI model. The three protocol layers for the B and D channel are defined in the following list and in Table 9-1:

• Layer 1—Defines the physical connection between the terminal equipment (TE) and the network termination (NT) including connectors, linecoding schemes, framing, and electrical characteristics. The physical connection can be point-to-point or point-to-multipoint with a short or extended passive bus.

• Layer 2—Describes the LAPD, also known as Q921, which provides error-free communication over the physical link and defines the communication between the user and the network. It also defines the rules for multiplexing in point-to-multipoint implementations.

• Layer 3—Defines the signaling messages for the initial call setup and the termination of the call as defined in Q.931.

Table 9-1 OSI and ISDN Layers

Related Posts

• ISDN Channels - Remote Access Networks
• ISDN Protocols - Interface Ethernet
• E1 Physical Characteristics
• ISDN Media Types - Voice over IP
• Pseudo Ternary Line Coding and the ST Interface
• Spoofing - Remote Access Networks
• Study Material For Cisco Students
• Outsourcing Your Business
• Vector Art, Images, and Graphics Download
• Excel Secrets Everyone Should Know
• Computer Repair Mastery Course

OSI Layer	ISDN Layer	ISDN Protocols	Description	Channel
Physical	Layer 1	I.430	Layer-1 specifications	Shared between
		I.431	PRI	B and D
				channels
		I.432	BRI

Table 9-1 OSI and ISDN Layers (Continued)

OSI Layer	ISDN Layer	ISDN Protocols	Description	Channel
Data Link	Layer 2	Q.920(I.440) Q.921(I.441) Q.921bis	Data link layer general aspects LAPD specifications LAPD conformance testing	D channel
		Point-to-Point Protocol (PPP), (high-level data link control (HDLC)		B channels
Network	Q.931 (I.450) Q.931bis Q.932 (I.451)	Layer-3 general aspects Basic call control Conformance testing Supplementary services	D channel
		AppleTalk, Connectionless Network Service (CLNS), DECnet, Internet Protocol (IP), Internetwork Packet Exchange (IPX), Banyan Virtual Integrated Network Service (VINES), Xerox Network Systems (XNS)		B channel

In the point-to-point physical connections, the NT (NT1 or NT2) and the TE (TE1 or TA) can be 1 km (3300 ft) apart. The passive bus (no repeaters or any active devices) point-to-multipoint design allows up to eight devices to be connected to a single NT on a bus length that can be up to 200 m (667 ft). The extended bus supports up to eight devices clustered together at the end of the passive bus and can be up to 1 km (3300 ft) apart from the NT.

The sections that follow discuss all three ISDN layers in greater detail.

Continue reading here: Layer 1 BRI

Was this article helpful?

0 0