Introducing ISDN ISDN (Integrated Services Digital Network) User-Network Interface (UNI),

Transcription

1 ISDN and DDR CCNA 4

2 Note to instructors If you have downloaded this presentation from the Cisco Networking Academy Community FTP Center, this may not be my latest version of this PowerPoint. For the latest PowerPoints for all my CCNA, CCNP, and Wireless classes, please go to my web site: The username is cisco and the password is perlman for all of my materials. If you have any questions on any of my materials or the curriculum, please feel free to me at (I really don t mind helping.) Also, if you run across any typos or errors in my presentations, please let me know. I will add (Updated date) next to each presentation on my web site that has been updated since these have been uploaded to the FTP center. Thanks! Rick 2

3 Overview Define the ISDN standards used for addressing, concepts, and signaling Describe how ISDN uses the physical and data link layers List the interfaces and reference points for ISDN Configure the router ISDN interface Determine what traffic is allowed when configuring DDR Configure static routes for DDR Choose the correct encapsulation type for DDR Be able to determine and apply an access list affecting DDR traffic Configure dialer interfaces 3

4 Introducing ISDN Telephone companies developed ISDN (Integrated Services Digital Network) as part of an effort to standardize subscriber services. This included the User-Network Interface (UNI), better known as the local loop. The ISDN standards define the hardware and call setup schemes for end-to-end digital connectivity. These standards help achieve the goal of worldwide connectivity by ensuring that ISDN networks easily communicate with one another. In an ISDN network, the digitizing function is done at the user site rather than the telephone company. 4

5 Introducing ISDN Unlike POTS, ISDN is digital from end to end. With asynchronous connections (POTS) the local loop is analog and requires PCM (Pulse Code Modulation) - explained later. Benefits of ISDN include: Carries a variety of user traffic signals, including data, voice, and video Offers much faster call setup than modem connections B channels provide a faster data transfer rate than modems B channels are suitable for negotiated Point-to-Point Protocol (PPP) links 5

6 ISDN Advantages ISDN also provides more bandwidth than a traditional 56 kbps dialup connection. ISDN uses bearer channels, also called B channels, as clear data paths. Each B channel provides 64 kbps of bandwidth. An ISDN connection with two B channels would provide a total usable bandwidth of 128 kbps. Each ISDN B channel can make a separate serial connection to any other site in the ISDN network. ISDN lines can be used in conjunction with PPP encapsulation. 6

7 ISDN Disadvantages BRI is slower than DSL and cable More expensive than DSL and cable Bottom line: ISDN, in its current form, is no longer a firstchoice technology. 7

8 Why 64Kbps channels and what is PCM? This will be explained in a later presentation on T1. For now, 64,000 bps is what s required to carry a single phone call over a link (an analog call which has been digitized). PCM (Pulse Code Modulation) is how the analog signal is translated to digital and visa versa. 8

9 ISDN standards and access methods ITU-T groups and organizes the ISDN protocols according to the following general topic areas: E Protocols Recommend telephone network standards for ISDN. For example, international addressing for ISDN. I Protocols Deal with concepts, terminology, and general methods. Q Protocols Cover how switching and signaling should operate. The term signaling in this context means the process of establishing an ISDN call. 9

10 ISDN standards and access methods ISDN standards define two main channel types The bearer channel, or B channel, is defined as a clear digital path of 64 kbps The second channel type is called a delta channel, or D channel. There can either be 16 kbps for the Basic Rate Interface (BRI) or 64 kbps for the Primary Rate Interface (PRI). 10

11 ISDN standards and access methods ISDN is widely available in two flavors: BRI: Basic Rate Interface 2 64 Kbps Bearer Channels,16 Kbps Delta Channel (for control information), 48 Kbps for framing and synchronization 2B + 1D (2B+D) 192 Kbps = PRI: Primary Rate Interface 23B + 1D (T1), the D channel is 64-kbps 30B + 1D (E1), European E Mbps (North America) or Mbps (E1) 11

12 B Channels The B channels can be used for relatively high-speed data transport. In this mode, the information is carried in frame format, using either HDLC or PPP as the Layer 2 protocol. PPP is more robust than HDLC because it provides a mechanism for authentication and negotiation of compatible link and protocol configuration. 12

13 D Channel When a TCP connection is established, there is an exchange of information called the connection setup. This information is exchanged over the path on which the data will eventually be transmitted. Both the control information and the data share the same pathway. This is called in-band signaling. ISDN however, uses a separate channel for control information, the D channel. This is called out-of-band signaling. The D channel carries signaling messages, such as call setup and teardown, to control calls on B channels. Traffic over the D channel employs the Link Access Procedure on the D Channel (LAPD) protocol. LAPD is a data link layer protocol based on HDLC. 13

14 ISDN 3-layer model and protocols Layer 3 Q.931 Layer 2 Q.921 I like the older chart. ISDN utilizes a suite of ITU-T standards spanning the physical, data link, and network layers of the OSI reference model. The ISDN BRI and PRI physical layer specifications are defined in ITU-T I.430 and I.431, respectively. The ISDN data link specification is based on LAPD and is formally specified in the following, ITU-T Q.920, ITU-T Q.921, ITU-T Q.922, ITU-T Q.923 The ISDN network layer is defined in ITU-T Q.930, also known as I.450 and ITU-T Q.931, also known as I.451. These standards specify user-to-user, circuit-switched, and packetswitched connections. 14

15 BRI Physical Layer BRI service is provided over a local copper loop that traditionally carries analog phone service. While there is only one physical path for a BRI, there are three separate information paths, 2B+D. Information from the three channels is multiplexed into the one physical path. ISDN physical layer, or Layer 1, frame formats differ depending on whether the frame is outbound or inbound. 15

16 BRI Physical Layer These Reference Points will be discussed in a moment, but this is where they get TE and NT from. If the frame is outbound, it is sent from the terminal to the network. Outbound frames use the TE frame format. If the frame is inbound, it is sent from the network to the terminal. Inbound frames use the NT frame format. 16

17 BRI Physical Layer 64k (16*4,000) - B1 channel 64k (16*4,000) - B2 channel 16k (4*4,000) - D channel 48k (12*4,000) Framing/Overhead kbps BRI Total 4,000 frames per second 144 kbps = B1 + B2 + D (2B+D) B1, B2, D and Framing Bits ISDN BRI frames contain 48 bits. Four thousand of these frames are transmitted every second, 4,000 x 48 = 192,000 bps. Each B channel, B1 and B2, have a capacity of 2(8*4000) = 64 kbps, 128 kbps for both B channels (B1 and B2) The D channel has a capacity of 4*4000 = 16 kbps (D) Framing and overhead 12*4,000 = 48,000 kbps. (F, L, E, A, S) 17

18 BRI Physical Layer 4,000 frames per second The overhead bits of an ISDN physical layer frame are used as follows: Framing bit Provides synchronization Load balancing bit Adjusts the average bit value Echo of previous D channel bits Used for contention resolution when several terminals on a passive bus contend for a channel Activation bit Activates devices Spare bit Unassigned 18

19 ISDN Data Link Layer The LAPD flag and control fields are identical to those of HDLC. The LAPD address field is 2 bytes long. Service access point identifier (SAPI), which identifies the portal at which LAPD services are provided to Layer 3. The command/response bit (C/R), indicates whether the frame contains a command or a response. The second byte contains the terminal endpoint identifier (TEI). Each piece of terminal equipment on the customer premises needs a unique identifier. The TEI may be statically assigned at installation, or the switch may dynamically assign it when the equipment is started up. Statically assigned TEIs range from 0 to 63. Dynamically assigned TEIs range from 64 to 126. A TEI of 127, or all 1s, indicates a broadcast. 19

20 ISDN Data Link Layer Router#show isdn status Global ISDN Switchtype = basic-ni ISDN BRI0 interface dsl 0, interface ISDN Switchtype = basic-ni Layer 1 Status: ACTIVE Layer 2 Status: TEI = 64, Ces = 1, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED TEI = 65, Ces = 2, SAPI = 0, State = MULTIPLE_FRAME_ESTABLISHED Spid Status: TEI 64, ces = 1, state = 5(init) spid1 configured, spid1 sent, spid1 valid TEI 65, ces = 2, state = 5(init) spid2 configured, spid2 sent, spid2 valid Layer 3 Status: 1 Active Layer 3 Call(s) Where you see this information. 20

21 Call Setup Not an end-to-end function but processed by the switch. Depending upon the switch type, you may or may not get all of the steps show above. To establish an ISDN call, the D channel is used between the router and the ISDN switch to control functions such as call setup, signaling, and termination. Signal System 7 (SS7) signaling is used between the switches within the service provider network. These functions are implemented in the Q.931 protocol. The Q.931 standard recommends a network layer connection between the terminal endpoint and the local ISDN switch, but it does not impose an end-to-end recommendation. 21

22 Call Setup In detail The following information discusses some of these steps. 22

23 Call Setup 1. The D channel is used to send the called number to the local ISDN switch. 2. The local switch uses the SS7 signaling protocol to set up a path and pass the called number to the remote ISDN switch. 3. The remote ISDN switch signals the destination over the D channel. 23

24 Call Setup (NT-1) (NT-1) 4. The destination ISDN NT-1 device sends the remote ISDN switch a call-connect message. 5. The remote ISDN switch uses SS7 to send a call-connect message to the local switch. 6. The local ISDN switch connects one B channel end-to-end, leaving the other B channel available for a new conversation or data transfer. Both B channels can be used simultaneously. 24

25 ISDN reference points 25

26 ISDN reference points 26

27 ISDN Interfaces To connect devices that perform specific functions, the interface between the two devices needs to be well defined. R References the connection between a non-isdn compatible device Terminal Equipment type 2 (TE2) and a Terminal Adapter (TA), for example an RS-232 serial interface. S References the points that connect into the customer switching device Network Termination type 2 (NT2) and enables calls between the various types of customer premises equipment. T Electrically identical to the S interface, it references the outbound connection from the NT2 to the ISDN network or Network Termination type 1 (NT1). U References the connection between the NT1 and the ISDN network owned by the telephone company. 27

28 ISDN reference points CAUTION: Some routers contain NT1 s. Never connect a router with a U interface into a NT1. It will most likely ruin the interface. Know what type of interface your router has! Gateway U U T S ISDN Cloud NT1 NT2 ISP Gateway S/T NT1 U U S/T R ISDN Cloud NT1 TA ISP Because the S and T references are electrically similar, some interfaces are labeled S/T interfaces. Although they perform different functions, the port is electrically the same and can be used for either function. 28

29 Cisco Interfaces S/T interface requires an NT1 connection. In the United States, the customer is required to provide the NT1. In Europe and various other countries, the telephone company provides the NT1 function and presents an S/T interface to the customer. 29

30 BRI S/T Interface Cisco