What is ISDN?• ISDN stands for Integrated Services Digital Network.• It is a design for a completely digital telephone/telecommunications network.• It is designed to carry voice, data, images, video, everything you could ever need.• It is also designed to provide a single interface (in terms of both hardware and communication protocols) for hooking up your phone, your fax machine, your computer, your videophone, your video-on-demand system.
ISDN Benefits• Carries a variety of user traffic, such as digital video, data, and telephone network services, using the normal phone circuit-switched network• Offers much faster call setup than modems by using out- of-band signaling (D channel) – Often less than one second• Provides a faster data transfer rate than modems by using the 64-kbps bearer channel (B channel) – Can combine multiple B channels to bandwidth of 128 kbps
Two Types of ISDN “Channels"or Communication Paths1. B-channel2. D-channel
1. B-channel• The Bearer ("B") channel is a 64 kbps channel which can be used for voice, video, data, or multimedia calls.• B-channels can be aggregated together for even higher bandwidth applications.
2. D-channel• The Delta ("D") channel can be either a 16 kbps or 64 kbps channel used primarily for communications (or "signaling") between switching equipment in the ISDN network and the ISDN equipment at your site.
1. Basic Rate Interface (BRI)• BRI is the ISDN service most people use to connect to the Internet.• An ISDN BRI connection supports two 64 kbps B-channels and one 16 kbps D-channel over a standard phone line.• BRI is often called "2B+D" referring to its two B-channels and one D-channel.• The D-channel on a BRI line can even support low-speed (9.6 kbps) X.25 data, however, this is not a very popular application in the United States.
2. Primary Rate Interface(PRI)• ISDN PRI service is used primarily by large organizations with intensive communications needs.• An ISDN PRI connection supports 23 64 kbps B- channels and one 64 kbps D-channel (or 23B+D) over a high speed DS1 (or T-1) circuit.• The European PRI configuration is slightly different, supporting 30B+D.
ISDN Devices• Terminal Adapter (TA) - Converter device that converts standard electrical signals into the form used by ISDN - allows non-ISDN devices to operate on an ISDN network.• Terminal Equipment Type 1 (TE1) - Compatible with the ISDN network. Example: Telephones, personal computers, fax machine or videoconferencing machine.• Terminal Equipment Type 2 (TE2) - Not compatible with the ISDN network. Example: Analog phone or modem, requires a TA (TE2 connects to TA).• Network termination type 1 & 2 (NT1 and NT2) - A small connection box that physically connects the customer site to the Telco local loop, provides a four-wire connection to the customer site and a two-wire connection to the network (PRI – CSU/DSU).
ISDN Reference Points• U - Two wire cable that connects the customer’s equipment to the telecommunications provider• R - Point between non-ISDN equipment (TE2) and the TA• S - Four-wire cable from TE1 or TA to the NT1 or NT2• T - Point between NT1 and NT2
Digital Subscriber Line – DSL• DSL technology provides high-speed, broadband network connections to homes and small businesses.• DSL utilizes the same cabling used for normal telephones, but it can offer higher data rates through use of the digital modem technology.
DSL• DSL modems comprise the heart of this technology and the lines themselves are actually just plain telephone lines.• Its possible for DSL subscribers to share the same line for their digital and analog traffic play web + receive a call.
DSL Technology• Speed – DSL offers more than 100 times the network performance of a traditional analog modem. – the precise speed of a connection depends on the variety of xDSL deployed. – DSL is a distance-sensitive technology.
DSL Technology• DSL works on the unused (high) frequencies of the telephone line.• DSL modems contain an internal signal splitter that carries voice signals on the usual low frequencies (from 0 up to 4kHz) and data signals above that.• This splitter, consequently, allows simultaneous access to the line by the telephone and the computer.
DSL Technology• Access – DSL service remains "on" all of the time. – People should be aware that long-lived connections like DSL can have security issues firewall.
DSL Technology• Availability – The technology used to implement DSL only works over a limited physical distance. At the maximum, DSL runs about 18,000 feet (3.5 miles or 5.5 kilometers) from a telephone exchange.
DSL Technology• Availability (cont.) – To be eligible for DSL service, the phone line involved must be "qualified." – the home or business must lie within the distance limitations of DSL (18,000 feet). – This phone line must also possess sufficient electrical quality characteristics.
DSL Availability ofBandwidth• The actual network bandwidth a customer will receive from DSL in the home depends on the span of their telephone wiring.• The longer the line, the less bandwidth DSL can support.• Likewise, its thickness (wire gauge) can affect performance.
xDSL family tree• The xDSL "family tree" includes two main branches – Symmetric DSL services provide identical data rates upstream and downstream. – Asymmetric DSL provides relatively lower rates upstream but higher rates downstream.
xDSL Family Tree• ADSL, G.Lite and RADSL• HDSL, SDSL, and SHDSL• VDSL (VADSL, BDSL)• IDSL
ADSL• Asymmetric Digital Subscriber Line was designed to provide higher downstream data rates at the expense of upstream rates.• ADSL is technically capable of up to 6 Mbps (roughly 6000 Kbps), but the service customers actually receive generally performs at 2 Mbps or lower for downloads and 512 Kbps for uploads.
ADSL• Example: – Many typical uses of the Web -- such as file downloads and general web browsing -- benefit from greater downstream bandwidth but require relatively little in the opposite direction.
G.Lite• Universal ADSL (also known as G.Lite) is a form of ADSL that improves on one of the weaknesses of regular ADSL -- installation.
ADSL & G.Lite• Regular ADSL generally requires a technician visit to the client site to install the splitter device that divides the frequency spectrum for voice and data.• G.Lite does not require that this splitter be installed, but it does so at the expense of lower data rates.
ADSL & G.Lite• G.Lite supports a maximum of 1,544 kbps (384 kbps upstream)• Whereas regular ("full-rate") ADSL can support more than 8,000 kbps.
RADSL• Rate-Adaptive DSL (RADSL), is an implementation of ADSL that automatically configures the modem at startup to adjust its rate according to the quality of the phone line.• Like G.Lite, RADSL supports a much lower maximum date rate (1,088 kbps) than regular ADSL.
HDSL• High Bit / Data-Rate DSL (HDSL) offers the same bandwidth both upstream and downstream.• HDSL requires two phone lines to deliver the basic data rate (1,544 kbps),• It can deliver a maximum rate of 2,048 kbps using three lines.
SDSL• Symmetric DSL(SDSL) improves on the older HDSL technology by implementing the same basic data rate (1,544 kbps) while requiring only a single phone line.• SDSL supports data rates up to 3,088 Kbps.
SHDSL• Symmetric High-Bit-Rate DSL (SHDSL) attempts to improve on both HDSL and SDSL by only requiring a single line and by integrating low-level services of interest to small businesses.• SHDSL technology can transport data symmetrically at data rates from 192 Kbps to 2,320 Kbps.
VDSL (BDSL)• Very High Data-Rate DSL (VDSL) originally named VADSL (A for asymmetric) but later was extended to support both symmetric and asymmetric varieties of DSL.• VDSL relies on fiber optic cabling.
VDSL• VDSL needs shorter cable lengths than most other forms of DSL (maximum 4,500 feet as compared to 18,000 feet for regular ADSL), but it also achieves the highest data rate (roughly 51,840 kbps).
VDSL• The bandwidth levels supported by VDSL are needed to support certain high-end applications such as High-Definition Television (HDTV) that requires, for example, up to 20,000 kbps.
VDSL• The performance of VDSL depends significantly on the physical distance traversed by wiring: Shorter distances mean faster networking.
IDSL• ISDN DSL (IDSL) implements a hybrid DSL/ISDN solution.• IDSL offers only limited data rates (128 kbps, although multiple circuits may be bonded).
DSL & Cable Modem• Speed – Cable modem generally wins the speed battle over DSL. – Cable technology can, in theory, achieve networking speeds of approximately 30 Mbps (using a 100 Mbps NIC) – Most forms of DSL cannot reach 10 Mbps.
DSL & Cable Modem• Speed (cont.) – cable modem technology delivers shared bandwidth within the local neighborhood – DSL delivers dedicated local bandwidth.
DSL & Cable Modem• Security – At Northwestern University, Kellogg Information Systems – “If ease of installation is important to you, KIS suggests a cable modem over DSL. The slightly more secure environment offered by DSL is not enough to justify the added cost and installation hassle."
DSL & Cable Modem• Security (cont.) – Many DSL and cable modem customers choose to purchase routers to protect their internal systems.