ICT–BVF 4.1 Telecommunication Network Structure Information & Communication Technology Module:ICT–BVF–4.1 fundamentals of Telecommunication Unit:ICT–AS–4.2 Telecommunication Network Structure TTC Riyadh, ICT - BVF – 4.21 Structure of the PSTN Hassan Mesfer ICT-TE-7

2 Public Switched Telephone Network - PSTN PSTN – Public Circuit-Switched Telephone Network –A global circuit switched telephone network –Originally a network of fixed-line analog telephone systems –Now almost entirely digital in its core – Includes mobile as well as fixed (plain old telephone service - POTS) telephones –Hierarchical structure TTC Riyadh, ICT - BVF – 4.111/20/2015

3 Three major component of the telephone network: –User equipments Enable users to access the PSTN (different phones, fax machines) –Switching offices (telephone exchanges or centers) Call forwarding, routing and management –Connection links Used to connect users to the network as well as switching offices to each other Local loops –Connect users to the network –Analog twisted pairs are used in houses and commercial buildings –Asymmetric Digital Subscriber Lines (ADSL), Modems –Wireless Trunks –Connects switching offices to each other – Use fiber optics, coaxial cable, free space (wireless) Structure of the PSTN TTC Riyadh, ICT - BVF – 4.1

11/20/2015TTC Riyadh, ICT - BVF – 4.14 Figure 1 : A typical structure of the telephone network Structure of the Telephone Network

5 End Office or Local Telephone Exchange Somewhere near to our houses is a local phone company's “end office“ or local telephone exchange. All of the telephone lines (wires) in our home or office connect directly to this telephone exchange or office. The end office contains a "switch“ –Device which route, or switch, telephone traffic from one destination to another. The end office is the gateway to the public telephone network which provides: –Connection to users telephone, dial tone, ringing, and connection to long distance carriers. – Features such as call waiting, call forwarding, call transfer, conferencing, caller id, and voic may also be available at the local phone company's end office. TTC Riyadh, ICT - BVF – 4.1 Structure of the Telephone Network

11/20/2015TTC Riyadh, ICT - BVF – 4.16 Each telephone has two copper wires (local loop) coming out and is connected to end office Each end office has number of outgoing links and is connected nearby switching centers (toll offices – tandem exchange) by using toll connecting trunks. If both calling and called subscribes do not belong to the same toll office, the path between them will be established somewhere higher up in the hierarchy. Structure of the Telephone Network

11/20/2015TTC Riyadh, ICT - BVF – 4.17 Structure of the Telephone Network Figure 2 : Lines, trunks and switches

11/20/2015 TTC Riyadh, ICT - BVF – Figure 3 : AT&T PSTN Office Classification Hierarchy Structure of the Telephone Network

9 Local Telephone Calls –Local telephone calls within a municipal area are often completed within a single end office; –If the call is destined for a telephone which is served by the same end office that serves the calling telephone: The end office simply switches the call from the incoming line to the destination line as defined by the called number. The end office does this by analyzing the dialed numbers. TTC Riyadh, ICT - BVF – 4.1 Structure of the Telephone Network

10 Local Telephone Calls (continued) –A local telephone call in a large metropolitan area will often be completed by two end offices. –If the number called is not served by the called end office, but is served by another local end office (almost always operated by the same local telephone company) The call is routed over trunks (lines between switches) to the tandem office and then to appropriate end office, as defined by the called number. The destination end office again analyzes the called number, and switches the call to the appropriate phone line. TTC Riyadh, ICT - BVF – 4.1 Structure of the Telephone Network

11/20/2015TTC Riyadh, ICT - BVF – Figure 4: Public switched telecommunication network Trunk exchange Trunk exchange DSLAM ADSL Structure of the PSTN

Figure 5 : Point-to-point communication network with n=5 users Subscribers need to communicate to many other subscribers all over the world For direct connection of a subscriber to n other subscribers n(n-1)/2 links are required  This is physically not possible  If it is possible, it is very expensive Solution to this problem is introduction of the switch  The increase in the size of the network (number of switches) is proportional to the increase of the number of devices at CPE  Thus increases the cost of maintaining in the network. The Switch TTC Riyadh, ICT - BVF – 4.1

11/20/2015TTC Riyadh, ICT - BVF – The Switch to/from other locations Local Exchange (switch) Figure 6 : Switched network

11/20/ Switching techniques Data Circuit Switching –path is established for the entire duration of the connection for information transmitting Figure 7: Circuit switched data transfer. TTC Riyadh, ICT - BVF – 4.1

11/20/ Switching techniques Data Packet Switching –message switching was modified as packet switching for data transmission by dividing long message into smaller parts (called as packets) –bandwidth is allocated dynamically for each packet so that many users can share the same link Figure 8: Packet switched data transfer. TTC Riyadh, ICT - BVF – 4.1

PSTN EU – End User Equipment – Voice Transmission 16 TTC Riyadh, ICT - BVF – 4.1

Multi user High Speed Internet Access 17 TTC Riyadh, ICT - BVF – 4.1 PSTN EU – End User Equipment

– Fax Transmission 18 TTC Riyadh, ICT - BVF – 4.1 PSTN EU – End User Equipment

11/20/ Telephone Line Bandwidth Figure 11: Telephone Line bandwidth allocation diagram For voice 300 Hz – 3400 Hz range is used For integrity of data, edges of this range are not used  The range used for data is 600 Hz – 3000 Hz = 2400 Hz TTC Riyadh, ICT - BVF – 4.1

11/20/ Modulation and Demodulation Figure 12: Modulation and Demodulation in Telephone Network TTC Riyadh, ICT - BVF – 4.1

11/20/ Modem : Modulator- Demodulator Modulator : converts the binary data into bandpass analog signal. Demodulator : recovers the binary data from the modulated signal codec – coder, decoder Figure 13: Use of analog and digital transmission for a computer to computer call. TTC Riyadh, ICT - BVF – 4.1

11/20/ Digital Subscriber Lines - 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. It's possible for DSL subscribers to share the same line for their digital and analog traffic  play web + receive a call. DSL modems comprise the heart of this technology and the lines themselves are actually just plain telephone lines. TTC Riyadh, ICT - BVF – 4.1

11/20/ 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 Digital Subscriber Lines - DSL TTC Riyadh, ICT - BVF – 4.1

11/20/ Figure 14 : DSL Modem Digital Subscriber Lines - DSL TTC Riyadh, ICT - BVF – 4.1

11/20/ 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. Digital Subscriber Lines - DSL TTC Riyadh, ICT - BVF – 4.1

11/20/ Access –DSL service remains "on" all of the time. –People should be aware that long-lived connections like DSL can have security issues  firewall. 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. Digital Subscriber Lines - DSL TTC Riyadh, ICT - BVF – 4.1

11/20/ Asymmetric Digital Subscriber Lines-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. TTC Riyadh, ICT - BVF – 4.1

11/20/ High Bit / Data-Rate DSL 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. TTC Riyadh, ICT - BVF – 4.1

11/20/ Symmetric DSL - 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. TTC Riyadh, ICT - BVF – 4.1

11/20/ Symmetric High-Bit-Rate DSL - 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. TTC Riyadh, ICT - BVF – 4.1

11/20/ Very High Data-Rate DSL - VDSL 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 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). TTC Riyadh, ICT - BVF – 4.1