Wide Area Networking

1. Wide Area Networking Chapter 7 Halloween Version 1.0

2. Knowledge Checkpoints • Common carriers and the nature of competition • How to improve WAN performance • Factors in selecting WAN services • The role of common carriers in organizational WANs • Four basic categories of WAN circuits • Dialed circuit services • Dedicated circuit services • Switched circuit services • Packet network services

3. Important WAN Terms • Virtual Circuit (VC) • The connection between two frame relay ports • Permanent Virtual Circuit (PVC) • A pre-defined VC • Switched Virtual Circuit (SVC) • A VC that is established dynamically • Data Link Connection Identifier (DLCI) • Virtual Circuit Identification Number

4. WAN ATM X.25 DTE/DCE DSU/CSU Multiplexer Mux Store and forward Frame relay PAD VoFR FRAD SNA CIR Cell More Terms to Learn

5. Checking on a Network Connection Why didn’t the host respond?

6. Tracing the Hops Which line is the router?

7. Introduction • Wide area networks (WANs) connect backbone networks and MANs across longer distances, often hundreds of miles or more • Most organizations cannot afford to build their own MANs and WANs, so they rent or lease circuits from common carriers such as AT&T, MCI, BellSouth, PACTEL or NYNEX

8. The Telephone Network • A common carrier is a private company that sells or leases communications services and facilities to the public • A common carrier that also provides local telephone services is called a local exchange carrier (LEC), while one that provides long distance services is called an interexchange carrier (IXC) • In the United States, 90 percent of the telephone system used to be run by one common carrier, AT&T

9. Comparison of Telco Areas

10. Carrier Service Areas

11. DIALED CIRCUIT SERVICES

12. Differences Between Pvcs And Svcs • SVCs • Dynamically Established When There is Information to Send (Call-by-Call Basis) • Connection is Released When There is No More Information to Send • PVCs • Statically Defined at Configuration, Unless PVC Parameters Need to be Modified • Connection is Always Configured Whether There is Information to Send or Not

13. Dialed Circuit Services • Dialed circuit services are the simplest and one of the most common types of MAN and WAN connection. • This type of connection uses the normal telephone network. To use dialed circuit services, the user simply leases connection points into the common carrier’s network, then dials the host computer using a modem, and connects to the host system. • Dialed circuit services may use different circuit paths between the two computers each time a number is dialed

14. Dialed Circuit Services

15. Direct Dialing • Direct dialing (also called dial-up) is the most commonly used direct circuit service. Every time you call your Internet service provider from your home phone, you are using direct dialing. • Charges for direct dialing are based on the distance between the two telephones (in miles) and the number of minutes the connection is used.

16. Wide Area Telephone Service (WATS) • Wide Area Telephone Service (WATS) are a special rate service that allows direct circuit calls for both voice and data transmission to be purchased in large quantities. • WATS is limited to one direction only; it is either outward dialing or inward dialing. In general, inward WATS uses the toll free 800, 877 and 888 area code series in North America, and similar numbers in other countries.

17. DEDICATED CIRCUIT SERVICES

18. Dedicated Circuit Services • There are two main problems with dialed circuits. • Each connection goes through the regular telephone network on a different circuit, which may vary in quality. • The data transmission rates on these circuits are usually low 28.8 to 56 Kbps. • An alternative is to establish a private dedicated circuit, which the user leases from the common carrier for their exclusive use, 24 hrs/day, 7 days/week.

19. Dedicated Circuit Services

20. Dedicated Circuit Services • Dedicated circuits are billed at a flat fee per month and the user has unlimited use of the circuit. Dedicated circuits require more care in network design than dialed circuits. • There are five types of dedicated circuits: • Voice grade circuits • Wideband analog services • T Carrier circuits • SONET circuits • Digital subscriber line circuits

21. Dedicated Circuits for a WAN

22. Voice Grade Circuits • Voice grade circuits are analog circuits that work in exactly the same manner as traditional telephone lines, except that you do not dial them. • Dedicated voice grade channels often have conditioning (or equalization) done on them to improve data transmission quality by reducing noise and distortion.

23. Wideband Analog Services • Wideband analog services are similar to voice grade circuits but they provide much greater bandwidth. • Typically wideband analog services provide one 48,000 hertz bandwidth channel for use with frequency division multiplexing or as 12 individual voice grade channels (4000 Hz each).

24. T Carrier Circuits • T Carrier circuits are dedicated digital circuits and are the most commonly used form of dedicated circuit services in North America today. • Instead of a modem, a channel service unit (CSU) or data service unit (DSU) are used to connect the circuit into the network.

25. T Carrier Circuits • A T-1 circuit (DS-1 circuit) provides a data rate of 1.544 Mbps. T-1’s allow 24 simultaneous 64 Kbps channels (with TDM) which transport data, or voice messages using pulse code modulation. • A T-2 circuit (6.312 Mbps) is basically a multiplexed bundle of four T-1 circuits. • A T-3 circuit (44.376 Mbps) is equal to the capacity of 28 T-1 circuits. • A T-4 circuit (274.176 Mbps) is equal to the capacity of 178 T-1s. • Fractional T-1, (FT-1) offers portions of a 1.544 Mbps T-1 for a fraction of its full costs.

26. T Carrier System T-Carrier Designation DS Designation Speed T-1 T-2 T-3 T-4 DS-0 DS-1 DS-2 DS-3 DS-4 64 Kbps 1.544 Mbps 6.312 Mbps 44.375 Mbps 274.176 Mbps

27. T-1 Frame Layout

28. Synchronous Optical Network (SONET) • The synchronous optical network (SONET) has recently been accepted by the U.S. standards agency (ANSI) as a standard for optical (fiber) transmission at gigabits per second speed. • The international telecommunications standards agency (ITU-T) also recently standardized a version of SONET under the name of synchronous digital hierarchy (SDH). The two are very similar and can be easily interconnected.

29. Synchronous Optical Network (SONET) • SONET transmission speeds begin at the OC-1 level (optical carrier level 1) of 51.84 Mbps. Each succeeding rate in the SONET fiber hierarchy is defined as a multiple of OC-1. • Several common carriers (MCI) now use OC-12 circuits at 622.08 Mbps to carry digitized voice traffic.

30. SONET OC-1 OC-3 OC-9 OC-12 OC-18 OC-24 OC-36 OC-48 OC-192 51.84 Mbps 155.52 Mbps 466.56 Mbps 622.08 Mbps 933.12 Mbps 1.244 Gbps 1.866 Gbps 2.488 Gbps 9.952 Gbps SONET Designation SDH Designation Speed STM-1 STM-3 STM-4 STM-6 STM-8 STM-12 STM-16

31. SONET Framing

32. NY Information Technology Center

33. Digital Subscriber Line (DSL) • DSL services are new and not all common carriers offer them. • Two general categories of DSL services have emerged in the marketplace. • Symmetric DSL (SDSL) provides the same transmission rates (up to 128 Kbps) in both directions on the circuits. • Asymmetric DSL (ADSL) provides different data rates to (up to 640 Kbps) and from (up to 6.144 Mbps) the carrier’s end office. It includes an analog channel for voice transmissions.

34. Digital Subscriber Line (DSL) • A new version of ADSL called Very high rate Digital Subscriber Line (VDSL) has been designed for use over local loops of 1000 feet or less. It uses FDM to provide three channels: • Normal analog channel • Upstream digital 1.6 Mbps channel • Downstream digital 51.84 Mbps channel.

35. ADSL Technology Implementation

36. CIRCUIT SWITCHED SERVICES

37. Circuit Switched Services • The major problem with dedicated circuit services it that the user must carefully plan all circuits needed. • In contrast, switched circuits work much like dialed circuits. The user buys a connection into the common carrier’s network from the end points of the WAN, without specifying all the interconnecting circuits needed. • The primary differences from dialed circuits is that the circuits are entirely digital and that they offer higher data transmission rates.

38. Circuit Switched Services

39. Narrowband Integrated Services Digital Network • The first generation of Integrated services digital network (ISDN), commonly called narrowband ISDN, combines voice, video, and data over the same digital circuit. • ISDN has long been more of a concept than a reliable service in North America. • Acceptance has been slowed because equipment vendors and common carriers conflicting interpretations of ISDN standards.

40. Narrowband Integrated Services Digital Network • Narrowband ISDN offers two types of service: • Basic rate interface (BRI, basic access service or 2B+D) provides two 64 Kbps bearer (B) channels and one 16 Kbps control signaling (D) channel. • One advantage of BRI is it can be installed over existing telephones lines. (if less than 3.5 miles). • Primary rate interface (PRI, primary access service or 23B+D) provides 23 64 Kbps ‘B’ channels and one 64 Kbps ‘D’ channel. (basically T-1 service)

41. Broadband Integrated Services Digital Network • The second generation of ISDN is called Broadband ISDN (B-ISDN). B-ISDN is a circuit switched service and is backwardly compatible with ISDN. • B-ISDN is currently offered in three services: • Full duplex channel at 155.2 Mbps. • Full duplex channel at 622.08 Mbps. • Asymmetrical service with two simplex channels (Upstream at 155.2 Mbps, downstream at 622.08 Mbps).

42. ISDN • Narrowband ISDN Architecture Information

43. ISDN Technology

44. ISDN Network ISDN Architecture

45. Multiple PVCs per Access Line

46. PACKET SWITCHED SERVICES

47. Packet Switched Services • Packet switched services enable multiple connections to exist simultaneously between computers. • With packet switching users buy a connection into the common carrier network, and connects via a packet assembly/ disassembly device (PAD). • Packet switching splits messages into small segments called packets (usually 128 bytes).

48. Packet Switched Services

49. Packet Switched Services • Packets from separate messages are interleaved with other packets for transmission. • Although the packets from one data stream may mix (interleave) with several other data streams during their journey, it is unlikely that packets from two different data streams will travel together during the entire length of their transmission.

50. Packet Switched Services There are two methods used to route packets: • A Datagram is a connectionless service which adds a destination and sequence number to each packet, in addition to information about the data stream to which the packet belongs. Packets may follow a different route, and are reassembled at the destination. • In a Virtual circuit the packet switched network establishes an end-to-end circuit between the sender and receiver. All packets for that transmission take the same route over the virtual circuit that has been set up for that transmission.