Wide-Area Networks

1. Wide-Area Networks Remote Access v3.1

2. Overview - Expectations • Over the last several years, web-based applications, wireless devices, and virtual private networking (VPN) have changed expectations about computer networks. • Today corporate networks are accessible virtually anytime from anywhere. • Corporate networks are typically built around one central site that houses key network resources. • It is the job of networking professionals to provide users with remote access to the networks. • Remote users may be working at branch offices or home offices. • They may even be on the road with a laptop or a handheld mobile device.

3. Range of services • Types of available WAN services and costs vary depending on the geographical region and the provider. Budgetary constraints and service availability are often the overriding selection criteria. • There are two basic methods of data communications: • Asynchronous transmission • Synchronous transmission • Typically, synchronous communications are more efficient, but dialup asynchronous transmission is cheaper and more readily available.

4. Asynchronous Transmission • Asynchronous means "without respect to time". • In terms of data transmission, asynchronous means that no clock or timing source is needed to keep both the sender and the receiver synchronized. • Without the benefit of a clock, the sender must signal the start and stop of each character so that the receiver knows when to expect data. • Asynchronous transmission is often described as "character-framed" or "start/stop" communication because this method frames each character with a start and stop bit.

5. Synchronous Transmission • Synchronous means "with time". • In terms of data transmission, synchronous means that a common timing signal is used between hosts. • A clock signal is either: • embedded in the data stream “encoding” • sent separately to the interfaces. • A field of synchronization bits, called a preamble or flag, forms a pattern of alternating ones and zeros. • The receiver uses this pattern to synchronize with the sender. • With sync, data is not sent in individual bytes, but as frames of large data blocks.

6. WAN Services • Service providers offer a variety of synchronous and asynchronous WAN services. • The following services can be grouped into three categories depending on their connection type: • Dedicated or leased-line connectivity such as 56K circuit, T1, T3, OC-12, and recently DSL and cable modem technologies • Circuit-switched networks such as dialup over PSTN or ISDN • Packet-switched networks such as Frame Relay, X.25, and ATM

7. Dedicated connections • A dedicated connection is a continuously available point-to-point link between two sites. • Dedicated connections typically carry high speed transmissions. • Because of the expense associated with building and maintaining transmission facilities, dedicated connections are almost always leased from the telephone company or some other carrier network, “leased lines.” • Leased lines are circuits that are reserved full time by the carrier for the private use of the customer. • The private nature of a dedicated line allows an organization to maximize its control over the WAN connection.

8. Dedicated connections • Because the line is not shared, they tend to be more costly. • The line must be paid for whether or not traffic is being sent over it. • Some services, such as T1, provide a fixed fee for local-loop access for both locations, and then provide a distance fee for linking those two locations. • The cost of maintaining multiple leased lines can add up quickly. • For this reason, most companies find a fully meshed WAN too costly to build using only dedicated lines. • A fully meshed WAN means that every site maintains a connection to every other site.

9. Dedicated connections – DSL & Cable Modems • Two new additions to the category of dedicated connection: • DSL • Cable modems • Very high bit-rate DSL (VDSL) is seen by many as the next step in providing a complete home-communications/entertainment package. There are already some companies, such as U.S. West (part of Qwest now), that offer VDSL service in selected areas. VDSL provides an incredible amount of bandwidth, with speeds up to about 52 megabits per second (Mbps). • Cable modems transfer data across local cable TV lines, toggling between analog and digital signals with data transfer rates comparable to DSL, cable modems (256k to 11 Mbps)!

10. CSU/DSU - Channel service unit / Data Service Unit • The CSU/DSU provides signal timing for communication and is used for interfacing with the digital transmission facility. • Essentially, the CSU/DSU is used by a router to connect to a digital line in much the same way that a PC uses a modem to connect to an analog line. • A CSU/DSU for T1 will typically provide: • Framing: ESF, D4(SF) • Line Coding: AMI, B8ZS • Multiplexing • Cabling to Router: V.35, RS-232 • (more on these later) To router To T1 circuit

11. CSU/DSU Interface Card • The CSU/DSU may also be built into the interface card in the router.

12. Circuit-switched connections • A circuit-switched network temporarily establishes a dedicated physical circuit for each communication session. • Switched circuits are established by an initial set-up signal. This process determines the caller ID, the destination ID, and the connection type. • A teardown signal disconnects the circuit when transmission is complete. • Anyone who pays a long distance phone bill knows that circuit-switched connections can be costly if left continuously established. • For this reason, routers connected to circuit-switched networks are configured to operate using dial-on-demand routing (DDR). POTS and ISDN (BRI/PRI)

13. Asynchronous dialup connections Primary remote access services Load balancing when needed Backup to a primary service

14. ISDN connections • Integrated Services Digital Network (ISDN) connections are typically synchronous dialup connections. • Like asynchronous dialup connections, ISDN provides WAN access when needed, rather than providing a permanent link. • ISDN offers more bandwidth than asynchronous dialup connections, and is designed to carry data, voice, and other traffic across a digital telephone network. • BRI service is provided over a local copper loop that traditionally carried analog phone service. The maximum length of most ISDN local loops in North America is approximately 5.5 kilometers (18,000 feet or 3.41 miles). • We will discuss ISDN in more detail in a later module.

15. Packet-switched networks • Unlike leased lines and circuit-switched connections, packet switching does not rely on a dedicated, point-to-point connection through the carrier network. • Instead, data packets are routed across the carrier network based on addressing contained in the packet or frame header. • Packet-switched WAN facilities can be shared with other customers • Typically, customers connect to the packet-switched network via a leased line, such as a T1 or fractional T1. • Frame Relay is the most common packet-switched WAN service in the United States, although ATM is widely used, and the older X.25 remains a prominent packet-switching technology worldwide.

16. Packet-switched networks • Packet-switched networks offer an administrator less control than a point-to-point connection. • However, the cost of a packet-switched VC is generally less than that of a leased line because the WAN facilities are shared. • A Frame Relay VC offers speeds of up to T3. • Multiplexing in a packet-switched network is made possible because a DTE (usually a router) encapsulates the packet with addressing information. • The ability to multiplex means that a single router port and CSU/DSU can support dozens of VCs, each leading to a different site. • Therefore, packet-switching makes a full or partial-mesh topology relatively affordable.

17. Packet-switched networks - ATM • Another popular packet-switching technology is Asynchronous Transfer Mode (ATM). • ATM is the international standard for cell relay in which multiple service types, such as voice, video, or data, are conveyed in fixed-length cells of 53-bytes. • Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays. • ATM is designed to take advantage of high speed transmission media, such as E3, SONET, and T3. • ATM is not studied in this course.

18. WAN protocols • Point-to-Point Protocol (PPP) –Standards-based protocol for router-to-router and host-to-network connections over synchronous and asynchronous circuits. • Serial Line Internet Protocol (SLIP) – SLIP is the forerunner to PPP • High-Level Data Link Control (HDLC) – HDLC implementations are proprietary, so Cisco HDLC is typically used only when connecting two Cisco devices. • X.25/LAPB – X.25 provides extensive error detection and windowing features because it was designed to operate over error-prone analog copper circuits. Other WAN protocols besides Frame Relay and ATM

19. Choosing a WAN connection • It is important to note that WAN usage costs are typically 80 percent of the entire Information Services budget for a company. • When possible, many different WAN service providers should be looked at. • There are other important factors to consider when choosing a WAN service, including ease of management, quality of service (QoS), and reliability. • Leased lines are easier to manage and configure than packet-switched connections. • In terms of QoS, some applications, such as Voice over IP (VoIP), require guaranteed bandwidth, minimal delay, and high reliability, which can make anything short of a leased line problematic.

20. Identifying site requirements and solutions • When selecting WAN services, a networking professional must evaluate the needs of each site within a company.

21. Central site considerations • The central site is the focal point of a company network. • Typically, all remote sites and users must connect to the central site to access information, either intermittently or continuously. • Because many users access this site in a variety of ways, a router at a central site should have a modular design so that interface modules can be added or swapped as needed.

22. Branch office considerations • A branch office, commonly referred to as a remote site, typically maintains at least one WAN connection to the central site and may have several links to other remote sites. • Generally, branch office networks support fewer users than the central site and therefore require less bandwidth. • Because remote site traffic can be sporadic or bursty, it will be important to determine whether it is more cost-effective to offer a permanent or dialup solution. The

23. Telecommuter site considerations • Over the past decade the improvement of WAN technologies, notably DSL and cable modems, has allowed many employees to do their jobs remotely. • As a result, the number of telecommuters and small offices has increased. • As with the corporate and branch office solutions, the telecommuter site WAN solution should be selected by weighing cost and bandwidth requirements.

24. Routers • Cisco offers access servers, routers, and other equipment that allow connection to various WAN services.

25. Fixed interfaces • Asynchronous serial – Supports asynchronous dialup connections using a modem • Synchronous serial – Supports leased lines, Frame Relay, and X.25 • High-speed serial interface (HSSI) – Supports high-speed serial lines, such as T3 • BRI – Supports ISDN BRI connections • T1 or E1 – Supports connections such as leased lines, dialup, ISDN PRI, and Frame Relay • DSL – Supports Asymmetric Digital Subscriber Line (ADSL), Symmetric DSL (SDSL), or ISDN DSL (IDSL) connections • ATM – Supports ATM connections • Cable – Depending upon the model of the Cisco router, an F-connector interface or an Ethernet interface connected to a cable modem may be used • The router that is selected for the WAN connection must offer the interfaces that will support the WAN service.

26. Modular Interface • The modular router allows the networking professional to choose some or all of the interfaces on the router by installing various feature cards, network modules, or WAN interfaces. • Although modular routers require that each interface card be purchased separately, they are more scalable than their fixed configuration counterparts. • For that reason, modular routers are typically installed at large remote sites and should always be used at the central site. • In the long run, it is cheaper to add new interface modules rather than to replace an entire router.

27. Network overview • Diagram presents three routers in a company network, one at the central site, one at the branch office, and one at a telecommuter site. • Each of these sites has different requirements in terms of bandwidth and availability.

28. Central site router equipment - 3600 • The 3600 series replaces the legacy 4000 series routers. Like the newer 3600 series, Cisco 4000 series routers are modular and can support many variations of protocols, line speeds, and transmission media. • To meet the requirements of a central site, a modular router that will allow for growth should be selected. • Cisco 3660 • Cisco AS5300 • Cisco 7200

29. Central site router equipment – AS5300 Modem pool of 282 modems at UC Irvine • The Cisco AS5x00 series access servers combine the functions of an access server, a router, and analog and digital modems in one chassis. • They provide a high level of scalability and multiprotocol capabilities for both ISPs and enterprises.

30. Central site router equipment - 7200 • The Cisco 7200 series routers allow for maximum scalability and flexibility, by combining high performance hardware and software with a modular design. • The 7200 series supports any combination of Ethernet, Fast Ethernet, Token Ring, Fiber Distributed Digital Interface (FDDI), ATM, serial, ISDN, and HSSI interfaces.

31. Branch office router equipment • In contrast to the central site solution, the branch office router needs only one primary WAN connection and a second WAN interface for dial backup. • The branch router must have the following interfaces: • Serial interface for Frame Relay connections • BRI interface for ISDN BRI • Cisco 1600, 1700, 2500, 2600

32. Branch office router equipment - 1600 • The Cisco 1600 series routers are designed to connect small offices with Ethernet LANs to the public Internet. • The Cisco 1601 R - 1604 R models have an Ethernet port, a built-in WAN port, and a slot for an optional second WAN port. • The 1605 R router has two Ethernet ports and one WAN slot. • 1601 – one Ethernet, one serial, one WAN interface card (WIC) slot • 1602 – one Ethernet, one serial with integrated 56-kbps DSU/CSU, one WIC • 1603 – one Ethernet, one ISDN BRI (S/T interface), one WIC • 1604 – one Ethernet, one ISDN BRI with integrated NT1 (U interface), one S-bus port for ISDN phones, one WIC slot • 1605 – two Ethernet slots, one WIC slot

33. Branch office router equipment - 1700 • The Cisco 1700 router is a small, modular desktop router that links small- to medium-size remote Ethernet and FastEthernet LANs over one to four WAN connections to regional and central offices. • Note: The 1600 and 1700 FastEthernet interfaces do not support VLAN trunking (IEEE802.1Q or ISL).

34. Branch office router equipment - 2500 • The Cisco 2500 series routers provide a variety of models that are designed for branch office and remote site environments. • These routers are typically fixed-configuration with at least two of the following interfaces, Ethernet, Token Ring, Synchronous serial, or ISDN BRI.

35. Branch office router equipment - 2600 • The Cisco 2600 series of modular routers features single or dual fixed LAN interfaces, a network module slot, two Cisco WAN interface card (WIC) slots, and a new Advanced Integration Module (AIM) slot. • LAN support includes 10/100 Mbps auto sensing Ethernet and Token Ring. WAN interface cards support a variety of serial, ISDN BRI, and integrated CSU/DSU options for primary and backup WAN connectivity. • The AIM slot supports integration of advanced services such as hardware-assisted data compression and data encryption for optimizing the 2600 series for VPNs.

36. Telecommuter site router equipment • Telecommuter site should have an ISDN BRI connection to the branch or central sites, Cisco 700, 800, 1000 series. • Today’s networks this might also include DSL, Cable Modem or second Ethernet interface (to connect to a separate DSL/Cable Modem. • The mobile user requires an asynchronous dialup connection to the central site.

37. Telecommuter site router equipment - 700 • The Cisco 700M family products are low cost, easy-to-manage multiprotocol ISDN access routers. • These devices provide small professional offices, home offices, and telecommuters with high speed remote access to enterprise networks and the Internet. • However, the 700 series does not support the Cisco IOS.

38. Telecommuter site router equipment - 800 • Cisco 800 Series router is the entry level platform that, unlike the 700 series, contains Cisco IOS technology. • The fixed configuration 800 series is designed to connect a small Ethernet LAN to a corporate network or ISP. • Various models include support for DSL, ISDN, and serial connections.

39. Telecommuter site router equipment - 1000 • The Cisco 1000 series routers are easy-to-install, inexpensive, multiprotocol access products, designed for small offices. • This IOS-based series currently includes three models: the 1003, 1004, and the 1005.