ITEC 275 Computer Networks – Switching, Routing, and WANs

1. ITEC 275 Computer Networks – Switching, Routing, and WANs Week 10 Robert D’Andrea Some slides provide by Priscilla Oppenheimer and used with permission

2. Agenda • Learning Activities • PPP • Cable Modems and DSL • Leased Lines, SONET, Frame Relay, Metro Ethernet, ATM • Selecting a WAN Service Provider

3. Enterprise Technologies and Devices • Remote access networks • Wide area networks (WANs) • Devices • End user remote access devices • Central site remote access devices • VPN concentrators • Routers

4. Selection Criteria • Business requirements and constraints • Cost • Technical goals • Bandwidth requirements • QoS requirements • Network topology • Traffic flow and load • Etc.

5. Remote Access Technologies • The Point-to-Point Protocol (PPP) • Integrated Services Digital Network (ISDN) • Cable modems • Digital Subscriber Line (DSL)

6. Point-to-Point Protocol (PPP) • PPP is used with synchronous, asynchronous, dial-up, and ISDN links • Defines encapsulation scheme for transport of different network-layer protocols • Supports authentication: • Password Authentication Protocol (PAP) • Challenge Handshake Authentication Protocol (CHAP). CHAP more secure than PAP

7. Point-to-Point Protocol (PPP) • The IETF developed PPP as a standard data link layer protocol for transporting various protocols across serial, point-to-point links. • PPP can be used to create point-to-point links between different vendor’s equipment. • PPP uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol.

8. Point-to-Point Protocol (PPP) • PPP can be used to connect a single remote user to a central office, or to connect a remote office with many users to a central office. • PPP is a data-link protocol that can be used over either asynchronous serial (dial-up) or synchronous serial (ISDN) media and that uses the LCP (Link Control Protocol) to build and maintain data-link connections.

9. PPP Layers Network Control Protocol (NCP) Link Control Protocol (LCP) Encapsulation based on High-Level Data-Link Control Protocol (HDLC) Physical Layer

10. Multilink MPPP • Add support for channel aggregation to PPP. Channel aggregation can be used for load sharing and providing extra bandwidth. With channel aggregation, a device can automatically bring up additional channels as bandwidth requirements increase. • MPPP ensures that packets arrive in order at the receiving device.

11. Multichassis MPPP • Cisco enhancement to MPPP. • Allows WAN administrator to group multiple access servers into a single stack group. User traffic can be split and reassembled across multiple access servers in the stack group.

12. ISDN Analog Multichassis Multilink PPP Stack group Offload server

13. CHAP • CHAP provides a three-way hand-shake. • Provides protection by verifying a remote node with a three-way hand shake and a variable challenge value that is unique and unpredictable.

14. Remote Node CHAP Access Server Connect Database of Users and Passwords Challenge Name: 760_1Password: sfy45 Name: 760_1Password: sfy45 Name: 760_2 Password: kingsford Hashed Response Accept or Deny

15. ISDN • Digital data-transport service offered by regional telephone carriers (telcos) • Circuit-switched service that carries voice and data. ISDN is a set of digital services that transmit voice and data over existing phone lines. • Cost-effective remote-access solution for telecommuters and remote offices • Cost of an ISDN circuit is usually based on a monthly fee plus usage time • Good choice as a backup link for another type of link, for example, Frame Relay • Channel aggregation is popular with ISDN links.

16. ISDN Interfaces Basic Rate Interface (BRI) 144 Kbps 2B D } 64 Kbps 64 Kbps 16 Kbps Primary Rate Interface (PRI) 1.544 Mbps in U.S. 2.048 Mbps in Europe 23B or 30B D } 64 Kbps 64 Kbps

17. TA NT1 NT1 NT1 NT2 NT1 ISDN Components Non-ISDN device (TE2) R S/T U To ISDN service 4-wire circuit 2-wirecircuit ISDNdevice (TE1) S/T U To ISDN service S T ISDNdevice (TE1) U To ISDN service U ISDN device (TE1) with built-in NT1 To ISDN service

18. Cable Modem Service • Operates over the coax cable used by cable TV • Much faster than analog modems, and usually much faster than ISDN (depending on how many users share the cable) • 25 to 50 Mbps downstream from the head end • 2 to 3 Mbps upstream from end users • Standard = Data Over Cable Service Interface Specification (DOCSIS)

19. Cable Modem Service • Coax Cable does not require dial-up. • Cable modem operates more like a LAN. • Cable-network providers off hybrid fiber/coax (HFC) systems that connect CATV networks to the service provider’s high-speed fiber-optic network. • HFC systems allow connections of home PCs and small LANs to high-speed access to the Internet or to a private network using VPN.

20. Cable Modem Service • CATV (Cable Modem Termination System) provides high-speed connectivity for cable modems. • Cable modem solution for remote users or remote offices is the sharing a single cable and the types of applications they use.

21. DSL • High-speed digital data traffic over ordinary telephone wires • Sophisticated modulation schemes mean higher speeds than ISDN • Speeds range from 1.544 to 9 Mbps • Actual bandwidth depends on type of DSL service, DSL modem, and many physical-layer factors • Symmetric communication (SDSL) traffic flow travels at the same speed up to 1.544 Mbps. • Asymmetric DSL (ADSL) very popular • Downstream faster than upstream

22. PPP and ADSL • ADSL use two popular PPP implementations - PPP and ATM (PPPoA) the CPE acts as an Ethernet-to-WAN router and the PPP session is established between the CPE and Layer 3 access concentrator in the service provider’s network. - PPP and Ethernet (PPPoE) the CPE acts as an Ethernet-to-WAN bridge.

23. PPP and ADSL - PPP and Ethernet (PPPoE) the CPE acts as an Ethernet-to-WAN bridge. The client initiates a PPP session by encapsulating PPP frames int MAC frames and then bridging the frames over ATM/DSL to a gateway router at the service provider. From that oint, the PPP session can be established, authenticated, and achieved. The client receives its IP address from the service provider, using PPP negotiation.

24. Provisioning WAN Bandwidth • A critical network design is considering capacity requirements. Selecting the right amount of capacity for current and future needs. • Provisioning requires an analysis of traffic flows, and analysis of scalability goals.

25. WAN Technologies • Leased lines • Synchronous Optical Network (SONET) • Frame Relay • Asynchronous Transfer Mode (ATM)

26. Leased Lines • Dedicated digital, copper circuits that a customer leases from a carrier for a predetermined amount of time, usually for months or years • Speeds range from 64 Kbps to 45 Mbps • Enterprises use leased lines for both voice and data traffic

27. Leased Lines • Dedicated connection or Point-to-Point connection. • Pre-established WAN communications path from the CPE, through the DCE switch, to the CPE of the remote site, allowing DTE networks to communicate at any time with no setup procedure before transmitting data.

28. Digital Signal (DS) • A channel in the NADH (North American Digital Hierarchy) is called a digital signal (DS). Digital signals are multiplexed together to form high-speed WAN circuits. DS-1 and DS-3 are the most commonly used capacities.

29. The North American Digital Hierarchy

30. Synchronous Optical Network (SONET) • Physical-layer specification for high-speed synchronous transmission of packets or cells over fiber-optic cabling • Service providers and carriers make wide use of SONET in their internal networks • Gaining popularity within private networks

31. Synchronous Optical Network (SONET) • Goals of SONET and SDH - Define higher speeds than the ones used by the NADH. - Support efficient multiplexing and de-multiplexing of individual signals. With SONET, it is easy to isolate one channel from a multiplexed circuit. With plesiochronous systems, like NADH and European E system, isolating one channel is more difficult.

32. Synchronous Optical Network (SONET) • Terminating multiplexers (implemented in switches and routers) provide user access to the SONET network. Terminating multiplexers convert electrical interfaces into optical signals and multiplex multiple payloads into STS-N signals required for optical transport.

33. SONET Optical Carrier (OC) Levelsaka Synchronous Transport Signal (STS) Levels STS Rate OC Level Speed STS-1 OC-1 51.84 Mbps STS-3 OC-3 155.52 Mbps STS-12 OC-12 622.08 Mbps STS-24 OC-24 1.244 Gbps STS-48 OC-48 2.488 Gbps STS-96 OC-96 4.976 Gbps STS-192 OC-192 9.952 Gbps

34. Typical SONET Topology SONET Multiplexer Backup Pair Working Pair

35. Frame Relay • Industry-standard data-link-layer protocol for transporting traffic across wide-area virtual circuits • Optimized for efficiency on circuits with low error rates • Attractively-priced in most parts of the world • Carriers agree to forward traffic at a Committed Information Rate (CIR)

36. Frame Relay and X.25 • X.25 was optimized for excellent reliability on physical circuits with high error rates. • X.25 was more complex to implement than Frame Relay. • X.25 works at the physical, data link, and network layers. • X.25 allows computers on different public networks (CompuServe, TCP/IP) to communicate through an intermediary computer at the network layer level.

37. Frame Relay (continued) To Router B: DLCI 100 To Router A: DLCI 200 Router A Router B Virtual Circuit (VC)

38. Virtual Circuit What is a virtual circuit? OSI model used in example. TCP takes large blocks of information from an application and beraks them into segments. It numbers and sequences each segment so that the destination ‘s TCP protocol can put the segments back into the order the application intended. After the segments are sent, TCP (trans host) waits for an acknowledgment of the receiving end’s TCP virtual circuit session, retransmitting those that aren’t acknowledged. Before a transmission occurs, a host sends segments down the OSI model, the sender’s TC protocol contacts the destination’s TCP protocol to establish a connection. This type of connection is considered to be connection-oriented. UDP is connectionless.

39. Frame Relay Hub-and-Spoke Uses Subinterfaces hostname central site interface serial 0 encapsulation frame-relay interface serial 0.1 ip address 10.0.1.1 255.255.255.0 frame-relay interface-dlci 100 interface serial 0.2 ip address 10.0.2.1 255.255.255.0 frame-relay interface-dlci 200 Central-Site Router DLCI 100 DLCI 200

40. Split Horizon • A routing technique in which information about routes is prevented from exiting the router interface through which that information was received. Split horizon updates are useful in preventing routing loops. - Use a subinterfaces. This is a logical interface that is associated with a physical interface. The central site could have five PPP subinterfaces defined, each communicating with one of the remotes sites. With this solution, the central site router applies the split horizon rule based on logical subinterfaces, instead of the physical interface, and includes remote sites in the routing updates it sends out the WAN interface.

41. Split Horizon - Split horizon can be eliminated using full mesh design with physical circuits between each site.

42. Asynchronous Transfer Mode (ATM) • Used in service provider internal networks • Gaining popularity within private networks, both WANs and sometimes LANs • Supports very high bandwidth requirements • Copper cabling: 45 Mbps (T3) or more • Fiber-optic cabling: OC-192 (9.952 Gbps) and beyond, especially if technologies such as wavelength-division multiplexing (WDM) are used

43. ATM • Provides efficient sharing of bandwidth among applications with various Quality of Service (QoS) requirements • Cell-based system inherently better for QoS than frame-based system, because frame-based system, large frames can monopolize bandwidth • ATM is with a connection-oriented technology • Application can specify upon connection establishment the QoS it requires • Peak and minimum cell rates, cell-loss ratio, and cell-transfer delay

44. ATM • A disadvantages of ATM is that ATM interfaces for routers and switches are expensive

45. Ethernet over ATM • ATM router interfaces are expensive • Some providers allow a customer to use an Ethernet interface to access the provider’s ATM WAN • May require a converter • Expected to gain popularity because it has the advantages of both worlds • Easy-to-use LAN • QoS-aware WAN

46. Metro Ethernet • A service offered by providers and carriers that traditionally only offered WAN services • Carriers offer Metro Ethernet to customers who are looking for cost-effective method to interconnect campus networks and to access the Internet. • Metro Ethernet allow users to continue using 10/100 Mbps Ethernet interfaces. • Supports copper and fiber optics interfaces.

47. Metro Ethernet • Allows providers to offer bandwidth in 1-Mbps increments.

48. Selection Criteria for Remote Access Devices • Support for VPN features • Support for NAT • Reliability • Cost • Ease of configuration and management • Support for one or more high-speed Ethernet interfaces • If desired, wireless support

49. Selection Criteria for VPN Concentrators • Support for: • Tunneling protocols such as IPSec, PPTP, and L2TP • Encryption algorithms such as 168-bit Triple DES, Microsoft Encryption (MPPE), RC4, AES • Authentication algorithms, including MD5, SHA-1, HMAC • Network system protocols, such as DNS, RADIUS, Kerberos, LDAP • Routing protocols • Certificate authorities • Network management using SSH or HTTP with SSL

50. Selection Criteria for Enterprise Routers • Number of ports • Processing speed • Media and technologies supported • MTTR and MTBF • Throughput • Optimization features