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 Internet Engineering Task Force (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. PPP
Point-to-Point (PPP) is a data link protocol commonly used in establishing a direct connection between two networking nodes. It provides connection authentication, transmission authentication, and compression. PPP is used over many types of physical networks including serial cable, phone line, trunk line, cellular telephone, and fiber optic links such as SONET. PPP is also used over the Internet access connections (broadband).

11. Multilink MPPP
An ordinary dial-up modem connection to the Internet through an Internet service provider (ISP) usually uses PPP as its wide area network (WAN) data-link protocol, but there are times when the 56-Kbps speed provided by V.90 modems is insufficient. MPPP allows multiple physical dial-up links to be inverse multiplexed together to form a single high-bandwidth logical PPP connection between the dial-up client and the ISP. MPPP works by ordering the data frames from the client across the multiple PPP channels and recombining them at the ISP’s termination point, and vice versa.

12. Multilink MPPP
MPPP defines protocols for splitting the data stream into PPP packets, sequencing the packets, transmitting them over separate logical data links, and then recombining them at the receiving station.

13. Multilink MPPP
Inverse multiplexing speeds up data transmission by dividing a data stream into multiple concurrent streams that are transmitted at the same time across separate channels (such as a T-1 or E-1 lines) and are then reconstructed at the other end back into the original data stream. Just the reverse of ordinary multiplexing , which combines multiple signals into a single signal, inverse multiplexing is a technique commonly used where data in a high-speed local area network ( LAN ) flows back and forth into a wide area network ( WAN ) across the "bottleneck" of a slower line such as a T-1 (1.544 Mbps ).

14. Multilink MPPP
Various multiplexing methods are possible in terms of the channel bandwidth and time, and the signal, in particular the frequency, phase or time. The two basic methods are:
Frequency Division Multiplexing (FDM) is derived from AM techniques in which the signals occupy the same physical ‘line’ but in different frequency bands. Each signal occupies its own specific band of frequencies all the time, i.e. the messages share the channel bandwidth.

15. Multilink MPPP
Time Division Multiplexing (TDM ) is derived from sampling techniques in which messages occupy all the channel bandwidth but for short time intervals of time, i.e. the messages share the channel time.

16. Multilink MPPP

17. 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.

18. Multi-chassis 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.

19. Multi-chassis Multilink PPP
Stack group
ISDN
Analog
Offload
server

20. 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.

21. CHAP Remote Node Access Server Connect Challenge Hashed Response
Database of Users and Passwords
Challenge
Name: 760_1 Password: sfy45
Name: 760_1 Password: sfy45
Name: 760_2
Password: kingsford
Hashed Response
Accept or Deny

22. 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.
ISDN is becoming obsolete, though it is still used some places.

23. Basic Rate Interface (BRI) Primary Rate Interface (PRI)
ISDN Interfaces
Basic Rate Interface (BRI)
144 Kbps 2B D }
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 }

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

25. 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)

26. 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.

27. 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.

28. DSL Downstream faster than upstream
High-speed digital data traffic over ordinary telephone wires
Sophisticated modulation schemes mean higher speeds than ISDN
Speeds range from 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 Mbps.
Asymmetric DSL (ADSL) very popular
Downstream faster than upstream

29. PPP and ADSL
Asymmetric DSL (ADSL) uses 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.

30. 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 in MAC frames and then bridging the frames over ATM/DSL to a gateway router at the service provider. From that point, the PPP session can be established, authenticated, and achieved. The client receives its IP address from the service provider, using PPP negotiation.

31. PPP and ADSL Point-To-Point Protocol (PPP) Vedio:

32. 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.

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

34. 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

35. 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.

36. 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.

37. The North American Digital Hierarchy

38. 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

39. 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.

40. 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.

41. SONET Optical Carrier (OC) Levels aka Synchronous Transport Signal (STS) Levels
STS Rate OC Level Speed
STS-1 OC Mbps
STS-3 OC Mbps
STS-12 OC Mbps
STS-24 OC Gbps
STS-48 OC Gbps
STS-96 OC Gbps
STS-192 OC Gbps

42. Typical SONET Topology
SONET Multiplexer
Backup Pair
Working Pair

43. 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)

44. 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.

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

46. Virtual Circuit
What is a virtual circuit? OSI model used in example. TCP takes large blocks of information from an application and breaks 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 connection.

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

48. Frame Relay Frame Relay Video:

49. 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 sub-interfaces. This is a logical interface that is associated with a physical interface. The central site could have five PPP sub-interfaces defined, each communicating with one of the remotes sites. With this solution, the central site router applies the split horizon rule based on logical sub-interfaces, instead of the physical interface, and includes remote sites in the routing updates it sends out the WAN interface.

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

51. 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

52. 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

53. ATM
A disadvantages of ATM is that ATM interfaces for routers and switches are expensive.
ATM Video:

54. 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

55. 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.

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

57. 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

58. 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

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

60. Selection Criteria for a WAN Service Provider
Extent of services and technologies
Geographical areas covered
Reliability and performance characteristics of the provider’s internal network
The level of security offered by the provider
The level of technical support offered by the provider
The likelihood that the provider will continue to stay in business

61. Selecting a Provider
The provider’s willingness to work with you to meet your needs
The physical routing of network links
Redundancy within the network
The extent to which the provider relies on other providers for redundancy
The level of oversubscription on the network
QoS support

62. Summary
A major task during the physical design phase is selecting technologies and devices for enterprise networks
Remote access networks
WANs
Service providers
Devices
End user remote access devices
Central site remote access devices
VPN concentrators
Routers

63. Review Questions
Compare and contrast technologies for supporting remote users.
Compare and contrast WAN technologies.
What selection criteria can you use when purchasing internetworking devices for enterprise network customers?
What criteria can you use when selecting a WAN service provider?

64. This Week’s Outcomes PPP Cable Modems and DSL
Leased Lines, SONET, Frame Relay, Metro Ethernet, ATM
Selecting a WAN Service Provider

65. Due this week
11-1 – Concept questions 8

66. Next week Read Chapters 12 and 13 in Top-Down Network Design
12-1 – Concept questions 9
1-5-3 – Network design project
New office network
FranklinLive session 13

67. Q & A
Questions, comments, concerns?