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

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

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

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

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

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

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.

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.

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

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 use over many types of physical networks including serial cable, phone line, trunk line, cellular telephone, and fiber optic links such as SONETT. PPP is also used over the Internet access connections (broadband).

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 sometimes 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.

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.

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.

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.

Multichassis Multilink PPP Stack group ISDN Analog Offload server

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.

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

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

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

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)

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.

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.

DSL 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

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.

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.

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.

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

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

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.

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.

The North American Digital Hierarchy

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

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.

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.

SONET Optical Carrier (OC) Levels aka Synchronous Transport Signal (STS) Levels STS RateOC LevelSpeed STS-1OC Mbps STS-3OC Mbps STS-12OC Mbps STS-24OC Gbps STS-48OC Gbps STS-96OC Gbps STS-192OC Gbps

Working Pair Backup Pair Typical SONET Topology SONET Multiplexer

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)

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.

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

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.

Frame Relay Hub-and-Spoke Uses Subinterfaces Central-Site Router 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 DLCI 100DLCI 200

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.

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

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

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

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

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

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.

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

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

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

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

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

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

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

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?

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

Due this week 11-1 – Concept questions 8

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

Q & A Questions, comments, concerns?