ITEC 275 Computer Networks – Switching, Routing, and WANs Week 10 Robert D’Andrea 2015

Agenda The course is 2/3 completed Learning Activities PPP Cable Modems and DSL Leased Lines, SONET, Frame Relay, Metro Ethernet, ATM Selecting a WAN Service Provider Metro Ethernet

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

Enterprise Selection Criteria Business requirements and constraints Cost Technical goals Bandwidth requirements Quality of Service (QoS) requirements Network topology Traffic flow and load

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 PPP defines an encapsulation scheme for transporting different network-layer protocols PPP supports authentication: – Password Authentication Protocol (PAP) – Challenge Handshake Authentication Protocol (CHAP). CHAP more secure than PAP

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.

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 with the use of 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 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).

PPP

PPP

PPP Leased lines: ISP is the service provider. PPP is the protocol. The user does not want to share the wire or the expense of leasing a wire with another user. Packet Switching: Telco is the service provider. Frame Relay protocol. The user shares the service with other users to save money. Frame Relay is an alternate technology to PPP. Circuit Switching: POTS or ISDN are the service providers. PPP is the protocol. Data is sent encapsulated over the public telephone network system.

PPP Metro Ethernet: Telco is the service provider. Ethernet protocol. The user wants the data sent at a very high speed. Broadband: Telco is the service provider. PPPoE, PPPoA, Ethernet protocols.

PPP PPP encapsulation includes: 1. Line set up using LCP. The link is established during this phase. 2. Authentication, encryption and compression (optional). 2.1 Password Authentication Protocol (PAP) Avoid using PAP because it sends the password in ASCII format (clear text). 2.2 Challenge Handshake Authentication Protocol (CHAP) never sends the password, but sends a challenged handshake processes.

PPP 3. PPP carries packets from many different protocol suites using NCP. The NCP sends packets to negotiate the needed settings. Is all data encrypted? No Encryption is used to simply verify the passwords.

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 recombs 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 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).

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 Amplitude Modulation (AM) technique 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.

AM vs FM

FDM

Multilink Point To Point (MPPP)

Multilink MPPP Adds support for channel aggregation of 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.

Multi-chassis MPPP Cisco’s enhancement to PPP is MPPP. MPPP allows WAN administrator to group multiple access servers into a single stack group. The user’s traffic can be split and reassembled across multiple access servers in the stack group.

Multi-chassis Multilink PPP Stack group ISDN Analog Offload server

CHAP Challenge-Handshake Authentication Protocol (CHAP) is a more secure procedure for connecting to a system than the Password Authentication Procedure (PAP). 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

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

CHAP used with RADIUS

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 transmits 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 TV Service CATV (originally "community antenna television," now often "community access television") is more commonly known as "cable TV." Television programs were brought to millions of people throughout the world who were connected to a community antenna, cable TV. Today, CATV has become an increasingly popular way to interact with the World Wide Web and other new forms of multimedia information and entertainment services.

Cable TV Service Operates over the coax cable used by cable TV providers 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 TV Service Coax Cable does not require dial-up. Cable modem operates more like a LAN. Cable-network providers offer 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 TV 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.

Digital Subscriber Line (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

Digital Subscriber Line (DSL)

PPP and ADSL Asymmetric DSL (ADSL) uses two popular PPP implementations. 1. 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. 2. 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 Customer Premise Equipment (CPE), through the Data Communications Equipment (DCE) switch, to the CPE of the remote site, then allowing Data Terminal Equipment (DTE) networks to communicate at anytime with no set up procedure before transmitting data.

DTE and DCE The end instrument is a piece of equipment connected to the wires at the end of a telecommunication link. End instruments that relate to data terminal equipment (DTE) include printers, computers, barcode readers, automated teller machines (ATMs) and the console ports of routers.

DTE and DCE The data communication(s) equipment (DCE) is a device that sits between the DTE and a data transmission circuit. The DCE performs functions such as signal conversion, line clocking, and coding. The DTE/DCE classification was introduced by IBM.

DTE and DCE

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) Synchronous Optical Network (SONET) is the American National Standards Institute standard for synchronous data transmission on optical SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media.

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 1. Define higher speeds than the ones used by the NADH. 2. Support efficient multiplexing and de-multiplexing of individual signals. With SONET, it is easy to isolate one channel from a multiplexed circuit. In some instances where there are many different parts of the system are almost, but not quite, perfectly synchronised. Like the 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 (Synchronous Transport Signal) 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 Frame relay is a telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. For most services, the network provides a permanent virtual circuit (PVC), which means that the customer sees a continuous, dedicated connection without having to pay for a full-time leased line, while the service provider figures out the route each frame travels to its destination and can charge based on usage.

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

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

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

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 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 TCP 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.

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.

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-interface. 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. ATM Video:

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 What is Metro Ethernet? Metro Ethernet makes use of Carrier Ethernet technology in metropolitan area networks (MANs). Carrier Ethernet is the use of high- bandwidth Ethernet technology for Internet access and for communication among business, academic and government local area networks (LANs).

Metro Ethernet Widely available in larger cities, Metro Ethernet offers efficient and scalable network services within a specific metropolitan region. These regions are frequently meshed in fiber optic networks, making Ethernet more widely available in the specified metropolitan area. Comcast Metro Ethernet offers a simple solution for users that have a complex network.

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 Frame Relay 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?