ProCurve Networking by HP
Student guide
Technical training
WAN Technologies
Overview
Introduction ... 1
Course Objectives... 1
Prerequisites ... 2
Course Module Overviews ... 2
Module 1: Overview of WAN Connections
Objectives ... 1Introduction ... 2
A WAN Connection Defined ... 4
Basic Elements of a WAN Connection ... 5
Physical Transmission Media and Infrastructure ... 6
Types of WAN Circuits ... 7
PSTN (United States and Canada) ... 9
Public Telephone and Telegraph (PTT) Companies... 11
The Local Loop ... 12
Local Loop Transmission Media ... 14
Electrical Specifications and Related Technologies... 15
Digital Signal Zero (DS0) ... 16
Pulse Code Modulation (PCM)... 17
Time Division Multiplexing (TDM) ... 18
Digital Signal Hierarchies ... 19
Digital Signal X (DSX)... 20
CEPT Digital Signal Hierarchy... 22
Japanese Digital Signal Hierarchy ... 23
Encoding Schemes ... 24
Data-Link–Layer Protocols ... 26
Module 1 Summary ... 27
Module 2: Data-Link–Layer Protocols
Objectives ... 1Overview of the Data-Link Layer ... 2
Data-Link–Layer Protocols in the WAN ... 3
High-Level Data Link Control ... 5
Point-to-Point Protocol Suite... 7
Phases of a PPP Session... 9
Configuration Options ... 11
ii HP Restricted Rev. 5.21 Authentication Protocols ... 15 PAP ... 16 CHAP ... 17 EAP ... 18 NCP ... 19
Compression Control Protocol... 20
Encryption Control Protocol ... 21
Overview of Link-Aggregation Protocols ... 22
Multilink PPP ... 23
Bandwidth Allocation Protocol... 25
Bandwidth Allocation Protocol Frames ... 27
BAP Configuration Options... 29
Bandwidth Allocation Control Protocol... 31
Tunneling Overview ... 32
Generic Routing Encapsulation... 34
PPTP... 36
L2TP... 37
Module 2 Summary ... 38
Module 3: Carrier Line WAN Connections
Objectives ... 1Overview of Carrier Line WAN Connections... 2
Carrier Line WAN Connections ... 4
Physical Infrastructure Common to Carrier Line Local Loops ... 5
DSU... 7
CSU ... 8
Capabilities of WAN Routers ... 10
Characteristics of a T1 WAN Connection... 12
T1 CSU/DSU Connections ... 14
Characteristics of an E1 WAN Connection... 15
E1 DSU Connections ... 17
Characteristics of a J1 WAN Connection... 18
T1 WAN Connection over SONET (Japan) ... 20
Characteristics of a T3 WAN Connection... 21
T3 CSU/DSU Connections ... 23
Characteristics of an E3 WAN Connection... 25
E3 DSU Connections ... 27
Characteristics of a DS3 WAN Connection (Japan) ... 28
DS3 WAN Connection over SONET (Japan)... 29
Fiber Optic Carrier Networks ... 30
SONET and SDH Digital Hierarchies... 31
Fiber Optic Media and Connectors ... 34
Module 4: ISDN WAN Connections
Objectives ... 1
ISDN Overview ... 2
ISDN WAN Connection ... 4
Basic Rate Interface ... 6
Primary Rate Interface ... 8
Options for Higher Transmission Speeds... 10
ISDN Equipment at the Subscriber’s Premises ... 13
ISDN Interfaces... 15
Protocols for ISDN ... 17
Standards ... 19
Ordering ISDN ... 21
Recording Information About the ISDN Service... 23
Module 4 Summary ... 26
Module 5: DSL WAN Connections
Objectives ... 1Overview of DSL WAN Connections ... 2
Advantages and Disadvantages of xDSL... 4
xDSL Adoption: Number of xDSL Lines ... 6
Broadband Density... 8 xDSL WAN Connection ... 9 Two Groups of xDSL ... 10 Symmetric xDSL... 12 Asymmetric xDSL ... 15 ADSL Overview ... 16
ADSL Modulation Techniques ... 18
CAP Modulation ... 19
DMT Modulation ... 20
ADSL Components ... 21
Physical Infrastructure of ADSL WAN Connection... 23
ADSL Internet Connection ... 25
Protocols for ADSL ... 27
ADSL Lite and RADSL ... 29
ADSL2... 31
ADSL2+ ... 33
ADSL Standards ... 34
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Module 6: Frame Relay
Objectives ... 1
Overview of Frame Relay ... 2
Frame Relay WAN Connection... 4
Frame Relay Physical Access Options... 6
Data Link Connection Identifier (DLCI) ... 8
Committed Information Rate... 10
Excess Information Rate ... 12
Congestion Management: DE Bit ... 13
Congestion Management: FECN and BECN ... 14
Frame Relay Standards... 16
Frame Relay Signaling Protocols... 18
Service Level Agreements... 19
Module 6 Summary ... 21
Module 7: Virtual Private Networks
Objectives ... 1Defining VPNs ... 2
Types of VPNs ... 3
IPSec Versus PPTP ... 4
IPSec Standard... 5
IPSec Security Protocols ... 6
Security Associations ... 7
IPSec Modes ... 8
Tunnel Mode ... 9
Transport Mode... 10
IPSec Standard Key Management Process ... 11
IPSec Standard Authentication Process ... 13
Key Management and Authentication—Digital Certificates ... 14
Extended Authentication—RADIUS Server... 16
Extended Authentication—TACACS+ Server ... 17
IPSec Standard Encryption Process ... 18
Symmetric Key Encryption... 20
Asymmetric Key Encryption ... 23
How IPSec Sends a Packet ... 24
PPTP ... 26
Module 8: Firewalls
Objectives ... 1
Defining Firewalls ... 2
Firewall Architecture ... 4
Dual-Homed Host Firewall Architecture ... 5
Screened Host Firewall Architecture ... 6
Screened Subnet Firewall Architecture... 7
Types of Firewalls ... 8
Packet-Filtering Firewalls ... 9
Circuit-Level Gateways ... 11
Application-Level Gateways... 13
Stateful-Inspection Firewalls ... 15
Network Address Translation (NAT) ... 17
Single IP Address Translation... 19
Static and Dynamic NAT ... 20
Port Address Translation (PAT) ... 21
NAT Traversal (NAT T) ... 22
What to Block... 24
Module 8 Summary ... 27
Module 9: Quality of Service and Advanced WAN Routing
Objectives ... 1Traffic Congestion—Quality of Service ... 2
Quality of Service Mechanisms ... 3
DiffServ—Packet Marking ... 5
DiffServ—Per Hop Behaviors ... 7
Class-Based Queuing ... 9
Weighted Random Early Discard (WRED) ... 10
Committed Access Rate (CAR) ... 11
Generic Traffic Shaping and Frame Relay Traffic Shaping ... 13
Evaluating Traffic for QoS... 15
VLAN Support ... 16
Virtual Router Redundancy Protocol (VRRP) ... 17
Exterior Routing Protocols ... 19
Exterior Gateway Protocol... 20
Border Gateway Protocol... 22
Introduction
The ProCurve WAN Technologies course is designed to help support engineers and systems engineers understand the technologies used to create WAN
connections. It outlines the basic elements required to create a WAN connection and provides an in-depth explanation of different types of WAN connections. In addition, this course describes Virtual Private Networks (VPNs), which create secure, private communication across an existing public network. Because VPNs connect a trusted network to an untrusted network—primarily the Internet—this course also explains the firewall technologies that companies can use to protect their network.
Finally, this course discusses quality of service (QoS) mechanisms and advanced routing technologies such as exterior routing protocols.
Course Objectives
After completing this course, you should be able to: Describe the basic elements of a WAN connection
Explain the role that public carrier networks play in creating WAN connections
Define data-link–layer protocols and explain the role they play in creating WAN connections
Describe the specific characteristics and the physical infrastructure of carrier line WAN connections
Describe the specific characteristics and the physical infrastructure of Integrated Services Digital Network (ISDN) WAN connections Describe the specific characteristics of Digital Subscriber Line (DSL)
WAN connections
Describe the physical infrastructure of Asymmetric DSL (ADSL) WAN connections and describe how data is transmitted from the customer’s premises to the broadband network and the Internet
Explain the relationship between Frame Relay and WAN connections Describe how data travels through a Frame Relay network
Overview - 2 HP Restricted Rev. 5.21 Define a VPN and explain how Internet Protocol Security (IPSec) is used to
create VPNs
Describe the firewall architectures that can be used to provide security for a company’s internal network
Explain what QoS means and describe methods of enforcing QoS: classifying traffic, policing traffic, shaping traffic, and managing congestion
Explain the purpose of exterior routing protocols and describe the way they work
Prerequisites
Before taking this class, you should complete the HP ProCurve Adaptive Edge Fundamentals course and the HP ProCurve RSE course. For more information about HP ProCurve training, visit http://www.hp.com/go/procurvetraining.
Course Module Overviews
This course contains the following modules:
Module 1 provides the foundation for understanding WAN connections. It
introduces the three basic elements required for a WAN connection and describes the role each element plays in creating that connection.
Module 2 describes the data-link–layer protocols that control the transfer of data over a WAN connection. In particular, this module focuses on two general-purpose, data-link–layer protocols—High-level Data Link Control (HDLC) and Point-to-Point Protocol (PPP). This module also describes a network-layer tunneling protocol called Generic Routing Encapsulation (GRE).
Module 3 explains the specific characteristics and the physical infrastructure of carrier line WAN connections. This module also describes fiber optic carrier networks and the standards most commonly used to create them.
Module 4 describes ISDN WAN connections. It explains the two types of ISDN services available and the equipment required at the subscriber’s site. This module also outlines the information subscribers need to order an ISDN WAN connection. Module 5 provides an overview of the different types of DSL technologies used to create WAN connections. It then focuses on ADSL connections, explaining the physical infrastructure and the data flow from the customer’s premises to the public carrier network and the Internet. This module also describes the ADSL2 and ADSL2+ enhancements.
Module 6 explains the relationship between Frame Relay and WAN connections. It also describes the equipment necessary to create a Frame Relay network and the options offered by various Frame Relay carriers.
Module 7 introduces another method of connecting two sites—VPNs. It explains how VPNs create secure, private communication across an existing public network and then describes how IPSec can be used to connect private networks or remote users to the corporate network.
Module 8 explains how firewalls can be used to protect a trusted network from an untrusted network. It describes the firewall architectures that you can use to protect your network and explains how different types of firewalls work.
Module 9 defines QoS and describes some QoS mechanisms that you can use to manage traffic across a WAN connection. It also explains why WAN routers should support features such as virtual LAN (VLAN) tagging and Virtual
Redundancy Routing Protocol (VRRP). In addition, this module describes exterior routing protocols and CIDR.
Module 1
Objectives
This module introduces the basic elements of WAN connections and describes the role each element plays in creating that connection. After completing this module, you should be able to:
Describe the three basic elements of a WAN connection
Describe how public carrier networks are used to create a WAN connection Identify the three types of circuits used to create a WAN connection
Describe how local loops connect the subscriber’s premises to public carrier networks
Identify the electrical signaling specifications and related technologies used in public carrier networks
Explain the differences and similarities between T-, E-, and J-carrier WAN connections
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Introduction
Companies that have multiple offices need a cost-effective, efficient means to exchange data between those offices. Many companies have created intranets or extranets, which enable users at different locations to view, upload, and download information. However, intranets and extranets are only a partial solution to the problem because the sharing of data is limited to what can be posted on the intranet or extranet. Each office must maintain its own database, and users cannot access data stored at other locations. For example, the accounting department at each office must have a separate database, which cannot be shared over an intranet.
Security is also an issue because the intranet must be connected to the Internet, in order to serve multiple locations. The various offices connected through the intranet can be protected by firewalls, but firewalls are not impervious to attacks. For many companies, a Wide Area Network (WAN) is a better and more cost-effective solution for connecting multiple branch offices to a main office. A WAN allows companies to exchange all types of information, including voice and data. Combining voice and data traffic can reduce operating expenses for many
This course focuses on WAN connections created using public carrier networks. Businesses, organizations, and government entities use public carrier networks to create WAN connections for three primary reasons:
Using public carrier network infrastructure is almost always more cost effective than using privately owned infrastructure. Public carrier networks allow many subscribers to share the costs of installing, managing, and maintaining the infrastructure required to create WAN connections.
Using privately owned infrastructure to create long-distance and international WAN connections is impractical, sometimes even impossible, and cost prohibitive. WAN connections that use privately owned infrastructure are generally limited to relatively short distances, and installing them is beyond the capacity of all but the largest organizations.
WAN connections created through public carrier networks are substantially similar to WAN connections created using privately owned infrastructure in terms of security and performance. Public carrier networks also provide levels of reliability and redundancy that privately owned infrastructure typically cannot provide.
WAN routers connect the LANs at each location, identify the traffic addressed to another LAN, and route the traffic to the next hop. As explained throughout this course, WAN routers support a variety of WAN connection types, including: Dedicated T-, E-, and J-carrier lines
Integrated Services Digital Network (ISDN) Digital Subscriber Line (DSL)
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A WAN Connection Defined
In the most general sense, a WAN is a geographically dispersed
telecommunications network. For the purposes of this course, however, a WAN is defined as a network created to connect two or more LANs. WAN connections can connect LANs located in the same city or around the world. As the figure shows, a public carrier network is commonly used to create WAN connections between LANs in different parts of the world. Public carrier networks include the Public Switched Telephone Network (PSTN), which serves the United States and Canada, and Public Telephone and Telegraph (PTT) companies, which serve Mexico, Europe, Asia, South America, and other parts of the world.
Basic Elements of a WAN Connection
All WAN connections consist of three basic elements: The physical transmission media.
Electrical signaling specifications for generating, transmitting, and receiving signals through various transmission media.
Data-link–layer protocols that provide logical flow control for moving data between peers in the WAN. (Peers are the devices at either end of a WAN connection.)
As the figure shows, physical transmission media and electrical specifications are part of the physical layer (which is layer one) of the Open Systems Interconnection (OSI) model, and data-link–layer protocols are part of the data-link layer (which is layer two).
This module focuses on the physical transmission media, the electrical signaling specifications, and the related OSI layer-one technologies that are used to create WAN connections through public carrier networks.
Data-link–layer protocols are explained in detail in Module 2: Data-Link–Layer
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Physical Transmission Media and Infrastructure
The first basic element of a WAN connection is the physical transmission medium. The most common physical transmission medium used in public carrier networks is twisted-pair copper wire, originally installed for Plain Old Telephone Service (POTS) connections. Twisted pair is currently used in the last mile of 90 percent of all WAN connections.
Other physical transmission media include coaxial copper cable, fiber optic cable, and the Earth’s atmosphere, which carries signals by such means as infrared and microwave transmissions.
The physical transmission media are a large part of what is commonly called
infrastructure. Infrastructure also includes telecommunications switching and
routing equipment.
WAN connections can be created using public carrier network infrastructure, privately owned infrastructure, or a combination of the two.
Types of WAN Circuits
As the figure shows, three types of circuits are used to create WAN connections through public carrier networks:
Dedicated circuits
Permanent virtual circuits (PVCs) Switched virtual circuits (SVCs)
Dedicated Circuits
Dedicated circuits are permanent circuits dedicated to a single subscriber. The connection is always active. The subscriber purchases dedicated time slots, or channels, that provide a specific amount of bandwidth that is always available for the subscriber to use. The channels in a dedicated circuit are created using time division multiplexing (TDM), which is discussed later in this module.
In addition to providing guaranteed bandwidth at all times, dedicated circuits provide the most secure and reliable WAN connections available.
1 – 8 HP Restricted Rev. 5.21 Dedicated circuits are used to create the following point-to-point WAN
connections:
Carrier lines (which are explained later in this module and in
Module 3: Carrier Line WAN Connections)
DSL connections (which are explained in Module 5: DSL WAN Connections)
Permanent Virtual Circuits (PVCs)
PVCs are also permanent circuits dedicated to a single subscriber. The connection is always active. However, because multiple virtual circuits share a physical circuit, there is no guarantee that any specific amount of bandwidth will be available at any specific time. Sometimes there may not be any bandwidth available on the physical circuit because the physical circuit is saturated. When the physical circuit is saturated, the traffic is temporarily stored at a switching point until bandwidth becomes available. When bandwidth becomes available, the stored traffic is forwarded to its destination. This process is referred to as store-and-forward processing, or packet switching, which is the same
processing method used on LANs.
PVCs provide an average bandwidth guarantee through statistical multiplexing (STM), which underlies packet switching technology.
Because PVCs are more cost effective for the public carrier, PVCs are usually less expensive for the subscriber than dedicated circuits. PVCs are commonly used for Frame Relay, which is explained in detail in Module 6: Frame Relay.
Switched Virtual Circuits (SVCs)
SVCs are identical to PVCs in all respects, except that they are temporary physical circuits. SVCs are activated when a subscriber initiates a connection to transmit data. When all data have been transmitted, the connection is deactivated, and the physical circuit resources are made available to other subscribers.
SVCs are used to create dial-up WAN connections, including ISDN WAN connections, which are explained in Module 4: ISDN WAN Connections.
PSTN (United States and Canada)
In the United States and Canada, most WAN connections are created through the PSTN. As the figure shows, the PSTN consists of local exchange carriers (LECs) and interexchange carriers (IXCs). (LECs are also referred to as telcos.)
Local Exchange Carriers
LECs operate the infrastructure that provides access to the PSTN in a limited geographic area. The area served by a LEC is referred to as a local access and transport area (LATA). LECs include incumbent local exchange carriers (ILECs) and competitive local exchange carriers (CLECs).
ILECs are the Regional Bell operating companies (RBOCs) that provide service in a specific LATA. For example, SBC is the current ILEC in California. ILECs were created in 1983 when the U.S. government deregulated the telecommunications industry and mandated the breakup of AT&T.
Deregulation also led to the creation of CLECs, which provide the same services as ILECs and compete with ILECs in specific geographic areas. For example, Covad Communications is a CLEC that competes with SBC in California.
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Interexchange Carriers
IXCs aggregate voice and data traffic from numerous LECs. They operate the infrastructure that connects LATAs to the interLATAs that move traffic
throughout the United States and Canada. AT&T, Sprint, and MCI are all IXCs based in the United States. IXCs are commonly referred to as long-distance carriers.
IXCs also provide the infrastructure that enables PSTN subscribers to create WAN connections to PTT networks in Europe, Asia, South America, and other parts of the world.
Public Telephone and Telegraph (PTT) Companies
In most countries outside of the United States and Canada, the public telephone network is owned and operated by government-owned monopolies called PTTs. As the figure shows, a PTT operates the entire telecommunications infrastructure within a country’s borders. For example, British Telecom (BT) provides border-to-border service in the United Kingdom, while Deutsche Telecom (DTAG) provides this service in Germany.
PTTs provide both the local-access and long-distance transport infrastructure needed to create WAN connections through the public carrier network. As the figure shows, carrier interconnects link individual PTTs to provide an international public carrier system.
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The Local Loop
The connection between a subscriber’s premises and the public carrier’s nearest central office (CO) is referred to as the local loop. The local loop includes the entire telecommunications infrastructure—such as repeaters, switches, cable, and connectors—required to connect a subscriber’s premises to the CO.
A line of demarcation (demarc) separates a subscriber’s wiring and equipment from that of the public carrier. Each party owns, operates, and maintains the wiring and equipment on its side of the demarc.
Public carrier networks were originally designed to carry analog voice calls. Therefore, copper wire is the most common physical transmission medium used on the local loop. Because of the limits in the signal-carrying capacity of copper wire, local loops that use copper wire are the slowest, least capable component of a WAN connection. Public carriers are beginning to install coaxial and fiber optic cable in local loops to meet ever-increasing bandwidth demands.
Local loop connection types include carrier lines, which are described in
Module 3: Carrier Line WAN Connections. Local loop connection types also
include ISDN and DSL. ISDN and DSL are digital technologies designed to maximize the limited capabilities of existing local loop copper wiring. ISDN and DSL are discussed briefly in the next two sections.
ISDN Local Loops
ISDN provides integrated voice and data services by means of a fully digital local loop. An ISDN connection requires Category-3 (CAT-3) or higher twisted pair and is delivered by means of an SVC.
ISDN is a local loop-only technology. When ISDN traffic reaches the public carrier’s nearest CO, it is converted for transport through existing public carrier infrastructure.
ISDN is available in two levels of service: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI service provides 128 Kbps of bandwidth. PRI service provides 1.544 Mbps in total bandwidth in T-carrier systems and 2.048 Mbps in total bandwidth in E-carrier systems.
ISDN is discussed in-depth in Module 4: ISDN WAN Connections.
DSL Local Loops
DSL is a digital service that exists only in the local loop. DSL provides a digital connection between the subscriber and the public carrier’s CO.
Like ISDN, DSL requires CAT-3 or higher twisted pair wiring. Unlike ISDN, DSL uses PVCs (rather than SVCs), so DSL connections are always active. A DSL modem or WAN router connects the subscriber’s premises to the public carrier network.
Different types of DSL are available. Each public carrier determines the types of DSL that are available in a local service area. The following are some examples of the types of DSL:
Asymmetric DSL (ADSL) High bit rate DSL (HDSL) Symmetric DSL (SDSL)
Very high bit rate DSL (VDSL)
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Local Loop Transmission Media
CAT-3 and CAT-5 Unshielded Twisted Pair (UTP) are the most common types of copper wire used in the local loop. In some applications where signal interference is an issue, Shielded Twisted Pair (STP) is used. In some areas, including parts of the United Kingdom and the Netherlands, a pair of coaxial cables is used instead of twisted pair to complete local loop connections.
Other transmission media can be used to complete local loops if transmission speed is a primary consideration. For example, fiber optic cable and coaxial cable are both used to create T3 and E3 WAN connections, as discussed in Module 3:
Electrical Specifications and Related Technologies
An electrical specification defines a set of communication parameters, or rules, that determine the transmission speed through a WAN connection. When
engineers create an electrical specification, their objective is to find the best way to reliably transport traffic, as rapidly as possible, through a given transmission media.
The electrical specifications used for public carrier networks are based on cooperative standards developed by the American National Standards Institute (ANSI), the International Standards Organization (ISO), the Conference of European Postal and Telecommunications (CEPT), ITU-T, and ITU-T’s predecessor, the Consultative Committee for International Telegraph and Telephone (CCITT).
Electrical specifications enable both synchronous and asynchronous
communications over a WAN connection. Synchronous communications use a clock signal to precisely coordinate signal transport through the transmission media. Asynchronous communications use start and stop bits, rather than a clock, to coordinate signals.
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Digital Signal Zero (DS0)
DS0 is a digital channel operating at 64 Kbps, the amount of bandwidth required to transmit a single analog voice call through a digital telecommunications network. Based on the ANSI T1.107 specification, DS0 was originally created in the mid 1960s by Bell Laboratories to transport voice traffic over T-carrier systems. PTTs subsequently adopted a modified version of ANSI T1.107, the ITU-T G.703 specification, which is the basis of European and international E-carrier systems. J-carrier systems are also based on a modified version of T1.107 and are similar to T-carrier systems.
DS0 is the fundamental unit of bandwidth—the fundamental channel—in all copper-based T-, E-, and J-carrier systems. In E-carrier systems, DS0 is called E0, and in J-carrier systems, DS0 is called J0. However, the basic signal is virtually identical in all three carrier systems.
DS0, E0, and J0 channels all use a process called Pulse Code Modulation (PCM) to convert analog (voice) signals into digital signals.
Pulse Code Modulation (PCM)
PCM is the basis of a standard DS0, E0, and J0 channel. PCM converts a
continuously variable analog signal, such as a voice telephone call, into a stream of digital bits.
As the figure shows, the PCM sampling process creates a digital signal that represents the original analog waveform. The analog signal is converted (modulated) into a digital signal that is sent over the WAN connection. On the receiving side, the digital signal is demodulated (converted) back to an analog signal that closely approximates the original analog waveform.
In the PCM sampling process, the analog signal is sampled 8,000 times per second. Each sample is converted into an 8-bit binary code that represents the voltage of the analog waveform at the time the sample was taken. Thus, the PCM process is the mathematical basis for the bandwidth required for a standard DS0, E0, or J0 channel:
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Time Division Multiplexing (TDM)
As the figure shows, TDM creates a high-bandwidth channel by combining, or multiplexing, multiple DS0 signals into a larger, more complex signal. Each DS0 receives an equal time slice within the complex signal in a rotating, repeating sequence, and thus receives an equal amount of bandwidth. On the receiving end, TDM is used to recover the original DS0 signals through a reverse process called demultiplexing.
T-carrier and J-carrier systems use TDM to provision 24 DS0 channels for a T1 or J1 WAN connection. E-carrier systems use TDM to provision 32 DS0 channels for an E1 WAN connection. TDM is also used to provision larger channels that use T1/J1/E1 channels as base multiples, as described in the next section.
Digital Signal Hierarchies
Digital signaling hierarchies define the signal multiplexing used in each type of physical carrier and determine the transmission speed for each carrier. Digital signaling hierarchies use small bandwidth channels as base multiples for creating larger bandwidth channels, or carrier signals, in a carrier system.
DS0, E0, and J0 channels serve as the base multiples for creating T1, E1, and J1 carrier signals. T1, E1, and J1, in turn, serve as the base multiples for creating the more complex, higher-bandwidth carrier signals used in T2, E2, J2, and higher carrier systems.
T-, E-, and J-carrier systems use similar, but not identical, digital signaling hierarchies. T-carrier systems use Digital Signal X (DSX), E-carrier systems use the CEPT digital signal hierarchy, and J-carrier systems use the Japanese signal hierarchy. These signaling hierarchies are described in the following sections.
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Digital Signal X (DSX)
DSX is the digital signal hierarchy that defines the signal multiplexing used in T-carrier systems.
As the figure shows, DSX specifies that 24 DS0s are multiplexed to create the DS1 carrier signal used in a T1 carrier. A T1 carrier provides a total transmission rate of 1.544 Mbps (24 x 64 Kbps = 1,536 Kbps + 8 Kbps for framing bits and timing signal synchronization).
Similarly, DSX specifies the following:
Four DS1 signals are multiplexed to create the DS2 signal used in T2 carriers, which provide a transmission rate of 6.312 Mbps.
28 DS1 signals are multiplexed to create the DS3 signal used in T3 carriers, which provide a transmission rate of 44.736 Mbps.
168 DS1 signals are multiplexed to create the DS4 signal used in T4 carriers, which provide a transmission rate of 274.176 Mbps.
336 DS1 signals are multiplexed together to create the DS5 signal used in T5 carriers, which provide a transmission rate of 560.160 Mbps.
As the figure shows, DSX specifies the physical carriers used at each level in the hierarchy. (DSX does not define the physical carrier; ANSI T1.107 defines the physical components of T-carrier systems.) When combined, the physical carrier and the DSX hierarchy specify a usable physical layer for each type of carrier in a T-carrier system.
DSX defines Digital Signal Designators (DSDs), or signaling methods, used to create the carrier signals used at each level of the hierarchy. DSX also defines DSX interfaces, which describe the physical connections (pinouts) and signaling logic (send timing, receive timing, send data, and receive data) necessary for connected devices to communicate.
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CEPT Digital Signal Hierarchy
Like the DSX digital signal hierarchy used in T-carrier systems, the CEPT digital signal hierarchy defines the signal multiplexing used to create the signals carried in each E carrier. Unlike DSX, CEPT DSDs are identical to the physical carrier designator.
As the figure shows, the CEPT hierarchy multiplexes 32 E0 channels to create the signal that is carried within an E1 physical carrier. An E1 carrier provides a total transmission rate of 2.048 Mbps.
Similarly, the CEPT hierarchy specifies the following:
Four E1 signals are multiplexed to create the E2 signal used in E2 carriers, which provide a transmission rate of 8.448 Mbps.
16 E1 signals are multiplexed to create the E3 signal used in E3 carriers, which provide a transmission rate of 34.368 Mbps.
64 E1 signals are multiplexed to create the E4 signal used in E4 carriers, which provide a transmission rate of 139.264 Mbps.
256 E1 signals are multiplexed together to create the E5 signal used in E5 carriers, which provide a transmission rate of 565.148 Mbps.
Japanese Digital Signal Hierarchy
The Japanese digital signal hierarchy defines the signal multiplexing used to create the signals carried in each J carrier. Unlike DSX, Japanese DSDs are identical to the physical carrier designator.
As the figure shows, the Japanese hierarchy multiplexes 24 J0 channels to create the J1 carrier signal that is carried within a J1 physical carrier. A J1 carrier provides a total transmission rate of 1.544 Mbps.
Similarly, the Japanese hierarchy specifies the following:
Four J1 signals are multiplexed to create the J2 signal used in J2 carriers, which provide a transmission rate of 6.312 Mbps.
30 J1 signals are multiplexed to create the J3 signal used in J3 carriers, which provide a transmission rate of 32.064 Mbps.
240 J1 signals are multiplexed to create the J4 signal used in J4 carriers, which provide a transmission rate of 397.200 Mbps.
In Japan, most PTTs in Japan use the T1 standard for data; the J1 standard is used for voice. The reasons for using the T1 standard will be discussed in Module 3:
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Encoding Schemes
Encoding schemes define how digital signals are configured for transport through a physical transmission medium. Encoding schemes use electrical signals to represent the logical 0 and 1 bits in a data stream.
The public carrier that provides the local loop service determines the encoding scheme for the WAN connection. All of the subscriber’s equipment must be configured to use the public carrier’s encoding scheme. Three encoding schemes are widely used in T-, E-, and J-carrier systems.
Alternate mark inversion (AMI) Bipolar 8-zero substitution (B8ZS) High-density bipolar of order 3 (HDB3)
AMI
AMI uses alternating positive and negative voltage (referred to as alternating polarity or bipolarity) to represent logical 1s, and zero voltage to represent logical 0s. Because AMI uses zero voltage for logical 0, it can cause synchronization loss between peers at each end of a WAN connection when a data stream contains a long string of logical 0s.
B8ZS
B8ZS is a modified version of AMI. B8ZS prevents the synchronization loss associated with AMI by limiting the number of consecutive 0s in a data stream to eight. When eight zeros are detected, B8ZS replaces them with two successive logical 1s of the same polarity in a process referred to as a bipolar violation. B8ZS is the predominant encoding scheme used in T-carrier systems.
HDB3
HDB3 is based on AMI and prevents synchronization loss in a manner similar to B8ZS. HDB3 limits the number of consecutive zeros in a data stream to four, and it replaces them with three logical 0s and a violation bit with the same polarity as the last AMI logical 1 detected. HDB3 is the predominant encoding scheme used in E-carrier systems.
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Data-Link–Layer Protocols
Data-link–layer protocols are the third and final element of a basic WAN connection.
Data-link–layer protocols are found at layer two of the OSI model. They enable flow control, synchronization, integrity checking, and validation for data streams passing between the physical layer and the network layer (layer three in the OSI model).
Module 1 Summary
In this module, you learned about the following: Three basic elements of a WAN connection:
Physical transmission media Electrical signaling specifications Data-link–layer protocols
Local loops and the public carrier networks that provide them Three types of circuits used to create a WAN connection:
Dedicated circuit
Permanent virtual circuit Switched virtual circuit
Electrical specifications and related technologies:
Digital signal hierarchies: DSX, CEPT Digital Signal Hierarchy, and the Japanese Digital Signal Hierarchy
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Learning Check
1. What are the three basic elements of a WAN connection?
______________________________________________________________ ______________________________________________________________ ______________________________________________________________
2. Which type of circuit is used to create T-, E-, and J-carrier lines? a. Switched virtual circuit
b. Permanent circuit
c. Permanent virtual circuit d. Switched circuit
3. Which digital signaling hierarchy forms the basis of E-carrier lines? a. DSX
b. JSX c. CEPT d. EPT
4. How many DS0s are multiplexed into a T1-carrier line? a. 16
b. 24 c. 20 d. 32
5. How many E0s are multiplexed into an E1-carrier line? a. 16
b. 24 c. 20 d. 32
6. How many E1 signals are multiplexed to create the E3 signal used in E3-carrier lines?
a. 16 b. 24 c. 20 d. 32
Module 2
Objectives
This module discusses two general-purpose data-link–layer protocols—High-level Data Link Control (HDLC) and Point-to-Point Protocol (PPP). These protocols can be used to control the transfer of data over a WAN connection that is created using the physical media and electrical signaling specifications described in Module 1. This module also describes a network-layer tunneling protocol called Generic Routing Encapsulation (GRE). After completing this module, you should be able to:
Describe HDLC and its configuration options
Describe the PPP suite and the configuration options associated with specific protocols within the suite
Identify the phases of a PPP session
Describe the purpose of link-aggregation protocols and configuration options associated with Multilink Point-to-Point Protocol (MP)
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Overview of the Data-Link Layer
Layer two of the Open Systems Interconnection (OSI) model is called the data-link layer. In simplest terms, the data-link–layer describes the procedures (called protocols) that control data transfer across the physical infrastructure at layer one. To control data transfer, protocols at this layer perform two important functions: Establish a link between the sending peer and the receiving peer. (Peers are
the devices at either end of a point-to-point link.) Reliably transfer data across that link.
Data-link–layer WAN protocols establish point-to-point links, while data-link– layer LAN protocols provide multipoint connections. In other words, only the two endpoints of a WAN connection (usually two WAN routers) communicate with one another, while all nodes in a LAN can communicate with all other nodes.
Data-Link–Layer Protocols in the WAN
As mentioned in Module 1: Overview of WAN Connections, all WAN connections consist of three basic elements:
1. The physical transmission media
2. Electrical signaling specifications for generating, transmitting, and receiving signals through various transmission media
3. Data-link–layer protocols that provide logical flow control for moving data between peers in the WAN
This course focuses on three technologies that provide the physical-layer elements of a WAN connection:
Dedicated carrier lines
Integrated Services Digital Network (ISDN) Digital Subscriber Line (DSL)
For each of these WAN connections, a subscriber can choose among several data-link–layer protocols.
2 – 4 HP Restricted Rev. 5.21 Most WAN routers prompt you to choose a data-link–layer protocol by asking for your method of “encapsulation” and providing a list of supported data-link–layer protocols. Encapsulation, in this sense, is the process of wrapping a network-layer protocol’s packet (such as an IP packet) within a data-link–layer protocol’s frame. Encapsulating network-layer protocols enables their transfer across a point-to-point link.
This module discusses two general-purpose data-link–layer protocols: High-level Data Link Control (HDLC) and Point-to-Point Protocol (PPP).
PPP is the default encapsulation for many routers and is discussed in depth in this module. However, much of this discussion is informative. Unless you require changes to PPP’s default operation, configuring PPP is mostly automatic. In addition to HDLC and PPP, a number of data-link–layer protocols—such as Link Access Procedure for D-Channel (LAPD), Frame Relay, and Asynchronous Transfer Mode (ATM) protocols—can encapsulate WAN traffic. LAPD is discussed in Module 4: ISDN WAN Connections, and the Frame Relay protocols are discussed in Module 6: Frame Relay. ATM technology is discussed in
Module 5: DSL WAN Connections.
This module also describes two protocols that enable you to aggregate lines: Multilink PPP (MP) and Multilink Frame Relay (MFR). It then introduces the concept of tunneling and describes a tunneling protocol called Generic Routing Encapsulation (GRE). GRE is a network-layer protocol that is generally associated with security in a Virtual Private Network (VPN). VPNs establish secure
communications over public networks such as the Internet and are discussed in depth in Module 7: Virtual Private Networks.
However, GRE can also be used in private WANs—and in conjunction with data-link–layer protocols—as a solution to the following problems:
To provide connectivity for legacy network-layer protocols
To route multicast traffic through routers that are not configured for multicasting
High-Level Data Link Control
HDLC is one of the oldest data-link–layer protocols for the WAN. In fact, it predates the PC and was originally developed for mainframe environments. Because of this, HDLC was originally designed for use with primary and secondary devices, such as a mainframe with dumb terminals. Although HDLC has been updated for use in the PC environment, you may encounter the following terms, which originate from its early use:
Normal Response Mode (NRM)
A secondary device can transmit only when the primary device specifically instructs it to do so.
Asynchronous Response Mode (ARM)
A secondary device can initiate a transmission; however, the primary device controls the establishment and termination of the link.
Asynchronous Balanced Mode (ABM)
Devices at both ends of a connection are configured to be both primary and secondary devices and can establish a link, transmit data without permission, and terminate a link.
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Unnumbered frames establish a link.
Supervisory frames carry error and flow control information.
Point-to-Point Protocol Suite
Although PPP is the name of a single protocol, most often “PPP” refers to an entire suite of protocols that are related to PPP. Most of the PPP suite is shown above. Specific protocols are briefly mentioned in this section to give you an overview of PPP; these protocols are then described in more depth in later sections.
Every PPP connection requires the peers to exchange frames from at least three protocols—and to exchange them in a particular order:
1. Link Control Protocol (LCP)
2. One type of Network Control Protocol (NCP)—the one appropriate to the data being delivered
3. PPP
Link Control Protocol
Other than PPP itself, LCP is probably the most important protocol in the PPP suite. LCP frames are used to establish, configure, and maintain the link between peers. LCP frames must establish a link between peers before a PPP frame can be transferred across that link.
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Network Control Protocols
After LCP establishes a link, peers must exchange NCP frames before PPP frames can carry information over the link. Basically, NCPs carry information about how to control or manage other protocols, primarily network-layer protocols.
The network-layer protocol used by the information in the PPP frame determines which type of NCP frames must be exchanged. For example, if the PPP frames are carrying IP packets, then IP Control Protocol (IPCP) frames must be exchanged before the PPP frames can be sent.
Point-to-Point Protocol
PPP frames carry the actual information being transferred over the link from the upper layers of the OSI model. In PPP terminology, this information is called a datagram.
Optional Protocols in the Suite
The remaining protocols in the PPP suite are optional. Examples of these optional protocols include:
Encryption Control Protocol (ECP) is an NCP that can configure options for encrypting PPP datagrams.
Link Quality Reporting (LQR) is a link configuration protocol that monitors how many frames are being dropped on the link.
All authentication protocols provide different ways to authenticate passwords on links configured to require passwords.
Phases of a PPP Session
As the figure shows, a PPP session is divided into phases during which the various protocols may exchange frames. A PPP session proceeds in the following way: 1. During the link dead phase, the physical layer is unavailable, and there is no
activity. If a peer wants to begin a session, it signals the physical layer and waits for the physical layer to indicate that it is now “up.” The session then enters the link establishment phase.
2. Peers exchange LCP frames during the link establishment phase. If the peers successfully establish a link, the session enters the authentication phase. 3. During the authentication phase, peers exchange authentication protocol
frames. (Although authentication is optional, the session passes through this phase whether or not authentication was chosen.) If the sending peer
authenticates successfully or if no authentication is necessary, the session then enters the network-layer protocol phase.
2 – 10 HP Restricted Rev. 5.21 4. During the network-layer protocol phase, peers exchange NCP frames and
PPP frames. More than one protocol per session can be used during this phase. For example, peers might exchange IPCP frames, then send PPP frames with IP datagrams, then exchange AppleTalk Control Protocol
(ATCP) frames, then send PPP frames with AppleTalk datagrams, and so on. 5. During the link termination phase, peers exchange LCP link-termination
Configuration Options
You can configure WAN routers (or other devices) to use optional protocols in the PPP suite. In addition, many protocols in the PPP suite, such as LCP, allow you to manually configure options.
To choose a setting for an option, you may need to know a value assigned to the setting. For example, one of the authentication protocols discussed later in this module, the Challenge Handshake Authentication Protocol, allows you to choose among several authentication algorithms. To use the algorithm called MS-CHAP, you may need to know it has been assigned the value of 128 (although it is more likely that the router’s software developers will provide a text option from which to choose). All values associated with PPP are controlled by the Internet Assigned Numbers Authority (IANA) and are updated at this URL:
http://www.iana.org/assignments/ppp-numbers
When one of the peers in a PPP session has been configured to use protocols or options that are not used by default, the peers negotiate these options. They do so by exchanging configuration frames for the protocol in question. The figure shows a simplification of this frame-exchange process.
2 – 12 HP Restricted Rev. 5.21 Most of the protocols in the PPP suite include the following (or similar) types of configuration frames:
configure-request
The configure-request frame contains information about desired changes to the default configurations.
configure-ack
If the peer that receives a configure-request recognizes and accepts all of the optional configurations, it returns a configure-ack.
configure-nak
If the peer recognizes all optional configurations but refuses any or all of them, it returns a configure-nak. The configure-nak frame includes
information about which options are refused and which values of that option the receiving peer is unable to accept.
configure-reject
When a peer receives a configure-request that contains either unrecognizable configuration options or options that are non-negotiable, it returns a
Link Control Protocol Configuration Options
LCP frames are encapsulated in the Information Field of the PPP frame. LCP has a set of configuration options, and two PPP peers will use the default settings for these options, unless one peer signals a request to change the default configuration. To request such a change, the peer sends an LCP configure-request frame, and this frame type is specified in the LCP Code field.
The information about the configuration change is included in the LCP Data field. As shown here, the LCP Data field can contain information about multiple LCP configuration options. Configuration options that are not included in the configure-request frame remain at their default settings.
LCP configuration options include the following:
Maximum-Receive-Unit
When configuring a link, the peers must agree on how much data can be contained in the information field of PPP frames. The value that communicates this frame size is called the Maximum Receive Unit (MRU). The default value of the MRU is 1500 octets. To increase or decrease this value, the sending peer uses the
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Quality-Protocol
The quality-protocol option indicates whether or not peers will use the Link
Quality Report (LQR) protocol. LQR monitors the quality of a link by determining how much data is being dropped.
Magic-Number
The use of magic numbers enables the detection of looped-back links. When a link is looped back, frames are returned to the sending peer. Magic numbers are
random numbers that the sending peer assigns to its frames. When the receiving peer replies, it augments the magic number in the reply frames. The sending peer can then detect the difference between sent frames and received frames. By default, peers insert a zero where a magic number would otherwise be inserted. If you use LCP echo-request, echo-reply, and discard-request frames to test a link, enabling the magic-number option is useful. Also, if you choose to enable LQR, you must enable the magic-number option.
Protocol-Field-Compression
The protocol-field-compression option allows peers to compress the information in the protocol field of PPP frames from the default two bytes to one byte. The IANA assigns a protocol field value for each protocol; typically, this value is less
than 256. Because one byte is capable of representing the values 0 through 255, most protocol fields can be easily compressed to one byte.
Address-and-Control-Field-Compression
Enabling the address-and-control-field-compression option allows peers to compress address and control fields in the PPP frames. These fields have static values and thus are compressed easily.
Authentication-Protocol
The authentication-protocol option turns on authentication and enables you to choose among the three authentication protocols available in the PPP suite. These authentication protocols are described in the next section.
Authentication Protocols
Authentication for the PPP suite is what most people think of as password-protection. In other words, the user must provide a password to set up the PPP link.
The PPP protocol suite includes three authentication protocols: Password Authentication Protocol (PAP)
Challenge Handshake Authentication Protocol (CHAP) Extensible Authentication Protocol (EAP)
For this discussion, the peer that requires authentication is called the authenticator. The peer that wants to establish a link with the authenticator is called simply the peer. For example, when you connect to the Internet from a home computer, your modem or broadband router is the peer. Your Internet service provider’s router requires a password and is the authenticator.
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PAP
PAP is the simplest possible authentication scheme. The peer is provided a password, and the authenticator knows what that password is. The peer sends its password to the authenticator. The authenticator acknowledges the password, and the link is established.
CHAP
Passwords in PAP pass directly over the wire. Anyone capable of tapping into the wire can obtain the password. CHAP solves this security problem by using the following process:
1. The authenticator challenges the peer.
2. The peer combines its password with a string of text and then performs a calculation called hashing on the resulting string. Hashing results in an encryption, or hash value, that the peer sends to the authenticator.
3. The authenticator knows both the agreed-upon string of text and the peer’s password. The authenticator performs the same hashing calculation and compares its hash value to the hash value it received from the peer.
4. If the hash values match, the authenticator acknowledges the authentication, and the authenticator and the peer can proceed with the link. If the hash values do not match, the authenticator continues to issue challenges until the peer returns a matching hash value or runs out of retry attempts.
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EAP
CHAP is more secure than PAP, but it is not the most secure authentication protocol available today. EAP makes it possible for PPP to use authentication schemes that are not part of its own protocol suite. For example, the authenticator and the peer might use the authentication scheme defined by a network operating system. In this case, EAP encapsulates the authentication information from the network operating system and transmits it over the PPP link.
Although EAP enables you to use authentication schemes, it is not actually an authentication protocol.
NCP
PPP supports NCPs for many network-layer protocols, including IP, IPX,
AppleTalk, and Systems Network Architecture (SNA). Each protocol in the NCP family has a unique set of configuration options. These options specify parameters required by the protocol that NCP is managing.
For example, IPCP includes configuration options that communicate important IP addresses—such as the addresses for the primary and secondary Domain Name Services (DNS) servers—to the receiving peer before frames are sent. Most of the other network-layer NCPs include a configuration option that serves a similar purpose.
IPCP also includes an IP-Compression-Protocol configuration option, which indicates a request to compress the IP datagram in the PPP frames. Most of the other network-layer NCPs include configuration options that similarly indicate requests to compress their respective network-layer protocol packets encapsulated in the PPP frames.
For more information about IPCP and other network layer protocol configuration options, see http://www.iana.org/assignments/ppp-numbers.
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Compression Control Protocol
The PPP suite includes a protocol that enables data compression across the link: Compression Control Protocol (CCP). The CCP configuration options enable you to specify which type of data-compression algorithm is applied to the datagrams. CCP can support nearly any compression algorithm. The IANA has already assigned numbers to many of these compression algorithms, including those listed above. Developers of compression algorithms can apply to have the IANA assign a number to their algorithm.
Some developers may not need to get an IANA-assigned number. Organizations that have purchased an Organization Unique Identifier (OUI) from the Institute of Electrical and Electronic Engineers (IEEE) can use their OUIs to identify
proprietary blocks of code, including compression algorithms and encryption keys. (An OUI must be purchased by any organization that assigns MAC addresses to hardware; the OUI is the first 24 bits in a MAC address.)
Encryption Control Protocol
The PPP suite includes a protocol that enables data encryption across the link: Encryption Control Protocol (ECP). To encrypt text, devices that support ECP apply a mathematical algorithm to the text, and this algorithm changes the text into nonsense. The algorithm includes an assigned variable known as the key. Only devices with the appropriate key can decrypt the encrypted text.
The configuration options in ECP enable you to specify which type of encryption algorithm to apply to the datagrams. Like CCP, ECP includes the option to use proprietary encryption methods (indicated by their association with OUIs). The IANA has also assigned values to standard encryption methods, such as the Data Encryption Standard (DES) or the Triple Data Encryption Standard (3DES). (DES and 3DES are described in Module 7: Virtual Private Networks.)
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Overview of Link-Aggregation Protocols
PPP and other data-link–layer protocols, such as Frame Relay, establish a single point-to-point connection, which may not provide sufficient bandwidth to meet a business’ requirements. Link-aggregation protocols address this limitation. Theoretically, link aggregation is a simple idea: effectively double your available bandwidth by using two physical cables to connect your endpoints instead of only one, triple your bandwidth by using three cables, quadruple your bandwidth by using four cables, and so on. For example, you could aggregate two 1.544-Mbps T1 connections into a virtual single network connection with an underlying bandwidth of 3.088 Mbps.
However, to take advantage of multiple physical cables, data-link–layer protocols must be modified to fragment frames into smaller frames that can be passed simultaneously over separate cables and then reassembled by the receiving peer. Link-aggregation protocols, including Multilink PPP (MP) and Multilink Frame Relay (MFR), do exactly that.
The following sections describe MP, as well as two protocols that can be used with MP: Bandwidth Allocation Protocol (BAP) and Bandwidth Allocation Control Protocol (BACP).
Multilink PPP
As its name suggests, MP is an extension to PPP. There are only two differences between regular PPP and MP:
MP introduces three additional configuration options for LCP.
An MP header is added to the information field in the PPP frame format. This section discusses the additional LCP configuration options.
Maximum Receive Reconstructed Unit
The Maximum Receive Reconstructed Unit (MRRU) configuration option provides two important functions:
The inclusion of the MRRU in an LCP configure-request frame indicates that the sending peer wants to use MP. If the receiving peer acknowledges the option, it must assume that all of the frames received on different cables from the same peer should be processed as part of the same point-to-point link. The MRRU is required if a peer wants to use MP.
The MRRU replaces the MRU. The MRU specifies the size of the frame that can be sent over a link; the MRRU specifies the frame size once all fragments
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Short Sequence Number Header Format
The sequence number assigns an order to frame fragments so they can be properly reassembled. The MP header can have a long sequence number or a short one. A short sequence number is 12-bits and enables a frame to be split into a little less than 5,000 fragments. The 24-bit long sequence number provides enough bits to create more than 16 million fragments. Unless you are bundling a large number of cables together, the short sequence number is probably sufficient. The long
sequence number is the default, so if a peer wants to use the short number, it must request this option.
Endpoint Discriminator Options
When using MP, the receiving peer gets frame fragments from different cables. Because this is the case, the receiving peer must be able to distinguish between multiple sending peers. The receiving peer can distinguish between sending peers in one of three methods:
Authentication
Endpoint discriminator Manual configuration
Authentication
Using the normal PPP authentication option enables one peer to recognize fragments from the same authenticated peer.
Endpoint Discriminator
On links where authentication is not required, the endpoint discriminator option can be used instead. The endpoint discriminator enables a peer to distinguish frames from sending peers based on one of the following:
A locally assigned network address An IP address
A MAC address A PPP magic number A telephone number
Authentication and an endpoint discriminator can also be used together to provide a more secure method of distinguishing between peers.
Manual Configuration
In a situation where a dedicated bundle is set up between endpoints, the links can be manually configured to accept all frames from the bundle as if they are coming from the same peer. (A bundle is a group of aggregated links.)
Bandwidth Allocation Protocol
Bandwidth Allocation Protocol (BAP) is a link management protocol that can be used with MP to improve the management of multiple links. BAP configures, maintains, or terminates individual links in a bundle.
MP can be used without BAP, but when using MP alone, peers do not coordinate the adding and dropping of individual links. Like PPP, MP uses LCP to set up the initial link and to terminate the final one. Without BAP, however, peers can add or drop individual links indiscriminately. If a peer tries to send frames over a link that another peer has dropped, those frames are dropped.
Using BAP requires adding another configuration option to LCP—the
link-discriminator option. Negotiation of this option is required. It allows each link in a bundle to be numbered so that BAP can keep track of the individual links.
Keep in mind that BAP doesn’t replace LCP. LCP frames must still be used to configure the first link during the link configuration phase. (This includes
configuring MRRU and other options added by MP, the link discriminator option required by BAP, and the authentication and other LCP options available to basic PPP.)
2 – 26 HP Restricted Rev. 5.21 When BAP is being used, peers must exchange the following frames:
LCP frames that contain both the MRRU configuration option and a link discriminator option
BACP frames, to configure options for BAP
BAP frames, to configure the multiple links being used NCP frames, for the appropriate layer-3 protocol MP frames
Bandwidth Allocation Protocol Frames
BAP configurations are required in some types of frames but are optional in others. To understand when configuration options are required, you must understand BAP frame types.
Request frames are described here. Each BAP request frame has a corresponding response frame, as shown above.
Link Configuration Frames
A peer sends a call-request frame to request that a new link be added. A peer can also send a callback-request, which requests that the other peer add the link by “calling back” on that link.
Link Maintenance Frames
Every time a link is added using either a request or a callback-request, a call-status-indication frame must be sent to verify whether or not the new link was successfully added.
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Link Termination Frames
If a peer determines that a link in a bundle is no longer needed, it can send a link-drop-query-request. Unlike LCP terminate-requests, which must always be acknowledged, requests can be refused. If a link-drop-query-request is acceptable, the peer sends an LCP frame to terminate that particular link.
BAP Configuration Options
The table above summarizes which BAP configuration options are required and which are optional in different types of BAP frames.
Link-Type Option
The link-type option specifies the speed and the type of link. Peers are required to include the link-type option in call-request and callback-request frames. In call- or callback-response frames, peers are allowed (but not required) to include the link-type information.
Phone-Delta Option
The phone-delta option provides either an actual phone number or some other unique identifier for the port to which a link is connected. Peers must include this number in callback-request and call-response frames and are allowed to use this number in a call-status-indication frame.
