Download - FTP Directory Listing

rockyboygangNetworking and Communications

Oct 24, 2013 (3 years and 10 months ago)

227 views


ProCurve Networking by HP
Student guide
Technical training
WAN Technologies
Version 5.21


Rev. 5.21 HP Restricted
i
Contents

Overview
Introduction..............................................................................................................1
Course Objectives.....................................................................................................1
Prerequisites.............................................................................................................2
Course Module Overviews.......................................................................................2
Module 1: Overview of WAN Connections
Objectives.................................................................................................................1
Introduction..............................................................................................................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.................................................................................................................1
Overview 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
Link Control Protocol Configuration Options........................................................13
WAN Technologies
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.................................................................................................................1
Overview 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 3 Summary................................................................................................36
Contents
Rev. 5.21 HP Restricted
iii

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.................................................................................................................1
Overview 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
Module 5 Summary................................................................................................35
WAN Technologies
iv
HP Restricted

Rev. 5.21
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.................................................................................................................1
Defining 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 7 Summary................................................................................................28
Contents
Rev. 5.21 HP Restricted
v

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.................................................................................................................1
Traffic 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
Module 9 Summary................................................................................................24




Rev. 5.21 HP Restricted
Overview - 1
Course Overview

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
WAN Technologies
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.
Course Overview
Rev. 5.21 HP Restricted
Overview - 3

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.


Rev. 5.21 HP Restricted
1 – 1
Overview of WAN Connections
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
ProCurve WAN Technologies
1 – 2 HP Restricted
Rev. 5.21
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
companies.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 3

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)
ProCurve WAN Technologies
1 – 4 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 5

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
Protocols.
ProCurve WAN Technologies
1 – 6 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 7

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.
ProCurve WAN Technologies
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 9

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.
ProCurve WAN Technologies
1 – 10 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 11

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.
ProCurve WAN Technologies
1 – 12 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 13

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)
DSL is discussed in-depth in Module 5: DSL WAN Connections.
ProCurve WAN Technologies
1 – 14 HP Restricted
Rev. 5.21
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:
Carrier Line WAN Connections.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 15

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.
The remainder of this module focuses on the synchronous electrical specifications
and related technologies that define the basic unit of bandwidth (the DS0 channel)
used in copper-based public carrier networks.
ProCurve WAN Technologies
1 – 16 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 17

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:
8 bits per sample x 8,000 samples per second = 64 Kbps
ProCurve WAN Technologies
1 – 18 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 19

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.
ProCurve WAN Technologies
1 – 20 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 21

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.
ProCurve WAN Technologies
1 – 22 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 23

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:
Carrier Line WAN Connections.
ProCurve WAN Technologies
1 – 24 HP Restricted
Rev. 5.21
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.
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 25

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.
ProCurve WAN Technologies
1 – 26 HP Restricted
Rev. 5.21
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 2: Data-Link–Layer Protocols explains data-link–layer protocols in detail.

Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 27

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
Pulse code modulation
Time division multiplexing
ProCurve WAN Technologies
1 – 28 HP Restricted
Rev. 5.21
Learning Check
Module 1
Overview of WAN Connections
Rev. 5.21 HP Restricted
1 – 29

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


Rev. 5.21 HP Restricted
2 – 1
Data-Link–Layer Protocols
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)

Describe GRE
ProCurve WAN Technologies
2 – 2 HP Restricted
Rev. 5.21
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
Rev. 5.21 HP Restricted
2 – 3

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.
ProCurve WAN Technologies
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

To connect LANs that use incompatible IP addresses
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 5

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.
ProCurve WAN Technologies
2 – 6 HP Restricted
Rev. 5.21
HDLC uses three different types of frames:

Unnumbered frames establish a link.

Supervisory frames carry error and flow control information.

Information frames carry the network-layer packets across the WAN link.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 7

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.
ProCurve WAN Technologies
2 – 8 HP Restricted
Rev. 5.21
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.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 9

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.
ProCurve WAN Technologies
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
frames. The session is then terminated and returns to the link dead phase.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 11

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.
ProCurve WAN Technologies
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
configure-reject.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 13

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
maximum-receive-unit configuration option.
ProCurve WAN Technologies
2 – 14 HP Restricted
Rev. 5.21
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.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 15

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.
ProCurve WAN Technologies
2 – 16 HP Restricted
Rev. 5.21
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.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 17

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.
ProCurve WAN Technologies
2 – 18 HP Restricted
Rev. 5.21
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.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 19

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
.
ProCurve WAN Technologies
2 – 20 HP Restricted
Rev. 5.21
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.)
CCP includes the option to identify compression algorithms by an OUI.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 21

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.)
ProCurve WAN Technologies
2 – 22 HP Restricted
Rev. 5.21
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).
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 23

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
are reassembled. The default for the MRRU, like the default for the MRU, is
1500 octets.
ProCurve WAN Technologies
2 – 24 HP Restricted
Rev. 5.21
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.)
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 25

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.)
ProCurve WAN Technologies
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
BACP is explained in a later section.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 27

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 call-request or a callback-request, a call-
status-indication frame must be sent to verify whether or not the new link was
successfully added.
ProCurve WAN Technologies
2 – 28 HP Restricted
Rev. 5.21
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, link-drop-query-requests can be refused. If a link-drop-query-
request is acceptable, the peer sends an LCP frame to terminate that particular link.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 29

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.
ProCurve WAN Technologies
2 – 30 HP Restricted
Rev. 5.21
No-Phone-Number Option
The no-phone-number option informs the receiving peer that the sending peer
already has its phone number. A call-request frame can include the no-phone-
number option. If this option is included in the call-request frame, peers must not
include the phone-delta option in the call-response frame.
Link-Discriminator Option
The link-discriminator option designates which link the peer wants to drop and
refers to the link discriminator number that was set up by the LCP. This option is
required in link-drop-query-request frames.
Call-Status Option
The call-status option is used only in call-status-indication frames. A value of 0
indicates that a call was successful. Other values can be assigned to indicate why a
call failed. The call-status option also indicates whether or not a peer should retry
adding a link.
Reason Option
The reason option contains an ASCII text string that describes the reason for a
request or response. Peers can include the reason option in any BAP configuration
frame.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 31

Bandwidth Allocation Control Protocol


BACP is an NCP that manages configuration options for BAP. Before peers can
exchange BAP frames, they must exchange BACP frames to negotiate which peer
will be favored in the event of a race. That is, when peers attempt to transmit BAP
requests simultaneously, one of the peer’s requests must be favored. The favored
peer’s BAP request frame will be used.
BACP accomplishes this purpose through the use of configure-request frames that
contain the favored-peer configuration option. Each peer is assigned a magic
number. The peer with the lower number becomes the favored peer. (To review
magic numbers, refer back to the “Link Control Protocol Configuration Options:
section in this module.)
ProCurve WAN Technologies
2 – 32 HP Restricted
Rev. 5.21
Tunneling Overview


A tunnel is a virtual point-to-point link across a multipoint-access network, such as
the Internet. In a sense, a tunnel emulates a WAN link. Most data-link–layer
protocols that are used in WAN connections:

Encapsulate other protocols

Set up a point-to-point link
Tunnels can provide these same two services over the Internet or in an extranet.
They can also be used in a private WAN if some traffic is incompatible with
intermediate routers.
Using tunnels over the Internet or in an extranet usually requires additional
security to protect the data being exchanged. These additional security
requirements are discussed in Module 7: Virtual Private Networks.
This section focuses on how tunnels can be used to route incompatible traffic
through intermediate routers. When incompatible traffic is encapsulated in a
tunnel, that traffic travels unnoticed by routers other than those at the endpoints of
the tunnel. A tunnel also creates a routing system that hides addresses from
intermediate routers, which is useful if you need this level of security.
Data Link Layer Protocols
Rev. 5.21 HP Restricted
2 – 33

Three tunneling protocols are briefly introduced here:

Generic Routing Encapsulation (GRE)

Point-to-Point Tunneling Protocol (PPTP)

Layer 2 Tunneling Protocol (L2TP)
GRE can encapsulate multiple network-layer, data-link–layer, or multicast
protocols into an IP packet. GRE then uses source routing to create a virtual point-
to-point link through an IP network (such as the Internet). (GRE is described more
fully in the next section.)
PPTP is a proprietary tunneling protocol created by Microsoft. It encapsulates PPP
and creates a tunnel for a PPP frame to travel through an IP network. In the PPTP
tunneling system, PPP handles the encapsulation of network-layer or multicast
traffic.
L2TP is an Internet Engineering Task Force (IETF) standard based on PPTP and
the proprietary Layer 2 Forwarding (L2F) protocol created by Cisco Systems