Wide Area Network (WAN)

1
Wide Area Network (WAN)

• Protocols

2
Difference Between LAN and WAN

• In general, a LAN is internally owned in a
  business whereas a WAN is leased infrasctructure.
  (at least as far as the CCNA exam is concerned)
  (Lammle, p.478)
• The key to understanding WAN technologies is to
  be familiar with the different WAN terms and
  connection types often used by service providers.
  (Lammle, p.478)

3
Wide Area Network Terms (Lammle, p.478)

• Customer premises equipment (CPE) equipment
  owned by the subscriber and located on the
  subscribers premises.
• Demarcation point the spot where the service
  providers responsibility ends and the CPE begins.

4
WAN Terms (cont.) (Lammle, p. 479)

• Local loop connects the demarc to the closet
  switching office, called a central office.
• Central office (CO) connects the customers to
  the providers switching network. Sometimes
  referred to as a point of presence (POP).
• Toll network a trunk line inside a WAN
  providers network. This network is a collection
  of switches and facilities owned by the ISP.

5
WAN Connection Types(Lammle, p.479)

• Leased line a pre-established WAN
  communications path from the CPE, through the DCE
  switch, to the CPE of the remote site, allowing
  DTE networks to communicate at any time with no
  setup procedures before transmitting data.
• Circuit switching uses dial-up modems or ISDN
  and is used for low-bandwidth data transfers.
  Think phone call.

6
WAN Connection Types (cont.)(Lammle, p. 479)

• Packet switching allows you to share bandwidth
  with other companies to save money. Can be
  thought of as a network thats designed to look
  like a leased line, yet costs more like circuit
  switching.
• The downside if data transfer is needed
  constantly this option is not good. Speeds can
  range from 56Kbps to T3 (45 Mbps). Frame Relay
  and X.25 are packet-switching technologies.

7
Prominent WAN protocols used today(Lammle,
p.480)

• Frame Relay
• ISDN Integrated Services Digital Network
• LAPB Link Access Procedure, Balanced
• HDLC High-Level Data-Link Control
• PPP Point-to-Point Protocol
• ATM Asynchronous Transfer Mode

8
Frame Relay (Lammle, p.480)

• A packet-switched technology that emerged in the
  early 1990s
• A Data link and Physical layer specification that
  provides high performance
• Can be more cost effective than point-to-point
  links
• Can run at speeds of 64Kbps up to 45 Mbps (T3).

9
ISDN (Lammle, p. 480)

• Integrated Services Digital Network
• A set of digital services that transmit voice and
  data over existing phone lines.
• A possible cost-effective solution for remote
  users who need a higher-speed connection than
  analog dial-up links offer.
• Recommended as a backup link for other types of
  links such as Frame Relay or T-1 connections.

10
LAPB (Lammle, p.481)

• Link Access Procedure, Balanced
• Lammle says its not on the CCNA exam
• Created to be a connection-oriented protocol at
  the Data Link layer for use with X.25
• Causes high overhead because of its strict
  timeout and windowing techniques

11
HDLC (Lammle, p.481)

• High-Level Data-Link Control
• HDLC is a protocol at the Data Link layer, and
  has very little overhead compared to LAPB.
• The HDLC header carries no identification of the
  type of protocol being carried inside the HDLC
  encapsulation. Because of this, each vendors
  HDLC is proprietary for their equipment.

12
PPP (Lammle, p.481)

• Point-to-Point Protocol
• An industry standard protocol
• It uses a Network Control Protocol field in the
  Data Link header to identify the Network layer
  protocol. It allows authentication and multilink
  connections and can be run over asynchronous and
  synchronous links.

13
Asynchronous vs. Synchronous

• Asynchronous transmission digital signals sent
  without precise timing, usually with different
  frequencies and phase relationships. (Lammle, p.
  554)
• Synchronous transmission signals transmitted
  with precision clocking.
• (Lammle, p.604)

14
ATM (Lammle, p.481)

• Asynchronous Transfer Mode
• Lammle says its not on the CCNA exam
• Created for time-sensitive traffic (like video),
  providing simultaneous transmission of voice,
  video, and data
• ATM uses cells instead of packets that are a
  fixed 53 bytes long.

15
Serial Transmission(Lammle, p.482)

• Cisco serial connections support almost any type
  of WAN service.
• Typical WAN connections are dedicated leased
  lines using HDLC, PPP, ISDN, and Frame Relay.
• Typical speeds run anywhere from 2400 bps to 45
  Mbps (T3).
• HDLC, PPP, and Frame Relay can use the same
  Physical layer specifications, but ISDN has
  different pinouts and specifications at the
  Physical layer.

16
Serial Transmission(Lammle, p. 482)

• WAN serial connectors use serial transmission,
  which takes place one bit at a time over a single
  channel.
• Cisco routers use a proprietary 60-pin serial
  connector that you must get from Cisco or a
  provider of Cisco equipment.
• Serial links are described in frequency or
  cycles-per-second (hertz).
• The amount of data that can be carried within
  these frequencies is called bandwidth. Bandwidth
  is the amount of data in bits-per-second that the
  serial channel can carry.

17
DTE/DCE (Lammle, p.482)

• Router interfaces are, by default, data terminal
  equipment (DTE), and they connect into data
  communication equipment (DCE) for example a
  channel service unit/ data service unit
  (CSU/DSU).
• The CSU/DSU then plugs into a demarcation
  location (demarc) and is the service providers
  last responsibility.
• Most of the time, the demarc is a jack that has
  an RJ-45 female connector located in a
  telecommunications closet.

18
More on HDLC (Lammle, p.483)

• The High-Level Data-Link Control (HDLC) protocol
  is a popular ISO-standard, bit-oriented Data Link
  layer protocol.
• HDLC is a point-to-point protocol used on leased
  lines.
• No authentication can be used with HDLC.
• HDLC is the default encapsulation used by Cisco
  routers over synchronous serial links.
• Ciscos HDLC is proprietary as are all HDLC
  implementations.

19
More on HDLC (Lammle, p.483)

• In byte-oriented protocols, control information
  is encoded using entire bytes.
• On the other hand, bit-oriented protocols may use
  single bits to represent control information.
• Bit-oriented protocols include SDLC, LLC, HDLC,
  TCP, IP, and others.

20
Point-to-Point Protocol (PPP)(Lammle, p. 484)

• Point-to-Point Protocol (PPP) is a Data Link
  layer protocol that can be used over either
  asynchronous serial (dial-up) or synchronous
  serial (ISDN) media.
• It uses the LCP (Link Control Protocol) to build
  and maintain data-link connections.
• The basic purpose of PPP is to transport layer 3
  packets across a Data Link layer point-to-point
  link.

21
PPP Protocol stack compared to OSI Reference
Model (Lammle, p. 485)
22
PPP contains four main components (Lammle, p.485)

• 1) EIA/TIA-232-C, V.24, V.35, and ISDN a
  Physical layer international standard for serial
  communication.
• 2) HDLC a method for encapsulating datagrams
  over serial links.
• 3) LCP a method of encapsulating, configuring,
  maintaining, and terminating the point-to-point
  connection.
• 4) NCP a method of establishing and configuring
  different Network layer protocols. NCP is
  designed to allow the simultaneous use of
  multiple Network layer protocols.

23
PPP

• For more in depth PPP information see Lammle, Ch.
  11, p. 485-487
• Wendell Odom, INTRO, Ch. 4, p. 92 95
• Also, ICND, Ch. 9, p. 311 - 313

24
Frame Relay (Lammle, p. 489)

• Frame Relay has become one of the most popular
  WAN services deployed over the past decade due to
  cost.
• Frame Relay is a packet-switched technology.
• It doesnt work like a dedicated point-to-point
  leased line.
• Point-to-point vs. packet-switched example.

25
Frame Relay

• For more information refer to
• Todd Lammle, Ch. 11, p.489 503
• Wendell Odom (Cisco Press)
• ICND, Ch. 11, p.376 413
• INTRO, Ch. 4, p.96 - 100

26
Integrated Services digital Network (ISDN)
(Lammle, p. 503)

• ISDN is a digital service designed to run over
  existing telephone networks.
• Can support both data and voice.
• Typical ISDN applications and implementations
  include high-speed image applications, high-speed
  file transfer, videoconferencing, and multiple
  links into homes of telecommuters.

27
ISDN (Lammle, p.503)

• PPP is typically used with ISDN to provide data
  transfer, link integrity, and authentication.
• ISDN is not a replacement for PPP, HDLC, or Frame
  Relay, because its really an underlying
  infrastructure that any of these could use.
• PPP is the most common encapsulation across ISDN
  connections.

28
Benefits of ISDN (Lammle, p.503)

• It can carry voice, video, and data
  simultaneously.
• Call setup is faster than with an analog modem.
• Data rates are faster than on an analog
  connection.
• Full-time connectivity across the ISDN is spoofed
  by the Cisco IOS routers using dial-on-demand
  (DDR) routing.

29
Benefits of ISDN (cont.)(Lammle, p. 504)

• Small office and home office sites can be
  economically supported with ISDN BRI services.
• ISDN can be used as a backup service for a
  leased-line connection between the remote and
  central offices.
• Modem racking and cabling can be eliminated by
  integration of digital modem cards on Cisco IOS
  Network Access Server (NAS).

30
ISDN Connections(Lammle, p. 504)

• ISDN Basic Rate Interface (BRI) is two B (Bearer)
  channels of 64k each, and one D (Data) channel of
  16k for signaling.
• Primary Rate Interface (PRI) provides T-1 speeds
  (1.544 Mbps) but according to Lammle, its not
  on the CCNA exam.

31
Basic Rate Interface (BRI)(Lammle, p.508)

• ISDN BRI service, also known as 2BD, provides
  two B channels and one D channel.
• The BRI B-channel service operates at 64kps and
  carries data, while the BRI D-channel service
  operates at 16Kbps and usually carries control
  and signaling information.
• Total bandwidth for ISDN BRI is then 144Kbps (64
  64 16 144).

32
BRI (cont.)(Lammle, p.508)

• The D-channel signaling protocols (Q.921 and
  Q.931) span the OSI reference models Physical,
  Data Link, and Network layers.
• The D channel carries signaling information to
  set up and control calls.

33
Dial-on-Demand Routing (DDR)(Lammle, p. 510)

• Used to allow two or more Cisco routers to dial
  an ISDN dial-up connection on an as-needed basis.
• DDR is only used for low-volume, periodic network
  connections using either Plain Old Telephone
  Service (POTS) or ISDN connection.
• Designed to reduce WAN costs if youre billed on
  a per-minute or per-packet basis.

34
Thats All Folks

• .