WAN

1
WANs and Routers

• PJC CCNA Semester 2 Ver. 3.0
• by
• William Kelly

2
Wan Characteristics

• WANs cover a wide geographical area (1000 m is
  usually the cut-off point between a LAN and a
  WAN)
• They involve a service contract with a carrier
• WANs usually use serial connections (Why
  serial?)

3
WAN Performance Characteristics

• Uptime be careful about the timeframe used to
  state uptime (it may differ from your clients
  needs)
• Mean Time between Failure (MTBF)
• Ambient temperature
• Power Supply characteristics (filtered?)
• Quality and handling of the devices
• Uptime Monitors
• Netsaint, and MRTG (UNIX/WIN versions)

4
WAN Performance Characteristics

• Traffic Volumes -
• Maximum The peak volume you expect your network
  to handle
• Average Traffic you can expect in a typical
  business day
• Delay
• Propagation Delay
• Satellite uplink/downlink Delay
• Forwarding Delay

5
WAN Devices

• Routers - offer many services, including LAN and
  WAN interface ports. 
• Switches - connect to WAN bandwidth for voice,
  data, and video communication.
• Modems - interface voice-grade services. Modems
  include CSUs/ DSUs and TA/NT1 devices that
  interface ISDN services.
• Communications Servers - concentrate dial-in and
  dial-out user communication

6
WAN Standards

• EIA/TIA-232 developed by TIA/EIA, supports
  signal speeds of up to 64kbps, formerly called
  RS-232
• EIA/TIA-449 a faster version of EIA/TIA-232 (up
  to 2 Mbps), capable of longer cable runs.
• EIA/TIA-612/613 A standard describing HSSI,
  which provides access to services at T3 (45
  Mbps), E3 (34 Mbps), SONET (51.84 Mbps) rates.
• V.35 An ITU-T standard describing a
  synchronous, physical-layer protocol used for
  communications between a network access device
  and a packet network. For speeds up to 48kbps
• X.21 -- An ITU-T standard for serial
  communications over synchronous digital lines.
• G.703 - Connections between telephone company
  equipment and DTE using British Naval connectors
  (BNCs) Operating at E1 data rates.
• EIA-530 - Two electrical implementations of
  EIA/TIA-449 RS-422 (for balanced transmission)
  and RS-423 (for unbalanced transmission).

7
WAN Standards

• High-Level Data Link Control (HDLC)
• A proprietary Cisco format
• It is the default encapsulation on Point to Point
  and Circuit switched connections
• Only use HDLC with other Cisco equipment
• Frame Relay
• Uses high quality digital facilities
• NO ERROR CORRECTION!!!
• Handles multiple virtual circuits

8
WAN Standards

• Point-to-Point (PPP)
• Built in authentication such as Password
  Authentication Protocol (PAP) and Challenge
  Handshake Authentication Protocol (CHAP)
• PPP can check for link quality during connection
  establishment
• Link Access Procedure Balanced (LAPB) used by
  X.25 and has extensive error checking
• Link Access Procedure on the D channel (LAPD)
  used for signaling and call setup on ISDN

9
WAN Connection Services
10
Circuit vs. Packet Switched

• Circuit Switched A PHYSICAL connection through
  a carrier is established, maintained, and
  terminated
• Packet Switched Units of data called packets
  are routed through a network based on the
  destination address in the packet

11
Typical Packet Switched Network
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Packet/Cell Switched

• Packet
• X.25 old standard, extensive error correction
• Frame Relay no error correction, moderate cost,
  very popular
• CELL
• ATM uses fixed 53 byte length cells to carry
  data, cost is high
• SMDS Used in MANs, high cost, not in
  widespread use

13
Dedicated Digital Services

• T1, T3, E1, E3 Widespread, moderate cost, 1.544
  Mbps 44.736Mbps for T1 T3
• xDSL Many types such as AsynchronousDSL (ASDL),
  High Bit RateDSL (HDSL), etc., cost is moderate,
  bandwidth is high
• SONET very high speed, designed to run on
  fiber, not for home users

14
Nationwide SONET Network
15
Miscellaneous WAN Technologies

• Dialup modem (switched analog) widespread use,
  low speed, low cost, 56k max bandwidth
• Cable Modem (shared analog) low cost, bandwidth
  varies, uses coaxial cable
• Wireless requires no cable, use is widespread,
  cost is high (satellite or microwave)

16
WAN Routers (Router Internals)

• Random Access Memory (RAM/DRAM)
• Stores Routing Tables
• Packet buffering
• Provides temporary memory for running
  configuration
• ARP Cache is kept here
• Fast Switching Cache
• Packet-hold Queues
• All content is LOST when power is lost

17
WAN Routers (Router Internals)

• Nonvolatile random Access Memory (NVRAM)
• Stores Backup/Startup Configuration
• Retains content when router is powered down

18
WAN Routers (Router Internals)

• Flash Memory
• Erasable Programmable Read Only Memory (EPROM)
• Holds the Operating System and microcode
• Allows software to be updated without removing
  chips
• Content remains when powered down
• Multiple Cisco IOS Software can be stored here
  (depending on space)

19
WAN Routers (Interface)

• Interface
• Network connection where packets enter and exit
  the router
• Located either on the motherboard or a separate
  interface module

20
WAN Routers- Physical Components

• Routers are specialized computers containing
• Central Processing Unit (CPU)
• Random Access Memory (RAM)
• Basic Input Output System (BIOS)
• Operating System (OS)
• A motherboard
• Physical Input/Output Ports
• A power supply and chassis

21
WAN Routers- Functions of a Router

• Physical Interconnectivity
• ports
• Logical Interconnectivity
• Default Routes, Routing Tables
• Route calculation and maintenance
• Identify Potential routes
• Calculate best route based on a formula
• Monitor and detect topology changes
• Security
• Access Control Lists (ACLs)

22
WAN Routers- Evaluating Routing Protocols for
Performance

• Optimality ability to choose best route
• Efficiency Best use of RAM, CPU, etc.
• Robustness Does the protocol work well even
  during network failures?
• Convergence How fast can routers agree on
  network topology?
• Scalability Can my network grow?

23
WAN Routers- Router Functions

• Best Path Determination routers build routing
  tables with a list of paths to networks
• Switching of packets to proper outgoing interface
  routing tables list the interface with the
  network

24
WAN Routers- Important Terms

• WAN A collection of LANs
• Network a generic collection of related
  networking mechanisms belonging to a single
  organization
• Internetwork A collection of loosely related
  networks that are interconnected
• Autonomous system A network that is relatively
  self-contained and maintained by one person. You
  may have connections to other networks.

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WAN Routers- Internetworking Scenarios

• Routing Within a Network interior routers,
  minimal router overhead, possible static routes
• Routing Between Adjacent Networks Networks that
  are directly connected, Border routers may have
  summarized information
• Routing Between Nonadjacent Networks most
  complicated, risk of intrusion is much higher,
  border routers summarize internal network