CCDA 640-864 Summary Notes – Chapter 6 – Day 13

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Exam Topic 1: Wide-area networks (WAN) Overview

WAN – communication networks that are used to connect network locations that are geographically separated.

Tarrif – a fee charged by a service provider for providing WAN services to customers.

Service – WAN communications provided by service providers or telecommunication carriers

Choice of WAN Technology depends on :

  • cost
  • bandwidth
  • reliability
  • manageability
  • hardware capabilities

Design requirements depend on:

  • SLA – availability of the network. Example
    • bandwidth
    • allowed latency
    • permittable loss
  • Cost and Usage

Key WAN design objectives:

  • Design should meet company goals and policies
  • Design should support current application requirements and have room for future growth
  • Design should be within the allocated budget

WAN Connection Modules

Connectivity modules:

  • Connection to the Internet
  • Connection to the DMZ
  • Connection to the WAN

Technologies can be

  • Point to Point
  • Point toMultipoint
    • Frame Relay
    • MPLS WAN

 

Exam Topic 2: WAN Transport Technologies

Integrated Services Digital Network (ISDN)

Overview:

  • Standardized early 1980s
  • An all digital phone line connection
  • Both voice and data can be transmitted over the digital phone line
  • Comes in 2 service types;
    • ISDN Basic Rate Interface (BRI)
      • Channels:2B + 1 D
        • B channels operate at 64kbps and carry user data
        • D channels
          • 16 kbps carry signaling anc control information
          • 48 kbps used for framing and synchronization
      • Total bit rate = 64 + 64 + 16 + 48 = 192 kbps
    • ISDN Primary Rate Interface (PRI)
      • North American and Japan
        • channels: 23 B + 1 D
        • All channels operate at 64 kbps
        • Total bit rate = 23 * 64 + 1* 64 = 1.536 kbps + 8 kbps (framing overhead) = 1.544 kbps
      • Rest of the World
        • Channels: 30 B + 2 D (Typically)
          • Channel 0          –           D-channel (Used mainly for clocking and synchronisation)
          • Channel 1-15    –           B-channel (Voice)
          • Channel 16        –           D-channel (Signalling)
          • Channel 17-31  –           B-channel (Voice)
        • All channels operate at 64 kbps
        • Total bit rate = 30 *64 + 2 * 64 = 2048 kbps
  • Not frequently used now. Used where broadband services like DSL, Cable and wireless are unavailable

Characteristics:

  • Low Bandwidth
  • Medium Reliability
  • Medium Latency
  • Low Cost

Differences with the Old dialup connection

  • Voice and data were transmitted over analog signals
  • Greater bandwith than dial up
  • Lower latency than dil up

Digital subscriber line (DSL)

  • Uses ordinary copper telephone lines to provide high speed Internet data services
  • It uses frequencies that are not used for  normal telephone conversations
  • Primarily used in residential community but can be used for WAN too
  • xDSL – different forms of DSL
    • ADSL (Asymmetric digital subscriber line)
      • most popular and widely available
      • Downstream bandwidth is higher than the upstream bandwidth
      • Can only be used in close proximity to the digital subscriber line access multiplexer (DSLAM) (2km max)
      • DSLAM allows the telephone lines to be connected to the Internet
      • Download speed (768 kbps to 9 Mbps )
      • Upload speed (64 kbps to 1.5 Mbps)
      • Customer Premises Equipment
        • PC
        • DSL Modem or DSL router
      • CPE connects to network access provider (NAP) DSLAMs
      • ADSL circuit has the following channels
        • Medium-speed downstream channel
        • Low-speed upstream channel
        • Basic telephone service channel
      • DSL splitters separate basic phone services from the ADSL modem/router to provide service even when ADSL signal fails
    • SDSL (Symmetric digital subscriber line)
      • Volume of data flow is equal in both directions
  • Since it is a public network over the internet, it should be used with VPN or firewalls

Characteristics:

  • Low /Medium Bandwidth
  • Low Reliability
  • Medium Latency
  • Low Cost
  • High speeds

Broadband Cable

  • Uses coaxial cable to transport data over cable distribution systems
  • CPE
    • Cable Modem or Universal Broadband Router (uBR)
    • Support data, voice and video TCP/IP
    • Provide services to small business, branch and teleworkers
  • ISP side
    • Cable Modem Termination System (CMTS)
  • Data Over Cable Service Interface Specifications (DOCSIS) protocol defines the cable procedures that the equipment needs to support.
  • PC connects to TCP/IP network using PPPoE or DHCP

Characteristics:

  • Low /Medium Bandwidth
  • Low Reliability
  • Medium Latency
  • Low Cost

Wireless

  • Uses electromagnetic waves to carry the signal between end points
  • Wireless Implementations
    • Bridge wireless
      • Wireless bridge connects two separate wireless networks
      • High data rates provided
      • Used as a temporary solution for hard to wire sites, temporary networks, warehouses
    • Wireless LAN
      • Saves time and wiring by avoiding costly physical layer wiring solutions
    • Mobile wireless
      • Consists of cellular applications and mobile phones
      • Technologies:
        • Global System for Mobile Communications (GSM)
          • Digital mobile radio standard
          • Data transfer rate is 9600 bps
          • Can roam internationally
          • uses Time Division Multiplex Access (TDMA) in 3 frequency bands
            • 900 MHz
            • 1800 MHz
            • 1900 MHz
        • General Packet Radio Service (GPRS)
          • Increases GSM speeds from 64 kbps to 128 kbps
        • Universal Mobile Telecommunications Service (UMTS) / 3G broadband
          • Packet based transmission of digitized voice, video and data
          • Transmission rates of 2 Mbps
          • Provides location independent services to mobile users throught the world

Characteristics:

  • Low / Medium Bandwidth
  • Low Reliability
  • Medium Latency
  • Medium Cost

Frame Relay

  • Deployed since 1980s
  • Packet switched connection oriented Layer 2 WAN protocol
  • Uses virtual circuits between connected devices
  • Connection on the data link layer is established using  a DTE device (router) and DCE device (frame switch)
  • Circuit types:
    • Permanent Virtual Circuit (PVC)
      • Connections are permanent
      • Used predominantly
      • Uses Data Link Connection Identifier (DLCI) to identify the local end of the PVC
      • DLCI is locally significant numeric value
    • Switched Virtual Circuit (SVC)
      • Temporary connections are created for each data transfer session
  • Use is on the decline because of MPLS

Characteristics:

  • Low /Medium  Bandwidth
  • Medium Reliability
  • Low Latency
  • Medium Cost

Time-Division Multiplexing (TDM)

  • Interleaves bits from multiple data, voice  and video channels over one communication medium
  • Basic DS0 = 64 kbps
  • North America
    • DS1 or T1
      • 24 time slots = 64 kbps + 8 kbps control
      • 1.544 Mbps of bandwidth
    • DS3 or T3
      • 44.736 Mbps of bandwidth
  • Rest of the World
    • E1
      • 30 channels
      • 2.048 Mbps of bandwidth
  • Service providers can gurantee or reserve bandwidth
  • Customers are charged for exclusive access to the circuits
  • Network is typically shared hence ISPs are more flexible in managing the newtorks and the services offered

Characteristics:

  • Medium Bandwidth
  • High Reliability
  • Low Latency
  • Medium Cost

Metro Ethernet

  • Uses Ethernet to deliver low cost, high speed WAN MAN connectivity for organizations
  • Deliver converged network services on the same wire
  • Provides enterprise LAN type functionality out in the MAN and WAN increasing the throughput available for applications
  • Bandwidth : 10 Mbps to 1 Gbps or +
  • Supports higher performance
  • Increased QoS  requirements
  • Difference with TDM:
    • Easier to deploy
    • Easier to scale
    • Flexible bandwidth increaments
  • Appealing because of the use of Ethernet

Characteristics:

  • Medium / High Bandwidth
  • High Reliability
  • Low Latency
  • Medium Cost

Synchronous optical networking (SONET) / Synchronous Digital Hierarchy (SDH)

  • Has a circuit based architecture
  • Delivers high speed services over optical network
  • SONET
  • SDH
    • Defined by International Telecommunication Union (ITU)
  • Gurantees bandwidth
  • Line rates of 155 Mbps to 10 Gbps +
  • Uses a ring topology to connect sites
    • The rings support ATM or Packet over SONET (POS) IP encapsulations
  • Provides automatic recovery capabilities
  • Has self healing mechanisms
  • OC – optical carrier rates. These are digital bandwidth hierarchies
    • Supported speeds
      • OC-1 = 51.85 Mbps
      • OC-3 = 155.52 Mbps
      • OC-12 = 622.08 Mbps
      • OC-24 = 1.244 Gbps
      • OC-48 = 2.488 Gbps
      • OC-192 = 9.952 Gbps
      • OC-255 = 13.21 Gbps
    • Common circuit sizes
      • OC-3 = 155 Mbps
      • OC-12 = 622 Mbps
  • Redundancy and High availability is inbuilt in the architecture

Characteristics:

  • High Bandwidth
  • High Reliability
  • Low Latency
  • High Cost

MPLS

  • Uses labels (numbers) to forward packets
    • Marks packet headers that include label information
    • Specific paths in the network can be designed to correspond to the label
    • Packets that are destined to the same endpoint with the same requirements can be forwarded based on the labels, without a routing decision at every hop
  • MPLS labels can be set on parameters such as
    • Source addresses
    • L3 destination address (typically)
    • Layer 2 circuit ID
    • QoS Value
  • Labels can be used to implement traffic engineering
    • This overides the routing table
  • Can run over:
    • Layer 2 topologies
      • ATM
      • Frame Relay
      • Packet over SONET (POS)
      • Ethernet
  • Goals:
    • Maximize switching using labels
    • Minimize L3 routing
  • MPLS Implementation has the following
    • Customer Edge (CE)
      • Resides at customer premises
      • Internal and external routing information is exchanged
      • Connects to the PE
    • Provider Edge (PE)
      • Ingress to MPLS service provider network
      • Resides in service provider network

Characteristics:

  • High Bandwidth
  • High Reliability
  • Low Latency
  • High Cost

Dark Fiber

  • Fiber optic cables that have been installed in the ground or where right of way issues are evident
  • May use signalregenerators for:
    • Jitter control over long distances
    • Maintain signal integrity
  • Framing is determined by the enterprise not the provider
  • Can also be used for the edge devices
  • Usually owned by service providers but can be bought like leased lines for use in MAN and WAN
  • Reliability of these links is not provided by the SP but designed by the enterprise
  • Redundancy and High availability has to be designed with multiple links

Characteristics:

  • High Bandwidth
  • High Reliability
  • Low Latency
  • High Cost

Dense Wavelength-Division Multiplexing (DWDM)

  • Uses different wavelengths of light (channels) over the same fiber strands to increase fiber optics bandwidth capabilities
  • Each fiber channel is equivalent to several GE links
  • Increased use of bandwidth using existing fiber base by SP
  • SPs can increase services provided because of greater bandwidth
  • A variety of devices can access the network

Characteristics:

  • High Bandwidth
  • High Reliability
  • Low Latency
  • High Cost

Ordering WAN Technology and Contracts

Ordering:

  • Plan early
  • Takes ~ 60 days for the carrier to provision circuits. If overseas (60 to 120 days)

Cost of WAN

  • Access circuit charge
  • Distance-based charges (at times. Most carriers have eliminated this)

Metro Ethernet

  • Availability is spotty
  • Lead times are long
  • Construction may be necessary – more cost and time delay

Frame Relay and ATM

  • Charges:
    • Access circuit charges
    • per- PVC charges
    • per-bandwidth CIR charges. CIR – rate the SP guarantess to provide

Contract periods

  • Typically 1 – 5 years.
  • Dark fiber (usually 20 years). Need the right of non-reversion in SLA (no matter what happens to SP, the fiber belongs to the customer for 20 years)
  • Process to repair fiber cuts shouls also be defined

 

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