Transcript Lecture 03

NETE0510
Introduction to Transmission
Technologies
Supakorn Kungpisdan
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Outline
 General Network Topologies
 Connecting and Circuit Types and Services
 Private Leased Lines VS Switched Networks
 Transmission Basics
 Hardware Selection in the Design Process
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General Network Topologies
 5 most common used network topologies:
 Point-to-point
 Multipoint (bus)
 Star
 Ring (or loop)
 Mesh
 Node: a network data communication element e.g.
router, switch
 Link: a circuit connection between nodes
 Logical link  PVC (Permanent Virtual Circuit)
 Physical link  dedicated private link
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Point-to-Point
 Simplest, a single link between two nodes
 Can be composed of multiple physical and/or
logical circuits
 Most commonly used in MANs and WANs
 E.g. private line or dedicated circuit
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Point-to-Point (cont’d)
A. single link with single physical and logical circuit
B. single link with multiple logical circuits
C. single path with multiple physical circuits, each carrying multiple circuits
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Common Bus (Multipoint)
 All nodes are physically connected to a common bus
structure
 E.g. IEEE802.3 Ethernet protocol
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Common Bus (cont’d)
 Point-to-multipoint (broadcast) used in
Broadband Integrated Services Digital Network
(B-ISDN)
 Multipoint-to-point (incast)
 Multipoint-to-multipoint: combination of
broadcast and incast
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Common Bus (cont’d)
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Star
 Developed during mainframe era
 Central node only provides point-to-point connections
between any edge on wither a physical or a logical
switched basis
 Hub and switch: physical star, logical bus
 Hub-and-spoke: a central hub site where main
applications reside and to which all remote sites are
connected
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Star (cont’d)
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Ring
 Used in a network in which communications data flow is
unidirectional
 IEEE 802.5 Token Ring protocol and FDDI (Fiber
Distributed Data Interface)
 A bandwidth reservation scheme compare to the collision
scheme used in Ethernet
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Ring (cont’d)
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Mesh
 Many nodes are connected to multiple links
 Used in most switched networks, providing
alternate routes for backup and traffic loads
 Full VS partial mesh
 No. of links in full-mesh network = n(n-1)/2 links
 Networks with n greater than 4 to 8 nodes
employ partial mesh.
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Mesh (cont’d)
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Mesh (cont’d)
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Outline
 General Network Topologies
 Connecting and Circuit Types and Services
 Private Leased Lines VS Switched Networks
 Transmission Basics
 Hardware Selection in the Design Process
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DCE VS DTE
 Data Communications Equipment (DCE) sits between
Data Terminal Equipment (DTE) and transmission circuit
 DCE provides a local limited-distance physical
connection between DTEs and terminal equipment (TE)
e.g. computer
 DCE: e.g. modems or channel service unit/data service
unit (CSU/DSU)
 CSU/DSU is a digital-interface device connecting a router to a
digital circuit e.g. T1 and T3
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DCE VS DTE (cont’d)
 DCE performs signal conversion and coding and may be
part of DTE or intermediate equipment
 DTE converts user information into signals and
reconverts received signals into user information
 DCE device provides clock signal and DTE devices
synchronizes on the provided clock
 To connect DTEs, a DCE is needed
 Connecting 2 DTEs without DCE requires a null modem
(over RS-232 interface)
 Physical medium can be two-wire, four-wire, coaxial,
fiber optic, etc.
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Connection Types:
Simplex, Half-Duplex, and Duplex
Simplex and half-duplex
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Connection Types:
Simplex, Half-Duplex, and Duplex (cont’d)
Full-duplex
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Multidrop Circuits
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Multidrop Circuits (cont’d)
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Private Lines and Local Loops
 A circuit leased from a service provide for a specified period of
time
 Guarantee minimum availability, delay, throughput, and loss
 Access line or local loop: leased line used to connect other
services
 Leased access lines can be purchased through Local
Exchange Carriers (LECs), competitive access providers
(CAPs), or inter-exchange carriers (IXCs)
 Expensive especially transoceanic private-line service,
statistical multiplexing services like FR is a good alternative
 Ebrium-doping technique uses lasers to activate ebrium ion in
fiber optic to boost signal transmitted through the fiber.
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Outline
 General Network Topologies
 Connecting and Circuit Types and Services
 Private Leased Lines VS Switched Networks
 Transmission Basics
 Hardware Selection in the Design Process
 Review
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Data Transport Networks
 Private-line or dedicated leased-line networks
 Switched networks
 Hybrid networks
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Private (Leased) Line Networks
 Leased from providers, not share with others, available
24/7
 Simplest form of point-to-point communications
 Electrical speed conventions
 DS0 (Digital Signal 0) (56/64 Kbps)
 NxDS0 (56/64 Kbps increments)
 1.544 Mbps
 NxDS1 (1.5 Mbps increments)
 Optical speed conventions
 OC-N, where N is in increments of 51.83 Mbps
 Use leased line when always require entire bandwidth
between two points
 Reach the highest level of security and performance
predictability
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Private Line Networks (cont’d)
 Require modem to transfer over analog line, CSU/DSU for digital
line
 Traditional services:
 Analog grade service DS0, fractional DS0, DS1, fractional DS3, DS3
 Digital Data Service (DDS): more expensive, more reliability
 Optional higher bandwidth access
 SubRate Data Multiplexing (SRDM): same rate as DDS but enables
aggregation of many low-speed channels into a single DS0 for cost
savings
 Fractional T1 (FT1) and Fractional T3 (FT3): same type of service but at
a DS1 and DS3 levels
 To guarantee high availability and reliability, providers has
configured their SONET backbones to alternate facilities
during a backbone circuit or node failure
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Switched Networks
 Circuit and packet switched networks
 Characteristics of switched networks
Addressing capability
Multiple protocol and interface support
One-to-many, many-to-one, and many-to-many
connectivity
Network intelligence above the physical Open Systems
Interconnection Reference Model (OSI) layer
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Hybrid Networks
 Use private lines for predictable volumes of
constant-bandwidth traffic
 Use switched network for users requiring one-tomany connectivity, bandwidth-on-demand, and
flexible or more dynamic access
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Outline
 General Network Topologies
 Connecting and Circuit Types and Services
 Private Leased Lines VS Switched Networks
 Transmission Basics
 Hardware Selection in the Design Process
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Asynchronous and Synchronous Data
Transmission
No clock, but have start-stop bits instead
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Asynchronous and Synchronous Data
Transmission (cont’d)
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Asynchronous VS Synchronous
Time Division Multiplexing
The current approach is to carry ATDM cells over very high-speed STDM
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transmission networks, such
as SONET/Synchronous
Digital Hierarchy (SDH)
Communications
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Outline
 General Network Topologies
 Connecting and Circuit Types and Services
 Private Leased Lines VS Switched Networks
 Transmission Basics
 Hardware Selection in the Design Process
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Repeaters
 Offer the capability to extend an existing LAN or WAN
segment at the L1 protocol interface
 Commonly used as signal regenerators, protecting
against signal attenuation while improving signal quality
 Maintain integrity of all data being passed
 Completely transparent to all data content
 Form the core component of hubs
 May cause jitter
 An unwanted variation of one or more signal characteristics, such as the
interval between successive pulses, the amplitude of successive cycles,
or the frequency or phase of successive cycles
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Modems
 Signals are transmitted and received over unshielded
twisted pair phone lines
 56 Kbps using V.90 standard derived from the x2
technology of 3Com (US Robotics) and Rockwell’s
K56flex technology
 DSL modems use various modulation techniques
including Discrete Multi-tone Technology (DMT), Carrier
Amplitude Modulation (CAP), and Multiple Virtual Line
(MVL)
 Cable modems modulate between analog and digital
signals, and attach to the coaxial cable with a Cable
Modem Termination System (CMTS) at the local cable
TC company office
 27 Mbps downstream/2.5 Mbps upstream
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CSU/DSU
 Originally, Channel Service Unit (CSU) was developed to protect
CPE (Customer Premises Equipment) from voltage surges in the
access line
 Higher speed, used at DS1 rates
 Data Service Unit (DSU) was typically the lower-speed device,
providing signal format and protocol translation, timing recovery, and
synchronous sampling.
 Currently, CSU/DSU is a device that merges the CSU and DSU
functionality
 Have the capability of Extended Super Frame (ESF) (a T1 standard that
includes CRC check) monitoring and testing
 Advanced SNMP monitoring with their own management information
bases (MIBs)
 Multiplex traffic from multiple input ports into a single point-to-point or
multidrop circuit
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CSU/DSU (cont’d)
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CSU/DSU (cont’d)
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CSU/DSU (cont’d)
 With the emergence of broadband service e.g. SMDS (Switched
Multi-megabit Data Services) and ATM Data Exchange Interfaces
(DXIs), CSU has additional function:
 Some SMDS and ATM CSUs perform some protocol conversion and
cell segmentation
 E.g. with SMDS DXI, special SMDS CSUs takes L3_PDU frame and
segment it into L2_PDU cells, performing part of the SMDS protocol function
within the CSU
 Then CSU interfaces to the SMDS network through a SMDS Interface
Protocol (SIP)
 CSU/DSU standard interfaces include 56-Kbps, FT1 (Fractional T1),
and DS1 using EIA-232-C, V.35, and HSSI (on DS-3 models)
 CSU/DSU is a layer-1 device (except the SMDS, ATM DSU, and
some FR CSU/DSUs)
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CSU/DSU (cont’d)
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Hubs and LAN Switches
 Hub is Layer 1 device used to:
combine multiple workstations or servers onto a single
LAN segment
Combine multiple LAN segments onto a single LAN
segment
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Hubs and LAN Switches (cont’d)
 1st Generation hubs
 Single bus, single LAN architecture
 2nd Generation hubs
 Single bus, multiple architectures e.g. Ethernet and Token Ring
 Remote network management and configuration
 3rd Generation hubs/switches
 Multiple buses, add L2 bridging functions  L2 switch, aka smart
hubs
 Network management e.g. SNMP
 4th Generation switching hubs
 MAC-layer switching, transparent bridging, standard wide area
trunk interfaces
 Simple routing and elementary firewall functions
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Hubs and LAN Switches (cont’d)
NM = Network Management
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Hubs and LAN Switches (cont’d)
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Hubs and LAN Switches (cont’d)
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Hubs and LAN Switches (cont’d)
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Bridges
 Normally, bridges provide connectivity between LANs of
similar architecture
 Translation bridge can translate from one media format
to another
 Bridging can be performed in intelligent hubs, LAN
switches, L3 switches or routers
 Pass traffic from one segment to another based on
destination MAC address
 Store and forward packets between bridges as packet
switches
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Bridges (cont’d)
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Types of Bridging
 Transparent bridging
Both ends of a transmission support the same physical
media and link-layer protocols from IEEE 802.X suite
Transparent, no part in the route discovery or selection
process
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Transparent bridging
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Types of Bridging (cont’d)
 Translating bridging
Translate data between different physical media and link
(MAC) protocols
Protocols in the network layer and higher must still be
compatible
Do not provide segmentation services, so the frame size
must be configured for the same supportable length
 Encapsulating bridging
Provide a network interconnection or extension by
placing received frames within a media-specific
“envelope” and forwarding the encapsulated frame to
another bridge for delivery to the destination
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Encapsulation Bridging
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Source Route Bridging
 Source route bridging
Has the ability to perform routing based on L2
information
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Disadvantages of Bridges
 Susceptible to multicast of broadcast storms
 When bridging loop occurs
 Spanning-tree protocol (STP)
 Bridge should not be used in network designs calling for
multiple protocol support, dynamic networks requiring
frequent changes, or large networks of greater than 50
nodes
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Switches
 4 classes of switches
Workgroup or local switches: switch traffic within a
workgroup
Enterprise switches: connect multiple departments or
workgroups
Edge switches: serve as access or entry switches to a
public data service
 Can be packet (X.25 or IP), frame (FR, Ethernet, or
FDDI), or cell (ATM), or optical SONET/WDM switches.
Service provider backbone (CO) switches: act as
high-speed interconnects for edge switches
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Switches (cont’d)
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Types of Switches
 L2 switches (LAN switches)
Ethernet, Token Ring, FDDI, and ATM)
 Hybrid L2 and L3 switches
Used when some form of packet, frame, or cell
switching is being used, e.g. when routing IP or
accessing FR or ATM services
Used in backbone networks
Perform the same tasks as routers do, but operate
faster
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Routers
 Provide interconnectivity between devices on LANs and
WANs
 Route packets from node to node using packet-defined
protocol information used by routing protocols
(routing/forwarding tables)
 Routing protocols e.g. OSPF, IGRP, RIP
 Employ address scheme, 4-byte address
 Router’s main functionality reside in L2 and L3
 Applications of both ends do not need to support the same
LAN protocol
 Current routers can forward packets in excess of 40 mil
packets per second
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Routers (cont’d)
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Routers (cont’d)
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Bridging to routing Comparison
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Brouters
 Bridge + router
 Have the capability to route some protocols and
bridge others
 Routing function is done in L2 based on MAC
address.
Transparent to both the network-layer protocols and end
stations
Do not look at the network-level addresses
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Gateway
 Provide all interconnectivity provided by routers and
bridges, up to L7
 Can be performed in hardware, software, and both
 Slower than bridges, switches, and routers
 Protocol translator of architectures e.g. SNA, IPX.
TCP/IP and OSI
 Translate between IEEE 802.X architectures e.g.
between Ethernet and Token Ring
 Can reside within workstations, servers, etc.
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Gateway (cont’d)
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Disadvantages of Gateway
 Low throughput during peak traffic conditions
 May become the main network’s congestion point
 Spend to much time to translate between many protocol
suites
 User-to-gateway priority handling
 Store-and-forward characteristics
 However, gateway has a growing need for their
functionality
 E.g. voice gateway acts as the intermediate node
connecting a voice call between a packetized voice user
(from an IP network) and a circuit-switched user (from
PSTN)
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Questions?
Next Lecture
Multiplexing and Switching
Technologies: An Overview
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Communications
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