nete0510: communication media and data communications 1 nete0510 introduction to transmission...
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NETE0510: Communication Media and Data Communications
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NETE0510Introduction 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-to-many 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 transmission networks, such as SONET/Synchronous Digital Hierarchy (SDH)
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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 LectureMultiplexing and Switching Technologies: An Overview