Business data communications 4e chapter 15
Bạn đang xem bản rút gọn của tài liệu. Xem và tải ngay bản đầy đủ của tài liệu tại đây (381.23 KB, 20 trang )
Chapter 15:
LAN Systems
Business Data Communications, 4e
High-Speed LANs
✘ Why?
✘ Extraordinary growth in speed, power, and storage
capacity of PCs
✘ Increasing use of LANs as computing platforms
✘ Examples
✘ Server farms
✘ Workgroups with “power” requirements
✘ High-speed backbones
Business Data Communic
ations, 4e
2
Traditional Ethernet
✘ Ethernet and CSMA/CD (IEEE 802.3)
✘ Carrier sense multiple access with collision detection
✘ Four step procedure
✘ If medium is idle, transmit
✘ If medium is busy, listen until idle and then transmit
✘ If collision is detected, cease transmitting
✘ After a collision, wait a random amount of time before
retransmitting
Business Data Communic
ations, 4e
3
802.3 Medium Notation
✘ Notation format:
<data rate in Mbps><signaling method>
✘ e.g 10Base5 provides 10Mbps baseband, up to 500
meters
✘ T and F are used in place of segment length for
twisted pair and fiber
Business Data Communic
ations, 4e
4
802.3 10BaseX Media Options
Business Data Communic
ations, 4e
5
Fast Ethernet (100Mbps)
✘ Easy to integrate with existing systems
✘ Can use UTP (-TX) or fiber (-FX)
✘ Uses star-wired topology, using a central multiport
repeater (broadcast method)
✘ If NICs support full-duplex mode, switched hub
must be used
Business Data Communic
ations, 4e
6
802.3 100Base-T Options
Business Data Communic
ations, 4e
7
802.3 100BaseX Media Options
Business Data Communic
ations, 4e
8
Gigabit Ethernet
✘ Still under development
✘ Retains CSMA/CD protocol and Ethernet format,
ensuring smooth upgrade path
✘ Uses optical fiber over short distances
✘ 1-gbps switching hub provides backbone
connectivity
Business Data Communic
ations, 4e
9
Gigabit Ethernet Media Options
Business Data Communic
ations, 4e
10
Example 100-Mbps Ethernet
Backbone Strategy
Business Data Communic
ations, 4e
11
Token Ring LANs (802.5):
Medium Access Control
✘ Token “seized” by changing a bit on the circulating
frame to indicate start of frame rather than token
✘ Default configuration requires sender to complete
transmission and begin receiving transmitted frame
before releasing the token
✘ “Early token release” allows release of token after
transmission but before receipt of frame
Business Data Communic
ations, 4e
12
802.5 Transmission Media
✘ Original specified shielded twisted pair with data
rates of 4 and 16mbps
✘ New addition to standard allows use of UTP for
4mbps
✘ Utilizes differential Manchester encoding
✘ 1997 update to IEEE 802.5 introduced dedicated
token ring (DTR).
Business Data Communic
ations, 4e
13
Fibre Channel
✘ combine the best features of channel and protocolbased technologies
✘ the simplicity and speed of channel communications
✘ the flexibility and inter-connectivity that characterize
protocol-based network communications.
✘ more like a traditional circuit-switched or packetswitched network, in contrast to the typical sharedmedium LAN
Business Data Communic
ations, 4e
14
Fibre Channel Goals
✘ Full-duplex links with two fibers
per link
✘ Performance from 100 Mbps to
800 Mbps on a single link (200
Mbps to1600 Mbps per link)
✘ Support for distances up to 10
km
✘ Small connectors
✘ High-capacity utilization with
distance insensitivity
✘ Greater connectivity than existing
multidrop channels
✘ Broad availability (i.e., standard
components)
✘ Support for multiple
cost/performance levels, from
small systems to supercomputers
✘ Ability to carry multiple existing
interface command sets for
existing channel and network
protocols
Business Data Communic
ations, 4e
15
Fibre Channel Elements
✘ Nodes
✘ The end systems
✘ Includes one or more N_ ports for interconnection
✘ Fabric
✘ Collection of switching elements s between systems
✘ Each element includes multiple F_ ports
✘ Responsible for buffering and for routing frames between
source and destination nodes
Business Data Communic
ations, 4e
16
Fibre Channel
Protocol Architecture
✘ FC-0 Physical Media: Includes optical fiber, coaxial cable, and
shielded twisted pair, based on distance requirements
✘ FC-1 Transmission Protocol: Defines the signal encoding scheme
✘ FC-2 Framing Protocol: Defines topologies, frame format,
flow/error control, and grouping of frames
✘ FC-3 Common Services: Includes multicasting
✘ FC-4 Mapping: Defines the mapping of various channel and
network protocols to Fibre Channel
Business Data Communic
ations, 4e
17
Wireless LANS
✘ LAN extension
✘ Wireless network connected to a main wire-based network
✘ Cross-building interconnect
✘ Point-to-point link between networks in separate buildings
✘ Nomadic access
✘ Wireless link between a LAN hub and a mobile data terminal
✘ Ad hoc networks
✘ a peer-to-peer network (no centralized server) set up temporarily to
meet some immediate need.
Business Data Communic
ations, 4e
18
Wireless LAN Requirements
✘ Throughput
✘ Number of nodes:
✘ Connection to backbone
LAN
✘ Service area
✘ Battery power consumption
✘ Transmission robustness
and security
✘ Co-located network
operation
✘ License-free operation
✘ Handoff/roaming
✘ Dynamic configuration
Business Data Communic
ations, 4e
19
IEEE 802.11 Standards
✘ Association/Re-Association/Disassociation
✘ Authentication
✘ Privacy
✘ Physical Media
✘ Infrared at 1 or 2 Mbps at a wavelength of 850-950 nm
✘ Direct-sequence spread spectrum in the 2.4-GHz ISM band
✘ Frequency-hopping spread spectrum in the 2.4-GHz ISM band, at
data rates of 1 and 2 Mbps.
Business Data Communic
ations, 4e
20
