数据与计算机通信15
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12
Ring Topology
✓Repeaters joined by point to point links in closed
loop
➢ Receive data on one link and retransmit on another ➢ Links unidirectional ➢ Stations attach to repeaters
Each station has unique address
✓Full duplex connection between station and tap
➢ Allows for transmission and reception
✓Need to regulate transmission需要规定传输
➢ Hard disks, tape libraries, CD arrays
➢ Improved client-server storage access
➢ Direct storage to storage communication for backup
✓ High speed office networks
➢ To avoid collisions避免信号冲突 ➢ To avoid hogging(扰乱)避免信号混淆
Data in small blocks - frames
✓Terminator absorbs frames at end of medium 11
Frame Transmission on Bus LAN
✓Data in frames
➢ Circulate past all stations ➢ Destination recognizes address and copies frame ➢ Frame circulates back to source where it is removed
✓Media access control determines when station can
Key elements of a LAN are
✓Topologies ✓Transmission medium ✓Layout ✓Medium access control
8
15.2.1 Topologies
✓Tree ✓Bus
➢Special case of tree
One trunk, no branches
✓Ring ✓Star
9
LAN Topologies
10
Bus and Tree Topology
✓Multipoint medium ✓Transmission propagates throughout medium ✓Heard by all stations
➢ Need to identify target station
4
局域网应用
▪个人计算机局域网
• 客户/服务器计算模式
▪ 后端网络和存储区域网
• 大型系统互联：大型机、海量存储 • 特征： 高速高可靠性、有限数量和距离
▪ 高速办公室网络
• 大信息量数据处理
▪ 骨干局域网
• 高带宽、 高可靠性
• 实现速率相对较低的LAN的互联
5
15.2 Topologies and Transmission medium
➢ Expensive, hard to install and maintain
➢ No longer used in LANs
✓ Optical fiber
➢ Expensive taps
insert frame 13
Frame Transmission
Ring LAN
14
Star Topology
✓Each station connected directly to
central node
➢Usually via two point to point links
✓Central node can broadcast
✓Baseband coaxial cable
➢Uses digital signalling ➢Original Ethernet
17
Bus LAN
Transmission Media (2)
✓ Broadband coaxial cable
➢ As in cable TV systems
➢ Analog signals at radio frequencies
➢Physical star, logical bus ➢Only one station can transmit at a time
✓Central node can act as frame switch
15
15.2.2 Choice of Topology
✓Reliability ✓Expandability ✓Performance ✓Needs considering in context of:
➢ Desktop image processing
➢ High capacity local storage
✓ Backbone LANs
➢ Interconnect low speed local LANs
➢ Reliability
➢ Capacity
➢ Cost
3
Storage Area Networks
➢Medium ➢Wiring layout ➢Access control
16
Bus LAN Transmission Media (1)
✓Twisted pair
➢Early LANs used voice grade cable ➢Didn’t scale for fast LANs ➢Not used in bus LANs now
LAN Applications (2)
百度文库
✓ Storage Area Networks
➢ Separate network handling storage needs
➢ Detaches storage tasks from specific servers
➢ Shared storage facility across high-speed network
Ring Topology
✓Repeaters joined by point to point links in closed
loop
➢ Receive data on one link and retransmit on another ➢ Links unidirectional ➢ Stations attach to repeaters
Each station has unique address
✓Full duplex connection between station and tap
➢ Allows for transmission and reception
✓Need to regulate transmission需要规定传输
➢ Hard disks, tape libraries, CD arrays
➢ Improved client-server storage access
➢ Direct storage to storage communication for backup
✓ High speed office networks
➢ To avoid collisions避免信号冲突 ➢ To avoid hogging(扰乱)避免信号混淆
Data in small blocks - frames
✓Terminator absorbs frames at end of medium 11
Frame Transmission on Bus LAN
✓Data in frames
➢ Circulate past all stations ➢ Destination recognizes address and copies frame ➢ Frame circulates back to source where it is removed
✓Media access control determines when station can
Key elements of a LAN are
✓Topologies ✓Transmission medium ✓Layout ✓Medium access control
8
15.2.1 Topologies
✓Tree ✓Bus
➢Special case of tree
One trunk, no branches
✓Ring ✓Star
9
LAN Topologies
10
Bus and Tree Topology
✓Multipoint medium ✓Transmission propagates throughout medium ✓Heard by all stations
➢ Need to identify target station
4
局域网应用
▪个人计算机局域网
• 客户/服务器计算模式
▪ 后端网络和存储区域网
• 大型系统互联：大型机、海量存储 • 特征： 高速高可靠性、有限数量和距离
▪ 高速办公室网络
• 大信息量数据处理
▪ 骨干局域网
• 高带宽、 高可靠性
• 实现速率相对较低的LAN的互联
5
15.2 Topologies and Transmission medium
➢ Expensive, hard to install and maintain
➢ No longer used in LANs
✓ Optical fiber
➢ Expensive taps
insert frame 13
Frame Transmission
Ring LAN
14
Star Topology
✓Each station connected directly to
central node
➢Usually via two point to point links
✓Central node can broadcast
✓Baseband coaxial cable
➢Uses digital signalling ➢Original Ethernet
17
Bus LAN
Transmission Media (2)
✓ Broadband coaxial cable
➢ As in cable TV systems
➢ Analog signals at radio frequencies
➢Physical star, logical bus ➢Only one station can transmit at a time
✓Central node can act as frame switch
15
15.2.2 Choice of Topology
✓Reliability ✓Expandability ✓Performance ✓Needs considering in context of:
➢ Desktop image processing
➢ High capacity local storage
✓ Backbone LANs
➢ Interconnect low speed local LANs
➢ Reliability
➢ Capacity
➢ Cost
3
Storage Area Networks
➢Medium ➢Wiring layout ➢Access control
16
Bus LAN Transmission Media (1)
✓Twisted pair
➢Early LANs used voice grade cable ➢Didn’t scale for fast LANs ➢Not used in bus LANs now
LAN Applications (2)
百度文库
✓ Storage Area Networks
➢ Separate network handling storage needs
➢ Detaches storage tasks from specific servers
➢ Shared storage facility across high-speed network