MAU / multiple access unit token ring集線器
Logical topology:ring
MAU
MAC Method - Token Ring
Free-token - A special bit pattern (ex.11111111) Busy-token - The last bit of the free token is changed (e.g., 11111110) Any station gets the free-token may change it to a busy-token and followed by the frame to be transmitted. The source station will remove the frame from the ring A new free-token will be regenerated if the station has completed transmission of its frame.
Both use 802.2 at the LLC Layer MAC Layer: CSMA/CD versus tokenpassing PHY Layer Topology: Bus versus Ring 802.3 802.5 LLC MAC PHY Bus 802.2 CSMA/CD Token Passing Ring
indicates whether the frame contains data or control information.
As with IEEE 802.5, addresses are 6 bytes in length
Ring Network Configuration
Physical topology:star
Only stations with a priority equal to, or higher than, the priority value contained in a token can seize that token.
Data / Command Frame
frame control byte
FDDI Spec.
Station Management (SMT) - defines the FDDI station configuration, including:
ring configuration ring control features station insertion and removal initialization fault isolation and recovery scheduling collection of statistics
No Station is transmitting. Now Station B May Transmit
Station A is transmitting Station B must wait
A
Must Wait
A
Now may transmit
B
B
CSMA/CD Operation
Collision Detection
FDDI
FDDI
Although FDDI implementations are not as common today as Ethernet or Token Ring, FDDI has a substantial following, and continues to grow as its costs decrease. FDDI is frequently used as a backbone technology, and to connect high-speed computers in a LAN.
Remove error frames and token.
Token Ring Signals
Manchester encoding combines data and clock into bit symbols
802.3 Ethernet versus 802.5 Token-Ring Network
10Base-T Hub
3&6
Step 1 Station A Transmits on Upstream Pair (Wires 1&2)
1&2
Station A Station B Station C
Example of 10 base T Networks
10Base-T Hub
1&2
3&6
End delimiter
Priority System
Token Ring frames have two fields that control priority
the priority field and the reservation field. support eight level of priority
Station A Station B Station C
Step 2 Hub Repeats (Broadcasts) The Message To All Stations On Downstream Pairs (Wires 3&6)
10 base T+10 base 2 Networks
I 10 base 5 界面 10 base 2 界面 10 base T 集線器(hub) 集線器(hub) 串聯線 A B C D E H F G A B C 無遮蔽式 雙絞線 (UTP) 最長 100 公尺 D 10 base T 集線器(hub) 集線器(hub) K J 10 base 2 細線 Ethernet
FDDI Spec.
Physical Layer Protocol (PHY) defines data encoding/decoding procedures, including:
clocking requirements framing other functions
FDDI Spec.
Hub repeats each bit received out all of its ports. The procedure is called broadcast. To Hub (Pins 1 & 2)
From Hub (Pins 3 & 6)
Example of 10 base T Networks
E
H F G
Pure 10 base T 10 base T + 10 basion
If no one is transmitting, transmit If anyone is transmitting, wait until nobody is transmitting
MAC Method - Token Ring
B B B
A
C
A
C
A
C
D
D
D
(a)
(b)
(c)
Within an 802.5 Access Unit
Access unit connections maintain a ring (loop)
Access Unit Ring In Ring Out
Lobe
If two stations do transmit at the same time, each hears the other Both stop, wait random amounts of time Transmit after wait, but only if the line is free
FDDI Spec.
Physical Layer Medium (PMD) defines the characteristics of the transmission medium, including:
fiber optic link power levels bit error rates optical components connectors
Layer 2 - Technologies
Shawn Shuoh-Ren Tsai Cisco Academy Training Center David Ta-Wei Shih CGUIC
Ethernet Frame Format
Star Topology: 10Base-T
10 Mbps, Manchester encoding. Using UTP,RJ-45. Using hub-based Network Topology. Hub operates at the physical layer. Suffer greater attenuation and the maximum length is 100 m.
Bridges (Cont)
Switches
Switches (cont)
Ethernet LAN Segments
IBM Token Ring vs. IEEE 802.5
Token Ring Frame Format
Token Frame
3 bytes Start delimiter
alerts each station to the arrival of a token, or data/command frame
Access control byte
token bit distinguishes a token from a data/command frame a monitor bit determines whether a frame is continuously circling the ring priority and reservation field