Panasonic DP-180/190, Руководство по обслуживанию

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222
UF-9000
JAN 2004
Ver. 1.0
DP-180/190
9.2. Layer Functions and Technology
9.2.1. MAC (Media Access Control)
The MAC address is burnt into each network card for establishing addresses for nodes on the network.
These addresses are hexadecimal in nature and are unique for each card. The First three bytes from the
left end identify the manufacturer’s code that must be approved by IEEE (Institute of Electrical and
Electronics Engineers). The Remaining three bytes on the right half should be kept in a unique manner.
For Ethernet connections, multiple stations share the topology, therefore, the identification packet from
each station should be unique.
9.2.2. Network Control
CSMA/CD (Carrier Sense Multiple Access with Collision Detection) If a node is trying to make a link to the
network, transmission from another station is prohibited and halted until the data transfer is completed and
the link is off. CSMA/CD and Token Passing are typical techniques used to control the connection.
The General sequence is as follows:
Wait for the next available timing to send,
Send out a frame,
Perform collision sensing simultaneously,
Retry to send the same frame up to 16 times if necessary.
(Sequence goes by a binary exponential back-off algorithm to avoid periodical incident)
802.3 (Ethernet) Frame Format
Destination MAC address: 6 byte (uni-cast or broadcast)
If all "1" on 6 byte (FF-FF-FF-FF-FF-FF) means broadcast frame, it is detected by an applicable node,
it must be passed to the upper layer.
Also, if the destination MAC address is not matched with that node, the frame is discarded at that node
immediately.
Token Passing
Token passing utilizes a frame called a token, which circulates around the network. A computer that needs
to transmit must wait until it receives the token, at which time the computer is permitted to transmit.
When the computer is done transmitting, it passes the token frame to the next station on the network.
The first station that is powered up on a token-ring network automatically becomes the active monitor
station. Its responsibility is to announce itself to the next active downstream station as the active monitor
station and request that station to announce itself to its next active downstream station. After each station
announces itself to its next active downstream neighbor, the announcing station becomes the nearest active
upstream neighbor (NAUN) to the downstream station. After each station becomes aware of its NAUN, the
beaconing process continues every seven seconds.
XX-XX-XX-XX-XX-XX
Unique value
Manufacturer ID
MGCS:080023
Most significant bit
Pre-amble
8 byte
Destination MAC address
6 byte
Source MAC address
6 byte
Data type
2 byte
Data
46 1500 byte
FCS
4 byte
Least significant bit