Network topologies and hardware
| English | Chinese | Pinyin |
|---|---|---|
| topology | 拓扑 | tuò pū |
| NIC | 网络接口卡 | wǎng luò jiē kǒu kǎ |
| switch | 交换机 | jiāo huàn jī |
| router | 路由器 | lù yóu qì |
| bus | 总线 | zǒng xiàn |
| star | 星形 | xīng xíng |
| mesh | 网状 | wǎng zhuàng |
| MAC address | MAC地址 | MAC dì zhǐ |
| routing table | 路由表 | lù yóu biǎo |
| collision | 冲突 | chōng tū |
Wiring it together
- A network's topology 拓扑 is how its nodes and links are arranged.
- A handful of hardware boxes — NICs 网络接口卡, switches 交换机, routers 路由器 — make it work.
- The arrangement decides cost, speed and how well it survives a failure.
Topologies
- Bus 总线 — all devices on one shared cable. Cheap, but the whole LAN fails if the bus fails, and it slows as more devices share the bandwidth.
- Star 星形 — every device connects to a central switch. One device failing doesn't affect others, but the switch failing brings everything down. Most common today.
- Mesh 网状 — every device links directly to others, with many paths. Very fault-tolerant (traffic reroutes) but needs lots of cabling.
- Hybrid — a mix (a star per office, mesh between offices).
Compare the network topologies
Tap through the four topologies. Each trades off cost, speed and how well it survives a failure — notice what breaks the whole network in each one.
Match each topology to its defining feature.
Bus shares one cable, star uses a central switch, mesh has many paths, hybrid mixes them.
In a star topology, what happens if one device's cable fails?
Each device has its own link to the central switch, so one cable failing affects only that device. (If the switch fails, all go down.)
LAN hardware
- NIC (network interface card) — lets a device join the network; has a unique MAC address MAC地址 (a 48-bit hardware address).
- Switch — forwards each Ethernet frame only to the port for the destination MAC. (A hub, now obsolete, copied traffic to all ports.)
- Wireless access point (WAP) — lets wireless clients join a wired LAN.
- Cabling — twisted-pair for short runs, fibre-optic for longer/faster runs.
An RJ-45 plug on a twisted-pair Ethernet cable.
A switch forwards each frame only to the port for its destination MAC address.
A NIC's unique, fixed 48-bit hardware address is called its ______ address.
The MAC address is burned into the network interface card. (DHCP hands out IP addresses, which can change.)
How does a switch differ from a hub?
A switch sends each frame only out the destination's port (efficient, more secure). A hub copied to all ports. Routing by IP is a router's job.
A switch is smarter than a hub because it sends each frame only to the port for its destination, not to every port.
This makes a switched network faster and more secure than the old hub-based one.
Routers
- A router connects different networks and forwards data between them — usually at the LAN–internet boundary. It does:
- Forwarding — reads each packet's destination IP address and sends it the right way, using a routing table 路由表.
- NAT — lets many private LAN addresses share one public IP.
- DHCP — hands out private IP addresses to LAN devices; and a firewall blocks unwanted incoming traffic.
A router connects a LAN to the wider internet, forwarding packets by their destination IP.
The main job of a router is to:
A router joins networks (e.g. a LAN to the internet) and forwards packets using their destination IP and a routing table.
Ethernet and CSMA/CD
- On a shared medium two devices can transmit at once — a collision 冲突. Ethernet handled this with CSMA/CD:
- Carrier sense — listen first; wait if the cable is busy.
- Collision detection — keep listening while sending; on a clash, both stop, send a brief jam signal, then wait a random backoff before retrying.
- Modern switched, full-duplex Ethernet uses point-to-point links, so collisions no longer happen.
CSMA/CD: listen first, then send; on a collision both stop, jam, and wait a random backoff.
Put the CSMA/CD steps in order for a device that wants to transmit on a shared cable.
Carrier sense → transmit → detect collision → jam → random backoff. The random wait stops both devices clashing again immediately.
You've got it
- bus (shared cable), star (central switch — most common), mesh (many paths, fault-tolerant)
- NIC has a 48-bit MAC address; a switch forwards a frame only to the destination port
- a router connects networks and forwards by IP address (+ NAT, DHCP, firewall)
- CSMA/CD: listen, detect collisions, jam + random backoff (switched full-duplex avoids them)