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The 12E/2FE port adapter, shown in Figure 1-1, provides Cisco 7200 series routers (including a Cisco 7206 as a router shelf in a Cisco AS5800 Universal Access Server) and the Cisco uBR7246 with up to twelve 10-Mbps and two 10/100-Mbps switched Ethernet (10BASE-T) and Fast Ethernet (100BASE-TX) interfaces for an aggregate bandwidth of 435 Mbps, full-duplex.
The 12E/2FE port adapter off-loads Layer 2 switching from the host CPU by using store-and-forward or cut-through packet switching technology between interfaces within the same virtual LAN (VLAN) on the 12E/2FE port adapter. The 12E/2FE port adapter supports up to four VLANs (referred to in this document as bridge groups).
When using store-and-forward packet switching technology, the 12E/2FE port adapter receives and processes a packet completely (calculates the cyclic redundancy check [CRC] and checks the packet's destination address) before forwarding the packet through the outgoing interface; packets are temporarily stored until the outgoing interface is available. Store-and-forward packet switching is the default for the 12E/2FE port adapter.
When using cut-through packet switching technology, the 12E/2FE port adapter reads, processes, and forwards a packet as soon as the packet's destination address is looked up and the outgoing interface is determined. While cut-through packet switching technology greatly reduces the amount of time a packet spends in the 12E/2FE port adapter---the leading edge of the packet exits the output interface before the packet finishes entering the input interface---it enables the 12E/2FE port adapter to forward packets before calculating the CRC.
All 12E/2FE interfaces (port 0 through port 13) support autosensing and autonegotiation of the proper transmission mode (half-duplex or full-duplex) with an attached device. The first two 12E/2FE interfaces (port 0 and port 1) also support autosensing and autonegotiation of the proper connection speed (10-Mbps or 100-Mbps) with an attached device.
Each 12E/2FE interface connector is an RJ-45 receptacle that supports standard straight-through and crossover Category 3 or Category 5 UTP cables. Cisco Systems does not supply Category 3 and Category 5 UTP cables; these cables are available commercially.
The Cisco 7200 series routers support the online insertion and removal (OIR) of all port adapter types. OIR functionality allows you to install and replace port adapters while the router is operating; you do not need to notify the software or shut down the system power.
The term Ethernet is commonly used for all carrier sense multiple access/collision detection (CSMA/CD) local-area networks (LANs) that generally conform to Ethernet specifications, including IEEE 802.3 and Fast Ethernet under IEEE 802.3u.
Ethernet, IEEE 802.3, and IEEE 802.3u are broadcast networks, which means that all stations see all transmissions. Each station must examine received frames to determine whether it is the intended destination and, if it is, pass the frame to a higher protocol layer for processing.
Stations on a CSMA/CD LAN can access the network at any time. Before sending data, the station listens to the network to see if it is already in use. If it is, the station waits until the network is not in use, then transmits. A collision occurs when two stations listen for network traffic, hear none, and transmit simultaneously. When this happens, both transmissions are damaged, and the stations must retransmit. The stations detect the collision and use backoff algorithms to determine when to retransmit.
The 12E/2FE port adapter supports the Ethernet, IEEE 802.3, and IEEE 802.3u specifications for 10-Mbps and 100-Mbps transmission over UTP cables.
Table 1-1 lists the cabling specifications for 10-Mbps transmission over UTP cables.
| Parameter | RJ-45 Connector |
|---|---|
Cable specification | |
Maximum segment length | 328 ft (100 m) for 10BASE-T |
Maximum network length | 656 ft3 (200 m) (with 1 repeater) |
Table 1-2 lists the cabling specifications for 100-Mbps Fast Ethernet transmission over UTP cables.
| Parameter | RJ-45 Connector |
|---|---|
Cable specification | |
Maximum cable length | - |
Maximum segment length | 100 m (328 ft) for 100BASE-TX |
Maximum network length | 200 m (656 ft)4 (with 1 repeater) |
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