1. Router Types: Cisco has wide variety of router types starting from a low end fixed configuration models to that of
high-end carrier class routers.
The fixed configuration routers include 850, 870, and 1800(fixed) routers.
The modular class routers include 1800(Modular), 2800, and 3800.
Cisco Access Routers include Cisco SOHO, SB 100, 820/830, 1700, 2600, and 3700 Series;
Cisco Aggregation Routers include Cisco 7200/7301, 7304, and 7600 Series
2. Hardware Components:
Below figure shows the chassis rear view of Cisco 2504 that has CPU motherboard with an onboard LAN (Ethernet/TokenRing), multiple WAN ports, and a single
Fig : Typical 2504 chassis
2.2.1 Ethernet port using AUI Connector:
AUI connector used for Ethernet ports. These ports are designed for connecting to an external transceiver that converts to a specific media type
such as twisted pair, coax, or fiber. The transceiver may be connected to the AUI port either directly or through an AUI Cable.
2.2.2 Console and Auxiliary ports:
The console and auxiliary ports are asynchronous serial ports. They provide an out-of-band method for managing the device by providing an access to
Command Line Interface (CLI) with out affecting the traffic that is flowing through the device. Rollover cable is used for connecting these ports with the
external devices like PC (or terminal) and modem. Console port is connected to the COM port of the PC (or terminal) and Auxiliary port is connected to the
modem. The console port is configured as data communications equipment (DCE), and the auxiliary port is configured as data terminal equipment (DTE).
2.2.3 Ports Serial 0 and Serial 1:
These are used for connecting to synchronous serial interfaces. DB-60 is a connector used for connecting these synchronous serial interfaces to Cisco
2.2.4 BRI port:
This is used for connecting to an asynchronous BRI interface. RJ-45 is the connector used for ISDN BRI connection.
3. Router Architecture
3.a. Block Diagram:
3.b. The important architectural components of the router are given below:
The CPU used here is Motorola 68030 CISC. The following are the characteristics of the CPU
32 bit bus, 20 MHz clock (25 MHz on some platforms).
256 Bytes internal Data Cache, 256 Bytes internal Instruction Cache, both direct mapped.
3.b.2 System Control Logic
System Control Logic is used to help the main processor with device control, interrupt handling, counting and timing, data transfer, minimal First In, First
Out (FIFO) buffering, and communication with network interfaces and Dynamic RAM (DRAM).
CPU use Buses to access various components of the system. In addition, Buses are used transferring instructions and data to or from specified memory addresses.
It is used for high speed operations with direct Processor access.
This allows communication with Ethernet or Token Ring controllers, WAN port interfaces, and so on.
3.b.4. Dual UART
Dual Universal Asynchronous Receiver-Transmitter (UART) provides the necessary user interface. It has one RS232 port, Data Communications Equipment (DCE)
(for Console port) RJ45, and Data Terminal Equipment (DTE) (for Auxiliary port) RJ45.
3.b.5 This section describes memory details of a typical Cisco 25xx Series routers.
The DRAM has Main Processor Memory and Shared Input/Output (I/O) memory.
Main Processor Memory is used for routing tables, fast switching cache, running configuration, and so on. It can take unused shared I/O memory, if needed.
Shared I/O memory is used for temporary storage of packets in system buffers.
Flash is a permanent storage for the Cisco IOS software image, backup configurations, and any other files. Cisco IOS software is run from the flash
memory, these image files are defined as re-locatable, because the Cisco IOS software image can be executed from different locations in the Flash.
NVRAM is a Not-Volatile RAM used as permanent storage of the startup configuration. This memory is writeable. NVRAM size is 32 KB.
3.b.5.d BOOT ROM.
This refers to erasable programmable read-only memory (EPROM) and is used to permanently store the startup diagnostic code (ROM Monitor), and RxBoot. Boot
ROM size is 2 MB.
4.Hardware Features: The important features offered by Cisco™ routers include the following:
ease of management, and
advanced quality of service (QoS) for audio, video, broadcast and other real-time applications.