The Internet is rapidly becoming an electronic agent for commerce, entertainment, communication, and information retrieval. At the same time, new network-enabled intranet applications and powerful desktop computers are driving an exponential increase in network traffic. Its increasing popularity has forced several carriers, competitive local exchange carriers (CLECs), and Internet service providers (ISPs) to offer high-speed dedicated access. Currently the two most popular dedicated access connections are DS0 (transmission speed of 56 kbps) and T1 (transmission speed of 1.544 Mbps).
Many businesses that use these types of connections to gain access to the Internet are experiencing strains in throughput and slow response times. Network designers are searching for a new networking solution that can satisfy the ever-increasing need for bandwidth and transmission capacity. As a result of this emerging demand, carriers, CLECs, and ISPs are now offering DS3 (45 Mbps) dedicated access connections.
Anticipating these trends, Cisco Systems has responded by developing a channelized OC-12 (CHOC-12/DS3) line card; it is designed to simplify the deployment of DS3 services. The CHOC-12/DS3 line card provides up to 12 DS3 channels over a single optical interface.
- Cost reductionExpensive cables, DS3 equipment, and in some cases Frame Relay switching equipment can be removed from core networking sites.
- Simplified DS3 deploymentA simple optical fiber replaces a complex maze of cables and equipment.
- Easier managementWith the reduction in equipment, DS3 deployment will be easier and more efficient.
- Improved network availability and reliabilityThe card reduces the possibility of failure because it supports Synchronous Optical Network (SONET) automatic protection switching (APS) and reduces the amount of equipment required.
- Investment protectionThe CHOC-12/DS3 is compatible with the products of many of the leading DS3 data service unit/channel service unit (DSU/CSU) and Frame Relay equipment vendors.
Figure 1 Channelized OC-12/DS3 Line Card
The one-port CHOC-12/DS3 can transmit IP packets directly over SONET-based optical interfaces at wire speed. The card is based on an innovative transmission method that enables the Cisco 12000 to transmit and receive DS3-based IP packets across standard SONET transmission equipment. This type of connectivity is achieved without the need for additional equipment. As shown in Figure 1, an ISP or enterprise network designer can attach the Cisco 12000 directly to SONET-based equipment, such as Add Drop Multiplexers (ADMs) or digital crossconnects. The remaining equipment can be redeployed in the network.
IP packet data is encapsulated by means of the Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), or Frame Relay protocol. Based on the routing information contained in the IP packet, the line card routes the IP packet to 1 of 12 virtual DS3 ports. The converted IP packets are placed into DS3 frames, and the DS3 frames are mapped into 1 of 12 Synchronous Transport Signal level 1 (STS-1) SONET frames. The 12 STS-1 frames are multiplexed into a single STS-12 frame, also known as an Optical Carrier 12 (OC-12) frame. The line card takes advantage of the fail-safe features provided by SONET networks by supporting automatic protection switching, as defined in the SONET standard.
With the CHOC-12/DS3, the Cisco 12000 can exchange packets with Cisco 7000 family routers, using high-speed DS3 connections. The CHOC-12/DS3 interoperates with Cisco's PA-T3 and PA-2T3 packet-over-DS3 port adapters and with DS3 products from Digital Link, LarsCom, and ADC Kentrox. The line card is standard-compliant and compatible with all leading SONET ADMs. All gigabit switch router (GSR) models support the CHOC-12/DS3.
The CHOC-12/DS3 supports Frame Relay encapsulation of IP packets. With the CHOC-12/DS3 using Frame Relay encapsulation, the Cisco 12000 can exchange packets with Frame Relay routers and Frame Relay customer premises equipment (CPE) devices. The CHOC-12/DS3 connects directly to the SONET ADM network, and the Frame Relay traffic is transmitted and received across the SONET network at DS3 rates. The high port density of the CHOC-12/DS3 and the gigabit switching capacity of the Cisco 12000 negate the need for the Frame Relay switch in this application.
Figure 2 Migration from Copper-Based to Optical-Based DS3 IP Service
Figure 3 Migration from Copper-Based to Optical-Based Frame Relay Service
- Multiple virtual output queues, eliminating head-of-line blocking
- 512-KB burst buffers, which smooth out the arriving packet bursts
- 128-MB packet buffer memory or greater, to maximize TCP goodput
- A forwarding table that can accommodate up to one million forwarding entries
- Application-specific integrated circuit (ASIC)-based queuing
- Quality-of-service support
- 64- to 256-MB forwarding table memory
- Standards-compliant SONET/Synchronous Digital Hierarchy (SDH) interface
- SONET/SDH alarm processing
- SONET/SDH APS
- Support for SONET Data Country Code (DCC) channels
- Single-mode line card that complies with the Bellcore GR-235 Intermediate Reach specification
- Bellcore GR-253 Section 5-1 (OC-12 support)
- DS3 to STS-1 mapping (GR-253, Section 184.108.40.206)
- Full- and half-duplex connectivity at DS3 rate (44.736 MHz)
- Scrambling and subrate support of major DSU vendors
- Unframed, C-Bit, or M13 framing (software selectable)
- 16- and 32-bit cyclic redundancy check (CRC) supported (16-bit default)
- 24-hour history maintained for error statistics and failure counts
- DS3 alarm/event detection (once-per-second polling)
- Alarm indication signal (AIS)
- Out of frame (OOF)
- Far-end receive failure (FERF)
Fiber Power Budgets
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