Table Of Contents
Statement of Direction
1000BASE-T—Delivering Gigabit Intelligence on Copper Infrastructure
Gigabit Over Copper CablingAs the leading provider of Gigabit Ethernet and switched internetworking solutions, Cisco Systems is committed to the development of high-performance Ethernet technology and products that provide gigabit-per-second transmission rates to address both service provider and enterprise customer requirements. (See Figure 1, Breadth of Gigabit Ethernet Applications.) As a mark of that leadership, Cisco is extending its breadth of Gigabit product support to include the latest Ethernet application: 1000BASE-T or Gigabit on copper cabling. 1000BASE-T specifies Gigabit Ethernet operation over the Category 5 cabling systems installed according to the specifications of ANSI/TIA/EIA-568A (1995). 1000BASE-T also supports 1000 Mbps operation over the newest emerging EIA/TIA cabling specifications Category 5e.
Figure 1 Breadth of Gigabit Ethernet Applications
Cisco will provide not only 1000BASE-T products but also Gigabit Intelligent Network Services for all network managers and planners who require gigabit-per-second speed over Category 5 and Category 5e cabling. More than 80 percent of the cabling inside buildings today is Category 5 copper. By delivering a complete Gigabit on copper networking solution, Cisco enables network managers to scale their wiring closets and data centers to Gigabit speeds while leveraging their investment in installed copper cabling infrastructure.
Gigabit on Copper Applications and Intelligent Network ServicesBy supporting 1000BASE-T interfaces on its comprehensive product line, Cisco offers enter- prise network managers a unique and compelling solution. Because 1000BASE-T is Ethernet, it requires no change to the Ethernet media access control (MAC) or packet format. 1000BASE-T supports all upper- layer services, including all Cisco Intelligent Network Services that operate at Layer 2, Layer 3, and higher of the Open System Interconnection (OSI) seven-layered model: high availability, quality-of-service (QoS), security and policy enforcement, server load balancing (SLB), and Web caching, just to name a few. 1000BASE-T also supports all standard Layer 2 functions such as 802.1p, EtherChannel®, Inter- Switch Link (ISL), virtual local-area network (VLANs), 802.1Q, and spanning tree.
1000BASE-T is the ideal high-speed solution for three application spaces where horizontal copper cabling exists:
•1000BASE-T uplinks from desktop switches to aggregating switches
•Data centers for server switching
•Wiring closet switches for 10/100/1000 bandwidth to the desktop
1000BASE-T in the Data Center
Figure 2 1000BASE-T in the Data Center
When 1000BASE-T NICS become available in volume in mid- and late-CY2000, 1000BASE-T will be used in data centers for server switching and server connectivity as shown in Figure 2. High-performance servers performing such functions as application hosting may be connected to the data-center switch with 1000BASE-T network interface cards (NICs) and Gigabit EtherChannel can be used to create redundant links. Such Gigabit Intelligent Network Services may be applied as:
•Server load balancing (SLB)
•Web caching using web caching control protocol (WCCP)
•Packet inspection and classification
•Security features such as intrusion detection and access control lists (ACLs)
•High availability using technologies such as hot standby router protocol (HSRP) and Gigabit EtherChannel (GEC)
1000BASE-T in the Wiring ClosetAs 1000BASE-T desktop NICs emerge in early- or mid- CY2001, 1000BASE-T will mature into a high-performance alternative to connect workstations and power desktops to the network (see Figure 3). Figure 4 shows that, in the very near future, high-performance desktops may be attached to the network with 10/100 or 1000BASE-T. Multi-gigabit connectivity to the core of the network may be achieved using Gigabit EtherChannel. For this wiring close application of 1000BASE-T, such Gigabit Intelligent Network Services may be applied as:
•Traffic detection and classification
•QoS/class of service (CoS)
Figure 3 1000BASE-T in Wiring Closets
Figure 4 1000BASE-T for Desktop Aggregation
1000BASE-T UplinksAs Figure 5 shows, one of the first applications for 1000BASE-T will be to serve as an uplink technology offering high-bandwidth connectivity from desktop switches to the next point of aggregation. Often such switch links are deployed over Category 5 cabling with 10/100 Mbps Ethernet desktop connections and a 100BASE-TX uplink. Switches with a slide in uplink module may be upgraded to 1000BASE-T uplinks, giving end stations the opportunity to upgrade from 10 to 100 Mbps links and providing high- bandwidth, gigabit-per-second access to servers and other resources. Gigabit Intelligent Network services may be applied on such links as:
Figure 5 1000BASE-T Uplinks
1000BASE-T (Gigabit Ethernet over Copper) Technology
Figure 6 GbE Layer Diagram
As Figure 6 shows, 1000BASE-T is one of the four physical layers or transceivers defined by the two Gigabit Ethernet standards: IEEE 802.3z or 1000BASE-X and IEEE 802.3ab or 1000BASE-T. 1000BASE-X supports multimode and single- mode fiber media and a short-reach, 25-meter copper jumper. (See Figure 6.) Because most of the cabling installed inside buildings today is Category 5 copper, the IEEE 802.3 1000BASE-T standard supports Gigabit Ethernet operation over the Category 5 cabling systems installed according to the specifications of ANSI/TIA/EIA-568A (1995). As Figure 7 shows, 1000BASE-T works by using all four of the Category 5 pairs to achieve 1000 Mbps operation over the installed Category 5 copper cabling. 1000 Mbps data rates are achieved by sending and receiving a 250 Mbps data stream over each of the four pairs simultaneously (4 X 250 Mbps = 1 Gbps).
Figure 7 1000BASE-T: How It Works
In contrast, 100BASE-TX uses two pairs: one to transmit and one to receive. Fast Ethernet on Copper (100BASE-TX) achieves 100 Mbps operation by sending encoded symbols across the link at a symbol rate of 125 Mbaud. A 125 Mbaud symbol rate is required because the 100BASE-TX encoding scheme (called 4B/5B coding) has a bandwidth overhead of 20 percent, the difference between 100 Mbps and 125 Mbaud. Although 1000BASE-T uses a different encoding scheme (five level pulse amplitude modulation or PAM-5), because it maintains the 125 Mbaud symbol rate of 100BASE-TX, 1000BASE-T is backwards compatible with 100BASE-FX at the physical layer. (See Table 1.)
This compatibility feature is significant for network managers and planners because it means that forthcoming generations of 1000BASE-T NICs and switches will support both 100/1000 and 10/100/1000 autonegotiation between Fast Ethernet (100BASE-TX) and Gigabit Ethernet (1000BASE-T). These speed-agile products will enable network managers to deploy 1000BASE-T incrementally into the network. A 100/1000 server NIC may be installed into a new server while the server switch remains 100BASE-TX and vice versa, new 100/1000 server switches may be deployed while maintaining the investment in the existing 100 Mbps server NICs.Table 1 100BASE-TX, 1000BASE-X, and 1000BASE-T
Notes:MAC = media access control protocolPCS = physical coding sublayerPAM = pulse amplitude modulation
The Role of Fiber to the Desktop in the Structured Wiring ParadigmFor standard commercial applications, there is no need to depart from the conventional structured wiring model: fiber in the risers and copper in the horizontal cabling runs. Unless there are security or EMI/RFI concerns about copper cabling or the network manager cannot locate wiring closets 100 meters apart, there is no compelling business reason to deploy fiber to the desktop. Optical transceiver-based switch ports will always be more expensive than copper, and a network manager who runs fiber to the desk will be replacing switch ports three or four times over the life of the cabling plant. Such incremental costs add up over time.
Another reason to avoid running fiber to the desk is that there is currently no way to power network-attached devices from the fiber optic media. In contrast, a LAN phone, IP phones, Web cameras, and other devices may be powered today from the copper cabling. An IEEE 802.3 Task Force is under way to develop standards- based mechanisms to power devices over Category 5 and 5e cabling.
For horizontal runs the standard network application of choice will be 10/100/1000 Ethernet over copper. 1000BASE-T will run on Category 5 and Category 5e cabling at distances to 100 meters. 1000 Mbps at the edge of the network is going to be sufficient bandwidth for almost all customers for the next three to four years.
Looking toward future applications, network managers should note that, while the newer enhanced bandwidth multimode fiber products will support the next Ethernet application, 10 Gigabit Ethernet, enhanced multimode fiber won't support applications beyond 10 Gigabit Ethernet such as 40 Gigabit Ethernet or 100 Gigabit Ethernet. For vertical runs the best choice today is to deploy a hybrid multimode/single-mode product with the higher bandwidth multimode fiber. By using a hybrid product, network managers achieve backward compatibility with conventional 100BASE-FX, which uses light emitting diodes (LEDs) and will not run on single-mode fiber, and backward compatibility with 1000BASE-SX which is cheaper than 1000BASE-LX. The termination and connectors as well as the optical transceivers (switch ports) for single mode will be more expensive than multimode fiber. For building backbone cabling distances of 300 to 550 meters, single-mode fiber will be the only solution.
1000BASE-T is an important technology for three reasons. First, almost all the cabling installed inside buildings is Category 5. Therefore, 1000BASE-T products 1000BASE-T is an important technology for three reasons. First, almost all the cabling installed inside buildings is Category 5. Therefore, 1000BASE-T products enable network planners to deploy Gigabit Ethernet technology over their installed Category 5 cabling plants. Cisco support of the installed horizontal cabling infrastructure with standards- based 1000BASE-T is crucial because, while networking equipment can easily be pulled from a rack, horizontal cabling can be very difficult to replace since it is located inside a wall, ceiling, or raised floor and dispersed across many wiring closets. Second, on a price-per-port basis, 1000BASE-T ports will cost less than 1000BASE-X ports because copper physical sublayers (PHYs) are expected to be less expensive than optical PHYs. Finally, as explained above, 1000BASE-T enables network managers to preserve their investment in existing Ethernet equipment.
Testing the Installed Category 5 CablingAs stated above, 1000BASE-T specifies Gigabit Ethernet operation over the Category 5 cabling systems installed according to the specifications of ANSI/TIA/EIA-568A (1995). There should be no need to replace existing Category 5 cabling to use 1000BASE-T. The 1000BASE-T standard recommends two additional tests to qualify Category 5 cabling for Gigabit Ethernet operation: return loss and far- end crosstalk (FEXT). Return loss defines the amount of signal energy that is reflected back toward the transmitter due to impedance mismatches in the link (such as those caused by connectors). Far-end crosstalk is noise on a wire pair at the far end from the transmitter (for example, at the receiver) caused by signal leakage from adjoining wire pairs.
These tests are necessary for two reasons. First, Category 5 systems installed prior to the completion of ANSI/TIA/EIA568-A in 1995 may contain connecting hardware that does not comply with the standard. Second, the 1995 cabling standard did not specify these two critical performance parameters. Basic cable testing information is provided by ANSI/TIA/EIA-TSB-67- "Transmission Performance Specifications for Field Testing of Twisted Pair Cabling System." The additional test parameters are published in ANSI/TIA/EIA-TSB 95.Table 2 Cabling Systems
ISO/IEC11801 and ANSI/TIA/EIA568-AThe ISO/IEC118—the International and European cabling standard—is being modified to add return loss and ELFEXT measures to the specifications for Category 5 cabling and will not define a separate Enhanced Category 5 cabling. In contrast, the TIA 41.8.1 Task Force responsible for ANSI/TIA/EIA568-A chose to combine the definitions of current Category 5 cabling practices with the new measures for return loss and far-end crosstalk to create a Category 5e specification. For the installed base of legacy Category 5 cabling, the TIA will specify the measurements for return loss and far-end crosstalk in Technical Service Bulletin ANSI/TIA/EIA-TSB-95.
To sum up, 1000BASE-T specifies Gigabit Ethernet operation over the cabling installed according to the EIA/TIA Category 5 specification. Network managers should check that their installed cabling is indeed compliant with the Category 5 specifications. Also, the 1000BASE-T standard recommends two tests to qualify the installed Category 5 cable. If a Category 5 cabling plant supports 100BASE-TX operation today to distances of 100 meters, it should support 1000BASE-T to 100 meters.
Category 5e CablingAs Table 2 shows, the Category 5e cabling standard and the emerging Category 6 specification are supersets of the Category 5 specification. Because the Category 5e specification includes the testing parameters for return loss and far end cross talk, cabling plants certified as Category 5e will support 1000BASE-T operation. Category 5e cabling is recommended for all new installations.
Network managers and planners considering Category 6 installations, should be aware that the specification for Category 6 cabling is not yet formalized. In such cases, network managers should work with their cabling installer to ensure that an installation based on components labeled Category 6 will be upgraded to be compliant with the final Category 6 standard. Because the Category 6 specification will include the testing parameters for return loss and far end cross talk, cabling plants certified as Category 6 will support 1000BASE-T operation.
ConclusionsCisco is extending its breadth of Gigabit product support to include the latest Ethernet application: 1000BASE-T or Gigabit on copper cabling. 1000BASE-T specifies Gigabit Ethernet operation over the Category 5 cabling systems installed according to the specifications of ANSI/TIA/EIA-568A (1995). 1000BASE-T also supports 1000 Mbps operation over the newest EIA/TIA cabling specification Category 5e. Because 1000BASE-T is Ethernet, it requires no change to the Ethernet MAC or packet format. 1000BASE-T therefore supports all upper-layer services, including all Cisco Intelligent Network Services that operate at Layer 2, Layer 3, and higher of the OSI seven-layered model. 1000BASE-T also supports all standard Layer 2 functions: 802.1p, 802.1Q, Gigabit Ethernet- Channel, Fast EtherChannel, ISL, VLANs, and spanning tree. The primary initial applications for 1000BASE-T will be switch uplinks and data-center switching. As 1000BASE-T desktop NICs emerge, 1000BASE-T will eventually extend to the desktop for workstations demanding the highest-speed connections to the network.
•Echo—See return loss.
•FEXT—Far-end crosstalk is noise on a wire pair at the far end from the transmitter (for example, at the receiver) caused by signal leakage from adjoining wire pairs
•MAC—Media access control protocol which manages access to the physical media
•PAM—Pulse amplitude modulation
•PCS—Physical coding sublayer. Codes such as 8B/10B or 4B/10B are used to transmit data into forms suitable for the physical media and decoding it at the receiver
•Return loss—Echo or return loss defines the amount of signal energy that is reflected back toward the transmitter due to impedance mismatches in the link (such as those caused by connectors