Data Communications

This lists the issues with each data communications component in a PC.

Sound: “Transfer of data complete.”

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Functions of Network Management

The 5 Specific Management Functional Areas (SMFAs) defined by ISO:

1. Configuration management: Evaluate products. Plan, setup, and upgrade network software, hardware, and configuration settings.
2. Security management: maintain a secure system by managing access.
3. Accounting management: provide information on costs and account usage.
4. Performance management: gather statistics and logs to ensure maximum efficiency and performance. Prevent and correct system bottlenecks.
5. Fault management: maintain and analyze error logs and diagnostics to promptly detect, isolate, and correct problems, then thoroughly test the fixes.

Cabling Hardware

Ethernet N Base X Standard	Media Cable	$/Ft.	Material	Grade	Connector	Max. Segment Length	Speed
-	Phone station Quad RYGB	0.09	4 Copper wires	-	RJ-11	200 feet	3 Kbs
-	Flat grey/silver satin	0.09 -.18	4 tiny Copper wires	-	RJ-11, RJ-45	10-20 feet	14.4 Kbs
10BaseTX	UTP	0.10			RJ-45	100m
10BaseT	Twisted pair (also StarLAN10)	0.32			RJ-45	100m	10 Mbps
100BaseT	Fast Ethernet over UTP	0.10	Cat5		RJ-45	100m
100BaseTX	STP	0.40	8 wires in 4 pairs of cat 3,4,5 UTP cable		RJ-45 or IBM	100m	16 Mpbs
20Base5	Thicknet Coax	1.10	Cooper	RG-8	AUI & N-Series	500m	-
10Base5	Frozen yellow garden hose	1.10	solid copper	RG-11		500m	10 Mbps
10Base2	ThinNet, CheaperNet	0.32	copper strands	RG-58AU	BNC or IBM	185m	10 Mbps
10BaseFX	Fiber Optic	1.00			SI or SMA 905/906	400m	Gbps
10BaseF	Ethernet FOIRL	1.00			MIC	1000m (802.1j-1993)	Gbps

RG grades were defined by U.S. military specification MIL-C-17.

UTP = Untwisted Pair is catagorized by the number of twists per inch. POTS (Plain Old Telephone Service) part of the Public Switched Telephone Network (PSTN) uses Category 1 UTP of 4 wires in two twisted pairs. UTP has a propagation velocity of 0.59 times the speed of light (300,000,000 meters per second).

The AUI connector is also called a DB-15 connector because it has 15 pins. AUI is also called “DIX” from the first letter of companies that defined it: Digital, Intel, and Xerox. They are attached with vampire clamps.

BNC connectors use a bayonet and nut mechanism which can lock with a quarter twist. They are attached to cables using a crimper tool or a less reliable screw-on coupling.

Terminators placed on each end of the wire absorb unwanted echoes to prevent signal bounce. One terminator on a segment should be grounded, usually to the power supply housing of a PC that connects to a grounded plug. Grounding more than one terminator causes a ground loop.

Fiber-optic cables use Subminiature assembly (SMA) or Fiber Distributed Data Interface (FDDI) connectors. Fiber cables have a core of glass or plastic surrounded by reflective cladding to refract light back into the core. It's protected by a Kevlar armor coating sheated within plenum.

Plenum-rated cabling is rated to be strung through plenums that carry breathable air because it does not release toxic gases when burned.

Crossover cable between two workstations:

RJ45 pin            RJ45 pin 
========            ======== 
1 <--[TX+]--------[RX+]--> 3 
2 <--[TX-]--------[RX-]--> 6 
3 <--[RX+]--------[TX+]--> 1 
6 <--[RX-]--------[TX-]--> 2

The SQE (Signal Quality Error) test is used to verify the ability of a transceiver to detect collisions. It is also referred to as a 'heartbeat' and is sent after every transmission. Network devices generally have the ability to turn off this feature.

A Time Domain Reflectometer sends a signal down the cable to measure the time it takes for the signal to be reflected back. This is useful in measuring cable distances, breaks, and other things.

Network Interface Cards

Three of the most popular protocol suites:
• Network Basic Input/Output System (NetBIOS) used by early Microsoft OS,
• Internetwork Packet eXchange/Sequence Packet eXchange (IPX/SPX) used by Novell
• Transmission Control Protocol/Internet Protocol (TCP/IP) used by Sun, Microsoft, most others

Bus Transfer Rates:

• 16-bit cards 0.70 MB/sec.
• 32-bit cards 1.14 MB/sec.

Addresses 280, 300, 320, 360h

HDLC, PPP, and Frame Relay use connectors V.35, X.21, V.24, EIA/TIA-232, EIA/TIA-449 (EIA/TIA is the Electronic Industries Association / Telecommunications Industry Association)

NIC Card Manufacturers:

Fix that NIC!

Dictionary definitions: Ethernet (n):
Something used to catch the Etherbunny

Equipment: Hubs, Switches, Routers, Bridges, Gateways

On various OSI Network layer:

at the Core Layer providing fast transport to services		Gateway
		Bridge
at the Distribution Layer routing traffic (providing users "Policy-Based Connectivity" to non-local sevices with security)		Router
at the Access Layer connecting users to the network		Hub
		Switch
		Mux

A repeater simply amplifies the signal to allow a signal to travel greater distances.

Routers

Cisco Product Comparisons

• Cisco 7500 Routers
• Cisco 4500 Routers
• Cisco 2500 Routers

  For information on the status of hub ports on a 2505 router:
  

  show hub
• Cisco 1000 Routers

$122 Local Area Networks: A Client/Server Approach, 2nd Edition by James E. Goldman, Phillip T. Rawles (NY:John Wiley, Feb. 2000) 980 pages

Switches

A switch creates point-to-point connections for each packet. They read the destination media access control (or MAC) address on the inbound layer 2 frames Switches vary in these three physical designs:
• Shared-memory - stores all incoming packets in a common memory buffer area that is shared by all the switch ports and then sends them out the correct port for the destination node.
• Matrix - has an internal grid with the input ports and the output ports crossing each other. When a packet is detected on an input port, the MAC address is compared to the lookup table to find the appropriate output port. The switch then makes a connection on the grid where these two ports intersect.
• Bus-architecture - shares a common bus or an internal transmission path by all of the ports using time division multiple access, which is a technology used in digital cell phone communications, that divides each cellular channel into three time slots in order to increase the amount of data that can be carried. A switch based on this configuration has a dedicated memory-buffer for each port, as well as a processor to control the access to the internal bus.

Gateways

Bridges

LAN Troubleshooting

Brian Brown's Cable Testing and General network Troubleshooting using a multi-meter
• Ohm-meters can test resistance of cable, presence of terminators, open and short circuits, but are of limited use on a live network.
• Use a TDR (Time Domain Reflectometer) which reveals imperfections, shorts and open circuits, impedance mismatches from graphically displays of impedance over time from pulses fed into one end of the cable. A correctly terminated cable should not reflect energy back. The strength (amplitude) of how much of the original pulse is reflected shows the severity of the fault. velocity of propagation (VP) .66 for thinnet, .78 for thicknet.
• Divide and conquer: Split the cable segment in half, and take a measurement on both halves. This should isolate the fault into one half. Repeat the process till the fault is found.
• Network traces using Microsoft Network Monitor server service included in the Microsoft Systems Management Server (SMS) product.
• EMI ElectroMagnetic Interference from flourescent lights, etc.

Enterprise LAN

Below is an example of the typical (legacy) components an enterprise network.


©r; From the Intel Online Learning course "Fundamentals of Networking Technology"

Wide Area Networks

Serial Analog Modems

* The longest recommended RS-232 cable is 50 feet.

The 16-bit 16550 Universal Asynchronous Receiver/Transmitters (UARTs) improves on the original 8-bit 8250 UART to allow serial ports to transmit data up to 115 Kbps.

Integrated Circuits for serial communications use Asynchronous Communication Interface Adapters (ACIAs).

• 56K Modems MOdulation DEModulation 3Com/US Robotics X2 modems are supported by 70% of ISP's because Broadwatch Speed Tests show them faster than Rockwell/Lucent K56Flex modems. Future modems will use open V.90 56K ITU standard.

• DirecPC Satellite Dish (800-DirecPC) for 400 Kbps downloads (upload thru regular ISP)

• WAN Speed comparisons

  Dictionary definitions: Main-frame:
  The biggest PC peripheral available.

File Transfer Protocols (Trivial or not)

FTP have a syntax of
ftp:// username : password @ subdomain / hostnameURL

When a typical FTP connection is made (without SSL), the client embeds port information in the commands that it sends to the server. The firewall sees these ports requests and dynamically opens the ports so data can be sent back from the server to the client using those ports. This does not work when SSL is enabled because the firewall cannot read the encrypted commands. For this reason you will need your firewall not to block the high TCP ports.

If you set BlackICE firewall to Nervous or Paranoid security levels, it will block inbound FTP connections.

TFTP

Trivial File Transfer Protocol (TFTP) [ IETF RFC 1350,1993] is used by the software utility of the same name for transferring files over the Internet.

TFTP is simpler to use than File Transfer Protocol (FTP) [ RFC 959 published in 1985], but less capable. It is used where FTP's user authentication and directory visibility are not required, as TFTP uses the User Datagram Protocol (UDP)
rather than the Transmission Control Protocol (TCP).

TFTP is such a simple protocol that it can be implemented within firmware on network devices without hard-disks. TFTP is often used in conjunction with BOOTP to remotely boot diskless workstations, X-terminals, and routers [RFC 906]

Related RFCs:

• 2090 - TFTP Multicast Option
• 2347 - TFTP Option Extension
• 2348 - TFTP Blocksize Option
• 2349 - TFTP Timeout Interval and Transfer Size Options

FTP clients include:
• Microsoft Internet Explorer 5.5 (that comes with Windows Me) & 6 (that comes with Windows XP)
• WS_FTP
• Cute FTP
• Network Neighborhood for Windows
• Other FTP clients

  Webpage publishing programs such as Microsoft FrontPage feature a built-in FTP utility to publish files on the public web server.

Windows 2003/Vista TCP/IP parameters

Out-of-band (OOB) package 912222 for Windows 2003 SP1 and SP2/R2 (and Vista/2008) provides the Scalable Networking Pack [MS White Paper] to improve network performance on NDIS 6.0 (Network Device Interface Specification) hardware driver features.

There is no user interface to configure its options.

TCP Chimney Offload

netsh interface tcp set global chimney=enabled

or set in the Windows Registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters EnableTCPChimney=1 (1=enabled, 0=disabled)

The "chimney" analogy is used here because once TCP connection state is established, control is transfered to the NIC miniport driver runing on NIC hardware which completely replaces the entire Windows TCP stack implementation from top to bottom, handling the traffic between the application and the remote host. [MSDN Whitepaper] [WHDC Whitepaper]

Offloading to NIC hardware instead from the CPU improves the performance of long-lived connections with large-sized payloads, such as data streaming and large file transfers.

Chimney is disabled automatically in the presence of a software firewall (Windows Firewall), ICS (Internet Connection Sharing), IPsec, IPNAT.

Receive-side Scaling (RSS)

netsh interface tcp set global rss=enabled

Or in the Windows Registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters EnableRSS=1 (1=enabled, 0=disabled)

This enables use of multiple CPUs to handle received packets so that the NIC can spread load among available CPUs. [MS Whitepaper]

RSS should not be activated when using ICS (Internet Connection Sharing) or ISA server. More info: MS KB 927695, MS KB 927168

TCP Acceleration (TCPA)

netsh interface tcp set global rss=enabled

Or in the Windows Registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters EnableTCPA=1 (1=enabled, 0=disabled).

Notes: TCPA should not be activated if ISA server is enabled. See MS KB 947773

Network Direct Memory Access (NetDMA)

NetDMA minimizes the CPU processing needed to move packets between memory buffers. It has some hardware requirements, such as INtel I/O Acceleration Technology (Intel I/OAT) available with Xeon processors to function. NetDMA will not work together with "TCP Chimney Offload" and requires "Receive-side Scaling". Windows chooses NetDMA if it detects that both NetDMA and TCP Chimney Offload is supported.

NetDMA is disabled automatically in the presence of a software firewall, ICS, IPsec, IPNAT. Leave the MinPacketSizeToDma global registry value at its default value. It configures the minimum packet size that would trigger usage of DMA.

Compound TCP (CTCP)

This was introduced in the Tcpip.sys within Windows Vista and Windows Server 2008 and via Hotfix 949316 on Windows 2003 and Windows XP 64-bit.

It is highly recommended this setting be enabled in HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters TCPCongestionControl=1 (DWORD value, 1=enable, 0=disable)

CTCP improves on traditional slow-start and congestion-avoidance methods, (especially over high-speed internet connections) by monitoring delay variations and packet loss. It also ensures that its behavior does not impact other TCP connections negatively.

For Windows 2003/XP, to set CTCP, in the Windows Registry, navigate to:

See also: MS KB949316 - Hotfix for Windows 2003 Server and XP (64-bit) replaces Tcpip.sys dated 21-Feb-2008 and
MS KB947775 - Hotfix for Windows 2003 Server replaces Tcpip.sys dated 04-Mar-2008

Checksum Offloading

This NDIS 5 setting reduces CPU load by offloading to the network card tasks maintaining the TCP/IP stack:

• TCP/IP checksum calculation - each packet sent includes a verification checksum.
• TCP/IP segmentation - also known as "TCP Large Send" where Windows sends a large amount of data to the network card, and the NIC is then responsible for dividing it according to the network MTU. Experimental feature, not enabled by default.
• IPSec Encryption cyphers and message digests - provides encryption of packets at the hardware level.

Theoretically, Windows should automatically detect capable network hardware.

The recommendation is to leave this at default unless problems are being experienced. But to change the checksum offloading in the Windows Registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters DisableTaskOffload=0 (DWORD value, 0=enable offload, 1=disable offload, default not set)

Note: Checksum offloading should not be activated together with the Windows Firewall. Also see: MS KB 888750, MS KB 904946, MS KB 936702

The Cable Guy on Scalable Networking Pack