- PC - Buzz - 1 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z *

L2F = Layer 2 Forwarding

Protocol proposed by Cisco
> L2TP

---

L2TP = Layer 2 Tunneling Protocol

udviklet af Cisco - til VPN

A Layer 2 tunneling protocol that is an extension of the PPP protocol used for virtual private networks (VPNs). L2TP merges the best features of two existing tunneling protocols: Microsoft's PPTP and Cisco's PPTP. L2TP is the emerging IETF standard, currently being drafted by participants from Ascend, Cisco Systems, Copper Mountain Networks, IBM, Microsoft, and 3Com.

An IETF standard protocol for creating VPNs. An open standard with mutlivendor interoperability and acceptance.
An extension to the PPP protocol that enables ISPs to operate VPNs. L2TP merges the best features of two other tunneling protocols: PPTP from Microsoft and L2F from Cisco.
Used for integrating multi-protocol dial-up services into existing ISPs Point of Presence (POP). May also be used to solve the "multilink hunt-group splitting" problem. Multilink PPP, often used to aggregate ISDN B channels, requires that all channels composing a multilink bundle be grouped at a single Network Access Server (NAS). Because L2TP makes a PPP session appear at a location other than the physical point at which the session was physically received, it can be used to make all channels appear at a single NAS, allowing for a multilink operation even when the physical calls are spread across distinct physical NASs.
L2TP is an extension to PPP that enables remote users to access corporate networks in a secure fashion, using public networks such as the Internet. L2TP is an emerging IETF standard protocol. L2TP is an evolution of the earlier L2F proposed by Cisco and PPTP proposed by Microsoft. L2TP represents the next generation of tunneling protocols.
L2TP allows remote users to access the corporate network by placing local calls (to an ISP) and using the public network infrastructure to reach the corporate network. This reduces network access charges by eliminating costly toll calls. L2TP is a key tool in building VPNs.
L2TP Tunnels PPP traffic over public or private networks, including the Internet. It provides authentication of the PPP connection using PAP, CHAP, etc., just as in a typical PPP session. This is intended to prevent unauthorized individuals from intercepting the communications, which can occur over normal Internet connections.
When running MultiLink PPP sessions, all links that make up a Multilink bundle must terminate at the same access server. L2TP eliminates the need for the individual links to terminate at the same access server, by tunneling the individual PPP sessions to a common, sometimes remote point. This allows, for example, a corporation to implement the dial-in access servers in a more flexible fashion, and the remote users don't have to worry about which server they arrive at.

> tunneling

www.cisco.com/warp/public/732/l2tp/l2tun_ds.htm
www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t1/l2tpt.htm

---

LAN = Local Area Network

Lokalt netværk, som typisk ejes af en enkelt virksomhed - og er installeret i en enkelt bygning - eller i få bygninger i et lokalt område. (sammenlign WAN).
> Ethernet, LAN Manager, Token Ring
> topologi
 

http://www.techfest.com/networking/lan.htm

---

LAN Manager

PC lokalnetværk udviklet af Microsoft - benytter protokollen NetBEUI til deling af filer og og system ressourcer (fx printere)
> LAN, LMHOSTS, NetBIOS, UNC
> Microsoft networks

---

LAP = Link Access Protocol/Procedure

The basis of an error control protocol used in data communications. Examples are: LAP-B, LAP-D and LAP-M

LAP-B = LAP - Balanced

> X.25

LAP-D = LAP - Digital

 

LAP-M = LAP - Modem

The popular error correction protocol specified in the ITU's V.42 recommendation.
The proposed CCITT modem error control standard used to provide error correction in modems.
Two functional units of modems:
- User Interface Part (UIP) acts as a "User" of link layer. Issues requests and responses. Receives indications and confirmations.
- Error Correcting Part (ECP) implements HDLC. The local interface between the modem and the computer is asynchronous, although the data on the PSTN is transmitted using bit-oriented synchronous transmission.

---

Lasat

> modem

www.lasat.dk

---

LBA = Logical Block Adressing

Lineær adressering af harddisk-sektorer - understøttes af SCSI og ATA-2

---

LCD = Liquid Crystal Display

Skærm med små celler, som indeholder 'flydende krystaller', hvor de aflange molekyler kan ændre retning under påvirkning af et elektrisk felt - og dermed ændre cellens udseende: lys eller mørk.

Meget lavt energiforbrug. Benyttes til lommeregnere, digitale ure m.m.
LCD-skærme med farve findes i to typer: STN og TFT.

---

LCP = Link Control Protocol

part of PPP - A protocol that establishes, configures, and tests data link connections used by the PPP.

---

LDAP = Lightweight Directory Access Protocol

TCP/IP protokol - benyttes til automatisk at hente oplysninger fra en central adressebog.
LDAP is a software protocol for enabling anyone to locate organizations, individuals, and other resources such as files and devices in a network, whether on the Internet or on a corporate intranet. LDAP is a "lightweight" (smaller amount of code) version of DAP (Directory Access Protocol), which is part of X.500, a standard for directory services in a network. LDAP is lighter because in its initial version it did not include security features. LDAP originated at the University of Michigan and has been endorsed by at least 40 companies. Netscape includes it in its latest Communicator suite of products. Microsoft includes it as part of what it calls Active Directory in a number of products including Outlook Express. Novell's NetWare Directory Services interoperates with LDAP. Cisco also supports it in its networking products.
In a network, a directory tells you where in the network something is located. On TCP/IP networks (including the Internet), the Domain Name System (DNS) is the directory system used to relate the domain name to a specific network address (a unique location on the network). However, you may not know the domain name. LDAP allows you to search for an individual without knowing where they're located (although additional information will help with the search).
An LDAP directory is organized in a simple "tree" hierarchy consisting of the following levels:

• The "root" directory (the starting place or the source of the tree), which branches out to
• Countries, each of which branches out to
• Organizations, which branch out to
• Organizational units (divisions, departments, and so forth), which branches out to (includes an entry for)
• Individuals (which includes people, files, and shared resources such as printers)

An LDAP directory can be distributed among many servers. Each server can have a replicated version of the total directory that is synchronized periodically. An LDAP server is called a Directory System Agent (DSA). An LDAP server that receives a request from a user takes responsibility for the request, passing it to other DSAs as necessary, but ensuring a single coordinated response for the user.
> LDIF

---

LDIF = LDAP Directory Interchange Format

is a new standard text format for directory interchange. It's definition can be found at the IETF. It is part of a large directory server standardization project, LDAP (Lightweight Directory Access Protocol). For information on it you can check with it's originators at the University of Michigan, or look at Netscape's FAQ on their LDAP server.

---

LED = Light Emitting Diode

 

---

LHA

DOS pakkeprogram

LHA

---

licens

= 'brugsret'. En retsligt bindende aftale mellem en software-producent og brugeren. Anvendelse af produktet forudsætter, at brugeren har accepteret de regler for anvendelse, som producenten har specificeret i licens-aftalen.
>EULA, ophavsret, freeware, shareware

---

Link

1. Hyperlink
2. Netværksforbindelse - fx et kabel

---

Link Station

At each end of the phone line or LAN, the computer needs to keep track of a few items. What is the number that should be assigned to the next I-frame transmitted, what was the number of the last I-frame received, and has it been acknowledged yet? There are time limits to detect lost messages, and a counter to managed the window of unacknowledged frames. The IEEE 802.2 standard calls this a "connection component." In SNA, it is a Link Station.
 

The Link Station controls the flow of data between two network nodes. Successive I-frames may belong to the same session, or they may belong to different programs or terminals. When an I-frame is acknowledged on the LAN or SDLC line, this does not mean that the data in it is correct or has been processed. The Link Station dumps incoming data into buffers and queues them up for later processing.
 

The mainframe-based SNA network does not allow minicomputers to act as intermediate routers for messages from other nodes. No other communication protocol has such a rule, and as powerful microprocessors were integrated into other network devices, the SNA restriction became unbearable. The result is that IBM devices began to cheat. They violated the architecture by playing games with the Link Station activity.
 

If a device allows I-frames, RR, and RNR packets to flow through it, then it is a "bridge." Bridges are required to build any large Token Ring network. The IEEE 802 protocol is configured on most SNA devices to allow for the delay caused by a certain number of bridges between any two nodes.
 

When the device is connected to two different media with different speeds, as is the case when two LANs are connected by a phone line, then the I-frames may take too long to get to their destination. The solution is to create a dummy Link Station on each LAN to receive and acknowledge the I-frames before queuing them for remote transmission. As buffers fill up, the Receiver Not Ready (RNR) control packet can be used to temporarily halt further data until the previous data has been sent on.
 

To understand this trick, it is important to realize that when a Link Station acknowledges receipt of an I- frame, this does not imply that the data inside the I-frame has been processed. An IBM Token Ring adapter acknowledges frames as they are received by the adapter card. They may then be queued up and may be processed seconds or even minutes later by the programs inside the PC. So the Link Station acknowledgment only implies that the message got as far as the adapter card.
 

Most IBM customers that use modern equipment have some version of the Link Station hack without realizing that it is technically a violation of the SNA Architecture. For example, every 3174 control unit that acts as a Token Ring gateway (whether "remote" to an SDLC line or "local" to a mainframe channel) is essentially creating dummy Link Stations. The 3270 SNA Gateway function in a PC is also an example of the Link Station trick (though it also remaps LU numbers in the packet before sending the data on).

 
APPN provides a proper tool for using minicomputers as routers, but until recently it was not possible to send 3270 data through an APPN network. The IBM decision to initially make unreasonable restrictions, then fail to update the architecture, then solve the problem by subverting the original network design, and finally to mislead customers by refusing to admit the mess underscores all that has been wrong with IBM technical management.

---

Linux

free UNIX
 

[Techweb] Pronounced "linn-icks." A version of UNIX that runs on x86, Alpha and PowerPC machines. Linux is essentially freeware; however, the full distribution of Linux along with proprietary add-ons and support are available for a fee from vendors such as Red Hat Software (www.redhat.com) and Caldera (www.caldera.com). The distribution CD-ROMs include the complete source code as well as hundreds of tools, applets and utilities.
Due to its stability, Linux has gained popularity with ISPs as the OS for hosting Web servers. Its usage is expected to grow as a server OS as well as for the desktop (see KDE and GNOME).
In 1990, Finnish computer science student Linus Torvalds turned Minix, a popular classroom teaching tool, into Linux, which is closer to the real UNIX. Torvalds created the kernel, and most of the supporting applications and utilities came from the GNU project of the Free Software Foundation. Many programmers have contributed to the Linux/GNU system. VA Linux Systems provides a Web site devoted entirely to Linux (www.linux.com). See GNU and Trinux.

> FreeBSD, SSLUG, SuSE, UNIX
 

www.linuxjournal.com
www.linuxhq.org
www.linux.org

 

Linux GUI
> KDE, GNOME

---

LiveScript

Scriptsprog udviklet af Netscape til indlejring i HTML-dokumenter.
Da Java blev populært omdøbte Netscape LiveScript til JavaScript.

---

LiveWire

Scriptsprog udviklet af Netscape til afvikling på web-serveren. Baseret på JavaScript. Fungerer kun sammen med Netscapes egne server-programmer.

---

LLC = Logical Link Control

lokalnet data link protocol - flow kontrol, fejlhåndtering IEEE 802.2
> HDLC, SDLC

---

LMHOSTS (LAN Manager Hosts)

[Techweb] A text file in a Windows network (NetBIOS protocol) that provides name resolution of host names (NetBIOS names) to IP addresses. LMHOSTS files, which contain host names and IP addresses, are manually updated and replicated onto all the servers in the enterprise. Except in small networks, LMHOSTS files have given way to the WINS system. The LM in LMHOSTS came from LAN Manager, Microsoft's earlier network operating system (NOS).
 

LMHOSTS-filen findes normal i WINDOWS-mappen - her ligger en eksempelfil: LMHOSTS.SAM. Den fungerende LMHOSTS-fil har ingen filendelse! Indholdet i en LMHOSTS fil følger dette mønster (#PRE betyder, at oversættelsen bliver 'preloaded', så den ligger i RAM >NetBIOS navne cache):

102.54.94.97 rhino #PRE 102.54.94.123 popular #PRE 102.54.94.117 localsrv #PRE

 

>HOSTS

www.globetrotting.com/tcpip/lmhosts.htm
www.ezine.com/MapDrive.html : Mapping a Drive Across the Internet Using LMHOSTS
www.cisco.com/warp/public/789/24.html : How to Configure LMHOSTS for NetBIOS Name Resolution
www.lebarge.com/clark/tcpip/lmhosts.htm

---

Localhost

Denne computer - ofte synonymt med IP-adressen 127.0.0.1

---

Login

Brugernavn

---

lokalnet

> LAN

---

Loopback Address

>IP Address

---

Lotus

> cc:Mail

---

LPT = Line Printer

LPT1 og LPT2: parallelporte (printerporte)
> SPP, EPP, ECP
> COM

---

LSA = Local Security Authority

- in Windows NT

---

LU = Logical Unit

- In an IBM SNA network, a point denoting the beginning or end of a communications session.

---

Lucifer

IBM Encryption standard - a variation, DES, was adopted by NBS
128 bit blocks - 112 bit keys

---

Lycos

search engine

www.lycos.com

---

LZW compression

A compression algorithm named after Abraham Lempel, Jakob Ziv and Terry Welsh.
Used in GIF images.

---