網路原理(一) Section 7.2

Address Resolution
位址解析協定(ARP) 是通過解析網路層位址來找尋資料鏈路層位址的一個在網路協定包中極其重要的網路傳輸協定。

Assigned multicast
Assigned multicast addresses are reserved multicast addresses for predefined groups of devices.

Destination or Service Unreachable
When a host or gateway receives a packet that it cannot deliver, it can use an ICMP Destination Unreachable message to notify the source that the destination or service is unreachable.

Dual-stack
As shown in Figure 1, dual stack allows IPv4 and IPv6 to coexist on the same network segment. Dual stack devices run both IPv4 and IPv6 protocol stacks simultaneously.

Duplicate Address Detection
To ensure the uniqueness of any IPv6 unicast address, the client may use a process known as Duplicate Address Detection (DAD). 

EUI-64 Process
EEE defined the Extended Unique Identifier (EUI) or modified EUI-64 process. 

FF02::1 All-nodes multicast group
This is a multicast group that all IPv6-enabled devices join.

FF02::2 All-routers multicast group
This is a multicast group that all IPv6 routers join. 

Global Unicast Address
A global unicast address is similar to a public IPv4 address. These are globally unique, Internet routable addresses. Global unicast addresses can be configured statically or assigned dynamically. 

Hextet
In IPv6, a hextet is the unofficial term used to refer to a segment of 16 bits or four hexadecimal values. Each “x” is a single hextet, 16 bits or four hexadecimal digits.

Host confirmation
An ICMP Echo Message can be used to determine if a host is operational. The local host sends an ICMP Echo Request to a host.

ICMPv6
One example is Internet Control Message Protocol version 6 (ICMPv6), which includes address resolution and address auto-configuration not found in ICMP for IPv4 (ICMPv4). 

IPv4 Time-to-Live (TTL)
An ICMPv4 Time Exceeded message is used by a router to indicate that a packet cannot be forwarded because the Time to Live (TTL) field of the packet was decremented to 0.

IPv6
網際網路協定第六版

IPv6 Anycast
An IPv6 anycast address is any IPv6 unicast address that can be assigned to multiple devices. 

IPv6 Hop Limit
IPv6 does not have a TTL field; it uses the hop limit field to determine if the packet has expired.

IPv6 link-local address
Link-local addresses are used to communicate with other devices on the same local link.

IPv6 Loopback Address
To perform this test, we ping the local loopback address of 127.0.0.1 for IPv4 (::1 for IPv6). Testing the IPv4 loopback is shown in the figure.

IPv6 multicast
An IPv6 multicast address is used to send a single IPv6 packet to multiple destinations. 

IPv6 Unicast
An IPv6 unicast address uniquely identifies an interface on an IPv6-enabled device. 

Leading Zeros
The first rule to help reduce the notation of IPv6 addresses is to omit any leading 0s (zeros) in any 16-bit section or hextet. 

Link-local Address
Link-local addresses are used to communicate with other devices on the same local link.

Network Address Translation (NAT64)
Translation – As shown in Figure 3, Network Address Translation 64 (NAT64) allows IPv6-enabled devices to communicate with IPv4-enabled devices using a translation technique similar to NAT for IPv4.

Round Trip Time (RTT)
After all the requests are sent, the ping utility provides a summary that includes the success rate and average round-trip time to the destination.

Route redirection
ICMP messages common to both ICMPv4 and ICMPv6 include

Router Advertisement
Using SLAAC, devices rely on the local router’s ICMPv6 Router Advertisement (RA) messages to obtain the necessary information.

Router Solicitation
An RA message will also be sent in response to a host sending an ICMPv6 Router Solicitation (RS) message.

show ipv6 interface brief ; show ipv6 route
cisco設備的指令

Solicited node multicast
A solicited-node multicast address is similar to the all-nodes multicast address.

Stateless Address Autoconfiguration  (SLAAC)
Stateless Address Autoconfiguration (SLAAC) is a method that allows a device to obtain its prefix, prefix length, default gateway address, and other information from an IPv6 router without the use of a DHCPv6 server. 

Time exceeded
An ICMPv4 Time Exceeded message is used by a router to indicate that a packet cannot be forwarded because the Time to Live (TTL) field of the packet was decremented to 0. 

Tunneling
tunneling is a method of transporting an IPv6 packet over an IPv4 network. The IPv6 packet is encapsulated inside an IPv4 packet, similar to other types of data. 

Unique Local Address
Another type of unicast address is the unique local unicast address. IPv6 unique local addresses have some similarity to RFC 1918 private addresses for IPv4, but there are significant differences. Unique local addresses are used for local addressing within a site or between a limited number of sites. 

Unspecified Address
未指定的地址

網路原理(一) Section 7.1

ANDing
The actual process used to identify the network portion and host portion is called ANDing.

Binary Numbering System
Binary is a numbering system that consists of the numbers 0 and 1 called bits. In contrast, the decimal numbering system consists of 10 digits consisting of the numbers 0 – 9. 

Broadcast
廣播（英語：broadcast）是指將資訊封包發往指定網路範圍內的所有裝置[1]。其傳送範圍稱為「廣播域」。

Broadcast Address
乙太網和IPv4網都用全1的位址表示廣播，分別是ff:ff:ff:ff:ff:ff和255.255.255.255。

Broadcast Domain
廣播域

Class A
(0.0.0.0/8 to 127.0.0.0/8) – Designed to support extremely large networks with more than 16 million host addresses. 

Class B
(128.0.0.0 /16 – 191.255.0.0 /16) – Designed to support the needs of moderate to large size networks with up to approximately 65,000 host addresses.

Class C
(192.0.0.0 /24 – 223.255.255.0 /24) – Designed to support small networks with a maximum of 254 hosts.

Class D
Class D multicast block consisting of 224.0.0.0 to 239.0.0.0

Class E
Class E experimental address block consisting of 240.0.0.0 – 255.0.0.0. 

Classless Inter-domain Routing (CIDR)
The system in use today is referred to as classless addressing. The formal name is Classless Inter-Domain Routing (CIDR, pronounced “cider”).

DHCP Server
The DHCP server provides an IPv4 address, subnet mask, default gateway, and other configuration information. 


DHCP Client Dynamic Assignment
Therefore, these devices are assigned IPv4 addresses dynamically using the Dynamic Host Configuration Protocol (DHCP). 

Directed Broadcast
A directed broadcast is sent to all hosts on a specific network. 

Dotted Decimal Format
點分十進位是一個表達數字數據的形式。其形式為用句點分隔的多個十進位數。 

Dynamic Host Configuration Protocol (DHCP)
動態主機設定協定（英語：Dynamic Host Configuration Protocol，DHCP）是一個區域網路的網路協定，使用UDP協定工作，主要有兩個用途： 用於內部網路或網路服務供應商自動分配IP位址給用戶

Host Address
主機位址

Internet Assigned Numbers Authority (IANA)
網際網路號碼分配局，是一家網際網路位址指派機構，管理國際網際網路中使用的IP位址、域名和許多其它參數的機構。

Internet Service Providers (ISPs)
網路服務提供者

IPv4 Loopback Address
Loopback addresses (127.0.0.0 /8 or 127.0.0.1 to 127.255.255.254) – More commonly identified as only 127.0.0.1, these are special addresses used by a host to direct traffic to itself. 

Limited Broadcast
A limited broadcast is sent to 255.255.255.255. By default, routers do not forward broadcasts. 

Link-local Address
Link-Local addresses (169.254.0.0 /16 or 169.254.0.1 to 169.254.255.254) – More commonly known as the Automatic Private IP Addressing (APIPA) addresses, they are used by a Windows DHCP client to self-configure in the event that there are no DHCP servers available.

Multicast Transmission
Multicast transmission reduces traffic by allowing a host to send a single packet to a selected set of hosts that subscribe to a multicast group. 

Multicast
多播（英語：multicast，台灣又譯作多點傳送、多點廣播或群播，中國大陸又譯作組播）是指把資訊同時傳遞給一組目的位址。

Multicast Addresses
群播位址

Network Address
網路位址

Octet
在電腦領域裏，一個octet是指八個位元（bit）為一組的單位，中文稱作八位元組。 

Positional Notation
Learning to convert binary to decimal requires an understanding of positional notation.

Prefix Length
Fortunately, there is an alternate shorthand method of identifying a subnet mask called the prefix length.

Private Address
Private IPv4 addresses are not unique and can be used by an internal network.

Public Address
Public IPv4 addresses are addresses which are globally routed between ISP (Internet Service Provider) routers. 

radix
基數

Regional Internet Registries (RIRs)
The IANA manages and allocates blocks of IP addresses to the Regional Internet Registries (RIRs).  RIRs are responsible for allocating IP addresses to ISPs who in turn provide IPv4 address blocks to organizations and smaller ISPs.

RFC 1918
Private addresses are defined in RFC 1918. 

Slash Notation
Specifically, the prefix length is the number of bits set to 1 in the subnet mask. It is written in “slash notation”, which is a “/” followed by the number of bits set to 1. 

Static IP Addressing
靜態IP位址

Subnet Mask
子網路遮罩

TEST-NET Addresses
TEST-NET addresses (192.0.2.0/24 or 192.0.2.0 to 192.0.2.255) – These addresses are set aside for teaching and learning purposes and can be used in documentation and network examples. 

Unicast
Unicast communication is used for normal host-to-host communication in both a client/server and a peer-to-peer network. 

網路原理(一) Section 6.4

以下都是Cisco設備內部的常用指令

interface type-and-number

ip address ipv4-address subnet-mask

description description-text

no shutdown

show ip interface brief

ping ip address

show ip route

show ip interface brief

show interfaces

ip default-gateway ip-address

網路原理(一) Section 6.3

Power-on-self-test POST
After the POST, the bootstrap program is copied from ROM into RAM.

RAM
隨機存取記憶體，也叫主記憶體，是與CPU直接交換資料的記憶體。

ROM
唯讀記憶體（Read-Only Memory，ROM）是一種半導體記憶體，其特性是一旦儲存資料就無法再將之改變或刪除，且內容不會因為電源關閉而消失。

NVRAM
This is non-volatile memory is used as the permanent storage for the startup configuration file (startup-config).

Flash
This non-volatile computer memory used as permanent storage for the IOS and other system related files such as log files, voice configuration files, HTML files, backup configurations, and more.

Synchronous dynamic RAM (SDRAM)
Cisco routers use a fast type of RAM called synchronous dynamic random access memory (SDRAM). 


WIC
A serial WAN interface card (WIC) consisting of two interfaces - Serial 0/0/0 (S0/0/0) and Serial 0/0/1 (S0/0/1)

high-speed WIC (HWIC)
1 Cisco Series 1941 Router with one HWIC-4ESW switching port modular card and IOS version 15.1 or higher

ROMMON
Rommon mode - Cisco 系統異常. 一般Cisco Router出廠預設configuration register 是0x2102.

Advanced Integration Module (AIM)
The figure also includes images of other components found in a router, such as the power supply, cooling fan, heat shields, and an advanced integration module (AIM), which are beyond the scope of this chapter.

Enhanced high-speed WAN interface card (eHWIC)
The EHWIC provides Gigabit Ethernet connectivity but will not support line rate since throughput is limited by the platforms. 

Serial module
串行模塊

Ethernet interfaces
乙太介面

Auxiliary (AUX) RJ-45 port
另外 Router 通常還有一個用來接數據機的 RS-232 介面，這個介面叫 AUX Port

In-band router interfaces
Inband interfaces receive and forward IP packets.

Console
This is a physical management port that provides out-of-band access to a Cisco device. 

Out-of-band
在電腦領域，帶外管理（Out-of-band management）是指使用獨立管理通道進行裝置維護。

Secure Shell (SSH)
Secure Shell是一種加密的網路傳輸協定，可在不安全的網路中為網路服務提供安全的傳輸環境。

Telnet
Telnet協定是一種應用層協定，使用於網際網路及區域網中，使用虛擬終端機的形式，提供雙向、以文字字串為主的命令列介面互動功能。

startup-config ; running-config
cisco設備的設定

bootstrap program
開機程序

Trivial File Transport Protocol (TFTP)
簡單檔案傳輸協定也稱小型檔案傳輸協定（Trivial File Transfer Protocol, TFTP），是一種於1981年在RFC 783中定義的簡化的檔案傳輸協定（FTP）。

setup mode
安裝模式

show version
版本號

網路原理(一) Section 6.2

netstat -r  ;  route print
Entering the netstat -r command or the equivalent route print command, displays three sections related to the current TCP/IP network connections

interface list
Lists the Media Access Control (MAC) address and assigned interface number of every network-capable interface on the host, including Ethernet, Wi-Fi, and Bluetooth adapters.

IPv4 Route Table
Lists all known IPv4 routes, including direct connections, local network, and local default routes.

IPv6 Route Table
Lists all known IPv6 routes, including direct connections, local network, and local default routes.

directly-connected routes
These routes come from the active router interfaces. Routers add a directly connected route when an interface is configured with an IP address and is activated.

remote routes
These routes come from remote networks connected to other routers. Routes to these networks can be manually configured on the local router by the network administrator or dynamically configured by enabling the local router to exchange routing information with other routers using a dynamic routing protocol.

default route
Like a host, routers also use a default route as a last resort if there is no other route to the desired network in the routing table. 

show ip route
On a Cisco IOS router, the show ip route command can be used to display the router’s IPv4 routing table.

route source
Notice how directly connected networks with a route source of C and L have no next-hop address. This is because a router can forward packets directly to hosts on these networks using the designated interface.

destination network
When a packet arrives at the router interface, the router examines the packet header to determine the destination network.

outgoing interface
The switch looks up the destination MAC address in its switching table, determines the outgoing interface port, and forwards the frame onto its destination through the designated switch port.

administrative distance
行政距離

metric
If there are two or more possible routes to the same destination, the metric is used to decide which route appears in the routing table.

next-hop
If a match is found, the router forwards the packet to the next hop address out of the identified interface.

route timestamp
路由時間戳記

branch routers
Teleworkers, small businesses, and medium-size branch sites. Includes Cisco Integrated Services Routers (ISR) G2 (2nd generation).

WAN routers
Large businesses, organizations, and enterprises. Includes the Cisco Catalyst Series Switches and the Cisco Aggregation Services Routers (ASR).

service proivder routers
Large service providers. Includes Cisco ASR, Cisco CRS-3 Carrier Routing System, and 7600 Series routers.

網路原理(一) Section 6.1

encapsulation
封裝

routing
路由

de-encapsulation
解封裝

data
資料

packet
封包

frame
窗框

Internet Protocol Version 4 (IPv4)
網際網路協定第四版

Internet Protocol Version 6 (IPv6)
網際網路協定第六版

Network Layer PDU
IP Packet

Transport Layer PDU
Segment

Segment Header
segment標頭

IP Header
IP標頭

Auxiliary port (AUX)
Some devices, such as routers, may also support a legacy auxiliary port that was used to establish a CLI session remotely using a modem. Similar to a console connection, the AUX port is out-of-band and does not require networking services to be configured or available.

connectionless
IP is connectionless, meaning that no dedicated end-to-end connection is created before data is sent.

best effort delivery
The IP protocol does not guarantee that all packets that are delivered are, in fact, received. 

media independent
IP operates independently of the media that carry the data at lower layers of the protocol stack. 

unreliable
As an unreliable network layer protocol, IP does not guarantee that all sent packets will be received. 

maximum transmission unit (MTU)
The maximum size of the PDU that each medium can transport. This characteristic is referred to as the maximum transmission unit (MTU).

version
版本

differentiated Services (DS)
Formerly called the Type of Service (ToS) field, the DS field is an 8-bit field used to determine the priority of each packet. 

Time-to-Live (TTL)
Contains an 8-bit binary value that is used to limit the lifetime of a packet. The packet sender sets the initial TTL value, and it is decreased by one each time the packet is processed by a router.

Internet Control Message Protocol (ICMP)
網際網路控制訊息協定（英語：Internet Control Message Protocol，縮寫：ICMP）是網際網路協定套組的核心協定之一。

data payload
資料有效載荷

Identification, Flags, Fragment Offset fields
Other fields are used to reorder a fragmented packet. Specifically, the IPv4 packet uses Identification, Flags, and Fragment Offset fields to keep track of the fragments.

keyword
關鍵字

Network Address Translation (NAT)
Network Address Translation (NAT) is a technology commonly implemented within IPv4 networks. NAT provides a way for multiple devices to share a single public IPv4 address. 

Traffic Class
This 8-bit field is equivalent to the IPv4 Differentiated Services (DS) field.

Flow Label
This 20-bit field suggests that all packets with the same flow label receive the same type of handling by routers.

Payload length
This 16-bit field indicates the length of the data portion or payload of the IPv6 packet. 

next header
This 8-bit field is equivalent to the IPv4 Protocol field.

hop limit
This 8-bit field replaces the IPv4 TTL field. 

local host
本機

remote host
遠端

default gateway
The default gateway is the network device that can route traffic to other networks. It is the router that can route traffic out of the local network.

網路原理(一) Section 5.3

arp table ; arp cache
When a packet is sent to the data link layer to be encapsulated into an Ethernet frame, the device refers to a table in its memory to find the MAC address that is mapped to the IPv4 address. This table is called the ARP table or the ARP cache.

arp request
If the device locates the IPv4 address, its corresponding MAC address is used as the destination MAC address in the frame. If there is no entry is found, then the device sends an ARP request.

arp reply
Only the device with an IPv4 address associated with the target IPv4 address in the ARP request will respond with an ARP reply. 

show ip arp, arp -a
The Cisco IOS CLI show commands display relevant information about the configuration and operation of the device.

arp spoofing
In some cases, the use of ARP can lead to a potential security risk known as ARP spoofing or ARP poisoning.

網路原理(一) Section 5.2

burned-in address (BIA)
The MAC address is often referred to as a burned-in address (BIA) because, historically, this address is burned into ROM (Read-Only Memory) on the NIC.

ipconfig /all command
n a Windows host, the ipconfig /all command can be used to identify the MAC address of an Ethernet adapter.

ifconfig command
On a MAC or Linux host, the ifconfig command is used.

Unicast MAC Address
In Ethernet, different MAC addresses are used for Layer 2 unicast, broadcast, and multicast communications.  A unicast MAC address is the unique address used when a frame is sent from a single transmitting device to a single destination device.

Broadcast MAC Address
A broadcast packet contains a destination IPv4 address that has all ones (1s) in the host portion. This numbering in the address means that all hosts on that local network (broadcast domain) will receive and process the packet.

Multicast MAC Address
Multicast addresses allow a source device to send a packet to a group of devices. 

Content Addressable Memory (CAM)
The MAC address table is sometimes referred to as a content addressable memory (CAM) table. While the term CAM table is fairly common, for the purposes of this course, we will refer to it as a MAC address table.

Store-and-forward
A store-and-forward switch receives the entire frame, and computes the CRC.  If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface.  The frame is then forwarded out the correct port.

Cut-through
A cut-through switch forwards the frame before it is entirely received.  At a minimum, the destination address of the frame must be read before the frame can be forwarded.

Fast-forward switching
Fast-forward switching offers the lowest level of latency. Fast-forward switching immediately forwards a packet after reading the destination address.

Fragment-free switching
In fragment-free switching, the switch stores the first 64 bytes of the frame before forwarding. Fragment-free switching can be viewed as a compromise between store-and-forward switching and fast-forward switching. 

Port-based Memory Buffering
In port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports.

Shared Memory Buffering
Shared memory buffering deposits all frames into a common memory buffer that all the ports on the switch share. The amount of buffer memory required by a port is dynamically allocated. 

Half-duplex
半雙工（half-duplex）的系統允許二台裝置之間的雙向資料傳輸，但不能同時進行。因此同一時間只允許一裝置傳送資料，若另一裝置要傳送資料，需等原來傳送資料的裝置傳送完成後再處理。

Full-duplex
全雙工（full-duplex）的系統允許二台裝置間同時進行雙向資料傳輸。一般的電話、手機就是全雙工的系統，因為在講話時同時也可以聽到對方的聲音。 

Auto-MDIX
Most switch devices now support the mdix auto interface configuration command in the CLI to enable the automatic medium-dependent interface crossover (auto-MDIX) feature. 

Address Resolution Protocol (ARP)
位址解析協定 是通過解析網路層位址來找尋資料鏈路層位址的一個在網路協定包中極其重要的網路傳輸協定。

網路原理(一) Section 5.1

IEEE 802.2
IEEE 802.2，一種工業標準，被包含在IEEE 802標準之中，是電腦網路中的軟體元件標準。它定義了邏輯鏈路控制層，是OSI模型中數據鏈路層的上層部份。

IEEE 802.3
IEEE 802.3是IEEE制定在雙工模式(Full Duplex)中提供流量控管的機制(Flow Control) ，相關規格已制定於IEEE Std 802.3-2002(Annex 31B)中。

LLC Sublayer
The Ethernet LLC sublayer handles the communication between the upper layers and the lower layers.

MAC Sublayer
MAC constitutes the lower sublayer of the data link layer.

Data Encapsulation
The data encapsulation process includes frame assembly before transmission, and frame disassembly upon reception of a frame.

Frame Delimiting
The framing process provides important delimiters that are used to identify a group of bits that make up a frame.

Cyclic Redundancy Check
循環冗餘校驗（英语：Cyclic redundancy check，通稱「CRC」）是一種根據網路數據封包或電腦檔案等數據產生簡短固定位數驗證碼的一種散列函數，主要用來檢測或校驗數據傳輸或者保存後可能出現的錯誤。

Carrier Sense Multiple Access (CSMA)
載波偵聽多路存取（英語：Carrier Sense Multiple Access，縮寫：CSMA）是一種媒介存取控制（MAC）的協定。

Ethernet II
Ethernet II is the Ethernet frame format used in TCP/IP networks.

Frame Check Sequence (FCS)
The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes. This includes all bytes from the Destination MAC Address field through the Frame Check Sequence (FCS) field. 

Preamble
The Preamble field is not included when describing the size of a frame. 

runt
小;迷你

Collision Fragment
Any frame less than 64 bytes in length is considered a “collision fragment” or “runt frame” and is automatically discarded by receiving stations.

Jumbo ; Baby Giant Frame
Frames with more than 1500 bytes of data are considered “jumbo” or “baby giant frames”.

Hexadecimal
16進制

Organizationally Unique Identifier (OUI)
The IEEE assigns the vendor a 3-byte (24-bit) code, called the Organizationally Unique Identifier (OUI). 
 
 


 

網路原理(一) Section 4.4

802.11 frame
After a wireless device sends an 802.11 frame, the receiver returns an acknowledgment so that the sender knows the frame arrived.

802.11 wireless ; Frame Relay ; HDLC ; Point-to-Point Protocol (PPP)
Data link layer protocol

Bus
All end systems are chained to each other and terminated in some form on each end.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
is used in half-duplex Ethernet LANs.

Collision
碰撞

Contention-based access
Another form of CSMA that is used by IEEE 802.11 WLANs is Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). CMSA/CA uses a method similar to CSMA/CD to detect if the media is clear.

Control
Identifies special flow control services such as quality of service (QoS).

Controlled access
控制存取

Cyclic Redundancy Check (CRC) value
A transmitting node creates a logical summary of the contents of the frame, known as the cyclic redundancy check (CRC) value.

Data
Contains the frame payload (i.e., packet header, segment header, and the data).

Error Detection
These frame fields are used for error detection and are included after the data to form the trailer.

Ethernet
乙太網

Extended Star
In an extended star topology, additional Ethernet switches interconnect other star topologies.

Frame Check Sequence (FCS) Frame Relay
CRC value is placed in the Frame Check Sequence (FCS) field to represent the contents of the frame. 

Frame start and stop indicator flags
Used to identify the beginning and end limits of the frame.

Full-Duplex Communications
Both devices can transmit and receive on the media at the same time.The half-duplex mode is used in legacy bus topologies and with Ethernet hubs. WLANs also operate in half-duplex. Half-duplex allows only one device to send or receive at a time on the shared medium and is used with contention-based access methods.

Half-Duplex Communications
Both devices can transmit and receive on the media but cannot do so simultaneously. The data link layer assumes that the media is available for transmission for both nodes at any time. Ethernet switches operate in full-duplex mode by default, but can operate in half-duplex if connecting to a device such as an Ethernet hub. 

Header ; Trailer
Although there are many different data link layer protocols that describe data link layer frames, each frame type has three basic parts: 1.Header 2.Trailer 3.Data

Hub and Spoke
A WAN version of the star topology in which a central site interconnects branch sites using point-to-point links. 

Logical Point-to-Point Topology
The end nodes communicating in a point-to-point network can be physically connected via a number of intermediate devices. However, the use of physical devices in the network does not affect the logical topology.

Logical Topology 
Refers to the way a network transfers frames from one node to the next. This arrangement consists of virtual connections between the nodes of a network. These logical signal paths are defined by data link layer protocols. The logical topology of point-to-point links is relatively simple while shared media offers different access control methods. 

Mesh
This topology provides high availability, but requires that every end system be interconnected to every other system.

Point-to-Point
This is the simplest topology that consists of a permanent link between two endpoints. For this reason, this is a very popular WAN topology.


Physical Topology
Refers to the physical connections and identifies how end devices and infrastructure devices such as routers, switches, and wireless access points are interconnected. Physical topologies are usually point-to-point or star.

Media Access Control
媒體存取控制（英語：Media Access Control，縮寫：MAC）子層，是區域網路中資料鏈路層的下層部分，提供定址及媒體存取的控制方式，使得不同裝置或網路上的節點可以在多點的網路上通訊，而不會互相衝突，上述的特性在區域網路或者都會網路中格外重要。

Media Sharing
How the nodes share the media. The media sharing can be point-to-point, such as in WAN connections, or shared such as in LAN networks.

Quality of Service (QoS)
QoS is used to give forwarding priority to certain types of messages.

Ring
End systems are connected to their respective neighbor forming a ring.

Star
End devices are connected to a central intermediate device.

Topology
How the connection between the nodes appears to the data link layer.

type
類型

Virtual circuit
A virtual circuit is a logical connection created within a network between two network devices.

網路原理(一) Section 4.3

American National Standards Institute (ANSI)
美國國家標準協會是負責制定美國國家標準的非營利組織。

Data link layer (layer2)
資料鏈路層

Ethernet interface ; Serial interface
The router in the figure has an Ethernet interface to connect to the LAN and a serial interface to connect to the WAN.

Frames
在Data Link layer 將PDU加上標頭和標尾，此封裝資料稱為訊框（Frame），內含自己與對方網路卡位址及CRC。  

Institute of Electrical and Electronics Engineers (IEEE)
電機電子工程師學會是一個建立於1963年1月1日的國際性電子技術與電子工程師協會，亦是世界上最大的專業技術組織之一，擁有來自175個國家的36萬會員。 

International Organization for Standardization (ISO)
國際標準組織

International Telecommunication Union (ITU)
國際電信聯盟是一個國際組織，主要負責確立國際無線電和電信的管理制度和標準。  

Logical Link Control (LLC)
This upper sublayer communicates with the network layer. It places information in the frame that identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to utilize the same network interface and media.  

Media Access Control (MAC)
This lower sublayer defines the media access processes performed by the hardware. It provides data link layer addressing and access to various network technologies.

網路原理(一) Section 4.2

Cancelation
取消

Category 5 cable (Cat 5)
Category 5 (Cat5) cable is used commonly in 100BASE-TX Fast Ethernet installations.

Enhanced Category 5 cable (Cat5e)
5類雙絞線，一般稱為CAT-5線，是一種雙絞線，並設計為可提供高速度、低噪訊比的訊號傳輸線。

Category 6 cable (Cat6)
Category 6a cable (Cat6a)
Category 7 cable (Cat7)
各種線

Cladding & Jacket
Optical fiber is composed of two kinds of glass (core and cladding) and a protective outer shield (jacket).

Coaxial
同軸

Coaxial cabling
同軸電纜線

Core
芯

Coverage area
Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage.

Crosstalk
Crosstalk is a disturbance caused by the electric or magnetic fields of a signal on one wire to the signal in an adjacent wire.

Dispersion
Dispersion refers to the spreading out of a light pulse over time.

Duplex Multimode LC Connector
Some fiber connectors accept both the transmitting and receiving fibers in a single connector known as a duplex connector, as shown in the Duplex Multimode LC Connector

Electromagnetic interference (EMI)
Radio frequency interference (RFI)
distort and corrupt the data signals being carried by copper media. 

End gap
The media does not completely touch at the splice or connection.

End finish
The media ends are not well polished, or dirt is present at the termination.

Enterprise networks
Used for backbone cabling applications and interconnecting infrastructure devices.

Long-hual networks
Used by service providers to connect countries and cities. 

Fiber-to-the-home (FTTH)
Used to provide always-on broadband services to homes and small businesses. 

Institute of Electrical and Electronics Engineers (IEEE)
電機電子工程師學會是一個建立於1963年1月1日的國際性電子技術與電子工程師協會，亦是世界上最大的專業技術組織之一，擁有來自175個國家的36萬會員。

Interference
Wireless is susceptible to interference and can be disrupted by such common devices as household cordless phones, some types of fluorescent lights, microwave ovens, and other wireless communications.

Lasers ; Light Emitting Diodes (LEDs)
Light pulses representing the transmitted data as bits on the media are generated by either

Misalignment
The fiber-optic media are not precisely aligned to one another when joined.

Multi-mode fiber (MMF)
Consists of a larger core and uses LED emitters to send light pulses.

Single-mode fiber (SMF)
Consists of a very small core and uses expensive laser technology to send a single ray of light.

Optical fiber cable
光纖電纜

RJ45 connector
8P8C，也稱RJ45，是乙太網使用雙絞線連接時常用的一種連結器插頭。

Rollover

A Cisco proprietary cable used to connect a workstation to a router or switch console port.

Shared medium
WLANs operate in half-duplex, which means only one device can send or receive at a time. 

Shielded twisted pair cabling (STP)
provides better noise protection than UTP cabling.

Signal attenuation
訊號衰減

ST,SC and LC fiber-optic connectors
An optical fiber connector terminates the end of an optical fiber.

Submarine networks
Used to provide reliable high-speed, high-capacity solutions capable of surviving in harsh undersea environments up to transoceanic distances. 

TIA 568A ; TIA 568B
The UTP cable type, related standards, and typical application of these cables. It also identifies the individual wire pairs for the TIA-568A and TIA-568B standards.

TIA/EIA 568 standard
The TIA/EIA-568 standard describes the wire color codes to pin assignments (pinouts) for Ethernet cables.  

Unshielded twisted pair (UTP)
Unshielded twisted-pair (UTP) cabling is the most common networking media.

 Wireless Access Point (AP)
無限存取點

Wireless NIC adapters
無線網卡適配器
Provide wireless communication capability to each network host.

 

網路原理(一) Section 4.1

Access Point (AP)
To offer wireless capability, devices on a wireless network must be connected to a wireless access point (AP).

American National Standards Institute (ANSI)  
美國國家標準協會是負責制定美國國家標準的非營利組織。

Bandwidth
頻寬
Bandwidth is the capacity of a medium to carry data.

CENELEC (European Committee for Electrotechnical Standardization)
CSA (Canadian Standards Association)
there are often regional cabling standards groups  

Copper cable
The signals are patterns of electrical pulses.

European Telecommunications Standards Institute (ETSI) 
Federal Communication Commission (FCC)
JSA/JIS (Japanese Standards Association)
National telecommunications regulatory authorities 

Encoding
編碼

Fiber-optic cable
The signals are patterns of light. 

Gigabits per second (Gb/s)
Kilobits per second (kb/s)
Megabits per second (Mb/s)
每秒多少單位

Goodput
Goodput is throughput minus traffic overhead for establishing sessions, acknowledgments, and encapsulation. 

Institute of Electrical and Electronics Engineers (IEEE)
電機電子工程師學會是一個建立於1963年1月1日的國際性電子技術與電子工程師協會，亦是世界上最大的專業技術組織之一，擁有來自175個國家的36萬會員。

Integrated Service Router (ISR)
Provide fewer points of management for the branch.

International Organization for Standardization (ISO)
國際標準化組織成立於1947年2月23日，制定全世界工商業國際標準的國際標準建立機構。 

International Telecommunication Union (ITU)
國際電信聯盟是一個國際組織，主要負責確立國際無線電和電信的管理制度和標準。

Internet Engineering Task Force (IETF)
網際網路工程任務小組負責網際網路標準的開發和推動。 它的組織形式主要是大量負責特定議題的工作群組，每個都有一個指定主席。

Latency
Latency refers to the amount of time, to include delays, for data to travel from one given point to another.
 
Manchester encoding
Manchester encoding represents a 0 bit by a high to low voltage transition, and a 1 bit is represented as a low to high voltage transition. 

Modulation
Modulation is the process by which the characteristic of one wave (the signal) modifies another wave (the carrier).

Network Interface Cards (NICs)
網路介面卡

OSI Physical Layer
OSI物理層

Signaling
訊號

Telecommunications Industry Association/Electronic Industries Association (TIA/EIA)
International and national organizations, regulatory government organizations, and private companies involved in establishing and maintaining physical layer standards.  
 
Throughput
Throughput is the measure of the transfer of bits across the media over a given period of time.

Wireless
The signals are patterns of microwave transmissions.

Wireless Local Network (WLAN)
無線區域網路（英語：Wireless LAN，縮寫WLAN）是不使用任何導線或傳輸電纜連接的區域網路，而使用無線電波作為資料傳送的媒介，傳送距離一般只有幾十米。 無線區域網路的主幹網路通常使用有線電纜，無線區域網路用戶通過一個或多個無線接取器接入無線區域網路。