1、2022/12/301Major Characteristics of WANs WANs generally connect devices that are separated by a broader geographical area than can be served by a LAN.WANs use the services of carriers,such as telephone companies,cable companies,satellite systems,and network providers(e.g.中華電信).WANs use serial connec
2、tions of various types to provide access to bandwidth over large geographic areas.2022/12/302WANs and the OSI ModelWAN operations focus primarily on Layer 1 and Layer 22022/12/303WAN Physical Layer Terminology經營場地2022/12/304Customer Premises Equipment(CPE)The devices and inside wiring located at the
3、 premises of the subscriber and connected with a telecommunication channel of a carrier.The subscriber either owns the CPE or leases the CPE from the service provider.A subscriber,in this context,is a company that arranges for WAN services from a service provider or carrier.2022/12/305Data Communica
4、tions Equipment(DCE)Also called data circuit-terminating equipment DCE consists of devices that put data on the local loop.Primarily provides an interface to connect subscribers to a communication link on the WAN cloud 2022/12/306Data Terminal Equipment(DTE)The customer devices that pass the data fr
5、om a customer network or host computer for transmission over the WAN.The DTE connects to the local loop through the DCE.2022/12/307Demarcation Point A point established in a building or complex to separate customer equipment from service provider equipment.Physically,the demarcation point is the cab
6、ling junction box,located on the customer premises,that connects the CPE wiring to the local loop.It is usually placed for easy access by a technician.The demarcation point is the place where the responsibility for the connection changes from the user to the service provider.2022/12/308Local Loop&Ce
7、ntral Office Local Loop-The copper or fiber telephone cable that connects the CPE at the subscriber site to the CO of the service provider.The local loop is also sometimes called the last-mile.Central Office(CO)-A local service provider facility or building where local telephone cables link to long-
8、haul,all-digital,fiber-optic communications lines through a system of switches and other equipment.2022/12/309WAN Devices2022/12/3010WAN Physical Layer Standards2022/12/3011WAN Cable Connectors2022/12/3012WAN Data Link Protocols2022/12/3013WAN Encapsulation2022/12/3014WAN Link Connection Options2022
9、/12/3015Leased Lines2022/12/3016Leased Line TypesTDD？以 T1 專線為例 使用分時多工(TDM：Time Division Multiplexing)T1 專線每 125 微秒為一單位/訊框、每秒傳送 8000 個單位/訊框、每單位/訊框傳送(1+192)位元8000*193=1.544 Mb/sec2022/12/3019Circuit Switched Connection Option-PSTNPSTN:Public Switched Telephone Network2022/12/3020Circuit Switched Conne
10、ction Option-ISDNBasic Rate InterfacePrimary Rate Interface2022/12/3021Packet Switching X.25.X.25 is a legacy network-layer protocol.Typical X.25 applications are point-of-sale card readers.X.25 link speeds vary from 2400 b/s up to 2 Mb/s.-usually low capacity with speeds rarely exceeding above 64 k
11、b/s.X.25 networks are now in dramatic decline -replaced by newer layer 2 technologies such as Frame Relay,ATM,and ADSL2022/12/3022Packet Switching Frame Relay Network layout appears similar to X.25,Frame Relay differs from X.25 in several ways.it is a much simpler protocol that works at the data lin
12、k layer rather than the network layer.no error or flow control.The simplified handling of frames leads to reduced latency,measures taken to avoid frame build-up at intermediate switches help reduce jitter.Frame Relay offers data rates up to 4 Mb/s,with some providers offering even higher rates.2022/
13、12/3023Frame Relay2022/12/3024This shows why frame relay is much more efficient than X.25!2022/12/3025Packet Switching ATM Asynchronous Transfer Mode(ATM)technology is capable of transferring voice,video,and data through private and public networks.It is built on a cell-based architecture rather tha
14、n on a frame-based architecture.ATM cells are always a fixed length of 53 bytes ATM was designed to be extremely scalable and can support link speeds of T1/E1 to OC-12(622 Mb/s)and higher 2022/12/3026ATM2022/12/3027Broadband Services DSL ADSL Cable Wireless Municipal WiFi WiMAX Satellite Internet202
15、2/12/3028DSL2022/12/3029Cable2022/12/3030WirelessVPNVirtual Private Network虛擬私有網路2022/12/3032私有網路-出租專線2022/12/3034如果不用私有網路？(家用)2022/12/3035如果不用私有網路？(企業)當員工出差在外透過寬頻服務連上 Internet，並且連上公司網路、或分公司之間透過Internet 連接時 有否安全疑慮(Security risks)？有否兩全(便宜&安全)之道？Virtual Private Network(VPN)出場 (撒花)2022/12/3036VPN？VPN 的
16、想法其實就是取公用網路(e.g.,Internet)的便宜/免費特性，但將傳輸的資料加密，即使資料被截，對方未必能了解其內容 A VPN is an encrypted connection between private networks over a public network such as the Internet.2022/12/3037VPN Technology Security risks are incurred when a tele-worker or remote office uses broadband services to access the corpora
17、te WAN over the Internet.To address security concerns,broadband services provide capabilities for using Virtual Private Network(VPN)connections to a VPN server,which is typically located at the corporate site.2022/12/3038VPN IP VPN A VPN is an encrypted connection between private networks over a pub
18、lic network such as the Internet.Instead of using a dedicated Layer 2 connection such as a leased line,a VPN uses virtual connections called VPN tunnels,which are routed through the Internet from the private network of the company to the remote site or employee host.2022/12/3039Types of VPN Access S
19、ite-to-site VPNs Each site is equipped with a VPN gateway,such as a router,firewall,VPN concentrator,or security appliance.Remote-access VPNs2022/12/3040Site-to-site VPNs(IP VPN)2022/12/3041Remote-access VPNs(IP VPN)用戶遠端存取 VPNs(NCUE)用戶遠端存取 VPNs(NCUE)用戶遠端存取 VPNs(NCUE)使用 NCUE VPN 的目的不見得只在於安全性，而是讓在校外的您
20、得以使用校內之資源 圖書館資源 校園軟體資源 etc 當您建立 NCUE VPN 後，對於校內所有可用資源的伺服器而言，您的電腦使用的是校園內 IP address 自己人的意思啦VPN=翻牆？2022/12/3046Metro Ethernet A rapidly maturing networking technology that broadens Ethernet to the public networks run by telecommunications companies.IP-aware Ethernet switches enable service providers t
21、o offer enterprises converged voice,data,and video services such as IP telephony,video streaming,imaging,and data storage.2022/12/3047Benefits of Metro Ethernet Reduced expenses and administration-Metro Ethernet eliminates expensive conversions to ATM and Frame Relay Easy integration with existing n
22、etworks Enhanced business productivity take advantage of productivity-enhancing IP applications that are difficult to implement on TDM or Frame Relay networks,such as hosted IP communications,VoIP,and streaming and broadcast video Ethernet&IP are buddies2022/12/3048WAN 規劃 知道公司/企業對 WAN 的需求&限制 有哪些應用&多
23、少經費 不同 WAN Services 的特色、性質、費用&選擇性 Circuit/Packet/Cell Switching,Dedicated line Availability 根據需求&限制,選擇適當 Service2022/12/3049WAN Traffic Types(需求或特性)Packets 抵達間隔不一,造成聲音播放速度差異2022/12/3050Choosing a WAN Link Connection What is the purpose of the WAN?What is the geographic scope?What are the traffic req
24、uirements?Should the WAN use a private or public infrastructure?For a private WAN,should it be dedicated or switched?2022/12/3051Choosing a WAN Link Connection For a public WAN,what type of VPN access do you need?Which connection options are available locally?What is the cost of the available connec
25、tion options?2022/12/3052Choosing a WAN Link Connection2022/12/3053Choosing a WAN Link Connection2022/12/3054MPLS Multi-Protocol Label Switching2022/12/3055What is MPLS?Multi-Protocol Label Switching Multi-protocol because it may be applied with any Layer 3 protocols Our interest here will be concen
26、trated on using MPLS with IP traffic Label means frame/packet tagging Switching means faster forwarding(as compared to IP routing)2022/12/3056MPLS Route Once Switch ManySwitch while you canRoute if you must2022/12/3057A MPLS network example2022/12/3058How does MPLS works?2022/12/3059MPLS-based VPN20
27、22/12/3060IP vs MPLS VPN 傳統 IP VPN 通常是利用公共的網際網路進行資料傳輸 MPLS VPN 則大多以網路服務商的專屬網路為主，相對地減低資料外洩或被竊取的可能性 MPLS VPN上網路服務商可以依需求提供不同服務品質保證(Quality of Service,QoS)，解決了傳統 IP VPN 成本低廉但缺乏服務品質保證的缺點 This is similar to how conventional private network works2022/12/3061MPLS Summary MPLS 可以讓傳統 IP network 運作更有效率 很多傳統的 r
28、outers 只需要軟體昇級,即可具備 MPLS 功能,也就是說,MPLS 可以是與 IP network 共存的(This is GOOD!)MPLS 適合 VPN 的應用2022/12/3062ADSL2022/12/3063ADSL 之所以“Asymmetric”ADSL為一種用戶線路裝置，大部分的網路應用，用戶端的角色絕大部分的時間是去讀取資料。最明顯的例子是 Web This is what marketing guys would tell you typically.另一個原因是屬於技術層面的問題。next slides2022/12/3064ADSL 之“Asymmetric”
29、所有用戶端雙絞線，最後都會組成一條條包含許多雙絞線的電纜，接至局用設備（相當於電信局的機房）上去，若其訊號強度的不同，會有所謂的“串音”(cross-talk)問題出現。對下傳而言，資料流都是由同一個地方的設備傳送到不同的用戶(由電信局機房送到每個用戶家中)，送出的訊號強度一樣，較不會有“串音”的現象，因此速率“可以可以”較高 而由用戶端上傳的訊號，因為訊號是由不同的用戶端設備所產生，若某個用戶端設備所發出的訊號較強，而另外一個用戶所發出的訊號較弱，就會有串音的現象。這種串音的現象愈高頻就愈嚴重，所以使得上傳的速率會有所限制。2022/12/3065傳統的 POTS(or PSTN)頻道 利用
30、 04 KHz 的頻寬 POTS Plain Old Telephone Service/System PSTN Public Switched Telephone Network2022/12/3066ADSL頻道 ADSL 在其頻寬範圍內將線路分成三個頻道(channel)Downstream(接收頻道；download)：為單向高速率通道由電信公司傳輸至客戶端的方向其速率為1.536 Mbps 至 6.144 Mbps(subject to change)Upstream(傳送頻道；upload)：為雙向全雙工通道亦有產品設計成單向由客戶端傳輸至電信公司其速率為16 Kbps 至 640
31、 Kbps(subject to change)POTS 頻道：利用基本的4 KHz頻寬提供POTS服務(Plain Old Telephone Service),也就是目前講電話用的頻道。2022/12/3067ADSL頻道劃分 兩種技術 CAP(Carrier Amplitude/Phase)AT&T 發展,出現較早,實作較容易 DMT(Discrete Multi-Tone)Amati Communications公司發展出的,對網路的偵測性能較佳,傳輸速度也較高 ANSI 標準2022/12/3068CAP2022/12/3069DMTDMT 將電話線頻寬切成 247 個 4KHz 的
32、頻道,較低頻率的一些頻道作為雙向傳輸之用,你可以想像每個頻道就像是一條電話線,然後電話公司在每個頻道都幫你裝上一個數據機每個頻道都會被監控,假如其中某頻道傳輸品質不佳,就會動態地將傳輸資料的工作轉至另一頻道,上述頻道監控與轉移,導致 DMT 的技術較難以實作2022/12/3070ADSL 連線架構與設備所謂“低通濾波器”(LP filter),其實只是簡單的裝置,它的作用在於“只”讓“低頻訊號”通過(“低通”)Well,you know what it isNext 2 slides2022/12/3071DSL Access Multiplexer(DSLAM)電信公司局端與 User 的
33、 ADSL Modem 連接的裝置,它主要將來自許多不同 user 的連線集中後,透過高速的連線(usually ATM)接上 Internet DSLAM 通常亦提供 routing 及 dynamic IP assignment 的功能2022/12/3072DSL Access Multiplexer(DSLAM)DSLAM 也是讓 ADSL 與 Cable Modem 的共享頻寬有所區別的主要裝置 Cable Modem 通常讓某一區域的 users 共享同一網路迴路,增加 users 則意味個別 user 分享的頻寬減少 ADSL 則在 ADSL Modem 與 DSLAM 間讓每位
34、 user 享用專屬頻寬,若連線 users 達飽和,導致 DSLAM 無法負荷,則通常電信公司會提供 DSLAM 連外(Internet)頻寬的升級 2022/12/3073ADSL VPN ADSL VPN 乃提供用戶端使用固網業者之ADSL 連線，透過 ISP 的 ATM 骨幹網路收容回 BRAS，經由此 BRAS 之 Virtual Router 功能將各據點連成 VPN，但同時又可提供出 Internet 之頻寬、Firewall、NAT等功能 Broadband Remote Access Server 使用者多為中小型企業用戶，針對擁有大量據點或分公司之客戶而設計，且其各據點所需
35、之頻寬無須雙向對稱頻寬。LTE 多工(傳輸)方式 FDD FrequencyDivision Duplexing 分頻雙工 TDD Time Division Duplexing 分時雙工短波4G5G頻段與應用FM台灣 4G 現況http:/www.twd.cc/404734G 2100MHz 釋照載波聚合(CA)載波聚合頻寬需求(Netflix)https:/ 根據 4G LTE 技術規格每 5 MHz 頻段約可提供 35Mbps(理論值)的 4G 傳輸頻寬頻率高低之影響 頻率較高(1000 MHz)穿透力強、繞射能力弱、覆蓋能力弱、傳輸距離近 繞射：穿越障礙 頻率較低(1000 MHz)穿
36、透力弱、繞射能力強、覆蓋能力強、傳輸距離遠頻率與覆蓋率-wifihttp:/ 家用網路(窮人之解決方案)https:/ 家用網路(窮人之解決方案)https:/ 4G&etc)低時延高密度聯網設備高速頻寬高頻帶效率高通訊容量高網路效能、低功耗時延&速度(Wifi/4G)WiFi4G5G 速度高密度聯網設備 每平方公里範圍內的 100 萬台連網設備高頻帶效率 4G LTE 每 5 MHz 頻段可提供 35Mbps(理論值)的 4G 傳輸頻寬 5G 3 倍?高通訊容量 使用極高頻(EHF，30GHz&above)，比 4G 使用頻譜(如 700/900 MHz、1.8/2.1/2.6GHz)高出許多 需要更多基地台 每個基地台又可以連接更多裝置https:/ 聯網裝置更省電應用 車聯網/無人駕駛 線上開刀 個人化/專屬化視訊服務(e.g.,關注 NBA 球賽之某個特定球星)物聯網(IOT)&配合 AI 做即時決策 應用
