WAN Technologies. Classification of Networks. Subject. Layer in OSI/rm. WAN Characteristics. Telecommunication Network and Computer Networks

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1 Classification of Networks WAN Technologies Network and Information Center Beijing University of Posts and Telecommunications 2017 Interprocessor distance Processors located in same Example 1m Square meter Personal area network (PAN) 10m 100m 1km Room Building Campus Local area network (LAN) 10km City Metropolitan area network (MAN) 100km Country Wide area network 1000km Continent (WAN) 10,000km Planet The Internet WAN Characteristics LANs may use: Internal wiring such as coaxial cable, STP, UTP and fiber WANs may use: Public communications links or circuits, such as a telecommunication network provided by a local or long-distance telephone company to send data LANs can be a collection of multiple PCs connected via a Switch within a site. WANs typically connect one site to another site via a Router / Modem, linking LANs together. WANs and LANs both enable communications between clients and hosts that are not directly attached to each other. WANs use different transmission systems, topologies, and sometimes different media than LANs Subject Define WAN and identify the layers of the OSI reference model at which the WAN technologies operate. Define and describe the operation of point-topoint, circuit-switched, and packet-switched links through a WAN. Identify and describe the basic function of the devices commonly found in WANs. Typical WAN technologies: PPP,, Frame Relay, ATM, Layer in OSI/rm Telecommunication Network and Computer Networks Transmission Network: TDM, PDH, SDH/Sonet Service Network Voice - PSTN, PBX Data - /ISDN/DDN(Digital Data Network)/FR/Vsat LAN WAN LAN 1

2 Types of Topology Various topologies could be build Point to point Star Ring Tree Partially meshed Full meshed Point to Point Dedicated Campus 1 Star Advantages Easy to install and configure High Availability Easy fault identification and fault isolation Easy management on the center Economic reason Tree Top down structure Allows more devices to be connected to a single central hub and can therefore increase the distance a signals can travel between devices. Allows the network to isolate and prioritize communications from different computers. Office 3 Office 2 Office 1 Ring Easy to install and reconfigure Failure recovery Mesh High availability Full redundancy High privacy and security Easy fault identification and fault isolation Complicated routing design Cost analysis 2

3 Connection type Circuit Switch / Packet Switch Dedicated HDLC,SLIP/PPP Circuit switched PSTN Packet switched, FR, ATM Advantages: easily implemented guaranteed bandwidth Disadvantages: inflexible inefficient to bursty traffic limited bandwidth overhead due to connection setup Advantages: flexible to bursty traffic bandwidth-on-demand (statistical multiplexing) Disadvantages: long and unpredictable delay and jitter no QoS guarantee Address type Explicit type Global unique Associated with a location Relatively long, appear in routing table, by SW used in connection-less systems Label type Local meaning Short address, easy to be implemented by HW mainly used in connection-oriented system WAN transmission media Unshielded twisted pair (UTP) Shielded twisted pair (STP) Coaxial cable (Coax) Copper wire Optical fiber: multi-mode Optical fiber: single-mode Satellite Microwave WAN Devices PC to PC Modem DSU/CSU Mux, multiplexer/de-multiplexer Router Transmission system PDH/SDH/DWDM Wireless Satellite 3

4 PC to Network Network to Network By Cisco Sun Life Assurance Network Configuration T1 T1 Montreal Backbone / Access network Backbone Trunk service for Networks to Networks IPX Toronto T1 T1 IPX IPX T1 T1 T1 T1 T1 IPX T1 T1 IPX Access networks Private service to individual units Smaller public service networks IPX IPX Boston T1 IPX Examples One of the New Service Infrastructure Architecture 4

5 Speed and services Major types of WAN --- Technology that linking LANs together SDLC / HDLC HDLC High Level Data Link Control SDLC Developed by IBM for use w/ SNA HDLC is developed based on SDLC Most of L2 protocols are based on the SDLC format (HDLC, LAPB, 802.2, etc ) HDLC frames Information frames (I-frames) Transport user data and control information relating to user data Supervisory frames (S-frames) Transport control information, primarily data link layer flow and error controls Unnumbered frames (U-frames) Reserved for system management. Information carried by U-frames in intended for managing the link itself HDLC variations HDLC Subset SDLC (Synchronous data link control) LAP (Link Access Procedure) LAPB (Link Access Procedure, Balanced) LAPD (Link Access Procedure for the Integrated Services Digital Network D channel) LAPM (Link Access Procedure for Modems) Uses in Multipoint networks that typically use SDLC Early implementations ISDN B channel and current implementations ISDN D channel and frame relay Error-correcting modems (specified as part of V.42) 5

6 PPP PPP Point to Point Protocol PPP is an Internet standard protocol to provide point-to-point, routerto-router, and host-to-host connections RFC1171 / RFC1331 replace the old one RFC1377-OSI It supports network layer protocols IP: RFC1332-IP Novell IPX: RFC1362-IPX Apple Talk: RFC1378-Appletalk It can be used over several different physical interfaces Asynchronous serial ISDN synchronous serial High-speed Serial Interface Designed for Multiple Protocol support PPP model LCP Link control Protocol NCP Network control Protocol Full duplex-mode is needed Physical layer Frame format < Protocol is defined in RFC IP 1025-Link status C021 - LCP 4 steps operation of PPP Status transition LCP setup the link NCP setup the parameter for network layer protocol, and authentication conducted Password Authentication (PAP) Challenge Authentication Protocol (CHAP) Put data in PPP, communication is carried out LCP close the channel Fail Fail 6

7 LCP negotiation Max length of Data section ( default 1500Bytes) Authentication chosen (default non) Link quality monitoring (no) Protocol section compression (no) Address / control compression (no) NCP negotiation After LCP negotiation Network layer protocol (IP:IPCP) Protocol section set to IPCP accordingly PPP and Multi-link PPP Configuring PPP on Cisco Routers CHAP: Challenge Handshake Authentication Protocol PPP in reality Implemented in Win Linux Replace SLIP PPPoE/PPPoA PPPoE PPPoE=PPP Over Ethernet RFC2516 Two phases PPPoE Discovery Locate the server Get the session ID PPPoE session LCP echo request will be sent from client or server to keepalive, if no LCP echo reply replied for several times, the link will be terminated. 7

8 PSTN (Public Switched Telephone Network) PSTN Public Switched Telephone Network... Standard organization: ITU-T Circuit-switched network A Telephone Call Mobile phone network Local Loop End Office Trunks End Office End Office End Office Tandem Office LD Office ISDN overview ISDN ISDN standards Integrated Services Digital Network available since the 1970's Standardized by ITU Data rate: BRI-Basic Rate Interface 2B+D PRI-Prime Rate Interface 30B+D all signals must be digital End-toend user signaling (out-ofband) Q.931,,.. LAPD (Q.921) I.465/V.120 LAPB I.430 (BRI) + I.431 (PRI) D Channel B Channels 8

9 ISDN ISDN ISDN Interfaces and Functions ISDN Physical Interface ISDN Data Link Layer - LAPD (D Channel) ISDN Network Layer - Q.931 / Euro ISDN(D Channel) Fundamental ISDN Services ISDN Applications Flag Address Control Information FCS Flag PD CR field Message Type Layer 3 - Q.931 Information Elements Services Teleservices Bearer services Supplementary services SAPI (6) CR 0 TEI (7) 1 ISDN Components ISDN Channels B channel 64 kbps Carry any type of digital information in fullduplex mode D channel 16 or 64 kbps Carry control signaling for the B channels Out-of-band signaling ISDN Features BRI BRI: Basic rate interface PRI PRI: Primary rate interface 144kbps (2B+D) 2Mbps (30B+D) D D B1 B2 B1~B30 First telecommunication service designed for digital data communication. ISDN is a digital service designed to run over existing telephone networks. ISDN supports both voice, video, and data Call setup is faster than with a modem. Data rates are faster than one modem connection. However, it takes too long to be standardized. 9

10 in Brief First published in 1974 by CCITT Periodically revised Standardization: CCITT, now ITU-T Packet-switched wide area network Specifies the standard for layer 1,2,3 the Data link layer for is LAPB Use Go-Back-N protocol The Window size is 8 or 128 for low speed channel, like radio... Operates at speed up to 64 Kbps in Brief Layer 2: LAPB (Link Access Protocol - B ) Multiplexed channel: VC PVC - Permanent Virtual Circuit Permanently assigned by network provider SVC - Switched Virtual Circuit VC is disconnected at the end of each session SVC operational procedure: call setup data transfer call clearing Features: multiplexing, strong capability of error detection and recovery speed relatively slower Equipment: PSE, DCE, DTE, PAD With IP network: IP mapping, encapsulation issue Layer in the OSI/rm Network Multiplexing Up to 4096 channels may be established at PLP level at 64Kbps port, 256 VCs could be assigned initially at 9.6Kbps, 16 VC could be be assigned. Switch 1 Switch 2 10

11 VC : PVC / SVC In Cisco routers, show x25 vc command could be used to see the vc information router# show x25 map Serial0: IP PERMANENT BROADCAST, 2 LCN: 3 4* Serial0: appletalk PERMANENT Serial1: BRIDGE PERMANENT Error Control and Flow Control Go-back-N Slide-window mechanism Error Recovery In late 1970 s and early 1980s, Physical links are noisy and error-prone (copper wires) High bit error rates protocol Error-recovery on a hop-by-hop basis When a switch sends a packet, it keeps a copy of the packet until the next switch returns an acknowledgement Each switch on receiving a packet, performs error checking, and if error-free, it sends an acknowledgement to previous switch Large overhead incurred in error control and recovery Address Address: X.121-CalledDTE(4bits) CallingDTE(4bits) DNIC(4 digits) NTN(up to 10 digits), CAS: UESTC: Address mapping Example of configuration IP DCE IP: x25: DCE IP IP: x25: Router A interface serial 0 ip address x25 address x25 map ip broadcast x25: x25: IP: IP: Router B interface serial 0 ip address x25 address x25 map ip broadcast 11

12 IP Encapsulation in Encapsulation By Cisco Switch / PAD / Terminal / Host DCE / DTE Frame Relay PSTN FR Brief History A protocol proposed to ITU-T for use over ISDN in 1984 Cisco, StrataCom, Northern Telecom, DEC formed a consortium to focus FR in 1990 LMI extended FR features for complex internetworking environment Frame Relay is the predecessor Demand for higher bandwidth Quality of transmission guaranteed by new technologies Simplify the error control procedures Standardized by ANSI and ITU-T Specifies the standard for layer 1 and 2 CSU/DSU is located at customer location and used for encoding, filtering, and translating communication to and from the digital line. CSU/DSU (channel service unit/ digital service unit) 12

13 Features Layered structure of Frame Relay Supports many protocols, IP, Novell IPX, Decnet, AppleTalk,... Use high quality transmission system (optical fiber system) Low bit error rate Operates at high data rates (1.544Mbps and recently Mbps) No sequencing control and retransmission process, high efficiency achieved Doesn t provide error checking or require acknowledgement at data link layer Less overhead When FCS error occurred, the frame will be simply dropped Frame length check Congestion control facility Virtual Circuit Frame relay is a virtual circuit network PVCs & SVCs Each VC is identified by a number called a data link connection identifier (DLCI) A DTE is given a DLCI number that it can use to access the remote DTE DLCIs are assigned to define the VC between two DCEs (switches) inside the network Each switch has a table to route frames The table matches an incoming interface-dlci combination with an outgoing interface-dlci combination Address - DLCI Data-Link Connection Identifier DLCI in the FR Network A DLCI: Equivalent of s Logical Channel Number (LCN) Has local significance only early. Is unique between the router (DTE) and switch (DCE) and not necessarily unique in the network. Has global significance now. R1 交换机 A 的路由表 IN DLCI OUT DLCI A B R3 C 交换机 C 的路由表 IN DLCI OUT DLCI R2 交换机 B 的路由表 IN DLCI OUT DLCI R4 13

14 Address field format PVC Signaling Protocols High order DLCI C/R EA(0) Low order DLCI FECN BECN DE EA(1) High order DLCI C/R EA(0) DLCI FECN BECN DE EA(0) Low order DLCI or DL-Core ctrl D/C EA(1) High order DLCI C/R EA(0) DLCI FECN BECN DE EA(0) DLCI EA(0) Low order DLCI or DL-Core ctrl D/C EA(1) Communicate PVC status information and configuration changes between end-user devices such as routers or bridges, and network devices such as high speed frame relay switches. LMI (Local Management Interface) is one such protocol used to communicate a frame relay's link status. -a heart-beat signal that ensures both end-user and network devices are functioning properly; -informs the end-user device of the addition and deletion of PVCs; -reports the current operating status of each PVC. Congestion Control Congestion in network occurs when Users send data into the network at a rate greater than allowed by network resources Frame relay Allows users to transmit bursty traffic It thus has a potential to be congested with traffic Congestion Avoidance Frame relay protocol uses two bits in the frame to warn the source and destination of the presence of congestion BECN (Backward explicit congestion notification) Warns sender of congestion in network FECN (Forward explicit congestion notification) Used to warn the receiver of the congestion in network Receiver can then delay acknowledgement, thus forcing the sender to slow down. Traffic Control IP Encapsulation in FR If users do not respond to congestion notices The frame relay network has to discard frames Which frame to discard is subject to traffic control Committed Information Rate (CIR) Each VC has a CIR It is negotiated at VC set up time If user transmit at this rate on average, the network is committed to deliver the frames User may send data higher than CIR at times and lower at other times As long as average of predefined period is met, frames will be delivered. Customer pays based on CIR DE bit Frames in excess of CIR are marked with DE bit 14

15 Configuration in Router Comparison with system Router (config)#interface Serial1 Router (config-if)#ip address Router (config-if)#encapsulation frame-relay Router (config-if)#bandwidth 1024 Router (config-if)#frame-relay map ip broadcast IETF Comparison (cont ) Service Frame Relay Characteristic Access Speed Up to T1/E1 Up to T3/E3 Type of Services PVC and SVC PVC and SVC Data Delivery In sequence frames In sequence frames Guaranteed End-to-End Data Delivery Network Retransmission on Data Loss Congestion Control Mechanism Yes Yes Window Rotation/Closure No No Forward and Backward Congestion Notification Comparison (cont ) Operates at higher speed (1.544Mbps and recently Mbps) Frame relay operates in just the physical and data link layers. Easy to be used as a backbone network to provide services to protocols that already has a network layer protocol. Frame relay allows bursty data. It allows a frame size of 9000bytes, which can accommodate all local area network frames. Less expensive than other traditional WANs. PDH 2 Mb/s +_ 50 ppm 8 Mb/s +_ 30 ppm SDH/Sonet 34 Mb/s +_ 20 ppm 2 Mb/s 140 Mb/s +_ 15 ppm Difficult to extract single channels (de-multiplexing) NO System Management 15

16 Synchronous Digital Hierarchy Developed from PDH (Plesiochronous Digital Hierarchy) Both are TDM (Time Division Multiplex) Systems the lowest SDH rate STM-1 is Mb/s the lowest SONET rate STS-1 is Mb/s Documented in G.707,708,709 in 1989 SDH/Sonet SONET Add-Drop Mux L2/L3 Switch T1/E1 T3, OC-3 Frame Relay ATM SONET Ring OC-12 OC-48 OC-192. Excellent Resiliency Automatic Protection Switching (APS) < 50ms Price/Bandwidth is high SONET technology is expensive Half of bandwidth reserved for APS Typically Fixed Bandwidth TDM Based ATM SONET rings coming Multimedia Ready ATM provides mature QoS and guaranteed service mechanisms Native voice multiplexing over SONET SDH / SONET (Optical) SYNCHRONOUS DIGITAL HIERARCHIES SONET (Synchronous Optical Network) can provide data transfer rates from 64 Kbps to 39.8 Gbps using TDM Internationally, SONET is known as SDH (Synchronous Digital Hierarchy) (POS) Aggregates multiple T1s or T3s using Fiber Dual Ring technology for redundancy Speeds (OC X): OC1 52 Mbps OC3 155 Mbps OC Mbps OC Gbps OC Gbps (competes with 10 Gbps Ethernet) Raw Fiber Used for 10 Gbps Ethernet Multimode 550 meters / within buildings Singlemode 10 Km / across town Fail recovery time < 50ms WDM / DWDM - multiple light wavelengths to transmit signals over a single optical fiber versus TDM X4 STM kbit/s X4 STM kbit/s STM-4 X kbit/s X4 STM-16 STM kbit/s lower speed plesiochronous and synchronous tributaries STM-4 STM-1 S D H Add/Drop Multiplexer S D H Multiplex Section Shared Protection Ring ADM STM-16 west ADM STM-16 east ADM MSSpring ADM 140 Mb/s 45 Mb/s 34 Mb/s 2 Mb/s Digital Tributaries STM-1 / STM4 ADM X 16

17 IP over SONET IP over SONET A SONET ring provides point-to-point connections between routers. IP packets must, therefore, map to a point-to-point link, for which the most popular solution is using the Point-to-Point Protocol (PPP), defined by the IETF in RFC (the technology in 1997) DWDM WDM Dense wavelength division multiplexing (DWDM) is a fiber-optic transmission technique that employs light wavelengths to transmit data. Dense Wavelength Division Multiplexing permits multiple optical signals to travel on the same fiber at different optical wavelengths. Optical technology SDH / Sonet WDM / DWDM Optical internetworking SDH, IP, ATM transmitted over DWDM Currently, systems using 100Ghz spacing in WAN. Overall wavelength range is typically between 1530nm to 1560nm. Next generation transport technology WDM family Digital Hierarchy Type Full name Interleave Application CWDM NWDM Course Wavelength Division Multiplexing Narrow WDM 20nm 10nm Low cost, Short and middle range transmission DWDM Dense WDM 0.2~1.6nm Optical network, Long distance transmission 17

18 SDH/DWDM DWDM State-of-the-Art Data Rate Point-to-point systems 40l x OC-48 deployed 16l x OC-192 deployed 160l x OC-192 announced Configurable OADMs Metro rings 1-10 Tbps per fiber is just around the corner! OADM Optical Add/Drop Multiplexer Block Diagram of a DWDM System OADM l1, l2, l3,..., ln l1, l2, l3,..., ln l3 l3 Multi-layer Stack WAN Design Issue IP and DWDM - A Winning Combination 18

19 Migration path WAN services TYPE OF SERVICE Circuit Switching POTS ISDN B-ISDN DATA RATES kbps 64k-1.5Mbps Mbps REL. COST Low High RELIABILITY High Low NETWORK INTEGRATION Difficult Difficult Difficult Dedicate Circuit T-Carrier SONET 64k-274Mbps 52M-10Gbps High High High Packet Switching Frame Relay SMDS Ethernet/IP ATM 56k-2Mbps 56k-45Mbps 56k-45Mbps 1M-10Gbps 52M-10Gbps Low High High Low High Difficult Difficult Simple VPNs 56k-2Mbps Very Low Low Packet from the client computer Packet in transmission through the Internet WAN Design Consideration Telephone Line Employee s Home ISP Access Server VPN Device Internet VPN Tunnel VPN Device Packet from the VPN Access Server Demand Survey Schedule setting Site surveys System design Technologies analyze Network implementation plan Implementation of network Economic analysis Maintenance Strategy VPN encapsulation of packets Backbone Challenges of the Existing Technologies Circuit Switching less flexible low efficiency Packet Switching less QoS guarantee LAN/MAN/WAN and Internet specific technologies no QoS guarantee The Trend of Network Paradigm Simplicity flat architecture less management cost Flexibility traffic uncertainty traffic burstiness Intelligent easy service adding self-healing 19

20 SD-WAN Software-defined WAN To simplify the management and operation of a WAN by decoupling (separating) the networking hardware from its control mechanism. To simplify company s branch office and WAN deployments, and lower costs and risks with simple automation and orchestration. American marketing research firm Gartner predicted in 2015 that by the end of 2019, 30% of enterprises will deploy SD-WAN technology in their branches. URLs for reference Questions What is the future for telecommunications? Point-to-point solution? Which WAN tech support P-to-P link? How to implement SLA for WAN? What types of equipment are involved in WAN? Different Address schemes used in WAN Pros and cons? URLs of interest n/wan 谢谢! 20