ch3.pdf

Wide Area Network Protocols NET  Chapter 3: Selecting a WAN Technology © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1 WAN Services  There are several WAN access connection WAN Link Conne...

Wide Area Network Protocols NET  Chapter 3: Selecting a WAN Technology © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1 WAN Services  There are several WAN access connection WAN Link Connection Options options that ISPs can use to connect the local loop to the enterprise edge.  Each option has distinct advantages and disadvantages as well as differences with technology, speed, and cost.  There are two ways an enterprise can obtain WAN access: Private WAN infrastructure – Choices may include dedicated point-to-point leased lines, circuit-switched links such as PSTN or ISDN, and packet switched links such as Ethernet WAN, ATM, or Frame Relay. Public WAN infrastructure – Service providers may offer broadband Internet using DSL, cable, or satellite access. Data traveling between corporate sites over a public WAN should be protected using VPNs. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2 WAN Services Service Provider Network Infrastructure  Service provider networks are complex and consist mostly of high-bandwidth fiber-optic media, using either Synchronous Optical Networking (SONET) or Synchronous Digital Hierarchy (SDH) standard.  A newer fiber-optic media development for long-range communications is called dense wavelength division multiplexing (DWDM). Multiplies the amount of bandwidth that a single strand of fiber can support Enables bidirectional communications over one strand of fiber Can multiplex more than 80 different channels of data onto a single fiber Each channel can carry a 10 Gb/s multiplexed signal © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3 Private WAN Infrastructures  Point-to-point lines are usually leased from a Leased Lines service provider and are called leased lines. However, since they have been around since the 1950s, they are sometimes referred to as: Leased circuits Serial link Serial line Point-to-point link T1/E1 or T3/E3 lines  Leased lines vary in price depending on the bandwidth required and the distance between the two connected paths.  When permanent dedicated connections are required, a  In North America, service providers use the T- point-to-point link is used to provide a pre-established WAN carrier system to define the digital communications path from the customer premises to the provider network. transmission capacity of a serial copper media link. For example, a T1 link supports 1.544 Mb/s. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4 Private WAN Infrastructures  Dialup WAN access may be required when Dialup no other WAN technology is available.  For example, a remote location could use modems and analog telephone lines to provide low capacity and dedicated switched connections.  Traditional local loops, which use copper cabling, transport binary computer data through the voice telephone network using a modem.  A modem modulates the binary data into an analog signal at the source and demodulates the analog signal to binary data at the destination.  WAN built with an on demand connection using a modem  The physical characteristics of the local loop and the voice telephone network and its connected to the PSTN limit the rate of the signal to less than 56 kb/s. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5 Private WAN Infrastructures ISDN  Integrated Services Digital Network (ISDN) is a circuit-switching technology that enables the local loop of a PSTN to carry digital signals, resulting in higher capacity switched connections.  ISDN changes the internal connections of the PSTN from carrying analog signals to time-division multiplexed (TDM) digital signals.  TDM allows two or more signals, or bit streams, to be transferred as subchannels in one communication channel.  The ISDN connection may require a terminal adapter (TA) which is a device used to connect ISDN Basic Rate Interface (BRI) connections to a router. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6 Private WAN Infrastructures  There are two types of ISDN Interfaces: ISDN (Cont.) Basic Rate Interface (BRI) – ISDN BRI provides two 64 kb/s bearer channels (B) for carrying voice and data and a 16 kb/s delta channel (D) for signaling, call setup and other purposes. Primary Rate Interface (PRI) – In North America, PRI delivers 23 B channels with 64 kb/s and one D channel with 64 kb/s for a total bit rate of up to 1.544 Mb/s. This includes some additional overhead for synchronization.  A common application of ISDN is to provide additional capacity as needed on a leased line connection. ISDN can also be used as a backup if the leased line fails.  Although ISDN is still an important technology for telephone service provider networks, it has declined in popularity due to DSL and other broadband services. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7 Private WAN Infrastructures Frame Relay  Frame Relay is a Layer 2 non-broadcast multi-access (NBMA) WAN technology used to interconnect enterprise LANs. Data rates of up to 4 Mb/s with some providers offering higher rates  A single router can be used to connect multiple sites using PVCs which can carry both voice and data traffic.  An edge router only requires a single interface, even when multiple virtual circuits are used.  Frame Relay creates PVCs which are uniquely identified by a data-link connection identifier (DLCI). The PVCs and DLCIs ensure bidirectional communication between one DTE device to another. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8 Private WAN Infrastructures  Asynchronous Transfer Mode (ATM) technology is capable of transferring voice, ATM video, and data through private and public networks. ATM is built on a cell-based architecture rather than on a frame-based architecture. Cells are always a fixed length of 53 bytes. ATM cells contain a 5-byte ATM header followed by 48 bytes of ATM payload.  Small fixed-length cells are well-suited for voice and video traffic.  A typical ATM line needs almost 20% greater bandwidth than Frame Relay to carry the same volume of network traffic.  When the cell is carrying segmented network layer traffic, the overhead is higher since the ATM switch must be able to reassemble the packets at the destination. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9 Private WAN Infrastructures  Thanks to newer Ethernet standards using Ethernet WAN fiber-optic cables, Ethernet is now a reasonable WAN access option. The original maximum cable length for Ethernet was one kilometer. With fiber-optic cable, the maximum length is 5 km using IEEE 10000Base-LX, and 70 km using IEEE 1000BASE-ZX standards.  Service providers now offer Ethernet WAN service using fiber-optic cabling which provide several benefits: Reduced expenses and administration Easy integration with existing networks Enhanced business productivity  Ethernet WANs are commonly being used to replace Frame Relay and ATM WAN links. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10 Private WAN Infrastructures  Multiprotocol Label Switching (MPLS) is a MPLS multiprotocol high-performance WAN technology that directs data from one router to the next. MPLS is based on short path labels rather than IP network addresses. It is called Multiprotocol since it has the ability to carry any payload including IPv4, IPv6, Ethernet, ATM, DSL, and Frame Relay traffic. It uses labels which tell the router what to do with a packet.  Notice in the figure to the left that different sites can connect to the MPLS cloud using different access technologies.  MPLS can support a wide range of WAN technologies including T-carrier / E-carrier links, Carrier Ethernet, ATM, Frame Relay, and DSL.  MPLS is primarily a service provider WAN technology. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11 Private WAN Infrastructures  All private WAN technologies discussed so VSAT far used either copper or fiber-optic media.  What if an organization needed connectivity in a remote location where there are no service providers that offer WAN service?  Very small aperture terminal (VSAT) is a solution that creates a private WAN using satellite communications.  A VSAT is a small satellite dish used to create a private WAN that provides connectivity to remote locations.  The satellite is in geosynchronous orbit in space. The signals travel approximately 35,786 kilometers to the satellite and back. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12 Public WAN Infrastructures  DSL is an always-on connection DSL technology that uses existing twisted-pair telephone lines to transport high- bandwidth data, and provides IP services to subscribers.  A DSL modem is required which converts an Ethernet signal from the user device to a DSL signal, which is transmitted to the central office.  Multiple DSL subscriber lines are multiplexed into a single high-capacity link using a DSLAM at the provider location.  DSL is a popular choice for IT departments to support home workers.  A subscriber must first connect to an ISP and then an IP connection is made through © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13 the Internet to the enterprise network. Public WAN Infrastructures  Network access is available from many Cable cable television providers (using coaxial cable) which allows for greater bandwidth than the conventional telephone local loop.  Cable modems provide an always-on connection and a simple installation.  A subscriber connects a computer or a LAN router to the cable modem, which translates the digital signals into broadband frequencies used for transmitting on a cable television network.  The cable modem termination system (CMTS), which is a component located at the local cable TV office (headend), sends and receives digital cable modem signals on a cable network and is necessary for providing Internet services to subscribers. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14 Public WAN Infrastructures  Until recently, one limitation of wireless access has been the need to be within the Wireless local transmission range (typically less than 100 feet) of a wireless router or a wireless modem. The following new developments are changing this: Municipal Wi-Fi – Many cities have begun setting up municipal wireless networks for free or for substantially less than broadband. WiMAX (IEEE 802.16) – Worldwide Interoperability for Microwave Access (WiMAX) is a new high-speed broadband technology that is just beginning to come into use. WiMAX provides broad coverage similar to a cell phone network rather than through Wi-Fi hotspots. WiMAX operates similar to Wi- Fi, but at higher speeds and over longer © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15 distances. Public WAN Infrastructures Wireless (Cont.) WiMAX uses a network of WiMAX towers that are similar to cell phone towers. Subscribers must be within 30 miles of a tower. Satellite Internet – Typically used by rural users where cable and DSL are not available. A VSAT provides two-way (upload and download) data communications. The upload speed is about one- tenth of the 500 kb/s download speed. Cable and DSL have higher download speeds, but satellite systems are about 10 times faster than analog modems. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16 Public WAN Infrastructures  Increasingly, cellular service is 3G/4G Cellular another wireless WAN technology being used to connect users and remote locations where no other WAN access technology is available.  Phones, tablet computers, laptops, and even some routers can communicate through to the Internet using cellular technology.  These devices use radio waves to  There are two common cellular industry terms: communicate through a nearby 3G/4G Wireless – Abbreviation for 3rd and 4th generation mobile phone tower. The device has cellular access. a small radio antenna, and the Long-Term Evolution (LTE) – Refers to a newer and faster provider has a much larger antenna technology and is considered to be part of the fourth generation (4G) technology. sitting at the top of the tower somewhere within miles of the © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17 phone. Public WAN Infrastructures  Due to security risks, VPNs are VPN Technology needed when a teleworker or a remote office uses a broadband service to access the corporate WAN over the Internet.  A VPN is an encrypted connection between private networks over a public 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. © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18 Public WAN Infrastructures  There are several benefits to using VPNs: VPN Technology (Cont.) Cost savings Security Scalability Compatibility with broadband technology  There are two types of VPN access: Site-to-site VPNs – Connects entire networks to each other; for example, they can connect a branch office network to a company headquarters network. Remote-access VPNs – Enables telecommuters, mobile users, and extranet consumers to access a company network securely over the © 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19 Internet. Selecting WAN Services  There are many factors to consider when Choosing a WAN Link Connection choosing an appropriate WAN connection. Network administrators must answer numerous questions including: What is the purpose of the WAN? Will the enterprise connect local branches in the same city area, connect remote branches, or connect to a single branch? Will the WAN be used to connect internal or external employees or customers? What is the geographic scope? Is the WAN local, regional, or global? Is the WAN one-to-one (single branch), one- to-many branches, or many-to-many (distributed)? What are the traffic requirements? What type of traffic must be supported? What are© 2016 theCisco quality and performance and/or its affiliates. All rights reserved. Cisco Confidential 20 requirements? Selecting WAN Services Choosing a WAN Link Connection (Cont.)  Should the WAN use private or public infrastructure? Private infrastructure – offers the best security Public Internet infrastructure – not as secure, but offers the most flexibility and lowest ongoing expense  For a private WAN, should it be dedicated or switched?  For a public WAN, what type of VPN access is required?  Which connection options are available locally?  What are the© 2016 costs of the connection options Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21 available?