WAN Services cont. | CompTIA Network+ N10-007 | 2.5b

In this video you will learn about the characteristics of WAN services such as: MPLS, ATM, frame relay, PPPoE, PPP, DMVPN, SIP trunk; in addition to learning about WAN terminations such as: the demarcation point, CSU/DSU, and the smart jack.

Characteristics of Service

MPLS (Multiprotocol Label Switching)

MPLS is a routing technique in telecommunications networks that directs data from one node to the next based on short path labels rather than long network addresses, thus avoiding complex lookups in a routing table and speeding traffic flows.[1]  The labels identify virtual links (paths) between distant nodes rather than endpoints.  MPLS can encapsulate packets of various network protocols, hence the “multi-protocol” reference on its name.  MPLS supports a range of access technologies, including T1/E1, ATM, Frame Relay, & DSL.

ATM (Asynchronous Transfer Mode)

Asynchronous Transfer Mode is a telecommunications standard for digital transmission of multiple types of traffic, including telephony (voice), data, and video signals in one network without the use of separate overlay networks.[2][3]  ATM was designed to integrate telecommunication networks.[4]  It can handle both traditional high-throughput data traffic and real-time, low-latency content such as voice and video.  ATM provides functionality that uses features of circuit switching and packet switching networks.  It uses asynchronous time-division multiplexing.[5][6]  In the OSI reference model data link layer (layer 2), the basic transfer units are generically called frames.  In ATM these frames are of a fixed (53 octets or bytes) length and specifically called cells.  This differs from approaches such as IP or Ethernet that use variable sized packets of frames.  ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the data exchange begins.[6]  These virtual circuits may be either permanent, i.e. dedicated connections that are usually preconfigured by the service provider, or switched, i.e. set up on a per-call basis using signaling and disconnected when the call is terminated.

Frame Relay

Frame Relay is a standardized WAN technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology.  Originally designed for transport across ISDN (Integrated Services Digital Network) infrastructure, it may be used today in the context of many other network interfaces.  Network providers commonly implement Frame Relay for voice and data as an encapsulation technique used between LANs over a WAN.  Each end-user gets a private line (or leased line) to a Frame Relay node.  The Frame Relay network handles the transmission over a frequently changing path transparent to all end-user extensively used WAN protocols.  It is less expensive than leased lines and that is one reason for its popularity.  The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relay’s popularity.  With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, Frame Relay has become less popular in recent years.[7]

PPPoE (Point-to-Point Protocol over Ethernet)

PPPoE is a network protocol for encapsulating Point-to-Point Protocol (PPP) frames inside Ethernet frames.  It originally appeared in the context of the boom of DSL in 1999 as the solution for tunneling packets over the DSL connection to the ISP’s IP network, and from there to the rest of the Internet.  Typical use of PPPoE involves leveraging the PPP facilities for authenticating the user with a username and password.[8]  On the customer-premises equipment, PPPoE may be implemented either in a unified residential gateway device that handles both DSL modem and IP routing functions or in the case of a simple DSL modem (without routing support), PPPoE may be handled behind it on a separate Ethernet-only router or even directly on a user’s computer.

PPP (Point-to-Point Protocol)

Point-to-Point Protocol is a data link layer (layer 2) communication protocol between two routers without any host or any other networking in between.  It can provide connection authentication, transmission encryption[9], and data compression.  PPP is used over many types of physical networks, including serial cable, phone link, trunk line, cellular telephone, specialized radio links, ISDN, and fiber optic links.  Since IP packets cannot be transmitted over a modem line on their own without some data link protocol that can identify where the transmitted frames start and where it ends, ISPs have used PPP for customer dial-up access to the Internet.

DMVPN (Dynamic Multipoint Virtual Private Network)

DMVPN[10] is a dynamic tunneling form of a virtual private network (VPN) supported on Cisco IOS-based routers, AR G3 routers[11], & on Unix-like operating systems.  DMVPN provides the capability for creating a dynamic-mesh VPN network without having to pre-configure (static) all possible tunnel end-point peers.[12]

SIP Trunk

SIP trunking is a voice over Internet Protocol (VoIP) technology and streaming media service based on the Session Initiation Protocol (SIP) by which Internet telephony service providers (ITSPs) deliver telephone services and unified communications to customers equipped with SIP-based private branch exchange (IP-PBX) and unified communications facilities.[13]  Most unified communications applications provide voice, video, and other streaming media applications such as desktop sharing, web conferencing, and shared whiteboard.[14]


Demarcation Point

The demarcation point is the point at which the public switched telephone network ends and connects with the customer’s on-premises wiring.  It is the dividing line which determines who is responsible for installation and maintenance of wiring and equipment — customer/subscriber, or telephone company/provider.  The demarcation point varies between countries and has changed over time.[15]

CSU/DSU (Channel Service Unit/Data Service Unit)

A CSU/DSU is a digital-interface device used to connect data terminal equipment (DTE), such as a router, to a digital circuit, such as a T1 line.  The CSU/DSU implements two different functions.  The channel service unit (CSU) is responsible for the connection to the telecommunication network, while the data service unit (DSU) is responsible for managing the interface with the DTE.  A CSU/DSU can have an external connection point or it can be integrated into a modular card installer in a router.  A CSU/DSU is the equivalent of the modem for an entire LAN.  The DCE, commonly a modem or CSU/DSU, is the device used to convert the user data from the DTE into a form acceptable to the WAN service provider transmission link.[16]

Smart Jack

A smart jack is a smart and intelligent device placed right between the telephone company’s demarcation and customer premises that performs connectivity checks and diagnostic tests.  A very common capability provided by a smart jack is loopback, such that the signal from the telephone company is transmitted back to the telephone company.  This allows the telephone company to test the line from the central office, without the need to have test equipment at the customer site.[17]


  1. Rosencrance, L. “What is Multiprotocol Label Switching (MPLS)?” TechTarget.
  2. Telcordia Technologies, Telcordia Notes on the Network, Publication SR-2275 (Oct 2000).
  3. ATM Forum, The User Network Interface (UNI), v. 3.1, Prentice Hall PTR, 1995, pg 2.
  4. Ayanoglu, Ender; Akar, Nail. “B-ISDN (Broadband Integrated Services Digital Network)”. Center for Pervasive Communications and Computing, UC Irvine.
  5. “Recommendation I.150, B-ISDN Asynchronous Transfer Mode functional characteristics’. ITU.
  6. McDysan (1999), pg. 287.
  7. Frame Relay, Wikipedia.
  8. Philip Golden; Herve Dedieu; Krista S. Jacobsen (2007). Implementation and Applications of DSL Technology. Taylor & Francis. pg. 479.
  9. Request for Comments.  Wikipedia.
  10. Cisco engineers. “Dynamic Multipoint IPsec VPNs (Using Multipoint GRE/NHRP to Scale IPsec VPNs)”. Cisco. Cisco.
  11. Huawei DSVPN Configuration
  12. Kurniadi, S.H.; Utami, E.; Wibowo, F.W. (Dec 2018). “Building Dynamic Mesh VPN Network using MikroTik Router”. Journal of Physics:  Conference Series.
  13. SIP trunking migration:  Enterprise opportunities and challenges
  14. “SIP Trunking Explained”. Technology Convergence Group.
  15. Demarcation point. Wikipedia.
  16. Microsoft Official Academic Course (2012). 98-366:  MTA Networking Fundamentals. Hoboken, NJ: John Wiley & Sons, p. 151.
  17. Smartjack. Fandom.