This is part six in a seven-part series on how IT managers and communications service providers (CSPs) can work together to simplify their migration of premises-based communications to the cloud (read the first post in the series). This particular post is focused on types of access services, the types of circuits, the method of IP services delivery, the suitability for carrying communications services, and network services that can be layered on to prioritize communications traffic.


Layer 1 and 2 Access Connectivity Type

In the ISO (International Standards Organization) data connectivity model, Layer 1 and 2 represent the physical and data layers. The most common Layer 1 physical connectivity are copper, fiber, and radio frequencies. This layer includes both the wiring and switching equipment. Layer 2 data connectivity protocols include things such as Ethernet, PPP, and ATM. Using these layers help to understand how quality internet services are constructed. Like a building, the integrity of the foundation is critical for the overall quality of the final structure. Trying to deliver high quality internet services on poor quality wiring is both challenging and not recommended.

basic representation of the OSI model and examples for next-gen communication

In this next section, we will do a quick review of access types and their suitability for IP-based business communications. This is not intended as a technical overview of access types but instead provides guidance for IT and procurement managers for their migration planning process. Key access types we will discuss are DSL, T1 / PRI, Coax, Ethernet over Copper, and Fiber-based access.

DSL and DSL Variants:

DSL or digital subscriber line is a family of technologies designed to deliver internet services over telephone lines. DSL variants include “asynchronous” ADSL, “synchronous” SDSL, and higher speed technologies such as “very-high-bit-rate” VDSL and “G.fast.” Although DSL technologies continue to advance and produce higher and higher theoretical speeds (even up to 1Gb/s), these technologies are dogged by the quality problems with the underlying twisted-pair phone lines on which they are built. In addition, DSL service performance is sensitive to the distance from the central office (CO). This combination of challenges brings variability to the performance of what planners can expect for specific target sites. For these reasons, DSL should largely be avoided for access connectivity planning and only be considered in limited circumstances. One of the circumstances to consider DSL is when its access capacity can be bonded with another access circuit through advanced network service such as SD-WAN. We will discuss SD-WAN in the next section and will refer back to this scenario.

T1 (DS1) / T3 (DS3) Variants:

T1 or the T-carrier family of access connectivity services is built on a four wire transmission circuit. Originally developed at Bell Labs in the 60s, this family of services is built on the aggregation of “DS0” 64Kb/s channels. Typically delivered by telecom operators, offers in this class provide symmetrical internet service and speeds of 1.544 Mb/s (T1), 2.048Mb/s (E1), and up to 45 Mb/s (T3/DS3). These services are highly reliable and served as the primary method of “last mile” internet connectivity for most businesses in the late 90s and 2000s. While the T-carrier family is largely considered a legacy access methodology, there could be instances where businesses might consider some higher capacity variants, especially from a fractional T3 or above and where more modern managed Ethernet or fiber-based services are not available. Some CSPs that still sell T3 access circuits may offer these at substantial discounts.


This class of internet services are typically delivered by cable MSOs and lead with a coaxial copper cable for the Layer 1 physical delivery of internet service. Most cable networks are actually now engineered as hybrid fiber coaxial (HFC) with much of the regional internet traffic distributed over new fiber plant. Coaxial connectivity provides last mile connections to homes and businesses. Coax-based internet services from most Cable MSOs are offered at attractive prices and provide high bandwidth, with speeds starting in many cases at 100 Mb/s. Speeds are typically asymmetrical with higher download than upload. For communications services planning, IT managers should focus on upload speeds. Most business packages start at 10 Mb/s, enough to support a large number of IP voice channels and enough for limited HD video channels. Many coax-based services from cable MSOs are delivered as a “shared service” where all the users from a single street, neighborhood, or a strip mall may share a single pool of bandwidth. While shared services should be a concern for IT planners, consider that cable MSOs use the DOCSIS protocol to reserve bandwidth for high priority media traffic. DOCSIS is only offered on the cable MSOs’ own services and not for OTT-based services. For OTT services, IT planners should consider adding healthy buffers and/or overhead to their estimated bandwidth demands. Or, if they are engaging with a cable MSO for business internet, they should inquire about fiber and DIA-based solutions.

Carrier Ethernet (over copper):

Ethernet dominates enterprise and business networks. Ethernet has grown into this position with its ease of deployment, self-configuration, and excellent price per bit and price per port. The primary limitation for Ethernet, especially over copper, is on transmission distance. For this reason Ethernet is used for most in-building and small campus links but not used for access networks that may extend thousands of feet to several miles. Vendor innovation has extended the range of Ethernet services. These innovations have enabled CSPs to offer access Ethernet services with symmetrical speeds and high quality of service. Speeds are still dependent on the distance from the CO. In most cases, speeds available are well-understood by CSPs and can be easily provided and quoted based on site address. Carrier Ethernet services are considered a state-of-the-art offer from CSPs and provide an excellent platform for cloud-based IP communications services. Service pricing will depend on geography and local competitive alternatives.

Fiber-Based Services:

Just as much Ethernet over copper is an attractive option for business IP communications, Ethernet over fiber is even more attractive. Fiber provides far greater resistance to the signal degradation that occurs when some protocols are transmitted over copper. Requesting fiber-based access for a site is often prohibitively expensive. It is for this reason that most businesses should initiate their cloud migration plan for “what is available” from current providers at particular sites. As we’ve mentioned previously in this post, fiber-based connectivity is now available at more than 50% of business sites across the US. The main question facing planners is exactly what kind of premium the business needs to pay for securing fiber-based connectivity. In addition, IT planners should be prepared to layer service assurance and network services to provide QoS for voice and video connectivity. Though fiber offers an excellent transmission medium, it can still experience contention where fiber links are stressed with lots of demanding traffic such as HD video.

Network Services to Support Access Layer Service Quality

After physical connectivity above (fiber, copper, etc.), QoS of packets and traffic flow is managed through a variety of standards and protocols. There are benefits and drawbacks to most management approaches. In most cases, businesses prefer to apply some type of bandwidth reservation for real-time media such as voice and video traffic. A basic summary of traffic demands of various communications and data traffic is provided below and can help to show the sensitivity of traffic.

representation of traffic QoS demandsFigure 5: Representation of Traffic QoS Demands by Jason D. Hintersteiner, CWNE #171


Cable MSOs use DOCSIS, “data over cable service interface specification,” to deliver IP broadband service over their hybrid fiber-coaxial (HFC) infrastructure. Within the DOCSIS standards are methods for delivering a higher class of service for specific types of traffic, specifically real-time protocol (RTP) used for IP-based voice and some video communications traffic. Priority service is achieved using unsolicited grant synchronization (UGS), which provides an immediate grant of bandwidth access from the cable modem termination system (CMTS).


One of the most mature and proven methods for assuring call quality, MPLS or “multi-packet label switching,” provides a virtual tunnel across the CSPs access connection to assure transmission quality across potential points of traffic contention. Considered one of the most trusted and preferred methods for assuring resilience, MPLS is considered relatively costly and may not be available across all geos. The price of MPLS has represented a barrier for some planners who might be looking at cloud migration strictly on a cost comparison basis – where MPLS port charges eat away many of the savings of PBX maintenance and TDM access trunk charges.

While MPLS port charges have been coming down in recent years, and in some geographies at a compound rate of 10+% / year, reliance on MPLS alone for access connectivity assurance is proving challenging for both CSPs and IT planners. For the economics and flexibility needed to plan a multi-site and phased migration approach, IT planners should look to a mix of MPLS and other access methods.


Perhaps the most exciting innovation in access networking and WAN services has been the innovations around SD-WAN (SD = Software Defined). In fact, Frost & Sullivan recently revealed that 94% of businesses have deployed, are deploying, or will deploy an SD-WAN service in the next two years. A key benefit of SD-WAN is that it uses multiple paths for traffic to traverse a network. SD-WAN can improve service resilience across existing access circuits (by running several parallel traffics streams) or can improve resilience by running parallel traffic streams across multiple access circuits.

In the case of overlaying multiple circuits, consider a scenario where a particular business’s site may only have IP access via DSL and a shared cable broadband service. While either service might not provide the needed resilience for the business’s traffic demands, an SD-WAN service across a combination of both the DSL and cable circuits could offer the needed performance to deploy high quality hosted communications. From an economics standpoint, the combination of DSL and cable broadband circuits plus SD-WAN services would be very cost-effective.

Note that some SD-WAN resilience measures can add overhead traffic to voice and video media. Overhead can come in the form of multiple media streams and from the increased size of some packet headers. IT managers should work with their SD-WAN and CSPs to correctly size access circuits with these overhead factors in consideration. A more detailed discussion about VoIP, SD-WAN, and some testing can be found in this September, 2018 post, “Testing VoIP on SD-WANs” on No Jitter.

All in all, SD-WAN offers a lot of benefits and should certainly be seriously evaluated as a part of IP access services for cloud-based communications. Consider the 2018 report by Transparency Market Research. They forecast that the global SD-WAN market will expand at a 51.4% CAGR between 2017 and 2025 and be worth US $34.35 billion.


Planning for access and connectivity services strategy as part of cloud communications migration is one of the most important and yet complicated endeavors for the business’ IT team. There are several facets of this planning that are only briefly touched on here that could really deserve their own separate blog posts, especially around solutions such as security. For example, some businesses might lead their access connectivity procurement process with a focus on security. Communications service such as business voice and unified communications might be secondary in priority relative to how CSPs deter and defend against malicious attackers. CSPs should be careful to consider all the stakeholders in access connectivity procurement when building and positioning their core offers and bundles. To the extent that CSPs are prepared for a wide array of demands, both technical and commercial, the more quickly they can provide business IT managers with the confidence to move forward.


David Walters

Product Manager

Strategic Accounts and Initiatives