Wide Area Network (WAN) Communication Protocols

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Synchronous Optical Network (SONET)/SDH

SONET protocol got developed by Exchange Carriers Standards Association (ECSA) that defines the optical telecommunications transport. The standard is always evolving, and it is expected to get used for not more than three decades. The word ‘synchronous’ within SONET means that the digital transformation of the signal happens exactly at the same speed. SONET is similar to Synchronous Digital Hierarchy (SDH) however SONET is used in the US while SDH gets used outside the US. The idea is that each data is not transmitted separately but rather, multiplexed and into higher transmission rates (up to 10 Gigabytes) and then transmitted over SONET/SDH networks. The main reason for introducing SONET was to reduce the network cost and complexity (which was a problem inherent in Plesiochronous Digital Hierarchy systems) and to obtain low transmission rate signals from multiplexed high-transmission rate traffic (Goralski, 2002).

SONET is highly flexible and has high bandwidth over most other older system. The technology led reduced the number of equipment requirements, thereby increasing the network reliability. Most SONET/SDH networks usually have ring topology that increases the reliability of the entire network transmission such that if an optical fiber fails, the transmission path is restored in a short period also; it gets associated with overhead and payload bytes which enhance sectioning of centralized fault. With the set of generic standards that SONET provides, it has also facilitated easy connection of computing products from different manufacturers. More importantly, since SONET is highly flexible, it allows for future applications with various transmission rates to be added. Finally, SONET has proved to offer high security as the attackers find it hard to interfere with the fiber optic links (Vasseur et al., 2004).

The common disadvantage associated with SONET is that it is costly. Fiber optic cables are the most expensive transmission media among others and additionally, installing the network using the technology requires high expertise which is also an added cost.

ATM (Asynchronous Transfer Mode)

ATM technology is a component of broadband Integrated Services Digital Network (ISDN) organizes and transmits data as fifty three-byte units over the physical medium (usually fiber optic) using digital signal technology. The word ‘asynchronous’ means that the digital transmission happens at different rates. Each cell is processed individually and asynchronously comparative to other similar cells and queued before multiplexing over the media path. Because hardware and not software easily implement ATM, it is characterized by very high processing and switch transmission rates (usually up to ten billions-of-bits-per-second (Gbps)). Due to the high transmission speed of ATM, it supports voice and data communications over long distance networks (WAN). ATM functions within data-link layer or the Open System Interconnect (OSI) model. However it is different from the Ethernet in that ATM does not use routing but rather it uses switches to develop point to point connections, and data is transmitted directly between endpoints (Black, 1998).

ATM has several advantages and disadvantages. Some of the advantages are as follows. Due to its high transmission speed, ATM supports, data, voice, and video transmission over a single network. With ATM protocol, it gets easier to connect WAN and LAN networks. Also, ATM supports the high degree of delay tolerance and loss performance with the multiple Quality of Services (QoS) classes. Besides, it is highly scalable, and therefore, it allows for future expansion of the network applications. With ATM networks, you are assured of minimal delay (similar to the dedicated networks). Finally, with the help of AAALs, ATM provides the support of both connection-oriented and connectionless transmission (Kartalopoulos, 1999).

The common disadvantages of ATMs are cost and efficiency expenses. However, costs usually decrease as the network expands and as time goes on. Researchers claim that with time ATM will not exist because there are few applications that utilize ATM at the moment since there are other protocols such as SONET. ATM also faces competition from other technologies such as Ethernet, Fast Ethernet, and FDDI since with ATM there is the need to install new hardware and software, while for the other technologies, you do not have to do all those things.

Comparative Analysis

Both SONET and ATM are very similar. However, their transmission mode differs. As from their names, the transmission mode of SONET is synchronous while that of ATM is asynchronous, meaning that the rate of data transmission in SONET is static while that of ATM varies. Both technologies support very high transmission rates and high bandwidth, factors which are suitable for data, video and voice transmission over a network. Also, ATM is usually a switching technology while SONET cares only about transmission. ATM provides the logical way of bits organization without caring about the type of wire while SONET is highly sensitive as it is majorly concerned with bits transfer between end points of the wire.  Sonet works on fiber optics cable (from its name ‘synchronous’) (Alwayn, 2004).

Both ATM and SONET work together in spite of their opposing structures. ATM uses a queue to manage its information while SONET will use synchronous means to send a frame without worrying about the bandwidth since it gets optimized by ATM.



Alwayn, V. (2004). Optical network design and implementation. Indianapolis, Ind: Cisco Press. Retrieved from https://books.google.com/books?isbn=1587051052

Black, U. D. (1998). ATM: 2. Upper Saddle River, NJ: Prentice Hall.Retrieved fromhttps://books.google.com/books?isbn=0780334884

Goralski, W. (2002). SONET/SDH. New York: McGraw-Hill.Retrieved fromhttps://books.google.com/books?id=zO9SAAAAMAAJ

Kartalopoulos, S. V. (1999). Understanding SONET/SDH and ATM: Communications networks for the next millennium. Piscataway, NJ: IEEE Press.Retrieved from https://books.google.com/books?id=JhQfAQAAIAAJ

Vasseur, J.-P., Demeester, P., & Pickavet, M. (2004). Network recovery: Protection and restoration of optical, SONET-SDH, IP, and MPLS. Amsterdam [u.a.: Elsevier/Morgan Kaufmann.Retrieved from https://books.google.com/books?isbn=012715051X

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