ABC of GPON SFP: Understanding GPON OLT / ONU / ONT SFP Module

subota , 20.01.2018.

Since the advances in Ethernet technology, “last mile” connectivity is expected to realize between the network backbone and local area networks (end users). Gigabit Passive Optical Network (GPON) is a cost-effective point-to-multipoint access network, which brings great improvement in data transmission distance (up to 20km) and bandwidth (an downstream capacity of 2.5Gbit/s and an upstream capacity of 1.25Gbit/s ). However, GPON's higher bandwidth and split ratios are only achievable by using GPON-capable optical transceivers. It is well positioned to help meet the needs for higher bandwidth in FTTx applications, and continues to fuel growth in demand for GPON SFP modules. So this article will introduce the basics of GPON SFP, including GPON OLT, GPON ONU and GPON ONT SFP module.

GPON SFP is a new higher-speed bi-directional optical transceiver, which can deliver 2.5 Gbits/sec of bandwidth. And it is a kind of single fiber transceiver which comes with SC connector and can transmit data up to 20km. In addition, it features a 28-dB optical loss budget to enable 1:64 split ratios and provides adequate optical loop lengths. Most EPON and some BPON systems deployed today use 25-dB optics, which limit the split ratio and loop length. For this reason, GPON transceiver enjoys the added advantage of industrial demand. The key performance advantage is to reduce the upstream split loss arising from utilizing the mode-coupled-receivers (MCR) in a PON application. Moreover, this innovative module dose not outweigh the costs over a standard module. For these two reasons, the GPON SFP modules are very attractive to the network operators to improve the utilization of GPON network. On top of that, GPON SFP transceiver is an essential part of GPON system which is necessary both for optical network unit (ONU) installed at the subscriber’s premises and for the optical line terminal (OLT) at the central office (CO). The following part will respectively introduce the GPON OLT, GPON ONU and GPON ONT SFP module.

GPON OLT SFP is designed for OLT side in GPON network. OLT is a equipment integrating L2/L3 switch function, which is located in central office (CO). The main function is to control the information float in both directions: upstream and downstream. The GPON OLT module plays an inevitable role in the upstream and downstream transmission. In order to put across the transmission process, the downstream transmission is taken as an example. A single mode optical fiber coming from OLT (at the central office) PON port, runs to the passive optical splitter (POS) located near end users. And then the optical splitter will divide signals into separate paths which can provide service up to 64 end users. In this basic GPON topology, a GPON OLT module is used to connect a single-mode fiber patch cable to a passive optical splitter. Therefore, GPON OLT transceiver works to get the data, voice and video traffic from metro network or from a long-haul network.

Since the ONU and ONT are deployed at customer’s premises, they are connected to the OLT by means of optical fiber and no active elements are present in the link. In GPON network, the ONU/ONT transceiver is the physical connection between the customer premises and the central office OLT. This type of modules gets the signals from OLT, so they have the opposite characteristic of GPON OLT transceiver, incorporating a high performance 1310nm burst mode DFB transmitter and 1490nm CW mode APD receiver. By being plugged into advanced “triple play” (data, voice & video) ONT or ONU equipment (with SFP ports), such as Ethernet switches, routers, DSLAMs or home gateway, ONU/ONT SFP module fits seamlessly into existing communications equipment and provides end users with a smooth upgrade to GPON. Therefore, GPON ONU/ONT SFP module plays an important role in the applications for point-to-multipoint (P2MP) ONT / ONU equipment in GPON network.

GPON SFP transceiver meets the the requirements of FTTx network to accelerate the speed or capacity. GPON OLT, ONU and ONT SFP module have their respective roles to play in the GPON networks. Many people may worry the high attenuation losses from optical splitter in the GPON networks, as above mentioned, the GPON optical module is just used to solve this problem in that it utilizes the MCR technology that protects large numbers of signals. In a word, this new module is a compelling network alternative to save cost and increase bandwidth and security.

Related Article: ABC of PON: Understanding OLT, ONU, ONT and ODN

24-Port Gigabit Switch Selection

utorak , 09.01.2018.

An Ethernet switch acts as a bridge to connect different parts of a network together. Although many routers also possess the network switching capabilities and multiple Ethernet ports, the Ethernet switch is not the replacement for routers. It is worth emphasizing that Ethernet switches are smarter than routers in that they operate at the data link layer (Layer 2) and the network layer (Layer 3) of the OSI Reference Model and therefore support any packet protocol. Ideally, switches will make better use of bandwidth if you prefer wired to wireless connections but have more devices than available Ethernet ports. On the other hand, an Ethernet switch is a costly way to expend the network in home or small business. So it is very important to invest an Ethernet switch with the appropriate number of ports to fit your needs. In the midst of various Gigabit Ethernet switches, a 24-port switch is considered as the most common Gigabit switch that connect devices in a local area network. Then this article will explore how to select a suitable 24-port Gigabit switch.

FS S3800-24F4S 24-port Gigabit switch comes with 20x 100/1000BASE SFP, 4x 1GE combo and 4x 10GE SFP+ slots. The flexible port combination form provide a high bandwidth aggregation connectivity for multiple switch in network to enhance network capacity. Moreover, it is a stackable SFP managed switch, which can provide true stacking of up to 4 switches in a stack acting as a single unit with totally 106 ports (96x 1G Ports and 10x 10G ports). The switching capacity is 128Gbps. This 24-port Gigabit managed switch fits for enterprise network operators who need high performance and low power processor to provide full speed forwarding and line-dormant capacity.

Figure 1: FS S3800-24F4S 24-Port Gigabit Switch

Cisco SGE2000P comes with 24 10/100/1000BASE-T RJ45 ports and 4 shared Gigabit SFP slots. This 24-port Gigabit managed switch can provide ACL (access control lists), DoS (denial-of-service), VLAN and IEEE 802.1X port authentication. And the enhanced quality of service (QoS) and traffic-management features help ensure clear and reliable voice and video communications. This Gigabit network switch enable you to take advantage of the comprehensive feature set for a better-optimized, more secure network.

Figure 2: Cisco SGE2000 24-Port Gigabit Switch (Source: Cisco)

The Netgear ProSafe GS724T is armed with 24 copper 10/100/1000 ports and 2 SFP 100/1000 ports. Each port can transfer data at maximum throughput for a total maximum switching speed of up to 48 Gbps. This 24-port switch is intended for SMB organizations using the switch for applications like VoIP, video conferencing, and system security, etc. And it features a fanless system, allowing the switch to work silently without overheating. This is great for use on homelab, as its quiet operation won’t cause a distraction.

Figure 3: NETGEAR ProSAFE GS724T 24-Port Gigabit Switch (Source: NETGEAR)

The TP-Link TL-SG1024 features 24 Gigabit Ethernet ports and non-blocking switching, which can provide large file transferring and also be compatible with 10Mbps and 100Mbps Ethernet devices. Moreover, this network switch has 48Gbps switching capacity with 8K MAC address table, 10KB Jumbo Frame and 4MB buffer memory. This TP-Link switch is a fanless rack mount design with LED diagnostic lights, so you can easily tell which ports are in use. It can automatically adjust power consumption according to the link status to limit the carbon footprint of your network. The price is $69.99 on Amazon. So this fanless Ethernet switch is good for your wallet both because it is inexpensive to buy and because of its energy-saving technology.

Figure 4: TP-Link TL-SG1024 24-Port Gigabit Switch(Source: TP-Link)

From the chart we can see, all the Gigabit switches listed above provide 24 port Ethernet RJ45 ports, only FS S3800-24F4S 24-port Gigabit switch has 4 SFP+ uplink ports. They have some characteristics in common that make them suitable for being used in places like home or small business office. In terms of the power consumption, TP-Link TL-SG1024 and NETGEAR ProSafe GS724T are lower than others, but the huge price spread exists between these two switches because NETGEAR ProSafe GS724T has another two SFP ports for more flexible application. Among these four switches, if you have no limited cost budget, FS S3800-24F4S is a good choice. It has more flexible port combination and higher switching capacity, that is why it may cost a little more than the other three switches. If you need stronger data transferring capability, FS S3800-24F4S is a better choice considering its forwarding rate. On the contrary, TP-Link TL-SG1024 is the best budget choice. If you want a fanless switch, NETGEAR ProSafe GS724T is an inexpensive and reliable choice, but the install program only works on Windows and the secure management is very difficult to be enabled.

When choosing a Gigabit Ethernet switch, the first factor to consider is how many devices need to be networked together. Purchasing a network switch with too few ports and not enough capacity will prove ineffective, and one that is too large can be a waste of money. Generally, small offices with a few employees should start with a 16-port switch, but a business that is looking to expand its operations soon needs a 24-port switch. So 24-port Gigabit switch is the most future-proofing and cost-effective choice in small business network.

Related Article: 48-Port 10GE Switch Selection: What Is the Right Choice?