Most Popular Articles

• Ethernet Passive Optical Network Tutorial

  Feb 8, 2016 by Articles / 681 Views

  EPON is a PON-based network that carries data traffic encapsulated in Ethernet frames. Unlike other PON technologies which are based on the ATM standard, it uses a standard 8b/10b line coding and operates at standard Ethernet speed. This lets you utilize the economies-of-scale of Ethernet, and provides simple, easy-to-manage connectivity to Ethernet-based, IP equipment, both at the customer premises and at the central office.

  EPON Network Structure

  A typical EPON system is composed of OLT, ONU, and ODN (Figure 1).

  

  Figure 1. EPON Network Structure

  The OLT（Optical Line Terminal）resides in the Central Office (CO) and connects the optical network to the metropolitan-area network or wide-area network, also known as the backbone or long-haul network. OLT is both a switch or router and a multi-service platform which provides EPON-oriented optical interfaces. Besides the network assembling and access functions, OLT could also perform bandwidth assignments, network security and management configurations according to the customers’ different QoS/SLA requirements.

  The ONU（Optical Network Unit）is located either at the end-user location or at the curb and provides optical interfaces which are connected to the OLT and service interfaces at users’ side such as voice, data and video.

  The ODN（Optical Distributed Network）is an optical distribution network and is mainly composed of one or more passive optical splitters which connects the OLT and ONU. Its function is to split downstream signal from one fiber into several fibers and combine optical upstream signals from multiple fibers into one. Optical splitter is a simple device which needs no power and could work in an all-weather environment. The typical splitters have a splitting ratio of 2, 4, 8, 16 or 32 and be connected to each other. The longest distance the ODN could cover is 20 km.

  EPON Downlink and Uplink Technology

  In an EPON the process of transmitting data downstream from the OLT to multiple ONUs is fundamentally different from transmitting data upstream from multiple ONUs to the OLT.

  In the downstream direction, Ethernet frames transmitted by the OLT pass through a 1:N passive splitter and reach each ONU. N is typically between 4 and 64. This behavior is similar to a shared-medium network. Because Ethernet is broadcast by nature, in the downstream direction (from network to user), it fits perfectly with the Ethernet PON architecture: packets are broadcast by the OLT and extracted by their destination ONU based on the media-access control (MAC) address (Figure 2).

  
  Figure 2. Downstream Traffic in EPON

  In the upstream direction, due to the directional properties of a passive optical combiner, data frames from any ONU will only reach the OLT, and not other ONUs. In that sense, in the upstream direction, the behavior of EPON is similar to that of a point-to-point architecture. However, unlike in a true point-to-point network, in EPON data frames from different ONUs transmitted simultaneously still may collide. Thus, in the upstream direction (from users to 13 network) the ONUs need to employ some arbitration mechanism to avoid data collisions and fairly share the fiber-channel capacity (Figure 3).

  
  Figure 3. Upstream Traffic in EPON

  EPON and ADSL Comparison

  The requirement of bandwidth is increasing crazily with the incoming of digital age. Therefore the current high speed copper cable ADSL (Asymmetric Digital Subscriber Line) cannot meet our needs longer. The bandwidth of ADSL is limited to only a few megabit per second and the upstream and downstream bandwidth are not equal either. However, optical fiber has larger bandwidth and superior transmission capability which reaches gigabit per second. Hence, optical fiber used in access network is the future trend. And since Ethernet is low cost, uncomplicated widely-used in current network, and its application is very popular nowadays. So it is not hard to see that it is feasible and economical to combine them together. EPON technology combines a mature Ethernet technology and high-bandwidth PON technology, which is an ideal access method to achieve integrated services. In the future, highbandwidth business will surely drive up existing EPON which has the rate of 1.25Gbps in both the downstream and upstream directions.

  EPON Technical Advantages

  EPONs are simpler, more efficient, and less expensive than alternate multiservice access solutions. Key advantages of EPONs include the following:

  Higher bandwidth: up to 1.25 Gbps symmetric Ethernet bandwidthLower costs: lower up-front capital equipment and ongoing operational costsMore revenue: broad range of flexible service offerings means higher revenues

   

  With the growing of EPON technology, interaction standards and EPON devices, EPON has entered the large scale application phase driven by the huge market demands. EPON is fit for the access market which is at the end of the fibers and which has a certain density and these markets include FTTH, FTTP, FTTB, FTTN etc.

  EPON becomes a very economical and effective broadband access solution because of its predominance in equipment investment and also the operations, maintenance and etc. It could be said that the EPON technology has become the developing direction of access network’s technologies in the future as an ideal solution for FTTH.

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• Cisco StackWise and StackWise Plus Technology

  May 4, 2016 by Cisco Channel / 656 Views

  This white paper provides an overview of the Cisco StackWise and Cisco StackWise Plus technologies and the specific mechanisms that they use to create a unified, logical switching architecture through the linkage of multiple, fixed configuration switches. This paper focuses on the following critical aspects of the Cisco StackWise and Cisco StackWise Plus technologies: stack interconnect behavior, stack creation and modification; Layer 2 and Layer 3 forwarding; and quality-of-service (QoS) mechanisms. The goal of the paper is to help the reader understand how the Cisco StackWise and StackWise Plus technologies deliver advanced performance for voice, video, and Gigabit Ethernet applications. First, this white paper will discuss the Cisco Catalyst 3750 Series Switches and StackWise and second, the Cisco Catalyst 3750-E and Catalyst 3750-X Series Switches with StackWise Plus will be discussed, highlighting the differences between the two. Please note that the Cisco Catalyst 3750-E and Catalyst 3750-X will run StackWise Plus when connected to a stack of all Cisco Catalyst 3750-E and Catalyst 3750-X switches, while it will run StackWise if there is one or more Cisco Catalyst 3750 in the stack. (See Figures 1 and 2.)

  Figure 1. Stack of Cisco Catalyst 3750 Series Switches with StackWise Technology

  

  Figure 2. Stack of Cisco Catalyst 3750-E Series Switches with StackWise and StackWise Plus Technologies

  

  Technology Overview

  Cisco StackWise technology provides an innovative new method for collectively utilizing the capabilities of a stack of switches. Individual switches intelligently join to create a single switching unit with a 32-Gbps switching stack interconnect. Configuration and routing information is shared by every switch in the stack, creating a single switching unit. Switches can be added to and deleted from a working stack without affecting performance.

  The switches are united into a single logical unit using special stack interconnect cables that create a bidirectional closed-loop path. This bidirectional path acts as a switch fabric for all the connected switches. Network topology and routing information is updated continuously through the stack interconnect. All stack members have full access to the stack interconnect bandwidth. The stack is managed as a single unit by a master switch, which is elected from one of the stack member switches.

  Each switch in the stack has the capability to behave as a master or subordinate (member) in the hierarchy. The master switch is elected and serves as the control center for the stack. Both the master member switches act as forwarding processors. Each switch is assigned a number. Up to nine separate switches can be joined together. The stack can have switches added and removed without affecting stack performance.

  Each stack of Cisco Catalyst 3750 Series Switches has a single IP address and is managed as a single object. This single IP management applies to activities such as fault detection, virtual LAN (VLAN) creation and modification, security, and QoS controls. Each stack has only one configuration file, which is distributed to each member in the stack. This allows each switch in the stack to share the same network topology, MAC address, and routing information. In addition, it allows for any member to become the master, if the master ever fails.

  The Stack Interconnect Functionality

  Cisco StackWise technology unites up to nine individual Cisco Catalyst 3750 switches into a single logical unit, using special stack interconnect cables and stacking software. The stack behaves as a single switching unit that is managed by a master switch elected from one of the member switches. The master switch automatically creates and updates all the switching and optional routing tables. A working stack can accept new members or delete old ones without service interruption.

  Bidirectional Flow

  To efficiently load balance the traffic, packets are allocated between two logical counter-rotating paths. Each counter-rotating path supports 16 Gbps in both directions, yielding a traffic total of 32 Gbps bidirectionally. The egress queues calculate path usage to help ensure that the traffic load is equally partitioned.

  Whenever a frame is ready for transmission onto the path, a calculation is made to see which path has the most available bandwidth. The entire frame is then copied onto this half of the path. Traffic is serviced depending upon its class of service (CoS) or differentiated services code point (DSCP) designation. Low-latency traffic is given priority.

  When a break is detected in a cable, the traffic is immediately wrapped back across the single remaining 16-Gbps path to continue forwarding.

  Online Stack Adds and Removals

  Switches can be added and deleted to a working stack without affecting stack performance. When a new switch is added, the master switch automatically configures the unit with the currently running Cisco IOS ^® Software image and configuration of the stack. The stack will gather information such as switching table information and update the MAC tables as new addresses are learned. The network manager does not have to do anything to bring up the switch before it is ready to operate. Similarly, switches can be removed from a working stack without any operational effect on the remaining switches. When the stack discovers that a series of ports is no longer present, it will update this information without affecting forwarding or routing.

  Physical Sequential Linkage

  The switches are physically connected sequentially, as shown in Figure 3. A break in any one of the cables will result in the stack bandwidth being reduced to half of its full capacity. Subsecond timing mechanisms detect traffic problems and immediately institute failover. This mechanism restores dual path flow when the timing mechanisms detect renewed activity on the cable.

  Figure 3. Cisco StackWise Technology Resilient Cabling

  

  Subsecond Failover

  Within microseconds of a breakage of one part of the path, all data is switched to the active half of the bidirectional path (Figure 4).

  Figure 4. Loopback After Cable Break

  

  The switches continually monitor the stack ports for activity and correct data transmission. If error conditions cross a certain threshold, or there is insufficient electromagnetic contact of the cable with its port, the switch detecting this then sends a message to its nearest neighbor opposite from the breakage. Both switches then divert all their traffic onto the working path.

  Single Management IP Address

  The stack receives a single IP address as a part of the initial configuration. After the stack IP address is created, the physical switches linked to it become part of the master switch group. When connected to a group, each switch will use the stack IP address. When a new master is elected, it uses this IP address to continue interacting with the network.

  Stack Creation and Modification

  Stacks are created when individual switches are joined together with stacking cables. When the stack ports detect electromechanical activity, each port starts to transmit information about its switch. When the complete set of switches is known, the stack elects one of the members to be the master switch, which will be responsible for maintaining and updating configuration files, routing information, and other stack information. The entire stack will have a single IP address that will be used by all the switches.

  1:N Master Redundancy

  1:N master redundancy allows each stack member to serve as a master, providing the highest reliability for forwarding. Each switch in the stack can serve as a master, creating a 1:N availability scheme for network control. In the unlikely event of a single unit failure, all other units continue to forward traffic and maintain operation.

  Master Switch Election

  The stack behaves as a single switching unit that is managed by a master switch elected from one of the member switches. The master switch automatically creates and updates all the switching and optional routing tables. Any member of the stack can become the master switch. Upon installation, or reboot of the entire stack, an election process occurs among the switches in the stack. There is a hierarchy of selection criteria for the election.

  1. User priority - The network manager can select a switch to be master.

  2. Hardware and software priority - This will default to the unit with the most extensive feature set. The Cisco Catalyst 3750 IP Services (IPS) image has the highest priority, followed by Cisco Catalyst 3750 switches with IP Base Software Image (IPB).

  Catalyst 3750-E and Catalyst 3750-X run the Universal Image. The feature set on the universal image is determined by the purchased license. The "show version" command will list operating license level for each switch member in the stack.

  3. Default configuration - If a switch has preexisting configuration information, it will take precedence over switches that have not been configured.

  4. Uptime - The switch that has been running the longest is selected.

  5. MAC address - Each switch reports its MAC address to all its neighbors for comparison. The switch with the lowest MAC address is selected.

  Master Switch Activities

  The master switch acts as the primary point of contact for IP functions such as Telnet sessions, pings, command-line interface (CLI), and routing information exchange. The master is responsible for downloading forwarding tables to each of the subordinate switches. Multicast and unicast routing tasks are implemented from the master. QoS and access control list (ACL) configuration information is distributed from the master to the subordinates. When a new subordinate switch is added, or an existing switch removed, the master will issue a notification of this event and all the subordinate switches will update their tables accordingly.

  Shared Network Topology Information

  The master switch is responsible for collecting and maintaining correct routing and configuration information. It keeps this information current by periodically sending copies or updates to all the subordinate switches in the stack. When a new master is elected, it reapplies the running configuration from the previous master to help ensure user and network continuity. Note that the master performs routing control and processing. Each individual switch in the stack will perform forwarding based on the information distributed by the master.

  Subordinate Switch Activities

  Each switch has tables for storing its own local MAC addresses as well as tables for the other MAC addresses in the stack. The master switch keeps tables of all the MAC addresses reported to the stack. The master also creates a map of all the MAC addresses in the entire stack and distributes it to all the subordinates. Each switch becomes aware of every port in the stack. This eliminates repetitive learning processes and creates a much faster and more efficient switching infrastructure for the system.

  Subordinate switches keep their own spanning trees for each VLAN that they support. The StackWise ring ports will never be put into a Spanning Tree Protocol blocking state. The master switch keeps a copy of all spanning tree tables for each VLAN in the stack. When a new VLAN is added or removed, all the existing switches will receive a notification of this event and update their tables accordingly.

  Subordinate switches wait to receive copies of the running configurations from the master and begin to start transmitting data upon receipt of the most current information. This helps ensure that all the switches will use only the most current information and that there is only one network topology used for forwarding decisions.

  Multiple Mechanisms for High Availability

  The Cisco StackWise technology supports a variety of mechanisms for creating high resiliency in a stack.

  • CrossStack EtherChannel^® technology - Multiple switches in a stack can create an EtherChannel connection. Loss of an individual switch will not affect connectivity for the other switches.

  • Equal cost routes - Switches can support dual homing to different routers for redundancy.

  • 1:N master redundancy - Every switch in the stack can act as the master. If the current master fails, another master is elected from the stack.

  • Stacking cable resiliency - When a break in the bidirectional loop occurs, the switches automatically begin sending information over the half of the loop that is still intact. If the entire 32 Gbps of bandwidth is being used, QoS mechanisms will control traffic flow to keep jitter and latency-sensitive traffic flowing while throttling lower priority traffic.

  • Online insertion and removal - Switches can be added and deleted without affecting performance of the stack.

  • Distributed Layer 2 forwarding - In the event of a master switch failure, individual switches will continue to forward information based on the tables they last received from the master.

  • RPR+ for Layer 3 resiliency - Each switch is initialized for routing capability and is ready to be elected as master if the current master fails. Subordinate switches are not reset so that Layer 2 forwarding can continue uninterrupted. Layer 3 Nonstop Forwarding (NSF) is also supported when two or more nodes are present in a stack.

  Layer 2 and Layer 3 Forwarding

  Cisco StackWise technology offers an innovative method for the management of Layer 2 and Layer 3 forwarding. Layer 2 forwarding is done with a distributed method. Layer 3 is done in a centralized manner. This delivers the greatest possible resiliency and efficiency for routing and switching activities across the stack.

  Forwarding Resiliency During Master Change

  When one master switch becomes inactive and while a new master is elected, the stack continues to function. Layer 2 connectivity continues unaffected. The new master uses its hot standby unicast table to continue processing unicast traffic. Multicast tables and routing tables are flushed and reloaded to avoid loops. Layer 3 resiliency is protected with NSF, which gracefully and rapidly transitions Layer 3 forwarding from the old to new master node.

  High-Availability Architecture for Routing Resiliency Using Routing Processor Redundancy+

  The mechanism used for high availability in routing during the change in masters is called Routing Processor Redundancy+ (RPR+). It is used in the Cisco 12000 and 7500 Series Routers and the Cisco Catalyst 6500 Series Switch products for high availability. Each subordinate switch with routing capability is initialized and ready to take over routing functions if the master fails. Each subordinate switch is fully initialized and connected to the master. The subordinates have identical interface addresses, encapsulation types, and interface protocols and services. The subordinate switches continually receive and integrate synchronized configuration information sent by the current master and monitor their readiness to operate through the continuous execution of self-tests. Reestablishment of routes and links happens more quickly than in normal Layer 3 devices because of the lack of time needed to initialize the routing interfaces. RPR+ coupled with NSF provides the highest performance failover forwarding.

  Adding New Members

  When the switching stack has established a master, any new switch added afterward automatically becomes a subordinate. All the current routing and addressing information is downloaded into the subordinate so that it can immediately begin transmitting traffic. Its ports become identified with the IP address of the master switch. Global information, such as QoS configuration settings, is downloaded into the new subordinate member.

  Cisco IOS Software Images Must Be Identical

  The Cisco StackWise technology requires that all units in the stack run the same release of Cisco IOS Software. When the stack is first built, it is recommended that all of the stack members have the same software feature set - either all IP Base or all IP Services. This is because later upgrades of Cisco IOS Software mandate that all the switches to be upgraded to the same version as the master.

  Automatic Cisco IOS Software Upgrade/Downgrade from the Master Switch

  When a new switch is added to an existing stack, the master switch communicates with the switch to determine if the Cisco IOS Software image is the same as the one on the stack. If it is the same, the master switch sends the stack configuration to the device and the ports are brought online. If the Cisco IOS Software image is not the same, one of three things will occur:

  1. If the hardware of the new switch is supported by the Cisco IOS Software image running on the stack, the master will by default download the Cisco IOS Software image in the master's Flash memory to the new switch, send down the stack configuration, and bring the switch online.

  2. If the hardware of the new switch is supported by the Cisco IOS Software image running on the stack and the user has configured a Trivial File Transfer Protocol (TFTP) server for Cisco IOS Software image downloads, then the master will automatically download the Cisco IOS Software image from the TFTP server to the new switch, configure it, then bring it online.

  3. If the hardware of the new switch is not supported by the Cisco IOS Software image running on the stack, the master will put the new switch into a suspended state, notify the user of a version incompatibility, and wait until the user upgrades the master to a Cisco IOS Software image that supports both types of hardware. The master will then upgrade the rest of the stack to this version, including the new switch, and bring the stack online.

  Upgrades Apply to All Devices in the Stack

  Because the switch stack behaves like a single unit, upgrades apply universally to all members of the stack at once. This means that if an original stack contains a combination of IP Base and IP services software feature sets on the various switches, the first time a Cisco IOS Software upgrade is applied, all units in the stack will take on the characteristic of the image applied. While this makes it much more efficient to add functionality to the stack, it is important to make sure all applicable upgrade licenses have been purchased before allowing units to be upgraded from IP Base .to IP Services functions. Otherwise, those units will be in violation of Cisco IOS Software policy.

  Smart Unicast and Multicast - One Packet, Many Destinations

  The Cisco StackWise technology uses an extremely efficient mechanism for transmitting unicast and multicast traffic. Each data packet is put on the stack interconnect only once. This includes multicast packets. Each data packet has a 24-byte header with an activityJame list for the packet as well as a QoS designator. The activity list specifies the port destination or destinations and what should be done with the packet. In the case of multicast, the master switch identifies which of the ports should receive a copy of the packets and adds a destination index for each port. One copy of the packet is put on the stack interconnect. Each switch port that owns one of the destination index addresses then copies this packet. This creates a much more efficient mechanism for the stack to receive and manage multicast information (Figure 5).

  Figure 5. Comparison of Normal Multicast in Stackable Switches and Smart Multicast in Cisco Catalyst 3750 Series Switches Using Cisco StackWise Technology

  

  QoS Mechanisms

  QoS provides granular control where the user meets the network. This is particularly important for networks migrating to converged applications where differential treatment of information is essential. QoS is also necessary for the migration to Gigabit Ethernet speeds, where congestion must be avoided.

  QoS Applied at the Edge

  Cisco StackWise supports a complete and robust QoS model, as shown in Figure 6.

  Figure 6. QoS Model

  

  The Cisco Catalyst 3750-E, Catalyst 3750-X and Cisco Catalyst 3750 support 2 ingress queues and 4 egress queues. Thus the Cisco Catalyst 3750-E, Catalyst 3750-X and Cisco Catalyst 3750 switches. support the ability to not only limit the traffic destined for the front side ports, but they can also limit the amounts of and types of traffic destined for the stack ring interconnect. Both the ingress and egress queues can be configured for one queue to be serviced as a priority queue that gets completely drained before the other weighted queue(s) get serviced. Or, each queue set can be configured to have all weighted queues.

  StackWise employs Shaped Round Robin (SRR). SRR is a scheduling service for specifying the rate at which packets are dequeued. With SRR there are two modes, Shaped and Shared (default). Shaped mode is only available on the egress queues. Shaped egress queues reserve a set of port bandwidth and then send evenly spaced packets as per the reservation. Shared egress queues are also guaranteed a configured share of bandwidth, but do not reserve the bandwidth. That is, in Shared mode, if a higher priority queue is empty, instead of the servicer waiting for that reserved bandwidth to expire, the lower priority queue can take the unused bandwidth. Neither Shaped SRR nor Shared SRR is better than the other. Shared SRR is used when one wants to get the maximum efficiency out of a queuing system, because unused queue slots can be used by queues with excess traffic. This is not possible in a standard Weighted Round Robin (WRR). Shaped SRR is used when one wants to shape a queue or set a hard limit on how much bandwidth a queue can use. When one uses Shaped SRR one can shape queues within a ports overall shaped rate. In addition to queue shaping, the Cisco Catalyst 3750-E can rate limit a physical port. Thus one can shape queues within an overall rate-limited port value.

  As stated earlier, SRR differs from WRR. In the examples shown in figure 7, strict priority queuing is not configured and Q4 is given the highest weight, Q3 lower, Q2 lower, and Q1 the lowest. With WRR, queues are serviced based on the weight. Q1 is serviced for Weight 1 period of time, Q2 is served for Weight 2 period of time, and so forth. The servicing mechanism works by moving from queue to queue and services them for the weighted amount of time. With SRR weights are still followed; however, SRR services the Q1, moves to Q2, then Q3 and Q4 in a different way. It doesn't wait at and service each queue for a weighted amount of time before moving on to the next queue. Instead, SRR makes several rapid passes at the queues, in each pass, each queue may or may not be serviced. For each given pass, the more highly weighted queues are more likely to be serviced than the lower priority queues. Over a given time, the number of packets serviced from each queue is the same for SRR and WRR. However, the ordering is different. With SRR, traffic has a more evenly distributed ordering. With WRR one sees a bunch of packets from Q1 and then a bunch of packets from Q2, etc. With SRR one sees a weighted interleaving of packets. In the example in Figure 7, for WRR, all packets marked 1 are serviced, then 2, then 3, and so on till 5. In SRR, all A packets are serviced, then B, C, and D. SRR is an evolution of WRR that protects against overwhelming buffers with huge bursts of traffic by using a smoother round-robin mechanism.

  Figure 7. Queuing

  

  In addition to advanced queue servicing mechanisms, congestion avoidance mechanisms are supported. Weighted tail drop (WTD) can be applied on any or all of the ingress and egress queues. WTD is a congestion-avoidance mechanism for managing the queue lengths and providing drop precedences for different traffic classifications. Configurable thresholds determine when to drop certain types of packets. The thresholds can be based on CoS or DSCP values. As a queue fills up, lower priority packets are dropped first. For example, one can configure WTD to drop CoS 0 through 5 when the queue is 60% full. In addition, multiple thresholds and levels can be set on a per queue basis.

  Jumbo Frame Support

  The Cisco StackWise technology supports granular jumbo frames up to 9 KB on the 10/100/1000 copper ports for Layer 2 forwarding. Layer 3 forwarding of jumbo packets is not supported by the Cisco Catalyst 3750. However, the Cisco Catalyst 3750-E and Catalyst 3750-X. do support Layer 3 jumbo frame forwarding.

  Smart VLANs

  VLAN operation is the same as multicast operation. If the master detects information that is destined for multiple VLANs, it creates one copy of the packet with many destination addresses. This enables the most effective use of the stack interconnect (Figure 8).

  Figure 8. Smart VLAN Operations

  

  Cross-Stack EtherChannel Connections

  Because all the ports in a stack behave as one logical unit, EtherChannel technology can operate across multiple physical devices in the stack. Cisco IOS Software can aggregate up to eight separate physical ports from any switches in the stack into one logical channel uplink. Up to 48 EtherChannel groups are supported on a stack.

  StackWise Plus

  StackWise Plus is an evolution of StackWise. StackWise Plus is only supported on the Cisco Catalyst 3750-E and Catalyst 3750-X switch families. The two main differences between StackWise Plus and StackWise are as follows:

  1. For unicast packets, StackWise Plus supports destination striping, unlike StackWise support of source stripping. Figure 9 shows a packet is being sent from Switch 1 to Switch 2. StackWise uses source stripping and StackWise Plus uses destination stripping. Source stripping means that when a packet is sent on the ring, it is passed to the destination, which copies the packet, and then lets it pass all the way around the ring. Once the packet has traveled all the way around the ring and returns to the source, it is stripped off of the ring. This means bandwidth is used up all the way around the ring, even if the packet is destined for a directly attached neighbor. Destination stripping means that when the packet reaches its destination, it is removed from the ring and continues no further. This leaves the rest of the ring bandwidth free to be used. Thus, the throughput performance of the stack is multiplied to a minimum value of 64 Gbps bidirectionally. This ability to free up bandwidth is sometimes referred to as spatial reuse. Note: even in StackWise Plus broadcast and multicast packets must use source stripping, because the packet may have multiple targets on the stack.

  Figure 9. Stripping

  

  2. StackWise Plus can locally switch. StackWise cannot. Furthermore, in StackWise, since there is no local switching and since there is source stripping, even locally destined packets must traverse the entire stack ring. (See Figure 10.)

  Figure 10. Switching

  

  3. StackWise Plus will support up to 2 line rate 10 Gigabit Ethernet ports per Cisco Catalyst 3750-E.

  Combining StackWise Plus and StackWise in a Single Stack

  Cisco Catalyst 3750-E and Catalyst 3750-X StackWise Plus and Cisco Catalyst 3750 StackWise switches can be combined in the same stack. When this happens, the Cisco Catalyst 3750-E, or Catalyst 3750-Xswitches negotiate from StackWise Plus mode down to StackWise mode. That is, they no longer perform destination stripping. However, the Cisco Catalyst 3750-E and the Catalyst 3750-X will retain its ability to perform local switching.

  Management

  Products using the Cisco StackWise and StackWise Plus technologies can be managed by the CLI or by network management packages. Cisco Cluster Management Suite (CMS) Software has been developed specifically for management of Cisco stackable switches. Special wizards for stack units in Cisco CMS Software allow the network manager to configure all the ports in a stack with the same profile. Predefined wizards for data, voice, video, multicast, security, and inter-VLAN routing functions allow the network manager to set all the port configurations at once.

  The Cisco StackWise and StackWise Plus technologies are also manageable by CiscoWorks.

  Summary

  Cisco StackWise and StackWise Plus technologies allow you to increase the resiliency and the versatility of your network edge to accommodate evolution for speed and converged applications. 

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• The Composition and Classification of Fiber Optic Cables

  Feb 6, 2016 by Articles / 643 Views

  To satisfy optical, mechanical and environmental performances and specifications, fiber optic cable was born. The fiber optic cable uses one or more fibers that placed in the sheath as the transmission medium. Accompanied by the continuous advancement of network technology, fiber optic cable constantly participates in the construction of telecommunications networks, the construction of the national information highway, Fiber To The Home (FTTH) and other occasions for large-scale use. Although fiber optic cable is still more expensive than other types of cable, it's favored for today's high-speed data communications because it eliminates the problems of twisted-pair cable and so fiber optic cable is still a good choice for people. But how to really get a good performance, state-of-the-art products, we need to understand some basics to identify the types of fiber optic cables.

  Composition

  Fiber optic cable consists of the core, the cladding and the coating. The core is a cylindrical rod of dielectric material. Dielectric material conducts no electricity. Light propagates mainly along the core of the fiber. The core is generally made of glass. The core is described as having a radius of (a) and an index of refraction n1. The core is surrounded by a layer of material called the cladding. Even though light will propagate along the fiber core without the layer of cladding material, the cladding does perform some necessary functions. (The basic structure of an optical fiber is shown in the following figure.)

   

  Structure: Core: This central section, made of silica, is the light transmitting region of the fiber.Cladding: It is the first layer around the core. It is also made of silica, but not with the same composition as the core. This creates an optical wave guide which confines the light in the core by total reflection at the core-cladding interface.Coating: It is the first non-optical layer around the cladding. The coating typically consists of one or more layers of a polymer that protect the silica structure against physical or environmental damage.Strengthening Fibers: These components help protect the core against crushing forces and excessive tension during installation. The materials can range from Kevlar to wire strands to gel-filled sleeves.Cable Jacket: This is the outer layer of any cable. Most fiber optic cables have an orange jacket, although some may be black or yellow. The jacket material is application specific. The cable jacket material determines the mechanical robustness, aging due to UV radiation, oil resistance, etc.

   

  Jacket Material: PolyEthylene (PE): PE (black color) is the standard jacket material for outdoor fiber optic cables. PE has excellent moisture- and weather-resistance properties. It has very stable dielectric properties over a wide temperature range. It is also abrasion-resistant.PolyVinyl Chloride (PVC): PVC is the most common material for indoor cables, however it can also be used for outdoor cables. It is flexible and fire-retardant. PVC is more expensive than PE.PolyVinyl DiFluoride (PVDF): PVDF is used for plenum cables because it has better fire-retardant properties than PE and produces little smoke.Low Smoke Zero Halogen (LSZH) Plastics: LSZH plastics are used for a special kind of cable called LSZH cables. They produce little smoke and no toxic halogen compounds. But they are the most expensive jacket material. 

   

  Fiber Size

  The size of the optical fiber is commonly referred to by the outer diameter of its core, cladding and coating. Example: 50/125/250 indicates a fiber with a core of 50 microns, cladding of 125 microns, and a coating of 250 microns. The coating is always removed when joining or connecting fibers. A micron (µm) is equal to one-millionth of a meter. 25 microns are equal to 0.0025 cm. (A sheet of paper is approximately 25 microns thick).

   

  Classification

  Besides the basics, Fiber optic cables can be classified by other ways.

  Transmission Mode:

  • Multi-Mode Fiber (MMF) Cable: Center glass core is coarse (50 or 62.5 µm). It can transmit a variety of patterns of light. However, because its dispersion is large, which limits the frequency of the transmitted digital signal, and with increasing distance, the situation will be more serious. For example, 600Mb/km of 2km fibers provide the bandwidth of only 300 Mbps. Therefore, MMF cable's transmission distance is relatively short, generally only a few kilometers. General MMF patch cables are in orange, also some are gray, joints and protection are beige or black. 
  • Single-Mode Fiber SMF Cable: Center glass core is relatively fine (core diameter is generally 9 or 10 µm), only one mode of light transmission. Therefore, the dispersion is very small, suitable for remote communication, but it plays a major role in the chromatic dispersion, so that SMF cable has a higher stability requirement to the spectral width of the light source, just as narrower spectrum width, better stability. General SMF patch cables are in yellow, with joints and cases in blue.

   

  Transmission Way:

  • Simplex Cable: Single strand of fiber surrounded by a 900µm buffer then a layer of Kevlar and finally the outer jacket. Available in 2 mm or 3 mm and plenum or riser jacket. Plenum is stronger and made to share in fire versus riser is made to melt in fire. Riser cable is more flexible.
  • Duplex Cable: Two single strands of fiber optic cable attached at the center. Surrounded by a 900µm buffer then a layer of Kevlar and finally the outer jacket. In data communications, the simultaneous operation of a circuit in both directions is known as full duplex; if only one transmitter can send at a time, the system is called half duplex.

   

  Cable Core Structure:

  • Central Tube Cable: Fiber, optical fiber bundles or fiber optic cable with no stranding directly into the center position.
  • Stranded Tube Cable: A few dozens or more root fiber or fiber tape unit helically stranded around the central strength member (S twist or SZ twisted) into one or more layers of fiber optic cable.
  • Skeleton After Tube Cable: Fiber or fiber after spiral twisted placed into the plastic skeleton cable slot.

   

  Fiber Road Laying:

  • Aerial Cable: Aerial cables are for outside installation on poles. They can be lashed to a messenger or another cable (common in CATV) or have metal or aramid strength members to make them self supporting. The cable shown has a steel messenger for support. It must be grounded properly. A widely used aerial cable is optical power ground wire which is a high voltage distribution cable with fiber in the center. The fiber is not affected by the electrical fields and the utility installing it gets fibers for grid management and communications. This cable is usually installed on the top of high voltage towers but brought to ground level for splicing or termination. 
  • Direct-Buried Cables:
    • Armored Cable: Armored cable is used in direct-buried outside plant applications where a rugged cable is needed and/or rodent resistance. Armored cable withstands crush loads well, needed for direct burial applications. Cable installed by direct burial in areas where rodents are a problem usually have metal armoring between two jackets to prevent rodent penetration. Another application for armored cable is in data centers, where cables are installed underfloor and one worries about the fiber cable being crushed. Armored cable is conductive, so it must be grounded properly. 
    • Breakout Cable: Breakout cable is a favorite where rugged cables are desirable or direct termination without junction boxes, patch panels or other hardware is needed. It is made of several simplex cables bundled together inside a common jacket. It has a strong, rugged design, but is larger and more expensive than the distribution cables. It is suitable for conduit runs, riser and plenum applications. It's perfect for industrial applications where ruggedness is needed. Because each fiber is individually reinforced, this design allows for quick termination to connectors and does not require patch panels or boxes. Breakout cable can be more economic where fiber count is not too large and distances are not too long, because it requires so much less labor to terminate.
  • Submarine Cable: Submarine cable is the cable wrapped with insulating materials, laying at the bottom of the sea, to set up a telecom transmission between countries.

   

  Cable State. Based on 900µm tight buffered fiber and 250µm coated fiber there are two basic types of fiber optic cable constructions:

  • Tight Buffered Cable: Multiple color coded 900µm tight buffered fibers can be packed tightly together in a compact cable structure, an approach widely used indoors, these cables are called tight buffered cables. Tight buffered cables are used to connect outside plant cables to terminal equipment, and also for linking various devices in a premises network. Multi-fiber tight buffered cables often are used for intra-building, risers, general building and plenum applications. Tight buffered cables are mostly built for indoor applications, although some tight buffered cables have been built for outdoor applications too.
  • Loose Tube Cable: On the other hand multiple (up to 12) 250µm coated fibers (bare fibers) can be put inside a color coded, flexible plastic tube, which usually is filled with a gel compound that prevents moisture from seeping through the hollow tube. Buffer tubes are stranded around a dielectric or steel central member. Aramid yarn are used as primary strength member. Then an outer polyethylene jacket is extruded over the core. These cables are called loose tube cables. Loose tube structure isolates the fibers from the cable structure. This is a big advantage in handling thermal and other stresses encountered outdoors, which is why most loose tube fiber optic cables are built for outdoor applications. Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications. 

   

  Environment & Situation:

  • Indoor Cable: Such as distribution cables. Distribution cable is the most popular indoor cable, as it is small in size and light in weight. They contain several tight-buffered fibers bundled under the same jacket with Kevlar strength members and sometimes fiberglass rod reinforcement to stiffen the cable and prevent kinking. These cables are small in size, and used for short, dry conduit runs, riser and plenum applications. The fibers are double buffered and can be directly terminated, but because their fibers are not individually reinforced, these cables need to be broken out with a "breakout box" or terminated inside a patch panel or junction box to protect individual fibers.
  • Outdoor Cable: Outdoor fiber cable delivers outstanding audio, video, telephony and data signal performance for educational, corporate and government campus applications. With a low bending radius and lightweight feature, this cable is suitable for both indoor and outdoor installations. These are available in a variety of configurations and jacket types to cover riser and plenum requirements for indoor cables and the ability to be run in duct, direct buried, or aerial/lashed in the outside plant.

  To purchase your fiber cables, please click link below:

  Fiber Patch Cables

   

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• T-Mobile becomes number one US smartphone channel

  May 31, 2016 by Telecom News / 622 Views

  Written by Scott Bicheno  Telecoms.com

  

  Disruptive US operator T-Mobile has become the leading sales channel for smartphones in the US, according to new research from Counterpoint.

  T-Mobile overtook Verizon to take the number one smartphone sales spot, having been a distant fourth just two years ago. This change is viewed as indicative of a broader change in the way smartphones are being purchased in the US, with the cost of devices increasingly uncoupled from the service contracts and, if needed, paid for via conventional financing arrangements.

  “The US market has undergone significant shifts in the power of the different sales channels with the move to unsubsidized plans,” said Neil Shah of Counterpoint. “The growth of T-Mobile through its different ‘Uncarrier’ moves, the removal of subsidies and enticing subscribers with ‘Simple Choice’ & ‘Jump’ plans, has helped the operator to become the top smartphone sales channel in the USA.

  Samsung and Apple together captured almost two-thirds of the total smartphone shipments share at T-Mobile, with Samsung leading. However, it will be an uphill task for T-Mobile to maintain this lead ahead of Verizon and continue to attract millions of subscribers to its network. The move to unsubsidized and unlocked has also boosted demand in the open channel, which continued to contribute close to 10% of the total shipments in Q1 2016.”

  

  US smartphone sales on the whole declined by 4% year-on-year due to the maturity of the market (most people already have a smartphone) and a lengthening on the upgrade cycle. The latter factor will be a direct result of the shift in buying habits as fewer consumers are being prompted to upgrade their subsidized phones by the renewal of their postpaid contracts.

  “The US market decelerated due to softness in Apple iPhone demand and iPhone SE demand not materializing until Q2 2016,” said Jeff Fieldhack of Counterpoint. “Carriers continued to push subscribers to non-subsidy plans as for the first time more than half of the combined subscriber base of the top four carriers are now on non-subsidized plans. This is a significant shift from the subsidy-driven model just ten to twelve quarters ago. This has changed the basis of competition in US mobile landscape.

  “The focus has shifted to creating more value for the consumer, instead of being device-driven. Unsubsidized device sales have educated consumers that flagship smartphones are costly. This has led to a temporary softness in the device upgrade cycle; the in-carrier upgrade run rate continues to be in 5-6% range per quarter. Handset manufacturers will continue to push hardware and marketing limits to entice subscribers to not defer upgrading.”

   

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• Huawei Completes 5G Key Technology Tests in the Field Trial Sponsored by IMT-2020 5G Promotion Group

  May 30, 2016 by Telecom News / 621 Views

  [Shenzhen, China, May 27, 2016] Huawei completed the first phase of key 5G technology tests as a part of a series field trials defined by the IMT-2020 5G Promotion Group. In April 2016, the outdoor macro-cell tests, conducted in Chendu, China, consist of a number of the foundational key enabling technologies and an integrated 5G air-interface. The test results successfully demonstrated that the new 5G air interface technology can effectively improve spectrum efficiency and to meet diverse service requirements for 5G defined by ITU-R.

  
  Huawei completes 5G key technology tests in 5G field trial

  Strong Promotion for Global Partnership on 5G Technology Innovation and a Global 5G Standard

  Launched by China Academy of Information and Communication Technology (CAICT), the IMT-2020 5G Promotion Group aims to foster a joint effort to promote 5G technology evaluation and field test among the global mobile industry and ecosystem to ensure the successful commercial deployment by 2020. One of the key objectives for IMT-2020 5G Promotion Group is to realize the 5G vision for the enhanced mobile broadband service as well as to create the new capabilities for 5G to enable the IoT and vertical services, this represents the unprecedented technical challenges such as to realize 10Gbps or peak rate 20Gbps user data rate, 100 billion connections, and 1 ms of end-to-end network latency for the 5G air interface.

  Early this year, IMT-2020 5G Promotion Group announced a three phase 5G networks trial plan, spanning from 2016 to 2018, with a first phase test from September 2015 to September 2016. The first phase test is focused on key radio technologies and performance test.

  As one of the core members in the IMT-2020 5G Promotion Group, Huawei actively contributed IMT-2020 5G Promotion Group and 5G technology test. In addition, Huawei established an extensive collaboration with CAICT, China Mobile, China Unicom, and China Telecom in the Chinese operator community to explore the innovative air-interface technologies to achieve best spectral efficiency and massive links capabilities. Huawei’s effort is focused on New Radio (NR) technology, which includes the optimized new air-interface, full-duplex and massive MIMO technologies, these are the enabling technologies to achieve the superior end-user experience for the emerging mobile broadband service such as 4K, 8K and virtual reality and augmented reality.

  Best-in-Class Test Results Using 5G New Air Interface

  The 5G air interface technology has been implemented through three novel foundational technologies, i.e., filtered Orthogonal Frequency Division Multiplexing (F-OFDM), Sparse Code Multiple Access (SCMA) and Polar code to meet 5G requirements and performance targets.

  F-OFDM technology is the basis for creating ultra-flexible air-interface to adaptively fit all the 5G use-case scenarios defined by ITU-R with a single radio technology platform. It allows multiple concurrent radio numerologies and frame structure to deliver very diverse services; F-OFDM can ensure the future-proof for the 5G system to meet emerging innovative services requirements. The test results showed that F-OFDM can increase system throughput by 10% using those free guard bands in LTE system. In addition, F-OFDM supports asynchronous transmission from different users. Test results showed that it will provide 100% higher system throughput compared with that in LTE system in the presence of mixed service on the same carrier frequency with mixed radio numerologies. .

  SCMA is to support massive connections and obtain higher system throughput simultaneously via the joint optimization on sparse SCMA codebook design and multi-dimensional modulation. It can further consider optimization on power allocation among different SCMA layers especially in downlink to improve total system throughput. The test results showed that SCMA is to increase the uplink connection number by 300% and at the same time increased the downlink system throughput up to 80%.

  For Polar code, it allocates information to the highly reliable data locations in the code structure to transmit useful information of user and at the same time it supports channel coding of any code rate with an appropriate code construction to fit any future service requirements. The test results showed that Polar code provided coding gain from 0.5dB to 2.0dB compared with Turbo code used in LTE system.

  System Integration of Innovative 5G Air Interface Technologies

  The flexible system integration of several innovative 5G air-interface technologies, namely, F-OFDM, SCMA and massive MIMO has been verified in the first phase of key 5G technology tests. In the test, multi-user MIMO (MU-MIMO) supported up to 24 users and up to 24 parallel layers transmission on the same time-frequency resources. The test results showed that MU-MIMO can achieve 3.6Gbps cell average throughput using 100MHz system bandwidth, it is almost 10 times of that in LTE baseline system.

  The trial has validated the optimal integration of the above new radio technologies and the capability of flexible 5G air-interface technologies, the trial is also served as a technical re-risk to support the on-going 3GPP standardization work.

  Full Duplex Implemented in the First Phase of 5G Test

  Full Duplex mode has also been tested in the first phase of 5G test. In the initial test stage on Full Duplex, it allows simultaneous transmitting and receiving of data at the base station with three level cascaded technologies, namely, passive analog cancellation, active analog cancellation, and digital cancellation. The test results showed that the Full Duplex can provide self-interference cancellation capability more than 113dB in real world environment and result in a total 90% system throughput gain over the conventional half duplex mode used today.

  Huawei has successfully completed the first phase test of 5G technologies in China. "The trial of 5G technologies in China will be a great contribution to 5G applications in the future.” Dr. Wen Tong, Huawei 5G Chief Scientist emphasized that, "As a member of the IMT-2020 5G Promotion Group, Huawei is pleased to work with CAICT, China Mobile, China Unicom, and China Telecom, and took the initiative to be the first to complete 5G key technologies tests and corresponding system integration test based on our proposed 5G new air interface."

  He also announced the plan of the second phase of 5G test which will focus mainly on the wide coverage, high hotspot capacity, and massive connections with high reliability, low latency with reduced power consumption.

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